全文获取类型
收费全文 | 105490篇 |
免费 | 18003篇 |
国内免费 | 10098篇 |
专业分类
化学 | 71266篇 |
晶体学 | 1218篇 |
力学 | 6921篇 |
综合类 | 534篇 |
数学 | 11912篇 |
物理学 | 41740篇 |
出版年
2024年 | 369篇 |
2023年 | 2134篇 |
2022年 | 3644篇 |
2021年 | 3946篇 |
2020年 | 4248篇 |
2019年 | 4138篇 |
2018年 | 3551篇 |
2017年 | 3287篇 |
2016年 | 5185篇 |
2015年 | 4946篇 |
2014年 | 6020篇 |
2013年 | 7778篇 |
2012年 | 9426篇 |
2011年 | 9754篇 |
2010年 | 6440篇 |
2009年 | 6156篇 |
2008年 | 6532篇 |
2007年 | 5996篇 |
2006年 | 5478篇 |
2005年 | 4592篇 |
2004年 | 3399篇 |
2003年 | 2667篇 |
2002年 | 2414篇 |
2001年 | 1979篇 |
2000年 | 1762篇 |
1999年 | 2071篇 |
1998年 | 1846篇 |
1997年 | 1720篇 |
1996年 | 1888篇 |
1995年 | 1502篇 |
1994年 | 1460篇 |
1993年 | 1165篇 |
1992年 | 1069篇 |
1991年 | 984篇 |
1990年 | 791篇 |
1989年 | 563篇 |
1988年 | 464篇 |
1987年 | 382篇 |
1986年 | 374篇 |
1985年 | 318篇 |
1984年 | 241篇 |
1983年 | 154篇 |
1982年 | 142篇 |
1981年 | 106篇 |
1980年 | 76篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1976年 | 36篇 |
1975年 | 33篇 |
1974年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
172.
W.F. Wang 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,86(4):437-444
It is shown that by including the second term of Magnus expansion, improved convergence can be achieved for the non-perturbative pressure broadening formalism proposed by Neilson and Gordon (J. Chem. Phys. 58 (1973) 4131). The present method was applied to the line broadening calculations of CO in a bath of Ar. 相似文献
173.
174.
A. Y. Miguelote N. A. Tomimura Anzhong Wang 《General Relativity and Gravitation》2004,36(8):1883-1918
Perfect fluid with kinematic self-similarity is studied in 2+1 dimensional spacetimes with circular symmetry, and various exact solutions to the Einstein field equations are given. These include all the solutions of dust and stiff perfect fluid with self-similarity of the first kind, and all the solutions of perfect fluid with a linear equation of state and self-similarity of the zeroth and second kinds. It is found that some of these solutions represent gravitational collapse, and the final state of the collapse can be either a black hole or a null singularity. It is also shown that one solution can have two different kinds of kinematic self-similarity. 相似文献
175.
F. R. Ling B. Wang T. Geng S. Q. Fang W. Yuan D. D. Teng C. X. Guan 《Optics & Laser Technology》2004,36(7):541-544
In this paper experimental studies of nonvolatile photorefractive holographic recording in Ce:Cu:LiNbO3 crystals doped with Sc(0,1,2,3 mol%) were carried out. The Sc:Ce:Cu:LiNbO3 crystals were grown by the Czochralski method and oxidized in Nb2O5 powders. The nonvolatile holographic recording in Sc:Ce:Cu:LiNbO3 crystals was realized by the two-photon fixed method. We found that the recording time of Sc:Ce:Cu:LiNbO3 crystal became shorter with the increase of Sc doping concentration, especially doping with Sc(3 mol%), which exceeds the so-called threshold, and there was little loss of nonvolatile diffraction efficiencies between Sc(3 mol%):Ce:Cu:LiNbO3 and Ce:Cu:LiNbO3 crystals. 相似文献
176.
Qinghai Wang 《Czechoslovak Journal of Physics》2004,54(1):143-146
This paper investigates finite-dimensional PT-symmetric Hamiltonians. It is shown here that there are two ways to extend real symmetric Hamiltonians into the complex domain: (i) The usual approach is to generalize such Hamiltonians to include complex Hermitian Hamiltonians. (ii) Alternatively, one can generalize real symmetric Hamiltonians to include complex PT-symmetric Hamiltonians. In the first approach the spectrum remains real, while in the second approach the spectrum remains real if the PT symmetry is not broken. Both generalizations give a consistent theory of quantum mechanics, but if D>2, a D-dimensional Hermitian matrix Hamiltonian has more arbitrary parameters than a D-dimensional PT-symmetric matrix Hamiltonian. 相似文献
177.
178.
用溶胶 凝胶法以磷钼酸 (MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2 催化剂 .使用ICP、XRD、TG DTA、IR、TPD MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能 .杂多钼酸盐与TiO2 通过O2 -在TiO2 表面发生了键合 .在 6 2 3K下 ,杂多阴离子仍保持原有的Keggin结构 .CO2 在Lewis酸位Ni(Ⅱ )和Lewis碱位Ni-O -Mo的桥氧协同作用下生成CO2 卧式吸附态Ni(Ⅱ )←O - (CO)← (O--Ni) .丙烯有多种吸附态在催化剂上吸附 .在 5 6 3K、1MPa和空速 15 0 0h-1的反应条件下 ,丙烯的摩尔转化率为 3.2 % ,产物MAA选择性为 95 % . 相似文献
179.
Qingfa Wang Li Wang Yaquan Wang Fei He Zhenhua Li Zhentao Mi 《Reaction Kinetics and Catalysis Letters》2004,81(2):297-304
Deactivated palladium catalysts in the hydrogenation of anthraquinione were regenerated with ethanol, nitric acid, hydrogen
peroxide, boiling water and steam, respectively. The deactivated and regenerated catalysts were characterized by XPS, ICP,
TG, FTIR, TPD, XRD, etc., and studied in the hydrogenation of anthraquinone. The results showed that the main cause of catalyst deactivation is the
coverage of the active component by deposits. The treatments by hydrogen peroxide and boiling water can effectively regenerate
the deactivated catalysts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
180.
多目标半定规划的互补弱鞍点和G-鞍点最优性条件 总被引:1,自引:0,他引:1
对于含矩阵函数半定约束和多个目标函数的多目标半定规划问题,给出Lagrange函数在弱有效意义下的互补弱鞍点和Geofrrion恰当有效意义下的G-鞍点的定义及其等价定义.然后,在较弱的凸性条件下,利用含矩阵和向量约束的择一性定理,建立多目标半定规划的互补弱鞍点和G-鞍点充分必要条件. 相似文献