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   2848篇
  免费   54篇
  国内免费   25篇
电工技术   21篇
综合类   51篇
化学工业   499篇
金属工艺   204篇
机械仪表   111篇
建筑科学   138篇
矿业工程   32篇
能源动力   222篇
轻工业   43篇
水利工程   19篇
石油天然气   3篇
无线电   234篇
一般工业技术   688篇
冶金工业   155篇
原子能技术   14篇
自动化技术   493篇
  2024年   43篇
  2023年   90篇
  2022年   34篇
  2021年   80篇
  2020年   101篇
  2019年   50篇
  2018年   101篇
  2017年   151篇
  2016年   138篇
  2015年   131篇
  2014年   172篇
  2013年   189篇
  2012年   124篇
  2011年   130篇
  2010年   105篇
  2009年   163篇
  2008年   88篇
  2007年   132篇
  2006年   109篇
  2005年   64篇
  2004年   51篇
  2003年   44篇
  2002年   49篇
  2001年   47篇
  2000年   36篇
  1999年   43篇
  1998年   37篇
  1997年   31篇
  1996年   26篇
  1995年   22篇
  1994年   22篇
  1993年   13篇
  1992年   17篇
  1991年   11篇
  1990年   12篇
  1989年   11篇
  1988年   28篇
  1987年   38篇
  1986年   31篇
  1985年   16篇
  1984年   19篇
  1983年   11篇
  1982年   11篇
  1981年   7篇
  1980年   9篇
  1978年   13篇
  1976年   7篇
  1972年   7篇
  1971年   7篇
  1967年   6篇
排序方式: 共有2927条查询结果,搜索用时 0 毫秒
1.
Industry widely uses rotary valves and blow tanks for the pneumatic conveying of products, each having their pros and cons depending on the specific application. This article shows the differing results obtained when low-velocity conveying a product through a common pipeline using both a drop-through rotary valve and a bottom-discharge blow tank feeder. A number of issues arise in the rotary valve system, the main one being rotary valve air leakage. A blow tank system, on the other hand, does not leak, as it is an enclosed system. The experimental results show dramatic differences in product throughput. Further exploration leads to a novel modification being made to the rotary valve system in an attempt to increase its capacity. The result of this modification shows a slight increase in output tonnage, but still significantly less than that obtained from the blow tank.  相似文献   
2.
Traditional flood forecasting and operation of reservoirs in China are based on manual calculations by hydrologists or through standalone computer programs. The main drawbacks of these methods are long forecasting time due to time-consuming nature, individual knowledge, lack of communication, absence of experts, etc. A Web-based flood forecasting system (WFFS), which includes five main modules: real-time rainfall data conversion, model-driven hydrologic forecasting, model calibration, precipitation forecasting, and flood analysis, is presented in this paper. The WFFS brings significant convenience to personnel engaged in flood forecasting and control and allows real-time contribution of a wide range of experts at other spatial locations in times of emergency. The conceptual framework and detailed components of the proposed WFFS, which employs a multi-tiered architecture, are illustrated. Multi-tiered architecture offers great flexibility, portability, reusability and reliability. The prototype WFFS has been developed in Java programming language and applied in Shuangpai region with a satisfactory result.  相似文献   
3.
The technology of high strength concrete has improved over the last decade. High strength concrete (HSC) is more brittle than normal strength concrete. The brittleness increases with the use of over-reinforced section, which fails suddenly without warning. Use of over reinforced sections is restricted in codes of practice of concrete design. This paper presents an experimental study of the behaviour of five HSC beams confined with helical reinforcement. Concrete compressive strength in the range 72–95 MPa and tensile reinforcement ratio in the range 5.24–7.86% were used. The main results indicate that as the concrete compressive strength increases the displacement ductility index decreases and the load at spalling-off the concrete cover increases. Also, the displacement ductility index increases as the longitudinal reinforcement ratio increases and the load at spalling-off the concrete cover decreases.  相似文献   
4.
<正>Ground control is the science of studying and controlling the behavior of rock strata in response to mining operations.Ground control related research has made significant advancements over the last 35 years and these accomplishments are well documented in the proceedings of the annual International Conference on  相似文献   
5.
Multi-agent technologies have been widely employed for the development of web-based systems, including web-based e-markets, web-based grid computing, e-governments and service-oriented software systems. In these service-oriented systems, service provider agents and service consumer agents are autonomous and rational entities, which can enter and leave the environments freely. For simplicity, we use terms ‘provider’ and ‘consumer’ to represent this two types of agents. How to select the most suitable service providers according to a service request from a consumer in such an open environment is a very challenging issue. In this paper, we propose an innovative trust model, called the GTrust model, for service group selection in general service-oriented environments. In the GTrust model, the trust evaluation for a service group is based on the functionality coverage of the group, the dependency relationships among individual services in the group, the ratings of individual services on the attributes of the service request and a similarity measurement of the extent to which reference reports can reflect the service request in terms of the priority distribution of attributes. The experimental results and analysis demonstrate the good performance of the GTrust model on the service group selection in service-oriented environments.  相似文献   
6.
Understanding the TCP congestion control mechanism from a global optimization point of view is not only important in its own right, but also crucial to the design of other transport layer traffic control protocols with provable properties. In this paper, we derive a global utility function and the corresponding optimal control law, known as TCP control law, which maximizes the global utility. The TCP control law captures the essential behaviors of TCP, including slow start, congestion avoidance, and the binary nature of congestion feedback in TCP. We find that the utility function of TCP is linear in the slow start phase and is proportional to the additive increase rate and approaches the well-known logarithm function as the data rate becomes large in the congestion avoidance phase. We also find that understanding the slow start phase with a fixed threshold is critical to the design of new transport layer control protocols to enable quality of service features. Finally, as an application, we design a Minimum Rate Guaranteed (MRG) traffic control law that shares the same utility function as the TCP control law. Our simulation study of the MRG control law indicates that it is indeed TCP friendly and can provide minimum rate guarantee as long as the percentage of network resource consumed by the MRG flows is moderately small.  相似文献   
7.
The paper reports on the experiments undertaken at the University of Wollongong to characterise fading profiles and delay parameters of an indoor wireless channels at 5 GHz U-NII bands. The measurements were undertaken at different locations around the campus with results recorded for a post-processing to calculate the Rician K-factor, the level crossing rate and the average fade duration as well as mean excess delay, rms delay spread, and the coherence bandwidth of the channel. The presented measurement results can be useful in developing a Markov chain based model of the transport channel for IEEE802.11a or HYPRLAN-2 networks. The results also indicate scenarios where the coherence bandwidth of the channel is smaller than the width of the sub-carrier OFDM channels in either of the mentioned systems.  相似文献   
8.
9.
A method for the control of time delay systems is presented. The systems are represented by moving models established by the use of block pulse functions. This approach permits the linear feedback control law to be applied to non-linear systems. The moving model representation and the optimal feedback control of time delay systems are presented to demonstrate that the method exhibits satisfactory results.  相似文献   
10.
Located approximately 100 km west of Brisbane, Toowoomba is home to approximately 95,000 people. Surface water from dams is the main source of water for the city. In 2006 the residents of Toowoomba were invited to vote in a referendum (plebiscite) concerning whether or not an indirect potable wastewater reuse scheme should be constructed to supply additional water to the area. At that stage dam levels in Toowoomba were at approximately twenty percent of capacity. Toowoomba residents, after intense campaigning on both sides of the referendum debate, voted against the proposal. In July 2008 dam levels dropped to eleven percent. Stage 5 water restrictions have been in place since September 2006, subsequently mains water must not be used for any outdoor uses. This paper describes in detail how public opposition in the case of Toowoomba's referendum, defeated the proposal for a water augmentation solution. Reasons for the failure are analysed. In so doing, the paper provides valuable insights with respect to public participation in indirect potable reuse proposals, and discusses factors including politics, vested interest and information manipulation. This paper is significant because of the lack of detailed information published about failed water infrastructure projects.  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