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   11073篇
  免费   1148篇
  国内免费   6篇
  2021年   133篇
  2020年   81篇
  2019年   115篇
  2018年   145篇
  2017年   127篇
  2016年   196篇
  2015年   321篇
  2014年   428篇
  2013年   511篇
  2012年   599篇
  2011年   615篇
  2010年   393篇
  2009年   379篇
  2008年   518篇
  2007年   562篇
  2006年   496篇
  2005年   455篇
  2004年   480篇
  2003年   456篇
  2002年   459篇
  2001年   256篇
  2000年   274篇
  1999年   255篇
  1998年   168篇
  1997年   117篇
  1996年   120篇
  1995年   103篇
  1994年   124篇
  1993年   123篇
  1992年   207篇
  1991年   183篇
  1990年   168篇
  1989年   163篇
  1988年   159篇
  1987年   129篇
  1986年   137篇
  1985年   160篇
  1984年   116篇
  1983年   104篇
  1982年   102篇
  1981年   111篇
  1980年   103篇
  1979年   109篇
  1978年   87篇
  1977年   79篇
  1976年   86篇
  1975年   100篇
  1974年   92篇
  1973年   74篇
  1971年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Metabolic regulation of the trehalose content of vegetative yeast.   总被引:6,自引:0,他引:6  
We have investigated the mechanism by which heat shock conditions lead to a reversible accumulation of trehalose in growing yeast. When cells of S. cerevisiae M1 growing exponentially at 30 degrees C were shifted to 45 degrees C for 20 min, or to 39 degrees C for 40 min, the concentration of trehalose increased by about 25-fold; an effect reversed upon lowering the temperature to 30 degrees C. This was compared to the more than 50-fold rise in trehalose levels obtained upon transition from the exponential to the stationary growth phase. Whereas the latter was paralleled by a 12-fold increase in the activity of trehalose-6-phosphate synthase, no significant change in the activities of trehalose-synthesizing and -degrading enzymes was measured under heat shock conditions. Accordingly, cycloheximide did not prevent the heat-induced accumulation of trehalose. However, the concentrations of the substrates for trehalose-6-phosphate synthase, i.e. glucose-6-phosphate and UDP-glucose, were found to rise during heat shock by about 5-10-fold. Since the elevated levels of both sugars are still well below the Km-values determined for trehalose-6-phosphate synthase in vitro, they are likely to contribute to the increase in trehalose under heat shock conditions. A similar increase in the steady-state levels was obtained for other intermediates of the glycolytic pathway between glucose and triosephosphate, including ATP. This suggests that temperature-dependent changes in the kinetic parameters of glycolytic enzymes vary in steady-state levels of intermediates of sugar metabolism, including an increase of those that are required for trehalose synthesis. Trehalose, glucose-6-phosphate, UDP-glucose, and ATP, were all found to increase during the 40 min heat treatment at 39 degrees C. Since this also occurs in a mutant lacking the heat shock-induced protein HSP104 (delta hsp104), this protein cannot be involved in the accumulation of trehalose under these heat shock conditions. However, mutant delta hsp104, in contrast to the parental wild-type, was sensitive towards a 20 min incubation at 50 degrees C. Since this mutant also accumulated normal levels of trehalose, we conclude that HSP104 function, and not towards a 20 min incubation at 50 degrees C. Since this mutant also accumulated normal levels of trehalose, we conclude that HSP104 function, and not the accumulation of trehalose, protects S. cerevisiae from the damage caused by a 50 degrees C treatment.  相似文献   
32.
We have shown that the platelet tropomyosin binding protein described in the accompanying paper (Gerhard, M. D., DiGirolamo, P. M., and Hitchcock-DeGregori, S. E. (1985) J. Biol. Chem. 260, 3221-3227) is identical with human serum albumin. The immunological determinants are completely shared; the tryptic peptide maps are the same; the proteins comigrate on two-dimensional gels; and the amino acid sequences of the first 33 amino acids are the same. Although human serum albumin in plasma or commercially prepared protein will not bind tropomyosin-Affi-Gel 15, it will bind following purification from plasma by chromatography on hydroxylapatite.  相似文献   
33.
The new hormonal preparation Physioquens was administered during the study to 181 women during 1.634 cycles and has proved to be very effective in the treatment of various gynaecological disturbances. A definitive reduction has been observed in premenstrual and pre and postmenopausal complaints, dysmenorrhoea, amenorrhoea, intermenstrual pain and endometriosis. Physiquens is also a perfect regulatory device of the cycle in the case of menorrhagia, metrorrhagia and irregular menstrual cycles connected with a hormonal insufficiency. The normophasic treatment with Physioquens is made up of the cyclical administration of a tablet of 0.050 mg ethinyloestradiol for the first 7 days, followed by a tablet of 1 mg lynestrenol and 0.050 mg ethinyloestradiol for the next 15 days. Because of its effectiveness and good tolerance both clinically and biologically Physioquens can be considered an important new step in the treatment of gynaecological problems.  相似文献   
34.
35.
36.
37.
38.
39.
Patients suffering from peripheral vascular disease have been "ultima ratio"-treated with PGI2 at a rate of 5 ng/kg/min for 6 hours a day and 5 consecutive days i.v. 20 of them underwent surgery thereafter as therapy was not sufficient. A histological examination and quantification of vascular tissue revealed that the number of activated smooth muscle cells was significantly lower in treated patients vascular segments than in untreated ones in all the different age groups. A comparable suppression was found in the intima and the media as well. It is thus concluded, that PGI2 inhibits smooth muscle cell proliferation most probably by inhibiting PDGF-release from the platelets and stimulation of smooth muscle cell cAMP. To achieve a more beneficial PGI2-effect at the vascular level, a prolonged PGI2-therapy looks rather promising.  相似文献   
40.
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