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   8550篇
  免费   944篇
  国内免费   93篇
  2023年   25篇
  2022年   57篇
  2021年   186篇
  2020年   99篇
  2019年   131篇
  2018年   120篇
  2017年   115篇
  2016年   215篇
  2015年   378篇
  2014年   430篇
  2013年   452篇
  2012年   647篇
  2011年   648篇
  2010年   353篇
  2009年   340篇
  2008年   498篇
  2007年   529篇
  2006年   476篇
  2005年   499篇
  2004年   475篇
  2003年   462篇
  2002年   422篇
  2001年   92篇
  2000年   72篇
  1999年   126篇
  1998年   134篇
  1997年   109篇
  1996年   99篇
  1995年   91篇
  1994年   89篇
  1993年   87篇
  1992年   71篇
  1991年   62篇
  1990年   57篇
  1989年   56篇
  1988年   52篇
  1987年   67篇
  1986年   47篇
  1985年   58篇
  1984年   63篇
  1983年   59篇
  1982年   85篇
  1981年   55篇
  1980年   61篇
  1979年   39篇
  1978年   28篇
  1977年   40篇
  1976年   25篇
  1975年   22篇
  1974年   24篇
排序方式: 共有9587条查询结果,搜索用时 15 毫秒
91.
Fasting produces an increased mobilization of lipid from adipose tissue to the liver and a decreased hepatic lipogenesis, but the administration of glucose stimulates lipid synthesis by the liver. After fasting of C3H mice numerous electron-opaque bodies and large lipid droplets were present in the liver. In the liver of untreated controls only a few small electron-opaque bodies and an occasional fat droplet were observed. After glucose injection the number of electron-opaque bodies in the liver was no greater than that observed in livers of saline-injected controls. In the livers of all groups these bodies were located intracellularly within cytoplasmic vesicles; those in extracellular locations were not membrane bounded and were located at indented and thickened hepatocyte plasma membranes or within the space of Disse. In fasted liver the dense bodies were often associated with large fat droplets.  相似文献   
92.
A regulator gene mutation (capR) that causes increased synthesis of capsular polysaccharide and derepressed synthesis of several enzymes involved in polysaccharide synthesis also derepresses phosphomannose isomerase (PMI) synthesis. In contrast, a second mutation (capS, which maps separately from capR) that causes increased production of the same polysaccharide does not lead to increased synthesis of PMI (nor of several of the other enzymes involved in polysaccharide synthesis). Introduction of the capR9 allele by transduction or mutation of capR(+) to capR can change the phenotype of a mannose-negative nonmucoid strain to a mannose-positive mucoid phenotype. Thus, genotype capR(+)man-2 is mannose-negative and nonmucoid, but genotype capR9 man-2 is mannose positive and mucoid. Other interactions between these alleles in the synthesis of capsular polysaccharide are recorded.  相似文献   
93.
A psychological and psychiatric study of 11 children with cystic fibrosis revealed major psychological problems in all of them. Among the parents of the majority of these children, marked psychopathology and gross marital discord were noted. Popular literature concerning cystic fibrosis had a negative effect on the child''s attitude toward the disease. Virtually all of these patients showed a preoccupation with death. In this study, the necessity of psychiatric consultation as an integral part of current intensive treatment programs in cystic fibrosis clinics was demonstrated.  相似文献   
94.
95.
96.
Summary When tissue slices or small blocks of unfixed rat cerebrum are incubated in various anisotonic physiological media, distinctive morphological changes are induced in glial cells, neurons, and endothelial cells. The variation in observed cellular swelling and shrinkage may be related to differences in ionic content of the cytoplasm of these cells. When HAA, glutal, and osmium tetroxide fixed tissue is incubated in this manner, only the cerebrum fixed in HAA responds to osmotic inequilibrium in a manner similar to unfixed tissue. Although HAA does not fix tissues very well, the permeability of plasma membranes in the brain appears to be less altered by HAA than by glutal or osmium tetroxide. The relationship of these findings to a demonstration of the extracellular space in HAA fixed tissues is discussed.This work was supported by grants (U-1293) from the Health Research Council of the City of New York and (NB 04161-02) from the National Institute of Neurological Disease and Blindness of the National Institutes of Health.  相似文献   
97.
98.
糙叶败酱挥发油镇静作用的研究   总被引:4,自引:1,他引:3  
本文观察了败酱科植物糙叶败酱(Patrinia scabra Bunge)根和根茎中制得的挥发油的镇静作用,井与黄花败酱挥发油做了比较。结果表明,此油灌胃给予数组小鼠,剂量0.45ml/kg,显示如下的作用:[1]能显著延长由于腹腔注射戊巴比妥钠(50mg/kg)引起的小鼠睡眠时间,但其作用强度弱于黄花败酱挥发油。(2)一次灌胃给予小鼠大剂量10.46g/kg的糙叶败酱挥发油,连续观察10天,动物外观正常,无一死亡,体重增加与对照组相似。  相似文献   
99.
Red clover (Trifolium pratense L.) seedlings were screened for the ability to regenerate plantlets from hypocotyl-derived callus tissue. Media sequences described by Beach and Smith (1979) and Collins and Phillips (1982) and a variation using media from both sequences were tested. Plantlets were regenerated from three out of 642 genotypes. In all three cases, callus was initiated on B5C medium and regeneration was accomplished on SPL medium. Attempts to regenerate plants from petiole-derived callus tissue have so far been successful only with regenerants of clone F49. Petiole callus from epicotyl-derived F49 plants proved to be non-regenerative. Pollen viability varied significantly among individuals regenerated from callus cultures of clone F49. Root tip squashes from F49 regenerants revealed the normal diploid chromosome number (2n=14). The frequency of regeneration within progeny from reciprocal crosses between F49 regenerants and several non-regenerative genotypes was 29%.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP benzylaminopurine - KN kinetin - NAA -naphthaleneacetic acid  相似文献   
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