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   93508篇
  免费   19706篇
  国内免费   5811篇
  2024年   111篇
  2023年   832篇
  2022年   1544篇
  2021年   3734篇
  2020年   4241篇
  2019年   6321篇
  2018年   6395篇
  2017年   6124篇
  2016年   6992篇
  2015年   7585篇
  2014年   8314篇
  2013年   9063篇
  2012年   7723篇
  2011年   6910篇
  2010年   6685篇
  2009年   4967篇
  2008年   4442篇
  2007年   3638篇
  2006年   3185篇
  2005年   2779篇
  2004年   2542篇
  2003年   2380篇
  2002年   2036篇
  2001年   1648篇
  2000年   1416篇
  1999年   1120篇
  1998年   628篇
  1997年   585篇
  1996年   545篇
  1995年   507篇
  1994年   458篇
  1993年   349篇
  1992年   446篇
  1991年   381篇
  1990年   315篇
  1989年   273篇
  1988年   186篇
  1987年   213篇
  1986年   174篇
  1985年   172篇
  1984年   120篇
  1983年   118篇
  1982年   98篇
  1981年   86篇
  1980年   55篇
  1979年   66篇
  1978年   66篇
  1976年   50篇
  1973年   63篇
  1972年   52篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The structure of the tightly bound complex of the globular myosin head with F-actin is the key to understanding important details of the mechanism of how the actin-myosin motor functions. The current notion on this complex is based on the docking of known atomic structures of constituent proteins into low-resolution electron-density maps. The atomic structure of the complex was refined by the molecular mechanics method, which consists in minimizing the energy of molecular interaction and which makes it possible to optimize not only the relative position of protein backbones as rigid bodies, but also the position of side chains on the protein interface. The structure calculated using ICM-Pro software, on the one hand, is close to the model obtained using electron microscopy; on the other hand, it ensures the best calculated interaction energy and accounts for the results of mutagenesis experiments. On the basis of the structure obtained, we can suggest the molecular mechanisms underlying the actin-activated release of ATP hydrolysis products from myosin and the decrease in the affinity of myosin for actin upon binding of nucleotides.  相似文献   
72.
The 1701-base nucleotide sequence (not including the poly(A) tail) of a cDNA for the gamma subunit of the ATP synthase from Chlamydomonas reinhardtii was determined. A start translation sequence, 23 bases in from the 5' end, initiates an 1074-base-long open reading frame. The sequence of the first 21 amino acids at the amino-terminal end of the mature gamma subunit from C. reinhardtii was determined and compared to the deduced amino acid sequence of the open reading frame. From this it was determined that the mature protein contains 323 amino acids, with the first 35 amino acids probably being part of the transit peptide. The length of the mature protein is the same as that for the mature gamma subunit from spinach, for which only a few of the amino acids of the transit peptide are known. The similarity of the two mature proteins at the nucleotide level is 56% while at the amino acid level it is 77%. In addition, the 3 cysteines, which in spinach are involved in the energy-linked catalytic functions of the ATP synthase, are conserved in the predicted amino acid sequence for the gamma subunit from C. reinhardtii. In contrast, the mature C. reinhardtii gamma subunit contains 3 additional cysteine residues not found in the spinach gamma subunit.  相似文献   
73.
74.
75.
76.
77.
During the past 40 years, more than 400 Sudden Unexplained Deaths (SUDs) have occurred in Yunnan, southwestern China. Epidemiological and toxicological analyses suggested that a newly discovered mushroom called Trogia venenata was the leading culprit for SUDs. At present, relatively little is known about the genetics and natural history of this mushroom. In this study, we analyzed the sequence variation at four DNA fragments among 232 fruiting bodies of T. venenata collected from seven locations. Our ITS sequence analyses confirmed that all the isolates belonged to the same species. The widespread presence of sequence heterozygosity within many strains at each of three protein-coding genes suggested that the fruiting bodies were diploid, dikaryotic or heterokaryotic. Within individual geographic populations, we found significant deviations of genotype frequencies from Hardy-Weinberg expectations, with the overall observed heterozygosity lower than that expected under random mating, consistent with prevalent inbreeding within local populations. The geographic populations were overall genetically differentiated. Interestingly, while a positive correlation was found between population genetic distance and geographic distance, there was little correlation between genetic distance and barium concentration difference for the geographic populations. Our results suggest frequent inbreeding, geographic structuring, and limited gene flow among geographic populations of T. venenata from southwestern China.  相似文献   
78.
The applicability of the nucleophilicity/electrophilicity concept to the explanation of mechanisms of formation and transformation of humic substances was considered. Sequential time changes in the structure and properties of humic substances in phosphatic soil have been revealed. Different elemental composition of humic and fulvic acids at different stages of humus transformation was due to different patterns of electron density distribution in phosphorus-modified fragments of humic molecules. The important role of metals and phosphorus in realization of different pathways of humic substance transformation was demonstrated.  相似文献   
79.
80.
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