全文获取类型
收费全文 | 5312篇 |
免费 | 884篇 |
国内免费 | 587篇 |
专业分类
化学 | 1272篇 |
晶体学 | 74篇 |
力学 | 815篇 |
综合类 | 116篇 |
数学 | 2168篇 |
物理学 | 2338篇 |
出版年
2024年 | 11篇 |
2023年 | 48篇 |
2022年 | 97篇 |
2021年 | 98篇 |
2020年 | 133篇 |
2019年 | 111篇 |
2018年 | 130篇 |
2017年 | 186篇 |
2016年 | 214篇 |
2015年 | 160篇 |
2014年 | 254篇 |
2013年 | 461篇 |
2012年 | 295篇 |
2011年 | 373篇 |
2010年 | 277篇 |
2009年 | 340篇 |
2008年 | 325篇 |
2007年 | 363篇 |
2006年 | 327篇 |
2005年 | 260篇 |
2004年 | 247篇 |
2003年 | 275篇 |
2002年 | 241篇 |
2001年 | 177篇 |
2000年 | 179篇 |
1999年 | 180篇 |
1998年 | 154篇 |
1997年 | 105篇 |
1996年 | 96篇 |
1995年 | 95篇 |
1994年 | 90篇 |
1993年 | 76篇 |
1992年 | 61篇 |
1991年 | 46篇 |
1990年 | 52篇 |
1989年 | 34篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1957年 | 3篇 |
排序方式: 共有6783条查询结果,搜索用时 203 毫秒
991.
Deriving the Properties of Linear Bilevel Programming via a Penalty Function Approach 总被引:7,自引:0,他引:7
Z. K. Xu 《Journal of Optimization Theory and Applications》1999,103(2):441-456
For the linear bilevel programming problem, we propose an assumption weaker than existing assumptions, while achieving similar results via a penalty function approach. The results include: equivalence between (i) existence of a solution to the problem, (ii) existence of an exact penalty function approach for solving the problem, and (iii) achievement of the optimal value of the equivalent form of the problem at some vertex of a certain polyhedral convex set. We prove that the assumption is both necessary and sufficient for the linear bilevel programming problem to admit an exact penalty function formulation, provided that the equivalent form of the problem has a feasible solution. A method is given for computing the minimal penalty function parameter value. This method can be executed by solving a set of linear programming problems. Lagrangian duality is also presented. 相似文献
992.
交联低密度聚乙烯交联程度表征方法的研究 总被引:2,自引:0,他引:2
硅烷交联法和过氧化物交联法是聚乙烯交联改性的两种重要方法[1],以往的文献上通常都以凝胶含量来表征这两种方法制备的交联产物的交联程度[2~6],但是在实践中我们发现,凝胶含量基本相同的硅烷交联聚乙烯和过氧化物交联聚乙烯的性能存在着很大的差异,例如在70℃的二甲苯中凝胶含量为62%的过氧化物交联低密度聚乙烯(LDPE)的平衡溶胀比是相同凝胶含量的硅烷交联LDPE的4倍,150℃时凝胶含量为70%的硅烷交联聚乙烯的热延伸率比相同凝胶含量的过氧化物交联聚乙烯小三倍,而且二者的结晶行为和结晶度也有很大的… 相似文献
993.
Y.-Q. Zhang X.-C. Zeng Y. Chen X.-G. Meng A.-M. Tian 《Journal of Thermal Analysis and Calorimetry》1999,58(2):463-475
On the basis of the theory of thermokinetics proposed in the literature, a novel thermokinetic method for determination of the reaction rate, the characteristic parameter method, is proposed in this paper. Mathematical models were established to determine the kinetic parameters and rate constants. In order to test the validity of this method, the saponifications of ethyl benzoate, ethyl acetate and ethyl propionate, and the formation of hexamethylenetetramine were studied with this method. The rate constants calculated with this method are in agreement with those in the literature, and the characteristic parameter method is therefore believed to be correct.In the light of the characteristic parameter method, we have developed further two thermo-kinetic methods, the thermoanalytical single and multi-curve methods, which are convenient for simultaneous determination of the reaction order and the rate constant. The reaction orders and rate constants of the saponifications of ethyl acetate and ethyl butyrate and the ring-opening reaction of epichlorohydrin with hydrobromic acid were determined with these methods, and their validity was verified by the experimental results.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
994.
995.
基于p偏振光双面反射的薄膜传感器光学参数的优化 总被引:4,自引:1,他引:3
p偏振光在镀膜平板玻璃上、下表面反射光强比γ的角度调制曲线的性状与膜层光学参数密切相关。分析了γ与膜层折射率、消光系数及膜厚的相对梯度随光参数变化的着急为基于p偏振光双面反射的薄膜传感器选择最佳参数提供了理论依据,计算表明该类型传感器对膜层折射率的测量分辨率高达10^-7。对不同工艺条件下得到的溶胶-凝胶SnO2膜进行光学参数测定及初步气敏实验,结果表明p偏振光双面反射可作为高灵敏度光化学传感器的 相似文献
996.
研究了带电粒子在射频四极透镜中的运动方程,导出了传输矩阵元,讨论了透镜聚焦特性和透镜各参数间的关系. 相似文献
997.
In the present paper, an equation of state has been obtained in case of liquid alkali metals like Na, K, Rb and Cs from sound
velocity measurements. The theory developed gives very good agreement for both the sound velocity and the volume as a function
of pressure at different temperatures in these liquid alkali metals. Further, the variation of non-linear parameter,B / A, as a function of pressure and temperature is also studied. 相似文献
998.
陈应天 《应用数学和力学(英文版)》1983,4(3):431-434
The general form of J-integral conservation law in three di-mensions has been derived from the principle of virtual work.The necessary conditions for J-integral conservation are alsogiven. 相似文献
999.
When sound waves of high amplitude propagate, several non-linear effects occur. Ultrasonic studies in liquid mixtures provide
valuable information about structure and interaction in such systems. The present investigation comprises of theoretical evaluation
of the acoustic non-linearity parameter B/A of four binary liquid mixtures using Tong and Dong equation at high pressures and T=303.15 K. Thermodynamic method has also been used to calculate the non-linearity parameter after making certain approximations. 相似文献
1000.
用Bohr-Mottelson的两参数、三参数和四参数公式对A~190区61条超形变带进行了系统分析. 结果显示:3个公式都能较好地拟合190区超形变带的E2跃迁谱,而且带首自旋的确定基本一致. 大部分带Bohr-Mottelson的三参数数值关系符合ab公式的理论预期值,小部分带的三参数数值关系符合Harris公式的理论预期值. 一半以上带的四参数数值关系与ab公式的预期值接近,而与Harris公式的预期值偏离较大. 表明两参数ab公式比Harris公式具有更广泛的实用性. 相似文献