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   204364篇
  免费   16647篇
  国内免费   5651篇
电工技术   13134篇
技术理论   24篇
综合类   12597篇
化学工业   32125篇
金属工艺   11271篇
机械仪表   12720篇
建筑科学   14662篇
矿业工程   5974篇
能源动力   6175篇
轻工业   13947篇
水利工程   3605篇
石油天然气   11593篇
武器工业   1502篇
无线电   24640篇
一般工业技术   24756篇
冶金工业   9468篇
原子能技术   2361篇
自动化技术   26108篇
  2025年   792篇
  2024年   5169篇
  2023年   4742篇
  2022年   6988篇
  2021年   9454篇
  2020年   7872篇
  2019年   6428篇
  2018年   6395篇
  2017年   7019篇
  2016年   6526篇
  2015年   8314篇
  2014年   10179篇
  2013年   11924篇
  2012年   12868篇
  2011年   13633篇
  2010年   11580篇
  2009年   10970篇
  2008年   10551篇
  2007年   9805篇
  2006年   9911篇
  2005年   8499篇
  2004年   5675篇
  2003年   4829篇
  2002年   4430篇
  2001年   3936篇
  2000年   3771篇
  1999年   4362篇
  1998年   3651篇
  1997年   3106篇
  1996年   2900篇
  1995年   2349篇
  1994年   1928篇
  1993年   1363篇
  1992年   1114篇
  1991年   826篇
  1990年   596篇
  1989年   504篇
  1988年   390篇
  1987年   278篇
  1986年   221篇
  1985年   143篇
  1984年   131篇
  1983年   93篇
  1982年   98篇
  1981年   70篇
  1980年   69篇
  1979年   30篇
  1978年   25篇
  1977年   24篇
  1976年   32篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Collaboration representation-based classification (CRC) was proposed as an alternative approach to the sparse representation method with similar efficiency. The CRC is essentially a competition scheme for the training samples to compete with each other in representing the test sample, and the training class with the minimum representation residual from the test sample wins the competition in the classification. However, the representation error is usually calculated based on the Euclidean distance between a test sample and the weighted sum of all the same-class samples. This paper exploits alternative methods of calculating the representation error in the CRC methods to reduce the representation residual in a more optimal way, so that the sample classes compete with each other in a closer range to represent the test sample. A large number of face recognition experiments on three face image databases show that the CRC methods with optimized presentation residual achieve better performance than the original CRC, and the maximum improvement in classification accuracy is up to 12 %.  相似文献   
32.
Xiaozhen Yang 《Polymer》2004,45(12):4241-4248
The conformational distribution change of amorphous poly(lactic acid) (PLA) induced by deformation has been studied using Raman spectroscopy. Spectroscopic features associated with the rotational isomeric states (ttt, ttg′, tgt, tgg′) have been established experimentally and supported by normal coordinate analysis. Deformation induced a significant increase in the most favorable tgt conformation. Based on the relative intensities of Raman-active skeletal modes, a quantitative method has been developed that can be used to elucidate structural changes in a variety of deformed polymer samples. For biaxially oriented PLA films, the overall tgt conformation increased from the 76% in undeformed sample to a value as high as 92%. The change in conformational distribution in the amorphous phase follows a different trend (76-88%) as compared to the increase in sample crystallinity (0-43%). A large change in amorphous chain conformation occurred at relatively low draw ratios. In contrast, the large change in the degree of crystallinity occurred at higher draw ratios.  相似文献   
33.
Bio-cryptography is an emerging security technology which combines cryptography with biometrics. A good bio-cryptosystem is required to protect the privacy of the relevant biometric data as well as achieving high recognition accuracy. Fingerprints have been widely used in bio-cryptosystem design. However, fingerprint uncertainty caused by distortion and rotation during the image capturing process makes it difficult to achieve a high recognition rate in most bio-cryptographic systems. Moreover, most existing bio-cryptosystems rely on the accurate detection of singular points for fingerprint image pre-alignment, which is very hard to achieve, and the image rotation transformation during the alignment process can cause significant singular point deviation and minutiae changes. In this paper, by taking full advantage of local Voronoi neighbor structures (VNSs), e.g. local structural stability and distortion insensitivity, we propose an alignment-free bio-cryptosystem based on fixed-length bit-string representations extracted from modified VNSs, which are rotation- and translation-invariant and distortion robust. The proposed alignment-free bio-cryptosystem is able to provide strong security while achieving good recognition performance. Experimental results in comparison with most existing alignment-free bio-cryptosystems using the publicly-available databases show the validity of the proposed scheme.  相似文献   
34.
针对在国产软硬件环境下,应用系统读取、浏览大量图像数据的速度慢问题,设计了图像组织浏览构件。通过改进图像组织方式,将基础影像和目标对象图像分开组织管理,并对目标对象图像的属性和分层、分类进行探讨,实现图像信息的快速展现。对图像组织浏览构件进行了插件化设计与实现,利用QT跨平台开发工具,实现了应用集成框架,并通过实现统一集成接口,进行各业务插件的集成。  相似文献   
35.
Essential fatty acid (EFA)-deficient rats were fed highly purified methyl esters of docosahexaenoate (22∶6n−3), arachidonate (20∶4n−6), alpha-linolenate (18∶3n−3) or oleate (18∶1n−9) (100 mg/day, tube fed for 3–10 days), and their plasma triacylglycerol (TG) secretion rates were measured. Secretion rates of TG into plasma were reduced by tube-feeding 22∶6n−3, 20∶4n−6, 18∶3n−3, but not 18∶1n−9, to EFA-deficient rats. A significant reduction occurred after feeding 22∶6n−3 for only three days. Feeding 22∶6n−3 or 18∶3n−3 to EFA-deficient rats for three days also reduced the activities of liver lipogenic enzymes and sharply increased the proportions of 22∶6n−3 and 20∶5n−3 in liver phospholipid fractions. Mechanisms by which these EFA may reduce lipogenesis are discussed.  相似文献   
36.
以棉浆为原料,废盐酸为水解催化剂,所得合成革用微晶纤锥素增粘剂的质量指标达到了德国和日本同类产品的标准。  相似文献   
37.
上好<马克思主义基本原理课概论>,要对这门课的性质、地位和任务、基本要求以及课程的重点和难点有一个基本认识,并能正确面对教学中的困境.思想政治课教师要苦练内功,不断提高自己的学识水平,开动脑筋,转变观念,采取灵活多样的教学方法和手段,把教师的"教"与学生的"学"有机结合起来,想方设法提高学生的学习积极性,要把理论课教学和实践课教学结合起来,改革思想政治课的评价体系和方式,不断增强思想政治课教学的实效性.  相似文献   
38.
针对我国农业保险发展现状,分析了农业保险发展中存在的问题.认为目前我国农业保险的发展正处于最困难和最关键的时期.为推动农业保险的快速发展,提出了建立和完善有关法规、加大政策扶持力度,确立农业法定险种、成立综合性农业保险公司、建立再保险机制和多渠道农业保险体系等措施建议.  相似文献   
39.
高校大学生"精神贫困"现象已引起人们重视,成为多方关注话题。本文在梳理前人研究成果基础上,对"精神贫困"测量指标进行研究,以获得科学的测量指标体系,为获得真实科学的一手资料打进行理论论证。  相似文献   
40.
A new type of high temperature energy storage material was obtained through the melt infiltration method, using compounding SiC ceramic foam as matrix and Na2SO4 as phase change material. The resulting composite material was measured by XRD, SEM, TG-DSC methods. The experimental results indicate that the composite is composed of silicon carbide, sodium sulfate and square quartz, and no chemical reactions occurs between Na2SO4 and SiC matrix. Na2SO4 has a good bonding with the SiC ceramic foam matrix. As the composite material is characterized by high thermal energy storage density and high thermal conductivity, it is suit for energy storage under high temperature. Funded by the “863” Hi-Tech Research and Development Program of China (2008AA05Z418)  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