全文获取类型
收费全文 | 26700篇 |
免费 | 3674篇 |
国内免费 | 4572篇 |
专业分类
化学 | 19366篇 |
晶体学 | 2641篇 |
力学 | 802篇 |
综合类 | 111篇 |
数学 | 301篇 |
物理学 | 11725篇 |
出版年
2024年 | 31篇 |
2023年 | 156篇 |
2022年 | 394篇 |
2021年 | 522篇 |
2020年 | 723篇 |
2019年 | 676篇 |
2018年 | 720篇 |
2017年 | 972篇 |
2016年 | 1203篇 |
2015年 | 958篇 |
2014年 | 1542篇 |
2013年 | 2657篇 |
2012年 | 1556篇 |
2011年 | 1594篇 |
2010年 | 1398篇 |
2009年 | 1656篇 |
2008年 | 1821篇 |
2007年 | 1863篇 |
2006年 | 1893篇 |
2005年 | 1763篇 |
2004年 | 1717篇 |
2003年 | 1386篇 |
2002年 | 1144篇 |
2001年 | 828篇 |
2000年 | 802篇 |
1999年 | 773篇 |
1998年 | 646篇 |
1997年 | 595篇 |
1996年 | 608篇 |
1995年 | 517篇 |
1994年 | 457篇 |
1993年 | 341篇 |
1992年 | 330篇 |
1991年 | 218篇 |
1990年 | 99篇 |
1989年 | 87篇 |
1988年 | 66篇 |
1987年 | 57篇 |
1986年 | 29篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
61.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
62.
63.
64.
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
65.
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
66.
锥形光纤间耦合特性的分析与检测 总被引:2,自引:0,他引:2
将通信光纤的末端拉制成锥形,利用光信号在光纤锥形区特有的传输和耦合特性,实现了光纤的耦合、连接和分束。用耦合模理论分析了锥形光纤间的传输和耦合性质,给出了光信号两锥形光纤间的耦合与两锥形光纤的距离和锥形区重叠长度等实验结果。 相似文献
67.
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
68.
《Fiber and Integrated Optics》2007,26(6):335-342
A fiber-optic chemical sensor (FOCS) for detection of nitrogen dioxide (NO2) molecules is reported. The FOCS presents an optropode structure because of the transmission properties of the sensitive material. The NO2 FOCS is activated by using the semiconductor polymer: regioregular head-to-tail poly(3-octylthiophene-2,5-diyl). The operation wavelength of the sensor is 543.5 nm such that a simple LED and detector can be used for the design of this device. The sensor response decreases after each exposure, demonstrating the reduction in sensitivity as well as irreversibility lower than 5%. However, its properties such as rapid response, high selectivity, high sensitivity (0.43 ± 0.01 muW/ppm), hygroscopic properties, and its operation at room temperature make this kind of FOCS a good alternative for NO2 toxic gas detection. 相似文献
69.
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
70.
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