全文获取类型
收费全文 | 59502篇 |
免费 | 4875篇 |
国内免费 | 5405篇 |
专业分类
化学 | 32858篇 |
晶体学 | 539篇 |
力学 | 2019篇 |
综合类 | 336篇 |
数学 | 4991篇 |
物理学 | 8687篇 |
综合类 | 20352篇 |
出版年
2024年 | 86篇 |
2023年 | 549篇 |
2022年 | 1232篇 |
2021年 | 1416篇 |
2020年 | 1615篇 |
2019年 | 1499篇 |
2018年 | 1363篇 |
2017年 | 1648篇 |
2016年 | 1900篇 |
2015年 | 1828篇 |
2014年 | 2540篇 |
2013年 | 3432篇 |
2012年 | 3249篇 |
2011年 | 3399篇 |
2010年 | 2846篇 |
2009年 | 3499篇 |
2008年 | 3234篇 |
2007年 | 3541篇 |
2006年 | 3261篇 |
2005年 | 2979篇 |
2004年 | 2843篇 |
2003年 | 2413篇 |
2002年 | 2734篇 |
2001年 | 1895篇 |
2000年 | 1702篇 |
1999年 | 1464篇 |
1998年 | 1228篇 |
1997年 | 1213篇 |
1996年 | 1145篇 |
1995年 | 1331篇 |
1994年 | 1137篇 |
1993年 | 933篇 |
1992年 | 962篇 |
1991年 | 764篇 |
1990年 | 685篇 |
1989年 | 505篇 |
1988年 | 338篇 |
1987年 | 209篇 |
1986年 | 160篇 |
1985年 | 99篇 |
1984年 | 90篇 |
1983年 | 34篇 |
1982年 | 85篇 |
1981年 | 109篇 |
1980年 | 117篇 |
1979年 | 122篇 |
1978年 | 98篇 |
1977年 | 70篇 |
1976年 | 65篇 |
1973年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
281.
Feng S.-W. Tsai C.-Y. Cheng Y.-C. Liao C.-C. Yang C.C. Lin Y.-S. Ma K.-J. Chyi J.-I. 《Optical and Quantum Electronics》2002,34(12):1213-1219
A side-bump feature in a photoluminescence (PL) spectrum of an InGaN compound was widely observed. With reasonable fitting to PL spectra with three Gaussian distributions, the temperature variations of the peak positions, integrated PL intensities, and peak widths of the main and first side peaks of three InGaN/GaN multiple quantum well samples with different nominal indium contents are shown and interpreted. The existence of the side peaks is attributed to phonon–replica transitions. The variations of the peak position separations and the decreasing trends of the first side peak widths beyond certain temperatures in those samples were explained with the requirement of phonon momentum condition for phonon–replica transitions. In the sample with 25% nominal indium content, the phonon–replica transition could become stronger than the direct transition of localized states. 相似文献
282.
X.F. Hu 《Applied Surface Science》2006,252(13):4625-4627
The synthetic antiferromagnets (SAF) have been used in spin-valve sensor in data storage industry [1]. We report a new hard/Ru/soft sandwich structure (SHBL) fabricated by pulsed lased deposition to replace current single layer structure for information recording application. SHBL consists of two magnetic layers separated by thin nonmagnetic layers, typically with Ru layers of 0.7-1.2 nm, through which antiferromagnetic coupling is induced. Varying the relative thickness of the magnetic layers, the spacer layers, and the type of magnetic materials can alter magnetic properties of CoCrPt/Ru/CoFe superlattice. The coercivity Hc and grain size of magnetic layer is also dependent on the laser fluence. High laser fluence results in both small grain size and high Hc. The observed phenomena are related to high quenching and deposition rates during PLD at high fluence, resulting in more pronounced phase segregation. 相似文献
283.
Z. Sebestyén 《Periodica Mathematica Hungarica》1989,20(1):85-87
We prove, as an application of our positive extension argument, a theorem of Parrott concerning the quotient norm with respect to spaces of Hilbert space operators. 相似文献
284.
This paper is based on the M. Sc. thesis written by the third author under the supervision of the first two authors. It was submitted to the University of Baghdad in 1986. 相似文献
285.
XU Yichao CHEN Minru & MA Songya Academy of Mathematics Systems Science Chinese Academy of Sciences Beijing China College of Mathematics Information Sciences Henan University Kaifeng China 《中国科学A辑(英文版)》2006,49(10):1392-1404
We known that the maximal connected holomorphic automorphism group Aut (D)(0) is a semi-direct product of the triangle group T(D) and the maximal connected isotropic subgroup Iso(D)(0) of a fixed point in the complex homogeneous bounded domain D and any complex homogeneous bounded domain is holomorphic isomorphic to a normal Siegel domain D(VN,F). In this paper, we give the explicit formula of any holomorphic automorphism in T(D(VN, F)) and Iso(D(VN,F))(0), where G(0) is the unit connected component of the Lie group G. 相似文献
286.
287.
用区域分解算法结合蒙特卡罗法求坦克温度场和红外辐射出射度 总被引:3,自引:0,他引:3
本文将区域分解算法和蒙特卡罗法相结合,求坦克温度场和红外辐射出射度.采用蒙特卡罗法计算辐射传递系数,可以考虑界面的复杂辐射特性,如:镜反射、各向异性发射、各向异性反射等;可直接考虑界面的复杂几何特性,如:相互遮挡、太阳入射方向上的投影面积等.引入辐射传递系数,分离了计算的难点,使得在时间域(计算步骤)上能把整个问题分解为若干个子问题并行处理、在空间域(计算区域)上将坦克分解为若干个子区域,缩小计算规模,并可使用多个处理器并行计算;同时减轻了蒙特卡罗法编程的难度,缩短了计算时间. 相似文献
288.
相型同步启动时间的M/M/c排队系统 总被引:4,自引:0,他引:4
本文研究带有同步启动时间的M/M/c系统,其中启动时间是相型变量,给出了稳态和等待时间分布等结果。 相似文献
289.
The fluorescence dynamics parameters of the fluorescent transient flavin-luciferase species from the typesVibrio fischeri andPhotobacterium leiognathi are presented. The fluorescence anisotropy decay is a single exponential function for both types. The correlation time is 70 ns for theP. leiognathi fluorescent transient intermediate (2°C, aqueous buffer, pH 7.0), consistent with the rotational correlation time of the luciferase macromolecule (77 kD) to which the flavin fluorophore is rigidly attached. In contrast, for theV. fischeri species the observed correlation time for the anisotropy decay function is 133 ns. This suggests that protein self-association occurs in theV. fischeri case and this is confirmed by filtration, where the fluorescent transient fromV. fischeri does not pass through a 100,000 molecular weight cutoff membrane, whereas theP. leiognathi species does. The filtration method also demonstrates self-association in the luciferase peroxyflavin and photoflavin fromV. fischeri. A monomer-dimer equilibrium also explains the previously reported high correlation times for theV. harveyi luciferase-flavin species. It is proposed that the self-association competes with the lumazine protein interaction in the bioluminescence reaction. 相似文献
290.
根据目前Cernet校园网典型结构,设计了一种适应性广、通用性强的校园网计费管理系统,探讨了使用代理服务器进行计费的主要功能和工作流程. 相似文献