全文获取类型
收费全文 | 181040篇 |
免费 | 17918篇 |
国内免费 | 10113篇 |
专业分类
电工技术 | 14455篇 |
技术理论 | 8篇 |
综合类 | 18876篇 |
化学工业 | 17682篇 |
金属工艺 | 7289篇 |
机械仪表 | 16258篇 |
建筑科学 | 20694篇 |
矿业工程 | 6845篇 |
能源动力 | 8001篇 |
轻工业 | 13292篇 |
水利工程 | 7667篇 |
石油天然气 | 9173篇 |
武器工业 | 2166篇 |
无线电 | 11669篇 |
一般工业技术 | 17539篇 |
冶金工业 | 6785篇 |
原子能技术 | 2646篇 |
自动化技术 | 28026篇 |
出版年
2024年 | 381篇 |
2023年 | 2129篇 |
2022年 | 4210篇 |
2021年 | 5367篇 |
2020年 | 5566篇 |
2019年 | 4725篇 |
2018年 | 4562篇 |
2017年 | 5587篇 |
2016年 | 6787篇 |
2015年 | 7225篇 |
2014年 | 11622篇 |
2013年 | 11790篇 |
2012年 | 13616篇 |
2011年 | 15046篇 |
2010年 | 10762篇 |
2009年 | 11067篇 |
2008年 | 10338篇 |
2007年 | 12407篇 |
2006年 | 10747篇 |
2005年 | 9033篇 |
2004年 | 7623篇 |
2003年 | 6459篇 |
2002年 | 5234篇 |
2001年 | 4322篇 |
2000年 | 3683篇 |
1999年 | 3086篇 |
1998年 | 2628篇 |
1997年 | 2219篇 |
1996年 | 1756篇 |
1995年 | 1528篇 |
1994年 | 1359篇 |
1993年 | 998篇 |
1992年 | 916篇 |
1991年 | 674篇 |
1990年 | 578篇 |
1989年 | 492篇 |
1988年 | 408篇 |
1987年 | 277篇 |
1986年 | 239篇 |
1985年 | 223篇 |
1984年 | 258篇 |
1983年 | 253篇 |
1982年 | 203篇 |
1981年 | 102篇 |
1980年 | 102篇 |
1979年 | 69篇 |
1978年 | 56篇 |
1977年 | 48篇 |
1976年 | 44篇 |
1959年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
991.
提出用CO作为早期火灾探测的观察对象,利用红外光谱法进行气体探测,并在此基础上建立了基于FTIR的试验系统.通过该方法成功获得CO的浓度值.并用时间序列分析方法建立二阶自回归模型,提取出特征参数进行分析,能在较短时间内将真假火灾区分开来. 相似文献
992.
993.
二元复合驱阶段见效特征 总被引:2,自引:0,他引:2
针对孤东油田油藏条件,通过室内试验研究,确定了以胜利石油磺酸盐为活性剂主剂和聚合物的二元复合驱油体系,通过两者之间的协同效应,增加水驱波及体积和洗油效率。该体系在孤东油田七区西馆上54—61层进行试验,取得了较好的阶段性降水增油效果。本文分析了复合驱见效特征和影响见效因素,为下步跟踪分析调整具有指导意义。 相似文献
994.
徐宝成 《石油化工安全环保技术》2006,22(1):31-34
有机过氧化物是烯烃聚合工业中重要的引发剂。针对烯烃聚合工业用有机过氧化物自分解温度低、易发生反应失控引发火灾爆炸等情况,简要叙述了有机过氧化物的结构、分类、化学性质以及反应特性,重点对其储存、使用、管理等过程中的危险性进行了分析。提出过氧化物储存、运输、使用、报废等方面的风险消减与事故预防措施。 相似文献
995.
Optimum thermoeconomic and thermodynamic performance characteristics of an irreversible three-heat-source heat pump 总被引:1,自引:0,他引:1
The coefficient of performance and specific heating load of an irreversible three-heat-source heat pump are given by using a general cycle model affected by the finite-rate heat transfer, heat leak and internal irreversibility of the cyclic working fluid. The heat pumping load divided by the total cost per unit time is taken as a new objective function and used to investigate the performance of the heat pump. The thermoeconomic and thermodynamic performance characteristics of the heat pump are discussed in detail. Some important performance parameters such as the thermoeconomic objective function and coefficient of performance are optimized. The optimally operating regions of the heat pump and the bounds of several performance parameters are determined. Finally, it is pointed out that the Carnot heat pump may be taken as a special case of a three-heat-source heat pump and consequently its optimal performance can be directly derived from the results obtained here. 相似文献
996.
The research was conducted to evaluate the effects of cellulose and polyester fibers on the properties of porous asphalt mixes, using the tests of draindown, abrasion, volumetric properties, rutting, and moisture damage. Images of scanning electron microscopy and X-ray computerized tomography were adopted to identify the microstructure of the fiber and inner stone skeleton of porous asphalt. The influence of rutting parameter (G*/sin δ) of asphalt modified by different fibers on the rutting resistance of the mixes was investigated. Based upon MOHR-COULOMB theory, the cohesion and the angle of internal friction of the mixes were derived from both indirect tension and unconfined compression strength. The experimental results indicate that fibers mainly stabilize asphalt binder and thicken asphalt film around aggregates. Furthermore, they result in the improved mechanical strength of porous asphalt mixes at high temperature slightly. From comparison analysis, cellulose fibers appear to perform better than polyester fibers in porous asphalt mixes. 相似文献
997.
本文先从软件理论的角度对安全协议分析语言CPAL的语法和语义进行分析,指出这种语言控制流的缺陷,在语法和语义方面给出CPAL语言的完善方案,并从信息安全中的协议的广泛性方面说明其必要性。 相似文献
998.
We propose a simulation-based algorithm for inference in stochastic volatility models with possible regime switching in which the regime state is governed by a first-order Markov process. Using auxiliary particle filters we developed a strategy to sequentially learn about states and parameters of the model. The methodology is tested against a synthetic time series and validated with a real financial time series: the IBOVESPA stock index (São Paulo Stock Exchange). 相似文献
999.
Stress analysis of pin-loaded woven-glass fiber reinforced epoxy laminate conveying chain components
The aim of this study is to examine the effects of various loading conditions on the stress of a pin-loaded woven-glass fiber reinforced epoxy laminate conveying chain component. A numerical and experimental study was carried out to determine the stress distribution of composite conveying chain components used to convey loads. For the experimental study, an apparatus was developed to simulate chain components in real motion. Two different working conditions of the chain component were investigated. The first condition represents the movement of the chain components without loading. In the second condition, the chain component touches and moves the load. The commercial finite element package ANSYS was used to perform the numerical analysis using a three dimensional eight-noded layered structural solid elements. Chain tensile forces were loaded through pins and chosen as 250, 500, 750, 1000 and 1250 N for the two conditions of chain components. Experimental and numerical studies were compared and discussed for two conditions and five different tensile forces. A good agreement between experimental results and numerical predictions is obtained. 相似文献
1000.
Yangjun Chen 《Information Processing Letters》2006,99(1):19-26
A precise analysis of the retrieval of signature trees is presented. A signature tree is a data structure constructed over a signature file to speed up searching all those signatures, which match a given query signature. The methods used include a detailed study of probabilistic analysis in conjunction with suitable contour integration of complex variabled functions. 相似文献