全文获取类型
收费全文 | 178888篇 |
免费 | 3633篇 |
国内免费 | 2137篇 |
专业分类
化学 | 74458篇 |
晶体学 | 2699篇 |
力学 | 11459篇 |
综合类 | 72篇 |
数学 | 31578篇 |
物理学 | 64392篇 |
出版年
2022年 | 825篇 |
2021年 | 988篇 |
2020年 | 1069篇 |
2019年 | 1008篇 |
2018年 | 10582篇 |
2017年 | 11412篇 |
2016年 | 6049篇 |
2015年 | 2298篇 |
2014年 | 2017篇 |
2013年 | 3727篇 |
2012年 | 8293篇 |
2011年 | 17626篇 |
2010年 | 10760篇 |
2009年 | 10849篇 |
2008年 | 15061篇 |
2007年 | 18602篇 |
2006年 | 3475篇 |
2005年 | 10348篇 |
2004年 | 6240篇 |
2003年 | 5816篇 |
2002年 | 3562篇 |
2001年 | 3494篇 |
2000年 | 2759篇 |
1999年 | 1911篇 |
1998年 | 1384篇 |
1997年 | 1302篇 |
1996年 | 1331篇 |
1995年 | 1151篇 |
1994年 | 978篇 |
1993年 | 849篇 |
1992年 | 1172篇 |
1991年 | 1161篇 |
1990年 | 1044篇 |
1989年 | 935篇 |
1988年 | 910篇 |
1987年 | 953篇 |
1986年 | 787篇 |
1985年 | 1012篇 |
1984年 | 958篇 |
1983年 | 685篇 |
1982年 | 669篇 |
1981年 | 641篇 |
1980年 | 597篇 |
1979年 | 733篇 |
1978年 | 768篇 |
1977年 | 691篇 |
1976年 | 644篇 |
1975年 | 536篇 |
1974年 | 574篇 |
1973年 | 545篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
G. Panina 《Central European Journal of Mathematics》2003,1(2):157-168
All 3-dimensional convex polytopes are known to be rigid. Still their Minkowski differences (virtual polytopes) can be flexible
with any finite freedom degree. We derive some sufficient rigidity conditions for virtual polytopes and present some examples
of flexible ones. For example, Bricard's first and second flexible octahedra can be supplied by the structure of a virtual
polytope. 相似文献
72.
73.
74.
关于 Hilbert积分不等式(英) 总被引:29,自引:0,他引:29
本文通过引入一个适当的形如F(x,y)的正定二次型证明了Hilbert积分不等式可以得到改进.利用这一结果,Widder不等式得到了加强,并且建立了广义的Hardy-Littlewood不等式. 相似文献
75.
Stephen C. Littlechild 《The Journal of the Operational Research Society》1996,47(5):601-611
In this Blackett Lecture, Professor Littlechild, Director General of Electricity Supply in the UK's Office of Electricity Regulation, renews acquaintance with some models he has developed over the years, introduces some models he has recently met, and discusses models that it would seem to be worthwhile developing. He concludes that for all concerned in the electricity industry, success depends on ever improving decision-making, in which OR has a vital role. 相似文献
76.
Uhm H.S. Lee P.H. Kim Y.I. Kim J.H. Chang H.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):628-635
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data 相似文献
77.
In a previous paper (Ref. 1), an exact solution of the optimal planar interception with fixed end conditions was derived in closed form. The optimal control was expressed as an explicit function of the state variables and two fixed parameters, obtained by solving a set of nonlinear algebraic equations involving elliptic integrals. In order to facilitate the optimal control implementation, the present paper derives a highly accurate simplified solution assuming that the ratio of the pursuer turning radius to the initial range is small. An asymptotic expansion further reduces the computational workload. Construction of a near-optimal open-loop control, based on the approximations, completes the present paper. 相似文献
78.
间歇式高速同步相机新型全数字化微机控制系统 总被引:2,自引:2,他引:0
本文提出了一种间歇式高速同步相机的全新设计方法,介绍了系统的工作原理,硬件,软件设计以及核心控制算法,最后给出了实际应用结果。 相似文献
79.
The coordination chemistry of beryllium with particular emphasis on chelates under physiological or near physiological conditions is surveyed. Hard donors such as oxygen are emphasized; equilibrium data and formation constants are reported as an indication of the strength of the complex. 相似文献
80.