全文获取类型
收费全文 | 411753篇 |
免费 | 13506篇 |
国内免费 | 8279篇 |
专业分类
化学 | 234667篇 |
晶体学 | 5437篇 |
力学 | 19117篇 |
综合类 | 580篇 |
数学 | 46524篇 |
物理学 | 127213篇 |
出版年
2022年 | 3959篇 |
2021年 | 4738篇 |
2020年 | 5135篇 |
2019年 | 5258篇 |
2018年 | 5818篇 |
2017年 | 5627篇 |
2016年 | 8558篇 |
2015年 | 6686篇 |
2014年 | 9079篇 |
2013年 | 18897篇 |
2012年 | 17166篇 |
2011年 | 19970篇 |
2010年 | 13819篇 |
2009年 | 13678篇 |
2008年 | 17242篇 |
2007年 | 17014篇 |
2006年 | 15976篇 |
2005年 | 14498篇 |
2004年 | 12616篇 |
2003年 | 10895篇 |
2002年 | 10620篇 |
2001年 | 11350篇 |
2000年 | 8977篇 |
1999年 | 7238篇 |
1998年 | 6153篇 |
1997年 | 5950篇 |
1996年 | 5813篇 |
1995年 | 5241篇 |
1994年 | 5212篇 |
1993年 | 4877篇 |
1992年 | 5188篇 |
1991年 | 5263篇 |
1990年 | 4829篇 |
1989年 | 4635篇 |
1988年 | 4433篇 |
1987年 | 4307篇 |
1986年 | 4206篇 |
1985年 | 5414篇 |
1984年 | 5486篇 |
1983年 | 4577篇 |
1982年 | 4894篇 |
1981年 | 4555篇 |
1980年 | 4276篇 |
1979年 | 4552篇 |
1978年 | 4880篇 |
1977年 | 4802篇 |
1976年 | 4887篇 |
1975年 | 4546篇 |
1974年 | 4681篇 |
1973年 | 4732篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
P. C. Chen 《中国化学会会志》1995,42(5):755-760
Three ab initio calculations (HF/6-3IG, HF/6-3IG*, and HF/6-3IG**) on 2,4,6-trinitrotoluene were made, The results compare well with xray data, except dihedral angles of NO2 relative to the plane of the benzene ring. The deviations are attributed to packing forces and steric effects in the crystal. The most stable structure was a torsional angle 10° of the methyl top with the benzene ring, unlike toluene. The rotational barriers of the methyl top and the 4-nitro group are small. Hydrogen bonding, dipole moments and total atomic charges arc calculated. 相似文献
152.
153.
Studies show that branching the side chains of hexakis(acoyloxy)-benzenes (HAB) and -cyclohexanes (HAChx) does not modify the structure of the discotic mesophase formed. Shear fields appear to act on entire columns, not on individual discs, thereby causing alignment of columns in the shear direction. X-ray diffraction patterns of samples at temperatures between 30°C and 40°C above the clearing temperature provide evidence for the presence of mesophase order. 相似文献
154.
The reaction of CH3 with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 1013 cm3/mol-s was measured for removal of OH by CH3. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (?75%) for the removal of OH by CH3 at these conditions is their combination to form CH3OH. Rate coefficients of (5.3 ± 0.8) × 1012 and (9.0 ± 1.4) × 1012 cm3/mol-s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure. 相似文献
155.
156.
Novel 3-phenyloxy substituted propane-1,2-diol derivatives, 4-(4-n-hexyloxyphenyl)-butane-1,2-diol and 4-(trans-4-n-pyropylcyclohexyl)-butane-1,2-diol have been synthesized and their thermal behaviour has been studied. These compounds exhibit thermotropic and, after addition of water, also lyotropic liquid-crystalline behaviour. The clearing temperatures of the smectic mesophases were found to be strongly dependent on the alkyl chain length and on the structural units that link the aromatic ring to the alkyl chain and to the diol unit. The behaviour of the aromatic compounds is compared with that of the cyclohexane derivative. Thereby it has been realized that the mesophase stability of the amphiphilic diols incorporating a rigid unit is largely determined by both, the molecular geometry (molecular shape and intramolecular flexibility) and the amphiphilic structural pattern. 相似文献
157.
F. J. M. Farley 《Zeitschrift fur Physik C Particles and Fields》1992,56(Z1):S88-S96
Measurements of the anomalous magnetic moment of the muon are reviewed. The emphasis is put on the first one of a series of
three CERN experiments which led to an experimental value ofa=1165922.9 (8.5)·10−9 (±7.2ppm), and which compares well with the present theoretical resulta=1165919.2 (1.8)·10−9 (±1.5ppm). 相似文献
158.
159.
1989年发表的Bager第五图,包含关于三角形元素的35个二次规范画数之间的51个不等式通过细致的分析,本文给出了其中遗漏的12个基本不等式 相似文献
160.
A new microscopic model of anomalous muonium for the elemental semiconductors is proposed. The relevant configuration consisting
of both a diamagrentic molecule Si−Mu and an unpaired orbital e− is contained into a semivacancy of the real lattice. By using the unrestricted Hartree-Fock computational method the principal
properties of the system are established. A dynamical version of the model together with a question on the formation of such
system are discussed. 相似文献