全文获取类型
收费全文 | 23354篇 |
免费 | 2937篇 |
国内免费 | 1976篇 |
专业分类
化学 | 11801篇 |
晶体学 | 220篇 |
力学 | 952篇 |
综合类 | 120篇 |
数学 | 1809篇 |
物理学 | 6025篇 |
综合类 | 7340篇 |
出版年
2024年 | 84篇 |
2023年 | 406篇 |
2022年 | 618篇 |
2021年 | 730篇 |
2020年 | 782篇 |
2019年 | 688篇 |
2018年 | 628篇 |
2017年 | 583篇 |
2016年 | 855篇 |
2015年 | 948篇 |
2014年 | 1247篇 |
2013年 | 1488篇 |
2012年 | 1702篇 |
2011年 | 1715篇 |
2010年 | 1216篇 |
2009年 | 1160篇 |
2008年 | 1403篇 |
2007年 | 1213篇 |
2006年 | 1140篇 |
2005年 | 964篇 |
2004年 | 775篇 |
2003年 | 677篇 |
2002年 | 658篇 |
2001年 | 546篇 |
2000年 | 494篇 |
1999年 | 666篇 |
1998年 | 562篇 |
1997年 | 570篇 |
1996年 | 578篇 |
1995年 | 471篇 |
1994年 | 421篇 |
1993年 | 351篇 |
1992年 | 291篇 |
1991年 | 276篇 |
1990年 | 263篇 |
1989年 | 222篇 |
1988年 | 204篇 |
1987年 | 124篇 |
1986年 | 107篇 |
1985年 | 72篇 |
1984年 | 49篇 |
1983年 | 35篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 24篇 |
1976年 | 15篇 |
1974年 | 17篇 |
1970年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
René Meziat Diego Patiño Pablo Pedregal 《Computational Optimization and Applications》2007,38(1):147-171
We propose an alternative method for computing effectively the solution of non-linear, fixed-terminal-time, optimal control
problems when they are given in Lagrange, Bolza or Mayer forms. This method works well when the nonlinearities in the control
variable can be expressed as polynomials. The essential of this proposal is the transformation of a non-linear, non-convex
optimal control problem into an equivalent optimal control problem with linear and convex structure. The method is based on
global optimization of polynomials by the method of moments. With this method we can determine either the existence or lacking
of minimizers. In addition, we can calculate generalized solutions when the original problem lacks of minimizers. We also
present the numerical schemes to solve several examples arising in science and technology. 相似文献
82.
In the present paper, some types of general solutions of a first-order nonlinear ordinary differential equation with six degree are given and a new generalized algebra method is presented to find more exact solutions of nonlinear differential equations. As an application of the method and the solutions of this equation, we choose the (2 + 1) dimensional Boiti Leon Pempinelli equation to illustrate the validity and advantages of the method. As a consequence, more new types and general solutions are found which include rational solutions and irrational solutions and so on. The new method can also be applied to other nonlinear differential equations in mathematical physics. 相似文献
83.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
84.
By Hückel molecular orbital (HMO) theory, the calculation of the total energy of all π-electrons in conjugated hydrocarbons can be reduced to that of E(G)=|λ1|+|λ2|+?+|λn|, where λi are the eigenvalues of the corresponding graph G. Denote by Ψn the set of all fully-angular polyhex chains with n hexagons. In this paper, we show that Hn has the minimum total π-electron energy among chains in Ψn, where Hn is the helicene chain. 相似文献
85.
86.
A transient molecular network model is built to describe the nonlinear viscoelasticity of polymers by considering the effect
of entanglement loss and regeneration on the relaxation of molecular strands. It is an extension of previous network theories.
The experimental data on three thermoplastic polymers (ABS, PVC and PA6) obtained under various loading conditions are used
to test the model. Agreement between the theoretical and experimental curves shows that the suggested model can describe successfully
the relaxation behavior of the thermoplastic polymers under different loading rates by using relatively few relaxation modes.
Thus the micromechanism responsible for strain-rate dependence of relaxation process and the origin of nonlinear viscoelasticity
may be disclosed.
The project supported by the National Natural Science Foundation of China and Doctorial Fund 相似文献
87.
动态帧长ALOHA信令在集群移动通信中的应用 总被引:2,自引:0,他引:2
本文介绍了在集群动通信中,运用动态帧长ALOHA信令技术解决信道共用中停产碰撞问题的原理,并具体介绍了MPT-1327协议的接续原理,特点,信息格式及呼吊建立过程和举例,文中还对动态帧长的算法作了简介。 相似文献
88.
感应加热钢包炉是国外新发展的一种二次精炼及加热设备,具有高效、低能耗、无污染的特点,本文在感应加热钢包炉电磁与结构分析工作的基础上,用电磁场数值模拟方法对感应加热钢包炉的电磁设计和包壳结构进行优化。 相似文献
89.
聊城地区历史悠久,旅游资源丰富,但旅游事业起步晚,开发利用不够.为此,本文在分析聊城地区旅游资源的功能和分布的基础上,①对旅游资源的特色进行了初步评价,进而提出开发聊城地区游资源的几点设想. 相似文献
90.
本文研究了在不同pH值下吐温—80.Tritonx—100.SLS三种表面活性剂四—(对-三甲铵苯基)卟啉Soret带的影响。 相似文献