全文获取类型
收费全文 | 5017篇 |
免费 | 494篇 |
国内免费 | 1篇 |
专业分类
5512篇 |
出版年
2023年 | 25篇 |
2022年 | 77篇 |
2021年 | 134篇 |
2020年 | 76篇 |
2019年 | 87篇 |
2018年 | 112篇 |
2017年 | 75篇 |
2016年 | 161篇 |
2015年 | 236篇 |
2014年 | 286篇 |
2013年 | 295篇 |
2012年 | 389篇 |
2011年 | 373篇 |
2010年 | 227篇 |
2009年 | 186篇 |
2008年 | 246篇 |
2007年 | 253篇 |
2006年 | 202篇 |
2005年 | 216篇 |
2004年 | 203篇 |
2003年 | 174篇 |
2002年 | 146篇 |
2001年 | 74篇 |
2000年 | 73篇 |
1999年 | 52篇 |
1998年 | 60篇 |
1997年 | 48篇 |
1996年 | 37篇 |
1995年 | 42篇 |
1994年 | 42篇 |
1993年 | 37篇 |
1992年 | 64篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 38篇 |
1984年 | 32篇 |
1983年 | 27篇 |
1982年 | 24篇 |
1981年 | 30篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 34篇 |
1977年 | 26篇 |
1976年 | 27篇 |
1975年 | 30篇 |
1974年 | 24篇 |
排序方式: 共有5512条查询结果,搜索用时 15 毫秒
101.
102.
103.
New synaptic bouton formation is disrupted by misregulation of microtubule stability in aPKC mutants
The Baz/Par-3-Par-6-aPKC complex is an evolutionarily conserved cassette critical for the development of polarity in epithelial cells, neuroblasts, and oocytes. aPKC is also implicated in long-term synaptic plasticity in mammals and the persistence of memory in flies, suggesting a synaptic function for this cassette. Here we show that at Drosophila glutamatergic synapses, aPKC controls the formation and structure of synapses by regulating microtubule (MT) dynamics. At the presynapse, aPKC regulates the stability of MTs by promoting the association of the MAP1Brelated protein Futsch to MTs. At the postsynapse, aPKC regulates the synaptic cytoskeleton by controlling the extent of Actin-rich and MT-rich areas. In addition, we show that Baz and Par-6 are also expressed at synapses and that their synaptic localization depends on aPKC activity. Our findings establish a novel role for this complex during synapse development and provide a cellular context for understanding the role of aPKC in synaptic plasticity and memory. 相似文献
104.
105.
106.
We analyze two large datasets from technological networks with location and social data: user location records from an online location-based social networking service, and anonymized telecommunications data from a European cellphone operator, in order to investigate the differences between individual and group behavior with respect to physical location. We discover agreements between the two datasets: firstly, that individuals are more likely to meet with one friend at a place they have not visited before, but tend to meet at familiar locations when with a larger group. We also find that groups of individuals are more likely to meet at places that their other friends have visited, and that the type of a place strongly affects the propensity for groups to meet there. These differences between group and solo mobility has potential technological applications, for example, in venue recommendation in location-based social networks. 相似文献
107.
Mark Lyte Ashley Chapel Joshua M. Lyte Yongfeng Ai Alexandra Proctor Jay-Lin Jane Gregory J. Phillips 《PloS one》2016,11(1)
The increasing recognition that the gut microbiota plays a central role in behavior and cognition suggests that the manipulation of microbial taxa through diet may provide a means by which behavior may be altered in a reproducible and consistent manner in order to achieve a beneficial outcome for the host. Resistant starch continues to receive attention as a dietary intervention that can benefit the host through mechanisms that include altering the intestinal microbiota. Given the interest in dietary approaches to improve health, the aim of this study was to investigate whether the use of dietary resistant starch in mice to alter the gut microbiota also results in a change in behavior. Forty-eight 6 week-old male Swiss-Webster mice were randomly assigned to 3 treatment groups (n = 16 per group) and fed either a normal corn starch diet (NCS) or diets rich in resistant starches HA7 diet (HA7) or octenyl-succinate HA7 diet (OS-HA7) for 6 week and monitored for weight, behavior and fecal microbiota composition. Animals fed an HA7 diet displayed comparable weight gain over the feeding period to that recorded for NCS-fed animals while OS-HA7 displayed a lower weight gain as compared to either NCS or HA7 animals (ANOVA p = 0.0001; NCS:HA7 p = 0.244; HA7:OS-HA7 p<0.0001; NCS:OS-HA7 p<0.0001). Analysis of fecal microbiota using 16s rRNA gene taxonomic profiling revealed that each diet corresponded with a unique gut microbiota. The distribution of taxonomic classes was dynamic over the 6 week feeding period for each of the diets. At the end of the feeding periods, the distribution of taxa included statistically significant increases in members of the phylum Proteobacteria in OS-HA7 fed mice, while the Verrucomicrobia increased in HA7 fed mice over that of mice fed OS-HA7. At the class level, members of the class Bacilli decreased in the OS-HA7 fed group, and Actinobacteria, which includes the genus Bifidobacteria, was enriched in the HA7 fed group compared to the control diet. Behavioral analysis revealed that animals demonstrated profound anxiety-like behavior as observed by performance on the elevated-plus maze with time spent by the mice in the open arm (ANOVA p = 0.000; NCS:HA7 p = 0.004; NCS:OS-HA7 p = 1.000; HA7:OS-HA7 p = 0.0001) as well as entries in the open arm (ANOVA p = 0.039; NCS:HA7 p = 0.041; HA7:OS-HA7 p = 0.221; NCS:OS-HA7 p = 1.000). Open-field behavior, a measure of general locomotion and exploration, revealed statistically significant differences between groups in locomotion as a measure of transitions across quadrant boundaries. Additionally, the open-field assay revealed decreased exploration as well as decreased rearing in HA7 and OS-HA7 fed mice demonstrating a consistent pattern of increased anxiety-like behavior among these groups. Critically, behavior was not correlated with weight. These results indicate that diets based on resistant starch can be utilized to produce quantifiable changes in the gut microbiota and should be useful to “dial-in” a specific microbiome that is unique to a particular starch composition. However, undesirable effects can also be associated with resistant starch, including lack of weight gain and increased anxiety-like behaviors. These observations warrant careful consideration when developing diets rich in resistant starch in humans and animal models. 相似文献
108.
Abundance of common species,not species richness,drives delivery of a real‐world ecosystem service 下载免费PDF全文
Rachael Winfree Jeremy W. Fox Neal M. Williams James R. Reilly Daniel P. Cariveau 《Ecology letters》2015,18(7):626-635
Biodiversity‐ecosystem functioning experiments have established that species richness and composition are both important determinants of ecosystem function in an experimental context. Determining whether this result holds for real‐world ecosystem services has remained elusive, however, largely due to the lack of analytical methods appropriate for large‐scale, associational data. Here, we use a novel analytical approach, the Price equation, to partition the contribution to ecosystem services made by species richness, composition and abundance in four large‐scale data sets on crop pollination by native bees. We found that abundance fluctuations of dominant species drove ecosystem service delivery, whereas richness changes were relatively unimportant because they primarily involved rare species that contributed little to function. Thus, the mechanism behind our results was the skewed species‐abundance distribution. Our finding that a few common species, not species richness, drive ecosystem service delivery could have broad generality given the ubiquity of skewed species‐abundance distributions in nature. 相似文献
109.
Li WG Stoll LL Rice JB Xu SP Miller FJ Chatterjee P Hu L Oberley LW Spector AA Weintraub NL 《Free radical biology & medicine》2003,34(7):937-946
Oxidized lipids, such as 13-hydroperoxyoctadecadienoic acid (13-HPODE), have been implicated in the pathogenesis of atherosclerosis. 13-HPODE, a constituent of oxidized low-density lipoproteins, can induce cytotoxicity of vascular smooth muscle cells (SMC), which may facilitate plaque destabilization and/or rupture. 13-HPODE-induced cytotoxicity has been linked to oxidative stress, although the mechanisms by which this occurs are unknown. In the present study, we show that 13-HPODE and 9-HPODE (10-30 microM) increased superoxide (O2*-) production and induced cytotoxicity in SMC. The 13-HPODE-induced increase in O2*- was blocked by transfecting the cells with antisense oligonucleotides against p22phox, suggesting that the O2*- was produced by NAD(P)H oxidase. Similar concentrations of the corresponding HPODE reduction products, 13-hydroxyoctadecadienoic acid (13-HODE) and 9-HODE, neither increased O2*- production nor induced cytotoxicity, while 4-hydroxy nonenal (4-HNE), an unsaturated aldehyde lipid peroxidation product, induced cytotoxicity without increasing O2*- production. Treatment with superoxide dismutase or Tiron to scavenge O2*-, or transfection with p22phox antisense oligonucleotides to inhibit O2*- production, attenuated 13-HPODE-induced cytotoxicity, but not that induced by 4-HNE. These findings suggest that activation of NAD(P)H oxidase, and production of O2*-, play an important role in lipid hydroperoxide-induced smooth muscle cytotoxicity. 相似文献
110.
White Nicholas J Ashley Elizabeth A Recht Judith Delves Michael J Ruecker Andrea Smithuis Frank M Eziefula Alice C Bousema Teun Drakeley Chris Chotivanich Kesinee Imwong Mallika Pukrittayakamee Sasithon Prachumsri Jetsumon Chu Cindy Andolina Chiara Bancone Germana Hien Tran T Mayxay Mayfong Taylor Walter RJ von Seidlein Lorenz Price Ric N Barnes Karen I Djimdé Abdoulaye ter Kuile Feiko Gosling Roly Chen Ingrid Dhorda Mehul J Stepniewska Kasia Guérin Philippe Woodrow Charles J Dondorp Arjen M Day Nicholas PJ Nosten Francois H 《Malaria journal》2014,13(1):1-14