全文获取类型
收费全文 | 346947篇 |
免费 | 3066篇 |
国内免费 | 1049篇 |
专业分类
化学 | 177359篇 |
晶体学 | 5931篇 |
力学 | 15513篇 |
综合类 | 7篇 |
数学 | 40404篇 |
物理学 | 111848篇 |
出版年
2021年 | 2646篇 |
2020年 | 2949篇 |
2019年 | 3289篇 |
2018年 | 4318篇 |
2017年 | 4300篇 |
2016年 | 6431篇 |
2015年 | 3911篇 |
2014年 | 6239篇 |
2013年 | 15620篇 |
2012年 | 11975篇 |
2011年 | 14429篇 |
2010年 | 10178篇 |
2009年 | 10083篇 |
2008年 | 13299篇 |
2007年 | 13274篇 |
2006年 | 12670篇 |
2005年 | 11343篇 |
2004年 | 10568篇 |
2003年 | 9398篇 |
2002年 | 9146篇 |
2001年 | 10495篇 |
2000年 | 7989篇 |
1999年 | 6198篇 |
1998年 | 5098篇 |
1997年 | 5027篇 |
1996年 | 4663篇 |
1995年 | 4389篇 |
1994年 | 4224篇 |
1993年 | 4027篇 |
1992年 | 4597篇 |
1991年 | 4533篇 |
1990年 | 4414篇 |
1989年 | 4162篇 |
1988年 | 4220篇 |
1987年 | 4253篇 |
1986年 | 3962篇 |
1985年 | 5203篇 |
1984年 | 5472篇 |
1983年 | 4653篇 |
1982年 | 4891篇 |
1981年 | 4700篇 |
1980年 | 4576篇 |
1979年 | 4771篇 |
1978年 | 4898篇 |
1977年 | 4838篇 |
1976年 | 4937篇 |
1975年 | 4686篇 |
1974年 | 4631篇 |
1973年 | 4894篇 |
1972年 | 3175篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
We study a generalization of the notion of the chromatic number of a graph in which the colors assigned to adjacent vertices are required to be, in a certain sense, far apart. © 1993 John Wiley & Sons, Inc. 相似文献
62.
F. Rubio F. García H. D. Burrows A. A. C. C. Pais A. J. M. Valente M. J. Tapia J. M. García 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1788-1799
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007 相似文献
63.
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. 相似文献
64.
The effect of hydrostatic pressure on the structure of a plastic columnar discotic triphenylene has been investigated. The goal was to determine whether pressure can be used to modify electronic properties via changes in structural properties of columnar discotics to any significant extent. The findings are that (i) the intra- and inter-columnar distances are reduced in a nearly isotropic fashion, (ii) that the crystal sizes are reduced and (iii) that a transition takes place from a more highly ordered plastic columnar to a less ordered hexagonal columnar state with increasing pressure. The induced decrease of the molecular distances, amounting to 6% for pressures up to 17 kbar, are clearly too small to induce an appreciable modification of the electronic structure and thus opto-electronic properties. 相似文献
65.
66.
B. Ghosh 《等离子体物理论文集》1989,29(2):125-134
To describe the long time asymptotic behaviour of weakly nonlinear plasma waves propagating in a strongly magnetized plasmafilled cylindrical waveguide the usual KDV equation which is first order in wave amplitude is extended to second order including the effects of finite temperature, mobile ions and giving a proper treatment to the radial co-ordinate for all possible modes of propagation. The second-order effects on the first-order solitary wave profile, phase speed and first order correction to the wavelength are all determined and discussed. 相似文献
67.
Myron B. Allen Mark C. Curran 《Numerical Methods for Partial Differential Equations》1989,5(2):121-132
An adaptive grid refinement procedure allows accurate solutions to advection-dominated, time-dependent flows using finite-element collocation. The technique relies on a data structure that is readily amenable to parallel computing. The paper discusses computational aspects of the method. 相似文献
68.
We consider three one-dimensional quantum, charged and spinless particles interacting through delta potentials. We derive
sufficient conditions which guarantee the existence of at least one bound state. 相似文献
69.
V. B. Levenshtam 《Siberian Mathematical Journal》1989,30(4):554-559
Rostov-on-Don. Translated from Sibirskii Matematicheskii Zhurnal, Vol. 30, No. 4, pp. 69–75, July–August, 1989. 相似文献
70.
Butyltins were analyzed in waters from California river and lake marinas and were detected at the part per trillion (ppt) level in most locations. The tributyltin:dibutyltin (TBT/DBT) ratios in the fresh waters were similar to those in their saline counterparts indicating like rates of degradation in the two salinity regimes. 相似文献