全文获取类型
收费全文 | 4670篇 |
免费 | 400篇 |
国内免费 | 460篇 |
专业分类
化学 | 439篇 |
晶体学 | 3篇 |
力学 | 469篇 |
综合类 | 129篇 |
数学 | 3359篇 |
物理学 | 1131篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 61篇 |
2021年 | 69篇 |
2020年 | 99篇 |
2019年 | 74篇 |
2018年 | 95篇 |
2017年 | 141篇 |
2016年 | 165篇 |
2015年 | 108篇 |
2014年 | 221篇 |
2013年 | 291篇 |
2012年 | 255篇 |
2011年 | 302篇 |
2010年 | 258篇 |
2009年 | 320篇 |
2008年 | 326篇 |
2007年 | 340篇 |
2006年 | 303篇 |
2005年 | 257篇 |
2004年 | 228篇 |
2003年 | 226篇 |
2002年 | 182篇 |
2001年 | 155篇 |
2000年 | 136篇 |
1999年 | 137篇 |
1998年 | 146篇 |
1997年 | 109篇 |
1996年 | 92篇 |
1995年 | 52篇 |
1994年 | 47篇 |
1993年 | 41篇 |
1992年 | 42篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1936年 | 3篇 |
排序方式: 共有5530条查询结果,搜索用时 15 毫秒
1.
2.
Transformation hydrodynamics and the corresponding metamaterials have been proposed as a means to exclude the drag force acting on an object. Here, we report a strategy to deploy the hydrodynamic cloaks in a more practical manner by assembling different-shaped cloaking parts. Our strategy is to first model a square-shaped cloak and a carpet cloak and then combine them to conceal a more complex-shaped space in the three-dimensional hydrodynamic flow. With the derivation of transformation hydrodynamics, the coordinate transformations for each hydrodynamic cloaking are demonstrated with the calculated viscosity tensors. The pressure and velocity fields of the square, triangular (carpet), and exemplary three-dimensional house-shaped cloaks are numerically simulated, thus showing a cloaking effect and reduced drag. This study suggests an efficient way of cloaking complex architectures from fluid-dynamic forces. 相似文献
3.
The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent
state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour
of the nuclear ground states using the coherent states. 相似文献
4.
An Improved Gradient Projection-based Decomposition Technique for Support Vector Machines 总被引:2,自引:0,他引:2
Luca Zanni 《Computational Management Science》2006,3(2):131-145
In this paper we propose some improvements to a recent decomposition technique for the large quadratic program arising in
training support vector machines. As standard decomposition approaches, the technique we consider is based on the idea to
optimize, at each iteration, a subset of the variables through the solution of a quadratic programming subproblem. The innovative
features of this approach consist in using a very effective gradient projection method for the inner subproblems and a special
rule for selecting the variables to be optimized at each step. These features allow to obtain promising performance by decomposing
the problem into few large subproblems instead of many small subproblems as usually done by other decomposition schemes. We
improve this technique by introducing a new inner solver and a simple strategy for reducing the computational cost of each
iteration. We evaluate the effectiveness of these improvements by solving large-scale benchmark problems and by comparison
with a widely used decomposition package. 相似文献
5.
Paul Bankston 《Archive for Mathematical Logic》2006,45(1):97-112
The Chang-Łoś-Suszko theorem of first-order model theory characterizes universal-existential classes of models as just those
elementary classes that are closed under unions of chains. This theorem can then be used to equate two model-theoretic closure
conditions for elementary classes; namely unions of chains and existential substructures. In the present paper we prove a
topological analogue and indicate some applications. 相似文献
6.
曾六川 《数学物理学报(A辑)》2002,22(1):99-106
该文研究Banach空间中一类强增生型变分包含解的存在性及其具误差的Ishikawa迭代程序的收敛性问题.该文结果是几位作者早期与最近的相应结果的改进和推广. 相似文献
7.
8.
An applied cell mapping method for optimal control problems 总被引:1,自引:0,他引:1
W. H. Zhu 《Journal of Optimization Theory and Applications》1989,60(3):485-500
From the application point of view, a series of modifications are proposed for the cell mapping method discussed in Ref. 1 for the optimal control analysis of dynamical systems. The cell order around the target set is rearranged. A set of common discriminate principles is used for the selection of the optimal one among competing control strategies of the same cost. Inequality constraints of the system are taken into account. The number of elements in the set of allowable time intervals is not prescribed, but left open. These modifications seem to make the cell mapping method more efficient for analyzing feedback systems and for obtaining their global optimal control information. The algorithms presented in this paper could broaden the application of the cell mapping approach of Ref. 1 to a wider class of engineering problems. 相似文献
9.
考虑约束最优化问题:minx∈Ωf(x)其中:f:R^n→R是连续可微函数,Ω是一闭凸集。本文研究了解决此问题的梯度投影方法,在步长的选取时采用了一种新的策略,在较弱的条件下,证明了梯度投影响方法的全局收敛性。 相似文献
10.
本文首先将文[1]中的BLD映射推广为弱(L1,L2)-BLD映射,并证明了如下正则性结果:存在两个可积指数 P1=P1(n,L1,L2)<n<q1=q1(n,L1,L2),使得对任意弱(L1,L2)-BLD映射f∈(Ω,Rn),都有f∈(Ω,Rn),即f为(L1,L2)-BLD映射. 相似文献