全文获取类型
收费全文 | 10971篇 |
免费 | 399篇 |
国内免费 | 266篇 |
专业分类
化学 | 4511篇 |
晶体学 | 249篇 |
力学 | 806篇 |
综合类 | 44篇 |
数学 | 1196篇 |
物理学 | 4830篇 |
出版年
2023年 | 72篇 |
2022年 | 134篇 |
2021年 | 154篇 |
2020年 | 136篇 |
2019年 | 184篇 |
2018年 | 207篇 |
2017年 | 146篇 |
2016年 | 240篇 |
2015年 | 188篇 |
2014年 | 300篇 |
2013年 | 499篇 |
2012年 | 713篇 |
2011年 | 812篇 |
2010年 | 628篇 |
2009年 | 636篇 |
2008年 | 646篇 |
2007年 | 574篇 |
2006年 | 596篇 |
2005年 | 467篇 |
2004年 | 434篇 |
2003年 | 351篇 |
2002年 | 292篇 |
2001年 | 528篇 |
2000年 | 405篇 |
1999年 | 288篇 |
1998年 | 231篇 |
1997年 | 200篇 |
1996年 | 198篇 |
1995年 | 162篇 |
1994年 | 135篇 |
1993年 | 99篇 |
1992年 | 106篇 |
1991年 | 113篇 |
1990年 | 116篇 |
1989年 | 84篇 |
1988年 | 62篇 |
1987年 | 43篇 |
1986年 | 51篇 |
1985年 | 47篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 32篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 24篇 |
1978年 | 29篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1975年 | 20篇 |
1974年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
991.
In this paper we consider a class of polynomials P(z) = a0+∑n v=t a v z v, t ≥ 1not vanishing in |z|k, k≥1 and investigate the dependence of max|z|=1|P(Rz)-P(rz)on max|z|=1|P(z)|, where 1 ≤ r R. Our result generalizes and refines some know polynomial inequalities. 相似文献
992.
本文讨论半马氏环境连续时间马氏决策过程中的平均准则.首先讨论了半马氏报酬过程中的逼近问题,进而讨论平均目标函数逼近问题。 相似文献
993.
L.M. Chen W. Tao Z.Y. Zhao Q.J. Li W.P. Ke X.M. Wang X.G. Liu C. Fan X.F. Sun 《Journal of Crystal Growth》2010,312(21):3243-3246
The bulk single crystals of low-dimensional magnet (CH3)2NH2CuCl3 (DMACuCl3 or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 °C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of X-ray diffraction, specific heat and magnetic susceptibility. 相似文献
994.
995.
J. H. Liu L. P. Wang Q. M. Xiao Z. Yao H. Ding 《Plasma Chemistry and Plasma Processing》2010,30(3):349-361
This work reports laser ionization combined with Time-Of-Flight (TOF) mass spectrometry investigation on intermediate species
in the hydrocarbon plasma of atmospheric-pressure fast-flow pulsed dc-discharge. All neutral intermediate species including
transient radicals from benzene/Ar discharge have been characterized by a molecular beam sampling combined with TOF mass spectrometry.
This shows that with a hydrocarbon gas mixture of 0.3% C6H6 in Ar discharge the intermediate species consist of simple radicals (such as C2, C5H5, C7H7) and polycyclic organic molecules (C10H8, C13H10, C14H10). Theoretical studies on total energies and ionization potentials of the intermediate species have been carried out using
the hybrid density functional theory. Effect of the ionization potential on mass spectral intensity has been discussed. Based
on the observed data, the possible major neutral reaction channels of the plasma chemistry have been discussed. The developed
experimental method has implications in volatile organic compounds removing and impurities diagnosis in Tokamak edge-plasma. 相似文献
996.
In this paper, current-driven state-bistability and power-bistability in a distributed feedback (DFB) semiconductor laser
(LD) subject to external optical injection have been investigated experimentally. The results show that, by sweeping the bias
current of slave LD along different routes nearby the threshold, both the power-bistability and the state-bistability between
locking and bimodal regime can be observed under the suitable injection power, but these bistable phenomena will disappear
under much large injection power. Additionally, the dependence of the width of the state-bistablility loop on the injection
power has been discussed. 相似文献
997.
998.
Exact closed-form solutions are derived that completely characterize the effective behavior of a composite material made of elastic-perfectly plastic parallel plane layers perfectly bonded together. The derivation is framed within a rigorous theory of homogenization for elastoplastic composites, and based on the fundamental fact that the in-plane part of the strain tensor and the out-of-plane part of the stress tensor are uniform throughout the composite provided no free-edge effects occur. The obtained expressions are coordinate-free and valid in the general anisotropic case. As an example, a layered composite material with isotropic constituents is examined in detail. 相似文献
999.
1000.
This paper deals with the existence of positive solution to a strongly coupled system with homogeneous Dirichlet boundary
conditions describing a Schoener’s competitive interaction of two species. Making use of the Schauder fixed point theorem,
a sufficient condition is given for the system to have a coexistence. And true solutions are constructed based on monotone
iterative method. Our results show that this model possesses at least one coexistence state if cross-diffusions and intra-specific
competitions are weak. 相似文献