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   27690篇
  免费   2581篇
  国内免费   222篇
  2023年   142篇
  2022年   311篇
  2021年   627篇
  2020年   358篇
  2019年   445篇
  2018年   569篇
  2017年   474篇
  2016年   852篇
  2015年   1363篇
  2014年   1385篇
  2013年   1707篇
  2012年   2100篇
  2011年   1914篇
  2010年   1232篇
  2009年   1191篇
  2008年   1551篇
  2007年   1502篇
  2006年   1356篇
  2005年   1311篇
  2004年   1286篇
  2003年   1224篇
  2002年   1146篇
  2001年   538篇
  2000年   421篇
  1999年   465篇
  1998年   339篇
  1997年   235篇
  1996年   219篇
  1995年   249篇
  1994年   207篇
  1993年   199篇
  1992年   268篇
  1991年   275篇
  1990年   216篇
  1989年   226篇
  1988年   203篇
  1987年   181篇
  1986年   172篇
  1985年   201篇
  1984年   190篇
  1983年   134篇
  1982年   135篇
  1981年   121篇
  1980年   123篇
  1979年   111篇
  1978年   93篇
  1977年   97篇
  1975年   75篇
  1974年   79篇
  1973年   69篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
[Acyl CoA]monoacylglycerol acyltransferase 2 (MGAT2) is of interest as a target for therapeutic treatment of diabetes, obesity and other diseases which together constitute the metabolic syndrome. In this Letter we report our discovery and optimisation of a novel series of MGAT2 inhibitors. The development of the SAR of the series and a detailed discussion around some key parameters monitored and addressed during the lead generation phase will be given. The in vivo results from an oral lipid tolerance test (OLTT) using the MGAT2 inhibitor (S)-10, shows a significant reduction (68% inhibition relative to na?ve, p <0.01) in plasma triacylglycerol (TAG) concentration.  相似文献   
52.
53.
54.
Understanding drivers of biodiversity patterns is of prime importance in this era of severe environmental crisis. More diverse plant communities have been postulated to represent a larger functional trait‐space, more likely to sustain a diverse assembly of herbivore species. Here, we expand this hypothesis to integrate environmental, functional and phylogenetic variation of plant communities as factors explaining the diversity of lepidopteran assemblages along elevation gradients in the Swiss Western Alps. According to expectations, we found that the association between butterflies and their host plants is highly phylogenetically structured. Multiple regression analyses showed the combined effect of climate, functional traits and phylogenetic diversity in structuring butterfly communities. Furthermore, we provide the first evidence that plant phylogenetic beta diversity is the major driver explaining butterfly phylogenetic beta diversity. Along ecological gradients, the bottom up control of herbivore diversity is thus driven by phylogenetically structured turnover of plant traits as well as environmental variables.  相似文献   
55.
56.
Leuconostoc (Lc.) mesenteroides TA33a produced three bacteriocins with different inhibitory activity spectra. Bacteriocins were purified by adsorption/desorption from producer cells and reverse phase high-performance liquid chromatography. Leucocin C-TA33a, a novel bacteriocin with a predicted molecular mass of 4598 Da, inhibited Listeria and other lactic acid bacteria (LAB). Leucocin B-TA33a has a predicted molecular mass of 3466 Da, with activity against Leuconostoc/Weissella (W.) strains, and appears similar to mesenterocin 52B and dextranicin 24, while leucocin A-TA33a, which also inhibited Listeria and other LAB strains, is identical to leucocin A-UAL 187. A survey of other known bacteriocin-producing Leuconostoc/Weissella strains for the presence of the three different bacteriocins revealed that production of leucocin A-, B- and C-type bacteriocins was widespread. Lc. carnosum LA54a, W. paramesenteroides LA7a, and Lc. gelidum UAL 187-22 produced all three bacteriocins, whereas W. paramesenteroides OX and Lc. carnosum TA11a produced only leucocin A- and B-type bacteriocins. Received: 11 April 1997 / Accepted: 10 June 1997  相似文献   
57.
The present study sought to determine which of the common Poaceae species in the study area contribute most to the Poaceae pollen season curve, and to determine the phenological behaviour of the species studied. The different floral phenophases in thirty-three Poaceae species common in and around the city of Córdoba (SW Iberian Peninsula) were checked periodically over the period 2004–2006. Results showed that longer phenological ranges were recorded in the coolest and wettest year, and shorter ranges in the warmest and driest year. Moreover, ranges varied as a function of altitude: populations in lower-lying areas flowered earlier than those at higher altitudes. The results, taken in conjunction with the findings of preliminary research into potential pollen production, showed that probably only four of the Poaceae species studied—Dactylis glomerata, Lolium rigidum, Trisetaria panicea and Vulpia geniculata—were major contributors to the Poaceae airborne pollen curve.  相似文献   
58.
59.
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