全文获取类型
收费全文 | 797篇 |
免费 | 57篇 |
国内免费 | 43篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 21篇 |
2021年 | 47篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 42篇 |
2017年 | 27篇 |
2016年 | 33篇 |
2015年 | 40篇 |
2014年 | 58篇 |
2013年 | 61篇 |
2012年 | 77篇 |
2011年 | 66篇 |
2010年 | 42篇 |
2009年 | 35篇 |
2008年 | 34篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 24篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有897条查询结果,搜索用时 15 毫秒
111.
Leaf physiological and gas-exchange traits of a summer-green herbaceous perennial, Parasenecio yatabei, growing along a stream were examined in relation to leaf age. In its vegetative phase, the aerial part of this plant consists
of only one leaf and provides an ideal system for the study of leaf longevity. Volumetric soil water content (SWC) decreased
with increasing distance from the stream, whereas relative light intensity was nearly constant. The light-saturated net CO2 assimilation rate (A
sat) and leaf stomatal conductance (gs) were approximately 1.5-fold and 1.4-fold higher, respectively, in the lower slope near
the mountain stream than in the upper slope far from the mountain stream. The lifespan of aerial parts of vegetative plants
significantly increased with decreasing SWC. The leaf mass-based nitrogen content of the leaves (N
mass) was almost constant (ca. 2.2%); however, the maximum carboxylation rate by ribulose-1,5-biphosphate carboxylase/oxygenase
(rubisco) (V
cmax) and photosynthetic nitrogen use efficiency (PNUE, A
sat/N
area) decreased more slowly in the upper slope than in the lower slope. The higher leaf photosynthetic activity of P. yatabei plants growing lower on the slope leads to a decrease in V
cmax and PNUE in the early growing season, and to a shorter leaf lifespan. 相似文献
112.
为了进一步从蛋白水平上检测DAZAP2(deleted in azoospermia associated protein 2)在多发性骨髓瘤患者中的表达及研究DAZAP2的功能,以正常人的骨髓单个核细胞的总RNA为模板,RT-PCR扩增DAZAP2完整编码序列,构建原核表达重组质粒pQE30-DAZAP2,转化大肠杆菌JM109后,加IPTG诱导表达4h时,表达蛋白显著增加,Ni-NTA层析柱纯化蛋白。以该纯化蛋白免疫新西兰大白兔,制备抗DAZAP2抗体,ELISA检测抗体的效价在1:6400以上,Western blot检测抗体的特异性较好.用该抗体检测出DAZAP2雀6例正常人及4例多发性骨髓瘤患者中有表达,其他7例患者中没有表达,与RT-PCR结果一致,该抗体具有一定的临床应用前景,并能进一步用于功能研究. 相似文献
113.
Liang Y Pingali SV Jogalekar AS Snyder JP Thiyagarajan P Lynn DG 《Biochemistry》2008,47(38):10018-10026
Amino acid cross-strand pairing interactions along a beta-sheet surface have been implicated in protein beta-structural assembly and stability, yet the relative contributions have been difficult to evaluate directly. Here we develop the central core sequence of the Abeta peptide associated with Alzheimer's disease, Abeta(16-22), as an experimental system for evaluating these interactions. The peptide allows for internal comparisons between electrostatic and steric interactions within the beta-sheet and an evaluation of these cross-strand pair contributions to beta-sheet registry. A morphological transition from fibers to hollow nanotubes arises from changes in beta-sheet surface complementarity and provides a convenient indicator of the beta-strand strand registry. The intrinsic beta-sequence and pair correlations are critical to regulate secondary assembly. These studies provide evidence for a critical desolvation step that is not present in most models of the nucleation-dependent pathway for amyloid assembly. 相似文献
114.
Centrins are members of the centrosome protein family, which is highly conserved during revolution. The homologous genes of centrin in many organisms had been cloned, but the sequences of the rat centrin genes were not reported yet in GenBank. We cloned the cDNA fragments of centrin-1, -2 and -3 from the rat testis by RT-PCR, and analyzed the homology of the deduced amino acid sequences. The expression characterization of centrin genes in rat spermato-genesis was carried out by semi-quantitative RT-PCR. The results show that the homology of the corresponding centrin proteins in human, mouse and rat is high. The expression of centrin-1 is testis-specific, spermatogenic cell-specific and developmental stage-related. Centrin-1 begins to be transcribed when the meiosis occurs, and its mRNA level reaches the peak in round spermatids. Centrin-2 and centrin-3 are highly expressed in spermatogonia and their mRNA level decreases markedly when meiosis occurs. These results suggest that centrin-1 may play roles in 相似文献
115.
116.
Silas A. Buck Thomas Steinkellner Despoina Aslanoglou Michael Villeneuve Sai H. Bhatte Victoria C. Childers Sophie A. Rubin Briana R. De Miranda Emma I. O'Leary Elizabeth G. Neureiter Keri J. Fogle Michael J. Palladino Ryan W. Logan Jill R. Glausier Kenneth N. Fish David A. Lewis J. Timothy Greenamyre Brian D. McCabe Claire E. J. Cheetham Thomas S. Hnasko Zachary Freyberg 《Aging cell》2021,20(5)
Age is the greatest risk factor for Parkinson''s disease (PD) which causes progressive loss of dopamine (DA) neurons, with males at greater risk than females. Intriguingly, some DA neurons are more resilient to degeneration than others. Increasing evidence suggests that vesicular glutamate transporter (VGLUT) expression in DA neurons plays a role in this selective vulnerability. We investigated the role of DA neuron VGLUT in sex‐ and age‐related differences in DA neuron vulnerability using the genetically tractable Drosophila model. We found sex differences in age‐related DA neurodegeneration and its associated locomotor behavior, where males exhibit significantly greater decreases in both DA neuron number and locomotion during aging compared with females. We discovered that dynamic changes in DA neuron VGLUT expression mediate these age‐ and sex‐related differences, as a potential compensatory mechanism for diminished DA neurotransmission during aging. Importantly, female Drosophila possess higher levels of VGLUT expression in DA neurons compared with males, and this finding is conserved across flies, rodents, and humans. Moreover, we showed that diminishing VGLUT expression in DA neurons eliminates females'' greater resilience to DA neuron loss across aging. This offers a new mechanism for sex differences in selective DA neuron vulnerability to age‐related DA neurodegeneration. Finally, in mice, we showed that the ability of DA neurons to achieve optimal control over VGLUT expression is essential for DA neuron survival. These findings lay the groundwork for the manipulation of DA neuron VGLUT expression as a novel therapeutic strategy to boost DA neuron resilience to age‐ and PD‐related neurodegeneration. 相似文献
117.
We observed the preservation of microRNAs in unrefrigerated dried serum blots. Preservation was not adversely affected by drying or storing at 37, 45, or 60 °C instead of room temperature, but it was harmed when blots were dried incompletely before storage. Preservation of microRNAs in serum was not diminished if, instead of being kept frozen at −80 °C, it was stored as dried blots at room temperature for 5 months or at 37 °C for 4 weeks. Thus, dried blots can be a convenient and safer way to save, transport, and store serum for microRNA assays. 相似文献
118.
Supriya Khedkar Sushma Prabhakara Ramya Malarini Loganathan Chandana S Malali Gowda Gayathri Arakere Aswin Sai Narain Seshasayee 《Journal of bacteriology》2012,194(24):6946-6947
We report the draft genome sequence of methicillin-resistant Staphylococcus aureus (MRSA) strain ST672, an emerging disease clone in India, from a septicemia patient. The genome size is about 2.82 Mb with 2,485 open reading frames (ORFs). The staphylococcal cassette chromosome mec (SCCmec) element (type V) and immune evasion cluster appear to be different from those of strain ST772 on preliminary examination. 相似文献
119.
A. Sai Ramesh Imran Khan Md. Farhan Padma Thiagarajan 《Cell biochemistry and biophysics》2013,67(3):1391-1396
CYP1A1 gene belongs to the cytochrome P450 family and is known better as smokers’ gene due to its hyperactivation as a consequence of long term smoking. The expression of CYP1A1 induces polycyclic aromatic hydrocarbon production in the lungs, which when over expressed, is known to cause smoking related diseases, such as cardiovascular pathologies, cancer, and diabetes. Single nucleotide polymorphisms (SNPs) are the simplest form of genetic variations that occur at a higher frequency, and are denoted as synonymous and non-synonymous SNPs on the basis of their effects on the amino acids. This study adopts a systematic in silico approach to predict the deleterious SNPs that are associated with disease conditions. It is inferred that four SNPs are highly deleterious, among which the SNP with rs17861094 is commonly predicted to be harmful by all tools. Hydrophobic (isoleucine) to hydrophilic (serine) amino acid variation was observed in the candidate gene. Hence, this investigation aims to characterize a candidate gene from 159 SNPs of CYP1A1. 相似文献
120.
Clostridium thermocellum SS8 produced both carboxymethylcellulase (CMCase) and Avicelase when grown on cellulose. CMCase activity was unaffected by Ca2+, Mg2+, dithionate or dithiothreitol (DTT). Avicelase activity increased 2-fold with 5 mM DTT and 10 mM Ca2+. Cellulase and amylase were produced when a celluloseadapted culture was grown on starch. The mould grew best on sucrose and was inhibited by NaCl above 10 g/l. 相似文献