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   794900篇
  免费   89435篇
  国内免费   2689篇
  2018年   7086篇
  2016年   9377篇
  2015年   13726篇
  2014年   16060篇
  2013年   21848篇
  2012年   25093篇
  2011年   25455篇
  2010年   16815篇
  2009年   15490篇
  2008年   22136篇
  2007年   22813篇
  2006年   21527篇
  2005年   20574篇
  2004年   20411篇
  2003年   19214篇
  2002年   18851篇
  2001年   33577篇
  2000年   34015篇
  1999年   27289篇
  1998年   9841篇
  1997年   10104篇
  1996年   9481篇
  1995年   9076篇
  1994年   8757篇
  1993年   8753篇
  1992年   22494篇
  1991年   22086篇
  1990年   21567篇
  1989年   20822篇
  1988年   19515篇
  1987年   18538篇
  1986年   17579篇
  1985年   17572篇
  1984年   14527篇
  1983年   12524篇
  1982年   9666篇
  1981年   8955篇
  1980年   8196篇
  1979年   13853篇
  1978年   11271篇
  1977年   10168篇
  1976年   9557篇
  1975年   10933篇
  1974年   11961篇
  1973年   11771篇
  1972年   10767篇
  1971年   9852篇
  1970年   8426篇
  1969年   8303篇
  1968年   7598篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Molecular heterogeneity of D-end products detected by anti-H-2.28 sera   总被引:1,自引:0,他引:1  
Immunoprecipitation of NP-40 lysates of 125I-labeled lymph-node cells with different anti-H-2 sera and with anti-Qa-2 serum has shown that the BALB/cByA strain (H-2d, Qa-2-negative) expresses, besides H-2Ld, another molecule that is not detectable in the BALB/c-H-2dm2 strain. Electrophoresis in SDS polyacrylamide gels indicated that this molecule, provisionally designated Lq, has an apparent molecular weight of 41000 daltons, in contrast to approximately 49000 daltons for H-2Kd and H-2Ld, and 47000 daltons for H-2Dd molecules. The anti-Qa-2 serum precipitated from the Qa-2-positive strains BALB/cHeA but not from the Qa-2-negative strains BALB/cByA and BALB/c-H-2dm2 a protein that gave a very strong band corresponding to the molecular weight 41000 daltons in the gel electrophoresis. The biochemical characteristics of the Lq molecule are thus more similar to those of Qa-2 than of H-2 antigens.  相似文献   
992.
The total and unsedimentable activity of acid DNase, RNase, phosphatase and arylsulfatases A and B was examined in the rat kidneys during long-term compression of soft tissues in the presence of high excitability of the sympathoadrenal system. Injection of adrenalin to rats with trauma reduced the total activity of DNase, acid phosphatase and arylsulfatases A and B, particularly at the late periods of soft tissue compression, whereas the total activity of acid RNase slightly increased as compared with control. Compression of soft tissues after adrenalin preinjection was accompanied by a substantial rise of unsedimentable activity of the lysosomal enzymes under study in the kidneys. The activity of the enzymes in cytosol progressively ascended as the time of soft tissue injury increased.  相似文献   
993.
994.
Cyclic AMP is not detectable in Clostridium perfringens   总被引:3,自引:0,他引:3  
Cyclic AMP was not detected (less than 5 X 10(-9) M intracellular concentration) at any stage of growth or sporulation of two strains of Clostridium perfringens grown with or without methylxanthines. Only Bacillus and Lactobacillus, genera belonging to the same phylogenetic cluster, have previously exhibited undetectable levels of cyclic AMP.  相似文献   
995.
In vitro directly micropropagated plantlets from three selected five-year-old Eucalyptus grandis Hill ex. Maiden hybrids were compared to their related half-sib seedlings for growth and growth pattern parameters under greenhouse conditions used for operational seedling production. The oven dry weights were determined from stem, leaf, and root samples collected every 40 days for four times. Relative growth rate, net assimilation rates and shoot:root ratio were calculated. Survival was 98% and 95% for plantlets and seedlings, respectively. Significant differences were observed between parents in terms of shoot and root dry weights and their ratios with similar ranking among plantlets and seedlings, suggesting genetic control over these traits. Plantlets started with significantly higher root: shoot ratios and stem, leaf, root, and total dry weight. Although seedlings had higher relative growth and net assimilation rates, all the initial differences decreased sharply over time.  相似文献   
996.
997.
998.
Summary Viral leukemogenesis in mice is frequently initiated by proviral activation of a highly conserved cellular gene called Pim-1. Here we report the chromosomal localization of the human homologue by Southern blot analyses of DNAs obtained from human-rodent somatic cell hybrids. The single copy human homologue was assigned to the 6pter-q12 segment.  相似文献   
999.
The pH, the osmolality and the urea and ammonia concentrations in blood, as well as the net urea and ammonia excretions, were studied in the amphibian Xenopus laevis exposed for several weeks to increased osmotic pressure (OP) of the ambient water, as a result of the addition of either NaCl or mannitol to the water. The pH and the ammonia concentration of the blood were independent of the variations of the ambient osmolarity. On the contrary, the blood osmolality and its urea concentration increased markedly when the ambient OP was augmented. The increase of ambient OP by NaCl addition to the medium augmented the urea net excretion and slightly decreased the ammonia excretion. When the increase of ambient OP resulted from the addition of mannitol in the water, excretions of urea and ammonia became negligible.  相似文献   
1000.
Fractionation of human erythrocyte membrane proteins was performed using a modification of two-dimensional gel electrophoresis described by P. O'Farrel with isoelectric point plotted against molecular mass. All major erythrocyte proteins, including high molecular weight proteins, such as spectrin and band 3 protein, identified by one-dimensional sodium dodecyl sulfate gel electrophoresis, were visualized by silver staining of two-dimensional gels. All in all about 50 polypeptides were distinguished on two-dimensional electrophoretic patterns. Preliminary protein map was developed.  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