全文获取类型
收费全文 | 562924篇 |
免费 | 7910篇 |
国内免费 | 2588篇 |
专业分类
化学 | 268879篇 |
晶体学 | 6959篇 |
力学 | 20450篇 |
综合类 | 68篇 |
数学 | 58957篇 |
物理学 | 143493篇 |
无线电 | 74616篇 |
出版年
2020年 | 3857篇 |
2019年 | 4035篇 |
2018年 | 4622篇 |
2017年 | 4572篇 |
2016年 | 7661篇 |
2015年 | 5703篇 |
2014年 | 8128篇 |
2013年 | 22661篇 |
2012年 | 17691篇 |
2011年 | 21814篇 |
2010年 | 14957篇 |
2009年 | 15585篇 |
2008年 | 21884篇 |
2007年 | 22810篇 |
2006年 | 22004篇 |
2005年 | 20235篇 |
2004年 | 18365篇 |
2003年 | 16391篇 |
2002年 | 16156篇 |
2001年 | 17641篇 |
2000年 | 14095篇 |
1999年 | 11293篇 |
1998年 | 9612篇 |
1997年 | 9454篇 |
1996年 | 9421篇 |
1995年 | 8614篇 |
1994年 | 8433篇 |
1993年 | 8164篇 |
1992年 | 8676篇 |
1991年 | 8642篇 |
1990年 | 8053篇 |
1989年 | 7640篇 |
1988年 | 7672篇 |
1987年 | 6659篇 |
1986年 | 6513篇 |
1985年 | 8783篇 |
1984年 | 8893篇 |
1983年 | 7391篇 |
1982年 | 7933篇 |
1981年 | 7665篇 |
1980年 | 7272篇 |
1979年 | 7478篇 |
1978年 | 7624篇 |
1977年 | 7639篇 |
1976年 | 7598篇 |
1975年 | 7287篇 |
1974年 | 7185篇 |
1973年 | 7351篇 |
1972年 | 4916篇 |
1971年 | 3855篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The room temperature structure of perovskite CeAlO3 has been reinvestigated by X-ray powder diffraction. The Rietveld refinement has confirmed the tetragonal symmetry; but revealed a super cell, a=5.32489(6) Å and c=7.58976(10) Å, with the space group I4/mcm. In CeAlO3, the distortion from the ideal cubic perovskite is caused by the cooperative tilting of the AlO6 octahedra around the primitive cubic [001]p-axis. 相似文献
993.
The fine-structure parameters of a series of configurations of the first ion of indium and the gyromagnetic ratios in intermediate coupling are calculated by a semiempirical method in the single-configuration approximation. 相似文献
994.
Field emission study of thin water layers was performed to examine their properties and their changes after application of a high electric field. Comparison of field emission characteristics of water layers adsorbed on clean tungsten and gold-covered tungsten suggested that, whereas water molecules adsorbed on tungsten are oriented by oxygen atoms towards the metal surface, water layer on gold-covered tungsten has amorphous character with no preferential orientation. Both heated and non-heated layers are heavily influenced by applied high electric field strengths (F ≈30 MV/cm). Decrease of the work function and of the voltage needed for a constant emission current during successive increase of the electric field was tentatively interpreted in terms of chemical and morfological changes of the water layer due to the field dissociation and solvation. 相似文献
995.
996.
997.
Baldridge K.K. Greenberg J.P. Sudholt W. Mock S. Altintas I. Amoreira C. Potier Y. Birnbaum A. Bhatia K. Taufer M. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2005,93(3):510-521
Evolving technologies, as exemplified by computational grids and Web services, have made it possible to solve new scientific problems that would not have been feasible previously. In order to make such advances available to the community in general and to be able to solve new problems, not necessarily from the same discipline, it is imperative to build tools that provide a common user interface in order that application programmers and users do not have to be concerned with particulars of Web services and their underlying code, computational platforms, or with data file formats. We will describe our efforts in creating a computational chemistry environment that encompasses a general scientific workflow environment, a domain specific example for quantum chemistry, our ongoing design of a workflow user interface, and our efforts at database integration. 相似文献
998.
The letter describes a simple method for calculating the maximum bulk electric field in high-voltage semiconductor diodes with large bevel angles. It is based on the notion of a characteristic length, which is defined in the letter. The resulting model is a useful design aid. 相似文献
999.
A model is developed for the analysis of factors influencing organizational and technological changes associated with CAD and CAD/CAM (computer-aided design/computer-aided manufacture). Different pressures for adoption and the sociopolitical environment of the organization and related to managerial strategies and their impact on skills, tasks, training, and changes in work organization. Opportunities are illustrated through the experiences of seven British engineering companies implementing the technologies. Six of the companies are in manufacturing and one is an engineering services organization. Four of the companies are of small to medium size (under 500 employees) and the other three are large, multisite organizations. Key elements of the technological change are identified, and the position of the seven companies in relation to these elements is summarized and discussed 相似文献
1000.