全文获取类型
收费全文 | 107663篇 |
免费 | 6680篇 |
国内免费 | 5681篇 |
专业分类
化学 | 62333篇 |
晶体学 | 1409篇 |
力学 | 6144篇 |
综合类 | 401篇 |
数学 | 12758篇 |
物理学 | 36979篇 |
出版年
2023年 | 900篇 |
2022年 | 1965篇 |
2021年 | 2368篇 |
2020年 | 2589篇 |
2019年 | 2791篇 |
2018年 | 3113篇 |
2017年 | 3042篇 |
2016年 | 3841篇 |
2015年 | 2732篇 |
2014年 | 3951篇 |
2013年 | 5491篇 |
2012年 | 5761篇 |
2011年 | 6120篇 |
2010年 | 4758篇 |
2009年 | 4751篇 |
2008年 | 5048篇 |
2007年 | 4667篇 |
2006年 | 4225篇 |
2005年 | 3819篇 |
2004年 | 3356篇 |
2003年 | 3012篇 |
2002年 | 3143篇 |
2001年 | 2806篇 |
2000年 | 2210篇 |
1999年 | 1795篇 |
1998年 | 1712篇 |
1997年 | 1491篇 |
1996年 | 1447篇 |
1995年 | 1195篇 |
1994年 | 1293篇 |
1993年 | 1190篇 |
1992年 | 1175篇 |
1991年 | 1217篇 |
1990年 | 1190篇 |
1989年 | 1114篇 |
1988年 | 960篇 |
1987年 | 939篇 |
1986年 | 916篇 |
1985年 | 947篇 |
1984年 | 929篇 |
1983年 | 839篇 |
1982年 | 813篇 |
1979年 | 804篇 |
1978年 | 820篇 |
1977年 | 813篇 |
1976年 | 926篇 |
1975年 | 817篇 |
1974年 | 853篇 |
1973年 | 851篇 |
1972年 | 753篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
Jiguo Yu Qiuju Bian Guizhen Liu Na Wang 《Journal of Applied Mathematics and Computing》2007,25(1-2):283-291
A simple graphG is said to be fractionaln-factor-critical if after deleting anyn vertices the remaining subgraph still has a fractional perfect matching. For fractionaln-factor-criticality, in this paper, one necessary and sufficient condition, and three sufficient conditions related to maximum matching, complete closure are given. 相似文献
192.
193.
S. Yu. Kudryashov Yu. I. Arutyunov L. A. Onuchak 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(1):102-107
New methods for calculating the mean volumetric flow rate of the carrier gas and the retention time of the unretained substance in the column under conditions of gas chromatography were proposed. The methods are based on preliminary isothermal calibrations of the flow rate and holdup time for a packed column. A theoretical substantiation of the methods was given. Procedures of plotting calibration dependences for determining the indicated quantities at a desired temperature were described. The calculation results were compared to experimental data obtained by traditional methods. It was demonstrated that the use of calculation methods substantially simplifies the determination of the specific retention volume over a wide temperature range. 相似文献
194.
The surgery obstruction of a normal map to a simple Poincaré pair (X, Y) lies in the relative surgery obstruction group L *(π 1(Y) → π 1(X)). A well-known result of Wall, the so-called π-π-theorem, states that in higher dimensions a normal map of a manifold with boundary to a simple Poincaré pair with π 1(X) ? π 1(Y) is normally bordant to a simple homotopy equivalence of pairs. In order to study normal maps to a manifold with a submanifold, Wall introduced the surgery obstruction groups LP * for manifold pairs and splitting obstruction groups LS *. In the present paper, we formulate and prove for manifold pairs with boundary results similar to the π-π-theorem. We give direct geometric proofs, which are based on the original statements of Wall’s results and apply obtained results to investigate surgery on filtered manifolds. 相似文献
195.
Low-lying energy states of the [Fe3S4]0 cluster have been calculated by taking into account the double exchange, superexchange and vibronic interaction. It was found that the adiabatic potential of the excited state withS=0 corresponds to the full delocalization of the “excess” charge. From the analysis of experimental data of Mössbauer spectroscopy and the temperature dependence of the magnetic susceptibility the double exchange parametert≥4000 cm?1 and the vibronic interaction parameter λ2/2k cm?1 have been estimated. 相似文献
196.
197.
A. P. Solov’ev M. I. Perchenko Yu. P. Sinichkin O. V. Zyuryukina 《Technical Physics》2002,47(8):996-1001
An expression for a signal at the ultrasonic frequency from a photodetector arising when diffraction waves at the cathode
mix is obtained for the case when the optical and acoustic beams are space-limited and Bragg angles are small. The alternating
current generated when the scattering medium is crossed by a focused 3-MHz ultrasonic beam and illuminated by a cw He-Ne laser
is measured. Satisfactory agreement between experimental results and those calculated from the formulas obtained indicates
that our model treating acoustooptical interaction in the medium in terms of Raman-Nath diffraction is valid. Conditions for
measuring the alternating current (which is a parameter of acoustooptical imaging) that are optimal from the viewpoint of
maximizing the signal and signal-to-noise ratio are predicted theoretically and corroborated experimentally. 相似文献
198.
Yu You George W. Kattawar Ping Yang Yong X. Hu Bryan A. Baum 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,100(1-3):470-482
Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer. 相似文献
199.
200.
Based on the theory of calculus of variation, some suffcient conditions are given for some Euler-Lagrangcequations to be equivalently represented by finite or even infinite many Hamiltonian canonical equations. Meanwhile,some further applications for equations such as the KdV equation, MKdV equation, the general linear Euler Lagrangeequation and the cylindric shell equations are given. 相似文献