全文获取类型
收费全文 | 7467篇 |
免费 | 890篇 |
国内免费 | 278篇 |
专业分类
化学 | 4075篇 |
晶体学 | 47篇 |
力学 | 721篇 |
综合类 | 31篇 |
数学 | 373篇 |
物理学 | 3388篇 |
出版年
2024年 | 10篇 |
2023年 | 59篇 |
2022年 | 158篇 |
2021年 | 165篇 |
2020年 | 189篇 |
2019年 | 220篇 |
2018年 | 173篇 |
2017年 | 161篇 |
2016年 | 309篇 |
2015年 | 273篇 |
2014年 | 342篇 |
2013年 | 682篇 |
2012年 | 376篇 |
2011年 | 400篇 |
2010年 | 312篇 |
2009年 | 407篇 |
2008年 | 431篇 |
2007年 | 490篇 |
2006年 | 441篇 |
2005年 | 298篇 |
2004年 | 318篇 |
2003年 | 320篇 |
2002年 | 252篇 |
2001年 | 215篇 |
2000年 | 219篇 |
1999年 | 175篇 |
1998年 | 218篇 |
1997年 | 111篇 |
1996年 | 108篇 |
1995年 | 83篇 |
1994年 | 94篇 |
1993年 | 82篇 |
1992年 | 67篇 |
1991年 | 58篇 |
1990年 | 35篇 |
1989年 | 57篇 |
1988年 | 46篇 |
1987年 | 32篇 |
1986年 | 24篇 |
1985年 | 22篇 |
1984年 | 40篇 |
1983年 | 16篇 |
1982年 | 26篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1973年 | 11篇 |
排序方式: 共有8635条查询结果,搜索用时 15 毫秒
1.
2.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
3.
David K Bisset 《国际流体数值方法杂志》2002,39(10):961-977
Turbulent flow simulation methods based on finite differences are attractive for their simplicity, flexibility and efficiency, but not always for accuracy or stability. This paper demonstrates that a good compromise is possible with the advected grid explicit (AGE) method. Starting from the same initial field as a previous spectral DNS, AGE method simulations of a planar turbulent wake were carried out as DNS, and then at three levels of reduced resolution. The latter cases were in a sense large‐eddy simulations (LES), although no specific sub‐grid‐scale model was used. Results for the two DNS methods, including variances and power spectra, were very similar, but the AGE simulation required much less computational effort. Small‐scale information was lost in the reduced resolution runs, but large‐scale mean and instantaneous properties were reproduced quite well, with further large reductions in computational effort. Quality of results becomes more sensitive to the value chosen for one of the AGE method parameters as resolution is reduced, from which it is inferred that the numerical stability procedure controlled by the parameter is acting in part as a sub‐grid‐scale model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
Amine boranes bearing hydrophobic substituents were used to reduce aryl ketones in competition with a methyl ketone. Their high stability in protic solvents combined with their ease of preparation made amine boranes useful compounds in the study of hydrophobically directed selective reductions. Several characteristics of the reducing agent were found to be important in determining the reaction selectivity, including available hydrocarbon surface area, degree of fluorination, and proximity of the hydrophobic group to the active hydrides. 相似文献
5.
G. S. Asanov 《Foundations of Physics Letters》2002,15(2):199-207
Granted the post-Lorentzian relativistic kinematic transformations are described in the Finslerian framework, the uniformity between the actual light-velocity anisotropy change and the anisotropic deformation of measuring rods can be the reason proper for the null results of the Michelson-Morley-type experiments at the first-order level. 相似文献
6.
X-ray diffraction patterns of nanocrystalline Fe-Cu-Nb-Si-B (FINEMET) alloys reveal that bcc α-Fe/α-FeSi crystallites with
the average grain size of 20(5) nm are dispersed in amorphous matrix. Enhanced electron—electron interaction (EEI) and quantum
interference (QI) effects as well as electron-magnon (and/or electron-spin fluctuation) scattering turn out to be the main
mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon
scattering is the most effective mechanism to destroy phase coherence of electron wave functions. The diffusion constant,
density of states at the Fermi level and the inelastic scattering time have been estimated, for the first time, for the alloys
in question
Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and
Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India. 相似文献
7.
3-Hydroxy-4-hydroxymethyl pyrrolidin-2-ones, easily prepared from the Baylis–Hillman adduct 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate, are useful intermediates in the synthesis of bioactive compounds. In order to understand the mechanism involved in this reaction, vibrational and Montecarlo molecular mechanics conformational analysis on 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate were carried out, confirming the existence of a low energy intramolecular H-bonded five-member ring. 相似文献
8.
Numerical simulation aspects, related to low Reynolds number free boundary viscous flows at micro and mesolevel during the resin impregnation stage of the liquid composite moulding process (LCM), are presented in this article. A free boundary program (FBP), developed by the authors, is used to track the movement of the resin front accurately by accounting for the surface tension effects at the boundary. Issues related to the global and local mass conservation (GMC and LMC) are identified and discussed. Unsuitable conditions for LMC and consequently GMC are uncovered at low capillary numbers, and hence a strategy for the numerical simulation of such flows is suggested. FBP encompasses a set of subroutines that are linked to modules in ANSYS. FBP can capture the void formation dynamics based on the analysis developed. We present resin impregnation dynamics in two dimensions. Extension to three dimensions is a subject for further research. Several examples are shown and efficiency of different stabilization techniques are compared. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
9.
10.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220. 相似文献