全文获取类型
收费全文 | 26211篇 |
免费 | 4493篇 |
国内免费 | 3110篇 |
专业分类
化学 | 11543篇 |
晶体学 | 238篇 |
力学 | 2439篇 |
综合类 | 232篇 |
数学 | 4873篇 |
物理学 | 14489篇 |
出版年
2024年 | 41篇 |
2023年 | 243篇 |
2022年 | 758篇 |
2021年 | 797篇 |
2020年 | 910篇 |
2019年 | 810篇 |
2018年 | 794篇 |
2017年 | 949篇 |
2016年 | 1129篇 |
2015年 | 871篇 |
2014年 | 1386篇 |
2013年 | 2378篇 |
2012年 | 1603篇 |
2011年 | 1765篇 |
2010年 | 1449篇 |
2009年 | 1636篇 |
2008年 | 1687篇 |
2007年 | 1653篇 |
2006年 | 1583篇 |
2005年 | 1295篇 |
2004年 | 1180篇 |
2003年 | 1052篇 |
2002年 | 966篇 |
2001年 | 879篇 |
2000年 | 829篇 |
1999年 | 593篇 |
1998年 | 634篇 |
1997年 | 505篇 |
1996年 | 446篇 |
1995年 | 404篇 |
1994年 | 362篇 |
1993年 | 336篇 |
1992年 | 295篇 |
1991年 | 226篇 |
1990年 | 195篇 |
1989年 | 156篇 |
1988年 | 166篇 |
1987年 | 118篇 |
1986年 | 101篇 |
1985年 | 114篇 |
1984年 | 113篇 |
1983年 | 46篇 |
1982年 | 73篇 |
1981年 | 48篇 |
1980年 | 37篇 |
1979年 | 33篇 |
1978年 | 39篇 |
1977年 | 33篇 |
1976年 | 25篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
111.
P. Paasche T. Valenzuela D. Biswas C. Angelescu G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):295-300
We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation
is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the
number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation
of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass
resonance suggests that it is a parametric instability of a Mathieu type equation of motion.
Received 11 July 2001 and Received in final form 12 November 2001 相似文献
112.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
113.
114.
可提前还款的定期贷款是隐含着期权的利率衍生物,本文建立CIR利率模型下可提前还款的定期贷款的数学模型,通过离散偏微分方程,建立了模型的计算方法,讨论了随机利率对提前还贷的影响. 相似文献
115.
This paper proposes a new method that extends the efficient global optimization to address stochastic black-box systems. The
method is based on a kriging meta-model that provides a global prediction of the objective values and a measure of prediction
uncertainty at every point. The criterion for the infill sample selection is an augmented expected improvement function with
desirable properties for stochastic responses. The method is empirically compared with the revised simplex search, the simultaneous
perturbation stochastic approximation, and the DIRECT methods using six test problems from the literature. An application
case study on an inventory system is also documented. The results suggest that the proposed method has excellent consistency
and efficiency in finding global optimal solutions, and is particularly useful for expensive systems. 相似文献
116.
High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer (ML) up to 600 °C have been studied and reported in this paper. Ti/Ni multilayer samples having constant layer thicknesses of 50 Å each are deposited on float glass and Si(1 1 1) substrates using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions at room temperatures. The micro-structural parameters and their evolution with temperature for as-deposited as well as annealed multilayer samples up to 600 °C in a step of 100 °C for 1 h are determined by using X-ray diffraction (XRD) and grazing incidence X-ray reflectivity techniques. The X-ray diffraction pattern recorded at 300 °C annealed multilayer sample shows interesting structural transformation (from crystalline to amorphous) because of the solid-state reaction (SSR) and subsequent re-crystallization at higher temperatures of annealing, particularly at ≥400 °C due to the formation of TiNi3 and Ti2Ni alloy phases. Sample quality and surface morphology are examined by using atomic force microscopy (AFM) technique for both as-deposited as well as annealed multilayer samples. In addition to this, a temperature dependent dc resistivity measurement is also used to study the structural transformation and subsequent alloy phase formation due to annealing treatment. The corresponding magnetization behavior of multilayer samples after each stage of annealing has been investigated by using Magneto-Optical Kerr Effect (MOKE) technique and results are interpreted in terms of observed micro-structural changes. 相似文献
117.
Long JIANG 《数学年刊B辑(英文版)》2006,27(5):553-564
Abstract
Under the Lipschitz assumption and square integrable assumption on g, the author proves that Jensen’s inequality holds for backward stochastic differential equations with generator g if and only if g is independent of y, g(t, 0) ≡ 0 and g is super homogeneous with respect to z. This result generalizes the known results on Jensen’s inequality for g- expectation in [4, 7–9].
*Project supported by the National Natural Science Foundation of China (No.10325101) and the Science Foundation of China University
of Mining and Technology. 相似文献
118.
3d-metal antimonides: Fe1+x Sb, N+x Sb, Co+x Sb and the (Ni1?y Fe y )Sb solid solution have been studied by the Mössbauer effect method at 57Fe and 119Sn. It was found that the quadrupole interactions at the Fe and Sn nucleus in 3d-metal antimonides are very sensitive to the filling of different crystallographic sites with metal atoms. The metal atoms in trigonal-bipyramidal sites have a strong effect on the quadrupole splitting of 119Sn. They are nearest to anions (Sb or Sn) with the typical axial ratio of c/a = 1.25. The QS(x) dependence of 119 Sn in 3d-metal antimonides in the 0 ≤ x ≤ 0.1 concentration range can be used to determine x – the concentration of transition metal excess relative to the stoichiometric composition. 相似文献
119.
120.
Mark E. Filipkowski Edwin E. Hach III Michael Offenbacker 《Journal of magnetism and magnetic materials》2006
We show, via a straightforward calculation, that it is feasible to detect nuclear spin echoes in a ferromagnetic thin film by electrical means. The detection scheme is based on the deflection of the electronic magnetization when the nuclear magnetization reforms during an echo. This deflection is observed as a time-dependent magnetoresistive signal. 相似文献