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   10820篇
  免费   554篇
  国内免费   143篇
化学   7674篇
晶体学   93篇
力学   546篇
综合类   3篇
数学   1360篇
物理学   1841篇
  2024年   23篇
  2023年   88篇
  2022年   248篇
  2021年   462篇
  2020年   418篇
  2019年   487篇
  2018年   508篇
  2017年   403篇
  2016年   672篇
  2015年   465篇
  2014年   632篇
  2013年   1162篇
  2012年   876篇
  2011年   819篇
  2010年   599篇
  2009年   481篇
  2008年   524篇
  2007年   450篇
  2006年   321篇
  2005年   322篇
  2004年   196篇
  2003年   196篇
  2002年   160篇
  2001年   84篇
  2000年   57篇
  1999年   64篇
  1998年   41篇
  1997年   52篇
  1996年   48篇
  1995年   35篇
  1994年   39篇
  1993年   22篇
  1992年   37篇
  1991年   33篇
  1990年   30篇
  1989年   36篇
  1988年   33篇
  1987年   34篇
  1986年   30篇
  1985年   37篇
  1984年   35篇
  1983年   21篇
  1982年   26篇
  1981年   19篇
  1980年   23篇
  1979年   20篇
  1978年   18篇
  1977年   13篇
  1976年   15篇
  1974年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
ELSO is an environment for the solution oflarge-scale optimization problems. With ELSO the user is required to provide only code for the evaluation of a partially separable function. ELSO exploits the partialseparability structure of the function to computethe gradient efficiently using automatic differentiation.We demonstrate ELSO's efficiency by comparing thevarious options available in ELSO.Our conclusion is that the hybrid option in ELSOprovides performance comparable to the hand-coded option, while having the significantadvantage of not requiring a hand-coded gradient orthe sparsity pattern of the partially separable function.In our test problems, which have carefully coded gradients,the computing time for the hybrid AD option is within a factor of two of thehand-coded option.  相似文献   
32.
33.
Ali Liazid  Jamal Brigui 《Talanta》2007,71(2):976-980
The stability of Ochratoxin A during its extraction using different extraction techniques has been evaluated. Microwave-assisted extraction and pressurised liquid extraction, in addition to two other reference methods of extraction, i.e. ultrasound-assisted and magnetic stirring-assisted extraction, were evaluated. The effect of extraction temperature using the cited techniques was checked.The results show that Ochratoxin A can be extracted using microwave-assisted extraction at temperatures up to 150 °C without degradation. Pressurised liquid extraction can be used at temperatures up to 100 °C, for extraction times of less than 30 min. Further, both ultrasound-assisted extraction and magnetic stirring extraction can be applied at temperatures up to 65 °C.High-performance liquid chromatography combined with fluorescence detection using a Chromolith RP-18e column at a flow rate of 5 mL min−1 was used to quantify the Ochratoxin A. The retention time for the Ochratoxin A was 1.3 min. The limits of detection (LOD) and of quantification (LOQ) were 0.03 and 0.10 μg L−1, respectively.  相似文献   
34.
35.
Vibsanin O, isolated from the leaves and twigs of Viburnum awabuki, is an unprecedented bicyclic diterpenoid. The structures of vibsanin O was established by extensive analysis of spectroscopic data.  相似文献   
36.
In this paper, third-order 3-stage diagonally implicit Runge–Kutta–Nystrom method embedded in fourth-order 4-stage for solving special second-order initial value problems is constructed. The method has the property of minimized local truncation error as well as the last row of the coefficient matrix is equal to the vector output. The stability of the method is investigated and a standard set of test problems are tested upon and comparisons on the numerical results are made when the same set of test problems are reduced to first-order system and solved using existing Runge–Kutta method. The results clearly shown the advantage and the efficiency of the new method.  相似文献   
37.
High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO4) as the surfactant or methanol as the co-solvent.  相似文献   
38.
The purpose of this paper is to study a general Lienard type cubic system with one antisaddle and two saddles. We give some results of the existence and uniqueness of limit cycles as well as the evolution of limit cycles around the antisaddle for system (2) in the following when parameter a1 changes.  相似文献   
39.
We find the existence of a quantum thermal effect, “Hawking absorption.” near the inner horizon of the Kerr–Newman black hole. Redefining the entropy, temperature, angular velocity, and electric potential of the black hole, we give a new formulation of the Bekenstein–Smarr formula. The redefined entropy vanishes for absolute zero temperature of the black hole and hence it is interpreted as the Planck absolute entropy of the KN black hole.  相似文献   
40.
In this paper we construct a positive doubly power bounded operator with a nonpositive inverse on an AL-space.  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