全文获取类型
收费全文 | 70611篇 |
免费 | 7979篇 |
国内免费 | 7008篇 |
专业分类
化学 | 34867篇 |
晶体学 | 580篇 |
力学 | 2444篇 |
综合类 | 392篇 |
数学 | 5732篇 |
物理学 | 15950篇 |
综合类 | 25633篇 |
出版年
2024年 | 218篇 |
2023年 | 950篇 |
2022年 | 1685篇 |
2021年 | 1874篇 |
2020年 | 1802篇 |
2019年 | 1793篇 |
2018年 | 1629篇 |
2017年 | 1632篇 |
2016年 | 2331篇 |
2015年 | 2667篇 |
2014年 | 3398篇 |
2013年 | 4380篇 |
2012年 | 5043篇 |
2011年 | 5378篇 |
2010年 | 4100篇 |
2009年 | 4185篇 |
2008年 | 4655篇 |
2007年 | 4340篇 |
2006年 | 3810篇 |
2005年 | 3433篇 |
2004年 | 2790篇 |
2003年 | 2142篇 |
2002年 | 2278篇 |
2001年 | 2104篇 |
2000年 | 1721篇 |
1999年 | 1857篇 |
1998年 | 1609篇 |
1997年 | 1532篇 |
1996年 | 1478篇 |
1995年 | 1278篇 |
1994年 | 1193篇 |
1993年 | 956篇 |
1992年 | 911篇 |
1991年 | 779篇 |
1990年 | 699篇 |
1989年 | 613篇 |
1988年 | 547篇 |
1987年 | 373篇 |
1986年 | 301篇 |
1985年 | 263篇 |
1984年 | 136篇 |
1983年 | 99篇 |
1982年 | 88篇 |
1981年 | 64篇 |
1980年 | 62篇 |
1979年 | 62篇 |
1978年 | 43篇 |
1976年 | 41篇 |
1974年 | 41篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
The present study is concerned with the determination of the optimal shape for a package containing multiple heating elements.
The optimization tool has been developed based on the inverse heat transfer (IHT) approach, incorporating a direct problem
solver, a numerical grid generator, a direct-differentiation sensitivity analyzer, and the conjugate gradient method. Shape
design that leads to a specified outer surface temperature distribution is predicted by the approach. In this study, the effects
of internal heat generation on optimal shapes of the packagings have also been evaluated. Several practical cases with various
imbedded heating elements and thermal conditions are studied. Results show that the approach provides an efficient computer-aided
design scheme for the shape profile determination. 相似文献
212.
213.
颗粒物质的两个典型效应及其研究现状的分析 总被引:6,自引:0,他引:6
概述了颗粒物质领域中粮仓现象和巴西坚果效应两个典型现象及其解释理论,分析其理论的成功和不足之处,并给出了一些看法。 相似文献
214.
215.
In this paper, a projection method is presented for solving the flow problems in domains with moving boundaries. In order to track the movement of the domain boundaries, arbitrary‐Lagrangian–Eulerian (ALE) co‐ordinates are used. The unsteady incompressible Navier–Stokes equations on the ALE co‐ordinates are solved by using a projection method developed in this paper. This projection method is based on the Bell's Godunov‐projection method. However, substantial changes are made so that this algorithm is capable of solving the ALE form of incompressible Navier–Stokes equations. Multi‐block structured grids are used to discretize the flow domains. The grid velocity is not explicitly computed; instead the volume change is used to account for the effect of grid movement. A new method is also proposed to compute the freestream capturing metrics so that the geometric conservation law (GCL) can be satisfied exactly in this algorithm. This projection method is also parallelized so that the state of the art high performance computers can be used to match the computation cost associated with the moving grid calculations. Several test cases are solved to verify the performance of this moving‐grid projection method. Copyright © 2004 John Wiley Sons, Ltd. 相似文献
216.
界面应力的正确评价是分析薄膜涂层材料力学特性的难题之一。利用镜像点法和Dirichlet等值性原理,本文推导了等厚双层薄膜涂层材料受表面集中力作用的平面问题理论解。该显式理论解是以固定在各镜像点上的局部坐标系下的Goursat应力函数的形式给出的。对应于高阶镜像点的应力函数,可通过递推的方法,从对应于低阶镜像点的应力函数求得,而且也易于计算机编程。随着镜像点阶数的增大,它与界面的距离也越来越大,因而相对应的应力函数对界面应力的影响越来越小。最后的算例表明,只需考虑前面有限个镜像点,便可获得足够精度的解。该理论解可作为格林函数,以求解复杂问题的理论解,也可用作边界元法的基本解,提高数值计算的精度和效率。 相似文献
217.
Junsaku Nitta Yiping Lin Takaaki Koga Tatsushi Akazaki 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):429
We report on electron g-factor in an InAs-inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure. The gate voltage dependence of g-factor is obtained from the coincidence method. The obtained g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and it is close to the bare g-factor value of In0.53Ga0.47As. The large change in g-factor is observed by applying the gate voltage. The obtained gate voltage dependence is not simply explained by the energy dependence of g-factor. 相似文献
218.
219.
By using microlocal analysis, the propagation of weak singularities in Cauchy problems for quasilinear thermoelastic systems in three space variables are investigated. First, paradifferential operators are employed to decouple the quasilinear thermoelastic systems. Second, by investigating the decoupled hyperbolic-parabolic systems and using the classical bootstrap argument, the property of finite propagation speeds of singularities in Cauchy problems for the quasilinear thermoelastic systems is obtained. Finally, it is shown that the microlocal weak singularities for Cauchy problems of the thermoelastic systems are propagated along the null bicharacteristics of the hyperbolic operators. 相似文献
220.
Jing Lin CHEN Gang Qiang YIN Zhong Ning CHEN* State Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter Fuzhou 《中国化学快报》2003,(5)
Great attention is currently paid to the synthesis of polynuclear transition metal complexes as well as their photochemical, photophysical, and electrochemical properties. The design of multicomponent systems capable of performing useful light- and/or redox-induced function is of special interest1. The oxo-centered carboxylate-bridge trinuclear ruthenium clusters have been investigated extensively during recent decades because they have remarkable electron-transfer properties, intense visibl… 相似文献