全文获取类型
收费全文 | 85701篇 |
免费 | 25413篇 |
国内免费 | 22110篇 |
专业分类
化学 | 54999篇 |
晶体学 | 1647篇 |
力学 | 5786篇 |
综合类 | 577篇 |
数学 | 11462篇 |
物理学 | 58753篇 |
出版年
2024年 | 471篇 |
2023年 | 765篇 |
2022年 | 1110篇 |
2021年 | 994篇 |
2020年 | 1198篇 |
2019年 | 1728篇 |
2018年 | 1667篇 |
2017年 | 2582篇 |
2016年 | 2408篇 |
2015年 | 2840篇 |
2014年 | 2850篇 |
2013年 | 4793篇 |
2012年 | 5132篇 |
2011年 | 6837篇 |
2010年 | 10332篇 |
2009年 | 10616篇 |
2008年 | 4619篇 |
2007年 | 4002篇 |
2006年 | 3677篇 |
2005年 | 3841篇 |
2004年 | 4492篇 |
2003年 | 3528篇 |
2002年 | 3344篇 |
2001年 | 3628篇 |
2000年 | 2957篇 |
1999年 | 2836篇 |
1998年 | 2299篇 |
1997年 | 2044篇 |
1996年 | 2364篇 |
1995年 | 2798篇 |
1994年 | 2870篇 |
1993年 | 2945篇 |
1992年 | 2518篇 |
1991年 | 2140篇 |
1990年 | 1814篇 |
1989年 | 1898篇 |
1988年 | 1886篇 |
1987年 | 1171篇 |
1986年 | 1211篇 |
1985年 | 861篇 |
1984年 | 980篇 |
1982年 | 901篇 |
1981年 | 743篇 |
1980年 | 776篇 |
1979年 | 537篇 |
1978年 | 535篇 |
1977年 | 633篇 |
1976年 | 1044篇 |
1973年 | 439篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 210 毫秒
991.
P. Dawson J. W. Haas III K. B. Alexander J. Thompson T. L. Ferrell 《Surface science》1991,250(1-3):L383-L388
The intensity of surface enhanced Raman scattering from benzoic acid derivatives on mildly roughened, thermally evaporated Ag films shows a remarkably strong dependence on metal grain size. Large grained (slowly deposited) films give a superior response, by up to a factor of 10, to small grained (quickly deposited) films, with films of intermediate grain size yielding intermediate results. The optical field amplification underlying the enhancement mechanism is due to the excitation of surface plasmon polaritons (SPPs). Since surface roughness characteristics, as determined by STM, remain relatively constant as a function of deposition rate, it is argued that the contrast in Raman scattering is due to differences in elastic grain boundary scattering of SPPs (leading to different degrees of internal SPP damping), rather than differences in the interaction of SPPs with surface inhomogeneities. 相似文献
992.
993.
M. Aglietta B. Alessandro P. Antonioli F. Arneodo L. Bergamasco A. Campos Fauth C. Castagnoli A. Castellina C. Cattadori A. Chiavassa et al. 《Il Nuovo Cimento C》1992,15(4):441-446
Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower
array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement
the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y−1 (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E
0
)≈E
0
−2.5
, the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10−5erg cm−2. 相似文献
994.
995.
A numerical model is presented to calculate V(z) and V(x, z) curves for a line focus acoustic microscope and a specimen containing a subsurface crack. In this model, a Gaussian beam which is tracked through the lens into the coupling fluid and into the specimen, interacts with the crack. The numerical approach is based on the solution of singular integral equations by the boundary element method. The system of singular integral equations follows from the conditions at the interface of the coupling fluid and the specimen and on the faces of the crack. An electromechanical reciprocity relation is used to express the voltage at the terminals of the microscope's transducer in terms of the calculated incident and back-scattered fields. V(z) and V(x, z) curves are presented for various locations and orientations of the crack. The characteristic features of the V(z) and particularly the V(x, z) curves, as they relate to crack configuration, are discussed in some detail. 相似文献
996.
Summary A hypermedia environment was designed to set up a collection of reference data, reference spectra and computational tools. The system may serve as an aid for the combined interpretation of molecular spectra. This paper describes the context dependent presentation of the pieces of information. 相似文献
997.
998.
Kentaro Suzuya Tomoaki Kamiyama Takemi Yamamura Kiyohito Okamura Kenji Suzuki 《Journal of Non》1992,150(1-3):167-171
A small-angle X-ray scattering (SAXS) study was performed to reveal the nanometer scale hybrid structure of Si---Ti---C---O fibers prepared by the pyrolysis of polytitanocarbosilane. The SAXS profile for Si---Ti---C---O fibers is attributed to two different types of scattering entities: an anisotropic contribution from long filaments with diameters hundreds to thousands of Ångströms and an isotropic contribution from β-SiC fine clusters of about a nanometer in diameter. A drastic degradation in the tensile strength of the fibers is correlated to the characteristic variations in their long-and medium-range structure. 相似文献
999.
Joseph B. Schlenoff W. Jack Rink Lawrence Seger 《Physica C: Superconductivity and its Applications》1991,180(5-6):387-393
Single crystals and polycrystalline pellets of the high-temperature cuprate superconductor Bi2Sr2Ca1Cu2O8 were doped at room temperature by electrochemical reduction at > 95% Coulombic efficiency using lithium dopant ions in propylene carbonate electrolyte. Cyclic voltammetry and potential step measurements on single crystals suggest an unusual reduction mechanism, with a diffusion coefficient for Li+ in the c-axis direction of bulk superconductor of ca. 3 × 10−11 cm2s−1. Sintered pellets of polycrystalline powder could be doped more rapidly, with an apparent diffusion coefficient of 7 × 10−8 cm2s−1. X-ray susceptibility analysis show extensive disordering occurs on heavy Li doping, with a first-order transition from a crystalline/superconducting to an amorphous/non-superconducting phase. Single, crystals of Bi2Sr2Ca1Cu2O8 exhibited a color change on reduction from metallic gray to golden bronze. The reduced material was highly air-sensitive, forming a hydroxide surface film on exposure to ambient atmosphere. 相似文献
1000.
I. I. Antakov M. A. Moiseev E. V. Sokolov E. V. Zasypkin 《International Journal of Infrared and Millimeter Waves》1994,15(5):873-887
Using self-consistent field theory, the interaction of electron flow with HF fields in a gyroklystron has been analized. Optimal parameters of its output cavity corresponding to the maximum efficiency have been found. Experimental study of dependence of the efficiency on Q-factor and length of the output cavity has been carried out. The results of simulation are in good qualitative agreement with experimental data. 相似文献