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   56136篇
  免费   244篇
  国内免费   544篇
系统科学   1225篇
丛书文集   517篇
教育与普及   287篇
理论与方法论   515篇
现状及发展   32828篇
研究方法   726篇
综合类   18638篇
自然研究   2188篇
  2013年   800篇
  2012年   562篇
  2011年   2608篇
  2009年   606篇
  2008年   791篇
  2007年   891篇
  2006年   948篇
  2005年   1125篇
  2004年   2203篇
  2003年   1862篇
  2002年   1517篇
  2001年   1439篇
  2000年   1002篇
  1999年   945篇
  1998年   649篇
  1997年   772篇
  1996年   510篇
  1994年   684篇
  1993年   687篇
  1992年   901篇
  1991年   775篇
  1990年   869篇
  1989年   684篇
  1988年   648篇
  1987年   667篇
  1986年   724篇
  1985年   883篇
  1984年   776篇
  1983年   661篇
  1982年   791篇
  1981年   845篇
  1980年   927篇
  1979年   1450篇
  1978年   1303篇
  1977年   1326篇
  1976年   1125篇
  1975年   1103篇
  1974年   1066篇
  1973年   1256篇
  1972年   1305篇
  1971年   1345篇
  1970年   1438篇
  1969年   1324篇
  1968年   1234篇
  1967年   1149篇
  1966年   943篇
  1965年   770篇
  1964年   486篇
  1958年   587篇
  1957年   479篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
51.
The study of candidate genes over the past three decades has yielded notable successes in common-disease genetics. During this time, however, interpretation of genetic association studies has been hampered by the use of clinical cohorts of inadequate power and insufficient information on genetic variation in candidate genes. The unavailability of highthroughput and low-cost genotyping technologies has also limited the scope of complex-disease genetic studies. More recently, however, the sequencing and characterization of variation within the human genome has revolutionized genetic studies and enabled full genome-wide scans for genes associated with disease. The identification of disease-associated (causative) genes has illuminated disease mechanisms. The translation of this knowledge into direct clinical benefit in diagnosis, prognosis and therapy for an individual’s disease still remains a challenge. Received 11 September 2006; received after revision 17 December 2006; accepted 18 January 2007  相似文献   
52.
Duhem’s concept of ‘good sense’ is central to his philosophy of science, given that it is what allows scientists to decide between competing theories. Scientists must use good sense and have intellectual and moral virtues in order to be neutral arbiters of scientific theories, especially when choosing between empirically adequate theories. I discuss the parallels in Duhem’s views to those of virtue epistemologists, who understand justified belief as that arrived at by a cognitive agent with intellectual and moral virtues, showing how consideration of Duhem as a virtue epistemologist offers insights into his views, as well as providing possible answers to some puzzles about virtue epistemology. The extent to which Duhem holds that the intellectual and moral virtues of the scientist determine scientific knowledge has not been generally noticed.  相似文献   
53.
1 Results Acid-doped polybenzimidazoles[1] are particularly appealing because of high proton conductivity with no or low humidification and promising fuel cells performances. PBI, in fact, contains basic functional groups which can easily interact with strong oxo-acids, such as H3PO4 and H2SO4. The acid partially protonates the polymer and partially is freely dispersed in the polymer backbone, so allowing proton migration via Grotthuss mechanism along the anionic chains[2]. Anyway, a technological limit...  相似文献   
54.
The RecQ family of DNA helicases is highly conserved throughout evolution and plays an important role in the maintenance of genomic stability in all organisms. Mutations in three of the five known family members in humans, BLM, WRN and RECQL4, give rise to disorders that are characterized by predisposition to cancer and premature aging, emphasizing the importance of studying the RecQ proteins and their cellular activities. Interestingly, three autosomal recessive disorders have been associated with mutations in the RECQL4 gene: Rothmund-Thomson, RAPADILINO, and Baller-Gerold syndromes, thus making RECQL4 unique within the RecQ family of DNA helicases. To date, however, the molecular function of RECQL4 and the possible cellular pathways in which it is involved remain poorly understood. Here, we present an overview of recent findings in connection with RECQL4 and try to highlight different directions the field could head, helping to clarify the role of RECQL4 in preventing tumorigenesis and maintenance of genome integrity in humans. Received 31 October 2006; received after revision 4 January 2007; accepted 5 February 2007  相似文献   
55.
1 Results In the coordination system by using complexation with organic ligand, the ff emission of lanthanide(Ⅲ) (Ln(Ⅲ)) is induced the excitation energy transfer form the organic chromophore under the light-irradiation. However, there are not so much number of reports to discuss the energy relaxation mechanism in such complexes with Ln(Ⅲ). Recently, we succeeded firstly to estimate the rate constant of the energy transfer between the ligand and Ln(Ⅲ) in Pr(Ⅲ)-phenanthroline analogs[1]. Here, we will di...  相似文献   
56.
57.
58.
59.
分子间的范德华力是十分微弱的,但可以说普遍的存在着,在很多体系中起着巨大的作用,在物理学、化学、生物学等学科中得到了广泛的研究。但怎样计算范德华力?如何考虑各种条件对范德华力的影响?  相似文献   
60.
Summary The depressor action of small doses of adrenaline on the blood pressure (B.P.) of the decapitated cat may be abolished by pretreatment with pilocarpine; atropine restores the original depressor action. The fall in B.P. due to adrenaline after ergotamine once more becomes an increase when pilocarpine has been given earlier. After atropine a fall in B.P. again occurs. This effect of pilocarpine and atropine on a depressor response has already been described in the case of Aludrine (N-isopropyl-noradrenaline) byFromherz.  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