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   911篇
  免费   256篇
  国内免费   87篇
化学   175篇
晶体学   7篇
力学   194篇
综合类   12篇
数学   195篇
物理学   671篇
  2023年   12篇
  2022年   34篇
  2021年   32篇
  2020年   34篇
  2019年   33篇
  2018年   38篇
  2017年   47篇
  2016年   47篇
  2015年   40篇
  2014年   71篇
  2013年   84篇
  2012年   54篇
  2011年   66篇
  2010年   53篇
  2009年   54篇
  2008年   51篇
  2007年   56篇
  2006年   51篇
  2005年   50篇
  2004年   42篇
  2003年   40篇
  2002年   32篇
  2001年   31篇
  2000年   27篇
  1999年   23篇
  1998年   25篇
  1997年   13篇
  1996年   13篇
  1995年   15篇
  1994年   12篇
  1993年   13篇
  1992年   6篇
  1991年   7篇
  1990年   4篇
  1989年   6篇
  1988年   2篇
  1987年   4篇
  1986年   2篇
  1985年   6篇
  1984年   7篇
  1982年   1篇
  1981年   2篇
  1979年   3篇
  1978年   3篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
  1972年   1篇
  1969年   1篇
  1957年   1篇
排序方式: 共有1254条查询结果,搜索用时 0 毫秒
1.
半导体激光器发射光谱实验仪   总被引:1,自引:1,他引:0  
设计了一种半导体激光器发射光谱实验仪 ,可以用来观测LD发射的荧光光谱、激光光谱 ,以及了解光栅外腔选取单纵模、压窄线宽、波长调谐的机理 .该实验仪结构紧凑 ,物理概念清晰 ,适用于大专院校的光学实验教学  相似文献   
2.
Combining the results of Walczak (Ref. 1) and Lasiecka (Refs. 2 and 3), we extend the well-known Dubovicki-Milutin theorem in two directions: (i) We allow for treatment of several equality constraints in optimization problems; and (ii) We assume less regularity of optimization problems by requiring the existence of external cones instead of tangent cones. An example of an optimization problem is also considered.  相似文献   
3.
Dynamic systems described by nonlinear differential equations of the second order are studied. It is assumed that certain preliminary information on the dissipative or elastic characteristics of systems is known. A new approach is demonstrated to obtaining full information on unknown or partially known characteristics of a system from measurements of not only displacements but also velocities and accelerations __________ Published in Prikladnaya Mekhanika, Vol. 41, No. 6, pp. 139–143, June 2005.  相似文献   
4.
We have used potentiometric titration with tetrabutylammonium hydroxide to determine the acid center content on the outer surface of dealuminated natural and synthetic mordenites. We have established a symbatic relationship between the 2,2-dimethylbutane content in the hydroisomerization products of n-hexane on dealuminated palladium-containing mordenites and the number of their external acid centers. We have studied the possibility of partial deactivation of such centers during ion-exchange deposition of palladium on the catalysts, using a tetraammine palladium solution.  相似文献   
5.
We provide a quick elementary solution of the mean spherical model in a random external field. This also allows an immediate proof of the self-averaging property of the free energy. We calculate the free energy by means of the replica method, i.e., for any (not necessarily integer) replica numbern, and show that when a phase transition occurs the limits andn 0 are not interchangeable.  相似文献   
6.
Between 1992 and 1994, a new screening campaign for blood Pb monitoring in the Italian general population was carried out. Since the first campaign (started in 1978, in accomplishment of the European Community Directive 77/312/EEC) a working group of the Laboratory of Clinical Biochemistry at the Italian National Institute of Health (Istituto Superiore di Sanità), as the Reference Centre (RC), has coordinated the activity of various laboratories spread over the national territory. Appropriate quality assurance procedures, including an external quality assessment scheme (EQAS), were elaborated. Within the EQAS, three or four trials were carried out every year. Each laboratory participating in the trial analyzed eight control samples prepared from cow blood at different Pb concentrations. The results obtained by each peripheral laboratory and the RC between 1992 and 1994 have been compared by regression analysis. The same statistical method was adopted to compare the results obtained by each peripheral laboratory and the RC in the duplicate analysis of about 10 per cent of the human samples collected during the 1992–1994 monitoring campaign. There was no evidence of systematic differences between the regression lines obtained on control and human samples. In spite of the lower Pb concentration in the control samples analyzed during the 1992–1994 campaign, the analytical performance of the laboratories was better than that obtained in the previous screening campaign (1985–1986). Blood Pb levels observed in human samples collected between 1992 and 1994, confirm the downward time trend observed in the campaigns carried out in 1978–1979, 1980–1981 and 1985–1986. This study confirms that the results obtained in an EQAS are representative of the actual performance in the analysis of real (human) samples.  相似文献   
7.
In this paper, quantum correlation (QC) swapping between two Werner-like states, which are transformed from Werner states undergoing local and nonlocal unitary operations, are studied. Bell states measures are performed in the middle node to realize the QC swapping and correspondingly final correlated sates are obtained. Two different QC quantifiers, i.e., measurement-induced disturbance (MID) and ameliorated MID, are employed to characterize and quantify all the concerned QCs in the swapping process. All QCs in the concerned states are evaluated analytically and numerically. Correspondingly, their characteristics and properties are exposed in detail. It is exposed that, through the QC swapping process, one can obtain the long-distance QC indeed. Moreover, the similarities of monotony features of MID and AMID between the initial states and final states are exposed and analyzed.  相似文献   
8.
This paper researches the fixed-time leader-following consensus problem for nonlinear multi-agent systems (MASs) affected by unknown disturbances under the jointly connected graph. In order to achieve control goal, this paper designs a fixed-time consensus protocol, which can offset the unknown disturbances and the nonlinear item under the jointly connected graph, simultaneously. In this paper, the states of multiple followers can converge to the state of the leader within a fixed time regardless of the initial conditions rather than just converging to a small neighborhood near the leader state. Finally, a simulation example is given to illustrate the theoretical result.  相似文献   
9.
超分子化学领域的自组装研究是近年来研究的热点,对这种由一种或多种结构单元自发聚集而成具有一定尺寸和结构的过程研究已经取得了重大进展.以亲水基团和亲脂基团为主要构成单元的两亲性分子在自组装领域中的表现优异于其他分子,其亲水的刚性棒状基团和疏水的柔性线团基团通过不同方法共同构成了各种类型的刚柔两亲性分子,而在水溶液中自组装...  相似文献   
10.
根据红外光学系统的会聚特性,用光学增益方法分析了红外系统中各元件对应的光强分布,确定了位于焦面附近光学元件是激光破坏的易损部件,并提出了强激光对红外系统元件损伤,造成其探测、制导功能失效的硬破坏机理;由红外滤光片、探测器和信号处理电路与入射激光波长的光谱响应分析,提出了弱激光对红外系统干扰,导致其探测、制导功能在激光辐照一段时间内失效的软破坏机理;开展了激光辐照红外系统的失效验证实验,较好地解释了其失效的机理和效应。  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