全文获取类型
收费全文 | 53321篇 |
免费 | 13522篇 |
国内免费 | 3076篇 |
专业分类
化学 | 46847篇 |
晶体学 | 469篇 |
力学 | 1175篇 |
综合类 | 94篇 |
数学 | 3343篇 |
物理学 | 6116篇 |
无线电 | 11875篇 |
出版年
2024年 | 51篇 |
2023年 | 315篇 |
2022年 | 433篇 |
2021年 | 701篇 |
2020年 | 2162篇 |
2019年 | 3523篇 |
2018年 | 1803篇 |
2017年 | 1400篇 |
2016年 | 4409篇 |
2015年 | 4603篇 |
2014年 | 4686篇 |
2013年 | 5389篇 |
2012年 | 4390篇 |
2011年 | 3575篇 |
2010年 | 3942篇 |
2009年 | 3952篇 |
2008年 | 3485篇 |
2007年 | 2731篇 |
2006年 | 2322篇 |
2005年 | 2444篇 |
2004年 | 2122篇 |
2003年 | 1955篇 |
2002年 | 2809篇 |
2001年 | 2038篇 |
2000年 | 1742篇 |
1999年 | 716篇 |
1998年 | 381篇 |
1997年 | 262篇 |
1996年 | 229篇 |
1995年 | 211篇 |
1994年 | 167篇 |
1993年 | 156篇 |
1992年 | 111篇 |
1991年 | 126篇 |
1990年 | 76篇 |
1989年 | 69篇 |
1988年 | 60篇 |
1987年 | 40篇 |
1986年 | 28篇 |
1985年 | 32篇 |
1984年 | 38篇 |
1983年 | 41篇 |
1982年 | 26篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
溃坝问题的间断有限元方法 总被引:2,自引:0,他引:2
本文研究90年代初提出的Runge-Kutta间断Galerkin有限元方法,给出该方法的精度分析,通过经典算例验证该方法处理间断问题、捕捉锐利波形的能力,并将其推广到求解浅水问题.针对坝底无摩擦,无坡度的理想情形进行讨论,给出方溃坝和圆溃坝问题的数值模拟结果. 相似文献
173.
The structure of the title adduct comprises a phenanthroline derivative 2-phenyl-imidazo[4,5-f]1,10-phenanthroline and a methanol.The composition of the crystalline adduct was characterized as C19H12N4.CH3OH.It belongs to orthorhombic system,space group Pna21 with a=1.3693(4)nm,b=2.2988(7)nm,c=0.51338(15)nm,V=1.6160(8)nm^3.Z=4,and final R1=0.0423.wR2=0.1012 .Crystal structure shows that all the 19 carbon atoms and 4 nitrogen atoms are coplanar.The bond length data indicated that a very extensive conjugation system was formed.This conjugation makes the compound being a potentially excellent energy transformer used for luminescent materials. 相似文献
174.
Formation of p-type ZnO film on InP substrate by phosphor doping 总被引:3,自引:0,他引:3
Kyu-Hyun Bang Deuk-Kyu Hwang Min-Chul Park Young-Don Ko Ilgu Yun Jae-Min Myoung 《Applied Surface Science》2003,210(3-4):177-182
ZnO thin film was initially deposited on InP substrate by radio frequency (rf) magnetron sputtering and the diffusion process was performed using the closed ampoule technique where Zn3P2 was used as the dopant source. To verify the junction formation of ZnO thin films, the electrical properties were measured, and the effects of Zn3P2 diffusion on ZnO thin films were investigated. It is observed that the electrical property of the film is changed from n-type to p-type by dopant diffusion effect. Based on the results, it is confirmed that ZnO thin films can be a potential candidate for ultraviolet (UV) optical devices. 相似文献
175.
Effects of hysteretic and aerodynamic damping on supersonic panel flutter of composite plates 总被引:1,自引:0,他引:1
The governing equation for the finite element analysis of the panel flutter of composite plates including structural damping is derived from Hamilton's principle. The first order shear deformable plate theory has been applied to structural modelling so as to obtain the finite element eigenvalue equation. The unsteady aerodynamic load in a supersonic flow is computed by using the linear piston theory. The critical dynamic pressures for composite plates have been calculated to investigate the effects of structural damping on flutter boundaries. The effects are dependent on fiber orientation because flutter mode can be weak or strong in the fiber orientation of composite plates. Structural damping plays an important role in flutter stability with low aerodynamic damping but would not affect the flutter boundary with high aerodynamic damping. 相似文献
176.
S. Danto P. Houizot C. Boussard‐Pledel X.‐H. Zhang F. Smektala J. Lucas 《Advanced functional materials》2006,16(14):1847-1852
Conditions of formation of bulk tellurium chalcogenide glasses, containing 70–80 at % Te associated to Ga and Ge are described. The characteristic temperatures are measured: the glass‐transition temperature, Tg, is situated in the range 140–185 °C and the difference Tx – Tg, where Tx is the onset crystallization temperature, is in the range 76–113 °C. Moreover, the optical transmission window is exceptional, ranging from 1.99 μm in the bandgap up to 28 μm in the phonon region. Developed within the framework of requirements for the Darwin mission (a search for and study of extrasolar planets), feasibility of infrared optical fibers formed from these glasses is studied. Drawing experiments are conducted with the glass Ga2‐Ge3Te15, which possesses the maximum Tx – Tg, and a first optical fiber is presented. 相似文献
177.
178.
本文介绍一种将自适应算法、遗传算法和列表调度算法结合起来应用于软硬件划分问题的算法COPARTART,并提出了一种基于约束条件的开销系数自适应调整方法,该方法所获得的划分结果能够良好体现设计目标。 相似文献
179.
Li-Ching Hong Sheng-Jye Hwang 《Components and Packaging Technologies, IEEE Transactions on》2004,27(2):291-295
There were many studies about the prediction of warpage due to thermal mismatch , . However, cure induced warpage is usually ignored and the results can be inaccurate. To minimize this problem, a thorough understanding of epoxy molding compound (EMC) with pressure-volume-temperature-cure (P-V-T-C) relation is necessary. This paper used the P-V-T-C relation of an encapsulation material to formulate the stress-strain relationship. With the help of finite element method (FEM) and mold flow analysis, warpage predictions combined with P-V-T-C relation were performed and the results show that this approach is practical. For a given P-V-T-C relation, the shrinkage direction is pointing toward the gate and maximum warpage usually occurs at the boundary of an integrated circuit (IC) package. Variation of specific volume difference along the flow direction is larger than that perpendicular to the flow direction. When temperature difference is small in thickness direction, specific volume difference in thickness direction varies only slightly. 相似文献
180.