全文获取类型
收费全文 | 194593篇 |
免费 | 38931篇 |
国内免费 | 27718篇 |
专业分类
化学 | 129618篇 |
晶体学 | 2396篇 |
力学 | 12852篇 |
综合类 | 761篇 |
数学 | 24103篇 |
物理学 | 91512篇 |
出版年
2024年 | 586篇 |
2023年 | 2917篇 |
2022年 | 3461篇 |
2021年 | 4534篇 |
2020年 | 5492篇 |
2019年 | 5824篇 |
2018年 | 5172篇 |
2017年 | 5408篇 |
2016年 | 7615篇 |
2015年 | 7580篇 |
2014年 | 8635篇 |
2013年 | 12542篇 |
2012年 | 14458篇 |
2011年 | 16527篇 |
2010年 | 16199篇 |
2009年 | 16093篇 |
2008年 | 10783篇 |
2007年 | 9781篇 |
2006年 | 8844篇 |
2005年 | 8190篇 |
2004年 | 7493篇 |
2003年 | 6013篇 |
2002年 | 5598篇 |
2001年 | 5488篇 |
2000年 | 4386篇 |
1999年 | 4907篇 |
1998年 | 4184篇 |
1997年 | 3883篇 |
1996年 | 4364篇 |
1995年 | 4325篇 |
1994年 | 4328篇 |
1993年 | 4072篇 |
1992年 | 3583篇 |
1991年 | 3147篇 |
1990年 | 2633篇 |
1989年 | 2500篇 |
1988年 | 2368篇 |
1987年 | 1573篇 |
1986年 | 1640篇 |
1985年 | 1280篇 |
1984年 | 1291篇 |
1983年 | 554篇 |
1982年 | 1079篇 |
1981年 | 883篇 |
1980年 | 890篇 |
1979年 | 626篇 |
1978年 | 604篇 |
1977年 | 691篇 |
1976年 | 1119篇 |
1972年 | 568篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
191.
To investigate local ordering and segregation phenomenon in a Ni91Pt9-alloy after sputtering and annealing a 3D optical atom probe (OAP) has been used. The specimen tips have been prepared from polycrystalline samples. To sputter the samples a separate preparation chamber with a scannable Ar-sputter-gun is connected to the OAP vessel. When necessary, the sample can be electrically heated to induce segregation and cure the altered layer. After a heat treatment of a Ni91 at. %Pt 9 at.% specimen at 1100 K the surface of a (111)-oriented specimen is enriched in platinum by a factor of two in relation to the bulk. The phenomenon of short-range ordering has been investigated on the surface and in the subsurface volume. A 3D reconstruction of this annealed NiPt specimen shows regions with high concentration of platinum that gives an indication at short-range ordering. Uniform sputtering of the tip without a heat treatment induces a decisive depletion of Pt on the surface and the following subatomic layers. The atom-probe results of specimens in thermal equilibrium are in close agreement to further surface sensitive results obtained from Ion Scattering Spectroscopy (ISS) and Auger Electron Spectroscopy (AES). 相似文献
192.
193.
A method using capillary gel electrophoresis with laser-induced fluorescence detection is described which permits complete sequence determination of antisense DNA analogues of unknown sequence. This method, originally created as a tool to confirm the sequence of antisense oligonucleotides being developed as therapeutic drugs, utilizes data collected under a range of experimental conditions described by the Ogston model as applied to gel electrophoresis. A linear relationship independent of experimental conditions between the relative electrophoretic migration time and the oligonucleotide base number was observed and is shown to be consistent with a simplified version of this model and can be used to facilitate the sequence determination. 相似文献
194.
Ma Jiangle Yang Hong-shen Zhang Zhongxi Lu Zhong-zuo 《International Journal of Infrared and Millimeter Waves》1993,14(5):1069-1076
A simple method is introduced to improve the analysing accuracy of circular groove guide. With this method, the characteristic equation of circular groove guide is derived and its solution is given and discussed.The Project Supported by National Natural Science Foundation of P.R.China 相似文献
195.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
196.
197.
198.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
199.
Let V be a hypersurface with an isolated singularity at the origin in ? n+1. It is a natural question to ask when V is defined by weighted homogeneous polynomial or homogeneous polynomial up to biholomorphic change of coordinates. In 1971, a beautiful theorem of Saito gives a necessary and sufficient condition for V to be defined by a weighted homogeneous polynomial. For a two-dimensional isolated hypersurface signularity V, Xu and Yau found a coordinate free characterization for V to be defined by a homogeneous polynomial. Recently Lin and Yau gave necessary and sufficient conditions for a 3-dimensional isolated hypersurface singularity with geometric genus bigger than zero to be defined by a homogeneous polynomial. The purpose of this paper is to prove that Lin-Yau’s theorem remains true for singularities with geometric genus equal to zero. 相似文献
200.
采用基于第一性原理的密度泛函理论研究了四角晶相二氧化铪(t-HfO2)体相及 其(001)表面的原子几何与电子结构.理论计算结果表明,t-HfO2(001)表面不会 产生重构现象.与体相电子结构相比, t-HfO2(001)表面态密度明显高于体相态 密度.其次,表面原子的态密度更靠近费米能级(EF),价带往低能量处移动,并 有表面态产生.计算结果表明了t-HfO2表面禁带宽度明显低于体相的禁带宽度. t-HfO2(001)的表面态产生以及表面禁带宽度减小是由于Hf原子与O原子的配位 数减少,表面原子周围的环境发生变化而引起的.
关键词:
密度泛函理论
2(001)')" href="#">t-HfO2(001)
表面电子结构 相似文献