全文获取类型
收费全文 | 78462篇 |
免费 | 6469篇 |
国内免费 | 8969篇 |
专业分类
化学 | 55932篇 |
晶体学 | 2087篇 |
力学 | 5882篇 |
综合类 | 833篇 |
数学 | 10222篇 |
物理学 | 18944篇 |
出版年
2024年 | 138篇 |
2023年 | 717篇 |
2022年 | 1555篇 |
2021年 | 1830篇 |
2020年 | 2093篇 |
2019年 | 1961篇 |
2018年 | 1720篇 |
2017年 | 2148篇 |
2016年 | 2960篇 |
2015年 | 2531篇 |
2014年 | 3327篇 |
2013年 | 5572篇 |
2012年 | 5529篇 |
2011年 | 4291篇 |
2010年 | 3669篇 |
2009年 | 4672篇 |
2008年 | 4789篇 |
2007年 | 5121篇 |
2006年 | 4569篇 |
2005年 | 4166篇 |
2004年 | 4074篇 |
2003年 | 3439篇 |
2002年 | 3246篇 |
2001年 | 2281篇 |
2000年 | 2299篇 |
1999年 | 1931篇 |
1998年 | 1753篇 |
1997年 | 1494篇 |
1996年 | 1431篇 |
1995年 | 1324篇 |
1994年 | 1206篇 |
1993年 | 962篇 |
1992年 | 936篇 |
1991年 | 667篇 |
1990年 | 578篇 |
1989年 | 405篇 |
1988年 | 401篇 |
1987年 | 267篇 |
1986年 | 235篇 |
1985年 | 266篇 |
1984年 | 218篇 |
1983年 | 142篇 |
1982年 | 174篇 |
1981年 | 131篇 |
1980年 | 116篇 |
1979年 | 143篇 |
1978年 | 86篇 |
1977年 | 70篇 |
1976年 | 64篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
81.
82.
C. Maurel 《Surface science》2006,600(2):442-447
Light emitted in the tunneling junction of a scanning tunneling microscope has been used to establish the electrical characteristics of nanojunctions made of Au islands deposited on flat MoS2 surfaces. It is shown that these characteristics are those of rectifying contacts when the gold islands are isolated and that they evolve toward those of ohmic contacts when the island density increases. It is observed that the rectifying behavior also evolves over time as on infinite metal/semiconductor contacts. Using the STM tip, single gold islands can be manipulated on the MoS2 surface so that their electrical behavior can be changed depending on their position with regard to the other islands. 相似文献
83.
Blaise Faugeras Jé rô me Pousin Franck Fontvieille. 《Mathematics of Computation》2006,75(253):209-222
A numerical scheme based on an operator splitting method and a dense output event location algorithm is proposed to integrate a diffusion-dissolution/precipitation chemical initial-boundary value problem with jumping nonlinearities. The numerical analysis of the scheme is carried out and it is proved to be of order 2 in time. This global order estimate is illustrated numerically on a test case.
84.
Th. Seyller K.V. Emtsev F. Speck A. Tadich J.D. Riley O. Rader A.M. Shikin 《Surface science》2006,600(18):3906-3911
Photoelectron spectroscopy, low-energy electron diffraction, and scanning probe microscopy were used to investigate the electronic and structural properties of graphite layers grown by solid state graphitization of SiC(0 0 0 1) surfaces. The process leads to well-ordered graphite layers which are rotated against the substrate lattice by 30°. On on-axis 6H-SiC(0 0 0 1) substrates we observe graphitic layers with up to several 100 nm wide terraces. ARUPS spectra of the graphite layers grown on on-axis 6H-SiC(0 0 0 1) surfaces are indicative of a well-developed band structure. For the graphite/n-type 6H-SiC(0 0 0 1) layer system we observe a Schottky barrier height of ?B,n = 0.3 ± 0.1 eV. ARUPS spectra of graphite layers grown on 8° off-axis oriented 4H-SiC(0 0 0 1) show unique replicas which are explained by a carpet-like growth mode combined with a step bunching of the substrate. 相似文献
85.
Robert S. Strichartz 《Proceedings of the American Mathematical Society》2002,130(3):805-817
Harmonic mappings from the Sierpinski gasket to the circle are described explicitly in terms of boundary values and topological data. In particular, all such mappings minimize energy within a given homotopy class. Explicit formulas are also given for the energy of the mapping and its normal derivatives at boundary points.
86.
我国上市公司资本结构影响因素实证分析 总被引:17,自引:0,他引:17
本文选取了可能影响企业资本结构的多个指标变量进行分析 ,利用主成分分析提供的方法将变量综合成彼此互不相关的少数几个主成分。再用主成分 (作为回归自变量 )对企业的 5种资本负债比 (作为回归因变量 )进行多元回归分析 ,得出了影响企业资本结构的主要因素 ,以及这些因素与企业资本结构之间的关系 ,为企业确定资本结构提供参考依据 ,为企业财务决策提供支持。 相似文献
87.
A FUNDAMENTAL SOLUTION FOR THE LAPLACE OPERATOR ON THE QUATERNIONIC HEISENBERG GROUP 总被引:2,自引:0,他引:2
朱理 《数学物理学报(B辑英文版)》2002,22(3)
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group. 相似文献
88.
F. Iachello S. Oss 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):307-314
We present a brief review of algebraic techniques developed and applied in molecular spectroscopy in the last five years.
We also outline perspectives for new applications of the Lie algebraic method in the first decade of the new century.
Received 21 November 2001 相似文献
89.
Under idealized conditions, electroconvection in a nematic liquid crystal sets in at a well-defined threshold of the driving ac voltage. Fluctuating convection rolls of a small amplitude below that threshold have been observed recently. The measurement of the amplitude of these fluctuations is described in detail in this paper. It is based on averaging the light intensity signals using the structure function and a quantitative analysis of the light deflection. 相似文献
90.
Evolutionary algorithms are applied as problem-independent optimization algorithms. They are quite efficient in many situations. However, it is difficult to analyze even the behavior of simple variants of evolutionary algorithms like the (1+1) EA on rather simple functions. Nevertheless, only the analysis of the expected run time and the success probability within a given number of steps can guide the choice of the free parameters of the algorithms. Here static (1+1) EAs with a fixed mutation probability are compared with dynamic (1+1) EAs with a simple schedule for the variation of the mutation probability. The dynamic variant is first analyzed for functions typically chosen as example-functions for evolutionary algorithms. Afterwards, it is shown that it can be essential to choose the suitable variant of the (1+1) EA. More precisely, functions are presented where each static (1+1) EA has exponential expected run time while the dynamic variant has polynomial expected run time. For other functions it is shown that the dynamic (1+1) EA has exponential expected run time while a static (1+1) EA with a good choice of the mutation probability has polynomial run time with overwhelming probability. 相似文献