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   21280篇
  免费   1353篇
  国内免费   1055篇
  2023年   266篇
  2022年   370篇
  2021年   459篇
  2020年   511篇
  2019年   733篇
  2018年   727篇
  2017年   575篇
  2016年   554篇
  2015年   566篇
  2014年   1158篇
  2013年   1545篇
  2012年   800篇
  2011年   1143篇
  2010年   882篇
  2009年   1051篇
  2008年   1022篇
  2007年   979篇
  2006年   947篇
  2005年   860篇
  2004年   764篇
  2003年   693篇
  2002年   626篇
  2001年   346篇
  2000年   323篇
  1999年   354篇
  1998年   369篇
  1997年   320篇
  1996年   270篇
  1995年   295篇
  1994年   247篇
  1993年   220篇
  1992年   226篇
  1991年   175篇
  1990年   171篇
  1989年   153篇
  1988年   127篇
  1987年   131篇
  1986年   118篇
  1985年   206篇
  1984年   318篇
  1983年   299篇
  1982年   277篇
  1981年   260篇
  1980年   248篇
  1979年   209篇
  1978年   167篇
  1977年   150篇
  1976年   123篇
  1975年   116篇
  1974年   101篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
《Molecular cell》2021,81(17):3650-3658.e5
  1. Download : Download high-res image (183KB)
  2. Download : Download full-size image
  相似文献   
44.
The non-receptor tyrosine kinase Syk (spleen tyrosine kinase) is a pharmaceutical relevant target because its over-activation is observed in several autoimmune diseases, allergy, and asthma. Here we report the identification of two novel inhibitors of Syk by high-throughput docking into a rare C-helix-out conformation published recently. Interestingly, both compounds are slightly more active on ZAP70 (Zeta-chain-associated protein kinase 70), which is the kinase closest to Syk in the phylogenetic tree of human kinases. Taken together, the docking pose and experimental results suggest that the higher affinity of the inhibitors for ZAP70 than Syk originates from a more populated C-helix-out conformation in ZAP70. The latter observation is congruent with the 100-fold lower intrinsic activity of ZAP70 than Syk, as the C-helix-out conformation is inactive. The pharmacophore features of DFG-in, C-helix-out compounds are analyzed in relation to DFG-out inhibitors.  相似文献   
45.
46.
  相似文献   
47.
Bacterial resistance is inevitable and is a growing concern. It can be addressed only by discovery and development of new agents. However the discovery and development of new antibacterial agents are at an all time low. This article broadly examines the historical as well as current status of antibacterial discovery and provides some perspective as how to address some of the challenges.  相似文献   
48.
Rice is the most important crop for the majority of population across the world with sensitive behavior toward heavy metals such as chromium (Cr) in polluted regions. Although, there is no information on the Cr resistance phenotyping in rice. Herein, two different groups of rice cultivars (normal, and hybrid) were used, each group with 14 different rice cultivars. Firstly, seed germination analysis was conducted by evaluating various seed germination indices to identify the rice cultivars with greatest seed germination vigor. Furthermore, exposure of chromium (Cr) toxicity to 28 different rice varieties (NV1-NV14, HV1-HV14) caused noticeable plant biomass reduction. Subsequently, NV2, NV6, NV10, NV12, NV13 (normal type), HV1, HV4, HV8, and HV9 (hybrid types) were pragmatic as moderately sensitive varieties, while NV3, NV4, NV9, and NV14 (normal type), HV3, HV6, HV7, and HV13 were observed as moderately tolerant. Although, NV7, and HV10 were ranked most sensitive cultivars, and NV11, and HV14 were considered as most tolerant varieties as compared to the other rice (both groups) genotypes. Afterward, Cr induced reduction in chlorophyll pigments were significantly lesser in HV14 relative to NV11, NV7, and especially HV10, and as a result HV14 modulated the total soluble sugar level as well as reduced ROS accumulation, and MDA contents production by stimulating the antioxidant defense mechanism conspicuously which further reduced the electrolyte leakage as well. Our outcomes provide support to explore the Cr tolerance mechanism in cereal crops as well as knowledge about rice breeding with increased tolerance against Cr stress.  相似文献   
49.
A field experiment encompassing both neighbour- and nutrient-manipulations was conducted in a nutrient-impoverished old-field habitat to investigate how the intensity of plant competition was affected by soil nutrient level. Three perennial grasses were used as target species: Agropyron repens, Poa pratensis and Phleum pratense. Neighbour manipulations involved the removal (through herbicide application) of all neighbouring vegetation within a 20 cm or 40 cm radius around target plants. Target performance was measured under five levels of added nutrients (N-P-K) in both the neighbour-removal plots and in non-removal (control) plots. Both neighbour and nutrient manipulations had a highly significant effect on both biomass and tiller production but the interaction between these treatments was generally insignificant. Below-ground/above-ground biomass quotient was affected only by neighbour manipulations and was greatest in the control plots (with no neighbours removed) for all three species. The suppressive effect of neighbours was not markedly affected by nutrient level. However, yield suppression showed a significant decreasing trend with increasing nutrient level for biomass production in Agropyron and an increasing trend for tiller production in Phleum. For Poa, there was no trend in the intensity of competition across nutrient level. The results suggest that the general intensity of competition within this community neither increases nor decreases with increasing nutrient level. Rather, coexisting species appear to respond individually in terms of the intensity of competition that they experience. These results conflict with predictions from the triangular C-S-R model of plant strategies. However, they are consistent with a recently modified ‘habitat templet’ model for vegetation.  相似文献   
50.
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