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   345238篇
  免费   3691篇
  国内免费   1346篇
电工技术   6342篇
综合类   600篇
化学工业   48739篇
金属工艺   17265篇
机械仪表   13481篇
建筑科学   7676篇
矿业工程   2231篇
能源动力   7609篇
轻工业   23519篇
水利工程   4006篇
石油天然气   7052篇
武器工业   44篇
无线电   39729篇
一般工业技术   73840篇
冶金工业   56063篇
原子能技术   8422篇
自动化技术   33657篇
  2021年   2152篇
  2019年   2060篇
  2018年   11360篇
  2017年   11916篇
  2016年   8213篇
  2015年   2965篇
  2014年   4439篇
  2013年   12020篇
  2012年   9460篇
  2011年   17403篇
  2010年   14970篇
  2009年   14955篇
  2008年   15137篇
  2007年   17004篇
  2006年   7871篇
  2005年   10562篇
  2004年   8994篇
  2003年   8474篇
  2002年   7320篇
  2001年   6907篇
  2000年   6615篇
  1999年   6782篇
  1998年   16310篇
  1997年   11582篇
  1996年   8928篇
  1995年   6853篇
  1994年   6043篇
  1993年   6076篇
  1992年   4407篇
  1991年   4204篇
  1990年   4073篇
  1989年   4055篇
  1988年   3757篇
  1987年   3388篇
  1986年   3392篇
  1985年   3742篇
  1984年   3460篇
  1983年   3216篇
  1982年   3026篇
  1981年   3039篇
  1980年   3032篇
  1979年   2829篇
  1978年   2869篇
  1977年   3141篇
  1976年   4097篇
  1975年   2416篇
  1974年   2380篇
  1973年   2397篇
  1972年   2018篇
  1971年   1781篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
ABSTRACT

In recent times, the applications of multimedia are rising in a greedy mode and hence the amount of video transactions is also increasing exponentially. This has shouted great demands on effective models on video encoding and also for reducing the transmission channel congestion. This research work introduces a managing technique termed weighted encoding for High-Efficiency Video Coding (HEVC). HEVC, also termed as MPEG-H Part 2 and H.265 is a video compression standard that is widely utilized AVC (H.264 or MPEG-4 Part 10). When compared to AVC, HEVC grants double the ratio of data compression at a similar level of quality of the video or considerably enhanced video quality at a similar bit rate. This work intends to optimize the weight that adopted in HEVC for encoding. For this, this paper proposes a new Iterative based propagation update in the water wave Optimization Algorithm (IPU-WWO), which is the improved form of Water wave Optimization (WWO). The performance of proposed IPU-WWO is compared over other conventional methods like Artificial Bee Colony (ABC), Firefly (FF), Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) with respect to Peak Signal to Noise Ratio (PSNR). By doing the encoding process, it minimizes the video size with perceptually better quality video or PSNR.  相似文献   
172.
173.
174.
This study aims to evaluate the tribological behaviour of 3Y-TZP/Ta (20 vol%) ceramic-metal composites and 3Y-TZP monolithic ceramic prepared by spark plasma sintering (SPS) against ultrahigh molecular weight polyethylene (UHMWPE). According to the results of pin (UHMWPE)-on-flat wear test under dry conditions, the UHMWPE – 3Y-TZP/Ta system exhibited lower volume loss and friction coefficient than the UHMWPE – monolithic ceramic combination due to the presence of an autolubricating layer that provides sufficient lubrication for reducing the friction. Owing to the lubrication of the liquid media, under wet conditions obtained using simulated body fluid (SBF), similar behaviour is observed in both cases. Additionally, the ceramic and biocomposite materials were subjected to a low temperature degradation (LTD) process (often referred to as “ageing”) to evaluate the changes in the tribological behaviour after this treatment. In this particular case, the wear properties of the UHMWPE-biocomposite system were found to be less influenced by ageing in contrast to the case of the UHMWPE-zirconia monolithic material. In addition to their exceptional mechanical performance, 3Y-TZP/Ta composites also showed high resistance to low temperature degradation and good tribological properties, making them promising candidates for biomedical applications, especially for orthopaedic implants.  相似文献   
175.
Crossover designs are an extremely useful tool to investigators, and group sequential methods have proven highly proficient at improving the efficiency of parallel group trials. Yet, group sequential methods and crossover designs have rarely been paired together. One possible explanation for this could be the absence of a formal proof of how to strongly control the familywise error rate in the case when multiple comparisons will be made. Here, we provide this proof, valid for any number of initial experimental treatments and any number of stages, when results are analyzed using a linear mixed model. We then establish formulae for the expected sample size and expected number of observations of such a trial, given any choice of stopping boundaries. Finally, utilizing the four-treatment, four-period TOMADO trial as an example, we demonstrate that group sequential methods in this setting could have reduced the trials expected number of observations under the global null hypothesis by over 33%.  相似文献   
176.
177.
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies.  相似文献   
178.
179.
The shaping of the toroidal cutting section of end mills is considered. Methods are devised for selecting the positional parameters in shaping the helical rake surface on the toroidal section. Relations are established between the geometric parameters of the end mill in the toroidal section.  相似文献   
180.
Electrodewatering is a technique in which pressure dewatering is combined with electrokinetic effects to realize an improved solid/liquid separation and hence increased filter cake dry matter contents. In order to be energy efficient, it is shown that sludge should be dewatered by pressure dewatering to a high extent prior to electric field application, and a sufficient contact time for the electric field must be guaranteed. In order to realize these goals, a bench- and pilot-scale diaphragm filter press suited for electrodewatering were constructed for treatment of sewage and other types of sludges. It was shown that electrodewatering of sludge is a feasible technique, especially for biological sludge types. Other types of sludge are less suited for electrodewatering because of the restricted improvements that can be realized in cake dry matter content and the high electric energy consumption. Furthermore, it was shown in pilot-scale tests that the use of a diaphragm filter press with electrodewatering facilities was very well suited to deliver dry filter cakes of sewage sludge at a moderate energy consumption. Depending on local market prices for investment, operating and sludge disposal costs, this technology may therefore lead to important savings in the sludge management process.  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