首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   49049篇
  免费   3531篇
  国内免费   224篇
  2023年   191篇
  2022年   414篇
  2021年   1014篇
  2020年   665篇
  2019年   807篇
  2018年   1122篇
  2017年   980篇
  2016年   1587篇
  2015年   2428篇
  2014年   2801篇
  2013年   3116篇
  2012年   4127篇
  2011年   3947篇
  2010年   2489篇
  2009年   2275篇
  2008年   3122篇
  2007年   2985篇
  2006年   2599篇
  2005年   2396篇
  2004年   2219篇
  2003年   1900篇
  2002年   1647篇
  2001年   1320篇
  2000年   1261篇
  1999年   1009篇
  1998年   409篇
  1997年   348篇
  1996年   256篇
  1995年   230篇
  1994年   219篇
  1993年   180篇
  1992年   338篇
  1991年   303篇
  1990年   276篇
  1989年   238篇
  1988年   178篇
  1987年   172篇
  1986年   136篇
  1985年   110篇
  1984年   83篇
  1983年   90篇
  1982年   63篇
  1981年   56篇
  1980年   57篇
  1979年   70篇
  1978年   52篇
  1977年   52篇
  1975年   43篇
  1974年   67篇
  1973年   43篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
53.
54.
The tissue polarity genes control the polarity of hairs, bristles and ommatidia in the adult epidermis of Drosophila. We report here the identification of a new tissue polarity gene named starry night (stan). Mutations in this essential gene alter the polarity of cuticular structures in all regions of the adult body. The detailed polarity phenotype of stan on the wing suggested that it is most likely a component of the frizzled (fz) pathway. Consistent with this hypothesis, stan appears to be downstream of and required for fz function. We molecularly cloned stan and found that it encodes a huge protocadherin containing nine cadherin motifs, four EGF-like motifs, two laminin G motifs, and seven transmembrane domains. This suggests that Stan functions in signal reception, perhaps together with Fz.  相似文献   
55.
56.
Geotrichum candidum completely neutralized the acid brine and reduced its biochemical oxygen demand (BOD) by 88%. Yield of dry mycelium was 62 g per 100 g of BOD utilized.  相似文献   
57.
58.
Despite the efficacy of antiretroviral-based pre-exposure prophylactics (PrEP) in men who have sex with men, studies in women have produced widely varying outcomes. Recent evidence demonstrates that vaginal microbial communities are associated with increased HIV acquisition risk and may impact PrEP efficacy. Here, we investigate the mechanisms underlying how vaginal bacteria alter PrEP drug levels and impact HIV infection rates ex vivo. Using cervicovaginal lavages (CVLs) from women with or without bacterial vaginosis (BV), we identified microbial metabolism of PrEP drugs in BV samples through LC-MS/MS analysis of soluble drug levels and metabolite formation in dual T-cell cultures. CVL samples were assessed for microbiome analysis using sequencing of bacterial 16S rRNA genes. We also observed non-Lactobacillus bacteria that are associated with BV may potentially impact PrEP efficacy through increased HIV infection rates in co-cultures containing Lactobacillus or BV bacteria, PrEP drugs, CEM-GFP cells, and HIV-1LAI virus. Finally, we used these data to develop a novel predictive mathematical simulation modeling system to predict these drug interactions for future trials. These studies demonstrate how dysbiotic vaginal microbiota may impact PrEP drugs and provides evidence linking vaginal bacteria to PrEP efficacy in women.  相似文献   
59.
Two new beta-xylosyl derivatives of ginsenoside Re, 20(S)-protopanaxatriol 6-O-alpha-L-rhamnopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 4)]-beta-D-glucopyranosyl-20-O-beta-D-glucopyranoside and 20(S)-protopanaxatriol 6-O-alpha-L-rhamnopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 6)]-beta-D-glucopyranosyl-20-O-beta-D-glucopyranoside, were respectively synthesized from p-nitrophenyl beta-D-xylopyranoside and phenyl beta-D-xylopyranoside as donors and ginsenoside Re as the acceptor in 25% acetone and acetonitrile by a cellulase preparation from Trichoderma viride and a beta-galactosidase preparation from Aspergillus oryzae. The latter enzyme preparation also catalyzed the hydrolysis of ginsenoside Re to the minor saponin, ginsenoside Rg2.  相似文献   
60.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号