全文获取类型
收费全文 | 15151篇 |
免费 | 963篇 |
国内免费 | 3篇 |
专业分类
16117篇 |
出版年
2023年 | 102篇 |
2022年 | 182篇 |
2021年 | 390篇 |
2020年 | 304篇 |
2019年 | 315篇 |
2018年 | 385篇 |
2017年 | 353篇 |
2016年 | 533篇 |
2015年 | 813篇 |
2014年 | 873篇 |
2013年 | 1023篇 |
2012年 | 1303篇 |
2011年 | 1156篇 |
2010年 | 748篇 |
2009年 | 703篇 |
2008年 | 937篇 |
2007年 | 878篇 |
2006年 | 805篇 |
2005年 | 765篇 |
2004年 | 716篇 |
2003年 | 637篇 |
2002年 | 600篇 |
2001年 | 134篇 |
2000年 | 91篇 |
1999年 | 124篇 |
1998年 | 131篇 |
1997年 | 119篇 |
1996年 | 100篇 |
1995年 | 89篇 |
1994年 | 88篇 |
1993年 | 58篇 |
1992年 | 53篇 |
1991年 | 62篇 |
1990年 | 57篇 |
1989年 | 31篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 39篇 |
1984年 | 54篇 |
1983年 | 21篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 27篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1976年 | 17篇 |
1975年 | 18篇 |
1969年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Blanca Lidia Arroyo-Flores Carlos Calvo-Méndez Arturo Flores-Carreón Everardo López-Romero 《Antonie van Leeuwenhoek》1998,73(4):289-297
Incubation of a mixed membrane fraction isolated from C. albicans yeast cells with Nonidet P-40 at a detergent/protein ratio as low of 0.025 (0.016–0.019%, w/v) yielded a soluble fraction that catalyzed the transfer of mannose from GDP-[14C] Man into dolichol phosphate mannose and from this intermediate into mannoproteins. Over 95% of the sugar in mannoproteins was O-linked as judged from its release after -elimination. Mannose was identified as the sole product after this treatment. Transfer activity did not depend on exogenous lipid acceptor indicating that the latter was solubilized along with the mannosyl transferases. Synthesis of mannolipid and mannoproteins occurred at optima temperatures of 20 °C and 37 °C, respectively, and at a pH in the range of 7.5-9.5. Mannosyl transfer into the mannolipid was stimulated by Mg2+and inhibited by Ca2+and Mn2+whereas mannoprotein labeling was stimulated by Mn2+and to a lower extent by Mg2+. When measured as a function of substrate concentration, the synthesis of the mannolipid was a nearly linear function of GDP-Man concentration in the range of 5 to 32 M whereas protein mannosylation exhibited hyperbolic kinetics with saturation reached at about 10 M. The solubilized preparation was able to utilize an exogenous source of mannolipid as sugar donor for protein mannosylation. Dinucleotides and, to a higher extent trinucleotides, inhibited mannosyl transfer into the mannolipid and hence into mannoproteins. 相似文献
972.
Metabolism of Plant Polysaccharides by Leucoagaricus gongylophorus, the Symbiotic Fungus of the Leaf-Cutting Ant Atta sexdens L.
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Clia Gomes De Siqueira Maurício Bacci Jr. Fernando Carlos Pagnocca Odair Correa Bueno Maria Jos Aparecida Hebling 《Applied microbiology》1998,64(12):4820-4822
Atta sexdens L. ants feed on the fungus they cultivate on cut leaves inside their nests. The fungus, Leucoagaricus gongylophorus, metabolizes plant polysaccharides, such as xylan, starch, pectin, and cellulose, mediating assimilation of these compounds by the ants. This metabolic integration may be an important part of the ant-fungus symbiosis, and it involves primarily xylan and starch, both of which support rapid fungal growth. Cellulose seems to be less important for symbiont nutrition, since it is poorly degraded and assimilated by the fungus. Pectin is rapidly degraded but slowly assimilated by L. gongylophorus, and its degradation may occur so that the fungus can more easily access other polysaccharides in the leaves. 相似文献
973.
Palm heart harvesting in the Brazilian Atlantic forest: changes in industry structure and the illegal trade 总被引:1,自引:0,他引:1
1. Until the late 1960s, Euterpe edulis was the most important edible palm species in the Brazilian markets. Since then, overharvesting of natural stands and the limited scope of plantations have caused the industry to shift to the multistemmed E. oleracea from the Amazon river estuary.
2. As a result of the relocation of the industry, the structure of the palm harvesting industry has changed and illegal trade has continued to exploit the remaining natural stands of E. edulis .
3. It is suggested that, to avoid the total harvesting of E. edulis and to achieve sustainable management of the palm heart, it will be necessary to diversify the local economy, create incentives for small land owners to improve their management practices, while keeping their competitiveness against the illegal trade, create the incentive of new sources of palm hearts and create a 'green stamping' for management palms.
4. Transformation of the illegal structure of the palm heart industry is probably the only solution to avoid the total depletion of the wild stands of E. edulis . 相似文献
2. As a result of the relocation of the industry, the structure of the palm harvesting industry has changed and illegal trade has continued to exploit the remaining natural stands of E. edulis .
3. It is suggested that, to avoid the total harvesting of E. edulis and to achieve sustainable management of the palm heart, it will be necessary to diversify the local economy, create incentives for small land owners to improve their management practices, while keeping their competitiveness against the illegal trade, create the incentive of new sources of palm hearts and create a 'green stamping' for management palms.
4. Transformation of the illegal structure of the palm heart industry is probably the only solution to avoid the total depletion of the wild stands of E. edulis . 相似文献
974.
Regulation of Endothelial Cell Motility by Complexes of Tetraspan Molecules CD81/TAPA-1 and CD151/PETA-3 with α3β1 Integrin Localized at Endothelial Lateral Junctions
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
María Yez-M Arntzazu Alfranca Carlos Cabaas Mnica Marazuela Reyes Tejedor M. Angeles Ursa Leonie K. Ashman Manuel O. de Landzuri Francisco Snchez-Madrid 《The Journal of cell biology》1998,141(3):791-804
Cell-to-cell junction structures play a key role in cell growth rate control and cell polarization. In endothelial cells (EC), these structures are also involved in regulation of vascular permeability and leukocyte extravasation. To identify novel components in EC intercellular junctions, mAbs against these cells were produced and selected using a morphological screening by immunofluorescence microscopy. Two novel mAbs, LIA1/1 and VJ1/16, specifically recognized a 25-kD protein that was selectively localized at cell–cell junctions of EC, both in the primary formation of cell monolayers and when EC reorganized in the process of wound healing. This antigen corresponded to the recently cloned platelet-endothelial tetraspan antigen CD151/PETA-3 (platelet-endothelial tetraspan antigen-3), and was consistently detected at EC cell–cell contact sites. In addition to CD151/PETA-3, two other members of the tetraspan superfamily, CD9 and CD81/ TAPA-1 (target of antiproliferative antibody-1), localized at endothelial cell-to-cell junctions. Biochemical analysis demonstrated molecular associations among tetraspan molecules themselves and those of CD151/ PETA-3 and CD9 with α3β1 integrin. Interestingly, mAbs directed to both CD151/PETA-3 and CD81/ TAPA-1 as well as mAb specific for α3 integrin, were able to inhibit the migration of ECs in the process of wound healing. The engagement of CD151/PETA-3 and CD81/TAPA-1 inhibited the movement of individual ECs, as determined by quantitative time-lapse video microscopy studies. Furthermore, mAbs against the CD151/PETA-3 molecule diminished the rate of EC invasion into collagen gels. In addition, these mAbs were able to increase the adhesion of EC to extracellular matrix proteins. Together these results indicate that CD81/TAPA-1 and CD151/PETA-3 tetraspan molecules are components of the endothelial lateral junctions implicated in the regulation of cell motility, either directly or by modulation of the function of the associated integrin heterodimers. 相似文献
975.
Rodolfo FaríasRodríguez Robert B. Mellor Carlos Arias Juan José PeñaCabriales 《Physiologia plantarum》1998,102(3):353-359
Nine cultivars of common bean were grown in the presence of a natural microflora without exogenous rhizobial inoculation. Nodules were harvested 30 days post planting (early flowering stage) and the presence of trehalose determined. Amounts present varied according to cultivar and were between 0.20 and 1.63 mg g−1 nodule dry weight. Rhizobial strains were isolated from the nodules of three selected cultivars (Canario 101, Flor de Mayo Bajio and Flor de Mayo 38). Trehalose levels in nodules produced after either mixed strain reinfection, or after axenic homologous reinfection or after axenic cross‐reinfection could be manipulated by applying drought stress. Mixed reinfection nodules from stressed plants accumulated between two and six times the trehalose concentration found in non‐stressed control plants. After axenic cross‐reinfection up to 48‐fold increases in nodule trehalose content were recorded during drought stress. Those cultivars exhibiting high nodule trehalose levels and/or a high degree of trehalose stimulation in response to drought stress also exhibited a high leaf relative water content and were also the most drought resistant. During drought stress nodule trehalase levels rose only slightly. 相似文献
976.
Carlos Gil-Burmann Fernando Peláez Susana Sánchez 《Primates; journal of primatology》1998,39(4):473-484
Experiments were carried out to determine the influence of food distribution (clumped vs dispersed) on processes of competition
among seven captive male hamadryas-like baboons. Spatial cohesion, cohesive behaviours that males performed and received from
their females, and aggressive and feeding behaviours of the males were collected during 35 min after food supply. Median values
and variability of these variables were compared in both the feeding situations. Food distribution influenced both asymmetries
in access and the form of competition. When food was clumped, those with less access fed by means of compensatory or alternative
strategies (away from the main source and/or by feeding supplants), and they were more aggressive towards other males. When
food was dispersed, all individuals could feed simultaneously, males that were more aggressive were those with less cohesive
OMUs, despite the fact that cohesive behaviours remained constant. Females appeared to contribute to variation in the OMU's
cohesion through their responses to both food distribution and males' competitive ability. 相似文献
977.
Francisco J.L. Gordillo Carlos Jiménez Félix L. Figueroa F. Xavier Niell 《Journal of applied phycology》1998,10(5):461-469
The consequences of the addition of CO2 (1%) in cultures of S. platensis are examined in terms of biomass yield, cell composition
and external medium composition. CO2 enrichment was tested under nitrogen saturating and nitrogen limiting conditions. Increasing
CO2 levels did not cause any change in maximum growth rate while it decreased maximum biomass yield. Protein and pigments
were decreased and carbohydrate increased by high CO2, but the capability to store carbohydrates was saturated. C:N ratio
remained unchanged while organic carbon released to the external medium was enhanced, suggesting that organic carbon release
in S. platensis is an efficient mechanism for the maintenance of the metabolic integrity, balancing the cell C:N ratio in
response to environmental CO2 changes. CO2 affected the pigment content: Phycocyanin, chlorophyll and carotenoids were reduced
in around 50%, but the photosynthetic parameters were slightly changed. We propose that in S. platensis CO2 could act promoting
degradation of pigments synthetised in excess in normal CO2 conditions, that are not necessary for light harvesting. Nitrogen
assimilation was significantly not affected by CO2, and it is proposed that the inability to stimulate N assimilation by CO2
enrichment determined the lack of response in maximum growth rate.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
978.
979.
Miguel A. Blázquez Elisa Santos Carmenlisset Flores José M. MartínezZapater Julio Salinas Carlos Gancedo 《The Plant journal : for cell and molecular biology》1998,13(5):685-689
An Arabidopsis thaliana cDNA clone, AtTPS1, that encodes a trehalose-6-phosphate synthase was isolated. The identity of this protein is supported by both structural and functional evidence. On one hand, the predicted sequence of the protein encoded by AtTPS1 showed a high degree of similarity with trehalose-6-phosphate synthases of different organisms. On the other hand, expression of the AtTPS1 cDNA in the yeast tps1 mutant restored its ability to synthesize trehalose and suppressed its growth defect related to the lack of trehalose-6-phosphate. Genomic organization and expression analyses suggest that AtTPS1 is a single-copy gene and is expressed constitutively at very low levels. 相似文献
980.
Desensitization of the Neurokinin-1 Receptor (NK1-R) in Neurons:
Effects of Substance P on the Distribution of NK1-R,
Gαq/11, G-Protein Receptor Kinase-2/3, and
β-Arrestin-1/2
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Karen McConalogue Carlos U. Corvera Patrick D. Gamp Eileen F. Grady Nigel W. Bunnett 《Molecular biology of the cell》1998,9(8):2305-2324
Observations in reconstituted systems and transfected cells indicate that G-protein receptor kinases (GRKs) and β-arrestins mediate desensitization and endocytosis of G-protein–coupled receptors. Little is known about receptor regulation in neurons. Therefore, we examined the effects of the neurotransmitter substance P (SP) on desensitization of the neurokinin-1 receptor (NK1-R) and on the subcellular distribution of NK1-R, Gαq/11, GRK-2 and -3, and β-arrestin-1 and -2 in cultured myenteric neurons. NK1-R was coexpressed with immunoreactive Gαq/11, GRK-2 and -3, and β-arrestin-1 and -2 in a subpopulation of neurons. SP caused 1) rapid NK1-R–mediated increase in [Ca2+]i, which was transient and desensitized to repeated stimulation; 2) internalization of the NK1-R into early endosomes containing SP; and 3) rapid and transient redistribution of β-arrestin-1 and -2 from the cytosol to the plasma membrane, followed by a striking redistribution of β-arrestin-1 and -2 to endosomes containing the NK1-R and SP. In SP-treated neurons Gαq/11 remained at the plasma membrane, and GRK-2 and -3 remained in centrally located and superficial vesicles. Thus, SP induces desensitization and endocytosis of the NK1-R in neurons that may be mediated by GRK-2 and -3 and β-arrestin-1 and -2. This regulation will determine whether NK1-R–expressing neurons participate in functionally important reflexes. 相似文献