全文获取类型
收费全文 | 25649篇 |
免费 | 3013篇 |
国内免费 | 5668篇 |
专业分类
化学 | 19661篇 |
晶体学 | 488篇 |
力学 | 2714篇 |
综合类 | 203篇 |
数学 | 3073篇 |
物理学 | 8191篇 |
出版年
2024年 | 60篇 |
2023年 | 294篇 |
2022年 | 842篇 |
2021年 | 845篇 |
2020年 | 903篇 |
2019年 | 814篇 |
2018年 | 723篇 |
2017年 | 829篇 |
2016年 | 1079篇 |
2015年 | 901篇 |
2014年 | 1282篇 |
2013年 | 2198篇 |
2012年 | 2078篇 |
2011年 | 1484篇 |
2010年 | 1273篇 |
2009年 | 1606篇 |
2008年 | 1755篇 |
2007年 | 1840篇 |
2006年 | 1676篇 |
2005年 | 1498篇 |
2004年 | 1282篇 |
2003年 | 1118篇 |
2002年 | 996篇 |
2001年 | 809篇 |
2000年 | 807篇 |
1999年 | 735篇 |
1998年 | 671篇 |
1997年 | 539篇 |
1996年 | 508篇 |
1995年 | 468篇 |
1994年 | 442篇 |
1993年 | 320篇 |
1992年 | 349篇 |
1991年 | 267篇 |
1990年 | 212篇 |
1989年 | 165篇 |
1988年 | 127篇 |
1987年 | 107篇 |
1986年 | 93篇 |
1985年 | 77篇 |
1984年 | 58篇 |
1983年 | 35篇 |
1982年 | 48篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1957年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
Jordi Faraudo Alex Travesset 《Colloids and surfaces. A, Physicochemical and engineering aspects》2007,300(3):287-292
In this paper, we argue that many of the fascinating electrostatic effects that take place in amphiphilic systems are strongly related to the particular organization of the oxygen atoms within each individual molecule. In particular, we focus on two effects: charge inversion and dielectric overscreening. For that purpose, we present molecular dynamics simulations of phosphatidic acid (DMPA2−) in the presence of divalent counterions. Our results show that the many oxygens present in DMPA2− cooperatively create strong binding sites for counterions, which in some cases lead to charge inversion. We also present an analysis of the role of interfacial water and relate our analysis to the phenomenon of dielectric overscreening. Several experimental implications are discussed in the conclusions. 相似文献
162.
Akira Watanabe 《Tetrahedron letters》2004,45(33):6229-6233
Oxovanadium(V)(salen) complex 4 was found to catalyze Meerwein-Ponndorf-Verley cyanation of aliphatic aldehydes with good to high enantioselectivity. This cyanation showed a positive nonlinear effect. 相似文献
163.
The first MCM-41-supported bidentate phosphine palladium(0) complex has been prepared. This complex is a highly efficient catalyst for Sonogashira reaction and can be reused at least 10 times without any decrease in activity. 相似文献
164.
The polystyrene supported glutamic acid Schiff base complex of Mn ( Ⅱ ) (PS-Sal-Glue-Mn) was prepared with chloromethylated styrene polymer beads, 2,4-dihydroxybenzaldehyde, L-glutamic acid and manganese ( Ⅱ ) acetate tetrahyrate. The polymeric ligand and the complex were characterized by FT-IR, small area X-ray photoelectron spectroscopy (XPS) and 1CP-AES. In the presence of the manganese complex, cyclohexene (1) was effectively oxidized by molecular oxygen without reductant. The major products of the reaction were 2-cyclohexen-l-ol (2), 2-cyclohexen-l-one (3) and 2-cyclohexen-1- hydroperoxide (4), which was different with typical oxidation of cyclohexene. The influence of reaction temperature and additive for oxidation had been studied. The selectivity of 2-cyclohexen-1-hydroperoxide varied with reaction time and different additives. The mechanism of cyclohexene oxidation had also been discussed. 相似文献
165.
本文报道了在RLi-配位体络合体系中阴离子聚合方法合成窄分布聚苯乙烯的研究结果.在己烷、庚烷、甲苯等溶液中合成分子量范围为10~2~10~3。的窄分布聚苯乙烯(MWD<1.10)时,以鹰爪豆矸、N,N,N’,N’-四甲基乙二胺为配位体的络合体系,聚合操作简便,效果非常好.在非极性溶剂中加一定比例的THF以后,该体系也能合成分子量范围为10~4~10~5的窄分布聚苯乙烯. 相似文献
166.
D. V. Soldatov J. A. Ripmeester 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(1-2):81-84
Inclusion of tert-butylbenzeneinto the l-D channel of the titlehost matrix results in a-[CuL2]1/3(tert-butylbenzene)inclusion compound(trigonal, space groupR =3;a = 24.495(3),c = 10.510(2) Å,V = 5461(1) Å3,Z = 9;R = 0.049). The observed guest–host mole ratio of 1/3 was confirmed by X-ray diffraction and arises from the stoichiometric filling of the larger wide segments of the channel. This contrasts with the benzene inclusion compound studied previously, where both the larger and smaller wide segments were occupied to give a 2/3 guest–host stoichiometry. A comparison of these two structures explains the experimental fact that the guest–host mole ratios for inclusions of the title host lie between values of 1/3 and 2/3for 20 different benzene derivatives. 相似文献
167.
E. P. Honig 《Rheologica Acta》1987,26(1):2-6
Equations are derived for the coaxial cylinder system in the combined oscillatory and steady-state shear mode. The limitations of the use of the various equations are presented. If the usual linear equations are used, the main limitation, in the case of oscillatory shear only, is that the frequency of measurement should be below 0.016 |
*|/(r
2
–r
1
)2. Here |
*| is the modulus of the complex viscosity, is the density of the liquid andr
1
andr
2
are the radii of the cylinders. Furthermore it is shown that there is a small error in the numerical factor of the usually applied equations. The calculations are set up in such a way that extension to higher harmonics follows in a natural way. An experimental example illustrates the use of the derived equations. 相似文献
168.
We consider the equilibrium dynamics of a system consisting of a spin interacting with an ideal Fermi gas on the lattice , 3. We present two examples: when this system is unitarily equivalent to an ideal Fermi gas or to a spin in an ideal Fermi gas without interaction between them. 相似文献
169.
We use a driving field, of the type first suggested by Evans, to generate a steady heat current in the simplest possible system, a two-dimensional periodic fluid of three hard disks. Hard-disk motion equations can be conveniently derived from repulsive constant-force or linear-force potentials by considering the infinitely repulsive limit of these potentials. We show that the isoenergetic and isokinetic forms of the nonequilibrium equations of motion generate steady-state heat conductivities differing by terms of order 1/N, whereN is the number of particles. The resulting conductivities appear to vary as the logarithm of the driving field strength. Even at low fields, the three-body periodic-system results lie well below Enskog's infinite-system prediction. 相似文献
170.
Chen-Xi Zhang Zhi-Liang Liu Dai-Zheng Liao Zong-Hui Jiang Shi-Ping Yan 《Journal of Molecular Structure》2003,650(1-3):21-26
A novel complex [Cu(NIT2Py)(PDA)(H2O)]·(CH3OH)(H2O) has been synthesized and structurally characterized by X-ray diffraction methods. It crystallizes in the monoclinic space group P2(1)/c. The structure consists of [Cu(NIT2Py)(PDA)(H2O)] moiety, one solvent methanol molecule and one water molecule. The copper(II) ion is in a distorted octahedral environment: one nitrogen atom and one oxygen atom from the NIT2Py, one nitrogen atom from the PDA (2,6-pyridine dicarboxylic acid) and one oxygen atom from the aqueous in the basal plane; two oxygen atoms from the PDA in the axial position. The units of [Cu(NIT2Py)(PDA)(H2O)] were connected as one dimension chain by the intermolecular hydrogen bonds. The complex exhibits intramolecular antiferromagnetic interactions between the Cu(II) ion and the NIT2Py. 相似文献