全文获取类型
收费全文 | 21501篇 |
免费 | 3628篇 |
国内免费 | 3540篇 |
专业分类
化学 | 11949篇 |
晶体学 | 202篇 |
力学 | 1900篇 |
综合类 | 222篇 |
数学 | 4306篇 |
物理学 | 10090篇 |
出版年
2024年 | 63篇 |
2023年 | 258篇 |
2022年 | 480篇 |
2021年 | 655篇 |
2020年 | 851篇 |
2019年 | 710篇 |
2018年 | 688篇 |
2017年 | 753篇 |
2016年 | 896篇 |
2015年 | 803篇 |
2014年 | 1170篇 |
2013年 | 1831篇 |
2012年 | 1227篇 |
2011年 | 1350篇 |
2010年 | 1174篇 |
2009年 | 1483篇 |
2008年 | 1512篇 |
2007年 | 1548篇 |
2006年 | 1489篇 |
2005年 | 1172篇 |
2004年 | 1088篇 |
2003年 | 1008篇 |
2002年 | 867篇 |
2001年 | 750篇 |
2000年 | 752篇 |
1999年 | 608篇 |
1998年 | 552篇 |
1997年 | 447篇 |
1996年 | 381篇 |
1995年 | 345篇 |
1994年 | 284篇 |
1993年 | 221篇 |
1992年 | 185篇 |
1991年 | 178篇 |
1990年 | 116篇 |
1989年 | 98篇 |
1988年 | 100篇 |
1987年 | 87篇 |
1986年 | 78篇 |
1985年 | 72篇 |
1984年 | 58篇 |
1983年 | 27篇 |
1982年 | 39篇 |
1981年 | 40篇 |
1980年 | 37篇 |
1979年 | 36篇 |
1978年 | 19篇 |
1977年 | 22篇 |
1976年 | 17篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
用能量法求多自由度振动系统的角频率 总被引:2,自引:1,他引:1
利用简谐振动能量方程,通过分析振幅矢量的关系,用能量法求多自由度振动系统的角频率或简正振动频率。 相似文献
32.
Eldad Herceg 《Surface science》2006,600(19):4563-4571
The formation of a well-ordered p(2 × 2) overlayer of atomic nitrogen on the Pt(1 1 1) surface and its reaction with hydrogen were characterized with reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The p(2 × 2)-N overlayer is formed by exposure of ammonia to a surface at 85 K that is covered with 0.44 monolayer (ML) of molecular oxygen and then heating to 400 K. The reaction between ammonia and oxygen produces water, which desorbs below 400 K. The only desorption product observed above 400 K is molecular nitrogen, which has a peak desorption temperature of 453 K. The absence of oxygen after the 400 K anneal is confirmed with AES. Although atomic nitrogen can also be produced on the surface through the reaction of ammonia with an atomic, rather than molecular, oxygen overlayer at a saturation coverage of 0.25 ML, the yield of surface nitrogen is significantly less, as indicated by the N2 TPD peak area. Atomic nitrogen readily reacts with hydrogen to produce the NH species, which is characterized with RAIRS by an intense and narrow (FWHM ∼ 4 cm−1) peak at 3322 cm−1. The areas of the H2 TPD peak associated with NH dissociation and the XPS N 1s peak associated with the NH species indicate that not all of the surface N atoms can be converted to NH by the methods used here. 相似文献
33.
Mariano J. Valderrama 《商业与工业应用随机模型》1991,7(1):93-106
Alternative procedures for representing a stochastic signal as a denumerable series with uncorrelated terms are developed. The study includes considerations about parametric rescaling and its repercussions on the orthogonal expansion, as well as numerical techniques for approaching such an expansion. In addition, applications to the Gaussian characterization of stochastic signals, filtering and stochastic modelling are treated. 相似文献
34.
介绍了13~18世纪物理学史和科技史上曾名噪一时的第一类永动机的设计方案的破灭.第一类永动机幻梦破灭的历史引起了人们的反思与启示,有力地促进了19世纪中叶能量转化和守恒定律的确立. 相似文献
35.
《组合设计杂志》2002,10(5):283-293
An Orthogonal Double Cover (ODC) of the complete graph Kn by an almost‐hamiltonian cycle is a decomposition of 2Kn into cycles of length n?1 such that the intersection of any two of them is exactly one edge. We introduce a new class of such decompositions. If n is a prime, the special structure of such a decomposition allows to expand it to an ODC of Kn+1 by an almost‐hamiltonian cycle. This yields the existence of an ODC of Kp+1 by an almost‐hamiltonian cycle for primes p of order 3 mod 4 and its eventual existence for arbitrary primes p. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 283–293, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10011 相似文献
36.
This paper gives some global and uniform convergence estimates for a class of subspace correction (based on space decomposition) iterative methods applied to some unconstrained convex optimization problems. Some multigrid and domain decomposition methods are also discussed as special examples for solving some nonlinear elliptic boundary value problems.
37.
E. C. Ferreira J. A. P. da Costa J. A. K. Freire G. A. Farias V. N. Freire 《Applied Surface Science》2002,190(1-4):191-194
Confined excitons in non-abrupt GaAs/AlxGa1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al0.3Ga0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces. 相似文献
38.
本文首先将文[1]中的BLD映射推广为弱(L1,L2)-BLD映射,并证明了如下正则性结果:存在两个可积指数 P1=P1(n,L1,L2)<n<q1=q1(n,L1,L2),使得对任意弱(L1,L2)-BLD映射f∈(Ω,Rn),都有f∈(Ω,Rn),即f为(L1,L2)-BLD映射. 相似文献
39.
光纤的能量传输特性及应用 总被引:5,自引:0,他引:5
着重分析了影响光纤传输能量以及光纤传输中造成能量损耗的因素。这些因素主要包括光纤材料、构造、光纤的折射率分布、光纤的长度和芯径、光纤的数值孔径和热效应以及耦合等。同时 ,结合激光二极管点火的实例 ,分析探讨了其背景和应用价值。结论是 :为了尽可能减少能量损耗、提高光纤输出的激光功率和激光功率密度 ,应当选取合适的激光工作波长、较小的光纤长度、较小的芯径和较小的数值孔径 ,应采用渐变折射率分布光纤 ,应减少弯曲与耦合 相似文献
40.
D. Yafaev 《Proceedings Mathematical Sciences》2002,112(1):245-255
We find an explicit function approximating at high energies the kernel of the scattering matrix with arbitrary accuracy. Moreover,
the same function gives all diagonal singularities of the kernel of the scattering matrix in the angular variables.
This paper is dedicated to Jean-Michel Combes on the occasion of his sixtieth birthday. 相似文献