全文获取类型
收费全文 | 102652篇 |
免费 | 12469篇 |
国内免费 | 7347篇 |
专业分类
电工技术 | 9275篇 |
技术理论 | 3篇 |
综合类 | 11747篇 |
化学工业 | 9356篇 |
金属工艺 | 8475篇 |
机械仪表 | 10957篇 |
建筑科学 | 8258篇 |
矿业工程 | 6054篇 |
能源动力 | 6786篇 |
轻工业 | 1455篇 |
水利工程 | 4882篇 |
石油天然气 | 5845篇 |
武器工业 | 3450篇 |
无线电 | 8096篇 |
一般工业技术 | 9598篇 |
冶金工业 | 3181篇 |
原子能技术 | 1741篇 |
自动化技术 | 13309篇 |
出版年
2024年 | 487篇 |
2023年 | 1459篇 |
2022年 | 2915篇 |
2021年 | 3197篇 |
2020年 | 3530篇 |
2019年 | 2683篇 |
2018年 | 2726篇 |
2017年 | 3564篇 |
2016年 | 4288篇 |
2015年 | 4643篇 |
2014年 | 6783篇 |
2013年 | 6780篇 |
2012年 | 8392篇 |
2011年 | 8924篇 |
2010年 | 6454篇 |
2009年 | 6532篇 |
2008年 | 6124篇 |
2007年 | 7567篇 |
2006年 | 6534篇 |
2005年 | 5374篇 |
2004年 | 4551篇 |
2003年 | 3552篇 |
2002年 | 2814篇 |
2001年 | 2382篇 |
2000年 | 1894篇 |
1999年 | 1555篇 |
1998年 | 1264篇 |
1997年 | 1026篇 |
1996年 | 934篇 |
1995年 | 746篇 |
1994年 | 641篇 |
1993年 | 451篇 |
1992年 | 364篇 |
1991年 | 284篇 |
1990年 | 244篇 |
1989年 | 184篇 |
1988年 | 126篇 |
1987年 | 79篇 |
1986年 | 91篇 |
1985年 | 38篇 |
1984年 | 46篇 |
1983年 | 38篇 |
1982年 | 40篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 24篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1959年 | 24篇 |
1951年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Optimal operation of a multibasin reservoir system 总被引:1,自引:0,他引:1
A simulation-optimization procedure is presented for evaluating the extent of interbasin transfer of water in the Peninsular
Indian river system consisting of 15 reservoirs on four river basins. A system-dependent simulation model is developed incorporating
the concept of reservoir zoning to facilitate releases and transfers. The simulation model generates a larger number of solutions
which are then screened by the optimization model. The Box complex nonlinear programming algorithm is used for the optimization.
The performance of the system is evaluated through simulation with the optimal reservoir zones with respect to four indices,
reliability, resiliency, vulnerability and deficit ratio. The results indicate that by operating the system of 15 reservoirs
as a single unit the existing utilization of water may be increased significantly. 相似文献
92.
In the history of operations research in industry there has been an abundance of analyses and recommendations produced in millions of man hours by dedicated OR specialists. And yet the net improvement is significantly lower than expected. There are numerous reasons for this shortfall: incomplete analysis, too much theory, incomplete implementation, unreliable recommendations, or a combination of some of these reasons.
By describing several examples, the major reasons for the fragility of the link between recommendation and implementation will be reviewed. What has to be done today to increase the likelihood of implementing an OR recommendation and thus improve the performance of an industrial entity by using the power of OR tools will then be described. 相似文献
By describing several examples, the major reasons for the fragility of the link between recommendation and implementation will be reviewed. What has to be done today to increase the likelihood of implementing an OR recommendation and thus improve the performance of an industrial entity by using the power of OR tools will then be described. 相似文献
93.
Cui Gui-xiang Xu Wei-ran Department of Engineering Mechanics Tsinghua University Beijing P.R.China 《水动力学研究与进展(B辑)》1993,(4)
This paper presents a numerical method for simulation of the flow and thecalculated results of the quasi-steady axisymmetrical flow field and pressure distribution on valveball with power-law model for Non-Newtonian fluid in suck-rod pump.We believe the methodcan provide a foundation for further research and improvement of the design of suck-rod pump. 相似文献
94.
对于中和室内的脉冲气体,用蒙特卡罗方法模拟了气体压力沿轴向的分布。并用模拟进气系统和气压瞬时测量系统,对模拟结果进行了验证。得到与模拟结果较为一致的曲线,从而为注入器真空系统的设计提供了可靠的依据。并通过实验结果,给出了气体靶厚的建立时间约为60ms。 相似文献
95.
本文运用根轨迹法,分析了感应电动机转速对定子电流暂态过程的影响。并通过对稳态时定子电流在电压阶跃干扰下的暂太响应分析,验证了结论有效性。 相似文献
96.
Duan-Shin Lee Benjamin Melamed Amy R. Reibman Bhaskar Sengupta 《Performance Evaluation》1992,16(1-3):21-34
The transport of video images is likely to be a major application of high-speed networks of the future. These applications are capable of utilizing the high bandwidths that will become available with the advent of B-ISDN. In this paper, we propose a new methodology (called TES) for modeling the frame bitrate stream generated by compressed video sources. The main characteristic of this method is that it can model an arbitrary marginal distribution and approximate the autocorrelation structure of the random bitrate process generated by compressed frames. We present a modeling example utilizing this method, based on data from a video coding algorithm employing a layering technique. Using the source model, we develop a simulation model of a multiplexer of video sources. We show that this model can be used to address a number of design issues that arise in this class of problem. In particular, we show that for a layered video coding algorithm, it is possible to have a gain in the number of sources multiplexed at the cost of some loss of low priority packets. 相似文献
97.
O. V. Konstantinova A. V. Kuz’mov V. V. Skorokhod M. B. Shtern 《Powder Metallurgy and Metal Ceramics》2007,46(1-2):25-31
A theoretical method for determining the percolation limit and effective conductivity of composites based on polydisperse
mixtures of insulator and conductor powders is proposed. The effect of the particle size ratio between the insulator and conductor
on the percolation limit and effective conductivity is studied. Numerical simulation of the microstructure, effective properties,
and percolation limit in composites is discussed.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 31–40, 2007. 相似文献
98.
Phase-change thermal energy storage using spherical capsules: performance of a test plant 总被引:1,自引:0,他引:1
J.P Bédécarrats F Strub B Falcon J.P Dumas 《International Journal of Refrigeration》1996,19(3):187-196
The aim of this paper is the study of an industrial process of energy storage usable for air conditioning or refrigeration, investigating a test plant which is a tank with a reduced size, filled with randomly dispersed commercial nodules, placed in a refrigeration loop. The nodules are spherical capsules in which phase change materials (PCM) are encapsulated. This test plant permits the study at length of the behaviour of the tank with, in particular, the charge mode taking into account the undercooling and the discharge mode. A simulation program that considers aspects of both the surrounding heat transfer fluid and the phase-change material packed inside the nodules is developed here in the cases of the charge and the discharge processes. The simulation results are then compared with experimental observations. 相似文献
99.
The laser-induced thermal grating technique has been used to determine the thermal diffusivity of liquids and liquid mixtures. But the dynamic behaviour of the transient thermal grating has not yet been thoroughly investigated, and the systematic errors, which result from the departures from one-dimensional heat conduction, have scarcely been studied quantitatively. In this paper. a three-dimensional numerical simulation and results of the transient thermal grating technique are presented, which enable a good understanding of the dynamic behaviour of the transient thermal grating. The results of this simulation are important for the proper design of the experimental setup to keep the systematic errors for the diffusivity measurement small. Based on the simulation method, the systematic errors were analyzed quantitatively. Here, the following effects were studied: (I) sample thickness, (2) intersection angle, (3) absorption, (4) Gaussian beam intensity distribution and focusing of heating laser beam, and (5) heating pulse duration and laser power. This error analysis makes it possible to specify the criteria for optimum measuring conditions, to correct the measured thermal-diffusivity values for systematic errors, and to estimate the accuracy of the measurements. 相似文献
100.
i-line光刻高均匀照明系统光能分布的计算模拟 总被引:5,自引:0,他引:5
叙述了i-line光刻高均匀照明系统的均匀照明原理,以及其具有特殊面形(非球面)、特殊结构(非共轴)、超光学表面(由多个非共轴光学表面组成)的光学系统的光能分布计算模拟的原理、方法。作为例子,用所编写的程序计算模拟了我们近来设计的一曝光系统几个重要光学表面上具有权重的点列图和光能分布曲线。 相似文献