全文获取类型
收费全文 | 118996篇 |
免费 | 5790篇 |
国内免费 | 2831篇 |
专业分类
电工技术 | 4167篇 |
技术理论 | 3篇 |
综合类 | 5045篇 |
化学工业 | 16412篇 |
金属工艺 | 6790篇 |
机械仪表 | 5596篇 |
建筑科学 | 4777篇 |
矿业工程 | 1998篇 |
能源动力 | 2139篇 |
轻工业 | 6744篇 |
水利工程 | 2320篇 |
石油天然气 | 1863篇 |
武器工业 | 484篇 |
无线电 | 13674篇 |
一般工业技术 | 20043篇 |
冶金工业 | 4234篇 |
原子能技术 | 726篇 |
自动化技术 | 30602篇 |
出版年
2024年 | 263篇 |
2023年 | 844篇 |
2022年 | 1837篇 |
2021年 | 2384篇 |
2020年 | 1785篇 |
2019年 | 1324篇 |
2018年 | 15820篇 |
2017年 | 15079篇 |
2016年 | 11372篇 |
2015年 | 2759篇 |
2014年 | 2813篇 |
2013年 | 3051篇 |
2012年 | 6336篇 |
2011年 | 12552篇 |
2010年 | 10872篇 |
2009年 | 7747篇 |
2008年 | 8919篇 |
2007年 | 9596篇 |
2006年 | 1543篇 |
2005年 | 2342篇 |
2004年 | 1904篇 |
2003年 | 1790篇 |
2002年 | 1148篇 |
2001年 | 610篇 |
2000年 | 539篇 |
1999年 | 306篇 |
1998年 | 261篇 |
1997年 | 218篇 |
1996年 | 200篇 |
1995年 | 144篇 |
1994年 | 130篇 |
1993年 | 94篇 |
1992年 | 83篇 |
1991年 | 66篇 |
1990年 | 36篇 |
1989年 | 46篇 |
1988年 | 37篇 |
1969年 | 25篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 43篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1960年 | 30篇 |
1959年 | 39篇 |
1958年 | 37篇 |
1957年 | 37篇 |
1956年 | 34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
91.
92.
93.
Understanding consumer behaviour is of vital importance to consumer-oriented e-business models today. In this paper, we study the relationships between consumer perceptions of risk and trust and the attitude towards purchasing at a consumer-to-consumer electronic marketplace (EM). Typical for EM settings is that consumer behaviour is subject to perceptions of the selling party as well as of the institutional structures of the intermediary that is operating the EM. Building upon the well-established literature of trust, we consider the concepts of intermediary trust and seller trust. We extend this categorisation by introducing the concepts of intermediary risk and seller risk. We developed measurement instruments for intermediary risk and seller risk. All measurement scales have acceptable alphas and are unidimensional. An empirical study is conducted to explore the relationships between the risk and trust types and consumer purchase attitude. The results reveal significant, direct effects of seller trust and seller risk. Second-order effects of intermediary trust and intermediary risk are investigated and reported. The paper concludes with general observations and recommendations for research and practice. 相似文献
94.
95.
分片汇接的网状网结构是江苏省本地电话网的基本框架,而汇接局和连接汇接局的传输系统则是网路规划与通信建设的重点。 相似文献
96.
In connection with the specific features of high velocity aerated flow generated by hydraulic engineering structures, the mathematical model is developed for high turbulence air-water two-phase flow with the use of twin flow theoretical model in this paper. Furthermore the numerical method is proposed to treat bubbled flows. In addition, on the basis of air-water stratified twin flow model, the new calculation methods and free surface tracking technique are proposed to describe complicated movements of the free surface. Finally, the proposed model is used to calculate artificial aerated flows. The computed results coincide quite well with experimental results. This means that the proposed method can provide solid basis for practical engineering design. 相似文献
97.
Although the dams produce remarkable social and economic benefits, the threat made by unsafe dams to the life and property of people who live in the lower river area is un-negligible. Based on the monitoring data which reflect the safety condition of dams, the risk degree concept is proposed and the analysis system and model for evaluating risk degree (rate) are established in this paper by combining the reliability theory and field monitoring data. The analysis method for risk degree is presented based on Bayesian approach. A five-grade risk degree system for dam operation risk and corresponding risk degree is put forward according to the safety condition of dams. The operation risks of four cascade dams on some river are analyzed by the model and approach presented here and the result is adopted by the owner. 相似文献
98.
Fanggao Chang Tao Li Yongxia Ge Zhenping Chen Zhongshi Liu Xiping Jing 《Journal of Materials Science》2007,42(17):7109-7115
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x
Ho
x
)TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x
Ho
x
)TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The
local electron density and defect concentration estimated using positron annihilation technique conforms well to the features
found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model. 相似文献
99.
北京市部分学校教室采光照明现状分析 总被引:8,自引:2,他引:6
近年来我国学生视力不良检出率居高不下,并且呈现明显上升趋势,已经到了极为严重的程度.学校教室的采光照明问题是保护学生视力健康的重要部分.2004年我国重新修订了国家标准〈建筑照明设计标准〉GB50034-2004.本文对北京市部分大中小学校进行采光照明的调查分析,结果显示,北京市学校教室采光照明问题十分严重,与国家标准要求差距很大,在被调查的39间教室中,窗地面积比达标率为20.5%,课桌面照度达标率为25.6%,黑板照度达标率为零. 相似文献
100.
Document caching and connection caching are extensively studied problems. In document caching, one has to maintain caches
containing documents accessible in a network. In connection caching, one has to maintain a set of open network connections
that handle data transfer. Previous work investigated these two problems separately while in practice the problems occur together:
In order to load a document, one has to establish a connection between network nodes if the required connection is not already
open. In this paper we present the first study that integrates document and connection caching. We first consider a very basic
model in which all documents have the same size and the cost of loading a document or establishing a connection is equal to
1. We present deterministic and randomized online algorithms that achieve nearly optimal competitive ratios unless the size
of the connection cache is extremely small. We then consider general settings where documents have varying sizes. We investigate
a FAULT model in which the loading cost of a document is 1 as well as a BIT model in which the loading cost is equal to the
size of the document. 相似文献