全文获取类型
收费全文 | 18015篇 |
免费 | 3593篇 |
国内免费 | 2200篇 |
专业分类
化学 | 3466篇 |
晶体学 | 189篇 |
力学 | 1051篇 |
综合类 | 428篇 |
数学 | 10756篇 |
物理学 | 7918篇 |
出版年
2024年 | 47篇 |
2023年 | 202篇 |
2022年 | 436篇 |
2021年 | 540篇 |
2020年 | 581篇 |
2019年 | 598篇 |
2018年 | 566篇 |
2017年 | 742篇 |
2016年 | 819篇 |
2015年 | 743篇 |
2014年 | 1190篇 |
2013年 | 1492篇 |
2012年 | 1089篇 |
2011年 | 1326篇 |
2010年 | 1100篇 |
2009年 | 1177篇 |
2008年 | 1249篇 |
2007年 | 1393篇 |
2006年 | 1122篇 |
2005年 | 997篇 |
2004年 | 765篇 |
2003年 | 837篇 |
2002年 | 713篇 |
2001年 | 580篇 |
2000年 | 629篇 |
1999年 | 529篇 |
1998年 | 456篇 |
1997年 | 396篇 |
1996年 | 293篇 |
1995年 | 178篇 |
1994年 | 160篇 |
1993年 | 116篇 |
1992年 | 102篇 |
1991年 | 87篇 |
1990年 | 72篇 |
1989年 | 50篇 |
1988年 | 59篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 56篇 |
1984年 | 44篇 |
1983年 | 15篇 |
1982年 | 43篇 |
1981年 | 26篇 |
1980年 | 25篇 |
1979年 | 24篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
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
33.
E. A. Bailov N. Temirgaliev 《Computational Mathematics and Mathematical Physics》2006,46(9):1515-1525
Sharp estimates (in the power scale) are obtained for the discretization error in the solutions to Poisson’s equation whose right-hand side belongs to a Korobov class. Compared to the well-known Korobov estimate, the order is almost doubled and has an ultimate value in the power scale. 相似文献
34.
35.
We consider some Sobolev-type spaces and obtain a necessary and sufficient condition for their embedding in a Lebesgue space. 相似文献
36.
This paper gives some global and uniform convergence estimates for a class of subspace correction (based on space decomposition) iterative methods applied to some unconstrained convex optimization problems. Some multigrid and domain decomposition methods are also discussed as special examples for solving some nonlinear elliptic boundary value problems.
37.
This paper investigates the large scale travelling ionospheric disturbances (LSTIDs) using the observation data of an HF Doppler array located in Central China. The data observed in a high solar activity year (year 1989) are analyzed to obtain the main propagation parameters of LSTIDs such as period, horizontal phase velocity and propagating direction. Results are outlined as follows: Most of the LSTIDs propagate southward; others tend to propagate northward, mostly in summer; dispersion of most LSTIDs is matched with that of Lamb pseudomode, while others have the dispersion of long period gravity wave mode. The horizontal phase velocities of these two modes are about 220 and 450 m/s respectively. The analysis shows that LSTIDs are strongly pertinent to solar activity and space magnetic storms; thus the results presented here are significant for the research of ionospheric weather in mid-low latitude region. 相似文献
38.
Dalila B. M. M. Fontes Eleni Hadjiconstantinou Nicos Christofides 《Journal of Global Optimization》2006,34(1):97-125
In this paper we obtain Lower Bounds (LBs) to concave cost network flow problems. The LBs are derived from state space relaxations
of a dynamic programming formulation, which involve the use of non-injective mapping functions guaranteing a reduction on
the cardinality of the state space. The general state space relaxation procedure is extended to address problems involving
transitions that go across several stages, as is the case of network flow problems. Applications for these LBs include: estimation
of the quality of heuristic solutions; local search methods that use information of the LB solution structure to find initial
solutions to restart the search (Fontes et al., 2003, Networks, 41, 221–228); and branch-and-bound (BB) methods having as
a bounding procedure a modified version of the LB algorithm developed here, (see Fontes et al., 2005a). These LBs are iteratively
improved by penalizing, in a Lagrangian fashion, customers not exactly satisfied or by performing state space modifications.
Both the penalties and the state space are updated by using the subgradient method. Additional constraints are developed to
improve further the LBs by reducing the searchable space. The computational results provided show that very good bounds can
be obtained for concave cost network flow problems, particularly for fixed-charge problems. 相似文献
39.
基于同步辐射加速器的康普顿背散射γ射线源(Ⅰ)产生MeV量级γ光子的数值计算 总被引:1,自引:0,他引:1
提出在筹建的上海同步辐射装置上建造一条MeV量级γ射线束及应用站,采用μm波长的红外(或远红外)激光与储存环中3.5GeV电子束进行康普顿背散射,从而获得能区为1—25MeV的康普顿背散射γ光子束,该光子束具有高强度、高极化度(线和圆极化)、准单色、方向性好的优点,可以广泛地应用于核物理和核天体物理基础研究及相关的应用研究领域.介绍了康普顿背散射的基本原理,并结合储存环参数给出了光子束性能的数值计算结果. 相似文献
40.
An admissible minimax estimator of a bounded scale-parameter in a subclass of the exponential family under scale-invariant squared-error loss 总被引:3,自引:0,他引:3
Mohammad Jafari Jozani Nader Nematollahi Khalil Shafie 《Statistics & probability letters》2002,60(4):437-444
A subclass of the scale-parameter exponential family is considered and for the rth power of the scale parameter, which is lower bounded, an admissible minimax estimator under scale-invariant squared-error loss is presented. Also, an admissible minimax estimator of a lower-bounded parameter in the family of transformed chi-square distributions is given. These estimators are the pointwise limits of a sequence of Bayes estimators. Some examples are given. 相似文献