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   324855篇
  免费   3884篇
  国内免费   1649篇
电工技术   5567篇
综合类   2571篇
化学工业   46436篇
金属工艺   15483篇
机械仪表   10036篇
建筑科学   8341篇
矿业工程   1033篇
能源动力   7364篇
轻工业   27643篇
水利工程   3060篇
石油天然气   1677篇
武器工业   3篇
无线电   40028篇
一般工业技术   60557篇
冶金工业   52648篇
原子能技术   4099篇
自动化技术   43842篇
  2021年   1566篇
  2019年   1427篇
  2018年   16450篇
  2017年   15314篇
  2016年   12218篇
  2015年   2500篇
  2014年   3370篇
  2013年   10971篇
  2012年   8485篇
  2011年   16946篇
  2010年   14279篇
  2009年   12361篇
  2008年   14125篇
  2007年   15184篇
  2006年   7145篇
  2005年   7677篇
  2004年   7316篇
  2003年   7379篇
  2002年   6760篇
  2001年   6463篇
  2000年   5967篇
  1999年   6471篇
  1998年   16604篇
  1997年   11624篇
  1996年   8991篇
  1995年   6702篇
  1994年   5920篇
  1993年   5739篇
  1992年   4063篇
  1991年   4017篇
  1990年   3584篇
  1989年   3504篇
  1988年   3452篇
  1987年   2908篇
  1986年   2842篇
  1985年   3414篇
  1984年   3051篇
  1983年   2743篇
  1982年   2547篇
  1981年   2569篇
  1980年   2431篇
  1979年   2272篇
  1978年   2235篇
  1977年   2808篇
  1976年   4172篇
  1975年   1900篇
  1974年   1795篇
  1973年   1783篇
  1972年   1460篇
  1971年   1317篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
This paper presents a valve-regulated lead acid (VRLA) battery reserve life estimation scheme. The scheme is adaptive in both type and frequency of involvement. The scheme is based on capacity trending with the support of a number of state-of-health (SOH) indicators. These SOH indicators include accumulated thermal stress, float voltage, and indicators acquired from the start-of-discharge (coup de fouet) region. An implementation test case is given, indicating that the scheme is capable of providing an accurate estimation of reserve life long before the end of life. Furthermore, the estimation accuracy improves as the end of battery life approaches.  相似文献   
82.
The dispersion of potassium niobate (KNbO3) ceramics is analysed using the multiple-arc approach. This has revealed a high frequency arc that is unattainable by the Cole-Cole single arc analysis. The temperature dependence of the new arc is derived through the spread parameter of the relaxation distribution and interpreted in terms of the ferroelectric property of the KNbO3 ceramics. It is shown that the overall dispersion behaviour of the ceramics is mainly due to the existence of two distinctly different polarisation mechanisms. The arc approach has also provided an effective tool for network simulation of dispersion whereby the ceramics are modelled by nine parallel R-C branches over the frequency range 102-105 Hz used  相似文献   
83.
84.
Colour is the most widely used attribute in image retrieval and object recognition. A technique known as histogram intersection has been widely studied and is considered to be effective for color‐image indexing. The key issue of this algorithm is the selection of an appropriate color space and optimal quantization of the selected color space. The goal of this article is to measure the model performance in predicting human judgment in similarity measurement for various images, to explore the capability of the model with a wide set of color spaces, and to find the optimal quantization of the selected color spaces. Six color spaces and twelve quantization levels are involved in evaluating the performance of histogram intersection. The categorical judgment and rank order experiments were conducted to measure image similarity. The CIELAB color space was found to perform at least as good as or better than the other color spaces tested, and the ability to predict image similarity increased with the number of bins used in the histograms, for up to 512 bins (8 per channel). With more than 512 bins, further improvement was negligible for the image datasets used in this study. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 265–274, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20122  相似文献   
85.
Some of the factors affecting cloud point determination of palm oleins are described. These are the type of container used, method of stirring, rate of stirring and bath temperature. The repeatability and reproducibility standard deviations of the method are determined from collaborative trials. Recommendations for the test are made to reduce the large variations among laboratories.  相似文献   
86.
87.
The biological decolorization of two industrial, spent textile reactive dyebaths was investigated using a suspended-growth, halophilic mixed culture fed with glucose. Dyebath I contained mainly Reactive Blue 19 (RB19), an anthraquinone dye, whereas dyebath II contained mainly Reactive Blue 21 (RB21), a phthalocyanine dye. Batch assays under anaerobic conditions with the two neutralized dyebaths resulted in 87 and 37% extent of decolorization for dyebaths I and II, respectively. The rate of glucose utilization and the extent of acetate production were impacted in the presence of each dyebath as compared to the control culture. However, dyebath decolorization occurred despite moderate culture inhibition. Reuse of a biologically renovated RB19-containing dyebath in the dyeing process resulted in reproducible but not identical cotton fabric shades as compared to a standard dyeing (i.e., control) using fresh water. This difference is attributed to a variable degree of RB19 aggregation during the dyeing process and is not related to the efficiency of the biodecolorization process. Further improvement of the redyeing efficiency will lead to the development of an in-plant, closed-loop decolorization system resulting in significant water conservation and minimization of textile pollutants such as salt and dyes.  相似文献   
88.
Sure System 2000, a fault-tolerant computer that couples multiprocessors to offer low-priced, high-performance systems that deal effectively with faults and failures, is presented. The architecture is based on the local redundancy technique, ensuring that no hardware or software fault can cause a system crash. Software errors can be fixed, and hardware can be replaced, upgraded, or added dynamically. Existing fault-tolerant computers are briefly reviewed, and the logic hardware system configuration of the Sure System 2000 is described. The multiprocessor and I/O architecture are examined. The SXO Sure System 2000 expandable operating system is described  相似文献   
89.
The new Editor in Chief of IEEE Micro introduces himself and the first issue of 2007. He thanks outgoing Editor in Chief Pradip Bose for his outstanding work on Micro during his tenure. He assesses the current state of the microarchitecture field, speculates on the future, and asks readers for their suggestions on topics the magazine should cover in coming issues.  相似文献   
90.
High cycle fatigue of bolted connections Extensive tests regarding the influences on the fatigue of bolt‐nut‐connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence.  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