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   2343篇
  免费   567篇
  国内免费   94篇
电工技术   66篇
技术理论   1篇
综合类   218篇
化学工业   291篇
金属工艺   111篇
机械仪表   149篇
建筑科学   48篇
矿业工程   24篇
能源动力   181篇
轻工业   23篇
水利工程   10篇
石油天然气   14篇
武器工业   43篇
无线电   795篇
一般工业技术   428篇
冶金工业   29篇
原子能技术   45篇
自动化技术   528篇
  2025年   28篇
  2024年   112篇
  2023年   240篇
  2022年   131篇
  2021年   168篇
  2020年   164篇
  2019年   126篇
  2018年   137篇
  2017年   163篇
  2016年   161篇
  2015年   120篇
  2014年   167篇
  2013年   140篇
  2012年   181篇
  2011年   139篇
  2010年   124篇
  2009年   108篇
  2008年   52篇
  2007年   68篇
  2006年   68篇
  2005年   35篇
  2004年   20篇
  2003年   26篇
  2002年   45篇
  2001年   19篇
  2000年   17篇
  1999年   24篇
  1998年   7篇
  1996年   8篇
  1995年   9篇
  1994年   6篇
  1993年   7篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1989年   5篇
  1988年   20篇
  1987年   29篇
  1986年   37篇
  1985年   7篇
  1984年   7篇
  1970年   8篇
  1968年   5篇
  1967年   5篇
  1966年   6篇
  1965年   5篇
  1964年   4篇
  1963年   4篇
  1962年   4篇
  1960年   4篇
排序方式: 共有3004条查询结果,搜索用时 15 毫秒
1.
2.
Today, due to the availability of free remote sensing data, efficient algorithms for image classification and increased connectivity and computing power, together with international policy initiatives, such as the United Nations Programme on Reducing Emissions from Deforestation and Forest Degradation (UN-REDD), more and more countries are investing in their own national forest monitoring schemes. However, tropical forests remain under threat worldwide. Recently, a citizen science project that enables citizens around the globe to be involved in forest monitoring tasks has been proposed, called “ForestWatchers” (www.forestwatchers.net). Its main goal is to allow volunteers (many of them with no scientific training) around the globe, with their own smartphones, tablets and notebooks, review satellite images of forested regions and confirm whether automatic assignments of forested and deforested regions are correct. Inspected images are then sent to a central database where the results are integrated to generate up-to-date deforestation maps. This approach offers a low-cost way to both strengthen the scientific infrastructure and engage members of the public in science. Here, we describe the methods developed within the scope of the ForestWatchers project to assess the volunteers’ performance. These tools have been evaluated with data of two of the project’s preliminary tasks. The first, called “BestTile”, asks volunteers to select which of several images of the same area has the least cloud cover, while in the second, called “Deforestation”, volunteers draw polygons on satellite images delimiting areas they believe have been deforested. The results from more than 500 volunteers show that using simple statistical tests, it is possible to achieve a triple goal: to increase the overall efficiency of the data collecting tasks by reducing the required number of volunteers per task, to identify malicious behavior and outliers, and to motivate volunteers to continue their contributions.  相似文献   
3.
In this paper,the visualization of the thermo-hydrodynamic behavior in flat-plate pulsating heat pipe (FP-PHP) with HFE-347 is experimentally investigated.The F...  相似文献   
4.
支持向量机(Support Vector Machine,SVM)是在统计学习理论基础上发展起来的一种新的机器学习方法,已成为目前研究的热点,并在模式识别领域有了广泛的应用.首先分析了支持向量机原理,随后引入一种改进的径向基核函数,在此基础上,提出了一种改进核函数的SVM模式分类方法.与基于IRIS数据,进行了计算机仿真实验,与基干模糊k-近邻的模式分类仿真结果比较,结果表明改进的SVM方法分类性能比模糊k-近邻算法(Fuzzy k-Nearest Neighbor,FKNN)的分类性能更好,运算时间更短,更易于实时实现.  相似文献   
5.
管状熔断器是目前在电路设计中广泛采用的一种过流保护元件,分析了管状熔断器的熔断原理,总结了管状熔断器的典型失效模式和失效原因,给出管状熔断器的一般失效分析程序。  相似文献   
6.
This paper demonstrates research carried out towards the development of switched capacitors having miniature dimensions. Such devices are based on the Radio Frequency Micro Electro Mechanical Systems (RF MEMS) technique which has gained prominence in implementing a wide variety of microwave and millimetre devices till date. Switched capacitors having standard or conventional dimensions are prone to several limitations which are addressed by scaling down the standard dimensions by 150× times (in terms of area requirement). Such switched capacitors are employed to develop phase shifters working in K-band (22 GHz) frequency range to yield appreciable performance both in terms of electromechanical and RF characterizations. Such switched capacitors are utilized to develop phase shifters which find immense applications in the design of Phased Array RADARs. Switched capacitors fabricated on 500 µm thick quartz substrates, result in 30° phase shift (0.66 mm × 1 mm in dimension) with associated minimum −0.18 dB insertion loss and better than −21 dB reflection coefficient at 22 GHz frequency. Electromechanical characterization reports an actuation voltage of 14.6 V, mechanical vibration frequency of 2.5 MHz and a switching time of 620 ns respectively. Demonstrations showing complete realization of 180° phase shifter (4 mm × 1 mm) employing a cascaded arrangement of six similar 30° unit cells are also included in this paper.  相似文献   
7.
A new conflicting evidence fusion method is proposed for the deficiency of Dempster's rule which can not fuse the conflicting evidence. Evidence is divided into three categories:believable evidence, non-conflicting evidence and conflicting evidence. The influences of these three categories of evidences on fusion results when discounted are analyzed respectively. On these bases, the evidence distance and the conjunctive conflict are utilized in sequence to recognize the believable evidence and non-conflicting evidence. The discounting factors of these two categories of evidences are set to one, which keeps the evidences support the true hypothesis to the greatest degree, and makes the fusion results focus onto the true hypothesis. Examples of some missile fault diagnosis show that the new method can effectively fuse the conflicting evidences, and is suited to fuse the relievable evidences. The new method improves the reliability and rationality of fusion results compared with traditional methods.  相似文献   
8.
In FA laboratories a significant number of photon emission microscopy (PEM) systems are equipped with the most common detector, namely cooled Si-CCD camera. Backside reflected light microscopy (RLM) and photon emission microscopy (PEM) using this detector are possible but strongly limited by the interaction of light with silicon substrate. In this work, we show the improvement of the RLM and PEM performed from the chip backside using standard cooled Si-CCD camera by localized focused-ion-beam (FIB) assisted silicon substrate removal. Thinning down the silicon substrate significantly improves signal-to-noise ratio of the techniques as well as their resolving properties. It also enables extended spectral analysis, also in the visible regime of the light spectrum. This study has been done using 120 nm technology process test structures.  相似文献   
9.
A broadband eight-way differential substrate integrated waveguide (SIW) power divider with bandpass-filtering response by using novel hybrid multiple-via probe and multiple radial slots has been presented in this paper. The novel hybrid multiple-via probe are employed to achieve broadband impedance matching, while the multiple radial slots are used to improve the out-of-band rejection level. An eight-way differential SIW power divider with bandpass-filtering response is designed, fabricated, and measured. The measured results agree with the simulated ones closely in the desirable frequency range. The measured average insertion loss of the eight-way power divider is approximately 9.3 dB and input return loss is greater than 15 dB from 3.2 to 8.1 GHz. Moreover, the out-of-band rejection band with more than 25 dB attenuation from 9 GHz to more than 11 GHz is observed. A maximum amplitude imbalance of \(\pm 0.7\,\hbox { dB}\) is observed over the entire operating frequency range.  相似文献   
10.
文中针对二阶模拟、数字锁相环模型,推导了开环和闭环传递函数。对载波跟踪环鉴相器、清除滤波器和DDS增益等做了较为详尽的理论分析,得到了环路增益和带宽的数学推导结果。系统测试结果表明,此跟踪环路计算方法经测试证明是正确的、可靠的,分机满足实际载波跟踪和数字解调的动态特性要求。  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