全文获取类型
收费全文 | 318329篇 |
免费 | 3486篇 |
国内免费 | 1290篇 |
专业分类
电工技术 | 6612篇 |
综合类 | 339篇 |
化学工业 | 44885篇 |
金属工艺 | 17158篇 |
机械仪表 | 12940篇 |
建筑科学 | 7602篇 |
矿业工程 | 1262篇 |
能源动力 | 6929篇 |
轻工业 | 25288篇 |
水利工程 | 2960篇 |
石油天然气 | 2853篇 |
武器工业 | 3篇 |
无线电 | 38125篇 |
一般工业技术 | 64494篇 |
冶金工业 | 56137篇 |
原子能技术 | 4935篇 |
自动化技术 | 30583篇 |
出版年
2021年 | 1562篇 |
2019年 | 1430篇 |
2018年 | 11012篇 |
2017年 | 11609篇 |
2016年 | 7253篇 |
2015年 | 2459篇 |
2014年 | 3255篇 |
2013年 | 10864篇 |
2012年 | 8138篇 |
2011年 | 16356篇 |
2010年 | 14479篇 |
2009年 | 14004篇 |
2008年 | 14209篇 |
2007年 | 16383篇 |
2006年 | 7116篇 |
2005年 | 10260篇 |
2004年 | 8268篇 |
2003年 | 7888篇 |
2002年 | 6885篇 |
2001年 | 6448篇 |
2000年 | 5939篇 |
1999年 | 6449篇 |
1998年 | 16632篇 |
1997年 | 11623篇 |
1996年 | 8975篇 |
1995年 | 6714篇 |
1994年 | 5943篇 |
1993年 | 5763篇 |
1992年 | 4066篇 |
1991年 | 4021篇 |
1990年 | 3583篇 |
1989年 | 3511篇 |
1988年 | 3453篇 |
1987年 | 2911篇 |
1986年 | 2843篇 |
1985年 | 3418篇 |
1984年 | 3055篇 |
1983年 | 2749篇 |
1982年 | 2551篇 |
1981年 | 2571篇 |
1980年 | 2429篇 |
1979年 | 2273篇 |
1978年 | 2238篇 |
1977年 | 2812篇 |
1976年 | 4175篇 |
1975年 | 1900篇 |
1974年 | 1798篇 |
1973年 | 1786篇 |
1972年 | 1461篇 |
1971年 | 1317篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
951.
O. E. Narivs’kyi 《Materials Science》2007,43(1):124-132
We have studied the micromechanism of corrosion fracture of heat-transfer plates of a heat exchanger. The operation of heat
exchangers under conditions of contamination of the plates with a sediment from water leads to their local corrosion under
the sediment. The conditions of operation of the heat exchangers being equal, heat-transfer plates made of AiSi316Ti steel
worked 2.36 times as long as those of AiSi304L steel. The corrosion fracture of plates under the sediment began from pitting
initiation near nonmetallic inclusions of a certain nature. Afterwards, these pittings built up into corrosion spots by the
mechanism of stress corrosion and hydrogen embrittlement.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 110–116, January–February, 2007. 相似文献
952.
Published data on the preparation procedures, stability, and complexation of U(III) in aqueous solutions are summarized and correlated. Reactions with inorganic and organic free radicals studied by the flash radiolysis method, the spectroscopic properties, the extraction and ion-exchange behavior of U(III), and methods for isolation of solid U(III) compounds from aqueous solutions are discussed. 相似文献
953.
Boundary objects are a critical, but understudied, theoretical construct in CSCW. Through a field study of aircraft technical
support, we examined the role of boundary objects in the practical achievement of safety by service engineers. Their resolution
of repair requests was preserved in the organization’s memory via three compound boundary objects. These crystallizations
did not manifest a static interpretation, but instead were continually reinterpreted in light of meta-negotiations. This suggests
design implications for organizational memory systems which can more fluidly represent the meta-negotiations surrounding boundary
objects. 相似文献
954.
Materials with inherent microstructures like granular media, foams or spongy bones often show a complex constitutive behaviour
on the macroscale while the microscopic constitutive equations may be formulated in a simple fashion. Applying homogenization
procedures allows to transfer the information from the microlevel to the macrolevel.
In the present contribution the porous structure of hard biological tissues, i.e. of spongy bones, is investigated. On the
macroscale the approach is embedded into an extended continuum mechanical setting in order to capture size effects. The constitutive
equations are formulated on the microscopic level taking into account growth and reorientation of the microstructural elements.
By application of a strain-driven numerical homogenization procedure the macroscopic stress response is obtained. 相似文献
955.
956.
Chadwin D. Young Gennadi Bersuker Yuegang Zhao Jeff J. Peterson Joel Barnett George A. Brown Jang H. Sim Rino Choi Byoung Hun Lee Peter Zeitzoff 《Microelectronics Reliability》2005,45(5-6):806
Effects of constant voltage stress (CVS) on gate stacks consisting of an ALD HfO2 dielectric with various interfacial layers were studied with time dependent sensing measurements: DC I–V, pulse I–V, and charge pumping (CP) at different frequencies. The process of injected electron trapping/de-trapping on pre-existing defects in the bulk of the high-κ film was found to constitute the major contribution to the time dependence of the threshold voltage (Vt) shift during stress. The trap generation observed with the low frequency CP measurements is suggested to occur within the interfacial oxide layer or the interfacial layer/high-κ interface, with only a minor effect on Vt. 相似文献
957.
Reference feedforward in the idle speed control of a direct-injection spark-ignition engine 总被引:1,自引:0,他引:1
Scillieri J.J. Buckland J.H. Freudenberg J.S. 《Vehicular Technology, IEEE Transactions on》2005,54(1):51-61
The direct-injection spark-ignition engine has emerged as a focus of research in improving fuel economy and controlling emissions. This engine can operate in multiple modes, including a stratified charge mode with an air-fuel ratio as large as 50:1. Operating in stratified mode results in improved fuel economy and reduced CO/sub 2/ emissions. The stratified charge mode is employed during low speed and load conditions, such as during engine idle. The idle speed control problem is cast as a two-input-two-output control problem and a baseline feedback controller is developed based on an existing topology from the literature. Significant delays, however, inhibit our ability to improve the transient response via feedback alone. An improved scheme employing reference feedforward is proposed and several potential topologies are presented. A reference feedforward algorithm is derived and nonlinear simulation results are shown in which the system transient responses are improved considerably. 相似文献
958.
Phylogenetic scanning: a computer-assisted algorithm for mapping gene conversions and other recombinational events 总被引:1,自引:0,他引:1
An algorithm, 'phylogenetic scanning', is described for mapping gene conversion events where comparative DNA sequence data are available from different species. In this algorithm, sets of hypothetical phylogenetic trees are constructed that describe possible sequence relationships due to gene conversions in different species lineages; these trees are then evaluated by the principle of parsimony at intervals in the sequence alignment. When used to map gene conversion events that occurred between the pair of gamma-globin genes of higher primates, the algorithm gives results nearly identical to those obtained using a tedious manual approach. Suggestions are also provided for adaptation of this procedure to the analysis of other recombination events. 相似文献
959.
960.