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   39848篇
  免费   119篇
  国内免费   174篇
系统科学   163篇
丛书文集   606篇
教育与普及   100篇
理论与方法论   125篇
现状及发展   18207篇
研究方法   1550篇
综合类   18792篇
自然研究   598篇
  2013年   275篇
  2012年   520篇
  2011年   1099篇
  2008年   661篇
  2007年   777篇
  2006年   701篇
  2005年   750篇
  2004年   818篇
  2003年   679篇
  2002年   730篇
  2001年   1134篇
  2000年   1099篇
  1999年   764篇
  1994年   383篇
  1992年   705篇
  1991年   533篇
  1990年   617篇
  1989年   571篇
  1988年   573篇
  1987年   588篇
  1986年   657篇
  1985年   809篇
  1984年   566篇
  1983年   522篇
  1982年   459篇
  1981年   469篇
  1980年   549篇
  1979年   1275篇
  1978年   1016篇
  1977年   926篇
  1976年   757篇
  1975年   827篇
  1974年   1131篇
  1973年   979篇
  1972年   1045篇
  1971年   1212篇
  1970年   1553篇
  1969年   1249篇
  1968年   1144篇
  1967年   1117篇
  1966年   1030篇
  1965年   752篇
  1964年   289篇
  1959年   397篇
  1958年   772篇
  1957年   566篇
  1956年   453篇
  1955年   413篇
  1954年   449篇
  1948年   329篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
S J Weintraub  C A Prater  D C Dean 《Nature》1992,358(6383):259-261
  相似文献   
42.
43.
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma.  相似文献   
44.
45.
46.
Summary Traces of nor-adrenaline restore the vascular action of adrenaline altered in epinephrectomized dogs to the reaction of the normal animal. Therefore it is claimed that the adrenals discharge one or several substances into the blood stream, which are necessary for the usual peripheral vascular action of adrenaline. Further investigations are in progress.  相似文献   
47.
The visual field is topographically mapped onto the primary visual cortex (V1), forming a retinotopic map which is far more detailed for the foveal regions than for the periphery. We found that receptive field (RF) size in monkey V1 increases with eccentricity, and that a 1—2 m2 V1 region contains roughly a complete set of machinery necessary to analyze a visual-field area whose size is about that of the RFs of the cells. This allows V1 to be anatomically uniform, and is in sharp contrast with the retina.  相似文献   
48.
1 Results This paper presents the development of platinum nanocomposites structures based on organically modified c.a.2 nm core platinum nanoparticles.The chemical modification of the 4-mercaptoaniline functionalized particles by various in coming molecules is evidenced and precisely quantified.The particles can be dissolved like molecules in various solvents depending on the features of the new crown and X-rays shows that the interparticle distance is affected by the crown modification.These platinum n...  相似文献   
49.
煤矸石空心砖是一种新型环保墙体材料,符合国家及山西省出台的限制生产和使用实心黏土砖,鼓励发展新型建筑材料的政策。利用煤矸石制造的空心砖可以作为保温材料,既可节约建筑能耗,又可节约土地资源,减少环境污染。煤矸石空心砖同黏土实心砖相比,具有高强、轻质、隔音、隔热、保温、防震等优点,市场前景良好。  相似文献   
50.
Obese postmenopausal female volunteers were given timed daily oral dosages of bromocriptine, and tested for reduction of body fat stores. This dopamine agonist has been shown to reset circadian rhythms that are altered in obese animals and to reduce body fat levels in several animal models. The participants were instructed not to alter their existing exercise and eating behavior during treatment. Skinfold measurements were taken on 33 subjects as indices of body fat. The measurements (e.g., suprailiac) were reduced after six weeks by about 25%, which represents a reduction of 11.7% of the total body fat. These dramatic decreases in body fat, which are equivalent to that produced by severe caloric restriction, were accompanied by more modest reductions of body weight (2.5%), indicating a possible conservation of protein that is usually lost as a consequence of such caloric restriction. The effects of bromocriptine treatment on body fat and hyperglycemia were also examined in non-insulin dependent diabetics being treated with oral hypoglycemics (7 subjects) or insulin (7 subjects). Total body fat was reduced by 10.7% and 5.1% in diabetics on oral hypoglycemics and insulin, respectively, without any significant reductions in body weight. Hyperglycemia was reduced in most of the 15 diabetic subjects treated leading to euglycemia and even cessation of hypoglycemic drugs in 3 of the 7 subjects during 4-8 weeks of bromocriptine treatment. These findings support the hypothesis that obesity and type II diabetes may be treated effectively with bromocriptine when administered at the proper times and dosages.  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