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   7562篇
  免费   803篇
  国内免费   409篇
电工技术   121篇
综合类   476篇
化学工业   1157篇
金属工艺   1140篇
机械仪表   844篇
建筑科学   295篇
矿业工程   82篇
能源动力   133篇
轻工业   448篇
水利工程   62篇
石油天然气   96篇
武器工业   45篇
无线电   925篇
一般工业技术   1109篇
冶金工业   156篇
原子能技术   50篇
自动化技术   1635篇
  2024年   35篇
  2023年   142篇
  2022年   193篇
  2021年   190篇
  2020年   238篇
  2019年   251篇
  2018年   239篇
  2017年   286篇
  2016年   311篇
  2015年   294篇
  2014年   490篇
  2013年   703篇
  2012年   491篇
  2011年   674篇
  2010年   532篇
  2009年   507篇
  2008年   482篇
  2007年   451篇
  2006年   387篇
  2005年   294篇
  2004年   272篇
  2003年   228篇
  2002年   180篇
  2001年   152篇
  2000年   100篇
  1999年   97篇
  1998年   74篇
  1997年   62篇
  1996年   62篇
  1995年   50篇
  1994年   48篇
  1993年   37篇
  1992年   33篇
  1991年   23篇
  1990年   17篇
  1989年   31篇
  1988年   10篇
  1987年   15篇
  1986年   14篇
  1985年   17篇
  1984年   18篇
  1983年   11篇
  1982年   8篇
  1981年   8篇
  1979年   3篇
  1978年   3篇
  1975年   2篇
  1974年   2篇
  1973年   2篇
  1958年   1篇
排序方式: 共有8774条查询结果,搜索用时 15 毫秒
21.
22.
A cryo-specimen storage system for low-temperature scanning electron microscopy (LTSEM) specimens is described, which: liberates multi-specimen experiments from sampling restrictions imposed by the rate at which LTSEM specimens can be examined in the SEM; provides security against experiment loss resulting from breakdown of the SEM or cryo-system; enables collection of specimens in the field or in laboratories remote from the SEM laboratory; and facilitates international air transport of LTSEM specimens. The components of the system, which has a capacity of 98 stub-mounted specimens, are readily made in a laboratory workshop. The details of the design may be altered to suit particular specimen types or experimental approaches.  相似文献   
23.
This paper demonstrates how the problem of tracking targets, which appear as either straight or curved lines in two-dimensional display images (or data images) can be formulated in terms of a directed weighted graph model and how dynamic programming techniques can be efficiently applied to reach an optimal or sub-optimal solution. In general, track detection algorithms providing optimal solutions have good detective ability, but most of them suffer from the inability to detect discontinuous lines or to resolve efficiently pairs of crossing lines. A sub-optimal solution is provided that efficiently overcomes these weaknesses. We focus on modeling the track detection problem in terms of a graph, formulating fast sequential/parallel sub-optimal track detection algorithms and testing them on simulated data in order to show their detective ability. Moreover, we specify the conditions under which sub-optimal algorithms can perform at least as well as their corresponding optimal algorithms. This is significant for the track detection problem where fast, accurate and real-time detection is considered a necessity.  相似文献   
24.
This paper discusses the contested role of images in electronic editions, and summarizes some of the chief arguments for their inclusion. I then argue that, to truly determine the importance of images to the function of electronic editions, we must understand the contribution the image makes to the form of textual knowledge provided by the edition. I suggest a distinction between editions which are primarily pedagogical in their aims, those which aim above all at scholarly authority, and those which attempt to provide textual information as high-quality data which can be analysed and processed. I conclude that the latter represents the most significant future trend in electronic editing. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
25.
Recently, superconducting Nd1Ba2Cu3Oy (Ndl23) thin films with high superconducting transition temperature (T c) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by two-dimensional island growth mode. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half-integer number of thec-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. This result is supported byI-V STS measurements. The surface morphology of the Nd123 thin films is compared with that of thec-axis-oriented Y1Ba2Cu3Sy thin films. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films.  相似文献   
26.
A simplified method for the preparation of particles from liquid suspensions has been developed. Particles are deposited directly on carbon planchets for rapid analysis by environmental scanning electron microscopy or by conventional scanning electron microscopy after an additional drying step. This is accomplished by filtering the liquid through thin carbon planchets. Three different grades of graphite were investigated for their suitability as the source material for these planchets. The high quality isomolded graphite is recommended for the filtration and direct observation of particles by electron microscopy. This technique is demonstrated for particles in hydraulic fluid and aquatic suspended particulate material from a natural water source.  相似文献   
27.
汽车空调冷凝器腐蚀试验的表征与评价   总被引:3,自引:0,他引:3  
介绍了汽车空调冷凝器的腐蚀试验程度及方法,对试验后的冷凝器进行了密封性检查,并用光学显微镜和扫描电镜检测和分析了材料的显微结构,焊接质量,腐蚀性质及其腐蚀深度等。通过对冷凝器的宏微观检查与表征,评价了冷凝器质量的优劣,提出了改进措施与建议。  相似文献   
28.
Slate is a fine-grained, low-grade metamorphic rock derived from argillaceous sediments or occasionally volcanic ash. Although most slates contain mainly quartz, chlorite and white mica, they vary considerably in their durability, some lasting centuries while others fail after a few years of service. A detailed characterisation of their mineralogy is required for the assessment of performance, and to establish the provenance of a used slate. A combination of methods was used to examine Ballachulish slates; XRD analysis to determine the principal minerals present, XRF analysis to determine the total chemical composition, and scanning electron microscopy to determine the chemical composition of individual minerals. It was found that the white mica in Ballachulish slate is phengite and the chlorite is ripidolite. Feldspar is present as albite and carbonate as ferroan dolomite. Several accessory minerals were also identified, including chloritoid, monzonite and zircon. There was considerable variation in the ratio of the principal minerals, making it impossible to identify used slates by this criterion. Instead, chemical composition of the individual minerals, and possibly key accessory minerals, should be used to determine the provenance of slates.  相似文献   
29.
Martha J. Farah.     
Recognizes Martha J. Farah for rigorous empirical and theoretical analysis of visual cognition, in which understanding of normal function and analysis of neurological deficits illuminate and strengthen one another. Applying diverse experimental techniques within an integrated approach to the study of mind and brain, she has sharpened and helped to answer fundamental questions about how humans generate and manipulate visual images, recognize objects, and attend to positions in space. Along with a citation, a biography is presented for Farah, as well as a bibliography of her works. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
30.
A multiresolution analysis of digital gray-level images is presented. A gray-level multi-scale framework is determined from two main assumptions: the gray scale is binary at the finest spatial resolution, and the gray levels of composed regions are obtained additively. In order to interrelate the gray-level histograms of the same image at different resolutions, probabilistic linear models are developed, which are then applied for estimation. Linear-optimization theory is used as a way of constructing such models. A general procedure for image processing is sketched, based on gray-level estimation. A versatile algorithm for nonlinear filtering is derived. Some examples of prospective applications are given.This work was partially supported by grant TIC91-646 from the DGYCIT of the Spanish Government.  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