全文获取类型
收费全文 | 4899篇 |
免费 | 386篇 |
国内免费 | 260篇 |
出版年
2024年 | 6篇 |
2023年 | 54篇 |
2022年 | 90篇 |
2021年 | 232篇 |
2020年 | 161篇 |
2019年 | 194篇 |
2018年 | 186篇 |
2017年 | 115篇 |
2016年 | 215篇 |
2015年 | 313篇 |
2014年 | 327篇 |
2013年 | 355篇 |
2012年 | 430篇 |
2011年 | 409篇 |
2010年 | 235篇 |
2009年 | 226篇 |
2008年 | 276篇 |
2007年 | 246篇 |
2006年 | 203篇 |
2005年 | 156篇 |
2004年 | 150篇 |
2003年 | 148篇 |
2002年 | 117篇 |
2001年 | 89篇 |
2000年 | 81篇 |
1999年 | 64篇 |
1998年 | 30篇 |
1997年 | 41篇 |
1996年 | 51篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 47篇 |
1991年 | 30篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有5545条查询结果,搜索用时 390 毫秒
971.
2009年中国植物科学在水稻和拟南芥研究等方面取得“爆发性”的快速发展。中国科学家在植物科学各领域中取得了大量的原创性研究成果, 尤其是在基于新一代测序技术和计算生物学理论的基因组学、水稻功能基因挖掘、激素受体和信号转导以及转基因作物产业化和生态安全性研究等方面取得一系列重大进展, 受到了国内外广泛关注。该文对2009年中国本土植物生命科学若干领域取得的重要研究进展进行概括性评述, 旨在全面追踪当前中国植物科学领域发展的最新前沿和热点事件, 并展现我国科学家们所取得的杰出成就。 相似文献
972.
Wenqing Zhang Ronghui Zhou Yuting Yang Shuanglin Peng Dexuan Xiao Tingting Kong Xiaoxiao Cai Bofeng Zhu 《Cell proliferation》2021,54(9)
ObjectivesThe nano‐hydroxyapatite (nHAp) is widely used to develop imaging probes and drug carriers due to its excellent bioactivity and biocompatibility. However, traditional methods usually need cumbersome and stringent conditions such as high temperature and post‐modification to prepare the functionalized nHAp, which do not benefit the particles to enter cells due to the increased particle size. Herein, a biomimetic synthesis strategy was explored to achieve the AS1411‐targeted tumour dual‐model bioimaging using DNA aptamer AS1411 as a template. Then, the imaging properties and the biocompatibility of the synthesized AS‐nFAp:Gd/Tb were further investigated.Materials and methodsThe AS‐nFAp:Gd/Tb was prepared under mild conditions through a one‐pot procedure with AS1411 as a template. Besides, the anticancer drug DOX was loaded to AS‐nFAp:Gd/Tb so as to achieve the establishment of a multifunctional nano‐probe that integrated the tumour diagnosis and treatment. The AS‐nFAp:Gd/Tb was characterized by transmission electron microscopy (TEM), energy disperse X‐ray Spectroscopy (EDS) mapping, X‐ray photoelectron spectroscopy (XPS) spectrum, X‐ray diffraction (XRD), fourier‐transformed infrared (FTIR) spectroscopy, capillary electrophoresis analyses, zeta potential and particle sizes. The in vitro magnetic resonance imaging (MRI) and fluorescence imaging were performed on an MRI system and a confocal laser scanning microscope, respectively. The potential of the prepared multifunctional nHAp for a targeted tumour therapy was investigated by a CCK‐8 kit. And the animal experiments were conducted on the basis of the guidelines approved by the Animal Care and Use Committee of Sichuan University, China.ResultsIn the presence of AS1411, the as‐prepared AS‐nFAp:Gd/Tb presented a needle‐like morphology with good monodispersity and improved imaging performance. Furthermore, due to the specific binding between AS1411 and nucleolin up‐expressed in cancer cells, the AS‐nFAp:Gd/Tb possessed excellent AS1411‐targeted fluorescence and MRI imaging properties. Moreover, after loading chemotherapy drug DOX, in vitro and in vivo studies showed that DOX@AS‐nFAp:Gd/Tb could effectively deliver DOX to tumour tissues and exert a highly effective tumour inhibition without systemic toxicity compared with pure DOX.ConclusionsThe results indicated that the prepared multifunctional nHAp synthesized by a novel biomimetic strategy had outstanding capabilities of recognition and treatment for the tumour and had good biocompatibility; hence, it might have a potential clinical application in the future. 相似文献
973.
974.
Li Yu Dachuan Shi Junling Li Yingzhen Kong Yanchong Yu Guohua Chai Ruibo Hu Juan Wang Michael G. Hahn Gongke Zhou 《Plant physiology》2014,164(4):1842-1856
Mannans are hemicellulosic polysaccharides that are considered to have both
structural and storage functions in the plant cell wall. However, it is not yet known
how mannans function in Arabidopsis (Arabidopsis thaliana) seed
mucilage. In this study, CELLULOSE SYNTHASE-LIKE A2
(CSLA2; At5g22740) expression was observed in several seed
tissues, including the epidermal cells of developing seed coats. Disruption of
CSLA2 resulted in thinner adherent mucilage halos, although the
total amount of the adherent mucilage did not change compared with the wild type.
This suggested that the adherent mucilage in the mutant was more compact compared
with that of the wild type. In accordance with the role of CSLA2 in glucomannan
synthesis, csla2-1 mucilage contained 30% less mannosyl and glucosyl
content than did the wild type. No appreciable changes in the composition, structure,
or macromolecular properties were observed for nonmannan polysaccharides in mutant
mucilage. Biochemical analysis revealed that cellulose crystallinity was
substantially reduced in csla2-1 mucilage; this was supported by the
removal of most mucilage cellulose through treatment of csla2-1
seeds with endo-β-glucanase. Mutation in CSLA2 also resulted
in altered spatial distribution of cellulose and an absence of birefringent cellulose
microfibrils within the adherent mucilage. As with the observed changes in
crystalline cellulose, the spatial distribution of pectin was also modified in
csla2-1 mucilage. Taken together, our results demonstrate that
glucomannans synthesized by CSLA2 are involved in modulating the structure of
adherent mucilage, potentially through altering cellulose organization and
crystallization.Mannan polysaccharides are a complex set of hemicellulosic cell wall polymers that are
considered to have both structural and storage functions. Based on the particular chemical
composition of the backbone and the side chains, mannan polysaccharides are classified into
four types: pure mannan, glucomannan, galactomannan, and galactoglucomannan (Moreira and Filho, 2008; Wang et al., 2012; Pauly et al.,
2013). Each of these polysaccharides is composed of a β-1,4-linked
backbone containing Man or a combination of Glc and Man residues. In addition, the mannan
backbone can be substituted with side chains of α-1,6-linked Gal residues. Mannan
polysaccharides have been proposed to cross link with cellulose and other hemicelluloses
via hydrogen bonds (Fry, 1986; Iiyama et al., 1994; Obel et al., 2007; Scheller and
Ulvskov, 2010). Furthermore, it has been reported that heteromannans with
different levels of substitution can interact with cellulose in diverse ways (Whitney et al., 1998). Together, these observations
indicate the complexity of mannan polysaccharides in the context of cell wall
architecture.CELLULOSE SYNTHASE-LIKE A (CSLA) enzymes have been shown to have mannan synthase activity
in vitro. These enzymes polymerize the β-1,4-linked backbone of mannans or
glucomannans, depending on the substrates (GDP-Man and/or GDP-Glc) provided (Richmond and Somerville, 2000; Liepman et al., 2005, 2007;
Pauly et al., 2013). In Arabidopsis
(Arabidopsis thaliana), nine CSLA genes have been
identified; different CSLAs are responsible for the synthesis of different
mannan types (Liepman et al., 2005, 2007). CSLA7 has mannan synthase activity in vitro
(Liepman et al., 2005) and has been shown to
synthesize stem glucomannan in vivo (Goubet et al.,
2009). Disrupting the CSLA7 gene results in defective pollen
growth and embryo lethality phenotypes in Arabidopsis, indicating structural or signaling
functions of mannan polysaccharides during plant embryo development (Goubet et al., 2003). A mutation in CSLA9 results in
the inhibition of Agrobacterium tumefaciens-mediated root transformation
in the rat4 mutant (Zhu et al.,
2003). CSLA2, CSLA3, and CSLA9 are proposed to play nonredundant roles in the
biosynthesis of stem glucomannans, although mutations in CSLA2,
CSLA3, or CSLA9 have no effect on stem development or
strength (Goubet et al., 2009). All of the
Arabidopsis CSLA proteins have been shown to be involved in the biosynthesis of mannan
polysaccharides in the plant cell wall (Liepman et al.,
2005, 2007), although the precise
physiological functions of only CSLA7 and CSLA9 have been conclusively demonstrated.In Arabidopsis, when mature dry seeds are hydrated, gel-like mucilage is extruded to
envelop the entire seed. Ruthenium red staining of Arabidopsis seeds reveals two different
mucilage layers, termed the nonadherent and the adherent mucilage layers (Western et al., 2000; Macquet et al., 2007a). The outer, nonadherent mucilage is loosely
attached and can be easily extracted by shaking seeds in water. Compositional and linkage
analyses suggest that this layer is almost exclusively composed of unbranched
rhamnogalacturonan I (RG-I) (>80% to 90%), with
small amounts of branched RG-I, arabinoxylan, and
high methylesterified homogalacturonan (HG). By
contrast, the inner, adherent mucilage layer is tightly attached to the seed and can only
be removed by strong acid or base treatment, or by enzymatic digestion (Macquet et al., 2007a; Huang et al., 2011; Walker et al.,
2011). As with the nonadherent layer, adherent mucilage is also mainly composed
of unbranched RG-I, but with small numbers of
arabinan and galactan ramifications (Penfield et al.,
2001; Willats et al., 2001; Dean et al., 2007; Macquet et al., 2007a, 2007b; Arsovski et al., 2009; Haughn and Western, 2012). There are also minor amounts of pectic
HG in the adherent mucilage, with high
methylesterified HG in the external domain compared
with the internal domain of the adherent layer (Willats
et al., 2001; Macquet et al., 2007a;
Rautengarten et al., 2008; Sullivan et al., 2011; Saez-Aguayo et al., 2013). In addition, the adherent mucilage
contains cellulose (Blake et al., 2006; Macquet et al., 2007a), which is entangled with RG-I and is thought to anchor the pectin-rich mucilage
onto seeds (Macquet et al., 2007a; Harpaz-Saad et al., 2011, 2012; Mendu et al., 2011;
Sullivan et al., 2011). As such, Arabidopsis
seed mucilage is considered to be a useful model for investigating the biosynthesis of cell
wall polysaccharides and how this process is regulated in vivo (Haughn and Western, 2012).Screening for altered seed coat mucilage has led to the identification of several genes
encoding enzymes that are involved in the biosynthesis or modification of mucilage
components. RHAMNOSE SYNTHASE2/MUCILAGE-MODIFIED4 (MUM4) is responsible for the synthesis
of UDP-l-Rha (Usadel et al., 2004; Western et al., 2004; Oka et al., 2007). The putative GALACTURONSYLTRANSFERASE11 can
potentially synthesize mucilage RG-I or HG pectin from UDP-d-GalUA (Caffall et al., 2009). GALACTURONSYLTRANSFERASE-LIKE5
appears to function in the regulation of the final size of the mucilage RG-I (Kong et al.,
2011, 2013). Mutant seeds defective in
these genes display reduced thickness of the extruded mucilage layer compared with
wild-type Arabidopsis seeds.RG-I deposited in the apoplast of seed coat
epidermal cells appears to be synthesized in a branched form that is subsequently modified
by enzymes in the apoplast. MUM2 encodes a β-galactosidase that
removes Gal residues from RG-I side chains (Dean et al., 2007; Macquet et al., 2007b). β-XYLOSIDASE1 encodes an
α-l-arabinfuranosidase that removes Ara residues from RG-I side chains (Arsovski et al., 2009). Disruptions of these genes lead to defective hydration
properties and affect the extrusion of mucilage. Furthermore, correct methylesterification
of mucilage HG is also required for mucilage
extrusion. HG is secreted into the wall in a high
methylesterified form that can then be enzymatically demethylesterified by pectin
methylesterases (PMEs; Bosch and Hepler, 2005). PECTIN METHYLESTERASE INHIBITOR6 (PMEI6)
inhibits PME activities (Saez-Aguayo et al., 2013). The subtilisin-like Ser protease (SBT1.7)
can activate other PME inhibitors, but not PMEI6
(Rautengarten et al., 2008; Saez-Aguayo et al., 2013). Disruption of either
PMEI6 or SBT1.7 results in the delay of mucilage
release.Although cellulose is present at low levels in adherent mucilage, it plays an important
adhesive role for the attachment of mucilage pectin to the seed coat epidermal cells. The
orientation and amount of pectin associated with the cellulose network is largely
determined by cellulose conformation properties (Macquet
et al., 2007a; Haughn and Western,
2012). Previous studies have demonstrated that CELLULOSE SYNTHASE A5 (CESA5) is
required for the production of seed mucilage cellulose and the adherent mucilage in the
cesa5 mutant can be easily extracted with water (Harpaz-Saad et al., 2011, 2012; Mendu et al., 2011; Sullivan et al., 2011).Despite all of these discoveries, large gaps remain in the current knowledge of the
biosynthesis and functions of mucilage polysaccharides in seed coats. In this study, we
show that CSLA2 is involved in the biosynthesis of mucilage glucomannan. Furthermore, we
show that CSLA2 functions in the maintenance of the normal structure of the adherent
mucilage layer through modifying the mucilage cellulose ultrastructure. 相似文献
975.
Wenqian Kong Hui Guo Valorie H. Goff Tae-Ho Lee Changsoo Kim Andrew H. Paterson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2014,127(11):2387-2403
Key message
We identified quantitative trait loci influencing plant architecture that may be valuable in breeding of optimized genotypes for sustainable food and/or cellulosic biomass production, and advancing resilience to changing climates.Abstract
We describe a 3-year study to identify quantitative trait loci (QTLs) for vegetative branching of sorghum in a recombinant inbred line population of 161 genotypes derived from two morphologically distinct parents, S. bicolor × S. propinquum. We quantify vegetative branching based on morphological position and physiological status. Different sets of QTLs for different levels of branching were identified. QTLs discovered on chromosomes 1, 3, 7 and 8 affect multiple vegetative branching variables, suggesting that these regions may contain genes that control general axillary meristem initiation. Other regions that only influence one vegetative branching trait could contain genes that influence developmental processes contributing to divergent patterns of plant architecture. We investigate the relationship between vegetative branching patterns and dry biomass, and conclude that tillers with mature panicles and immature secondary branches each show consistent positive correlation with dry biomass. Among 19 branching-related genes from rice, eight sorghum homologs of seven rice genes are in syntenic blocks within branching-related QTL likelihood intervals. Five of these eight genes are within 700 kb of SNPs significantly associated with differences in branching in genome-wide association study of a diversity panel of 377 sorghum accessions, and three contain striking allelic variations between S. bicolor and S. propinquum that are likely to impact gene functions. Unraveling genetic determinants for vegetative branching may contribute to deterministic breeding of optimized genotypes for sustainable food and cellulosic biomass production in both optimal and marginal conditions, which are resilient to future climates that are more volatile and more stressful. 相似文献976.
Song M Yi X Chen W Yuan Y Zhang X Li J Tong M Liu G You S Kong X 《Biochemical and biophysical research communications》2011,415(1):152-156
Liver fibrosis represents a process of healing and scarring in response to chronic liver injury. Augmenter of liver regeneration (ALR) has been shown to protect hepatocytes from various toxins. The aim of this study was to investigate the effects of ALR gene therapy on liver injury and fibrosis induced by CCl(4) in rats and further explore the underlying mechanisms. Human ALR expression plasmid was delivered via the tail vein. ALR gene therapy might protect the liver from CCl(4)-induced injury and fibrogenesis by attenuating the mitochondrial dysfunction, suppressing oxidative stress, and inhibiting activation of HSCs. This report demonstrated that ALR gene therapy protected against the ATP loss, increased the activity of ATPase, decreased intrahepatic reactive oxygen species level, and down-regulated transforming growth factor-β1, platelet-derived growth factor-BB, and α-smooth muscle actin expression. Following gene transfer liver function tests were significantly improved. In brief, ALR gene therapy might be an effective therapeutic reagent for liver fibrosis with potential clinical applications. 相似文献
977.
Hao Y Kong X Ruan Y Gan H Chen H Zhang C Ren S Gu J 《Biochemical and biophysical research communications》2011,407(1):169-174
CDK11p46, a 46 kDa isoform of the PITSLRE kinase family, is a key mediator of cell apoptosis, while the precise mechanism remains to be elucidated. By using His pull-down and mass spectrometry analysis, we identified the ribosomal protein S8 (RPS8), a member of the small subunit ribosome, as an interacting partner of CDK11p46. Further analysis confirmed the association of CDK11p46 and RPS8 in vitro and in vivo, and revealed that RPS8 was not a substrate of CDK11p46. Moreover, RPS8 and CDK11p46 synergize to inhibit the translation process both in cap- and internal ribosomal entry site (IRES)-dependent way, and sensitize cells to Fas ligand-induced apoptosis. Taken together, our results provide evidence for the novel role of CDK11p46 in the regulation of translation and cell apoptosis. 相似文献
978.
979.
Yan Xiao Junbing Tang Hua Qing Changfang Zhou Weijing Kong Shuqing An 《Hydrobiologia》2011,658(1):353-363
The purpose of this article was to study the trade-offs among vegetative growth, clonal, and sexual reproduction in an aquatic
invasive weed Spartina alterniflora that experienced different inundation depths and clonal integration. Here, the rhizome connections between mother and daughter
ramets were either severed or left intact. Subsequently, these clones were flooded with water levels of 0, 9, and 18 cm above
the soil surface. Severing rhizomes decreased growth and clonal reproduction of daughter ramets, and increased those of mother
ramets grown in shallow and deep water. The daughter ramets disconnected from mother ramets did not flower, while sexual reproduction
of mother ramets was not affected by severing. Clonal integration only benefited the total rhizome length, rhizome biomass,
and number of rhizomes of the whole clones in non-inundation conditions. Furthermore, growth and clonal reproduction of mother,
daughter ramets, and the whole clone decreased with inundation depth, whereas sexual reproduction of mother ramets and the
whole clones increased. We concluded that the trade-offs among growth, clonal, and sexual reproduction of S. alterniflora would be affected by inundation depth, but not by clonal integration. 相似文献
980.