全文获取类型
收费全文 | 63442篇 |
免费 | 3075篇 |
国内免费 | 825篇 |
专业分类
化学 | 40312篇 |
晶体学 | 411篇 |
力学 | 1348篇 |
综合类 | 50篇 |
数学 | 11205篇 |
物理学 | 14016篇 |
出版年
2023年 | 552篇 |
2022年 | 758篇 |
2021年 | 988篇 |
2020年 | 1156篇 |
2019年 | 1134篇 |
2018年 | 1312篇 |
2017年 | 1203篇 |
2016年 | 2353篇 |
2015年 | 1972篇 |
2014年 | 2103篇 |
2013年 | 4127篇 |
2012年 | 4162篇 |
2011年 | 4127篇 |
2010年 | 2680篇 |
2009年 | 2427篇 |
2008年 | 3449篇 |
2007年 | 3260篇 |
2006年 | 2904篇 |
2005年 | 2847篇 |
2004年 | 2340篇 |
2003年 | 1894篇 |
2002年 | 1732篇 |
2001年 | 1287篇 |
2000年 | 1277篇 |
1999年 | 940篇 |
1998年 | 733篇 |
1997年 | 633篇 |
1996年 | 793篇 |
1995年 | 621篇 |
1994年 | 668篇 |
1993年 | 591篇 |
1992年 | 619篇 |
1991年 | 513篇 |
1990年 | 547篇 |
1989年 | 435篇 |
1988年 | 445篇 |
1987年 | 404篇 |
1986年 | 392篇 |
1985年 | 517篇 |
1984年 | 474篇 |
1983年 | 366篇 |
1982年 | 388篇 |
1981年 | 379篇 |
1980年 | 308篇 |
1979年 | 302篇 |
1978年 | 298篇 |
1977年 | 283篇 |
1976年 | 295篇 |
1974年 | 267篇 |
1973年 | 270篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased. 相似文献
32.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献
33.
The capability of gated saturable absorbers for single-pulse selection is studied theoretically using the classical space-time-dependent rate-equation model. The dynamics of operation is followed experimentally by the well-known pump—probe technique. Comparing the theoretical and experimental results, it is found that gated saturable absorbers can efficiently be used for pulse forming and pulse selection of pulses longer than picosecond. 相似文献
34.
35.
36.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献
37.
38.
Lubomír Kubáček 《Applications of Mathematics》2006,51(6):565-582
Some remarks to problems of point and interval estimation, testing and problems of outliers are presented in the case of multivariate
regression model.
This work was supported by the Council of Czech Government J14/98:153100011. 相似文献
39.
We present the design and study of waveguide structures based on porous silicon where the light confinement is not due to the usual total reflection effect but to the use of photonic crystals (PCs) as confining walls. These PC are omnidirectional mirrors (OMs), consisting of the periodic repetition of two porous silicon layers with different refractive indices and thicknesses. They reflect the radiation for all angles of incidence within a frequency range called the omnidirectional band gap (OBG). We have followed the PC formalism to investigate the properties of the OM as a multimode waveguide: the number of modes within the band gap, their field spatial distribution and their confinement as a function of the frequency and the core thickness. 相似文献
40.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献