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   546篇
  免费   62篇
  国内免费   17篇
化学   104篇
晶体学   4篇
力学   22篇
综合类   4篇
数学   290篇
物理学   201篇
  2024年   5篇
  2023年   6篇
  2022年   31篇
  2021年   21篇
  2020年   18篇
  2019年   16篇
  2018年   16篇
  2017年   21篇
  2016年   16篇
  2015年   13篇
  2014年   26篇
  2013年   52篇
  2012年   22篇
  2011年   24篇
  2010年   19篇
  2009年   25篇
  2008年   23篇
  2007年   30篇
  2006年   32篇
  2005年   26篇
  2004年   24篇
  2003年   19篇
  2002年   16篇
  2001年   17篇
  2000年   8篇
  1999年   14篇
  1998年   9篇
  1997年   10篇
  1996年   13篇
  1994年   6篇
  1993年   5篇
  1992年   3篇
  1991年   2篇
  1990年   4篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
  1986年   4篇
  1985年   6篇
  1984年   4篇
  1983年   1篇
  1982年   6篇
  1981年   2篇
  1980年   4篇
  1978年   1篇
  1974年   1篇
排序方式: 共有625条查询结果,搜索用时 15 毫秒
121.
报道了天然气吸附剂的基本制备技术,并采用体积法评定了吸附剂的储气性能。结果表明,采用作者开发的吸附剂制备工艺可获得性能优良的天然气吸附剂。以木质素为原料制备的粉状吸附剂,其比表面积可达2912m2/g,微孔体积可达1-48cm3/g,平均孔径为1-48nm ,堆密度为0-30g/cm3 。在6-0MPa、25 ℃下,天然气的吸附储存量可达到140V/V。天然气吸附剂的储气性能与其比表面、微孔数量、填充密度等参数有重要关系  相似文献   
122.
Helicobacter pylori (H. pylori) infections affect almost half of the world’s population, with gradually increasing incidence in developed countries. Eradication of H. pylori may provide significant benefits to the affected individual by healing a number of gastrointestinal and extra-digestive disorders. But due to increased microbial resistance and lack of patient adherence to the therapy, the eradication rate of H. pylori is below 80% with current pharmacological therapies. The usage of botanicals for their therapeutic purposes and medicinal properties have been increased in last decades. They can be use as alternative H. pylori treatments, especially against drug-resistant strains. Epidemiological studies have revealed that people with lower vegetable and micronutrient intake may be at increased risk of H. pylori infection. We have undertaken a review of clinical trials to evaluate the efficacy of vegetable extracts and micronutrients in patients with H. pylori. Various databases, such as Google Scholar, PubMed, Scopus, Web of Science, and the Cochrane Library, were searched for the articles published in English. A total of 24 clinical studies (15 for vegetable extracts and 9 for micronutrients) were selected to be reviewed and summarized in this article. Vegetable extracts (Broccoli sprouts, curcumin, Burdock complex, and Nigella sativa) and micronutrients (vitamin C and E) were not found to be as effective as single agents in H. pylori eradication, rather their efficacy synergized with conventional pharmacological therapies. Conversely, GutGard was found to be significantly effective as a single agent when compared to placebo control.  相似文献   
123.
In [1] G. Margulis proved Ghys's conjecture stating the validity of the following analog of the Tits alternative: either the group of homeomorphisms of the circle possesses a free subgroup with two generators or there is an invariant probabilistic measure on S 1 . In the present paper, we prove the following strengthening of Margulis's statement: an invariant probabilistic measure for a group exists if and only if the quotient group does not contain a free subgroup with two generators (here is some specific subgroup of G defined in a canonical way). We also formulate and prove analogs of the Tits alternative for groups of homeomorphisms of the line.  相似文献   
124.
125.
This paper concerns the finite element simulation of the diffraction of a time-harmonic acoustic wave in the presence of an arbitrary mean flow. Considering the equation for the perturbation of displacement (due to Galbrun), we derive a low-Mach number formulation of the problem which is proved to be of Fredholm type and is therefore well suited for discretization by classical Lagrange finite elements. Numerical experiments are done in the case of a potential flow for which an exact approach is available, and a good agreement is observed.  相似文献   
126.
We present several equivalent conditions for the Karush–Kuhn–Tucker conditions for weak? compact convex sets. Using them, we extend several existing theorems of the alternative in terms of weak? compact convex sets. Such extensions allow us to express the KKT conditions and hence necessary optimality conditions for more general nonsmooth optimization problems with inequality and equality constraints. Furthermore, several new equivalent optimality conditions for optimization problems with inequality constraints are obtained.  相似文献   
127.
128.
《Optimization》2012,61(5-6):405-423
The topological degree theory is applied to study the problem of existence of solutions to the semi-definite complementarity problem (SDCP). A notion of an exceptional family of matrices is introduced, and assertions of a non-strict alternative type are obtained. Namely, for a continuous mapping, there exists at least one of the following two items: either a solution to the SDCP, or an exceptional family of matrices. Hence, if there is no exceptional family, then at least one solution exists  相似文献   
129.
A system of first order equations of mixed type, which may be reduced to a general second order equation of mixed type, is considered. Uniqueness of solution to the generalized Tricomi problem is proved by the method of auxiliary function. Existence of H¹ strong solution is based on a characteristic problem and is proved by the Fredholm's alternative properties.  相似文献   
130.
We explain the reason for the existence of a gap between multiobjective and scalar optimization proposed in Ref. 1, giving a characterization of this gap.  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