全文获取类型
收费全文 | 24306篇 |
免费 | 2528篇 |
国内免费 | 1355篇 |
专业分类
化学 | 12852篇 |
晶体学 | 63篇 |
力学 | 1770篇 |
综合类 | 223篇 |
数学 | 7027篇 |
物理学 | 6254篇 |
出版年
2024年 | 23篇 |
2023年 | 254篇 |
2022年 | 362篇 |
2021年 | 670篇 |
2020年 | 831篇 |
2019年 | 745篇 |
2018年 | 629篇 |
2017年 | 676篇 |
2016年 | 1046篇 |
2015年 | 890篇 |
2014年 | 1172篇 |
2013年 | 2214篇 |
2012年 | 1260篇 |
2011年 | 1255篇 |
2010年 | 1030篇 |
2009年 | 1322篇 |
2008年 | 1453篇 |
2007年 | 1581篇 |
2006年 | 1314篇 |
2005年 | 1055篇 |
2004年 | 927篇 |
2003年 | 913篇 |
2002年 | 891篇 |
2001年 | 668篇 |
2000年 | 689篇 |
1999年 | 592篇 |
1998年 | 499篇 |
1997年 | 388篇 |
1996年 | 322篇 |
1995年 | 309篇 |
1994年 | 254篇 |
1993年 | 261篇 |
1992年 | 237篇 |
1991年 | 164篇 |
1990年 | 139篇 |
1989年 | 125篇 |
1988年 | 139篇 |
1987年 | 104篇 |
1986年 | 100篇 |
1985年 | 130篇 |
1984年 | 105篇 |
1983年 | 32篇 |
1982年 | 64篇 |
1981年 | 59篇 |
1980年 | 62篇 |
1979年 | 53篇 |
1978年 | 42篇 |
1977年 | 41篇 |
1976年 | 39篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
CONG Fuzhong & LI YongSchool of Mathematics Information Science Shandong Institute of Business Technology Yantai China Office of Mathematics Changchun Flight Academy of the Air Force Changchun China Department of Mathematics Jilin University Changchun China 《中国科学A辑(英文版)》2004,47(5):675-686
An effective stability result for generalized Hamiltonian systems is obtained by applying the simultaneous approximation technique due to Lochak. Among these systems, dimensions of action variables and angle variables might be distinct. 相似文献
62.
63.
Hybrid numerical—experimental approach for investigation of dynamics of microcantilever relay system
V. Ostasevicius S. Tamulevicius A. Palevicius M. Ragulskis R. Palevicius V. Grigaliunas 《Optics and Lasers in Engineering》2005,43(1):199
The time average holography measurements of the vibrating microelectromechanical switch (MEMS) were performed in this study. Experimental measurement results exhibit good agreement with computer generated holographic interferogram analysis. The validation of experimental investigations versus numerical analysis provides the necessary background to analyze the dynamical characteristics of micromechanical systems in virtual numerical environments. Direct application of fringe counting techniques for reconstruction of motion from time average holograms cannot be straightforward if the analyzed micromechanical systems contain motion limiters. Modifications of a classical time average holographic technique enable qualitative analysis of MEMS and can be applied for investigation of dynamical properties of much broader classes of MEMS systems. 相似文献
64.
从现有的PCDFs分子的正辛醇 /水分配系数 (logKow)实验数据出发 ,建立定量结构 性质关系方程(QSPR) .采用G98W程序包中的PM3方法对 13 5个多氯代二苯并呋喃 (PCDFs)分子和二苯并呋喃进行了优化计算 ,作业命令为 #pPM3optfreqscf(conver =9) ,以计算所得的分子轨道能量、碳原子电荷作为PCDFs分子结构描述符 ,运用多元线性回归技术建立了PCDFs的logKow与分子结构描述符的四元方程 ,最优相关系数为 0 .95 0 7,标准偏差为 0 .173 7,经检验该模型的稳健性好 ,并对未有实验数据的 85个PCDFs的logKow进行预测 相似文献
65.
本文对一般微分代数方程给出了几类可解集的概念,并讨论了多项式微分代数方程的可解集,得到子多项式系统具有唯一解。特别是有多于一个的解的条件,并得到了低次多项式在一定意义下的充分必要条件。 相似文献
66.
67.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
68.
We derive a test problem for evaluating the ability of time-steppingmethods to preserve the statistical properties of systems inmolecular dynamics. We consider a family of deterministic systemsconsisting of a finite number of particles interacting on acompact interval. The particles are given random initial conditionsand interact through instantaneous energy- and momentum-conservingcollisions. As the number of particles, the particle density,and the mean particle speed go to infinity, the trajectory ofa tracer particle is shown to converge to a stationary Gaussianstochastic process. We approximate this system by one describedby a system of ordinary differential equations and provide numericalevidence that it converges to the same stochastic process. Wesimulate the latter system with a variety of numerical integrators,including the symplectic Euler method, a fourth-order Runge-Kuttamethod, and an energyconserving step-and-project method. Weassess the methods' ability to recapture the system's limitingstatistics and observe that symplectic Euler performs significantlybetter than the others for comparable computational expense. 相似文献
69.
A.R.ELAMROUSS 《数学学报(英文版)》2005,21(1):129-142
This paper contains a generalization of the well-known Palais-Smale and Cerami compactness conditions. The compactness condition introduced is used to prove some general existence theorems for critical points. Some applications are given to differential equations. 相似文献
70.
One of the most ignored, but urgent and vital challenges confronting society today is the vulnerability of urban areas to extreme events. Current organization of response systems, predominantly based on a command and control model, limits their effectiveness and efficiency. Particularly, in decision‐making processes where a large number of actors may be involved. In this article, a new distributed collaborative decision‐making model is proposed to overcome command and control limitations encountered in stressful, hostile, chaotic, and large‐scale settings. This model was derived by borrowing concepts from the collective decision making of honeybees foraging, a successful process in solving complex tasks within complex settings. The model introduced in this article was evaluated through differential equations, i.e., continuous analysis, and difference equations, i.e., discrete analysis. The most important result found is that the best available option in any large‐scale decision‐making problem can be configured as an attractor, in a distributed and timely manner. We suggest that the proposed model has the potential to facilitate decision‐making processes in large‐scale settings. © 2005 Wiley Periodicals, Inc. Complexity 11:28–38, 2005 相似文献