全文获取类型
收费全文 | 3054篇 |
免费 | 139篇 |
国内免费 | 98篇 |
专业分类
化学 | 499篇 |
晶体学 | 7篇 |
力学 | 167篇 |
综合类 | 10篇 |
数学 | 229篇 |
物理学 | 474篇 |
综合类 | 1905篇 |
出版年
2024年 | 4篇 |
2023年 | 33篇 |
2022年 | 70篇 |
2021年 | 68篇 |
2020年 | 61篇 |
2019年 | 64篇 |
2018年 | 56篇 |
2017年 | 83篇 |
2016年 | 73篇 |
2015年 | 97篇 |
2014年 | 149篇 |
2013年 | 192篇 |
2012年 | 157篇 |
2011年 | 214篇 |
2010年 | 146篇 |
2009年 | 180篇 |
2008年 | 192篇 |
2007年 | 189篇 |
2006年 | 166篇 |
2005年 | 160篇 |
2004年 | 141篇 |
2003年 | 129篇 |
2002年 | 89篇 |
2001年 | 99篇 |
2000年 | 81篇 |
1999年 | 67篇 |
1998年 | 46篇 |
1997年 | 64篇 |
1996年 | 36篇 |
1995年 | 40篇 |
1994年 | 25篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1975年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有3291条查询结果,搜索用时 281 毫秒
1.
2.
关于化学实验教学改革的研究 总被引:2,自引:0,他引:2
李秀琴 《安庆师范学院学报(自然科学版)》2003,9(3):99-101
当前化学实验内容陈旧,联系实际较少,为适应素质教育的要求,应对实验教学进行改革,逐步形成科学的、先进的化学实验教学思路,以充分、全面的发挥化学实验教学的探究功能和育人功能。 相似文献
3.
William J. Reed 《Natural Resource Modeling》1989,3(4):463-480
It is assumed that the probability of destruction of a biological asset by natural hazards can be reduced through investment in protection. Specifically a model, in which the hazard rate depends on both the age of the asset and the accumulated invested protection capital, is assumed. The protection capital depreciates through time and its effectiveness in reducing the hazard rate is subject to diminishing returns. It is shown how the investment schedule to maximize the expected net present value of the asset can be determined using the methods of deterministic optimal control, with the survival probability regarded as a state variable. The optimal investment pattern involves “bang-bang-singular” control. A numerical scheme for determining jointly the optimal investment policy and the optimal harvest (or replacement) age is outlined and a numerical example involving forest fire protection is given. 相似文献
4.
高师武术普修课分块教学的实验研究 总被引:1,自引:0,他引:1
黄秀玉 《曲靖师范学院学报》2002,21(6):102-104
采用实验对比的方法 ,探讨武术普修课分块教学的可行性效果 .结果表明 ,武术普修课采用分块教学是可行的 ,且使学生的学习目的性更加明确 ,提高了教学效果 相似文献
5.
In this paper, the special construction of a parallel robot, called spatial servopneumatic multi-axis test facility, will be discussed. The investigations include the following aspects: (i) the laboratory set-up of the robot, (ii) various results obtained in laboratory experiments, taking into account quite different control algorithms and command-input signals, (iii) a comparison of the laboratory experiments with the computer simulations of Part I of this paper, and ({vi}) a quality check of the results compared with the cost of the different controller realizations. The results of both the computer simulations and the laboratory experiments show: (i) The dynamic behavior of the parallel structure can be tremendously improved by using sophisticated nonlinear control algorithms. (ii) This improvement has to be paid by a drastically increased amount of work for deriving the model equations and control algorithms, and by augmented hardware cost of the sensing elements and controller electronics. (iii) Carefully developed model equations and identified model parameters provide theoretical models of the complex parallel structure that are very close to reality. This enables the design engineer to systematically investigate constructive alternatives of the design parameters, sensor and actuator concepts, and control strategies of the MAP prior to their hardware realization.This work has been supported by the German Science Foundation (DFG) under Contract No. Ha 1666/6-3. 相似文献
6.
7.
8.
Liquid-liquid phase equilibria of aqueous two-phase systems containing salts and polyethylene glycol 总被引:2,自引:0,他引:2
Liquid-liquid phase equilibria of the ternary systems: (a) polyethylene glycol - ammonium sulfate- water and (b) polyethylene glycol - sodium carbonate -water have been determined experimentally at 15°, 25°, 35° and 45°C and for two different molecular weights of the polymer (Avg. M.W. 1000 and 2000). Details of the glass cell and of the equilibration and analytical procedures used are described. Equilibrium data along with phase diagrams are presented. Finally the effect of temperature and of the molecular weight of the polymer are also discussed. 相似文献
9.
10.