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   107722篇
  免费   1717篇
  国内免费   896篇
  110335篇
  2023年   50篇
  2022年   149篇
  2021年   295篇
  2020年   148篇
  2019年   224篇
  2018年   12060篇
  2017年   10858篇
  2016年   7913篇
  2015年   1359篇
  2014年   1098篇
  2013年   1284篇
  2012年   5445篇
  2011年   13856篇
  2010年   12648篇
  2009年   8904篇
  2008年   10636篇
  2007年   12212篇
  2006年   1107篇
  2005年   1342篇
  2004年   1743篇
  2003年   1794篇
  2002年   1510篇
  2001年   394篇
  2000年   247篇
  1999年   181篇
  1998年   202篇
  1997年   165篇
  1996年   127篇
  1995年   125篇
  1994年   121篇
  1993年   140篇
  1992年   120篇
  1991年   119篇
  1990年   85篇
  1989年   72篇
  1988年   82篇
  1987年   64篇
  1986年   63篇
  1985年   69篇
  1984年   91篇
  1983年   64篇
  1982年   78篇
  1981年   56篇
  1980年   63篇
  1979年   41篇
  1977年   34篇
  1975年   28篇
  1974年   30篇
  1972年   268篇
  1971年   296篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
An automated follow-up register for the detection of iatrogenic thyroid disease has been established as a joint venture between the general practitioners in the north-east of Scotland and the thyroid clinic of Aberdeen General Hospitals.The data-processing operations in the system are handled by an International Computers Limited 4/50 computer. Patients are followed up at predetermined intervals and the system has been designed to process, screen, and store clinical and biochemical follow-up data and report results to the patients, general practitioners, and the hospital records department.  相似文献   
62.
Purine Ribonucleosidase g from Aspergillus foetidus   总被引:1,自引:0,他引:1  
Nucleosidase g was prepared by growing Aspergillus foetidus on bran, and was purified by passage through a diethylaminoethyl-Sephadex column. The enzyme acted on the purine ribosides (except xanthosine) and on their 5'-phosphates. Action on the latter was a good means for preparing ribose-5-phosphate.  相似文献   
63.
64.
65.
66.
Anther culture medium was prepared with different types and concentrations of cytokinins to gain greater insight into the control of embryo formation during Brassica oleracea L. var. italica (broccoli) anther culture. The independent addition of the four cytokinins tested had widely divergent effects dependent upon cytokinin concentration and the genetic background of the test plants. All cytokinins were generally inhibitory at high concentrations, however, individual plants showed significant stimulation of embyro formation at typical physiological levels. The influence of cytokinins was highly cultivar-specific, some lines were stimulated, others inhibited and still other test lines were largely unaffected. Although the addition of cytokinins was needed for embryo formation for some plants, in no instance were cytokinins able to replace the inductive effect of high-temperature treatments.  相似文献   
67.
68.
69.
70.
Carbohydrate and energy metabolism of the flooding- and anoxia-tolerant Iris pseudacorus and the intolerant Iris germanica rhizomes were investigated under experimental anoxic conditions. Rhizomes of I. pseudacorus and I. Germanica were incubated in the absence of oxygen from 0 to 60 and 16 days, respectively. Amounts of glucose, total reducing sugars and non-reducing sugars (starch, fructan and oligosaccharides) in the rhizomes were measured. Ethanol concentration and adenylate energy charge were determined enzymatically. Glucose content of I. pseudacorus rhizomes decreased gradually during the first 30 days under anoxia and then increased at the same time as adenylate energy charge values started to decline. In I. germanica rhizomes the changes were more dramatic and the time scale was much shorter than in I. pseudacorus but the changes were similar. Non-reducing sugar content of I. pseudacorus rhizomes decreased rapidly during the first 15 days under oxygen deprivation and then increased again, to near starting levels at 35 days. In I. germanica the amount of non-reducing sugars decreased gradually during the anoxic incubation. Under aerobic control conditions, adenylate energy charge (AEC) of I. pseudacorus and I. germanica rhizome tissue was 0.87±0.01 and 0.81±0.01, respectively. In I. pseudacorus AEC remained high until 30 days under anoxia. In contrast, the energy charge of I. germanica rhizome tissue remained above 0.6 for 4 days only. Large amounts of ethanol were found in anoxic rhizome tissues of I. pseudacorus (up to 0.21 M ) and I. germanica (0.06 M ) after 45 days and 8 days, respectively. The results are discussed in relation to flooding tolerance of these species.  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