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   314339篇
  免费   3753篇
  国内免费   1091篇
化学   170611篇
晶体学   4457篇
力学   13033篇
综合类   7篇
数学   36263篇
物理学   94812篇
  2020年   1983篇
  2019年   1954篇
  2018年   1965篇
  2017年   1875篇
  2016年   3858篇
  2015年   3235篇
  2014年   4422篇
  2013年   13976篇
  2012年   10728篇
  2011年   13363篇
  2010年   8270篇
  2009年   8258篇
  2008年   12335篇
  2007年   12571篇
  2006年   12212篇
  2005年   11154篇
  2004年   10034篇
  2003年   8848篇
  2002年   8700篇
  2001年   10109篇
  2000年   7711篇
  1999年   6115篇
  1998年   4894篇
  1997年   4733篇
  1996年   4774篇
  1995年   4363篇
  1994年   4114篇
  1993年   3940篇
  1992年   4431篇
  1991年   4293篇
  1990年   4011篇
  1989年   3830篇
  1988年   4120篇
  1987年   3785篇
  1986年   3677篇
  1985年   5317篇
  1984年   5395篇
  1983年   4377篇
  1982年   4753篇
  1981年   4793篇
  1980年   4545篇
  1979年   4664篇
  1978年   4665篇
  1977年   4645篇
  1976年   4598篇
  1975年   4508篇
  1974年   4356篇
  1973年   4526篇
  1972年   2569篇
  1971年   1879篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP.  相似文献   
92.
The variational approach based on the covariant quantization method for the curved Einstein space is applied.  相似文献   
93.
The precision of intensity modulated fiber optic sensor systems mainly is restricted by the attenuation characteristics of the analog fiber optical data link. Special encoding and referencing schemes are used to overcome this data link dependence. In this paper encoding and referencing principles for optical sensors are outlined and compared. Especially the two wavelengths referencing and the optical delay line processing techniques are discussed in more detail and results are presented.  相似文献   
94.
95.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive projections in Dedekind complete vector lattices and f-algebras. AMS Classification: 47B65, 46A40, 06F25  相似文献   
96.
97.
98.
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting.  相似文献   
99.
The stress-strain state in the zone of load transfer in a uniaxially stretched specimen made of a unidirectional epoxy carbon-fiber-reinforced plastic (CFRP) is investigated. A parametric analysis of the influence of geometric and mechanical characteristics of the specimen on its stress-strain state is performed by means of finite-element modeling. The parameters allowing us to significantly reduce the dangerous concentration of transverse and tangential stresses are revealed. The mechanical tensile characteristics of a high-strength pultruded unidirectional CFRP are determined experimentally, and the size effect of its strength is estimated.  相似文献   
100.
Summary The adsorption of gaseous molecular iodine on clean silver surfaces proceeds in the first stage by dissociative chemisorption. After the formation of half a monolayer of chemisorbed iodine atoms the formation of silver iodide begins, which forms a very regular overlayer on top of the substrate. Both iodine species can be distinguished due to a difference in chemical shift of the M4N4, 5N4, 5-Auger transitions. After completion of this overlayer further iodine uptake is slowed down significantly. Above an overlayer thickness of about 10 nm a further progress of the reaction cannot be followed anymore due to the limited information depth of XPS.  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