全文获取类型
收费全文 | 490055篇 |
免费 | 37359篇 |
国内免费 | 19798篇 |
专业分类
电工技术 | 27334篇 |
技术理论 | 47篇 |
综合类 | 32026篇 |
化学工业 | 77372篇 |
金属工艺 | 28468篇 |
机械仪表 | 30084篇 |
建筑科学 | 34550篇 |
矿业工程 | 13746篇 |
能源动力 | 12397篇 |
轻工业 | 31844篇 |
水利工程 | 9381篇 |
石油天然气 | 25977篇 |
武器工业 | 3441篇 |
无线电 | 54970篇 |
一般工业技术 | 59912篇 |
冶金工业 | 22880篇 |
原子能技术 | 4644篇 |
自动化技术 | 78139篇 |
出版年
2024年 | 2886篇 |
2023年 | 6954篇 |
2022年 | 12009篇 |
2021年 | 16601篇 |
2020年 | 12674篇 |
2019年 | 10133篇 |
2018年 | 24497篇 |
2017年 | 25101篇 |
2016年 | 21135篇 |
2015年 | 17019篇 |
2014年 | 20816篇 |
2013年 | 24656篇 |
2012年 | 29769篇 |
2011年 | 38179篇 |
2010年 | 33764篇 |
2009年 | 30011篇 |
2008年 | 30883篇 |
2007年 | 30586篇 |
2006年 | 23556篇 |
2005年 | 21412篇 |
2004年 | 14930篇 |
2003年 | 13477篇 |
2002年 | 12362篇 |
2001年 | 10644篇 |
2000年 | 10204篇 |
1999年 | 10316篇 |
1998年 | 7771篇 |
1997年 | 6629篇 |
1996年 | 6227篇 |
1995年 | 5091篇 |
1994年 | 4131篇 |
1993年 | 2797篇 |
1992年 | 2231篇 |
1991年 | 1703篇 |
1990年 | 1307篇 |
1989年 | 1067篇 |
1988年 | 888篇 |
1987年 | 559篇 |
1986年 | 428篇 |
1985年 | 280篇 |
1984年 | 221篇 |
1983年 | 172篇 |
1982年 | 142篇 |
1981年 | 86篇 |
1980年 | 108篇 |
1979年 | 49篇 |
1968年 | 46篇 |
1959年 | 46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
991.
992.
993.
Although many link patterns have been identified at the university level, departmental interlinking has been relatively ignored.
Universities are multidisciplinary by nature and various disciplines may employ the Web differently, thus patterns identified
at the university level may hide subject differences. Departments are typically subject-oriented, and departmental interlinking
may therefore illustrate interesting disciplinary linking patterns, perhaps relating to informal scholarly communication.
The aim of this paper is to identify whether and how link patterns differ along country and disciplinary lines between similar
disciplines and similar countries. Physics, Chemistry and Biology departments in Australia, Canada and the UK have been chosen.
In order to get a holistic picture of departments' Web use profiles and link patterns, five different perspectives are identified
and compared for each set of departments. Differences in link patterns are identified along both national and disciplinary
lines, and are found to reflect offline phenomena. Along national lines, a likely explanation for the difference is that countries
with better research performances make more general use of the Web; and, with respect to international peer interlinking,
countries that share more scholarly communication tend to interlink more with each other. Along disciplinary lines, it seems
that departments from disciplines which are more willing to distribute their research outputs tend to make more general use
of the Web, and also interlink more with their national and international peers. 相似文献
994.
本文介绍了如何用分析嵌套选择语句的逻辑关系,主要方法是借助分裂图画出N-S图,最后再根据IF…ELSE…语句配对原理分析出各子句的关系。 相似文献
995.
爆炸冲击波作用下核电站安全壳动力分析模型 总被引:5,自引:0,他引:5
根据某国防科研课题,建立核电站安全壳在爆炸冲击波作用下的动力分析模型,讨论并分析了质点杆模型在安全壳预应力混凝土结构中的应用。质点杆模型可用于计算爆炸冲击波作用下的结构响应。 相似文献
996.
刘军 《武汉理工大学学报(材料科学英文版)》2003,18(1):61-64
1 IntroductionThehighmechanicalproperties ,gooddurabilityandappropriateworkabilityarenecessaryforhighperformanceconcretetosatisfytheconstructionrequirementoflarge scaleconcreteengineering .Accordingtodifferentapplica tionsandpurposes ,inordertoimprovethe… 相似文献
997.
TiO2 fims have been deposited on glass substrates using DC reactive magnetron sputtering at different oxygen partial pressures
from 0. 10 Pa.to 0.65 Pa. The transmittance (UV-vis) and photoluminescence (PL) spectra of the films were recorded. The results
of the UV-vis spectra show that the deposition rate of the films decreased at oxygen partial pressure P(O2)≥0.15 Pa, the band gap increased from 3.48 eV to 3.68eV for direct transition and from 3.27 eV to 3.34 eV for indirect transition
with increasing the oxygen partial pressure. The PL spectra show convincingly that the transition for films was indirect,
and there were some oxygen defect energy levels at the band gap of the films. With increasing the O2 partial pressure, the defect energy levels decreased. For the films sputtered at 0.35 and 0.65 Pa there were two defect energy
levels at 2.63 eV and 2.41 eV, corresponding to 0.72 eV and 0.94 eV below the conduction band for a band gap of 3.35 eV, respectively.
For the films sputtered at 0.10 Pa and 0.15 Pa, there was an energy band formed between 3.12 eV and 2.06 eV, corresponding
to 0.23 eV and 1.29 eV below the conduction band.
ZHAO Qing-nan : Born in 1963
Funded by Natural Science Foundation of Hubei Province, China. 相似文献
998.
The hydration characteristics and expansion impetus of three kinds of cement paste under free-and confined-curing conditions
were investigated, which were respectively mixed with three different kinds of expansive agent at low W/B ratio. The results
show that the hydration products of pure cement paste and paste mixed with expansive agent are same, but the amount of hydration
products, un-hydrated C3S and C2S are obviously different at the same hydration age. At 3 d age, the amount of CH in pure cement paste is less than that of
paste mixed with expansive agent, but it is reverse when at 28 d age. The amount of AFt at 3d and 28d age in pure cement paste
is less than those of paste mixed with expansive agent. Regardless of under free- or confined-curing condition, the amount
of ettringite produced varies little since 3d age. The joint effect of the tumefaction of gel-ettringite due to water absorption
and the expansive pressure on the pore caused by the crystalloid ettringite is the cause of the volume expansion of cement
paste, and the former effect is much greater than the latter.
LU Lin-nu : Born in 1972
Funded by 973 High-tech Project of China (No. 2001CB610704-2) and the Natural Science Foundation of Hubei Province(No. 2002AB075) 相似文献
999.
1000.
SATCHMORE was introduced as a mechanism to integrate relevancy testing with the model-generation theorem prover SATCHMO. This
made it possible to avoid invoking some clauses that appear in no refutation, which was a major drawback of the SATCHMO approach.
SATCHMORE relevancy, however, is driven by the entire set of negative clauses and no distinction is accorded to the query
negation. Under unfavorable circumstances, such as in the presence of large amounts of negative data, this can reduce the
efficiency of SATCHMORE. In this paper we introduce a further refinement of SATCHMO called SATCHMOREBID: SATCHMORE with BIDirectional
relevancy. SATCHMOREBID uses only the negation of the query for relevancy determination at the start. Other negative clauses
are introduced on demand and only if a refutation is not possible using the current set of negative clauses. The search for
the relevant negative clauses is performed in a forward chaining mode as opposed to relevancy propagation in SATCHMORE which
is based on backward chaining. SATCHMOREBID is shown to be refutationally sound and complete. Experiments on a prototype SATCHMOREBID
implementation point to its potential to enhance the efficiency of the query answering process in disjunctive databases.
Donald Loveland, Ph.D.: He is Emeritus Professor of Computer Science at Duke University. He received his Ph.D. in mathematics from New York University
and taught at NYU and CMU prior to joining Duke in 1973. His research in automated deduction includes defining the model elimination
proof procedure and the notion of linear resolution. He is author of one book and editor/co-editor of two other books on automated
theorem proving. He has done research in the areas of algorithms, complexity, expert systems and logic programming. He is
an AAAI Fellow, ACM Fellow and winner of the Herbrand Award in Automated Reasoning.
Adnan H. Yahya, Ph.D.: He is an associate professor at the Department of Electrical Engineering, Birzeit University, Palestine. He received his
Diploma and PhD degrees from St. Petersburg Electrotechnical University and Nothwestern University in 1979 and 1984 respectively.
His research interests are in Artificial Intelligence in general and in the areas of Deductive Databases, Logic Programming
and Nonmonotonic Reasoning in particular. He had several visiting appointments at universities and research labs in the US,
Germany, France and the UK. Adnan Yahya is a member of the ACM, IEEE and IEEE Computer Society. 相似文献