全文获取类型
收费全文 | 21807篇 |
免费 | 4115篇 |
国内免费 | 2705篇 |
专业分类
化学 | 13433篇 |
晶体学 | 205篇 |
力学 | 3025篇 |
综合类 | 188篇 |
数学 | 1563篇 |
物理学 | 10213篇 |
出版年
2024年 | 33篇 |
2023年 | 160篇 |
2022年 | 517篇 |
2021年 | 590篇 |
2020年 | 723篇 |
2019年 | 620篇 |
2018年 | 588篇 |
2017年 | 785篇 |
2016年 | 933篇 |
2015年 | 1020篇 |
2014年 | 1392篇 |
2013年 | 1836篇 |
2012年 | 1499篇 |
2011年 | 1636篇 |
2010年 | 1368篇 |
2009年 | 1501篇 |
2008年 | 1580篇 |
2007年 | 1449篇 |
2006年 | 1415篇 |
2005年 | 1170篇 |
2004年 | 1127篇 |
2003年 | 972篇 |
2002年 | 723篇 |
2001年 | 648篇 |
2000年 | 575篇 |
1999年 | 438篇 |
1998年 | 485篇 |
1997年 | 400篇 |
1996年 | 353篇 |
1995年 | 304篇 |
1994年 | 286篇 |
1993年 | 242篇 |
1992年 | 245篇 |
1991年 | 180篇 |
1990年 | 166篇 |
1989年 | 111篇 |
1988年 | 124篇 |
1987年 | 85篇 |
1986年 | 60篇 |
1985年 | 51篇 |
1984年 | 51篇 |
1983年 | 21篇 |
1982年 | 39篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 9篇 |
1973年 | 15篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Homohelicity induction of a series of propylene-linked zinc bilinone (ZnBL; linear tetrapyrrople-zinc(II) complex) dimers upon complexation with chiral amine and α-amino esters was investigated. Introduction of substituents such as dimethyl and diisobutyl to the central carbon of the propylene spacer gave rise to stabilization of the homohelical (PP and MM) conformers rather than the heterohelical (PM) conformer. As bulkiness of the substituent increased, stability of the homohelical conformers was raised. The preorganization of the homohelical structures led to significantly amplified homohelicity induction upon complexation with chiral amine and α-amino esters. 相似文献
33.
Zhao Hanzhong 《Acta Mechanica Solida Sinica》2002,15(2):156-162
A finite difference/boundary integral procedure to determine the acoustic reflected pressure from a fluid-loaded bi-laminated
plate is described. The bi-laminate is composed of a piezoelectric layer and an elastic layer in contact with the fluid, and
is held by an acoustically hard baffle. In the numerical model, the fluid pressure at fluid/solid interface is replaced by
a continuum of point sources weighted by the normal acceleration of the elastic plate, and the governing equation system is
solved in the solid domain. With the normal acceleration found, the reflected pressure in the fluid is determined by an integral
expression involving the Green's function. It is demonstrated that an appropriate applied voltage potential across the piezoelectric
layer has the effect of cancelling either the reflected or scattered pressure of the plate at any chosen field points in the
fluid.
Project supported by the National Natural Science Foundation of China (No. 10172039). 相似文献
34.
多普勒效应测试仪的改进 总被引:3,自引:0,他引:3
为了解决电磁波多普勒效应在实验室演示的困难,采用单片机和一系列大规模集成电路设计了一种演示电磁波多普勒效应的测试仪器,分析了电磁波的多普勒效应原理,给出了该仪器的组成结构,介绍了该仪器铁特点。 相似文献
35.
36.
Stress-Strain State in the Zone of Load Transfer in a Composite Specimen under Uniaxial Tension 总被引:2,自引:2,他引:0
Kulakov V. L. Tarnopol'skii Yu. M. Arnautov A. K. Rytter J. 《Mechanics of Composite Materials》2004,40(2):91-100
The stress-strain state in the zone of load transfer in a uniaxially stretched specimen made of a unidirectional epoxy carbon-fiber-reinforced plastic (CFRP) is investigated. A parametric analysis of the influence of geometric and mechanical characteristics of the specimen on its stress-strain state is performed by means of finite-element modeling. The parameters allowing us to significantly reduce the dangerous concentration of transverse and tangential stresses are revealed. The mechanical tensile characteristics of a high-strength pultruded unidirectional CFRP are determined experimentally, and the size effect of its strength is estimated. 相似文献
37.
38.
乐毅 《宁波大学学报(理工版)》2004,17(4):437-440
从正交各向异性三维弹性动力学的控制方程出发,在求得四边简支矩形板自由振动频率和位移振型的基础上,构造了受迫振动的位移函数;利用自由振动位移振型的正交性,将控制方程的空间变量和时间变量分离,得到了广义质量、广义力和频率表示的关于时间的2阶常微分方程,从而得到了正交各向异性弹性矩形板在受迫振动下的位移场和应力场.给出了本文方法与薄板理论的算例. 相似文献
39.
Chen Xiaoyang 《中国科学G辑(英文版)》2004,47(Z1)
The occurrence of time-dependent cavitation and tensile stress in an oscillatory oil squeeze film were investigated experimentally. The test apparatus was a simple thrust bearing consisting of two parallel circular plates separated by a thin viscous oil film. During the test, one plate was at rest while the other (transparent) oscillated in a direction normal to its surface. This test configuration was chosen to avoid the rotational motion and complicated geometry of a squeeze film journal bearing. The frequency of oscillation was in the range of 5 to 50 Hz and was controlled by an electro-magnetic exciter. The process of cavity formation and its subsequent development was recorded by a high-speed video camera. Concomitant pressure in the oil film was measured both within and without the cavitation region. It was found that both tensile stress and cavities existed in a squeeze film under certain working conditions. 相似文献
40.