全文获取类型
收费全文 | 14950篇 |
免费 | 3268篇 |
国内免费 | 934篇 |
专业分类
化学 | 2453篇 |
晶体学 | 159篇 |
力学 | 2743篇 |
综合类 | 248篇 |
数学 | 5235篇 |
物理学 | 8314篇 |
出版年
2024年 | 25篇 |
2023年 | 179篇 |
2022年 | 302篇 |
2021年 | 344篇 |
2020年 | 377篇 |
2019年 | 332篇 |
2018年 | 333篇 |
2017年 | 573篇 |
2016年 | 667篇 |
2015年 | 596篇 |
2014年 | 907篇 |
2013年 | 1097篇 |
2012年 | 860篇 |
2011年 | 1011篇 |
2010年 | 868篇 |
2009年 | 1023篇 |
2008年 | 1077篇 |
2007年 | 1047篇 |
2006年 | 906篇 |
2005年 | 718篇 |
2004年 | 705篇 |
2003年 | 675篇 |
2002年 | 589篇 |
2001年 | 499篇 |
2000年 | 481篇 |
1999年 | 417篇 |
1998年 | 358篇 |
1997年 | 291篇 |
1996年 | 252篇 |
1995年 | 237篇 |
1994年 | 182篇 |
1993年 | 155篇 |
1992年 | 123篇 |
1991年 | 121篇 |
1990年 | 100篇 |
1989年 | 81篇 |
1988年 | 78篇 |
1987年 | 65篇 |
1986年 | 48篇 |
1985年 | 72篇 |
1984年 | 40篇 |
1983年 | 32篇 |
1982年 | 37篇 |
1981年 | 31篇 |
1980年 | 50篇 |
1979年 | 48篇 |
1978年 | 27篇 |
1977年 | 35篇 |
1976年 | 39篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
研究一类由任意有限多个线性子系统组成的切换系统的动态输出反馈H∞控制问题.利用共同Lyapunov函数方法和凸组合技术,给出由矩阵不等式表示的控制器存在的充分条件,并设计了相应的子控制器和切换规则.采用消元法,将该矩阵不等式转化为一组线性矩阵不等式(LMIs).最后给出一个数值仿真实例证明结论的有效性. 相似文献
992.
993.
994.
D. A. Carlson 《Journal of Optimization Theory and Applications》1986,49(2):207-225
In this paper, we are concerned with the question of the existence of optimal solutions for infinite-horizon optimal control problems of Lagrange type. In such problems, the objective or cost functional is described by an improper integral. As dictated by applications arising in mathematical economics, we do nota priori assume that this improper integral converges. This leads us to consider a weaker type of optimality, known as catching-up optimality. The results presented here utilize the classical convexity and seminormality conditions typically imposed in the existence theory for the case of finite intervals. These conditions are significantly weaker than those imposed by other authors; as a consequence, their existence results are contained as special cases of the results presented here. The method of proof utilizes the Carathéodory-Hamilton-Jacobi theory previously developed by the author for infinite-horizon optimal control problems.This research forms part of the author's doctoral dissertation written at the University of Delaware, Newark, Delaware under the supervision of Professor T. S. Angell. 相似文献
995.
利用破产理论和随机控制理论研究保险基金最优投资策略,建立生存概率最大化的目标函数,得到最优投资策略满足的随机微分方程;在初始金逼近0时得到保险基金的最优投资策略的显示解;采用递推算法,得到初始准备金为任意值时的最优投资策略. 相似文献
996.
The adsorption kinetics (by thermal desorption spectroscopy) and adsorption dynamics (by molecular beam scattering) have been determined for a number of alkanes, methanol, thiophene, and water on a silica wafer—SiO2/Si(1 1 1). No indications for bond activation were present, i.e., all probe molecules adsorb molecularly obeying 1st order kinetics. The coverage-dependent heat of adsorption has been determined accordingly. The adsorption dynamics are precursor-mediated with Kisliuk-like shapes of the adsorption probabilities at low impact energies and adsorbate-assisted adsorption at large impact energies. 相似文献
997.
It is shown in this paper that the finite-time optimal control of polynomial systems can be obtained by solving a sequence of optimal control problems for the linearized problem. The paper provides proof of convergence as well as illustration of the procedure by two examples. 相似文献
998.
To simulate fracture behaviors in concrete more realistically, a theoretical analysis on the potential question in the quasi-static method is presented, then a novel algorithm is proposed which takes into account the inertia effect due to unstable crack propagation and meanwhile requests much lower computational efforts than purely dynamic method. The inertia effect due to load increasing becomes less important and can be ignored with the loading rate decreasing, but the inertia effect due to unstable crack propagation remains considerable no matter how low the loading rate is. Therefore, results may become questionable if a fracture process including unstable cracking is simulated by the quasi-static procedure excluding completely inertia effects. However, it requires much higher computational effort to simulate experiments with not very high loading rates by the dynamic method. In this investigation which can be taken as a natural continuation, the potential question of quasi-static method is analyzed based on the dynamic equations of motion. One solution to this question is the new algorithm mentioned above. Numerical examples are provided by the generalized beam (GB) lattice model to show both fracture processes under different loading rates and capability of the new algorithm. 相似文献
999.
1000.
Jürgen Durner Dr. Dr. 《Angewandte Chemie (International ed. in English)》2010,49(6):1026-1051
Clinical chemistry and laboratory medicine can look back over more than 150 years of eventful history. The subject encompasses all the medicinal disciplines as well as the remaining natural sciences. Clinical chemistry demonstrates how new insights from basic research in biochemical, biological, analytical chemical, engineering, and information technology can be transferred into the daily routine of medicine to improve diagnosis, therapeutic monitoring, and prevention. This Review begins with a presentation of the development of clinical chemistry. Individual steps between the drawing of blood and interpretation of laboratory data are then illustrated; here not only are pitfalls described, but so are quality control systems. The introduction of new methods and trends into medicinal analysis is explored, along with opportunities and problems associated with personalized medicine. 相似文献