首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   341581篇
  免费   34244篇
  国内免费   25553篇
电工技术   44325篇
技术理论   30篇
综合类   40732篇
化学工业   21251篇
金属工艺   11576篇
机械仪表   27240篇
建筑科学   30750篇
矿业工程   13091篇
能源动力   13850篇
轻工业   8887篇
水利工程   14482篇
石油天然气   13526篇
武器工业   5530篇
无线电   31825篇
一般工业技术   22700篇
冶金工业   11303篇
原子能技术   3531篇
自动化技术   86749篇
  2024年   1416篇
  2023年   3913篇
  2022年   7718篇
  2021年   9294篇
  2020年   10021篇
  2019年   7930篇
  2018年   7449篇
  2017年   9883篇
  2016年   11555篇
  2015年   12831篇
  2014年   21242篇
  2013年   19696篇
  2012年   25105篇
  2011年   26821篇
  2010年   20596篇
  2009年   20922篇
  2008年   21270篇
  2007年   25964篇
  2006年   23077篇
  2005年   20486篇
  2004年   16724篇
  2003年   14941篇
  2002年   11497篇
  2001年   9619篇
  2000年   8057篇
  1999年   6415篇
  1998年   5031篇
  1997年   4082篇
  1996年   3697篇
  1995年   3150篇
  1994年   2613篇
  1993年   1784篇
  1992年   1514篇
  1991年   1129篇
  1990年   901篇
  1989年   751篇
  1988年   507篇
  1987年   309篇
  1986年   207篇
  1985年   212篇
  1984年   202篇
  1983年   135篇
  1982年   133篇
  1981年   96篇
  1980年   97篇
  1979年   90篇
  1978年   48篇
  1977年   34篇
  1976年   26篇
  1959年   37篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
OSQL is the object-oriented database language developed for the Iris object-oriented database management system at Hewlett-Packard Laboratories. Its three fundamental constructs are objects, types, and functions. This paper provides an overview of the underlying concepts and some important features of OSQL.  相似文献   
73.
74.
Quenching with gases rather than oil or other liquid media has the advantages of reducing the risks concerning health and environment, while simultaneously homogenizing the quenching results and minimizing distortion due to a wide range of possible process parameter variations and the pure convective heat transfer. In this contribution, a coupled solution for increasing homogenization of quenching results within high pressure gas quenching will be presented. In the first stage, an experimental test facility was set up for flow investigations and in the second stage a numerical simulation model was generated. The numerical and experimental results of the flow through the chamber were compared for several boundary conditions. Finally, after complete verification of the simulation, the model may be used to assist in parameter variation for optimization of homogeneous high pressure gas quenching.  相似文献   
75.
Extracted and unextracted black cherry (Prunus serotina), red oak (Quercus rubra), and red pine (Pinus resinosa) wood specimens were exposed to artificial weathering, and their discoloration process was investigated to obtain basic understanding on the role of wood extractives in the weathering of hardwoods and softwoods. Color measurements were made with a spectrometer according to ISO 2470 standards, using the CIELAB system. Results obtained showed that the rate of whiteness was not significantly affected by extractives removed with organic solvents, but were significantly affected when organic solvent extraction was followed by water extraction. The total discoloration rate had the same pattern, and chromaticity coordinates were less affected by wood extractives. These results confirm the hypothesis that some extractives contained in wood act as antioxidants and are able to provide some protection to wood surfaces against weathering degradation. However, more work is needed to understand the chemistry and mechanism of action of these extractives so as to develop any practical use for this property. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 425–434, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20248  相似文献   
76.
The Rainbow net simulation technique is applied to modelling the impact of system load and fault handling on the availability of a fault-tolerant multiprocessor architecture. Rainbow nets are described along with the motivation for creating this modelling technique. A Rainbow net fault-handling model is created for the fault-tolerant multiprocessor architecture and the topology is shown to remain constant in size, independent of the number of processor, memory and I/O elements configured in the system. Simulation is performed with a varying load in terms of the number of active jobs the system must support. Results are given showing how the fault-tolerant capability varies with load. Two new metrics for evaluating fault tolerance are introduced; namely full fault-tolerability and partial fault-tolerability. They are based on simple observations in the model.  相似文献   
77.
Power system control equipment needs higher sensitivity and operational reliability. Advanced voltage control equipment is needed for reducing the frequency of tap changes and improving the characteristics (the relationship between the actual voltage and reference voltage) of the voltage to meet today's power system requirements. However, these objectives are in a trade-off relationship. Studies of voltage control derived from a knowledge base suitable for electric power systems can satisfy these objectives using fuzzy inference. Compared with corresponding conventional equipment, the new equipment improved the deviation of 30 min average voltage of 30 percent. This paper describes the design concept of new voltage control equipment using fuzzy inference. In addition, field test results are described along with rules of fuzzy inference, membership functions, and the deviation of 30 min average voltage through detailed simulation.  相似文献   
78.
In today's competitive business environment, it is important that customers are able to obtain their preferred items in the shops they visit, particularly for convenience store chains such as 7–Eleven where popular items are expected to be readily available on the shelves of the stores for buyers. To minimize the cost of running such store chains, it is essential that stocks be kept to a minimum and at the same time large varieties of popular items are available for customers. In this respect, the replenishment system needs to be able to cope with the taxing demands of minimal inventory but at the same time keeping large varieties of needed items. This paper proposes a replenishment system which is able to respond to the fluctuating demands of customers and provide a timely supply of needed items in a cost–effective way. The proposed system embraces the principle of fuzzy logic which is able to deal with uncertainties by virtue of its fuzzy rules reasoning mechanism, thereby leveraging the responsiveness of the entire replenishment system for the chain stores. To validate the feasibility of the approach, a case study has been conducted in an emulated environment with promising results.  相似文献   
79.
钢纤维聚合物混凝土抗压本构关系   总被引:2,自引:0,他引:2  
钢纤维聚合物混凝土是由聚合物混凝土基体和钢纤维共同组成的纤维增强复合材料,它的力学行为不仅依赖于聚合物混凝土基体的行为,而且与钢纤维的掺量、分散特征以及钢纤维的几何尺寸有关,本文将基于损伤力学原理研究在不同纤维掺量下的钢纤维聚合物混凝土的全程压力-应变曲线及其本构模型。  相似文献   
80.
苗青云 《山西建筑》2003,29(15):69-70
介绍了热水采暖系统运行及调整的注意事项,分析了立支管阀门、集气罐的作用,提出了使热水采暖系统的调节和集排气操作达到理想程度的有效措施,以实现良好的供暖效果。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号