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   20551篇
  免费   1660篇
  国内免费   11篇
  2023年   64篇
  2022年   47篇
  2021年   306篇
  2020年   226篇
  2019年   322篇
  2018年   379篇
  2017年   349篇
  2016年   556篇
  2015年   949篇
  2014年   1073篇
  2013年   1345篇
  2012年   1564篇
  2011年   1461篇
  2010年   955篇
  2009年   882篇
  2008年   1142篇
  2007年   1086篇
  2006年   1099篇
  2005年   1061篇
  2004年   999篇
  2003年   873篇
  2002年   923篇
  2001年   273篇
  2000年   228篇
  1999年   244篇
  1998年   262篇
  1997年   195篇
  1996年   207篇
  1995年   206篇
  1994年   221篇
  1993年   211篇
  1992年   196篇
  1991年   153篇
  1990年   125篇
  1989年   144篇
  1988年   141篇
  1987年   101篇
  1986年   103篇
  1985年   123篇
  1984年   142篇
  1983年   107篇
  1982年   133篇
  1981年   108篇
  1980年   107篇
  1979年   93篇
  1978年   90篇
  1977年   81篇
  1976年   53篇
  1974年   54篇
  1973年   67篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
A 68-year-old man presented with hemiparesis, lymphocytosis, and cerebral lesions on MRI. Flow cytometry of blood, bone marrow and cerebrospinal fluid showed B-CLL lymphocytes with bright CD20 expression, slg, and absence of CD23 antigen. Fluorescencein situ hybridisation showed trisomy 12 in 50% of analysed peripheral mononuclear cells. The patient died 6 months after the diagnosis. Rapidly progressive and fatal course of the disease was consistent with known bad prognostic significance of CD20 bright expression and trisomy 12.  相似文献   
72.
73.
74.
75.
The influence of silicon treatment on the levels of calcium and magnesium in blood serum and tissues was studied in rats. The concentrations of both elements were estimated in samples of sera and tissues of rats receiving per os a soluble, inorganic silicon compound—sodium metasilicate nonahydrate (Na2SiO3·9H2O (REACHIM, USSR)), dissolved in the animals' drinking water. A decrease of magnesium concentration in serum was observed with accompanying elevation of registered calcemia. Moreover, a reduction of tissue calcium levels was found with a simultaneous increase of magnesium tissue pool. The results provide evidence for silicon involvement in mineral metabolism. It could result in a modification of pathological processes concerning bone tissue.  相似文献   
76.
Cryptic species are common in the ocean, particularly among marine invertebrates such as octopuses. Delineating cryptic species is particularly problematic in octopus taxonomy where the plasticity recorded among taxonomic characters often results in low resolution at the species level. This study investigated the morphological relationships among seven phylogenetic clades (identified using cytochrome c oxidase subunit I) of the broadly distributed Octopus vulgaris species complex and close relatives. Morphological analyses in this study were successful in delimiting O. sinensis, Brazilian Ovulgaris and O. vulgaris sensu stricto, which was congruent with the molecular findings of this study. Analyses based on male morphology were successful in distinguishing 14 of 15 total pairwise comparisons and proved to be a more reliable indicator of species‐level relationships in comparison with female morphology. The majority of characters with the greatest discriminatory power were male sexual traits. Significant morphological differences were also recorded among sampling localities of conspecifics, with phenotype showing correlation with local environmental data. The findings of this study support the hypothesis that multiple O. vulgaris‐like species are currently being incorrectly treated under a single species name, O. vulgaris. Octopuses being exported globally under the name O. vulgaris are of extremely high fisheries market value and profile. Our findings have potentially significant implications for the naming and conservation of commercially harvested members of this species complex throughout their ranges.  相似文献   
77.
Abstract. The aim of this study was to evaluate the critical phases of the life cycle of Gentiana pneumonanthe, the marsh gentian, a threatened species of the Bohemian flora. The effect of various conditions on germination and seedling establishment and the possible effect of competition on the performance of the species were tested. Seeds were sown in plots which were subjected to four treatments in a randomized complete blocks experiment: unmanaged meadow, mown meadow, burned meadow, and meadow with cut sod. The significantly highest recruitment was found in plots with cut sod, the lowest in the unmanaged control plots. Seedling survival also differed among the treatments. In the following year surviving individuals were only found in plots with cut sod. The influence of neighbouring vegetation on target gentian individuals was evaluated by removing the surrounding vegetation and comparing the performance of these individuals with controls. The initial height of each individual was measured and used as a covariable. No significant effect of neighbouring vegetation on performance was detected. Thus, the establishment phase appears to be critical for population persistence and is also more influenced by the management regime than other stages of the life cycle.  相似文献   
78.
79.
Jan Klein 《Immunogenetics》1990,31(3):215-216
B. Dupont (ed.): Immunobiology of HLA, Vol. I, Histocompatibility Testing 1987; Vol. II, Immunogenetics and Histocompatibility, Springer, New York, 1989.  相似文献   
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