全文获取类型
收费全文 | 33745篇 |
免费 | 5242篇 |
国内免费 | 6111篇 |
专业分类
化学 | 26214篇 |
晶体学 | 2797篇 |
力学 | 2043篇 |
综合类 | 204篇 |
数学 | 1556篇 |
物理学 | 12284篇 |
出版年
2024年 | 47篇 |
2023年 | 298篇 |
2022年 | 701篇 |
2021年 | 790篇 |
2020年 | 1115篇 |
2019年 | 1042篇 |
2018年 | 1043篇 |
2017年 | 1247篇 |
2016年 | 1605篇 |
2015年 | 1333篇 |
2014年 | 1962篇 |
2013年 | 3530篇 |
2012年 | 2171篇 |
2011年 | 2098篇 |
2010年 | 1872篇 |
2009年 | 2071篇 |
2008年 | 2205篇 |
2007年 | 2333篇 |
2006年 | 2284篇 |
2005年 | 2057篇 |
2004年 | 1999篇 |
2003年 | 1636篇 |
2002年 | 1309篇 |
2001年 | 1020篇 |
2000年 | 1005篇 |
1999年 | 924篇 |
1998年 | 826篇 |
1997年 | 687篇 |
1996年 | 727篇 |
1995年 | 623篇 |
1994年 | 588篇 |
1993年 | 446篇 |
1992年 | 415篇 |
1991年 | 265篇 |
1990年 | 142篇 |
1989年 | 134篇 |
1988年 | 114篇 |
1987年 | 86篇 |
1986年 | 63篇 |
1985年 | 71篇 |
1984年 | 55篇 |
1983年 | 21篇 |
1982年 | 34篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
陈海珍 《宁波大学学报(理工版)》2004,17(4):444-448
选用了钛酸丁酯、硬脂酸和乙二醇作为表面活性剂,采用表面化学修饰和表面物理修饰2种方法修饰纳米氧化钛,然后分散在乙二醇溶剂中形成溶胶溶液.并通过红外光谱仪、紫外分光计、原子力显微镜,分析了表面化学修饰后的纳米氧化钛表面化学结构的变化,观测了纳米氧化钛溶胶在乙二醇溶剂中稳定性.试验结果表明表面活性剂与纳米氧化钛的表面的不饱和键之间形成了新的化学结构,粒子表面可能接枝上有机长链,提高了纳米粒子在溶剂中的相容性.表面化学修饰后的纳米氧化钛与乙二醇溶剂形成了较稳定的溶胶体系,而且纳米溶胶粒径较小.表面活性剂添加量与纳米粒子添加量控制在(1~1.2):1时,可以获得纳米溶胶粒径较小,同时溶胶稳定性较好的纳米氧化钛-乙二醇溶胶体系. 相似文献
62.
The title compound is a centrosymmetric dimer with each cadmium in a distorted CdS5 square pyramidal geometry. The Cd–S bond distances range from 2.5626(11) to 2.8459(11) Å. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
63.
A lithium(I) coordination polymer has been formed from LiClO4 and the 2,2′‐bipyrimidine (bpym) ligand in which each square pyramidal lithium(I) atom is coordinated in the basal plane by four nitrogen donor atoms derived from two bpym ligands and one water molecule at the apical position. These are connected into a layer structure via hydrogen‐bonding interactions involving the perchlorate anions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
64.
Richard Brown 《Geometriae Dedicata》2003,97(1):129-150
In this note, we show that given a closed, orientable genus-g surface S
g
, any hyperbolic toral automorphism has a positive power which induces a quadratic, orientable pseudo-Anosov homeomorphism on S
g
. To show this, we lift Anosov toral automorphisms through a ramified topological covering and present the lifted homeomorphism via a standard set of Lickorish twists. This construction provides a general method of producing pseudo-Anosov maps of closed surfaces with predetermined orientable foliations and quadratic dilatation. Since these lifted automorphisms have orientable foliations, this construction is a sort of converse to that of Franks and Rykken [Trans. Amer. Math. Soc. 1999], who established that one can associate to a quadratic pseudo-Anosov homeomorphism with oriented unstable foliation a hyperbolic toral automorphism. 相似文献
65.
A group representation of radiation propagation in an anisotropic medium is developed. The system of wave equations for electromagnetic potentials, obtained from the Maxwell equations with account for the constitutive equations, has been factorized. It is shown that the linear differential operator of the factorized system is orthogonal in transparent crystals and unitary in gyrotropic ones and is represented through the momentum operator. On the basis of the commutation relations for the components of this operator, the eigenvalue problem has been solved and the expression for the change in the radiant energy in the crystal in the form of spherical waves has been obtained. The dependences of the ray and phase velocities and the polarization vectors of waves on the birefringence anisotropy and gyrotropy as well as on the angular momentum, displacement current, and bound charge determining them have been analyzed. It has been established that in the general case of gyrotropic crystals where the nonreciprocity phenomenon takes place and in magnetoelectrics Maxwell equations are represented in a form similar to the Dirac equations and the electromagnetic radiation is correctly described by means of bispinors and is quantized as fermions. 相似文献
66.
The title compound (C2H7NO·C7H4N2O6) has been obtained by the reaction of etha- nolamine with 3,5-dinitrobenzoic acid in deionized water at room temperature. The crystal crystal- lizes in orthorhombic, space group P212121 with a = 6.048(2), b = 9.146(3), c = 21.955(7)(A), C9H11N3O7, Mr = 273.21, Z = 4, V = 1214.3(7)(A)3, Dc = 1.494 g/cm3, F(000) = 568, μ(MoKα) = 0.131 mm-1, R1 = 0.0338 and wR2 = 0.0497. The new organic adduct is composed of one ethanolamine and one 3,5-dinitrobenzoic acid, which are linked up by O-H…O and N-H…O types of hydrogen bonds to form a nine-membered ring and an eleven-membered ring, extending into a one-dimensional network structure. 相似文献
67.
68.
热致型胆甾酯液晶的相变研究 总被引:2,自引:0,他引:2
使用偏光显微镜观察胆甾烯壬酸酯液晶的相变,发现在不同的温度变化条件下液晶相变过程是不同的.本文讨论了其变化规律. 相似文献
69.
Ray Leslie Withers Carlos Otero-Diaz Adrian Gómez-Herrero Albert Prodan Lasse Norén 《Journal of solid state chemistry》2005,178(10):3159-3168
Ternary derivatives of 1T-TaS2 have been synthesized and the variation in the highly structured diffuse intensity distributions characteristic of such materials carefully monitored to investigate the effect that such substitution has upon the band structures and Fermi surfaces (FSs) of the materials. Removal of d electrons via the replacement of Ta ions with lower valent transition metal ions leads to a systematic increase in the radii of the characteristic structured diffuse intensity distribution. Extended Hückel tight binding calculations of the FSs of the doped samples are carried out and used to predict possible nesting wave-vectors. The results are in reasonably good agreement with the radii of the experimentally observed diffuse intensity distributions. 相似文献
70.