全文获取类型
收费全文 | 17224篇 |
免费 | 1547篇 |
国内免费 | 809篇 |
专业分类
化学 | 2910篇 |
晶体学 | 70篇 |
力学 | 6846篇 |
综合类 | 176篇 |
数学 | 4790篇 |
物理学 | 4788篇 |
出版年
2024年 | 16篇 |
2023年 | 158篇 |
2022年 | 267篇 |
2021年 | 343篇 |
2020年 | 433篇 |
2019年 | 358篇 |
2018年 | 412篇 |
2017年 | 449篇 |
2016年 | 480篇 |
2015年 | 507篇 |
2014年 | 678篇 |
2013年 | 1273篇 |
2012年 | 856篇 |
2011年 | 1063篇 |
2010年 | 794篇 |
2009年 | 1003篇 |
2008年 | 1020篇 |
2007年 | 1032篇 |
2006年 | 896篇 |
2005年 | 781篇 |
2004年 | 780篇 |
2003年 | 679篇 |
2002年 | 630篇 |
2001年 | 488篇 |
2000年 | 498篇 |
1999年 | 431篇 |
1998年 | 400篇 |
1997年 | 390篇 |
1996年 | 367篇 |
1995年 | 300篇 |
1994年 | 260篇 |
1993年 | 228篇 |
1992年 | 221篇 |
1991年 | 172篇 |
1990年 | 158篇 |
1989年 | 125篇 |
1988年 | 110篇 |
1987年 | 73篇 |
1986年 | 79篇 |
1985年 | 85篇 |
1984年 | 73篇 |
1983年 | 39篇 |
1982年 | 84篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1971年 | 6篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
21.
The molding processes of polymer melts involve geometrically complex dies. Such dies are usually tapered or streamlined to achieve a maximum output rate under conditions of laminar flow. The model of a generalized second-grade fluid of power-law type is used and the results obtained are illustrated by examples of convergent flows in conical and wedge-shaped dies. 相似文献
22.
As borders between different entities, lines are an important element of natural images. Indeed, the neurons of the mammalian
visual cortex are tuned to respond best to lines of a given orientation. This preferred orientation varies continuously across
most of the cortex, but also has vortex-like singularities known as pinwheels. In attempting to describe such patterns of
orientation preference, we are led to consider underlying rotation symmetries: Oriented segments in natural images tend to
be collinear; neurons are more likely to be connected if their preferred orientations are aligned to their topographic separation.
These are indications of a reduced symmetry requiring joint rotations of both orientation preference and the underlying topography.
This is verified by direct statistical tests in both natural images and in cortical maps. Using the statistics of natural
scenes we construct filters that are best suited to extracting information from such images, and find qualitative similarities
to mammalian vision.
PACS84.35+i 89.70.+c 87.57.Nk 相似文献
23.
采用甚高频等离子体增强化学气相沉积技术制备了系列微晶硅薄膜太阳电池,指出了气体总流量和背反射电极的类型对电池性能参数的影响.电池的I-V测试结果表明:随反应气体总流量的增加,对应电池的短路电流密度、开路电压和填充因子都有很大程度的提高,结果使得电池的光电转换效率得以提高.另外,ZnO/Ag/Al背反射电极能明显提高电池的短路电流密度,进而也提高了电池的光电转换效率.对气体总流量和背反射电极类型影响电池效率的原因进行了分析.
关键词:
微晶硅薄膜太阳电池
气体流量
ZnO/Ag/Al背反射电极 相似文献
24.
25.
26.
27.
We introduce a new scheme for the future application of Real-coded Lattice Gas (RLG) to the numerical simulation of suspended solid objects in a fluctuating fluid environment. The reproduction of Brownian motion for a single solid object is verified through the Gaussian distribution of its displacements. The effectiveness of the solid–solid interaction model is also confirmed in an N-body simulation. 相似文献
28.
29.
A convective flow CO laser composed of polytetrafluoroethylene discharge tubes, nickel–chromium steel components, a cupric heat exchanger and other components is described. Operating in liquid nitrogen condition, output power of 60 W has been obtained from a non-selective cavity. 相似文献
30.
We establish the existence and stability of multidimensional transonic shocks for the Euler equations for steady potential compressible fluids. The Euler equations, consisting of the conservation law of mass and the Bernoulli law for the velocity, can be written as a second-order, nonlinear equation of mixed elliptic-hyperbolic type for the velocity potential. The transonic shock problem can be formulated into the following free boundary problem: The free boundary is the location of the transonic shock which divides the two regions of smooth flow, and the equation is hyperbolic in the upstream region where the smooth perturbed flow is supersonic. We develop a nonlinear approach to deal with such a free boundary problem in order to solve the transonic shock problem. Our results indicate that there exists a unique solution of the free boundary problem such that the equation is always elliptic in the downstream region and the free boundary is smooth, provided that the hyperbolic phase is close to a uniform flow. We prove that the free boundary is stable under the steady perturbation of the hyperbolic phase. We also establish the existence and stability of multidimensional transonic shocks near spherical or circular transonic shocks.