全文获取类型
收费全文 | 319509篇 |
免费 | 3542篇 |
国内免费 | 943篇 |
专业分类
化学 | 178372篇 |
晶体学 | 5193篇 |
力学 | 13147篇 |
综合类 | 7篇 |
数学 | 31083篇 |
物理学 | 96192篇 |
出版年
2018年 | 2809篇 |
2017年 | 2782篇 |
2016年 | 4629篇 |
2015年 | 3112篇 |
2014年 | 4595篇 |
2013年 | 13228篇 |
2012年 | 9631篇 |
2011年 | 11804篇 |
2010年 | 8096篇 |
2009年 | 8046篇 |
2008年 | 10975篇 |
2007年 | 10865篇 |
2006年 | 10472篇 |
2005年 | 9580篇 |
2004年 | 8660篇 |
2003年 | 7903篇 |
2002年 | 7659篇 |
2001年 | 10070篇 |
2000年 | 7533篇 |
1999年 | 5910篇 |
1998年 | 4461篇 |
1997年 | 4586篇 |
1996年 | 4437篇 |
1995年 | 4099篇 |
1994年 | 4006篇 |
1993年 | 3725篇 |
1992年 | 4534篇 |
1991年 | 4519篇 |
1990年 | 4344篇 |
1989年 | 4326篇 |
1988年 | 4222篇 |
1987年 | 4246篇 |
1986年 | 3960篇 |
1985年 | 5188篇 |
1984年 | 5244篇 |
1983年 | 4323篇 |
1982年 | 4493篇 |
1981年 | 4316篇 |
1980年 | 4227篇 |
1979年 | 4570篇 |
1978年 | 4937篇 |
1977年 | 4691篇 |
1976年 | 4597篇 |
1975年 | 4374篇 |
1974年 | 4290篇 |
1973年 | 4347篇 |
1972年 | 2888篇 |
1968年 | 2720篇 |
1967年 | 2793篇 |
1966年 | 2457篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
991.
The problem with unknown boundaries for a first-order semilinear hyperbolic system is studied in the case where the curve of definition of the initial conditions degenerates to a point. An existence and uniqueness theorem for a classical solution of the problem is proved for small t. 相似文献
992.
Details are given of a new method allowing an exact calculation of the spontaneous magnetization in the corner as well as along the edge at an arbitrary distance of the corner for a rectangular planar Ising ferromagnet. 相似文献
993.
Diane L. Levesque Eng-Chi Wang Dau-Chang Wei Cherng-Chyi Tzeng Raymond P. Panzica Fardos N. M. Naguib Mahmoud H. El Kouni 《Journal of heterocyclic chemistry》1993,30(5):1399-1404
A new series of potent uridine phosphorylase inhibitors have been prepared from barbituric acid. Among them, 1-[(2-hydroxyethoxy)methyl]-5-)(m--benzyloxy)benzylbarbituric acid ( 37 , BBBA) is the most promising having a Ki value of 1.1 ± 0.2 nM with uridine phosphorylase from human liver. The new inhibitors are easily synthesized and are better inhibitors of human uridine phosphorylase than their uracil counterparts. 相似文献
994.
After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results. 相似文献
995.
L. B. Sjogren H. -X. L. Liu X. -H. Qin C. W. Domier N. C. Luhmann 《International Journal of Infrared and Millimeter Waves》1993,14(6):1201-1216
Device alternatives for millimeter-wave beam control arrays are examined. For the control function, a wide range of semiconductor device as well as bulk material alternatives are considered. In addition, alternatives to the traditional metal strip are considered for the passive electromagnetic array element. This work should provide a broader perspective regarding the choices available for the optimized design of new beam control arrays. 相似文献
996.
Veerasingam R. Campbell R.B. Mcgrath R.T. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):688-697
A one-dimensional multispecies model of a helium filled AC plasma display cell is described. The model includes a continuity equation for each species. Poisson's equation and a circuit equation. The fill gas is helium for which the cross sections for ionization and excitation for the various atomic states are well known. The reaction rates for the different species were parametrized as functions of E/N using a zero-dimensional spatial and two velocity multispecies Boltzmann kinetic code. Calculations are performed using address and sustain voltages operating at a frequency of 50 kHz to model the pulse behavior of a dielectric barrier discharge which occurs over a time scale on the order of 200 ns or less. The code simulates multipulse behavior and shows reasonably good agreement with experimental data. The simulations show that the circuit filters out the discharge dynamics and that the pulse width of the discharge current depends on the circuit RC time constant. Using a 123 V sustain voltage, the calculated discharge current is 0.4 A with a full width at half maximum (FWHM) of 28 ns. Experimental values using a 120 V sustain voltage are 0.32 A discharge current and 42 ns FWHM 相似文献
997.
Heat transfer in lattice BGK modeled fluid 总被引:1,自引:0,他引:1
The thermal lattice BGK model is a recently suggested numerical tool aiming at solving problems of thermohydrodynamics. The quality of the lattice BGK simulation is checked in this paper by calculating temperature profiles in the Couette flow under different Eckert and Mach numbers. A revised lower order model is proposed to improve the accuracy and the higher order model is proved to be advantageous in this respect, especially in the flow regime with a higher Mach number. 相似文献
998.
The detailed characterization of multifunctional hybrid organosilazane/organosilylamine telechelic oligomers by IR and 1H, 13C and 29Si NMR spectroscopy in one and two dimenions has been undertaken. The specific multifunctional oligomers, comprising NH/NH2 or SiCl functionalities depending on the monomer feed-ratio, were prepared from mono- and di-functionally reacted dichlorodimethylsilane (DDS) and mono-, di-, tri- and tetra-functionally reacted ethylenediamine (EDA). Varying the feed-ratio afforded control of the microstructures of the oligomers and the preparation of oligomers with, in some cases, conterminously located silicon–chlorine (SiCl) groups. The combination of the NMR methods with the IR technique has enabled the detailed microstructural characterization of the oligomers and the identification of the functionalities therein. This approach and the knowledge gained from the DDS/EDA system has been applied to the microstructural characterization of other hybrid organosilazane/silylamine preceramic telechelic oligomers. 相似文献
999.
1000.
Summary A new buffer system for the separation of cations with capillary electrophoresis using indirect UV-detection is described. p-Aminopyridine can be used in the wide pH-range between 3 and 10. High-speed separations of positively charged non-UV absorbing ions are possible. Separation of ions with similar mobilities can be achieved by the addition of complexation reagents. The separation of potassium and ammonium is possible either with the addition of crown ether or at high pH-values. Transition metals can be separated by adding 2-hydroxybutyric acid to the buffer.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献