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   248938篇
  免费   1801篇
  国内免费   265篇
电工技术   4039篇
综合类   91篇
化学工业   40347篇
金属工艺   15144篇
机械仪表   10061篇
建筑科学   4175篇
矿业工程   3759篇
能源动力   3874篇
轻工业   9720篇
水利工程   4087篇
石油天然气   13006篇
武器工业   28篇
无线电   20193篇
一般工业技术   62758篇
冶金工业   32157篇
原子能技术   11134篇
自动化技术   16431篇
  2021年   2757篇
  2019年   2731篇
  2018年   5431篇
  2017年   5711篇
  2016年   6044篇
  2015年   3053篇
  2014年   5324篇
  2013年   10081篇
  2012年   7308篇
  2011年   8930篇
  2010年   7297篇
  2009年   8106篇
  2008年   8173篇
  2007年   7858篇
  2006年   6356篇
  2005年   5564篇
  2004年   5484篇
  2003年   5304篇
  2002年   5135篇
  2001年   4954篇
  2000年   4939篇
  1999年   4255篇
  1998年   7181篇
  1997年   5839篇
  1996年   4429篇
  1995年   3657篇
  1994年   3424篇
  1993年   3629篇
  1992年   3215篇
  1991年   3361篇
  1990年   3481篇
  1989年   3371篇
  1988年   3268篇
  1987年   3260篇
  1986年   3157篇
  1985年   3314篇
  1984年   3252篇
  1983年   3146篇
  1982年   2993篇
  1981年   3046篇
  1980年   3071篇
  1979年   3257篇
  1978年   3490篇
  1977年   3460篇
  1976年   3911篇
  1975年   3209篇
  1974年   3293篇
  1973年   3341篇
  1972年   2988篇
  1971年   2754篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids.  相似文献   
52.
53.
54.
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite.  相似文献   
55.
Tsyplenkov  V. V.  Shastin  V. N. 《Semiconductors》2019,53(10):1334-1339
Semiconductors - Long-wavelength acoustic phonon-assisted relaxation rates for the excited 1s(T), 2p0, 2s, 3p0, 2p±, 4p0, and 3p± states of antimony donors in a germanium crystal are...  相似文献   
56.
The data on the use of solar photovoltaic plants (PVPs) for providing a reliable and guaranteed power supply to telecommunication systems and cellular communication systems in the conditions prevalent in Uzbekistan are given. The research-based structures developed by OOO MIR SOLAR and the selection of PVP elements ensuring their reliable operation are described. The main influencing factors are discussed, and the use of effective combinations of different types of panels (from monocrystalline and polycrystalline silicon) and a specially developed controller are considered.  相似文献   
57.
58.
An explicit extraction of the retinal vessel is a standout amongst the most significant errands in the field of medical imaging to analyze both the ophthalmological infections, for example, Glaucoma, Diabetic Retinopathy (DR), Retinopathy of Prematurity (ROP), Age-Related Macular Degeneration (AMD) as well as non retinal sickness such as stroke, hypertension and cardiovascular diseases. The state of the retinal vasculature is a significant indicative element in the field of ophthalmology. Retinal vessel extraction in fundus imaging is a difficult task because of varying size vessels, moderately low distinction, and presence of pathologies such as hemorrhages, microaneurysms etc. Manual vessel extraction is a challenging task due to the complicated nature of the retinal vessel structure, which also needs strong skill set and training. In this paper, a supervised technique for blood vessel extraction in retinal images using Modified Adaboost Extreme Learning Machine (MAD-ELM) is proposed. Firstly, the fundus image preprocessing is done for contrast enhancement and in-homogeneity correction. Then, a set of core features is extracted, and the best features are selected using “minimal Redundancy-maximum Relevance (mRmR).” Later, using MAD-ELM method vessels and non vessels are classified. DRIVE and DR-HAGIS datasets are used for the evaluation of the proposed method. The algorithm’s performance is assessed based on accuracy, sensitivity and specificity. The proposed technique attains accuracy of 0.9619 on the DRIVE database and 0.9519 on DR-HAGIS database, which contains pathological images. Our results show that, in addition to healthy retinal images, the proposed method performs well in extracting blood vessels from pathological images and is therefore comparable with state of the art methods.  相似文献   
59.
Water Resources Management - A number of models have been developed to simulate seawater intrusion in coastal aquifers, which differ in the accuracy level and computational demands, based on the...  相似文献   
60.
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