全文获取类型
收费全文 | 23808篇 |
免费 | 1675篇 |
国内免费 | 1935篇 |
专业分类
化学 | 21461篇 |
晶体学 | 682篇 |
力学 | 732篇 |
综合类 | 81篇 |
数学 | 182篇 |
物理学 | 4280篇 |
出版年
2024年 | 24篇 |
2023年 | 213篇 |
2022年 | 358篇 |
2021年 | 407篇 |
2020年 | 705篇 |
2019年 | 700篇 |
2018年 | 766篇 |
2017年 | 1012篇 |
2016年 | 1189篇 |
2015年 | 906篇 |
2014年 | 956篇 |
2013年 | 2429篇 |
2012年 | 1472篇 |
2011年 | 1294篇 |
2010年 | 1159篇 |
2009年 | 1450篇 |
2008年 | 1231篇 |
2007年 | 1353篇 |
2006年 | 1167篇 |
2005年 | 1015篇 |
2004年 | 872篇 |
2003年 | 752篇 |
2002年 | 640篇 |
2001年 | 569篇 |
2000年 | 571篇 |
1999年 | 511篇 |
1998年 | 471篇 |
1997年 | 386篇 |
1996年 | 377篇 |
1995年 | 369篇 |
1994年 | 297篇 |
1993年 | 243篇 |
1992年 | 195篇 |
1991年 | 159篇 |
1990年 | 178篇 |
1989年 | 141篇 |
1988年 | 177篇 |
1987年 | 178篇 |
1986年 | 109篇 |
1985年 | 86篇 |
1984年 | 110篇 |
1983年 | 27篇 |
1982年 | 66篇 |
1981年 | 30篇 |
1980年 | 26篇 |
1979年 | 25篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1975年 | 7篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
Fernando M. Lanas Janete H. Y. Vilegas Srgio Martins Elaine A. F. Gobato 《Journal of separation science》1994,17(4):237-244
An overview is presented of the analytical approaches developed by our research group over the last ten years for analysis of alternative fuel, both biomass and fossil. The alternative fuels are analyzed successively by PLC-8 (preparative liquid chromatography–group-type) fractionation and high resolution gas chromatography. Some of the possibilities for fractionation and characterization of alternative fuels are herein exemplified with sugar cane bagasse pyrolysis products. 相似文献
93.
A new method is presented for spatially resolved thermal lensing measurements using multiple narrow probe beams and a two-dimensional array detector. The method is applied to an Er, Tm, Ho: YAG laser rod. No significant deviation from a parabolic temperature profile has been found although there is extraordinarily strong thermal lensing in the crystal. Thermo-optical constants of the material are reported. 相似文献
94.
Thermotropic copolyester fibers of oxynaphthoate and oxybenzoate have been subjected to conditions that promote solid-state polymerization as well as annealing. The annealing process causes the crystals to perfect with a simultaneous increase in heat of fusion and melting temperature. Solid-state polymerization, a reaction rate-controlled process, causes the polymer viscosity average molecular weight to increase by chain extension from about 14,000 g/mole to more than 87,000 g/mole with a simultaneous impressive increase in tenacity from about 10 g/d (1.2 GPa) to almost 30 g/d (3.7 GPa). To understand the changes in mechanical properties, we have modeled the fiber structure as short rod-like molecules poorly bonded to a continuous matrix of parallel molecules. Lengthening of the reinforcing molecules facilitates better transfer of load from matrix to molecules, resulting in higher tenacity fibers. © 1994 John Wiley & Sons, Inc. 相似文献
95.
The question about the definition of the “internal pressure” concept is being discussed. It is shown that the previously found differential relation between the cohesion energy density and the internal pressure is one of the examples of an absolutely general interrelation between definitely connected differential functions. It is ascertained that the ratio (the internal pressure divided by the cohesion energy density) is a structuresensitive parameter inherent to the calorific (thermal) equation of a liquid state. 相似文献
96.
A new, high performance liquid chromatography method has been developed for the separation of monovinyl- and divinyl-protochlorophyllides, using commercially available, C30 reverse phase column and isocratic elution. This method can be used both for analytical applications and preparative scale purification of monovinyl- and divinyl-protochlorophyllides using the same column where submilimolar concentrations of the crude protochlorophyllide extract can be separated in one run. The purity of the obtained protochlorophyllides was demonstrated by spectroscopic methods, as well by the formation of aggregates in toluene. 相似文献
97.
We investigated the features of the glass transition relaxation of two room temperature ionic liquids using DSC. An important
observation was that the heat capacity jump, that is the signature of the glass transition relaxation, shows a particularly
strong value in this type of new and promising materials, candidates for a range of applications. This suggests a high degree
of molecular mobility in the supercooled liquid state. The study of the influence of the heating rate on the temperature location
of the glass transition signal, allowed the determination of the activation energy at the glass transition temperature, and
the calculation of the fragility index of these two ionic glass-formers. It was concluded that this kind of materials belong
to the class of relatively strong glass-forming systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
Kaname SasakiHideyuki Nagai Shuichi MatsumuraKazunobu Toshima 《Tetrahedron letters》2003,44(30):5605-5608
The glycosidations of glucopyranosyl diethyl phosphite and alcohols using an ionic liquid, 1-n-hexyl-3-methylimidazolium trifluoromethanesulfonimidide (C6mim[NTf2]) containing a protic acid, trifluoromethanesulfonimide (HNTf2), as a novel solvent-catalyst system, effectively proceeded under mild conditions to give the corresponding glycosides in good to high yields. Furthermore, this acid-ionic liquid combination could be reused many times for the glycosidations without any loss in efficiency. 相似文献
99.
Summary Samples of synthetic leucite and boron-substituted leucite are investigated by infrared spectroscopy and spectrally resolved
thermoluminescence. Evidence is obtained in favour of the assumption that point defects in aluminosilicate lattices are originated
by exchanges of Si+4 and Al+3 ions lying in different cells. 相似文献
100.
光子晶体的原理与应用 总被引:1,自引:0,他引:1
光子晶体是一种在微米、亚微米等光波长量级上折射率呈现周期性变化的介质材料,它使某些频率范围内的光子态密度大大降低.甚至完全形成光子禁带.本文介绍了光子晶体的原理、制备及应用. 相似文献