全文获取类型
收费全文 | 348781篇 |
免费 | 7420篇 |
国内免费 | 5245篇 |
专业分类
化学 | 188360篇 |
晶体学 | 5255篇 |
力学 | 16916篇 |
综合类 | 331篇 |
数学 | 40177篇 |
物理学 | 110407篇 |
出版年
2021年 | 3612篇 |
2020年 | 4102篇 |
2019年 | 4450篇 |
2018年 | 5550篇 |
2017年 | 5448篇 |
2016年 | 7451篇 |
2015年 | 4848篇 |
2014年 | 7317篇 |
2013年 | 15026篇 |
2012年 | 12557篇 |
2011年 | 14542篇 |
2010年 | 10736篇 |
2009年 | 10455篇 |
2008年 | 13139篇 |
2007年 | 13007篇 |
2006年 | 12056篇 |
2005年 | 10876篇 |
2004年 | 9885篇 |
2003年 | 8928篇 |
2002年 | 9003篇 |
2001年 | 9372篇 |
2000年 | 7306篇 |
1999年 | 5724篇 |
1998年 | 5155篇 |
1997年 | 4946篇 |
1996年 | 4693篇 |
1995年 | 4252篇 |
1994年 | 4449篇 |
1993年 | 4104篇 |
1992年 | 4516篇 |
1991年 | 4562篇 |
1990年 | 4495篇 |
1989年 | 4257篇 |
1988年 | 4280篇 |
1987年 | 4137篇 |
1986年 | 3965篇 |
1985年 | 5062篇 |
1984年 | 5310篇 |
1983年 | 4471篇 |
1982年 | 4590篇 |
1981年 | 4464篇 |
1980年 | 4371篇 |
1979年 | 4465篇 |
1978年 | 4781篇 |
1977年 | 4708篇 |
1976年 | 4832篇 |
1975年 | 4430篇 |
1974年 | 4517篇 |
1973年 | 4672篇 |
1972年 | 3422篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Ph. Komninou Th. Kehagias A. Delimitis G.P. Dimitrakopulos J. Kioseoglou E. Dimakis A. Georgakilas Th. Karakostas 《Superlattices and Microstructures》2004,36(4-6):509
The structural properties of InN thin films, grown by rf plasma-assisted molecular beam epitaxy on Ga-face GaN/Al2O3(0001) substrates, were investigated by means of conventional and high resolution electron microscopy. Our observations showed that a uniform InN film of total thickness up to 1 μm could be readily grown on GaN without any indication of columnar growth. A clear epitaxial orientation relationship of , was determined. The quality of the InN film was rather good, having threading dislocations as the dominant structural defect with a density in the range of 109–1010 cm−2. The crystal lattice parameters of wurtzite InN were estimated by electron diffraction analysis to be a=0.354 nm and c=0.569 nm, using Al2O3 as the reference crystal. Heteroepitaxial growth of InN on GaN was accomplished by the introduction of a network of three regularly spaced misfit dislocation arrays at the atomically flat interface plane. The experimentally measured distance of misfit dislocations was 2.72 nm. This is in good agreement with the theoretical value derived from the in-plane lattice mismatch of InN and GaN, which indicated that nearly full relaxation of the interfacial strain between the two crystal lattices was achieved. 相似文献
112.
Sanzhizhapov D. B. Tonevitskii Yu. V. Mognonov D. M. Doroshenko Yu. E. 《Russian Journal of Applied Chemistry》2003,76(4):619-622
New polyimidates were prepared from bisphenols and mono- and dicarboxylic acid imidoyl chlorides. The structures of the polymers were determined, and their physicochemical, chemical, and thermal properties were studied. The possibility of preparing film and compression materials with good mechanical characteristics from these polymers was examined. 相似文献
113.
Hongyi Yu 《应用数学学报(英文版)》1991,7(3):284-288
In this paper, we study the PBVP for integro-differential equations of Volterra type in Banach spaces. By developing monotone iterative technique for the PBVP, we get some results concerning the existence of extremal solutions, which are the limits of monotone sequences.The project supported by the Natural Science Foundation of Shandong Province. 相似文献
114.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献
115.
116.
A. G. Chentsov 《Journal of Mathematical Sciences》2007,140(6):873-904
The paper considers the representations of attraction sets in topological spaces and their relations with the relaxation of
accessibility problems under the conditions of sequentially relaxed constraints. The author studies the structure of approximate
(in essence, asymptotic) solutions and generalized elements and establishes the possibility of their real identification for
a certain version (related to the Stone-Čech compactification and the Wallman relaxation) of relaxation of the initial problem.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 26, Nonlinear
Dynamics, 2005. 相似文献
117.
118.
The paper considers the problem of constructing an efficient automatic procedure for reducing the block size in the block conjugate gradient method insuring that the resulting rate of convergence is comparable with that of the block conjugate gradient method with constant block size. The numerical results provided show that, independently of the type of distribution of the smallest eigenvalues of the preconditioned matrix, the procedure suggested always leads to a decrease of the arithmetic costs with respect to those of the block method with constant block size. Bibliography: 8 titles. 相似文献
119.
M. Yu. Kulikov 《Radiophysics and Quantum Electronics》2004,47(9):662-673
On the example of the effect of an atmospheric wave with given amplitude on the density oscillations of minor gas constituents near the mesopause (at heights 80–90 km, we consider the influence of the quasi-resonant periodic spatial transport on a distributed system responding subharmonically to a periodic external action (diurnal sunlight variations). Numerical modeling revealed the formation of a coherent horizontal distribution of the dynamical variables (i.e., the concentrations of small constituents). Application of this effect to the mesopause conditions is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 9, pp. 739–752, September, 2004. 相似文献
120.
W. G. Habashi G. Baruzzi M. F. Peeters M. M. Hafez 《Numerical Methods for Partial Differential Equations》1991,7(2):193-207
Finite element solutions of the Euler and Navier-Stokes equations are presented, using a simple dissipation model. The discretization is based on the weak-Galerkin weighted residual method and equal interpolation functions for all the unknowns are permitted. The nonlinearity is iterated upon using a Newton method and at each iteration the linear algebraic system is solved by a direct solver with all unknowns fully coupled. Results are presented for two-dimensional transonic inviscid flows and two- and three-dimensional incompressible viscous flows. Convergence of the algorithm is shown to be quadratic, reaching machine accuracy in very few iterations. The inviscid results demonstrate the existence of nonunique numerical solutions to the steady Euler equations. 相似文献