全文获取类型
收费全文 | 252908篇 |
免费 | 15989篇 |
国内免费 | 8148篇 |
专业分类
电工技术 | 11555篇 |
技术理论 | 11篇 |
综合类 | 13712篇 |
化学工业 | 40026篇 |
金属工艺 | 14218篇 |
机械仪表 | 13905篇 |
建筑科学 | 15923篇 |
矿业工程 | 5152篇 |
能源动力 | 6125篇 |
轻工业 | 15089篇 |
水利工程 | 4474篇 |
石油天然气 | 9959篇 |
武器工业 | 1347篇 |
无线电 | 29252篇 |
一般工业技术 | 36919篇 |
冶金工业 | 10091篇 |
原子能技术 | 2233篇 |
自动化技术 | 47054篇 |
出版年
2024年 | 606篇 |
2023年 | 2652篇 |
2022年 | 4719篇 |
2021年 | 6939篇 |
2020年 | 5163篇 |
2019年 | 4433篇 |
2018年 | 18492篇 |
2017年 | 18242篇 |
2016年 | 14404篇 |
2015年 | 7465篇 |
2014年 | 8654篇 |
2013年 | 10321篇 |
2012年 | 14109篇 |
2011年 | 21091篇 |
2010年 | 18560篇 |
2009年 | 15285篇 |
2008年 | 16339篇 |
2007年 | 16780篇 |
2006年 | 9588篇 |
2005年 | 9392篇 |
2004年 | 6849篇 |
2003年 | 6337篇 |
2002年 | 5796篇 |
2001年 | 4725篇 |
2000年 | 4581篇 |
1999年 | 4443篇 |
1998年 | 3710篇 |
1997年 | 3115篇 |
1996年 | 2889篇 |
1995年 | 2479篇 |
1994年 | 2029篇 |
1993年 | 1471篇 |
1992年 | 1162篇 |
1991年 | 925篇 |
1990年 | 666篇 |
1989年 | 571篇 |
1988年 | 472篇 |
1987年 | 303篇 |
1986年 | 200篇 |
1985年 | 126篇 |
1984年 | 82篇 |
1983年 | 52篇 |
1982年 | 81篇 |
1981年 | 55篇 |
1980年 | 46篇 |
1968年 | 43篇 |
1965年 | 47篇 |
1959年 | 43篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Phase-change read-and-write memory (PRAM) is a promising memory that can solve the problems of conventional memory—scalability, read/write speed, and reliability. We will review the opportunities and technical challenges of PRAM. The most important challenge of PRAM is the reduction of the writing current. Various approaches to reduce the writing current will be reviewed and the prospects of PRAM are discussed. 相似文献
972.
K-9曲拐质量不合格主要是由于热处理后,珠光体数量太少所引起。因此应用正交试验,合理地选择了热处理工艺参数,提高了出炉温度,增加了珠光体数量,解决了K-9曲拐的质量问题。 相似文献
973.
The synthesis of rare-earth perovskite-type composition thin films of LaNiO3 by means of the inorganic-sol-gel (ISG) method was studied. The structural stability under high temperature in reducing atmospheres and the oxygen-sensitivity mechanism of the LaNiO3 thin films were examined. It is shown that under the experimental conditions, LaNiO3 decomposes and the valance states of nickel are +2 and +3. 相似文献
974.
In this paper, the detectivity is calculated and analyzed with the front-or backside illuminated case for both N-GaSb/p2-Ga0.8In0.2As0.19Sb0.81/p1-Ga0.9In0.1As0.09Sb0.91 and N1-GaSb/n2-Ga0.9In0.1As0.09Sb0.91/p-Ga0.8In0.2As0.19Sb0.81 infrared photovoltaic detectors, respectively. The analysis results show that the main absorption appears in the p-type Ga0.8In0.2As0.19Sb0.81 material with either front- or backside illuminated case for above two structures. In each structure, the carrier concentration obviously affects the detectivity. The carrier concentration in the wide-bandgap material for the isotype heterojunction should be reduced as low as possible to reduce the tunneling rate at the isotype heterointerface. Moreover, the change of the detectivity with the p-side surface recombination velocity for the N1-n2-p structure is more sensitive than that with the p1-side surface recombination velocity for the N-p2-p1 structure. In the N-p2-p1 structure with the incident light from the p1-side surface, two-color detection is achieved. 相似文献
975.
976.
Ag-BaO thin films doped with lanthanum were prepared by vacuum deposition. Compared with the normal Ag-BaO thin film, there is almost no change with the shape and the peak site of the fluorescence spectrum; however, fluores-cence emission strength of the whole observation band(325 -600 nm)increases about 40%, and the increase of short wavelength range is more remarkable than that of long wavelength range, which we named “blue-stronger“ phenomenon. Analytic results show that, with the forming of intermetallic compounds between silver and lanthanum, the 4f-state energy levels lie just below the Fermi level within 5 eV. It is the energy exchange between the 4f energy levels and the conduction band that causes the increase effect of fluorescence emission, and it is the optical absorption cross section of 4f electron, which increases with the increase of energy of incidence photon, that gives rise to the “blue-stronger“ phenomenon. 相似文献
977.
2,6-二甲基萘生产技术进展 总被引:2,自引:0,他引:2
许杰 《精细石油化工进展》2003,4(2):44-47
概述了国外2,6-二甲基萘生产技术现状,详细介绍了ExxonMobil公司2,6-二甲基萘的工艺路线和日本神户制钢所的提纯方法,指出了实现我国2,6-二甲基萘工业化生产应注意的问题。 相似文献
978.
Feature-based classifiers for design optimization 总被引:1,自引:0,他引:1
We present a design optimization method for systems with high-dimensional parameter spaces using inductive decision trees.
The essential idea is to map designs into a relatively low-dimensional feature space, and to derive a classifier to search
for high-performing design alternatives within this space. Unlike learning classifier systems that were pioneered by Holland
and Goldberg, classifiers defined by inductive decision trees were not originally developed for design optimization. In this
paper, we explore modifications to such classifiers to make them more effective in the optimization problem. We expand the
notions of feature space, generalize the tree construction heuristic beyond the original information-theoretic definitions,
increase the reliance on domain expertise, and facilitate the transfer of design knowledge between related systems. There
is a relatively small but rapidly growing body of work in the use of inductive trees for engineering design; the method presented
herein is complementary to this research effort. 相似文献
979.
Sebastián Bruque-Cámara Alfonso Vargas-Sánchez M. Jesús Hernández-Ortiz 《欧洲信息系统杂志》2004,13(2):133-146
The aim of this paper is to propose new organizational factors that might explain the differences in the extent and the speed of IT adoption. With this in mind, we carried out an analysis of 16 cases in the pharmaceutical distribution sector in Spain. The results indicate that there are certain intangible assets that favour the introduction and development of IT. Among these are a frank and fluid communication between departments and members of the organization, low levels of conflict, the explicit support of top management towards IT adoption and learning and creative skills of IT-staff. In addition to these factors, we found others that we propose as catalysts of IT adoption. Among these we might mention the special relationship between the member-clients and the company in the case of cooperative firms. 相似文献
980.