全文获取类型
收费全文 | 154885篇 |
免费 | 14425篇 |
国内免费 | 7960篇 |
专业分类
电工技术 | 11744篇 |
技术理论 | 7篇 |
综合类 | 10570篇 |
化学工业 | 27082篇 |
金属工艺 | 11126篇 |
机械仪表 | 7275篇 |
建筑科学 | 11999篇 |
矿业工程 | 8034篇 |
能源动力 | 10388篇 |
轻工业 | 9807篇 |
水利工程 | 2578篇 |
石油天然气 | 23375篇 |
武器工业 | 1123篇 |
无线电 | 10737篇 |
一般工业技术 | 12626篇 |
冶金工业 | 9648篇 |
原子能技术 | 2173篇 |
自动化技术 | 6978篇 |
出版年
2024年 | 468篇 |
2023年 | 2014篇 |
2022年 | 4035篇 |
2021年 | 4978篇 |
2020年 | 5249篇 |
2019年 | 4506篇 |
2018年 | 4058篇 |
2017年 | 4829篇 |
2016年 | 5687篇 |
2015年 | 5786篇 |
2014年 | 9604篇 |
2013年 | 9399篇 |
2012年 | 11863篇 |
2011年 | 12518篇 |
2010年 | 8600篇 |
2009年 | 8519篇 |
2008年 | 7535篇 |
2007年 | 9608篇 |
2006年 | 9385篇 |
2005年 | 7762篇 |
2004年 | 6661篇 |
2003年 | 5934篇 |
2002年 | 4936篇 |
2001年 | 4486篇 |
2000年 | 3697篇 |
1999年 | 2922篇 |
1998年 | 2211篇 |
1997年 | 1915篇 |
1996年 | 1656篇 |
1995年 | 1309篇 |
1994年 | 1098篇 |
1993年 | 783篇 |
1992年 | 687篇 |
1991年 | 571篇 |
1990年 | 454篇 |
1989年 | 348篇 |
1988年 | 209篇 |
1987年 | 141篇 |
1986年 | 131篇 |
1985年 | 123篇 |
1984年 | 124篇 |
1983年 | 81篇 |
1982年 | 59篇 |
1981年 | 105篇 |
1980年 | 77篇 |
1979年 | 33篇 |
1977年 | 15篇 |
1975年 | 13篇 |
1959年 | 18篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
J.M.P.Q. Delgado 《Journal of Phase Equilibria and Diffusion》2007,28(5):427-432
Molecular (or tracer) diffusion coefficient data were obtained for 2-naphthol, benzoic acid, salicylic acid, camphor, and
cinnamic acid in water at temperatures that differ significantly from ambient value. Experimental values were determined for
the dissolution of 2-naphthol in water at 283 to 368 K, of benzoic acid in water at 283 to 338 K, of salicylic acid in water
at 283 to 343 K, of camphor in water at 283 to 318 K, and of cinnamic acid in water at 283 to 318 K. Empirical correlations
are presented for the prediction of molecular diffusion coefficient over the entire range of temperatures studied, and they
are shown to predict the obtained data with very good accuracy. 相似文献
993.
In this study, experimental and three-dimensional numerical studies were performed to investigate the effects of plate spacing and temperature difference on natural convection between isothermally heated upward-facing lower horizontal plate and externally insulated horizontal upper plate. Air is used as the heat transfer medium. Rayleigh number varied in the 1108–2.339 × 105 range. Several numerical simulations for three-dimensional steady laminar and turbulent flows heat transfer were carried out using a commercial CFD code Fluent 6.2. Results have shown that there is a good agreement between the numerical and present experimental results as well as with available data in literature. 相似文献
994.
引滦入唐工程某渡槽裂缝成因及对策分析 总被引:3,自引:0,他引:3
针对引滦入唐工程中某渡槽的开裂情况,从渡槽的两个使用状态入手进行分析,考虑按旧规范计算对设计造成的误差,采用大型有限元分析程序分析了渡槽各种工况的运行情况,并根据使用情况分析了开裂原因,提出了加固意见和同类渡槽设计的建议。 相似文献
995.
分析了型钢厂试制热轧美标H型钢低温冲击韧性偏低的原因,并在此基础上提出了对生产工艺的优化与改进。 相似文献
996.
The Beaver Creek confluence with the main‐stem Klamath River was studied to assess salmonid use in a thermal mixing zone under various summer hydrological and meteorological conditions. Main‐stem flow releases from Iron Gate Dam ranged from 17 cms (615 cfs) to 37 cms (1320 cfs) during the study period and main‐stem water temperatures ranged from 19.5 to 26°C. A grid was constructed to define the thermal refuge as a system of cells. Temperatures were monitored using remote temperature loggers and fish counts were conducted using daytime snorkelling. Most juvenile salmonids were observed moving into the refuge when main‐stem temperatures exceeded 22–23°C. Salmonids in the thermal refuge did not necessarily seek the coolest water, but were generally located in habitats commensurate with species‐specific behavioural needs within their thermal tolerance range. Such ranges largely occurred within refuge areas. Variable meteorological conditions confounded observable biological thermal benefit to fish resulting from higher or lower main‐stem flows. Thermal regime dynamics indicated that under the hydrological and meteorological conditions observed, higher flows from Iron Gate Dam showed some ability to change the structure of the refuge area. It appeared that without the thermal refuge, main‐stem flows alone could not sustain the salmonid population because high water temperatures usually exceeded their published thermal tolerance limits. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
997.
注水开发的低渗透油藏存在启动压力和压力敏感性,使开发难度加大。当流压低于饱和压力以后,流入动态指示曲线凹向压力轴,会出现一个产量最大点。在前人研究的基础上,从平面径向拟稳态渗流规律出发,考虑启动压力梯度和压力敏感效应对油藏渗流的影响,与油相和液相相对流动能力方程相结合,建立了具有最大产量点的低渗透压力敏感油藏直井流入动态方程,据此可对油藏产能进行评价预测,确定出油井最低允许流动压力和油井的合理工作制度。在龙南、新站油田的应用表明,预测值与实测值比较吻合,满足矿场工程精度要求,说明所建立的流入动态方程能有效评价预测油井产能和确定油井允许的最小流压界限,为充分发挥油井生产能力、合理高效开发低渗透压力敏感油藏提供了理论依据。 相似文献
998.
There have been extensive attempts in recent years to perform spatial equilibrium analysis of commodity markets, particularly that of energy. Most of these attempts have been based on linear programming transportation models, and more recently quadratic programming models. Unfortunately, neither of these modelling approaches can deal with the case of multi-commodity analysis with non-symmetric regression coefficients. In this paper, we overcome this problem by employing the linear complementarity programming model. In addition, we show how the model can be applied to coal and gas energy flows within a single region. Future potential applications of the model are also implied. 相似文献
999.
S. A. Mousavi Dehghani 《Petroleum Science and Technology》2007,25(11):1435-1446
Natural depletion of petroleum reservoirs as well as gas injection for enhance oil recovery, are unavoidable processes in the oil industry. Foremost, prediction of the problems due to these two processes is very necessary and important. So many field and experimental experiences have shown that heavy organic depositions, especially asphaltene deposition, are principal results during these processes. Results of laboratory simulation of asphaltene deposition during the natural depletion of petroleum reservoirs and also during gas injection and enhanced oil recovery (EOR) processes are reported here. This is achieved through the design of a new experimental setup for the investigation of pressure and composition effects on asphaltene deposition in petroleum fluids at high pressure and high temperature conditions. In this work, asphaltene deposition during decreasing pressure, from pressures greater than reservoir pressure to pressures below the bubble point pressure (natural depletion) and also asphaltene deposition during natural gas injection in reservoir conditions, are studied for three samples—one recombined sample and two bottomhole samples. All of the obtained results from this work conform to theoretical and other experimental works. 相似文献
1000.
通过载体改性及催化剂制备工艺研究,中国石化齐鲁分公司研究院成功开发了QLH-02低温型裂解汽油二段加氢催化剂。在中国石化齐鲁分公司烯烃厂裂解汽油二段加氢装置应用结果表明,该催化剂强度高,装填量少,在二段加氢反应器入口温度为265℃、压力为2.65 MPa、液体空速4.0 h-1、氢油体积比800~1 000的操作条件下,产品中硫含量小于1μg.g-1,双烯值(B r2值/100 mL,以下同)小于0.05 g,溴值(B r值/100 mL,以下同)小于0.09 g,远低于控制指标,具有很好的低温加氢活性,明显降低了能源消耗。 相似文献