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   22520篇
  免费   882篇
  国内免费   82篇
电工技术   287篇
综合类   43篇
化学工业   4914篇
金属工艺   477篇
机械仪表   460篇
建筑科学   1711篇
矿业工程   160篇
能源动力   685篇
轻工业   2148篇
水利工程   180篇
石油天然气   55篇
武器工业   1篇
无线电   1479篇
一般工业技术   4150篇
冶金工业   2767篇
原子能技术   137篇
自动化技术   3830篇
  2023年   141篇
  2022年   115篇
  2021年   525篇
  2020年   312篇
  2019年   328篇
  2018年   494篇
  2017年   429篇
  2016年   529篇
  2015年   479篇
  2014年   690篇
  2013年   1506篇
  2012年   1083篇
  2011年   1518篇
  2010年   1092篇
  2009年   1043篇
  2008年   1266篇
  2007年   1098篇
  2006年   939篇
  2005年   865篇
  2004年   774篇
  2003年   688篇
  2002年   660篇
  2001年   392篇
  2000年   376篇
  1999年   412篇
  1998年   409篇
  1997年   371篇
  1996年   340篇
  1995年   294篇
  1994年   301篇
  1993年   297篇
  1992年   250篇
  1991年   214篇
  1990年   200篇
  1989年   225篇
  1988年   181篇
  1987年   177篇
  1986年   171篇
  1985年   235篇
  1984年   212篇
  1983年   182篇
  1982年   166篇
  1981年   195篇
  1980年   127篇
  1979年   144篇
  1978年   141篇
  1977年   123篇
  1976年   137篇
  1975年   116篇
  1974年   103篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Dusts,scale, slags,sludges... Not wastes,but sources of profits   总被引:3,自引:0,他引:3  
Historically, the steel industry has focused on the need for and the many benefits of recycling steel that is discarded either in its own or in its customers’ manufacturing processes, as well as in recovery and reuse of steel scrap that arises after the product has served its intended purpose. In fact, modern steelmaking relies on the use of recycled iron units for at least half of its production. The other side of the story is the fate of the non-steel by-products (e.g., oxide dusts, sludges, scales, slags, spent refractories and the contained “low grade” energy units that are generated as natural adjuncts to iron and steelmaking processes). These valuable by-products often are classified as “wastes” and are discarded to landfills, at significant cost, although in reality they offer significant potential for cost savings or profit if reintroduced into the industrial arena via well planned programs. Examples of such instances will be presented, including energy credit issues, in the hope of pointing the way for future expansion of benefits from these opportunities. Preparing for a challenge and honor such as the Howe Memorial Lecture, one has to stand in awe of the accomplishments of the predecessor we honor in this forum. He worked in the early days of our industry without the benefits of the many technological improvements he and his successors brought to play as the years went by. John Stubbles, in his Howe Memorial Lecture in 1997,[1] presented a masterful and entertaining biography of Howe and his very active and prolific life. Perhaps the most telling quotation he attributed to Howe is very pertinent to the topic we will address presently: “Metallurgy lives by profit, not logic,” to which I would like to add a comment that bears on the topic of this lecture from the 1991 Howe lecturer, my friend and mentor Bill Dennis, “Where there is muck, there is money.” There are numerous examples of “one hand washes the other” in this business; that is, of the synergism between needs and capabilities. We will address some of these situations, such as in a new process under development for dezincing of post consumer scrap, and in the use of iron units in by-product oxides and recycling of ladle slags and of spent refractories. Peter J. Koros, the Iron and Steel Society’s 77th Howe Memorial Lecturer (2001), is Principal of Koros Associates, Inc. (Pittsburgh, PA), a consultancy he founded following retirement from the former LTV Steel Company where he worked for nearly 41 years, retiring as Senior Research Consultant. He earned the Bachelor of Science degree in Metallurgical Engineering from Drexel University, and his master’s and doctoral degrees in Metallurgy from the Massachusetts Institute of Technology (MIT). In 1958, he joined Jones and Laughlin Steel (which became LTV Steel Company), where he held positions in research (Director, Process Metallurgy), Technical Services and Quality Control, with most activities focused on steelmaking and related areas. He was responsible for J&L’s development work in injection technology for desulfurization of hot metal and steel, was the inventor of the patented co-injection concept now in use worldwide, and had the lead role in LTV Steel’s programs for degalvanizing scrap and for recovery and utilization of by-product oxides. He led the AISI Opt-In program for degalvanizing scrap and the LTV-USS pilot program for processing “by-product” oxides. Koros has authored more than 75 publications and presentations, and holds eight U.S. patents, the latest issued in 2000. Dr. Koros was elected a Distinguished Member and Fellow of the ISS in 1984 and a Fellow of ASM International in 1988. Other honors include the ISS Distinguished Service Award (1998), ISS Electric Furnace Honorable Mention Citation (1987), International Magnesium Association Design and Applications Award (1978), AISI Gold (1977) and Silver (1969) Medals, ISS Herty (1963), McKune (1963), and Toy (1962) Awards. Koros served on the Technical Advisory Committee of the AISI-DOE Direct Steelmaking Program and its follow-on Waste Oxide Recycling Program. He was chairman of the AISI Task Force on Degalvanizing Steel Scrap and of the Industrial Advisory Panel to the Argonne Lab-MRI Program on Dezincing Steel Scrap. The 2001 Howe Memorial Lecture, titled “Dusts, Scale, Slags, Sludges ... Not Wastes But Sources of Profits,” as well as an invited Keynote Lecture for an International Recycling Conference in Sweden (June 2002, “Iron Units in Search of a Home: New Steel”) were based on the experience from these programs. Koros has been an active member of the ISS Advanced Technology Committee for which he participated in and chaired several symposia, including New Melting Technologies II (October 2002) and the first New Melting Technologies Symposium (1997). He was Director of the ISS 2000 Short Course on Injection Technology, a lecturer in the 2000 ISS/AISI Course on BOF Steelmaking, lead Co-chairman for the Elliott Symposium (1990), and Chairman of the Program Committee for the Fifth International Iron and Steel Congress (1986). Dr. Koros served on the Industrial Advisory Board of MIT’s Materials Processing Center (1995–98) and the AISI’s Iron and Steel Research Subcommittee (1976–86.) He was chairman of the ISS National Science Foundation Advisory Committee, the Advisory Council of the U.S. Bureau of Mines Generic Minerals Technology Center for Pyrometallurgy Research (1983–85), and of the Advisory Board for Carnegie Mellon University’s Center for Iron and Steel Research, for which he served as chairman (1991–1992). Service included participation in the NRC-NAS Alternative Energy and Development Strategy Study (1989–90.) Koros was very active in the creation of the ISS, having served as Chairman of the predecessor TMS Iron and Steel Division in 1972–73 and on the AIME Board of Directors (1974). Professional Society memberships: ISS (elected Distinguished Member and Fellow, Life Member), TMS (Senior or Life Member), ASM International (elected Fellow, Life Member), and AISE.  相似文献   
132.
In last month’s column we started the correlation process. This early work simply looked at individual pieces of evidence as they might relate to other pieces of evidence. However, there are some potential pitfalls if we stop here. First, digital evidence can be ambiguous. In other words, we can see the same event reported by various sources in various ways. Are we really looking at the same event, or are we looking at different ones? The second issue is that events may be reported in unusual ways leading the analyst to believe that the event occurred multiple times when, in fact, it did not. We need processes to analyze all the events that are reported and to help us to understand the actual data that we are seeing. Fortunately, we actually have two: normalization and deconfliction. Those two processes will be the topics of this month’s offering.  相似文献   
133.
The technological limits for ultra high speed devices are now rapidly expanding due to the use of quantum well (QW) materials. This new class of materials gives the opportunity of tailoring materials parameters by controlling geometries on an atomic scale. They look very promising as materials for lasers, detectors and transistors suitable even above 10 Gb/s. It will be demonstrated that state of the art MQW structures can be realized in both material systems, InGaAsP/InP and InGaAlAs/InP. Parallel lateral laser structures (e.g. SIBH, BRS and TBH) have been designed to take full benefit of QW technology. Ultimate reduction of parasitics, whilst using potential low cost fabrication technologies is the basis for achieving high bitrate (10 Gb/s) MQW lasers, even with the stronger damping in QW material. Using the DFB-SIBH laser structure 10 Gb/s large signal experiments are successfully performed with bulk, MQW and SLMQW lasers. Extremely low fall times of 44 ps are achieved. Additional MQW based improvements are observed such as: −3 times higher differential gain, increased output power (>110 mW), 2.5 times lower chirp (Δλ−20dB = 0.40 nm at 10 Gb/s modulation), and 2 dB gain in power budget at 10 Gb/s digital transmission.  相似文献   
134.
Although regulations on work hours usually include a minimum weekly rest period, there is little empirical evidence concerning recovery from work. Shift-working nurses (N?=?61) used a handheld computer for 28 days to complete self-ratings, cognitive-performance tasks, and a sleep diary. Many measures were worse on rest days that followed a night shift rather than a day shift and tended to be worse on 1st rest days compared with subsequent rest days. Alertness was lowest on the 1st rest day following a night shift. Social satisfaction was better on workdays that were preceded by 2 rather than 1 rest day. Reaction time (RT) decreased over consecutive night shifts and tended to increase over rest days following night shifts. The results are interpreted as being consistent with the combined adaptive costs of fatigue and adjustment to and from a nocturnal routine. The practical implications for scheduling rest days are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
135.
To calculate the intensity of x-ray emission in electron beam microanalysis requires a knowledge of the energy distribution of the electrons in the solid, the energy variation of the ionization cross section of the relevant subshell, the fraction of ionizations events producing x rays of interest and the absorption coefficient of the x rays on the path to the detector. The theoretical predictions and experimental data available for ionization cross sections are limited mainly to K shells of a few elements. Results of systematic plane wave Born approximation calculations with exchange for K, L, and M shell ionization cross sections over the range of electron energies used in microanalysis are presented. Comparisons are made with experimental measurement for selected K shells and it is shown that the plane wave theory is not appropriate for overvoltages less than 2.5 V.  相似文献   
136.
This article describes the development and validation of scales to measure clients' outcome optimism, perceived progress, and self-agency related to change in problems presented in therapy. In Study 1, initial confirmatory and subsequent exploratory factor analyses (N?=?257) identified effort and persistence as an additional unique factor and guided selection of items to measure the 4 constructs. In Study 2, confirmatory factor analysis of the revised scales with a new sample (N?=?93) confirmed the measurement model. Results of convergent and discriminant validity analyses generally were in the predicted directions. The Perceived Progress scale demonstrated criterion validity with changes in dyadic adjustment and family functioning. The Outcome Optimism and Self-Agency scales showed variability in their relationship to the Perceived Progress scale over the first 3 sessions of therapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
137.
138.
Um Auskunft über die wirtschaftliche Bedeutung von Kaffee, Tee und Kakao zu geben, werden in diesem Mini-Review u.a. aktuelle Angaben zur weltweiten Produktion dieser drei „Exoten“ gemacht (Menge und Herkunftsl?nder), die jeweiligen Import-Anteile der Produktionsl?nder nach Deutschland (bzw. in die EU) benannt, der Pro-Kopf-Verbrauch an Kaffee, Tee oder Kakao in Deutschland mit dem anderer Staaten verglichen und – sofern m?glich – Einblick gegeben in die Entwicklung von weltweitem Angebot und Nachfrage und die damit verbundene Preisentwicklung in den vergangenen Jahren.  相似文献   
139.
140.
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