全文获取类型
收费全文 | 3976篇 |
免费 | 261篇 |
国内免费 | 145篇 |
专业分类
化学 | 402篇 |
晶体学 | 2篇 |
力学 | 192篇 |
综合类 | 67篇 |
数学 | 3152篇 |
物理学 | 567篇 |
出版年
2023年 | 41篇 |
2022年 | 61篇 |
2021年 | 85篇 |
2020年 | 137篇 |
2019年 | 93篇 |
2018年 | 87篇 |
2017年 | 85篇 |
2016年 | 125篇 |
2015年 | 94篇 |
2014年 | 159篇 |
2013年 | 320篇 |
2012年 | 216篇 |
2011年 | 228篇 |
2010年 | 200篇 |
2009年 | 272篇 |
2008年 | 258篇 |
2007年 | 265篇 |
2006年 | 194篇 |
2005年 | 180篇 |
2004年 | 124篇 |
2003年 | 117篇 |
2002年 | 91篇 |
2001年 | 79篇 |
2000年 | 83篇 |
1999年 | 78篇 |
1998年 | 56篇 |
1997年 | 70篇 |
1996年 | 54篇 |
1995年 | 55篇 |
1994年 | 50篇 |
1993年 | 43篇 |
1992年 | 30篇 |
1991年 | 27篇 |
1990年 | 35篇 |
1989年 | 25篇 |
1988年 | 17篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 36篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1980年 | 30篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 16篇 |
1976年 | 9篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有4382条查询结果,搜索用时 15 毫秒
11.
关新民 《新疆大学学报(理工版)》2002,19(1):95-99
介绍了采用MATLAB V5.2提供的模糊逻辑工具箱来设计研究电孤纺电极调节系统中的模糊--PD控制器,讨论了在SIMULINK环境下模糊-PD控制器的参数自调速原理、结构、建立模糊控制规则库和模糊推论方法,并给出仿真结果与结论。 相似文献
12.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
13.
Geng Sheng WANG 《数学学报(英文版)》2005,21(5):1005-1014
This work is concerned with Pontryagin's maximum principle of optimal control problems governed by some non-well-posed semilinear heat equations. A type of approach to the non-well-posed optimal control problem is given. 相似文献
14.
关联规则是数据挖掘中的重要研究内容之一,对在事务数据库不变,只对最小支持度和最小可信度进行改变的情况下,针对关联规则的维护问题,设计了一个增量式更新的改进算法AIUA。 相似文献
15.
The paper deals with the riskiness analysis for a large portfolio of life annuities. By means of the limiting distribution of the present value of the portfolio, in the first part of the paper a model for evaluating the investment and the projection risks is presented. In the second part, with regard to the investment risk's effects, the insolvency risk is measured considering the cumulative probability distribution function of the discounted average cost per policy. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
16.
17.
18.
The crystallization of poly(ethylene terephthalate) under uniaxial tensile strain at different extension rates was investigated with optical polarimetry in a temperature range between the glass-transition temperature and the quiescent crystallization temperature. The evolution of the optical properties of the polymer, including the turbidity, birefringence, and dichroism, were monitored simultaneously with the mechanical parameters. To complete the semicrystalline microstructure characterization of the polymer under strain, an online wide-angle X-ray diffraction (WAXD) technique was used in separate experiments, which were performed under the same thermomechanical conditions. For real-time measurements, a high-energy synchrotron radiation source was used. The optical properties provided information about both the crystalline and amorphous phases, whereas the WAXD patterns essentially gave information about the crystalline phase. The two experimental techniques were then used in a complementary way to characterize the semicrystalline microstructure. Significant deviations from the stress-optical rule were found. This was attributed to both transient effects and the appearance of crystallites, which consisted of highly oriented molecular segments that could contribute to the optical anisotropy but not necessarily to the stress. The behavior of the optical dichroism was found to be qualitatively different from that of the birefringence. The latter monotonically increased with the strain, whereas the former first increased with the strain, passed through a maximum, and then decreased to a steady-state value. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1915–1927, 2004 相似文献
19.
We consider an optimal growth (multi-sector) model with nonconvex technology. Using the Clarke results on generalized gradients, we prove that the value function has left and right derivatives with respect to the initial capital stock, without requiring supermodularity assumptions. 相似文献
20.
Efficient Sequential Quadratic Programming Implementations for Equality-Constrained Discrete-Time Optimal Control 总被引:1,自引:0,他引:1
Efficient sequential quadratic programming (SQP) implementations are presented for equality-constrained, discrete-time, optimal control problems. The algorithm developed calculates the search direction for the equality-based variant of SQP and is applicable to problems with either fixed or free final time. Problem solutions are obtained by solving iteratively a series of constrained quadratic programs. The number of mathematical operations required for each iteration is proportional to the number of discrete times N. This is contrasted by conventional methods in which this number is proportional to N
3. The algorithm results in quadratic convergence of the iterates under the same conditions as those for SQP and simplifies to an existing dynamic programming approach when there are no constraints and the final time is fixed. A simple test problem and two application problems are presented. The application examples include a satellite dynamics problem and a set of brachistochrone problems involving viscous friction. 相似文献