全文获取类型
收费全文 | 117589篇 |
免费 | 10605篇 |
国内免费 | 12481篇 |
专业分类
化学 | 39707篇 |
晶体学 | 2105篇 |
力学 | 10592篇 |
综合类 | 813篇 |
数学 | 17023篇 |
物理学 | 22238篇 |
综合类 | 48197篇 |
出版年
2024年 | 273篇 |
2023年 | 1063篇 |
2022年 | 2062篇 |
2021年 | 2352篇 |
2020年 | 2865篇 |
2019年 | 2660篇 |
2018年 | 2456篇 |
2017年 | 3372篇 |
2016年 | 3720篇 |
2015年 | 3603篇 |
2014年 | 5623篇 |
2013年 | 7319篇 |
2012年 | 6920篇 |
2011年 | 7864篇 |
2010年 | 6443篇 |
2009年 | 7391篇 |
2008年 | 7073篇 |
2007年 | 8075篇 |
2006年 | 7144篇 |
2005年 | 6669篇 |
2004年 | 5888篇 |
2003年 | 5250篇 |
2002年 | 4590篇 |
2001年 | 3885篇 |
2000年 | 3573篇 |
1999年 | 3194篇 |
1998年 | 2687篇 |
1997年 | 2447篇 |
1996年 | 2154篇 |
1995年 | 1919篇 |
1994年 | 1713篇 |
1993年 | 1512篇 |
1992年 | 1346篇 |
1991年 | 1118篇 |
1990年 | 962篇 |
1989年 | 821篇 |
1988年 | 720篇 |
1987年 | 498篇 |
1986年 | 305篇 |
1985年 | 225篇 |
1984年 | 183篇 |
1983年 | 96篇 |
1982年 | 127篇 |
1981年 | 98篇 |
1980年 | 77篇 |
1979年 | 86篇 |
1978年 | 65篇 |
1977年 | 64篇 |
1976年 | 28篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
331.
其中m,P,q>1.利用试验函数方法,首先推导一些积分不等式,然后对方程组爆破解的生命跨度 [0,T)给出估计. 相似文献
332.
A. B. Vasil’eva A. A. Plotnikov 《Computational Mathematics and Mathematical Physics》2006,46(5):762-767
A singularly perturbed parabolic equation with a nonlinear right-hand side of a special form is examined. A numerical analytical study of such equations is performed. 相似文献
333.
O. Yu. Dashkova 《Algebra and Logic》2007,46(5):297-302
We are concerned with infinite-dimensional locally soluble linear groups of infinite central dimension that are not soluble
A3-groups and all of whose proper subgroups, which are not soluble A3-groups, have finite central dimension. The structure of groups in this class is described. The case of infinite-dimensional
locally nilpotent linear groups satisfying the specified conditions is treated separately. A similar problem is solved for
infinite-dimensional locally soluble linear groups of infinite fundamental dimension that are not soluble A3-groups and all of whose proper subgroups, which are not soluble A3-groups, have finite fundamental dimension.
__________
Translated from Algebra i Logika, Vol. 46, No. 5, pp. 548–559, September–October, 2007. 相似文献
334.
尚英姿 《武汉大学学报(理学版)》2007,53(1):37-40
为了解决蛋白质三维结构比对需要处理大量的旋转、平移变换,直接用动态规划将变得十分繁琐这一问题,在保留蛋白质空间结构属性特征的基础上,对蛋白质三维数据进行了预先的处理.通过计算蛋白质结构在旋转和平移下的几何不变量,将蛋白质的三维结构坐标变换为具有旋转、平移不变性的一维序列.进一步给出了“距离”以及“相似得分”的定义.在此基础上采用动态规划方法给出了新的蛋白质结构比对算法.对专家分类的蛋白质结构数据库进行测试,结果显示准确、快速. 相似文献
335.
D.L. Skuratov Yu.L. Ratis I.A. Selezneva J. Pérez P. Fernández de Córdoba J.F. Urchueguía 《Applied Mathematical Modelling》2007
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method. 相似文献
336.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
337.
338.
In this paper we describe the design and manufacture of an axial-torsion test specimen, and provide relationships needed when
conducting stress-strain characterization experiments with the specimen. The specimen is a short hollow cylinder of rubber
bonded between two steel mounting rings, in which simultaneous axial and shear strains are produced via independently controlled
axial and twist displacements. We present calculations for the strain-displacement and stress-load relationships, and strain
energy density. These relationships have been established and validated via a combination of analytical and experimental techniques,
and finite element analysis. We have investigated the extent and effects of strain and stress field non-uniformity in the
test specimen. The specimen design is sufficiently simple that a closed-form expression for the strain-displacement relationship
has been successfully developed. 相似文献
339.
L. Bergamaschi G. Gambolati G. Pini 《Journal of Computational and Applied Mathematics》2007,210(1-2):64-70
Integration of the subsurface flow equation by finite elements (FE) in space and finite differences (FD) in time requires the repeated solution to sparse symmetric positive definite systems of linear equations. Iterative techniques based on preconditioned conjugate gradients (PCG) are one of the most attractive tool to solve the problem on sequential computers. A present challenge is to make PCG attractive in a parallel computing environment as well. To this aim a key factor is the development of an efficient parallel preconditioner. FSAI (factorized sparse approximate inverse) and enlarged FSAI relying on the approximate inverse of the coefficient matrix appears to be a most promising parallel preconditioner. In the present paper PCG using FSAI, diagonal and pARMS (parallel algebraic recursive multilevel solvers) preconditioners is implemented on the IBM SP4/512 and CLX/768 supercomputers with up to 32 processors to solve underground flow problems of a large size. The results show that FSAI may allow for a parallel relative efficiency larger than 50% on the largest problems with p=32 processors. Moreover, FSAI turns out to be significantly less expensive and more robust than pARMS. Finally, it is shown that for p in the upper range may be much improved if PCG–FSAI is implemented on CLX. 相似文献
340.
Nanocomposites (NC) were formed using cationic poly(L ‐lysine) (PLL), a semicrystalline polypeptide, that was reinforced by sodium montmorillonite (MMT) clay via solution intercalation technique. By varying solution conditions such as pH, temperature, and polypeptide concentration in the presence of clay platelets, the secondary structure of PLL was controllably altered into α‐helical, β‐sheet, and random coil. The high molecular weight polypeptide shows a strong propensity to fold into the β‐sheet structure when cast as films, irrespective of the initial secondary structure in solution. Nanocomposite local morphology confirms intercalated MMT platelets with PLL over a wide range of compositions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 239–252, 2007. 相似文献