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   2922篇
  免费   50篇
  国内免费   2篇
电工技术   33篇
综合类   2篇
化学工业   367篇
金属工艺   64篇
机械仪表   47篇
建筑科学   91篇
矿业工程   4篇
能源动力   39篇
轻工业   225篇
水利工程   14篇
石油天然气   6篇
无线电   349篇
一般工业技术   349篇
冶金工业   1103篇
原子能技术   51篇
自动化技术   230篇
  2021年   23篇
  2019年   16篇
  2018年   29篇
  2017年   29篇
  2016年   39篇
  2015年   22篇
  2014年   35篇
  2013年   110篇
  2012年   70篇
  2011年   92篇
  2010年   53篇
  2009年   70篇
  2008年   93篇
  2007年   92篇
  2006年   85篇
  2005年   70篇
  2004年   89篇
  2003年   61篇
  2002年   79篇
  2001年   58篇
  2000年   53篇
  1999年   76篇
  1998年   298篇
  1997年   151篇
  1996年   138篇
  1995年   71篇
  1994年   78篇
  1993年   81篇
  1992年   39篇
  1991年   47篇
  1990年   40篇
  1989年   36篇
  1988年   36篇
  1987年   32篇
  1986年   39篇
  1985年   46篇
  1984年   28篇
  1983年   37篇
  1982年   22篇
  1981年   32篇
  1980年   28篇
  1979年   19篇
  1978年   28篇
  1977年   37篇
  1976年   55篇
  1975年   18篇
  1973年   14篇
  1972年   14篇
  1971年   20篇
  1969年   14篇
排序方式: 共有2974条查询结果,搜索用时 31 毫秒
71.
Sports nutrition is a constantly evolving field with hundreds of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper is a five year update of the sports nutrition review article published as the lead paper to launch the JISSN in 2004 and presents a well-referenced overview of the current state of the science related to how to optimize training and athletic performance through nutrition. More specifically, this paper provides an overview of: 1.) The definitional category of ergogenic aids and dietary supplements; 2.) How dietary supplements are legally regulated; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of the ergogenic value of nutrition and dietary supplementation in regards to weight gain, weight loss, and performance enhancement. Our hope is that ISSN members and individuals interested in sports nutrition find this review useful in their daily practice and consultation with their clients.  相似文献   
72.
73.
Bright ductile deposits of tin have been obtained from acid stannous sulphate to which wood tar dispersed in aqueous solution by a suitable agent has been added. The dispersing agent used was octyl sulphuric acid but some alternatives are possible. Whole distillates from either hardwood or softwood have been found to contain the active agent but fractions of tar prepared and marketed for special uses may not contain it. The agent is a neutral component of the tar, distilling in the range of 150–200° and may be destroyed by prolonged heating.

Operation of a 90 l. plating bath containing 8 g/1. tar has consistently given bright deposits at current densities of 8–30 A/sq ft with cathode agitation and has given good promise of solution stability. Barrel-plating at 12–18 A/sq ft has given good results.

Brittle deposits may be produced by the use of unsuitable dispersing agents for the tar, excessive tar additions or too high a current density, but the limits imposed are not impractical.

Promising results have also been obtained with the addition of the tar preparation to chloride/fluoride tin plating baths.  相似文献   
74.
The increasing demand for micro-formed and stamped parts such as connectors in the electronic industry is forcing manufacturers to push the speed limit of conventional press technologies to improve throughput. Designing dies/tooling for higher speeds and obtaining extended tool life requires a thorough understanding of the process. This paper discusses an experimental study of the interaction between punch, stripper plate and sheet material at various blanking velocities up to 1600 mm/s. The effect of velocity on punching force is also studied. A methodology to obtain high strain and strain rate dependent material flow stress data using blanking test and finite element modelling is presented.  相似文献   
75.
76.
Benthic invertebrate communities were examined in Compensation Creek, a man‐made stream in south‐central Newfoundland, Canada. Samples taken in September 2006 and September 2007 from large woody debris (LWD) were compared with samples from benthic environments to determine whether LWD supported a more diverse and abundant invertebrate community. Benthic habitats in a nearby natural stream were also sampled. Taxa composition was similar between the man‐made and the natural stream, highlighting successful colonization for the majority of taxa. Within Compensation Creek, taxa richness was higher in benthic habitats than on LWD, likely influenced by the successional age of the stream and surrounding habitat. The more complex benthic substrate provided refugia and allowed for the accumulation of fine detritus as a food source. Scrapers were almost completely absent from LWD and collector‐gatherer abundance was greater in the benthos. Collector‐filterer abundance was more than six times greater near the pond outflow than farther downstream when discharge was high, but abundances were almost equal when discharge was reduced. Riparian vegetation has not fully established around the man‐made stream, whereas it is overhanging and extensive at the natural stream, leading to more leaf‐litter input for shredders. As the morphology of Compensation Creek changes, the invertebrate community will continue to develop and likely increase utilization of accumulated detritus at LWD. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
77.
The DSC thermogram of the title compound (1) reveals the following characteristics: When a 3.34 mg sample of 1 was heated at 10°C-min?1, exotherm onset occurred at 272°C, reached a maximum at 308°C, and subsided at 331°C. A second smaller exotherm was initiated at 331°C, reached a maximum at 338°C, and subsided at 355°C. A study of the shock sensitivity of 1 as measured by the exploding foil slapper technique revealed that 1 is less shock-sensitive than TNT. Explosive output calculations show that it is a substantially more powerful explosive than is TNT.  相似文献   
78.
This three-part study was designed to determine aflatoxin M recovery from pasteurized and/or stored cow's milk. (a) Aflatoxin M was added to samples of raw Holstein milk at a concentration of 2.0 mug/liter. Half of each sample then was pasteurized at 63 C for 30 min, and both raw and pasteurized portions were stored at 4 C up to 17 days. (b) Samples of raw milk, pasteurized (77 C, 16 s) skim milk, dry cottage cheese curd, and cottage cheese whey were taken from a commercial operation in an area in which natural contamination had been encountered. (c) Milk from a cow dosed with aflatoxin B1 was stored frozen (-18 C) in bulk and in assay-size sample containers for 120 days. Aflatoxin M was recovered completely after either storage or pasteurization in (a) and (b). In (c), a recovery deficiency was detectable after 68 days of storage, which increased to 45% of the original value by 120 days. These observations differ from those of others in that loss of aflatoxin M was significant after pasteurization or storage of raw milk, totaling 87% loss after 120 days of frozen storage. Aflatoxin M partitioning between curd and whey in the preparation of cottage cheese agrees with more recent studies, but differs from previous reports. Three possible explanations for the differences are offered.  相似文献   
79.
A new species of Hemicheyletia Volgin was found on Scottish farms and in a creamery. This mite falls into the bakeri group according to the arrangement of the dorso-median setae. A short key to some related species is given.  相似文献   
80.
Assessment scientists and managers depend on social values to identify the goals that will be used to guide environmental assessments. These goals are commonly identified by examining the vested interests of the various social groups that are stakeholders in a region. However, knowledge about what people value represents only part of the information needed to identify comprehensive assessment goals for environmental systems that include both economic and ecological components and processes. All parties also need to understand what is valuable to ecosystems because that determines the ecological patterns and processes that prevail in the long run. The competition among alternate system designs for available energy determines the viability of the choices that people make for their environment. Ecosystems that prevail in competition use the process of self-organization to create system designs that maximize the use of ever-changing sources of available energy. The efficacy of ecosystem designs can be evaluated using the maximum empower principle, which states that ecosystems evolve toward designs that maximize empower (energy use per unit time). Energy is an accounting quantity that normalizes the different kinds of energy developed in a system so that they may be compared. The counter-intuitive and sometimes controversial results that come from energy analyses are illustrated by examining three environmental problems on the interface between ecology and economics. A process for identifying and using social and ecosystem values to guide environmental assessments is proposed using a conceptual energy systems model that shows how these processes might interact within a region. The probability of realizing a given change in system empower production is suggested as a decision criterion that can be used by managers to evaluate the efficacy of alternatives.  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