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   192197篇
  免费   10393篇
  国内免费   6956篇
  209546篇
  2023年   1478篇
  2022年   3264篇
  2021年   5515篇
  2020年   3646篇
  2019年   4403篇
  2018年   5216篇
  2017年   4256篇
  2016年   7317篇
  2015年   12690篇
  2014年   13485篇
  2013年   13686篇
  2012年   14471篇
  2011年   10676篇
  2010年   7415篇
  2009年   6690篇
  2008年   6054篇
  2007年   5342篇
  2006年   4832篇
  2005年   9765篇
  2004年   8123篇
  2003年   5957篇
  2002年   3242篇
  2001年   3065篇
  2000年   2162篇
  1999年   3287篇
  1998年   1331篇
  1997年   1297篇
  1996年   1114篇
  1995年   1067篇
  1994年   1098篇
  1992年   2905篇
  1991年   2842篇
  1990年   2682篇
  1989年   2555篇
  1988年   2433篇
  1987年   2220篇
  1986年   2009篇
  1985年   2041篇
  1984年   1296篇
  1983年   1029篇
  1979年   1188篇
  1978年   837篇
  1975年   926篇
  1974年   1068篇
  1973年   1058篇
  1972年   1015篇
  1971年   970篇
  1970年   860篇
  1969年   864篇
  1967年   778篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Flow cytometer measurements were made of the basal variations in peripheral blood functional monocytes and granulocytes over the course of a training season (January to November) of a cycling team. Parallel determinations were made of plasma concentration of catecholamines (chromatography) and cortisol (RIA) in a search for neuroendocrine markers. The results showed the greatest phagocytic capacity to occur in the central months (March, May, and July), coinciding with the greatest number and highest level of competitive events with good correlation with a peak in epinephrine during these months (r(2) = 0.998 for monocytes and r(2) = 0.674 for granulocytes). No good correlations were found between phagocytosis and norepinephrine or cortisol. The highest values for phagocytosis and epinephrine concentration were found in May. These results suggest that blood epinephrine concentration could be a good neuroendocrine marker of sportspeople's phagocytic response.  相似文献   
63.
64.
S L Wardlaw  P J Wang  A G Frantz 《Life sciences》1985,37(20):1941-1947
The effect of estradiol on the brain concentration of immunoreactive beta-endorphin (beta-EP) and C-terminal ACTH (CLIP) was studied in ovariectomized rats. Dopamine, a known inhibitor of pituitary intermediate lobe pro-opiomelanocortin (POMC), was examined as a possible mediator of the estradiol induced changes in brain POMC. Animals were treated for 1 or 3 weeks with either 1) saline; 2) silastic estradiol implants; or 3) estradiol implants plus haloperidol 1 mg/kg/day. After one week of treatment no significant change in hypothalamic beta-EP content was noted in any group compared to the control level of 4.13 +/- .33 (SEM) pmoles although in the neurointermediate lobe beta-EP increased from 566 +/- 72 to 942 +/- 73 pmoles after haloperidol (p less than .005). After 3 weeks, however, hypothalamic beta-EP decreased from 3.96 +/- .28 to 2.74 +/- .19 pmoles (p less than .005) and C-terminal ACTH decreased from 3.78 +/- .33 to 2.82 +/- .18 pmoles (p less than .02) in the estradiol treated rats. This estradiol induced decrease in the hypothalamic content of beta-EP and C-terminal ACTH was not blocked by haloperidol. We conclude that estradiol lowers the hypothalamic content of beta-EP and CLIP and that this effect does not appear to be mediated by dopamine.  相似文献   
65.
Following treatment of hen erythrocyte nuclei with dimethyl 3,3'-dithiobispropionimidate, dimers between histones H1a, H1b, and H5 were extracted with 5% perchloric acid. They resolved electrophoretically into four sub-bands and these were identified by non-reducing/reducing gel electrophoresis. The H5-H5 homodimer species was purified by gel electrophoresis and was treated sequentially with BrCN and dithiothreitol. The pattern of resulting fragments indicates that cross-links were mainly formed between the COOH-terminal portions and at a significantly lower frequency between the COOH-terminal and the NH2-terminal portions.  相似文献   
66.
Enzyme activity capable of converting the glycine-extended substance P precursor, substance P-Gly12, into substance P was purified from human cerebrospinal fluid. The conversion reaction was monitored by radioimmunoassay measurement of substance P formation. The chemical identity of the product was verified by reversed-phase HPLC. The enzyme reaction was stimulated by Cu(II) ion and ascorbic acid and inhibited by the presence of diethyldithiocarbamate. By HPLC molecular sieving, the major enzyme activity appeared as a protein of 26,000 molecular weight.  相似文献   
67.
68.
In has been shown that cortisol immobilized on polyvinylpyrrolidone (PVP-GC) affects cyclic AMP production stimulated by adenosine and isoproterenol in rat thymocytes. This effect of PVP-GC is specific for cortisol: antiglucocorticoid progesterone (at a concentration of 10(-5) M) inhibited completely the action of PVP-GC on the intracellular cAMP level. It is suggested that cortisol effect on cAMP production is one of the mechanisms of glucocorticoid hormone action in target cells.  相似文献   
69.
70.
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