全文获取类型
收费全文 | 98766篇 |
免费 | 8383篇 |
国内免费 | 4402篇 |
专业分类
电工技术 | 4707篇 |
技术理论 | 12篇 |
综合类 | 9010篇 |
化学工业 | 17338篇 |
金属工艺 | 1788篇 |
机械仪表 | 2400篇 |
建筑科学 | 15142篇 |
矿业工程 | 5681篇 |
能源动力 | 5677篇 |
轻工业 | 5900篇 |
水利工程 | 19407篇 |
石油天然气 | 8216篇 |
武器工业 | 270篇 |
无线电 | 2325篇 |
一般工业技术 | 4590篇 |
冶金工业 | 4095篇 |
原子能技术 | 1243篇 |
自动化技术 | 3750篇 |
出版年
2024年 | 324篇 |
2023年 | 1116篇 |
2022年 | 2253篇 |
2021年 | 2734篇 |
2020年 | 2951篇 |
2019年 | 2419篇 |
2018年 | 2358篇 |
2017年 | 2841篇 |
2016年 | 3213篇 |
2015年 | 3192篇 |
2014年 | 6028篇 |
2013年 | 6010篇 |
2012年 | 7336篇 |
2011年 | 7503篇 |
2010年 | 5573篇 |
2009年 | 5814篇 |
2008年 | 5100篇 |
2007年 | 6761篇 |
2006年 | 6247篇 |
2005年 | 5673篇 |
2004年 | 4483篇 |
2003年 | 4089篇 |
2002年 | 3516篇 |
2001年 | 2873篇 |
2000年 | 2395篇 |
1999年 | 1855篇 |
1998年 | 1345篇 |
1997年 | 1092篇 |
1996年 | 861篇 |
1995年 | 771篇 |
1994年 | 577篇 |
1993年 | 435篇 |
1992年 | 361篇 |
1991年 | 269篇 |
1990年 | 203篇 |
1989年 | 212篇 |
1988年 | 137篇 |
1987年 | 141篇 |
1986年 | 107篇 |
1985年 | 108篇 |
1984年 | 97篇 |
1983年 | 59篇 |
1982年 | 30篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
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
152.
根据黄河中游多沙粗区暴雨洪水及产流产沙特点,提出了为控制水沙危害,黄河中游治理应分两步走的战略。第一步解决近期水沙控制和耕地问题,主要措施是建设淤地坝和骨干坝。研究表明,在现状坝地,梯田条件下,为满足粮食生产需要,每平方公里需新增坝地3.18ha,且能港口控制水沙的要求。第二步是进行坡面治理,改善生态环境,以达到根治水沙的目的。 相似文献
153.
挟沙水流中沙粒对底壁湍流猝发的影响 总被引:2,自引:0,他引:2
本文在常规的边界层方程中保留了法向压力梯度项和增加了固粒对流体的使用项,结合Batcheolr对交界面提供的分析方法和小扰动稳定性理论,由理论分析和计算得到了包括沙粒之类的悬浮体的尺寸,比重,流动Re数,两相速度差以及扰动波数与水流底壁湍流猝发角的关系,计算结果与Rashidi等的实验结果相符。文中所得结果有助于进一步了解江河底部水流的流动特性以及泥沙的沉积和输运机理。 相似文献
154.
A two-dimensional cross-section finite difference model is presented to simulate density dependent leachate migration in leaky aquifers. Unlike existing models, a new approach is adopted to couple the groundwater-flow equation and the hydrodynamic dispersion equation with the elimination of the intermediate step of calculating velocities. The concept of the reference density is employed, permitting increased accuracy (over pressure-based models) in the representation of the transport process. The model is then used to study the effect of several hydraulic and transport parameters on the flow pattern and plume migration which are found to be very sensitive to most of these parameters. Equiconcentration and equipotential lines are overlapped to provide a better understanding of the coupling effect. 相似文献
155.
Sabha Kesraoui-Ouki Christopher R. Cheeseman Roger Perry 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(2):121-126
This paper assesses the potential of natural zeolite utilization as a low-cost ion-exchange and sorbent material in pollution control and recovery of metals. The improvement of the purity of natural zeolites coupled with their chemical modification capabilities in order to provide specific properties may provide a cost-effective alternative for the treatment of heavy metal contaminated soil and water. The application of natural zeolites in industrial pollution control is becoming important and the level of technical effort is increasingly expanding. The extent of application is unlikely to be related solely to their low cost, but also to improved properties and performance characteristics, which will advance the practical implementation of natural zeolites' technology. 相似文献
156.
157.
从侧钻井层、开窗工艺、井身剖面的优选和井眼轨迹控制、固井措施优化等方面,详细总结了套管开窗定向侧钻技术在吐哈油田老井改造中应用的经验,系统地描述了该技术应用的地质条件和工程要素,提出了吐哈侧钻井层优选的量化指标和固井质量的优化措施。近两年,该技术在老井治理、开采难动用储量、提高采收率、降低开发钻井成本等方面展现出广阔的前景。 相似文献
158.
高水固结尾砂充填采矿充填体合理配比的研究 总被引:7,自引:4,他引:3
高水固结尾砂充填采矿是一种新型充填采矿法。试验测定了高水固结尾矿充填体的强度和变形特征;研究分析了影响充填体强度的主要因素、高水充填工艺的特殊要求,以及上向,下向进路开采对充填体强度和稳定性的要求,提出了满足支护强度,工艺及经济需求的充填材料的合理配比范围。 相似文献
159.
Mao Ze yu Chen Chang zhi Department of Hydraulic Engineering Tsinghua University Beijing P.R.China 《水动力学研究与进展(B辑)》1999,(3)
1. INTRODUCTIONThesimulationofstreamwatertemperatureissignificantlyimportantforthestudyofnumericalmodelingofrivericeprocesses[1] .Historically,themathematicalmodelingofthetransportandfateofheatinawaterbodyhasbeenthesubjectofextensivestudyforvariousre… 相似文献
160.
Bharat Doshi 《International Journal of Communication Systems》1992,5(1):49-61
While static open loop rate controls may be adequate for handling continuous bit rate (CBR) traffic, relatively smooth data traffic, and relatively low speed bursty data traffic over broadband integrated networks, high speed bursty data sources need more dynamic controls. Burst level resource allocation is one such dynamic control. Potential benefits and other issues for burst level resource parameter negotiations for bursty data traffic over high speed wide area packet networks have been discussed earlier.1–6 A detailed analysis of an adaptive buffer/window negotiation scheme for long file transfers using these concepts is presented in Reference 1. In this paper we discuss two burst level buffer/window negotiation schemes for short intermittent file transfers, focusing on the specific needs of such traffic streams. We develop closed network of queues models to reflect the behaviour of the proposed schemes. These models, while being simple, capture essential details of the control schemes. Under fairly general assumptions, the resulting network of queues is of product form and can be analysed using the mean value analysis. We use such an analysis to compare the proposed schemes and to determine appropriate sizes of trunk buffers to achieve the desired balance between bandwidth utilization and file transfer delay. The effects of other parameters on the performance of these schemes as well as on the buffer sizing rules are also discussed. Burst level (in-call) parameter negotiation may be carried out by the end system with the network elements or by an interface system (access controller) with the broadband network elements. We discuss implications of this location as well as the needed protocol features. Finally, the service discrimination capabilities desired at the trunk controllers in switching nodes are briefly discussed. 相似文献