全文获取类型
收费全文 | 43561篇 |
免费 | 4510篇 |
国内免费 | 2620篇 |
专业分类
化学 | 5750篇 |
晶体学 | 226篇 |
力学 | 7775篇 |
综合类 | 238篇 |
数学 | 4541篇 |
物理学 | 13052篇 |
综合类 | 19109篇 |
出版年
2024年 | 101篇 |
2023年 | 439篇 |
2022年 | 728篇 |
2021年 | 854篇 |
2020年 | 1017篇 |
2019年 | 821篇 |
2018年 | 871篇 |
2017年 | 1074篇 |
2016年 | 1184篇 |
2015年 | 1364篇 |
2014年 | 1930篇 |
2013年 | 2507篇 |
2012年 | 2329篇 |
2011年 | 2612篇 |
2010年 | 2053篇 |
2009年 | 2369篇 |
2008年 | 2339篇 |
2007年 | 2634篇 |
2006年 | 2447篇 |
2005年 | 2262篇 |
2004年 | 2178篇 |
2003年 | 1963篇 |
2002年 | 1739篇 |
2001年 | 1492篇 |
2000年 | 1464篇 |
1999年 | 1236篇 |
1998年 | 1147篇 |
1997年 | 1052篇 |
1996年 | 975篇 |
1995年 | 798篇 |
1994年 | 740篇 |
1993年 | 628篇 |
1992年 | 590篇 |
1991年 | 507篇 |
1990年 | 466篇 |
1989年 | 442篇 |
1988年 | 332篇 |
1987年 | 258篇 |
1986年 | 184篇 |
1985年 | 137篇 |
1984年 | 104篇 |
1983年 | 50篇 |
1982年 | 98篇 |
1981年 | 42篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1978年 | 22篇 |
1976年 | 12篇 |
1971年 | 8篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 844 毫秒
61.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
62.
A. Khrennikov 《Annalen der Physik》2003,12(10):575-585
We study the probabilistic consequences of the choice of the basic number field in the quantum formalism. We demonstrate that by choosing a number field for a linear space representation of quantum model it is possible to describe various interference phenomena. We analyse interference of probabilistic alternatives induced by real, complex, hyperbolic (Clifford) and p‐adic representations. 相似文献
63.
We establish the existence and stability of multidimensional transonic shocks for the Euler equations for steady potential compressible fluids. The Euler equations, consisting of the conservation law of mass and the Bernoulli law for the velocity, can be written as a second-order, nonlinear equation of mixed elliptic-hyperbolic type for the velocity potential. The transonic shock problem can be formulated into the following free boundary problem: The free boundary is the location of the transonic shock which divides the two regions of smooth flow, and the equation is hyperbolic in the upstream region where the smooth perturbed flow is supersonic. We develop a nonlinear approach to deal with such a free boundary problem in order to solve the transonic shock problem. Our results indicate that there exists a unique solution of the free boundary problem such that the equation is always elliptic in the downstream region and the free boundary is smooth, provided that the hyperbolic phase is close to a uniform flow. We prove that the free boundary is stable under the steady perturbation of the hyperbolic phase. We also establish the existence and stability of multidimensional transonic shocks near spherical or circular transonic shocks.
64.
吴军海 《莆田高等专科学校学报》2008,(4):35-39
通过对中外商业银行操作风险管理流程的比较研究,指出我国商业银行与国外商业银行存在的差距和不足,并就我国商业银行如何构筑科学的操作风险管理流程提出若干建议。 相似文献
65.
魏毅 《淮北煤炭师范学院学报(自然科学版)》2007,28(3):65-68
在田径教学、训练与比赛中,由于没有完全遵循人体运动的生理规律和调控生物节律,不能使机体的工作运行保持在良好的竞技状态,导致各种各样的运动创伤,严重地影响教学、训练与运动成绩的提高.文章从运动医学理论对田径运动中肌肉损伤的原因进行分析,寻找科学的田径运动损伤康复手段。 相似文献
66.
Noboru Nakatani 《Optical Review》2003,10(4):206-210
This paper describes a compulsorily phase locked differential interferometer using an orthogonally polarized light source of a modulated LD with high extinction ratio to reduce non-linearity of the interferometer caused by polarization cross-talk. The current modulated LD is used as a light source to make the interferometer compact and for the scanning phase of the interferometer. The interferometer is operated compulsorily at the maximum inclination point of the fringe intensity curve by fringe scanning and an electric system. A Wollaston prism of high extinction ratio (50 dB) is used to combine the polarizing beams and to make the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis; in the other they have a small crossing angle (2.5 mrad ∼ 10 mrad) to completely exclude non-linearity of the interferometer causded by polarization cross-talk. Using jets of a gas mixture of nitrogen and ethylene, this interferometer was demonstrated to be useful in detecting the photothermal effect of a photothermal velocimeter under phase fluctuation in a turbulent flow. 相似文献
67.
介绍了车用压差式气体流量传感器的结构设计和电测电路,指出了传感器的使用范围,由实验测出了特性曲线.该仪器可检测车用发动机曲轴箱窜气量,适用于发动机不解体故障诊断. 相似文献
68.
The modification of the number field sieve which Joux and Lercier recently used to compute logarithms in a prime field of a record 120 decimal digits makes use of the notion of a virtual logarithm of a prime ideal in a number ring. We provide necessary and sufficient conditions for their method to succeed and give an explicit formula for the virtual logarithm of an ideal. 相似文献
69.
70.
The turbulent flow in a compound meandering channel with a rectangular cross section is one of the most complicated turbulent flows, because the flow behaviour is influenced by several kinds of forces, including centrifugal forces, pressure‐driven forces and shear stresses generated by momentum transfer between the main channel and the flood plain. Numerical analysis has been performed for the fully developed turbulent flow in a compound meandering open‐channel flow using an algebraic Reynolds stress model. The boundary‐fitted coordinate system is introduced as a method for coordinate transformation in order to set the boundary conditions along the complicated shape of the meandering open channel. The turbulence model consists of transport equations for turbulent energy and dissipation, in conjunction with an algebraic stress model based on the Reynolds stress transport equations. With reference to the pressure–strain term, we have made use of a modified pressure–strain term. The boundary condition of the fluctuating vertical velocity is set to zero not only for the free surface, but also for computational grid points next to the free surface, because experimental results have shown that the fluctuating vertical velocity approaches zero near the free surface. In order to examine the validity of the present numerical method and the turbulent model, the calculated results are compared with experimental data measured by laser Doppler anemometer. In addition, the compound meandering open channel is clarified somewhat based on the calculated results. As a result of the analysis, the present algebraic Reynolds stress model is shown to be able to reasonably predict the turbulent flow in a compound meandering open channel. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献