全文获取类型
收费全文 | 42308篇 |
免费 | 597篇 |
国内免费 | 359篇 |
专业分类
化学 | 19092篇 |
晶体学 | 393篇 |
力学 | 1692篇 |
综合类 | 13篇 |
数学 | 11194篇 |
物理学 | 10880篇 |
出版年
2021年 | 268篇 |
2020年 | 269篇 |
2019年 | 296篇 |
2018年 | 1370篇 |
2017年 | 1644篇 |
2016年 | 1182篇 |
2015年 | 916篇 |
2014年 | 871篇 |
2013年 | 1427篇 |
2012年 | 3795篇 |
2011年 | 3080篇 |
2010年 | 2282篇 |
2009年 | 2009篇 |
2008年 | 1189篇 |
2007年 | 1289篇 |
2006年 | 1123篇 |
2005年 | 4971篇 |
2004年 | 4369篇 |
2003年 | 2683篇 |
2002年 | 867篇 |
2001年 | 493篇 |
2000年 | 294篇 |
1999年 | 330篇 |
1998年 | 269篇 |
1997年 | 234篇 |
1996年 | 222篇 |
1995年 | 191篇 |
1994年 | 182篇 |
1993年 | 187篇 |
1992年 | 298篇 |
1991年 | 274篇 |
1990年 | 259篇 |
1989年 | 223篇 |
1988年 | 187篇 |
1987年 | 175篇 |
1986年 | 142篇 |
1985年 | 190篇 |
1984年 | 187篇 |
1983年 | 160篇 |
1982年 | 139篇 |
1981年 | 139篇 |
1980年 | 119篇 |
1979年 | 152篇 |
1978年 | 144篇 |
1976年 | 174篇 |
1975年 | 142篇 |
1974年 | 135篇 |
1973年 | 123篇 |
1972年 | 103篇 |
1966年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 623 毫秒
21.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
22.
In order to investigate the relative effects of the differences between the structures and lipophilicities of 1, 10-dioxa-4, 7, 13, 16-tetra-azacyclo-octadecane (TA-18-crown-6) and the tetrabenzyl derivative of 1,10-dioxa-4, 7, 13, 16-tetra-azacyclo-octadecane (TBTA-18-crown-6) on their extraction-abilities and -selectivities for transition metal cations, constants of the overall extraction (logK
ex) of 1:1 (M:L) complexes, the distribution (K
D) for two diluents (CH2Cl2 and CHCl3) with different dielectric constants have been determined at 25 ± 0.1 °C. The magnitude of logK
ex is largely determined by that of K
D. The equilibrium constants of TA-18-crown-6 have been compared with those of TBTA-18-crown-6. It is found that:(i) logK
ex sequences of TA-18-crown-6 and TBTA-18-crown-6 for transition metals in CH2Cl2 lie in order: Fe3+ > Cu2+ > Mn2+ > Co2+ > Cd2+ > Ni2+ > Zn2+ and Fe3+ > Cu2+ > Co2+ > Mn2+ > Ni2+ > Cd2+ > Zn2+ respectively; (ii) the stability sequences of two types of tetra-aza-crown ethers with the transition metal cations in CHCl3 are the same as follows: Fe3+ > Ni2+ > Cu2+ > Co2+ > Zn2+ > Cd2+ > Mn2+, and (iii) unusual selectivities are observed for transition metal-tetra-aza-crowns, e.g. the high Fe3+/M
n+ selectivity factors (Sf) of TA-18-crown-6, except for the competitive-extractions for the special case in CHCl3 of TBTA-18-crown-6, it was found that the Mn2+/M
n+ values were relatively higher according to the other transition metal cations. A systematic sequence in these two types of solvents is not found for a given transition metal cation in terms of the variation of selectivity with the tetra-aza-crown ethers. The results provide alternatives for the rational design of other specific ligands on the transition metal cations. 相似文献
23.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献
24.
S. B. Ellis S. J. Kiehl W. S. Hughes K. Schwabe W. C. Gardiner H. L. Sanders H. Yoshimura Hanna Jablezynska-Jedrzewska J. Domański W. A. Dorfman P. Nylén Barbara Stone F. Hovorka W. C. Dearing E. Biilmann W. Kordatzki P. Wulff G. Florence A. Drilhon P. Szigeti O. Tomiček F. Poupě O. Redlich W. Stricks 《Analytical and bioanalytical chemistry》1937,111(2-4):94-104
25.
Amorphization of Al32Ge68 at normal pressure, starting from the thermobarically quenched high-pressure crystalline metallic γ-phase, was studied in a slow heating run by performing NMR field-sweep experiments. In the temperature interval from 77 to 300 K the 27Al central line exhibits a continuous broadening and a positive frequency shift. Close to 300 K rather abrupt changes were observed, where the shift changed its sign, and the line width jumped to its highest value. The discontinuous course of the phase changes indicates that the amorphization process proceeds via a sequence of intermediate metastable states, which can be ‘overheated’ in a slow heating run and consequently transform in an explosion-like manner to the final amorphous state at a well-defined temperature. The frequency shift could be decomposed into the negative second-order quadrupolar shift and the positive Knight shift. The change of the shift sign from positive to negative at 300 K reflects the vanishing tendency of the Knight shift upon heating and is compatible with the conduction-electron localization upon structure amorphization. 相似文献
26.
Jan Schmidt 《Mathematische Semesterberichte》2007,54(2):261-301
Ohne Zusammenfassung 相似文献
27.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented. 相似文献
28.
29.
Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations. 相似文献
30.
Micha? Chmielewski 《Tetrahedron letters》2004,45(31):6007-6010
Comparison of the anion binding properties of a series of uncharged macrocyclic tetraamides reveal significant effects of the receptor's size on the strength of its anion complexes. This study allowed for estimation of the optimal size of a macroring for complexation of common anions. 相似文献