全文获取类型
收费全文 | 161102篇 |
免费 | 7984篇 |
国内免费 | 4750篇 |
专业分类
化学 | 93796篇 |
晶体学 | 2519篇 |
力学 | 7314篇 |
综合类 | 290篇 |
数学 | 16489篇 |
物理学 | 53428篇 |
出版年
2022年 | 1441篇 |
2021年 | 1710篇 |
2020年 | 2106篇 |
2019年 | 1975篇 |
2018年 | 1840篇 |
2017年 | 1684篇 |
2016年 | 2981篇 |
2015年 | 2653篇 |
2014年 | 3367篇 |
2013年 | 7351篇 |
2012年 | 6508篇 |
2011年 | 7683篇 |
2010年 | 4993篇 |
2009年 | 4749篇 |
2008年 | 6354篇 |
2007年 | 6155篇 |
2006年 | 6101篇 |
2005年 | 5569篇 |
2004年 | 4740篇 |
2003年 | 4231篇 |
2002年 | 4055篇 |
2001年 | 4344篇 |
2000年 | 3502篇 |
1999年 | 2993篇 |
1998年 | 2592篇 |
1997年 | 2532篇 |
1996年 | 2478篇 |
1995年 | 2379篇 |
1994年 | 2076篇 |
1993年 | 1958篇 |
1992年 | 2169篇 |
1991年 | 2063篇 |
1990年 | 1974篇 |
1989年 | 1915篇 |
1988年 | 1887篇 |
1987年 | 1841篇 |
1986年 | 1735篇 |
1985年 | 2283篇 |
1984年 | 2362篇 |
1983年 | 1958篇 |
1982年 | 2269篇 |
1981年 | 2063篇 |
1980年 | 2089篇 |
1979年 | 2068篇 |
1978年 | 2186篇 |
1977年 | 2092篇 |
1976年 | 2115篇 |
1975年 | 2053篇 |
1974年 | 1895篇 |
1973年 | 2102篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
911.
A survey of ionospheric effects on space-based radar 总被引:2,自引:0,他引:2
912.
913.
914.
We demonstrate a 511 W laser diode pumped composite Nd:YAG ceramic laser. The optical pumping system is consisted of five laser diode stacked arrays arranged in a pentagonal shape around the ceramic rod whose size is φ6.35×144mm. When the pumping power is 1600 W, the cw laser output up to 511 W at 1064nm can be obtained with a linear piano-piano cavity, and the optical-to-optical efficiency is 31.9%. To our knowledge, this is the highest value of laser output by using a newly invented composite Nd:YAG ceramic rod as the gain medium. 相似文献
915.
J. Y. Lee J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto K. Godo H. Makino M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):611-614
Luminescence properties of CdTe/ZnSe fractional monolayer grown by atomic layer epitaxy have been investigated. To investigate the origin of the highly efficient luminescence, various optical spectroscopic methods such as, photoluminescence (PL), temporal/spatial resolved PL, temperature dependence PL, and excitation power dependence PL have been used. It is found that structural inhomogeneities affect dominant influence on the line width and line shape of luminescence. The luminescence intensity greatly enhanced by the localization of exciton at the disorder induced localized states. 相似文献
916.
Unstable, short-lived BiH3 has been synthesized and investigated by rotational spectroscopy in the range 158 (J=1-0) to 1280 GHz (J=8-7). Quadrupole and spin-rotation hyperfine structures (eQq=584.676(96) MHz), and the A1A2 splitting of the K=3 ground state level, have been resolved. By merging the pure rotational data with 1764 ground state combination differences obtained from the analysis of high resolution Fourier transform infrared spectra of the ν1-ν4 bands [J. Mol. Spectrosc. (2004) (in press)] spanning J and K values up to 16 and 14, respectively, with 0?ΔK?9, the ground state rotational and centrifugal distortion constants up to octic and sextic terms for reductions A and B, respectively, have been determined. Of the reductions of the ground state rovibrational Hamiltonian, reduction B including ε rather than h3 as off-diagonal element is clearly favored. An experimental r0 structure of the very-near spherical oblate symmetric top BiH3, r(BiH)=178.82 pm and α(HBiH)=90.320°, has been deduced from the rotational constants B0=2.64160172(18) and C0=2.6010403(31) cm−1. The derived experimental re structure, re(BiH)=177.834(50) pm and αe(HBiH)=90.321(10)°, was determined. This is in excellent agreement with the most recent ab initio structure, re(BiH)=177.84 pm, and αe(HBiH)=90.12°. 相似文献
917.
Rü diger W. Braun Reinhold Meise B. A. Taylor 《Proceedings of the American Mathematical Society》2003,131(8):2423-2433
We give a sufficient condition for a local radial Phragmén-Lindelöf principle on analytic varieties. This condition is expressed in terms of existence of hyperbolic directions.
918.
Scanning probe microscopy characterization of gold-chemisorbed poplar plastocyanin mutants 总被引:1,自引:0,他引:1
L. Andolfi B. Bonanni G. W. Canters M. Ph. Verbeet S. Cannistraro 《Surface science》2003,530(3):181-194
Two poplar plastocyanin mutants adsorbed onto gold electrodes have been characterized at single molecule level by scanning probe microscopy. Immobilization of the two redox metalloprotein mutants on Au(1 1 1) surface was achieved by either a disulphide bridge (PCSS) or a single thiol (PCSH), both the anchoring groups having been introduced by site-directed mutagenesis. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) analysis gives evidence of a stable and robust binding of both mutants to gold. The lateral dimensions, as estimated by STM, and the height above the gold substrate, as evaluated by AFM, of the two mutants well agree with crystallographic sizes. A narrower height distribution is observed for PCSS compared to PCSH, corresponding to a more homogeneous orientation of the former mutant adsorbed onto gold. Major differences between the mutants are observed by electrochemical STM. In particular, the image contrast of adsorbed PCSS is affected by tuning the external electrochemical potential to the redox levels of the mutant, consistent with some involvement of copper active site in the tunneling process. On the contrary, no contrast variation is observed in electrochemical STM of adsorbed PCSH. Moreover, scanning tunneling spectroscopy experiments reveal asymmetric I–V characteristics for single PCSS proteins, reminiscent of a rectifying-like behaviour, whereas an almost symmetric I–V relation is observed for PCSH. 相似文献
919.
920.
Supramolecular side chain liquid crystalline polymers (SCLCPs) based on poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane) (PSIX, X=100, 76, 60, 41 or 23, denoting the mole percentage of 3-carboxypropylmethylsiloxane unit in the polymer) and stilbazole derivatives have been obtained through intermolecular hydrogen bonding (H-bonding) interactions between the carboxylic acid and the pyridyl moieties. The formation of H-bonding and self-assembly results in the formation of new mesogenic units, in which H-bonds function as molecular connectors. FTIR shows the existence of H-bonding in the complexes. The polymeric complexes behave as single component liquid crystalline polymers and exhibit stable and enantiotropic mesophases. The liquid crystalline properties of the supramolecular SCLCPs were studied using differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction, and were found to exhibit smectic A phases with focal-conic textures. The thermal stability of the SCLCP increases on increasing the carboxylic acid content in the polysiloxane and the concentration of the stilbazole derivative in the complex. However, the thermal stability decreases on increasing the chain length of the stilbazole derivative. The crystal phase was not formed even on cooling to the glass transition temperature of the polymeric complex. 相似文献