全文获取类型
收费全文 | 21926篇 |
免费 | 1637篇 |
国内免费 | 1042篇 |
专业分类
电工技术 | 1295篇 |
技术理论 | 1篇 |
综合类 | 2339篇 |
化学工业 | 2788篇 |
金属工艺 | 607篇 |
机械仪表 | 1130篇 |
建筑科学 | 1143篇 |
矿业工程 | 427篇 |
能源动力 | 884篇 |
轻工业 | 825篇 |
水利工程 | 850篇 |
石油天然气 | 1184篇 |
武器工业 | 229篇 |
无线电 | 960篇 |
一般工业技术 | 2152篇 |
冶金工业 | 2540篇 |
原子能技术 | 124篇 |
自动化技术 | 5127篇 |
出版年
2024年 | 31篇 |
2023年 | 211篇 |
2022年 | 269篇 |
2021年 | 428篇 |
2020年 | 423篇 |
2019年 | 431篇 |
2018年 | 404篇 |
2017年 | 564篇 |
2016年 | 610篇 |
2015年 | 652篇 |
2014年 | 951篇 |
2013年 | 1516篇 |
2012年 | 1137篇 |
2011年 | 1463篇 |
2010年 | 1108篇 |
2009年 | 1274篇 |
2008年 | 1245篇 |
2007年 | 1423篇 |
2006年 | 1357篇 |
2005年 | 1176篇 |
2004年 | 1018篇 |
2003年 | 933篇 |
2002年 | 806篇 |
2001年 | 691篇 |
2000年 | 583篇 |
1999年 | 588篇 |
1998年 | 610篇 |
1997年 | 410篇 |
1996年 | 368篇 |
1995年 | 291篇 |
1994年 | 251篇 |
1993年 | 186篇 |
1992年 | 198篇 |
1991年 | 158篇 |
1990年 | 155篇 |
1989年 | 90篇 |
1988年 | 82篇 |
1987年 | 60篇 |
1986年 | 65篇 |
1985年 | 90篇 |
1984年 | 71篇 |
1983年 | 67篇 |
1982年 | 48篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1975年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Dimitris Papadias M.Sc. Ph.D. candidate Timos Sellis Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):479-516
Various relation-based systems, concerned with the qualitative representation and processing of spatial knowledge, have been developed in numerous application domains. In this article, we identify the common concepts underlying qualitative spatial knowledge representation, we compare the representational properties of the different systems, and we outline the computational tasks involved in relation-based spatial information processing. We also describesymbolic spatial indexes, relation-based structures that combine several ideas in spatial knowledge representation. A symbolic spatial index is an array that preserves only a set of spatial relations among distinct objects in an image, called the modeling space; the index array discards information, such as shape and size of objects, and irrelevant spatial relations. The construction of a symbolic spatial index from an input image can be thought of as a transformation that keeps only a set of representative points needed to define the relations of the modeling space. By keeping the relative arrangements of the representative points in symbolic spatial indexes and discarding all other points, we maintain enough information to answer queries regarding the spatial relations of the modeling space without the need to access the initial image or an object database. Symbolic spatial indexes can be used to solve problems involving route planning, composition of spatial relations, and update operations. 相似文献
33.
34.
Wang Chao College of Water Resources Environment Hohai University Nanjing China 《水动力学研究与进展(B辑)》2001,(4)
1 . INTRODUCTIONWaterTransferFromSouthToNorthProject(WTFSTNP)isagreatdecisiontosolvetheproblemofwatershortageinthenorthandcentralpartsofChi na .Thisproject ,includingEast ,Central andWest Line ,willdrawwaterfromtheYangtzeRivertothenorthandcenterofChinasotha… 相似文献
35.
PLC 控制电梯教学模型的设计与调试 总被引:1,自引:0,他引:1
主要介绍了8层集选电梯的PLC控制系统的总体设计方案、组成,PLC的控制方案及模块化程序设计、在实际的安装与调试中遇到的问题,以及制作该教学模型的现实意义。 相似文献
36.
套管侧钻分支井钻井工程设计及应用原则 总被引:8,自引:3,他引:5
利用老井开窗侧钻分支井,可以提高原油采收率,增加产能和降低成本。对与分支井相关的分式设计。轨迹优化设计,钻柱设计,斜向器开窗方位的优化。开窗技术。轨迹控制应用等方面的主要原则进行了阐述。对进一步推广应用分支井技术,提高我国分支井钻井技术水平有一定的推动作用。 相似文献
37.
38.
M. Quecedo M. Pastor M. I. Herreros J. A. Fernndez Merodo 《International journal for numerical methods in engineering》2004,59(6):755-794
This paper proposes a two‐dimensional (2D) model for the analysis of the propagation of fast landslides involving a fluidized material such as debris and mud flows, flowslides and avalanching flows. The model is based on the Navier–Stokes depth‐integrated equations. To incorporate the effect of steep slopes and centrifugal forces due to the high velocities characterizing the flowslides and the bed curvature, a curvilinear system of reference is used. The corresponding equations of motion are complemented by depth‐averaged constitutive equations and bed friction laws. The resulting set of differential equations are solved using the two‐step Taylor–Galerkin algorithm. This algorithm has been used by the authors to solve hydraulic and dam‐break problems using the finite element method. Owing to the importance of the source term compared to the advection component, the proposed algorithm follows a splitting scheme using a fourth‐order Runge–Kutta method for integrating the friction and slope components. The performance of the overall approach has been checked in a number of examples. The analysis of the results provides insights into the key elements of the model and shows the adequacy of the method to solve real problems where merging and splitting of the flow occur. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
39.
D.H.R. Price J.A. Sharp 《International Journal of Electrical Power & Energy Systems》1985,7(3):131-137
Peak demand forecasts obtained from six different univariate forecasting methods, under a range of conditions, were used to drive a capacity acquisition model of a large electrical supply system; and the resulting physical and financial performance of the model was observed for each set of forecasts. The results obtained are discussed in the context of their implications for the choice of load forecasting method used in capacity acquisition planning by a power supply undertaking. 相似文献
40.
G. S. Ghali 《Water Resources Management》1989,3(1):35-47
The mathematical model which was developed in part I of this work for multi-dimensional analysis of soil moisture in irrigated fields is converted into computer algorithms. The algorithms are capable of emulating many field conditions of practical applications during both design and operation phases. The model is subjected to various tests, the results of which are reported here. The tests in various modes of simulations verified the numerical performance of the model and the accuracy of its predictions. The model provides a powerful tool for detailed studies of soil moisture dynamics in one or multi-dimensional problems irrigated fields 相似文献