全文获取类型
收费全文 | 44331篇 |
免费 | 5031篇 |
国内免费 | 3019篇 |
专业分类
化学 | 5289篇 |
晶体学 | 298篇 |
力学 | 3906篇 |
综合类 | 296篇 |
数学 | 5656篇 |
物理学 | 10770篇 |
综合类 | 26166篇 |
出版年
2024年 | 192篇 |
2023年 | 506篇 |
2022年 | 910篇 |
2021年 | 1135篇 |
2020年 | 1142篇 |
2019年 | 1054篇 |
2018年 | 989篇 |
2017年 | 1345篇 |
2016年 | 1525篇 |
2015年 | 1567篇 |
2014年 | 2371篇 |
2013年 | 2907篇 |
2012年 | 2769篇 |
2011年 | 2943篇 |
2010年 | 2293篇 |
2009年 | 2537篇 |
2008年 | 2633篇 |
2007年 | 3073篇 |
2006年 | 2642篇 |
2005年 | 2372篇 |
2004年 | 2028篇 |
2003年 | 1931篇 |
2002年 | 1687篇 |
2001年 | 1505篇 |
2000年 | 1335篇 |
1999年 | 1119篇 |
1998年 | 926篇 |
1997年 | 842篇 |
1996年 | 677篇 |
1995年 | 540篇 |
1994年 | 512篇 |
1993年 | 393篇 |
1992年 | 342篇 |
1991年 | 313篇 |
1990年 | 276篇 |
1989年 | 227篇 |
1988年 | 199篇 |
1987年 | 163篇 |
1986年 | 107篇 |
1985年 | 94篇 |
1984年 | 45篇 |
1983年 | 24篇 |
1982年 | 40篇 |
1981年 | 26篇 |
1980年 | 14篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 15篇 |
1955年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
分析了液压支架的压力特性并提出对压力变送器的技术要求,阐述了压力传感器的选择和外围电路的设计,对压力变送器的信号调理电路进行了仿真分析。 相似文献
72.
Al.Th. Kermanidis D.G. Stamatelos G.N. Labeas Sp.G. Pantelakis 《Theoretical and Applied Fracture Mechanics》2006,45(2):148-158
The synergetic effect of corrosion and corrosion induced hydrogen embrittlement damage processes which occur at local scale has been found to result in a dramatic macroscopic tensile ductility loss of the 2024 aluminum alloy. In the present work, the tensile behaviour of corroded 2024 T351 specimens has been estimated on the basis of FE analysis by taking into account the local material properties in the damaged areas. A parametric study is involved to account for the effect of thickness in the results. Calculated tensile properties obtained with the analysis agree well with experimental data. 相似文献
73.
FJZ-250型高速分幅相机时间测量不确定度分析 总被引:2,自引:1,他引:1
FJZ-250型高速转镜分幅相机因转镜速度的不可重复性,光机结构的构造原理和控制系统各路高压触发时间的漂移,导致了时间测量的不确定度。为此,须对相机测量数据进行校正。阐述了校正方法、提供了逐幅校正位置误差的修正系数。若以预置转速对应的名义周期值去处理测量结果,则相机的时间测量合成小确定度将达1%,对名义周期值和名义幅间间隔时间值进行修正后,则可降至0.3%。 相似文献
74.
Jeong Ryeol Choi 《International Journal of Theoretical Physics》2004,43(4):947-958
We derived the WKB wave function for the general time-dependent quadratic Hamiltonian system using a unitary transformation method. We applied our research to sinusodially drived Caldirola–Kanai oscillator and confirmed that the time evolution of our approximated WKB wave function is similar to that of the exact one. This wave function can be used to analyze the interference between the probability amplitudes contributed by the area of overlap in phase space of quantum states. 相似文献
75.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
76.
《科学通报(英文版)》2008,(6)
High precision elevation measurements using DGPS were carried out along three representative tran- sects for the "Great Ear" area, a dry salt lake within the Lop Nor basin. Results indicate that the Lop Nor basin is only 5.2 m deep and its lowest point occurs at the center of the "Great Ear". In addition, the basin is asymmetric - steeper in the southwest (0.19‰) and gentler in the northeast (0.09‰). Points along the same "Great Ear" ring were found to have an identical elevation value, but different when from different ones (lower towards the center). The spacing of the "Great Ear" rings was found to be closely related with the surface steepness. The closer the "Great Ear" rings are spaced, the steeper the ground surface, and vice versa. These findings support the argument that the "Great Ear" rings are the former shoreline trails left behind by Lop Nor water during the last few episodes of recession towards its total dry up. A comprehensive analysis of the high precision elevation data, historical accounts, aerial and satellite photographs and imagery, and official topographic maps of the study area suggests that the "Great Ear" area in the Lop Nor basin was incorrectly mapped as being covered by a great body of water on the 1963 topographic maps. A re-interpretation of the 1958 aerial photographs and newer remote sensing imagery indicated that the "Great Ear" ring structure was already in place in 1958 and it continued to appear on the subsequent remote sensing data without any major changes. It is estimated that lake water in the "Great Ear" area of the Lop Nor basin disappeared between the late 1930s and early 1940s. 相似文献
77.
基于MATLAB的控制系统CAI设计 总被引:1,自引:0,他引:1
基于MATLAB开发平台,利用其可视化编程能力的GUI,对控制系统进行分析、设计与仿真,开发了控制系统CAI应用软件,它具有较强的教学、实验、工程应用价值。 相似文献
78.
MATLAB/SIMULINK在电力系统仿真中的应用 总被引:2,自引:0,他引:2
介绍了Matlab/Simulink仿真工具在电力系统仿真中的应用方法. 相似文献
79.
Nanograins are characterized by a typical grain size from lto 100 nm.Mclecular dynamics aimubations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm.We study the influence of grain size on structure and diffusion properties of the nanograins.The results reveal that as the grain size is reduced,the fraction of grain surface increases significantly,and the surface width is approximately constant;the diffusicn coefficlent is increased sharply,and the relation of the diffusion coefficient and the grain size is close to exponential relation below 10nm. 相似文献
80.
We present all-atom molecular dynamics simulations ofn-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the
presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid
adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively
compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate
lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone
planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules
are observed to attain the perpendicular orientation at monolayer coverage.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献