全文获取类型
收费全文 | 87101篇 |
免费 | 7022篇 |
国内免费 | 5604篇 |
专业分类
化学 | 24569篇 |
晶体学 | 1823篇 |
力学 | 4019篇 |
综合类 | 512篇 |
数学 | 24406篇 |
物理学 | 44398篇 |
出版年
2022年 | 221篇 |
2021年 | 437篇 |
2020年 | 776篇 |
2019年 | 1123篇 |
2018年 | 1067篇 |
2017年 | 813篇 |
2016年 | 655篇 |
2015年 | 563篇 |
2014年 | 1365篇 |
2013年 | 2228篇 |
2012年 | 1515篇 |
2011年 | 2125篇 |
2010年 | 2652篇 |
2009年 | 7274篇 |
2008年 | 8300篇 |
2007年 | 6821篇 |
2006年 | 6229篇 |
2005年 | 4347篇 |
2004年 | 4087篇 |
2003年 | 4264篇 |
2002年 | 5497篇 |
2001年 | 4018篇 |
2000年 | 3769篇 |
1999年 | 3584篇 |
1998年 | 2958篇 |
1997年 | 2081篇 |
1996年 | 1862篇 |
1995年 | 2317篇 |
1994年 | 2221篇 |
1993年 | 1666篇 |
1992年 | 1157篇 |
1991年 | 893篇 |
1990年 | 737篇 |
1989年 | 644篇 |
1988年 | 591篇 |
1987年 | 440篇 |
1986年 | 221篇 |
1985年 | 984篇 |
1984年 | 648篇 |
1983年 | 506篇 |
1982年 | 676篇 |
1981年 | 817篇 |
1980年 | 739篇 |
1979年 | 581篇 |
1978年 | 604篇 |
1977年 | 555篇 |
1976年 | 550篇 |
1975年 | 321篇 |
1974年 | 361篇 |
1973年 | 469篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
NA序列部分和的矩完全收敛性 总被引:4,自引:0,他引:4
讨论了NA序列部分和的矩完全收敛性,在一定条件下获得了NA序列矩完全收敛的充要条件,显示了矩完全收敛和矩条件之间的关系,将独立同分布随机变量序列矩完全收敛的结果推广到NA序列,得到了与独立随机变量序列情形类似的结果. 相似文献
62.
Michel Weber 《Transactions of the American Mathematical Society》2006,358(2):911-936
We apply a majorizing measure theorem of Talagrand to obtain uniform bounds for sums of random variables satisfying increment conditions of the type considered in Gál-Koksma Theorems. We give some applications.
63.
Er-Si-O crystalline compounds, which exhibit superlattice structures and sharp and strong Er-related 1.54 μm photoluminescence (PL) spectra at room temperature have been formed by self-assembling growth mechanism. Oxidation of the starting materials which have Si and Er at an atomic ratio of 2:1 are prepared and then oxidation and succeeding high-temperature annealing in Ar above 1250 °C cause a self-assembled superlattice-structured Er-Si-O crystalline compounds. The control of the ratio of Si and Er, as well as the following oxidation and annealing processes, is found to be sensitive to the crystalline properties, PL spectra and electrical properties. In this study, Er-Si-O crystalline thin films are formed on Si substrates by sol-gel and MOMBE methods, and their crystalline properties such as crystalline orientation and concentration ratio of Er, Si and O are investigated. Crystalline Er-Si-O films of high orientation are successfully grown on Si(1 0 0) and its inclined surface. The PL and excitation spectra, fluorescence decay and the electrical properties are found to be strongly related to the crystalline properties. Excess O causes a broader 1.54 μm PL spectra, slower fluorescence decay, lower carrier-mediated excitation and higher resistivity. A precise control of O is found to be necessary to grow superlattice-structured Er-Si-O compounds, which are semiconducting and are excitable via carrier-mediated excitation mechanism. 相似文献
64.
We present a new approach to study the convergence of Newton's method in Banach spaces, which relax the conditions appearing in the usual studies. The approach is based on the bound required for the second derivative of the operator involved. An application to a nonlinear integral equation is presented. 相似文献
65.
〈I〉型三角剖分下非张量积连续小波基的构造 总被引:1,自引:0,他引:1
多维非张量积小波是近年小波研究领域中的热点问题之一 ,它们与多维张量积小波相比具有更多的优势 .关于高维张量积、非张量积小波 ,目前已有一些很好的工作 (见文[2 ] [3 ] [4 ] ) ,但关于样条小波 ,还有许多问题有待于研究 .本文针对〈I〉型三角剖分下的二维线性元空间 ,讨论其具有紧支集和对称性的半正交样条小波基 .给定 x1 x2 平面上的〈I〉型三角剖分 (图 1 ( a)所示 ) ,记 j=( j1 ,j2 ) ,| j| =j1 + j2 ,πm= { 0≤ |j|≤ mCj1j2 xj11 xj22 ,Cj1,j2 是任意实数 }为次数不超过 m的代数多项式全体 .引入剖分尺度为 1的线性元空间 V0… 相似文献
66.
This paper solves the problem of the duration of the total eclipseof a satellite of a body, provided that (a) the body is sphericalin shape and the mass distribution inside the body is sphericallysymmetrical; (b) the satellite is a very small object; (c) thesatellite's orbit around a body is circular and the satellitecan pass through the centre of its shadow; (d) a source of lightis the source of the conical body's shadow (umbra) and it doesnot change its apparent position in the sky; (e) there are noperturbations on the satellite's orbit. The solution presentedrepresents the general discussion of the problem based on utilizationof some parts of the theory of contraction mappings. 相似文献
67.
68.
依据GB/T 19941-2005标准,测定了皮革中的甲醛含量,对测量结果的不确定度来源进行了分析和评定,并计算出合成不确定度和有效自由度,最后根据JJF1059规范要求给出了甲醛测量不确定度表达式. 相似文献
69.
二维变系数反应扩散方程的紧交替方向差分格式 总被引:1,自引:0,他引:1
1 引言
在研究热传导过程、气体扩散现象和电磁场的传播等问题时,常常遇到抛物型偏微分方程。用有限差分方法研究这类问题的数值解法目前已经有了许多工作。对于二维、三维抛物方程的数值求解比较理想的方法是交替方向法。 相似文献
70.
N. Kiriushcheva 《Annals of Physics》2006,321(4):958-986
It is shown that the Lagrangian reduction, in which solutions of equations of motion that do not involve time derivatives are used to eliminate variables, leads to results quite different from the standard Dirac treatment of the first-order form of the Einstein-Hilbert action when the equations of motion correspond to the first class constraints. A form of the first-order formulation of the Einstein-Hilbert action which is more suitable for the Dirac approach to constrained systems is presented. The Dirac and reduced approaches are compared and contrasted. This general discussion is illustrated by a simple model in which all constraints and the gauge transformations which correspond to first class constraints are completely worked out using both methods to demonstrate explicitly their differences. These results show an inconsistency in the previous treatment of the first-order Einstein-Hilbert action which is likely responsible for problems with its canonical quantization. 相似文献