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   3018篇
  免费   160篇
  国内免费   1篇
  3179篇
  2022年   13篇
  2021年   24篇
  2019年   24篇
  2018年   19篇
  2017年   29篇
  2016年   35篇
  2015年   79篇
  2014年   86篇
  2013年   321篇
  2012年   130篇
  2011年   144篇
  2010年   85篇
  2009年   91篇
  2008年   114篇
  2007年   118篇
  2006年   121篇
  2005年   135篇
  2004年   116篇
  2003年   119篇
  2002年   95篇
  2001年   97篇
  2000年   112篇
  1999年   75篇
  1998年   30篇
  1997年   28篇
  1996年   26篇
  1995年   34篇
  1994年   25篇
  1993年   21篇
  1992年   77篇
  1991年   67篇
  1990年   53篇
  1989年   58篇
  1988年   48篇
  1987年   45篇
  1986年   44篇
  1985年   38篇
  1984年   29篇
  1983年   43篇
  1982年   34篇
  1981年   26篇
  1980年   27篇
  1979年   31篇
  1978年   17篇
  1977年   16篇
  1976年   25篇
  1975年   23篇
  1974年   12篇
  1973年   18篇
  1969年   13篇
排序方式: 共有3179条查询结果,搜索用时 15 毫秒
91.
Rhizobium leguminosarum bv. trifolii strain TA1 is an aerobic, motile, Gram-negative, non-spore-forming rod that is an effective nitrogen fixing microsymbiont on the perennial clovers originating from Europe and the Mediterranean basin. TA1 however is ineffective with many annual and perennial clovers originating from Africa and America. Here we describe the features of R. leguminosarum bv. trifolii strain TA1, together with genome sequence information and annotation. The 8,618,824 bp high-quality-draft genome is arranged in a 6 scaffold of 32 contigs, contains 8,493 protein-coding genes and 83 RNA-only encoding genes, and is one of 20 rhizobial genomes sequenced as part of the DOE Joint Genome Institute 2010 Community Sequencing Program.  相似文献   
92.
Cathepsin B was purified from the crude extract of carp (Cyprinus carpio) hepato-pancreas by the method involving ammonium sulfate fractionation and five sequential chromatographies monitored the activity with Z-Arg-Arg-MCA as a substrate, and the specific activity increased about 11,400 fold with a 2% recovery. Although the homogeneity of the purified cathepsin B was established on Native-PAGE, it migrated as two bands of 29,000 and 25,000 molecular weights by the single and heavy chains on SDS-PAGE, respectively. The monospecific antibody against the homogeneous cathepsin B was purified by the affinity chromatography on cathepsin B-Sepharose 4B, and did not immunologically react with rat cathepsin B, carp cathepsins H and L but only with carp cathepsin B by immunoelectrophoretic blot analysis. As the result of the tissue and liver distributions of cathepsin B, the remarkable immunological reactivities in the extracts of spleen, kidney and hepato-pancreas in carp and those of pacific cod, yellow fin tuna, skip jack tuna and common mackerel in pisces were detected with the anti-carp hepato-pancreas cathepsin B at molecular weight of nearby 29,000 or 25,000.  相似文献   
93.
94.
OBJECTIVES: To clarify the underlying molecular mechanism of corticosterone methyl oxidase type II (CMO II) deficiency, Japanese patients newly diagnosed with CMO II deficiency were investigated. METHODS: We analyzed the patients' genomic DNA sequence on all 9 exons of the CYP11B2 gene. In addition, restriction fragment length polymorphism (RFLP) analysis and expression studies were performed. RESULTS: The analysis showed that the patients homozygously retained a missense mutation, Gumacr;GC[435Gly]-->Aumacr;GC[Ser], in the CYP11B2 gene. Expression studies indicated that the steroid 18-hydroxylase/oxidase activities of the mutant enzyme were substantially reduced. CONCLUSION: These results support the hypothesis that this mutation causes CMO II deficiency in the patients, and are in accordance with our theory that the partial loss of P-450(C18) activities causes CMO II deficiency.  相似文献   
95.
Since green tea catechins are known to have antimicrobial activity against a variety of microorganisms, their possible effects on Helicobacter pylori in combination with antibiotics were examined. Fifty-six clinical isolates of H. pylori, including 19 isolates highly resistant to metronidazole (MTZ) and/or clarithromycin (CLR), were used to determine in vitro sensitivity to tea catechins. The MIC90 of both epigallocatechin gallate (EGCg) and epicatechin gallate (ECg) was 100 microg/ml. However, other tea catechins tested did not show any anti-H. pylori activity. Highly antibiotic-resistant clinical isolates showed a similar sensitivity to both EGCg and ECg. The kinetic study of antibacterial activity in liquid cultures revealed a relatively slow but strong activity on the growth of H. pylori. In combination with sub-MIC of amoxicillin (AMX), the antibacterial activity of AMX was significantly enhanced by the presence of EGCg. To estimate the general combination effect between EGCg and other antibiotics, such as MTZ and CLR, on the antibacterial activity against clinical isolates, the fraction inhibitory concentration (FIC) was determined by checkerboard study. The FIC indexes showed additive effects between EGCg and antibiotics tested. These results indicatethat EGCg may be a valuable therapeutic agent against H. pylori infection.  相似文献   
96.
The relative stereochemistry of cervicarcin, an antitumor antibiotic, was determined as shown in 1, which represents the absolute stereochemistry also.  相似文献   
97.
Methylglyoxal (MGO) is a metabolite of glucose. Since serum MGO level is increased in diabetic patients, MGO is implicated in diabetic complications related to vascular injury. We have recently demonstrated that glucose metabolite is a more powerful stimulant for endothelial cells (ECs) injury rather than glucose or advanced glycation-end products. Recent clinical trials suggest that angiotensin receptor blockers are effective to prevent diabetes-associated cardiovascular disorders beyond blood pressure lowering effect. To explore the mechanisms, we examined effects of telmisartan on MGO-induced ECs injury. Treatment of human umbilical vein ECs with MGO (560 μM) induced time-dependent (0-24 h) cell death. MGO-induced cell death was apoptosis since MGO increased cleaved caspase-3 expression. Telmisartan (0.1-10 μM) inhibited MGO-induced cell death and caspase-3 activation. These results indicate that telmisartan prevents MGO-induced apoptosis by inhibiting caspase-3 activation, which might explain at least in part the beneficial effects of telimisartan against diabetes-related cardiovascular diseases.  相似文献   
98.
Green cabbage (Brassica campestris, leafy variety) and turnip (Brassica campestris var. rapifera, rooty variety) were grown in both monocultures and mixtures at three nutrient levels to investigate their responses to nutrient availability with respect to biomass allocation, morphological plasticity and competitive ability. Their allocation parameters and leaf morphological traits were affected by both nutrient availability and developmental stage. Both of the varieties had a smaller biomass allocation to leaf blades, but a greater allocation to petioles at high nutrient levels. Root:shoot ratio (RSR) of green cabbage decreased with increasing nutrient availability, whereas that of turnip increased. Turnip had a smaller leaf blade weight ratio (LBWR) than cabbage, being compensated for by larger leaf area ratio (LAR) and specific leaf area (SLA). Leaf area ratio and SLA of both the varieties increased with increasing nutrient availability as did their mean dry weights. The mean dry weight of turnip was slightly greater than that of green cabbage in their respective monocultures, while that of green cabbage was greater than that of turnip in their 1:1 mixture. Therefore, green cabbage, having inherently greater biomass allocation to leaves, was generally more competitive than turnip with more biomass allocation to roots, especially at higher nutrient levels. However, within a variety, morphological plasticity (variation in LAR and SLA) was more important than the plasticity in biomass allocation (e.g. variation in RSR and LBWR) in determining competitive ability. The implication of our results is that competition models based on biomass allocation pattern alone may fail to predict competitive outcomes and that such models should also take morphological plasticity into full account.  相似文献   
99.
100.
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