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   31748篇
  免费   4504篇
  国内免费   2254篇
电工技术   805篇
综合类   2287篇
化学工业   6915篇
金属工艺   637篇
机械仪表   1189篇
建筑科学   526篇
矿业工程   1324篇
能源动力   378篇
轻工业   10158篇
水利工程   155篇
石油天然气   879篇
武器工业   185篇
无线电   2331篇
一般工业技术   1243篇
冶金工业   1369篇
原子能技术   474篇
自动化技术   7651篇
  2024年   109篇
  2023年   533篇
  2022年   991篇
  2021年   1263篇
  2020年   1339篇
  2019年   1096篇
  2018年   1034篇
  2017年   1183篇
  2016年   1282篇
  2015年   1511篇
  2014年   1995篇
  2013年   2392篇
  2012年   3347篇
  2011年   2977篇
  2010年   2057篇
  2009年   1908篇
  2008年   1801篇
  2007年   2185篇
  2006年   1874篇
  2005年   1433篇
  2004年   1122篇
  2003年   961篇
  2002年   718篇
  2001年   569篇
  2000年   499篇
  1999年   406篇
  1998年   309篇
  1997年   293篇
  1996年   227篇
  1995年   196篇
  1994年   137篇
  1993年   123篇
  1992年   125篇
  1991年   85篇
  1990年   85篇
  1989年   57篇
  1988年   42篇
  1987年   44篇
  1986年   36篇
  1985年   32篇
  1984年   30篇
  1983年   21篇
  1982年   15篇
  1981年   13篇
  1980年   13篇
  1979年   7篇
  1978年   6篇
  1977年   6篇
  1959年   6篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
51.
何莉  邹雄  叶昊天  李香琴  董宏光 《化工学报》2020,71(7):2993-2999
乙二醇可从含芳烃组分油品中选择性萃取酚类,为支撑焦化含酚油中的酚类化合物萃取分离新工艺开发,针对其组分特点,在现有相平衡数据基础上选定代表物,利用液液平衡釜法测出常压下303.15、313.15和323.15 K时邻甲酚-间二甲苯-乙二醇体系液液相平衡数据,并利用Othmer-Tobias方程、Hand方程、Bachman方程分别进行实验数据可靠性检验,其线性相关系数的平方均大于0.99。同时分别用NRTL和UNIQUAC活度系数模型对实验数据进行关联,回归得到不同温度下的模型参数,模型计算值与实验数据对比后发现其均方根偏差小于1.8%,说明NRTL和UNIQUAC模型均可较好地描述该三元体系相平衡行为。  相似文献   
52.
53.
One of the key challenges in organic light-emitting diodes (OLEDs) for lighting applications is efficient light extraction from the planar, multi-layered OLED stack. Several different light extraction approaches are being explored currently by researchers, however characterizing light extraction films after fabricating OLEDs is not a viable approach when the outcoupling films have large surface roughness and is time consuming as well. Here we apply prism coupling method (PCM), a simple and elegant tool, to characterize outcoupling films. We show the effectiveness of PCM in estimating light extraction efficiency of outcoupling films. PCM can expedite selection and optimization of various light extraction approaches without the need to build OLEDs. The experimental results are corroborated by the optical simulations done using ray tracing method taking into account Mie scattering from wavelength sized spherical inclusions in an outcoupling film.  相似文献   
54.
含油污泥处理是目前油田亟待解决的问题之一。介绍了国内外含油污泥处理技术的研究进展,主要处理技术有溶剂萃取处理技术、焚烧处理技术、热解处理技术、生物处理技术、调剖处理技术等,并介绍了国内部分油田的含油污泥处理工艺。  相似文献   
55.
56.
ABSTRACT

The effect of chloride ions on the copper extraction equilibria, the rate of extraction, copper/iron selectivity, and chloride extraction was studied for organic phases containing pure ketoxime (LIX 84-IC) and pure nonylaldoxime (LIX 860N-IC). In these systems, the used aqueous phase contained total chloride concentrations from 0 to 110 g/l. It was determined that the chloride ions in the aqueous solution had a large negative effect on the extraction equilibria for LIX 84-IC and a small effect for LIX 860N-IC. This deleterious effect is attributed to an increase in the hydrogen ion activity coefficient in the presence of chloride ions. The chloride accelerated the rate of copper extraction even though the reaction was fast in all the tested conditions. An increase in the temperature from 25°C to 35°C affected positively the extraction equilibria for LIX 84-IC.  相似文献   
57.
58.
59.
Simulating the psychological experience of human vision,a road extraction model based on the format tower is proposed to extract the road in the high resolution remote sensing image from the perspective of morphology.Firstly,based on the spectral and texture information,the suspected road targets are extracted by using segmentation technology.Then these targets are classified according to their reliability and extract the road targets for each category.Finally,three types of identified road information are verified and merged,and the continuous smooth road extraction results are obtained.Experiments on real high resolution images show that the results are consistent with the visual perception of the human eye,and the overall classification accuracy is higher,indicating that the algorithm is effective and feasible and has good use value.  相似文献   
60.
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   
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