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   40740篇
  免费   2148篇
  国内免费   36篇
电工技术   281篇
综合类   29篇
化学工业   7423篇
金属工艺   730篇
机械仪表   782篇
建筑科学   1264篇
矿业工程   74篇
能源动力   800篇
轻工业   5361篇
水利工程   375篇
石油天然气   188篇
武器工业   4篇
无线电   2289篇
一般工业技术   7183篇
冶金工业   10453篇
原子能技术   195篇
自动化技术   5493篇
  2023年   349篇
  2022年   349篇
  2021年   893篇
  2020年   735篇
  2019年   678篇
  2018年   1506篇
  2017年   1498篇
  2016年   1556篇
  2015年   1107篇
  2014年   1409篇
  2013年   2734篇
  2012年   2374篇
  2011年   2208篇
  2010年   1737篇
  2009年   1540篇
  2008年   1800篇
  2007年   1572篇
  2006年   1177篇
  2005年   979篇
  2004年   920篇
  2003年   817篇
  2002年   724篇
  2001年   465篇
  2000年   468篇
  1999年   615篇
  1998年   3357篇
  1997年   2010篇
  1996年   1299篇
  1995年   758篇
  1994年   651篇
  1993年   636篇
  1992年   207篇
  1991年   222篇
  1990年   220篇
  1989年   211篇
  1988年   189篇
  1987年   169篇
  1986年   179篇
  1985年   212篇
  1984年   184篇
  1983年   130篇
  1982年   161篇
  1981年   171篇
  1980年   154篇
  1979年   128篇
  1978年   119篇
  1977年   197篇
  1976年   419篇
  1975年   88篇
  1973年   82篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
This paper analyses the determination of visibility of journals in which researchers of INRA (National Institute for Agricultural Research) publish. The corpus is comprised of 671 articles published over a period of four years in 258 journals. The advantage of the method applied for determining the visibility of journals is that it combines two approaches: a) bibliometric indicators (coverage by the ISI-publications and by two specific French databases) and b) experts' opinions (10 economists and sociologists). The main results are: a) There is a convergence between the opinion of the experts and «visibility» in the databases, b) The impact factor confirms the main opinions of the experts. The first journals ranked by the experts and JCR Social Sciences are the same but represent only 40 per cent of the total journals analysed. The other journals were revealed by the experts and French databases.«Whoever seeks to pass a balanced but lucid judgement on the general trends of the activity carried out by the profession to which he belongs, is liable to say either banalities or to hurt his colleagues»The notion which we retain of core is that which is successively and conjointly validated by the experts and by the major databases representative of the field.This study was financed by the Department of Rural Economy and Sociology of INRA.  相似文献   
123.
Significative enhancement of free radical formation (FRO) in vivo is an important feature of hypertensive disorders of pregnancy (HDP), namely preeclampsia (PIH). The latest investigations about the pathology of HDP, showed the contribution of placental circulation to the development and evolution of such disease. The placental bed can be a potential source of FRO or activation of cells that can produce FRO. Glutathione, is an important molecule for cellular protection against damage, is a cofactor of many enzymes, in particular, for the glutathione peroxidase of the placental tissue; this enzyme in the placenta bed prevent the production of thromboxan and lipoperoxides; the latter are potentially damaging to the endothelium cells and can cause vasoconstriction, the most important feature of PIH. The activity of that enzyme is deficient in PIH. We studied, by fluorometric assay, the concentrations of the two states of glutathione in placental homogenates (PLH) from pregnant women without pathology (PWN) and from pregnant women with PIH (PWPIH). The data showed significant low concentrations in the PLH of the two states of glutathione in the PWN against high concentrations of this molecule in the PLH from PWPIH. This feature can result from a deficient user of the glutathione by the cellular mechanism for prevention against oxidative factors. In addition, our study shows a biochemical marker that is suggestive that the placental bed is a potential source of FRO production in PIH.  相似文献   
124.
125.
126.
Previously established dose-response curves indicated that modafinil 20-40 mg/kg i.p. elicited in mice an obvious stimulation of locomotor activity roughly similar to that induced by (+)amphetamine 2-4 mg/kg. The effects of various agents modifying dopamine transmission were compared on the locomotor response to both drugs. The preferential D2 dopamine receptor antagonist haloperidol 37.5-150 micrograms/kg i.p. suppressed the stimulant effect of (+)amphetamine in a dose dependent manner, but not that of modafinil. The D1 dopamine receptor antagonist SCH 23390 (7.5-30 micrograms/kg s.c.) reversed the (+)amphetamine but not the modafinil induced hyperactivity. The tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (200 mg/kg) suppressed the hyperactivity induced by 4 mg/kg dexamphetamine but not that induced by 20 mg/kg modafinil. Associating L-DOPA 150 mg/kg and benserazide 37.5 mg/kg with (+)amphetamine 2 mg/kg resulted in stereotyped climbing behavior, that was not observed with modafinil 10-80 mg/kg. The profound akinesia induced by reserpine (4 mg/kg s.c.; 5 h before testing) was reversed by (+)amphetamine 2 mg/kg but not by modafinil 40 mg/kg. Finally, on synaptosomes prepared from mouse striata preloaded with [3H]dopamine, modafinil 10(-5) M did not increase the spontaneous [3H]dopamine release whereas (+)amphetamine, at the same concentration, doubled it. From all these differences between the two drugs, it is concluded that the mechanism underlying the modafinil induced stimulant locomotor effect differs completely from that of (+)amphetamine.  相似文献   
127.
128.
This ecologic study aimed to investigate whether differences in population mortality from lung, stomach and colorectal cancer among the 16 cohorts of the Seven Countries Study could be explained by differences in the average intake of anti-oxidant (pro)vitamins. In the 1960s, detailed dietary information was collected in small sub-samples of the cohorts by the dietary record method. In 1987, food-equivalent composites representing the average food intake of each cohort at baseline were collected locally and analyzed in a central laboratory. The vital status of all participants was verified after 25 years of follow-up. The average intake of vitamin C was strongly inversely related to the 25-year stomach-cancer mortality (r = -0.66, p = 0.01), also after adjustment for smoking and intake of salt or nitrate. The average intake of alpha-carotene, beta-carotene, and alpha-tocopherol were not independently related to mortality from lung, stomach or colorectal cancer, nor was vitamin C related to lung and colorectal cancer.  相似文献   
129.
We studied the incidence of infection with Helicobacter pylori in Panamanians with chronic dyspepsia, gastric or duodenal ulcer, gastritis or gastric cancer. The histopathology was positive in 54 (81%) of 66 patients; the urea test was positive in 52 (82.5%) of 63 cases; the impromptu was positive in 51 (79.6) of 64 patients; the endoscopic examination was positive in 64 (82.9%) of 77 examinations.  相似文献   
130.
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