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   3252篇
  免费   58篇
  国内免费   3篇
电工技术   13篇
综合类   6篇
化学工业   278篇
金属工艺   73篇
机械仪表   24篇
建筑科学   68篇
矿业工程   4篇
能源动力   46篇
轻工业   208篇
水利工程   13篇
石油天然气   2篇
无线电   187篇
一般工业技术   246篇
冶金工业   1937篇
原子能技术   17篇
自动化技术   191篇
  2021年   25篇
  2020年   15篇
  2019年   21篇
  2018年   35篇
  2017年   38篇
  2016年   47篇
  2015年   20篇
  2014年   34篇
  2013年   74篇
  2012年   49篇
  2011年   79篇
  2010年   61篇
  2009年   53篇
  2008年   75篇
  2007年   79篇
  2006年   68篇
  2005年   55篇
  2004年   53篇
  2003年   45篇
  2002年   44篇
  2001年   49篇
  2000年   31篇
  1999年   61篇
  1998年   575篇
  1997年   351篇
  1996年   203篇
  1995年   138篇
  1994年   97篇
  1993年   127篇
  1992年   36篇
  1991年   45篇
  1990年   47篇
  1989年   43篇
  1988年   46篇
  1987年   42篇
  1986年   30篇
  1985年   34篇
  1984年   23篇
  1983年   29篇
  1982年   25篇
  1981年   13篇
  1980年   29篇
  1979年   11篇
  1978年   16篇
  1977年   30篇
  1976年   62篇
  1975年   32篇
  1974年   14篇
  1973年   12篇
  1972年   15篇
排序方式: 共有3313条查询结果,搜索用时 15 毫秒
101.
An algorithm is presented in this paper to facilitate the exploration of large image collections based on visual similarities. Starting with an unordered and unannotated set of images, the algorithm first extracts the salient details into feature vectors using both color and gradient information. The feature vectors are then used to train a self-organizing map which maps high-dimensional feature vectors onto a 2D canvas so that images with similar feature vectors are grouped together. When users browse the image collection, an image collage is generated that selects and displays the most pertinent set of images based on which portion of the 2D canvas is currently in view. Flowing from an overview to details is a seamless operation controlled simply by pan and zoom, with representative images selected in a consistent and predictable way. To make organizing larger image collections practical in interactive time, the organization algorithm is designed to run in parallel on graphics processing units. Overall this paper presents an end-to-end solution that facilitates the surfing of image collections in a fresh way.  相似文献   
102.
Incremental Evolution in ANNs: Neural Nets which Grow   总被引:1,自引:1,他引:0  
This paper explains the optimisation of neuralnetwork topology using Incremental Evolution;that is, by allowing the network to expand byadding to its structure. This method allows anetwork to grow from a simple to a complexstructure until it is capable of fulfilling itsintended function. The approach is somewhatanalogous to the growth of an embryo or theevolution of a fossil line through time, it istherefore sometimes referred to as anembryology or embryological algorithm. Thepaper begins with a general introduction,comparing this method to other competingtechniques such as The Genetic Algorithm, otherEvolutionary Algorithms and SimulatedAnnealing. A literature survey of previous workis included, followed by an extensive newframework for application of the technique.Finally, examples of applications and a generaldiscussion are presented.  相似文献   
103.
Grant W. Petty 《Software》2001,31(11):1067-1076
Physical dimensions and units form an essential part of the specification of constants and variables occurring in scientific programs, yet no standard compilable programming language implements direct support for automated dimensional consistency checking and unit conversion. This paper describes a conceptual basis and prototype implementation for such support within the framework of the standard Fortran 90 language. This is accomplished via an external module supplying appropriate user data types and operator interfaces. Legacy Fortran 77 scientific software can be easily modified to compile and run as ‘dimension‐aware’ programs utilizing the proposed enhancements. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
104.
105.
Since the introduction of sodium metabisulfite as a food preservative, it has been associated with several idiosyncratic reactions (eg, bronchospasm, oculonasal symptoms, and urticaria/angioedema) in sulfite-sensitive individuals. The pathogenic mechanism of these reactions is not yet understood. We report the case of two crewmen on a shrimp trawler who were found dead in the ship's hold. Their deaths had occurred while they were applying dry sodium metabisulfite, referred to as "shrimp dip" in the shrimping industry. Postmortem examinations showed diffuse pulmonary edema consistent with death secondary to asphyxia. Associated findings were visceral congestion. Although it is possible to measure death from sodium metabisulfite with available records, its potential morbidity cannot be estimated. It is known that sodium metabisulfite can react with acids and water, releasing toxic sulfur dioxide (SO2) gas. In addition, SO2 gas reacts with respiratory tissue forming sulfureous acid, and inducing a pulmonary reaction causing hypoxemia. Furthermore, sodium metabisulfite, compared with sodium bisulfite, has a much greater propensity to release SO2 gas. We conclude that there is a need for improved education regarding the potential side effects of sodium metabisulfite, thus eliminating needless occupational morbidity and mortality.  相似文献   
106.
The potential position of and drivers for inorganic polymers (“geopolymers”) as an element of the push for a sustainable concrete industry are discussed. These materials are alkali-activated aluminosilicates, with a much smaller CO2 footprint than traditional Portland cements, and display very good strength and chemical resistance properties as well as a variety of other potentially valuable characteristics. It is widely known that the widespread uptake of geopolymer technology is hindered by a number of factors, in particular issues to do with a lack of long-term (20+ years) durability data in this relatively young research field. There are also difficulties in compliance with some regulatory standards in Europe and North America, specifically those defining minimum clinker content levels or chemical compositions in cements. Work on resolving these issues is ongoing, with accelerated durability testing showing highly promising results with regard to salt scaling and freeze–thaw cycling. Geopolymer concrete compliance with performance-based standards is comparable to that of most other high-strength concretes. Issues to do with the distinction between geopolymers synthesised for cement replacement applications and those tailored for niche ceramic applications are also discussed. Particular attention is paid to the role of free alkali and silicate in poorly-formulated systems and its deleterious effects on concrete performance, which necessitates a more complete understanding of the chemistry of geopolymerisation for the technology to be successfully applied. The relationship between CO2 footprint and composition in comparison with Portland-based cements is quantified.  相似文献   
107.
Two hundred twenty-seven cardiac transplant procedures have been performed in 206 patients from January, 1968, to April, 1981. Postoperative survival rates, calculated by the actuarial method for program years 1968 to 1973 (66 patients), are 44%, 33%, 27%, 21%, and 18% at 1, 2, 3, 4, and 5 years after transplantation, respectively. Postoperative survival rates for program years 1974 to 1981 (140 patients) are 63%, 55%, 51, 44%, and 39% at 1, 2, 3, 4, and 5 years after transplantation, respectively. This increase results primarily from improvement in survival achieved in the first 3 postoperative months (59% +/- 7%, 1968 to 1973, versus 80% +/- 40%, 1974 to 1980), reflecting improved patient management. Infection remains the primary cause of death following transplantation (76/131 patients, 58%), followed by acute rejection (24/181, 18.3%), graft arteriosclerosis (14/131, 10.7%), and malignancy (6/131, 4.6%). The development of graft arteriosclerosis has been examined in 85 one-year survivors studied by annual coronary arteriograms. Coronary lesions of varying severity have developed in 21 patients. HLA-A2 incompatibility was associated with a higher incidence of graft arteriosclerosis than was apparent for all other A locus incompatibilities (p less than 0.0003). Lymphoma has been shown to be associated with younger recipient age, a primary disease diagnosis of idiopathic cardiomyopathy, and retransplantation. One hundred six patients have survived at least 1 year after transplantation; 97% were in NYHA Class 1 at that time interval and 82% returned to employment or activity of choice. The longest survival time is new 11 years, 3 months. Cardiac transplantation can be considered "reasonable and therapeutic treatment to extend life" in selected individuals.  相似文献   
108.
Password memorability and security: empirical results   总被引:2,自引:0,他引:2  
Users rarely choose passwords that are both hard to guess and easy to remember. To determine how to help users choose good passwords, the authors performed a controlled trial of the effects of giving users different kinds of advice. Some of their results challenge the established wisdom.  相似文献   
109.
Lewison  Grant 《Scientometrics》2004,59(3):311-320
This paper investigates two bibliometric problems: the listing of books in a specialist area (ornithology) and the determination of the citation pattern to individual authors, who often re-issue their books in later editions. James Bond, a Philadelphia ornithologist, who specialised in the birds of the West Indies, is used as an example of a naturalist whose long career led to many journal articles and enduring scientific fame through a well-known book. He also attained some unexpected notoriety through the use of his name by a popular novelist. Methods for the evaluation of his book and associated bird checklists in comparison with other similar works are presented on the basis of their citations. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
110.
Remote memory was assessed in persons with HIV-associated dementia (HIV-D), probable Alzheimer's disease (AD), and Huntington's disease (HD) and in healthy controls. The clinical groups were similar in overall dementia severity. Each clinical group exhibited impairments on remote memory tests relative to controls; however, temporally graded memory loss with selective preservation of older information was observed in the AD group but not the HD or HIV-D group. Analysis of cued retrieval indicated a preferential cuing benefit for the HIV-D and HD groups relative to the AD group. The similar pattern of remote memory performance demonstrated by the HIV-D and HD groups is a novel finding and suggests a subcortically mediated retrograde amnesia in HIV-D. The temporally graded pattern and the abnormal cued retrieval performance in the AD group are consistent with a consolidation deficit associated with extrahippocampal (cortical) and hippocampal damage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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