全文获取类型
收费全文 | 11877篇 |
免费 | 2015篇 |
国内免费 | 3482篇 |
专业分类
化学 | 8060篇 |
晶体学 | 464篇 |
力学 | 914篇 |
综合类 | 142篇 |
数学 | 2832篇 |
物理学 | 4962篇 |
出版年
2024年 | 32篇 |
2023年 | 108篇 |
2022年 | 319篇 |
2021年 | 392篇 |
2020年 | 455篇 |
2019年 | 402篇 |
2018年 | 379篇 |
2017年 | 532篇 |
2016年 | 748篇 |
2015年 | 516篇 |
2014年 | 715篇 |
2013年 | 1251篇 |
2012年 | 1059篇 |
2011年 | 1058篇 |
2010年 | 861篇 |
2009年 | 906篇 |
2008年 | 919篇 |
2007年 | 914篇 |
2006年 | 790篇 |
2005年 | 667篇 |
2004年 | 555篇 |
2003年 | 507篇 |
2002年 | 453篇 |
2001年 | 381篇 |
2000年 | 342篇 |
1999年 | 306篇 |
1998年 | 271篇 |
1997年 | 216篇 |
1996年 | 225篇 |
1995年 | 182篇 |
1994年 | 174篇 |
1993年 | 132篇 |
1992年 | 106篇 |
1991年 | 71篇 |
1990年 | 82篇 |
1989年 | 54篇 |
1988年 | 53篇 |
1987年 | 38篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
对于具有周期单元的分层介质材料高反射区的波长范围,提供一种简明的估计分析方法.基于Floquet定理,分析了有限周期单元分层介质的光子带隙特性,给出分层介质的高反射区波长范围.讨论了分层介质高反射区和周期单元禁带之间的关系.计算表明,高反射区和周期单元禁带的中心波长彼此一致.并且,随着分层介质周期单元数的增多,高反射区的深度和带宽就越接近于周期单元禁带的深度和宽度.最后,讨论周期分层介质的光子带隙特性与入射角及其与极化的变化关系.
关键词:
分层介质
带隙特性
周期单元
高反射区 相似文献
72.
Stability of tokamak plasmas with internal transport barriers against high n ideal magnetohydrodynamic ballooning mode 下载免费PDF全文
A ballooning mode equation for tokamak plasma, with the toroidicity and the Shafranov shift effects included, is derived for a shift circular flux tokamak configuration. Using this equation, the stability of the plasma configuration with an internal transport barrier (ITB) against the high n (the toroidal mode number) ideal magnetohydrodynamic (MHD) ballooning mode is analysed. It is shown that both the toroidicity and the Shaftanov shift effects are stabilizing. In the ITB region, these effects give rise to a low shear stable channel between the first and the second stability regions. Out of the ITB region towards the plasma edge, the stabilizing effect of the Shaftanov shift causes the unstable zone to be significantly narrowed. 相似文献
73.
Christian Wolf 《Journal of statistical physics》2006,122(6):1111-1138
In this paper we introduce the notion of generalized physical and SRB measures. These measures naturally generalize classical
physical and SRB measures to measures which are supported on invariant sets that are not necessarily attractors. We then perform
a detailed case study of these measures for hyperbolic Hènon maps. For this class of systems we are able to develop a complete
theory about the existence, uniqueness, finiteness, and properties of these natural measures. Moreover, we derive a classification
for the existence of a measure of full dimension. We also consider general hyperbolic surface diffeomorphisms and discuss
possible extensions of, as well as the differences to, the results for Hènon maps. Finally, we study the regular dependence
of the dimension of the generalized physical/SRB measure on the diffeomorphism. For the proofs we apply various techniques
from smooth ergodic theory including the thermodynamic formalism.
2000
Mathematics Subject Classification. Primary: 37C45, 37D20, 37D35, Secondary: 37A35, 37E30 相似文献
74.
John Ginsburg 《Order》1989,6(2):137-157
For a partially ordered setP and an elementx ofP, a subsetS ofP is called a cutset forx inP if every element ofS is noncomparable tox and every maximal chain ofP meets {x}∪S. We letc(P) denote the smallest integerk such that every elementx ofP has a cutsetS with ‖S‖?k: Ifc(P)?n we say thatP has then-cutset property. Our results bear on the following question: givenP, what is the smallestn such thatP can be embedded in a partially ordered set having then-cutset property? As usual, 2 n denotes the Boolean lattice of all subsets of ann-element set, andB n denotes the set of atoms and co-atoms of 2 n . We establish the following results: (i) a characterization, by means of forbidden configurations, of whichP can be embedded in a partially ordered set having the 1-cutset property; (ii) ifP contains a copy of 2 n , thenc(P)?2[n/2]?1; (iii) for everyn>3 there is a partially ordered setP containing 2 n such thatc(P)<c(2 n ); (iv) for every positive integern there is a positive integerN such that, ifB m is contained in a partially ordered set having then-cutset property, thenm?N. 相似文献
75.
p型未掺杂富锌ZnO薄膜的形成和性能研究 总被引:1,自引:1,他引:0
以高纯ZnO为靶材,氩气为溅射气体,利用射频磁控溅射技术在石英衬底上生长出纤锌矿结构的富锌ZnO薄膜.薄膜沿(002)择优取向生长,厚约为1.2μm,呈现电绝缘特性.将溅射的ZnO薄膜在10-3Pa,510~1 000 K的温度范围等温退火1 h,室温Hall测量结果表明ZnO薄膜的导电性能经历了由绝缘—n型—p型—n型半导体的变化.XPS测试表明ZnO薄膜的Zn/O离子比随退火温度的升高而降低,但一直是富锌ZnO,说明未掺杂的富锌ZnO也可以形成p型导电.p型未掺杂富锌ZnO薄膜的形成可归因于VZn受主浓度可以克服VO和Zni本征施主的补偿效应. 相似文献
76.
采用模匹配方法,研究了非均匀磁场下开放的四端量子波导中的电子输运性质. 结果表明,从一端入射的电子可以透射到两个与之垂直的输出端和一个与之平行的输出端. 在没有外加磁场的情况下,两个垂直输出端的输运概率是相同的,但垂直端与水平端的输运概率不同;在外加磁场下,由于磁边缘态效应,两个垂直输出端的输运概率也有着相当大的差别. 通过施加不同的磁场,我们能获得丰富的电子输运结构,如台阶,宽谷,尖峰等;通过调节磁场的大小和比例以及结构参数可控制该量子结构在各输出端的输运概率.
关键词:
电子输运
介观体系
磁效应 相似文献
77.
78.
We report viscometric data collected in a Couette rheometry on dilute, single‐solvent polystyrene (PS)/dioctyl phthalate (DOP) solutions over a variety of polymer molecular weights (5.5 × 105 ≤ Mw ≤ 3.0 × 106 Da) and system temperatures (288 K ≤ T ≤ 318 K). In view of the essential viscometric features, the current data may be classified into three categories: The first concerns all the investigated solutions at low shear rates, where the solution properties are found to agree excellently with the Zimm model predictions. The second includes all sample solutions, except for high‐molecular‐weight PS samples (Mw ≥ 2.0 × 106 Da), where excellent time–temperature superposition is observed for the steady‐state polymer viscosity at constant polymer molecular weights. No similar superposition applies at a constant temperature but varied polymer molecular weights, however. The third appears to be characteristic of dilute high‐molecular‐weight polymer solutions, for which the effects of temperature on the viscosity curve are further complicated at high shear rates. The implications concerning the relative importance of hydrodynamic interactions, segmental interactions, and chain extensibility with increasing polymer molecular weight, system temperature, and shear rate are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 787–794, 2006 相似文献
79.
Yu Jun ZHU Jin Lian ZHANG Lian Fa HE 《数学学报(英文版)》2006,22(5):1321-1328
In this paper, we consider the shadowing and the inverse shadowing properties for C^1 endomorphisms. We show that near a hyperbolic set a C^1 endomorphism has the shadowing property, and a hyperbolic endomorphism has the inverse shadowing property with respect to a class of continuous methods. Moreover, each of these shadowing properties is also "uniform" with respect to C^1 perturbation. 相似文献
80.