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   7146篇
  免费   328篇
  国内免费   3篇
  2023年   35篇
  2022年   29篇
  2021年   76篇
  2020年   89篇
  2019年   120篇
  2018年   272篇
  2017年   248篇
  2016年   318篇
  2015年   231篇
  2014年   333篇
  2013年   508篇
  2012年   403篇
  2011年   561篇
  2010年   316篇
  2009年   209篇
  2008年   376篇
  2007年   427篇
  2006年   468篇
  2005年   393篇
  2004年   331篇
  2003年   375篇
  2002年   289篇
  2001年   184篇
  2000年   162篇
  1999年   108篇
  1998年   60篇
  1997年   22篇
  1996年   14篇
  1995年   20篇
  1994年   15篇
  1993年   13篇
  1992年   13篇
  1991年   21篇
  1990年   12篇
  1988年   14篇
  1987年   15篇
  1986年   14篇
  1985年   27篇
  1984年   22篇
  1983年   14篇
  1982年   16篇
  1981年   13篇
  1979年   20篇
  1978年   18篇
  1977年   16篇
  1974年   10篇
  1953年   18篇
  1952年   40篇
  1888年   14篇
  1887年   14篇
排序方式: 共有7477条查询结果,搜索用时 15 毫秒
971.
972.
The analysis of offsprings from the partial diallel crosses is presented. In considered type of crossing, p parental forms into H separate groups are devided. Single crosses among parental forms, from separate groups only, are performed. The analysis for experiments laid out in efficiency balanced block designs is given.  相似文献   
973.
974.
Betaine when present in the culture medium could induce the activity of betaine: homocysteine methyltransferase (EC 2.1.1.5) in mouse L-cells, and leukemic L1210 cells, as well as in mouse embryo fibroblasts grown in vitro. We found this process to be time- and concentration-dependent. A persisting contact of the cells with betaine was indispensible for expressing and maintaining the enzyme activity. The treatment of cells with cycloheximide or actinomycin D abolished the process of induction. Methionine as well as homocysteine, when present either in the culture medium or in the reaction mixture, strongly depressed the activity of this enzyme. The L-cells with the induced betaine: homocysteine methyltransferase survived but did not multiply in the methionine-deficient medium, therefore, they did not become prototrophs with respect to methionine.  相似文献   
975.
976.
Environmental factors play an essential role in the etiology of diseases of the hematopoietic system. Such factors include soil and water pollution and the presence of metals and toxic compounds in the air. Measuring the content of metallic elements in rainwater has become an accepted procedure for environmental pollution monitoring. In accordance with the above, it was decided to study relations between the content of selected elements in rainwater and hospitalization frequency due to chronic lymphocytic leukemia (CLL, C91 on ICD-10) and chronic myeloid leukemia (CML, C92 on ICD-10). It can be assumed that hospitalization frequency is a reliable indicator of exacerbations of these diseases. The annual average of hospitalizations due to a given disease during the years 2000–2002 was correlated with the annual average content of a given element in rainwater using the Spearman’s correlation indicator to describe the relationship between the element content and the disease that is possibly a consequence of the element’s presence in rainwater. In cases of CLL for all the subjected population and for men, no statistically significant correlations were found. For women, statistically significant correlations were found for chromium (r?=?0.66), lead (r?=?0.58), copper (r?=?0.58), and cadmium (r?=?0.51). For CML in all the studied population significant, negative correlations were found for magnesium (r?=??0.6) and zinc (r?=?-0.52). In men, significant negative correlations were seen for magnesium (r?=??0.69 and zinc (r?=??0.55). No significant correlations were found in women. These results indicate the need of taking into account the environmental and gender factors in research connected with these diseases, which can be probably of help in improvements of therapy efficiency.  相似文献   
977.
Based on published information about the glacial, postglacial, and recent distribution of the root vole, Microtus oeconomus, we hypothesized that a population inhabiting the pristine wetland in eastern Poland (Bialowieza Primeval Forest) might comprise a high diversity of haplotypes. The support for this hypothesis was provided by an analysis of partial cytb gene sequences from 149 voles sampled within a two-hectare plot during a nine-year study. In this population, we identified eight haplotypes (PLB1–PLB8), four of which were new to the root vole. These haplotypes were characterized by low nucleotide diversity (π?=?0.0054, SE?=?0.0019), the absence of transversional differences between sequences, and no changes in the encoded amino acid sequence: features suggesting a lack of immigration from the distant populations. The haplotype number and their frequency distribution in males and females did not differ significantly. An assessment of the persistence of matrilines in the local population throughout the study period revealed that the haplotype composition was relatively stable for only about 3 years. A more complete haplotype network for root voles in Europe was constructed by combining the newly identified haplotypes with the 45 previously described haplotypes. Two of the haplotypes detected in this study occupy key positions in this network: PLB5, as the closest link to the North European group, and PLB8, as an ancestor to many other Central European haplotypes.  相似文献   
978.
979.
Ohne Zusammenfassung  相似文献   
980.
Correspondenz     
Ohne Zusammenfassung  相似文献   
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