全文获取类型
收费全文 | 741700篇 |
免费 | 11913篇 |
国内免费 | 3194篇 |
专业分类
电工技术 | 14178篇 |
技术理论 | 5篇 |
综合类 | 2286篇 |
化学工业 | 112867篇 |
金属工艺 | 28080篇 |
机械仪表 | 21409篇 |
建筑科学 | 18618篇 |
矿业工程 | 4033篇 |
能源动力 | 18822篇 |
轻工业 | 65652篇 |
水利工程 | 7696篇 |
石油天然气 | 13491篇 |
武器工业 | 284篇 |
无线电 | 80552篇 |
一般工业技术 | 138270篇 |
冶金工业 | 151470篇 |
原子能技术 | 14282篇 |
自动化技术 | 64812篇 |
出版年
2021年 | 6826篇 |
2020年 | 4811篇 |
2019年 | 6086篇 |
2018年 | 10399篇 |
2017年 | 10373篇 |
2016年 | 11361篇 |
2015年 | 8319篇 |
2014年 | 12697篇 |
2013年 | 32838篇 |
2012年 | 21594篇 |
2011年 | 29287篇 |
2010年 | 22118篇 |
2009年 | 24294篇 |
2008年 | 25231篇 |
2007年 | 24986篇 |
2006年 | 21962篇 |
2005年 | 22145篇 |
2004年 | 20328篇 |
2003年 | 19336篇 |
2002年 | 17780篇 |
2001年 | 17768篇 |
2000年 | 16159篇 |
1999年 | 16994篇 |
1998年 | 45176篇 |
1997年 | 31734篇 |
1996年 | 24015篇 |
1995年 | 17793篇 |
1994年 | 15607篇 |
1993年 | 15266篇 |
1992年 | 10869篇 |
1991年 | 10261篇 |
1990年 | 10135篇 |
1989年 | 9910篇 |
1988年 | 9250篇 |
1987年 | 8112篇 |
1986年 | 8052篇 |
1985年 | 8923篇 |
1984年 | 8401篇 |
1983年 | 7515篇 |
1982年 | 7027篇 |
1981年 | 7303篇 |
1980年 | 6833篇 |
1979年 | 6763篇 |
1978年 | 6516篇 |
1977年 | 7933篇 |
1976年 | 10852篇 |
1975年 | 5771篇 |
1974年 | 5331篇 |
1973年 | 5487篇 |
1972年 | 4510篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
971.
This paper sets out to share BT's leadership and experience by determining the identity management opportunities and issues,
then document the lessons learnt in previous deployments and recommend strategies for all types and sizes of organisation.
Today's ICT environment has created a mixed approach to access management across sectors. Browser-based any time, anywhere,
anyone access, coupled with the business need to access more systems and services across a changing infrastructure of distributed
platforms and networked services, has changed the administrative landscape. Enterprises are being forced to add administrative
support staff or invest in technology-driven process change. At the same time, users are undergoing significant change, creating
new expectations in service quality. Moreover, regulatory bodies are demanding confirmation that processes granting access
are controlled and documented. In this world of increasing demands, complexity and expectation, the service management tools,
techniques and options available to improve user access management are as varied and numerous as the issues faced by management
in their deployment.
Identity management is widely heralded as an opportunity to improve the end user experience, reduce costs, improve security
and deliver regulatory compliance — but is often misunderstood. Projects regularly fail to achieve the expected benefits.
These failures are the result of expectations being inappropriately set, deployment of solutions turning out to be more complex
or taking longer than expected, and/or products selected before required functionality has been determined.
For the larger more mature organisations, or those organisations that are the amalgamation of mergers and acquisitions, the
dilemma is where to start and what approach to take. 相似文献
972.
J Alemany J Comas C Turon M D Balaguer M Poch M A Puig J Bou 《Water science and technology》2005,51(10):179-186
The identification of adequate wastewater treatment for small communities is a complex problem since it demands a combination of data from different sources, such as aspects of the community and landscape, the receiving environment and the available wastewater treatment technologies. The Catalan Water Agency (Agència Catalana de l'Aigua) considered using an EDSS (Environmental Decision Support System) as a tool to help water managers select the most adequate treatment for the urban wastewater of nearly 3,500 small communities in Catalonia (Spain). From that moment, EDSS was applied to all the river basins in Catalonia. In this paper the authors present the results obtained for the 76 small communities located in one of these river basins: the Fluvia River Basin. The characteristics of the community used in the reasoning process of the EDSS, the list of selected wastewater treatment alternatives, the technical environmental justification for the selected treatments and the reasons for discarding, favouring or disadvantaging them are presented. Finally, some results for the Fluvia River Basin are compared with those obtained in other Catalan river basins with different characteristics in order to evaluate which are the significant features in identifying adequate wastewater treatments. 相似文献
973.
Continuous simulation is performed using the US Environmental Protection Agency (USEPA) Storm Water Management Model (SWMM) to evaluate regional differences around the United States in hydrologic and water quality performance of wet-weather controls. Controls are characterised as being limited by peak inflow rate (i.e. any device with little or no storage, such as screens, filters and some proprietary devices) or by storage capacity (e.g., ponds, tanks). For flow-limited devices, results are presented in the form of percentage of annual runoff volume captured (passing through the device) for a given inflow capacity. For storage-limited devices, results are presented in two forms: percentage of annual runoff volume captured as a function of unit basin size and drawdown (drain) time, and as a percentage of total suspended solids captured, for the same two variables. Regional differences are apparent, driven mainly by variations in rainfall patterns around the country. 相似文献
974.
Polyelectrolite hydrogels are crosslinked polymers which display high sorption capacity in water and water solutions. They are widely used in the marked of personal hygiene products, as well as in other biomedical and industrial applications. In the most industrial application they are not biodegradable and prepared starting from acrylamide.In this work, the chemical-physical analysis of a novel class of natural polymers-based microporous superabsorbent hydrogels has been presented. The main focus is the definition of the relationship between material's chemical-physical structure and its equilibrium sorption properties.The effect of the variation of the degree of crosslinking, the polyelectrolyte nature of the backbone and the hydrogel microporosity on its swelling properties has been analysed, and a good agreement with the theoretical statements has been displayed.The effect of the ionic strength and the pH of the external solution in contact with the hydrogel on its equilibrium sorption properties has also been assessed, and an high sensitivity to these variations was detected for all the tested chemical compositions and physical structures.This work have to be considered part of the efforts towards the reduction of the environmental impact of the large scale consumption industrial polymer based products. 相似文献
975.
T.L. Phillips 《Polymer》2005,46(24):11035-11050
Results are presented from atomistic molecular dynamics simulations of the mobile pseudo-hexagonal phase of polyethylene, which occurs under conditions of elevated pressure and temperature. Three different types of model are considered, all of which employ periodic boundary conditions. The first model consists of n-alkane sequences (48×-C24H48-) that are bonded across the simulation box boundaries to produce chains that are effectively infinite in extent. On heating, at high pressure, this system displays a rotator phase, in which the chains retain an all-trans conformation, and rotate as semi-rigid units. A second model, consisting of finite n-alkanes (48×C24H50) displays the same behaviour at low temperatures, but at high temperature and pressure forms a conformationally disordered rotator phase, characterised by a large proportion of gauche defects and a significant lattice expansion. The final model considered contains long n-alkanes (24×C102H206) which contain jog defects and each pass twice through the simulation box. This model forms a conformationally disordered rotator phase at high temperature and ambient pressure. The behaviour of the three models, in terms of the variations in chain conformation and rotational and translational dynamics, are compared. The conformationally disordered phases provide useful representations of the experimentally observed mobile phase. 相似文献
976.
3D characterization and analysis of particle shape using X-ray microtomography (XMT) 总被引:2,自引:0,他引:2
C.L. Lin 《Powder Technology》2005,154(1):61-69
977.
978.
Microbial sensor for preliminary screening of mutagens utilizing a phage induction test 总被引:1,自引:0,他引:1
For the preliminary screening of mutagens, a novel microbial sensor system was developed utilizing a phage induction test. Escherichia coli lysogenic strain GY5027 and nonlysogenic strain GY5026 were used in this study. The number of living cells was determined by measuring the respiration of cells immobilized onto an oxygen electrode. The injection of a mutagen, such as AF-2 and MNNG, caused the phage induction in the lysogenic strain, resulting in the decreased respiration of only the lysogenic strain immobilized onto the oxygen electrode but not of nonlysogenic strain. The rate of current increase correlated well with the concentration of mutagens. The sensor responses to the antibiotics and bactericides were definitely different from those of mutagens. Therefore, utilization of this microbial sensor system makes possible the estimation of a substrate's mutagenicity. 相似文献
979.
The composition of the Co-Cr-Mo alloy has been modified by additions of nickel and some trace elements aluminium, titanium and boron. In this paper, the first part of the present study, the effects of alloy additions on the microstructures and tensile properties of the as-cast Co-Cr-Mo alloy are discussed. The effects of alloy additions on the fatigue behaviour of the alloy will be discussed in the second part of the present study. It is found that alloy additions do not seem to result in changes in the nature of the casting structure. A directional, coarse dendritic cast structure is produced in the modified alloys as in the base alloY. However, the alloy additions affect the carbide precipitations and the formation of some fine details of the microstructure such as dislocations, stacking faults and twins produced during the solidification. A considerable improvement in the transient mechanical properties, especially in the tensile ductility, is achieved by modifying the base alloy with alloy additions. 相似文献
980.
L. Vandewalle 《Journal of Materials Science Letters》1989,8(2):147-149