全文获取类型
收费全文 | 148244篇 |
免费 | 11090篇 |
国内免费 | 5219篇 |
专业分类
电工技术 | 7326篇 |
技术理论 | 8篇 |
综合类 | 13262篇 |
化学工业 | 21319篇 |
金属工艺 | 3613篇 |
机械仪表 | 4236篇 |
建筑科学 | 23901篇 |
矿业工程 | 6726篇 |
能源动力 | 6096篇 |
轻工业 | 21329篇 |
水利工程 | 20212篇 |
石油天然气 | 9726篇 |
武器工业 | 431篇 |
无线电 | 4413篇 |
一般工业技术 | 7153篇 |
冶金工业 | 6828篇 |
原子能技术 | 1367篇 |
自动化技术 | 6607篇 |
出版年
2024年 | 606篇 |
2023年 | 1842篇 |
2022年 | 3311篇 |
2021年 | 4164篇 |
2020年 | 4458篇 |
2019年 | 3700篇 |
2018年 | 3483篇 |
2017年 | 4244篇 |
2016年 | 4645篇 |
2015年 | 4835篇 |
2014年 | 9617篇 |
2013年 | 8766篇 |
2012年 | 10954篇 |
2011年 | 11122篇 |
2010年 | 8451篇 |
2009年 | 8863篇 |
2008年 | 7804篇 |
2007年 | 9921篇 |
2006年 | 9173篇 |
2005年 | 7998篇 |
2004年 | 6513篇 |
2003年 | 5901篇 |
2002年 | 5171篇 |
2001年 | 3998篇 |
2000年 | 3341篇 |
1999年 | 2588篇 |
1998年 | 1803篇 |
1997年 | 1459篇 |
1996年 | 1175篇 |
1995年 | 1020篇 |
1994年 | 758篇 |
1993年 | 573篇 |
1992年 | 468篇 |
1991年 | 351篇 |
1990年 | 252篇 |
1989年 | 260篇 |
1988年 | 174篇 |
1987年 | 177篇 |
1986年 | 122篇 |
1985年 | 127篇 |
1984年 | 104篇 |
1983年 | 67篇 |
1982年 | 43篇 |
1981年 | 18篇 |
1980年 | 39篇 |
1979年 | 19篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1959年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
文章介绍了期货交易所由于其特殊的机制,而对其注册上市产品的质量提高有显著的促进作用,同时介绍了“铜冠”牌阴极铜在LME注册成功,取得进入国际市场通行证中的一些情况。 相似文献
42.
43.
On irrigation schemes with rotational irrigation systems in semiarid tropics, the existing rules for water allocation are based on applying a fixed depth of water with every irrigation irrespective of the crops, their growth stages, and soils on which these crops are grown. However, when water resources are scarce, it is necessary to allocate water optimally to different crops grown in the irrigation scheme taking account of different soils in the command area. Allocating water optimally may lead to applying less water to crops than is needed to obtain the maximum yield. In this paper, a three stage approach is proposed for allocating water from a reservoir optimally based on a deficit irrigation approach, using a simulation-optimization model. The allocation results with a deficit irrigation approach are compared for a single crop (wheat) in an irrigation scheme in India, first with full irrigation (irrigation to fill the root zone to field capacity) and second with the existing rule. The full irrigation with a small irrigation interval was equivalent to adequate irrigation (no stress to the crop). It is found that practicing deficit irrigation enables the irrigated area and the total crop production in the irrigation scheme used for the case study to be increased by about 30–45% and 20–40%, respectively, over the existing rule and by 50 and 45%, respectively, over the adequate irrigation. Allocation of resources also varied with soil types. 相似文献
44.
45.
建(构)筑物机械拆除方法综述 总被引:1,自引:0,他引:1
介绍了几种常用的建(构)筑物机械拆除方法,对其工作原理、特点、应用条件及局限性加以分析和说明。 相似文献
46.
47.
H. Perez-Blanco 《International Journal of Refrigeration》1993,16(6):429-433
The search for high-efficiency, gas-fired cooling cycles has led to the development of dual-loop absorption machines with cooling coefficients of performance (COPs) in the 1.2 to 1.7 range. This increased performance may call for high generator temperatures, new working fluids or new materials of construction. In most cases, two different sets of working fluids are required. The conceptual design presented here is aimed at obtaining high efficiencies with relatively low temperatures, employing only one set of fluids. The concept consists of two loops coupled in a configuration aimed at minimizing the loss of thermodynamic availability incurred when transferring refrigerant between the loops. The working fluid pair is a solution of lithium bromide-water. The calculated COPs are of the order of 1.8. The cycle relies on an elaborate evaporator-absorber combination. The paper presents the conceptual design, the critical assumptions, and the performance calculations for the concept. 相似文献
48.
Paul W. Oman 《Software Quality Journal》1993,2(1):13-27
Software quality assurance (SQA) audits are becoming a standard practice in corporations seeking to enter contractual relations with other organizations, or just evaluating their own state of readiness. This paper describes one approach to conducting SQA audits. Excerpts from reports of actual audits conducted on several organizations engaged in software development are used to show how an audit is conducted and what can be achieved through the auditing process. The paper is not meant to be a definitive answer or guide to doing SQA audits. Rather, it serves as an annotated case study of how SQA audits can be conducted with an emphasis on data gathering and reporting.Dr Paul W. Oman is an associate professor of computer science at the University of Idaho, and an independent software consultant who specializes in software analysis. He is the director of the Software Engineering Test Lab within the UI College of Engineering, where he conducts research in software development methods, CASE tools, and software maintainability issues. Oman has published over 50 articles and reports on software tools, software development, and computer science education. He has a PhD in computer science and is a member of the IEEE, IEEE Computer Society, and ACM. 相似文献
49.
鄱阳湖流域水土流失加剧了洪涝灾害。治理水土流失能增强山丘地涵养水源的能力,削洪减沙,减少库容损失,降低河床,具有明显的防洪效益。进行流域防洪规划时,应将防治水土流失与防洪治涝结合起来,因地制宣,综合治理。 相似文献
50.
M. J. Assael S. Polimatidou W. A. Wakeham 《International Journal of Thermophysics》1993,14(4):795-803
The paper reports new, preliminary measurements of the viscosity of liquid water along two isotherms as a function of pressure up to 32 MPa. The measurements have been performed with a vibrating-wire viscometer especially modified for the purpose. The instrument has been calibrated with respect to the viscosity of water at a pressure of 0.1 MPa and a temperature of 293.15 K, for which an accurate reference value is available. With due regard to the precision of the determination of individual quantities and the accuracy of the calibration data, it is estimated that the accuracy of the present results is one of ±0.3% under all conditions.Paper dedicated to Professor Joseph Kestin. 相似文献