全文获取类型
收费全文 | 114243篇 |
免费 | 6931篇 |
国内免费 | 5691篇 |
专业分类
化学 | 56409篇 |
晶体学 | 1355篇 |
力学 | 5585篇 |
综合类 | 322篇 |
数学 | 11841篇 |
物理学 | 33835篇 |
无线电 | 17518篇 |
出版年
2023年 | 1253篇 |
2022年 | 2000篇 |
2021年 | 2715篇 |
2020年 | 2803篇 |
2019年 | 3000篇 |
2018年 | 3338篇 |
2017年 | 3333篇 |
2016年 | 4020篇 |
2015年 | 2994篇 |
2014年 | 4291篇 |
2013年 | 5777篇 |
2012年 | 6016篇 |
2011年 | 6244篇 |
2010年 | 5019篇 |
2009年 | 5174篇 |
2008年 | 5413篇 |
2007年 | 5047篇 |
2006年 | 4648篇 |
2005年 | 4164篇 |
2004年 | 3579篇 |
2003年 | 3303篇 |
2002年 | 3372篇 |
2001年 | 2992篇 |
2000年 | 2387篇 |
1999年 | 1974篇 |
1998年 | 1824篇 |
1997年 | 1583篇 |
1996年 | 1497篇 |
1995年 | 1224篇 |
1994年 | 1267篇 |
1993年 | 1200篇 |
1992年 | 1176篇 |
1991年 | 1201篇 |
1990年 | 1171篇 |
1989年 | 1075篇 |
1988年 | 934篇 |
1987年 | 939篇 |
1986年 | 890篇 |
1985年 | 934篇 |
1984年 | 927篇 |
1983年 | 837篇 |
1982年 | 810篇 |
1979年 | 811篇 |
1978年 | 820篇 |
1977年 | 824篇 |
1976年 | 925篇 |
1975年 | 818篇 |
1974年 | 846篇 |
1973年 | 849篇 |
1972年 | 760篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
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
62.
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
63.
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
64.
65.
66.
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
67.
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
68.
69.
We consider a particular case of the matrix Carleman problem for two pairs of functions in a ring and find a constructive
solution of this problem. In addition, we propose an algorithm for the construction of solutions for two infinite systems
of smooth transition and for a system of two singular equations of special type.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 5, pp. 662–671, May, 1997 相似文献
70.
V. P. Evtikhiev I. V. Kudryashov E. Yu. Kotel’nikov V. E. Tokranov A. N. Titkov I. S. Tarasov Zh. I. Alferov 《Semiconductors》1998,32(12):1323-1327
The electroluminescence and stimulated emission of lasers with one layer of InAs quantum dots (QD’s) grown in a single molecular-beam
epitaxial process on vicinal GaAs(001) surfaces misoriented in the direction [010] by 2, 4 and 6° are investigated. It is
discovered that an increase in the misorientation angle leads to a blue shift and a decrease in the full width at half maximum
(FWHM) of the electroluminescence spectrum. This effect is attributed to a decrease in the size of the quantum dots and improvement
in their size uniformity. A strong dependence of the threshold current density on the width of the spontaneous luminescence
spectrum is discovered. The room-temperature threshold current density of the lasers with one layer of quantum dots and the
spontaneous luminescence spectrum having the smallest FWHM (54 meV) equals 210 A/cm2.
Fiz. Tekh. Poluprovodn. 32, 1482–1486 (December 1998) 相似文献