全文获取类型
收费全文 | 591319篇 |
免费 | 7042篇 |
国内免费 | 2182篇 |
专业分类
电工技术 | 11316篇 |
综合类 | 535篇 |
化学工业 | 88087篇 |
金属工艺 | 24720篇 |
机械仪表 | 18737篇 |
建筑科学 | 13477篇 |
矿业工程 | 2556篇 |
能源动力 | 16162篇 |
轻工业 | 47827篇 |
水利工程 | 5572篇 |
石油天然气 | 8932篇 |
武器工业 | 20篇 |
无线电 | 71937篇 |
一般工业技术 | 116167篇 |
冶金工业 | 113880篇 |
原子能技术 | 11990篇 |
自动化技术 | 48628篇 |
出版年
2021年 | 5037篇 |
2020年 | 3765篇 |
2019年 | 4870篇 |
2018年 | 8190篇 |
2017年 | 8137篇 |
2016年 | 8719篇 |
2015年 | 5762篇 |
2014年 | 9402篇 |
2013年 | 28216篇 |
2012年 | 15297篇 |
2011年 | 20823篇 |
2010年 | 16637篇 |
2009年 | 18719篇 |
2008年 | 19470篇 |
2007年 | 19307篇 |
2006年 | 17478篇 |
2005年 | 15848篇 |
2004年 | 15010篇 |
2003年 | 14977篇 |
2002年 | 14482篇 |
2001年 | 14369篇 |
2000年 | 13350篇 |
1999年 | 14259篇 |
1998年 | 36314篇 |
1997年 | 25309篇 |
1996年 | 19640篇 |
1995年 | 14605篇 |
1994年 | 12881篇 |
1993年 | 12823篇 |
1992年 | 9242篇 |
1991年 | 8862篇 |
1990年 | 8523篇 |
1989年 | 8131篇 |
1988年 | 7829篇 |
1987年 | 6856篇 |
1986年 | 6705篇 |
1985年 | 7655篇 |
1984年 | 6972篇 |
1983年 | 6288篇 |
1982年 | 5854篇 |
1981年 | 5960篇 |
1980年 | 5558篇 |
1979年 | 5315篇 |
1978年 | 5276篇 |
1977年 | 6236篇 |
1976年 | 8556篇 |
1975年 | 4529篇 |
1974年 | 4283篇 |
1973年 | 4310篇 |
1972年 | 3625篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
701.
Planning is an essential function of project management. Yet, many small- and medium-sized contractors do a relatively poor job of operational planning. Better prebid plans will reduce costs, shorten schedules, and improve labor productivity. Unfortunately, the published literature offers little guidance for smaller contractors on what constitutes effective planning. Most papers describe planning as a macrolevel process for owners. Most emphasize scope definition for industrial projects. This paper describes a microlevel planning process for contractors. It consists of eight steps which are: (1) assess contract risks; (2) develop a preliminary execution plan; (3) develop site layout plans; (4) identify the sequences that are essential-to-success; (5) develop detailed operational plans; (6) develop proactive strategies to assure construction input into design; (7) revise the preliminary plan; and (8) communicate and enforce the plan. The entire process is illustrated with a case study project and is fully illustrated with figures which show how to integrate the work of multiple contractors, keep key resources (crews or equipment) fully engaged with no downtime, provide time buffers so the work of follow on crews can be efficiently done, expedite the schedule using multiple work stations and concurrent work, ways to communicate the work plan to the superintendent and foremen, and how to assess the feasibility of various work methods. The steps are easy to understand and implement. They will yield immediate positive results. 相似文献
702.
This paper investigates the effect of chelating agents on the bioavailability of Fe and Cu during anaerobic digestion. The results on metal speciation and methane production in anaerobic serum bottles showed that biomass was able to grow in the presence of citrate 1?mM and nitrilotriacetic acid (NTA) 1?mM, suggesting that the binding sites at the cell surface competed efficiently for the metals with the chelating agents added. The presence of free ethylenediaminetetraacetic acid 1?mM inhibited methanogenesis, and this seemed to be related to a loss in metal uptake capacity. Although the addition of soluble microbial products (SMP) did not change metal distribution in anaerobic systems, it caused an increase in the rate of methane production, and it is believed that direct uptake of Cu-SMP complexes was responsible for this increase. The best protection against Cu toxicity occurred when stoichiometric amounts of NTA, which should complex and solubilize most of the Cu, was added, and it is likely that NTA prevented lethal concentrations of Cu from being adsorbed onto the cell and hence internalized. 相似文献
703.
A new spreadsheet-cell-object-oriented algorithm for the first-order reliability method is proposed and illustrated for cases with correlated nonnormals and explicit and implicit performance functions. The new approach differs from the writers earlier algorithm by obviating the need for computations of equivalent normal means and equivalent normal standard deviations. It obtains the solution faster and is more efficient, robust, and succinct. Other advantages include ease of initialization prior to constrained optimization, ease of randomization of initial values for checking robustness, and fewer required optimization constraints during spreadsheet-automated search for the design point. Two cases with implicit performance functions, namely an asymmetrically loaded beam on Winkler medium and a strut with complex supports are analyzed using the new approach and discussed. Comparisons are also made between the proposed approach and that based on Rosenblatt transformation. 相似文献
704.
705.
706.
William D. Tape John B. Kennedy Murty K. S. Madugula 《Canadian Metallurgical Quarterly》2007,11(1):91-98
The current methods of connecting the flanges of precast double tee members, and their respective short comings in specific situations, are described. A new carbon fiber-reinforced polymer (CFRP) flange-to-flange connection is proposed to eliminate the problems associated with repair requirements for the current connections. Design expressions for the currently used mechanical anchorage and the proposed CFRP connection are presented. A comparative calculation for the two systems is given. 相似文献
707.
708.
709.
710.