全文获取类型
收费全文 | 1679篇 |
免费 | 524篇 |
国内免费 | 229篇 |
专业分类
化学 | 527篇 |
晶体学 | 132篇 |
力学 | 273篇 |
综合类 | 17篇 |
数学 | 191篇 |
物理学 | 1292篇 |
出版年
2024年 | 3篇 |
2023年 | 20篇 |
2022年 | 72篇 |
2021年 | 62篇 |
2020年 | 75篇 |
2019年 | 61篇 |
2018年 | 67篇 |
2017年 | 57篇 |
2016年 | 89篇 |
2015年 | 73篇 |
2014年 | 96篇 |
2013年 | 225篇 |
2012年 | 120篇 |
2011年 | 131篇 |
2010年 | 104篇 |
2009年 | 134篇 |
2008年 | 132篇 |
2007年 | 107篇 |
2006年 | 115篇 |
2005年 | 94篇 |
2004年 | 83篇 |
2003年 | 75篇 |
2002年 | 49篇 |
2001年 | 39篇 |
2000年 | 52篇 |
1999年 | 46篇 |
1998年 | 44篇 |
1997年 | 25篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有2432条查询结果,搜索用时 31 毫秒
101.
王立中 《中国科学A辑(英文版)》2002,45(12):1578-1581
In this paper, we focus on the structure of p-blocks with defect group satisfying some special condition. These special conditions
include: two elements of the defect group are conjugate to each other in defect D if and only if they are conjugate to each
other in G; the number of conjugacy classes whose p-part is contained in P by conjugacy is not larger than ∣P∣ 相似文献
102.
W.H. Enright 《Numerical Algorithms》2002,31(1-4):125-137
In the last decade it has become standard for students and researchers to be introduced to state-of-the-art numerical software through a problem solving environment (PSE) rather than through the use of scientific libraries callable from a high level language such as Fortran or C. In this paper we will identify the constraints and implications that this imposes on the ODE software we investigate and develop. In particular, the way a numerical solution is displayed and viewed by a user dictates that new measures of performance and quality must be adopted. We will use the MATLAB environment and ODE software for initial value problems, boundary value problems and delay problems to illustrate the issues that arise and the progress that has been made. One of the major implications is the expectation that accurate approximations at off-mesh points must be provided. Traditional numerical methods for ODEs have produced approximations to the underlying solution on an associated discrete, adaptively chosen mesh. In recent years it has become common for the ODE software to also deliver approximations at off-mesh values of the independent variable. Such a feature can be extremely valuable in applications and leads to new measures of quality and performance which are more meaningful to users and more consistently interpreted and implemented in contemporary ODE software. Numerical examples of the robust and reliable behaviour of such software will be presented and the cost/reliability trade-offs that arise will be quantified. 相似文献
103.
Resonance Raman spectra (RRS) of Co(II) and Co(III)5,10,15,20tetrakis(4Nmethylpyridinium)porphyrin ((CoII(TmpyP4), and CoIII(TMPyP4)) in aqueous solutions at different pH as well as in organic solvents (methanol, ethanol, DMSO, DMF) are obtained. The increased sensitivity of the oscillation frequencies 2, 4, 8, and 6 — the markers of the oxidation state of a metal — to the nature of an axial ligand has been revealed. For CoIII(TmpyP4), the shifts of the indicated frequencies in extracoordination have turned out to be twofold larger than those for CoII(TmpyP4). The spectral effects observed are related to different electron influence of the extraligands on the system of the porphyrin ring. In the case of Co(III)porphyrin, interaction of the d
orbitals of the metal and the e
g
*orbitals of the macrocycle is more efficient since its ionic radius is smaller than for the Co(II)complex. For CoIII(TmpyP4), a linear correlation between the oscillation frequencies 2, 4, 8, and 6 and the experimental Gutmann parameters characterizing the electronacceptor properties of solvents is found. 相似文献
104.
N. B. Éshkobilov 《Journal of Applied Spectroscopy》2002,69(3):477-479
The main series of a silver atom with n = 5–70 are investigated. Perturbations of the np
2
P
1/2,3/2 states with n = 10 and 17 caused by interaction with the selfionization 4d5s5p
4
P
1/2,3/2 states are detected. Energies of the selfionization states are determined. 相似文献
105.
The effect of the grain boundary microstructure on the anisotropy and coercivity was investigated in an HDDR Nd-Fe-B permanent
magnetic alloy. Considering the special microstructure of its magnetic powder grain, an anisotropic theoretical model influenced
simultaneously by the structure defect at the grain boundary and the exchange coupling interaction was put forward. The variations
of the structure defect factors based on the nucleation and pinning mechanism with 2r
0/lex (where r
0 and lex are the defect thickness and the length of exchange coupling, respectively) were calculated. The results show that the coercivity
mechanism of an HDDR Nd-Fe-B permanent magnetic alloy is greatly related to its microstructure defect at the grain boundary.
For a fixed lex, when 2r
0/lex < 1.67, the coercivity is controlled by the pinning mechanism; when 2r
0/lex > 1.67, it is determined by the nucleation mechanism. The coercivity reaches the maximum when 2r
0/lex = 1.67. The calculation result is consistent well with the experimental result given by Morimoto et al.
Supported by the National Natural Science Foundation of China (Grant No. 50671055) 相似文献
106.
Several aspects of localized defects in the Frenkel-Kontorova, classicalXY chain and analogous models with a finite range of interactions are discussed from a general point of view. Precise definitions are given for defect phase shifts (charges) and for creation, pinning, and interaction energies. Corresponding definitions are also provided for interfaces (localized regions separating two phases). For the nearest-neighbor Frenkel-Kontorova model, the various defect energies are related to areas enclosed by contours joining heteroclinic points of the area-preserving map generated by the conditions of mechanical equilibrium. 相似文献
107.
分析了制作高功率连续激光反射镜材料的热性能、缺陷及其加工工艺, 提出了制作高功率激光反射镜应考虑的几个关键问题: 反射镜材料的综合热性能比值S, 材料的微观结构、缺陷的大小和晶向的选择, 以及加工工艺的设计。并介绍了实验结果。 相似文献
108.
A relativistic model of independent quarks based on Dirac equation with an equally mixed scalar-vector square root confining
potential is used to compute the quark core contributions to the static properties like magnetic moments, charge radii and
axial vector coupling constant ratios of the baryon octet. The results obtained with appropriate corrections due to centre-of-mass
motion agree fairly well with experimental values. The model is also extended to the study of magnetic moments of the quark
core of baryons in the charmed andb-flavoured sectors and the overall predictions so obtained compare well with other model predictions. 相似文献
109.
G.V. Lewis C.R.A. Catlow A.N. Cormack 《Journal of Physics and Chemistry of Solids》1985,46(11):1227-1233
We present the results of a computer simulation study of the defect formation and migration energies in Fe3O4. Calculated Frenkel and Schottky energies are found to be similar in magnitude and both are considerably reduced by screening due to electron redistribution around the charged-defect species. The calculations also suggest that cation diffusion is mainly effected by a colinear interstitialcy mechanism at low Po2 and by a simple octahedral vacancy mechanism at higher Po2. 相似文献
110.
Vollmer A Jurchescu OD Arfaoui I Salzmann I Palstra TT Rudolf P Niemax J Pflaum J Rabe JP Koch N 《The European physical journal. E, Soft matter》2005,17(3):339-343
We use ultraviolet photoelectron spectroscopy to investigate the effect of oxygen and air exposure on the electronic structure of pentacene single crystals and thin films. It is found that O2 and water do not react noticeably with pentacene, whereas singlet oxygen/ozone readily oxidize the organic compound. Also, we obtain no evidence for considerable p-type doping of pentacene by O2 at low pressure. However, oxygen exposure lowers the hole injection barrier at the interface between Au and pentacene by 0.25 eV, presumably due to a modification of the Au surface properties. 相似文献