全文获取类型
收费全文 | 38718篇 |
免费 | 625篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 410篇 |
综合类 | 64篇 |
化学工业 | 8051篇 |
金属工艺 | 702篇 |
机械仪表 | 658篇 |
建筑科学 | 2222篇 |
矿业工程 | 80篇 |
能源动力 | 1025篇 |
轻工业 | 3321篇 |
水利工程 | 371篇 |
石油天然气 | 183篇 |
武器工业 | 4篇 |
无线电 | 2825篇 |
一般工业技术 | 6993篇 |
冶金工业 | 6347篇 |
原子能技术 | 265篇 |
自动化技术 | 5847篇 |
出版年
2024年 | 254篇 |
2023年 | 362篇 |
2022年 | 494篇 |
2021年 | 851篇 |
2020年 | 688篇 |
2019年 | 801篇 |
2018年 | 794篇 |
2017年 | 765篇 |
2016年 | 1057篇 |
2015年 | 924篇 |
2014年 | 1150篇 |
2013年 | 2078篇 |
2012年 | 1824篇 |
2011年 | 2306篇 |
2010年 | 1689篇 |
2009年 | 1612篇 |
2008年 | 1933篇 |
2007年 | 1792篇 |
2006年 | 1597篇 |
2005年 | 1333篇 |
2004年 | 1205篇 |
2003年 | 1071篇 |
2002年 | 1022篇 |
2001年 | 672篇 |
2000年 | 640篇 |
1999年 | 662篇 |
1998年 | 855篇 |
1997年 | 698篇 |
1996年 | 635篇 |
1995年 | 542篇 |
1994年 | 521篇 |
1993年 | 528篇 |
1992年 | 444篇 |
1991年 | 282篇 |
1990年 | 381篇 |
1989年 | 376篇 |
1988年 | 306篇 |
1987年 | 339篇 |
1986年 | 335篇 |
1985年 | 340篇 |
1984年 | 304篇 |
1983年 | 297篇 |
1982年 | 283篇 |
1981年 | 248篇 |
1980年 | 214篇 |
1979年 | 226篇 |
1978年 | 204篇 |
1977年 | 213篇 |
1976年 | 214篇 |
1975年 | 169篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Terrorism: A Reference Handbook, Stephen Atkins, Santa Barbara, ABC-CLIO (1992), 199 pp. Terrorism: Roots, Impact, Responses, Lawrence Howard (Ed.), Prager, New York (1992), 193 pp. Hostage-Taking Terrorism: Incident Response Strategy, Alastair MacWillson, St Martins, New York (1992), 263 pp. 相似文献
13.
The reduction of nitric oxide with ammonia on an unsupported iron oxide catalyst has been studied in a continuous-flow recycle reactor using simulated flue gas. The responses of the employed reactor system to step and pulse inputs of tracer indicate that the system could be regarded as a continuous stirred tank reactor (CSTR). Preliminary tests were carried out to determine the effect of temperature and particle size on the measured reaction rates. Additional experiments were performed in order to study the influence of oxygen and water concentration on these rates. A gas chromatographic system has been developed to analyze the gas components NO, N2O, NO2, NH3, H2O, O2, CO2 and N2. In addition, the concentrations of NO and NO2 were measured with a nondisperse infrared (NDUV/NDIR) analyzer. 相似文献
14.
15.
16.
Michael Brady 《Energy》1985,10(10):1113-1118
Current energy policies have severely eroded the earth's natural atmospheric waste-receptor capacity. Present acid rain concentrations may require a switch to an alternative energy-resource emphasis. This policy recommendation follows directly from a deductive control theory demonstration which shows that, if fossil-fuel use is continued at present rates, then there is an ever-increasing risk of a man-made environmental crisis of uncertain nature and scope. 相似文献
17.
The University of Maryland's Computer Aided Life Cycle Engineering (CALCE) research effort is aimed at developing techniques for design, analysis, prediction, and optimization of electronics with respect to a variety of design goals. Performance, producibility, reliability, maintainability, life-cycle cost, safety, etc., are the design criteria which are being integrated through the application of interactive heuristic and algorithmic design optimization techniques. The University of Maryland Reliability and Maintainability Computer-Aided Design (RAMCAD) research is CALCE and is focused on second- and third-level electronic package design with respect to interfacing thermal, mechanical, and reliability analysis. The goal is to make reliability and maintainability an integral, real-time, and upfront part of the design process, such that the need to resubmit designs will be eliminated. The motivation behind this project was the fact that schedule constraints are often compromising the effectiveness and efficiency of the design process. To achieve the goal of CALCE/RAMCAD, a cohesive and extensible design environment for analysis and tradeoff tools was developed. A system executive controller that integrates tools for analysis while providing system transparency, design data management, and process management was developed to guide the user through the design process and provide direct access to the design tools. These developments required the integration of computer-aided design (CAD), artificial intelligence (AI), and decision support (DS) techniques. Attention to human factors and the use of interactive graphics were also instrumental in the development. 相似文献
18.
Government energy pricing policies have multiple and often conflicting objectives: economic efficiency, government revenues (for both parastatal supply companies and the treasury), maintenance or improvement of income distribution, promotion of particular sectors (such as industrial exporters and local resource development) demand management and security of supply. It is important to examine the impacts on and the trade-offs between these objectives resulting from alternative policies in order to assist in policy selection. This article discusses the more important objectives and their conflicts and outlines an approach for the quantitative examination of alternative policies. 相似文献
19.
20.
Michael E. Prudich M. Khairul Alam Noor-Un Nahar 《Particulate Science and Technology》1994,12(2):127-137
The objective of the present study was to generate submicrometer calcium hydroxide aerosols and to investigate the effectiveness of such aerosols in sulfur capture. The effectiveness of SO2 removal by Ca(OH)2 aerosol has been investigated in an isothermal reactor. Ca(OH) 2 aerosol was generated by a novel fluidizer system in which submicrometer-sized powders were entrained in gases. SO2 was added to this aerosol to a concentration of 2000 ppm. The aerosol-SO2 mixture was heated to 550°C-750°C in an isothermal tube reactor. The SO2 removal efficiency, which varied from 20% to 70%, was determined to be a function of the aerosol concentration, reactor temperature and residence time. The fraction of aerosol reacted was not affected strongly by the aerosol concentration. The reaction kinetics were determined from the experimental data using a simple analytical model in which the rate is first order in both SO2 and calcium hydroxide aerosol concentrations. 相似文献