全文获取类型
收费全文 | 15512篇 |
免费 | 234篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 186篇 |
综合类 | 3篇 |
化学工业 | 1987篇 |
金属工艺 | 361篇 |
机械仪表 | 338篇 |
建筑科学 | 512篇 |
矿业工程 | 60篇 |
能源动力 | 306篇 |
轻工业 | 1215篇 |
水利工程 | 89篇 |
石油天然气 | 118篇 |
无线电 | 1508篇 |
一般工业技术 | 2333篇 |
冶金工业 | 5194篇 |
原子能技术 | 159篇 |
自动化技术 | 1399篇 |
出版年
2021年 | 97篇 |
2019年 | 102篇 |
2018年 | 135篇 |
2017年 | 101篇 |
2016年 | 94篇 |
2015年 | 107篇 |
2014年 | 225篇 |
2013年 | 569篇 |
2012年 | 304篇 |
2011年 | 406篇 |
2010年 | 333篇 |
2009年 | 336篇 |
2008年 | 450篇 |
2007年 | 439篇 |
2006年 | 432篇 |
2005年 | 386篇 |
2004年 | 323篇 |
2003年 | 361篇 |
2002年 | 308篇 |
2001年 | 321篇 |
2000年 | 315篇 |
1999年 | 398篇 |
1998年 | 1459篇 |
1997年 | 911篇 |
1996年 | 663篇 |
1995年 | 449篇 |
1994年 | 397篇 |
1993年 | 428篇 |
1992年 | 280篇 |
1991年 | 244篇 |
1990年 | 262篇 |
1989年 | 217篇 |
1988年 | 224篇 |
1987年 | 207篇 |
1986年 | 199篇 |
1985年 | 253篇 |
1984年 | 209篇 |
1983年 | 205篇 |
1982年 | 203篇 |
1981年 | 180篇 |
1980年 | 201篇 |
1979年 | 128篇 |
1978年 | 134篇 |
1977年 | 252篇 |
1976年 | 349篇 |
1975年 | 136篇 |
1974年 | 125篇 |
1973年 | 107篇 |
1972年 | 78篇 |
1970年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V Hawkins D Doll R Bumgarner T Smith C Abajian L Hood PS Nelson 《Canadian Metallurgical Quarterly》1999,27(1):204-208
Naloxone is generally considered to be a pure antagonist, but it may produce several behavioral effects, such as hyperalgesia or stimulation of respiration. We studied the effect of naloxone on gastric emptying and gastrointestinal transit in rats. Six to eight Wistar rats (200-250 g) were used for each experiment. Either saline or naloxone (0.01-10 mg/kg) was injected intraperitoneally at 0 min. At 30 min, radiolabeled saline or milk 1 mL was infused into the stomach. At 60 min, gastric emptying and gastrointestinal transit were calculated by measuring the radioactivity in the gastrointestinal tract. Naloxone significantly inhibited gastric emptying of saline (P = 0.002) and of milk (P < 0.05), but not the gastrointestinal transit of either (P > 0.05). Gastric emptying of saline showed a significant peak (P < 0.05) in the dose-response curve at 0.7 mg/kg. Therefore, naloxone significantly inhibits gastric emptying of saline and milk, but not the gastrointestinal transit of either. IMPLICATIONS: Although naloxone is generally considered to be a pure opioid receptor antagonist, it delays gastric emptying of saline or milk, as does morphine in the rat. However, it is uncertain from our results whether naloxone inhibited gastric emptying by antagonizing the effects of endogenous opioids. 相似文献
992.
Describes the performance evaluation of a limited-angle torque motor, using a simple piecewise analytical approach to overcome system nonlinearities. A block-diagram model developed from a combination of measurement and manufacturer's data is shown to be capable of accurately predicting both the steady-state and the dynamic performance. The approach described is of valuable assistance in the design of a complex multiloop nonlinear controller that is needed for a drive system containing the motor 相似文献
993.
994.
The Bureau of Engineering is a part of the City of Los Angeles' Department of Public Works and is responsible for the planning, design, and construction management of capital improvement projects for the city. In February 1997, the Bureau of Engineering executive staff and the Board of Public Works mandated a dramatic shift to improve project delivery. All of the non-wastewater elements of the Bureau were organized into a program-based matrix organization with a Project Manager as the focus for project delivery with project conception-to-conclusion responsibility. This paper describes the project management method of project delivery being implemented at the City of Los Angeles Bureau of Engineering and explains the implementation elements and their status. The paper reviews the new project management organizational structure and the organizational options considered by the Bureau. The work details the roles and responsibilities for the project delivery team members. The new tools used to manage projects are described, and the problems and solutions encountered are documented for use on future engineering management efforts. 相似文献
995.
MC Mahon MP Driscoll WJ Glover KM Borchert ZT Kelleher GJ Smith WB Coleman 《Canadian Metallurgical Quarterly》1999,14(2):337-346
We have previously identified and mapped a locus within human chromosome 11p11.2-p12 that suppresses the tumorigenic potential of a rat liver tumor cell line (termed GN6TF) which contains well defined chromosomal aberrations involving rat chromosomes 1, 4, 7, and 10. In the present study, we investigated the potential of this human 11p11.2-p12 liver tumor suppressor locus to suppress the tumorigenic potential of two other rat liver tumor cell lines (GN3TG and GP10TA) following microcell-mediated introduction of human chromosome 11. These tumor cell lines are aneuploid and contain chromosomal abnormalities that are similar to the GN6TF tumor line. The tumorigenic potential and other phenotypic characteristics of GN3TG-11neo and GP10TA-11neo microcell hybrid (MCH) cell lines were variable, and dependent upon the status of the introduced human chromosome 11. MCH cell lines that retained the region of 11p11. 2-p12 delineated by microsatellite markers D11S1385 and D11S903 exhibited suppression of tumorigenicity in vivo (decrease in tumorigenicity and/or elongation of latency), whereas, the tumorigenic potential of one MCH line that lacked markers in this region of human 11p11.2-p12, but retained flanking markers, was not changed from that of the parental tumor cell line. The chromosomal interval between microsatellite markers D11S1385 and D11S903 encompasses the previously localized minimal liver tumor suppressor region, suggesting that a common locus is responsible for tumor suppression among the rat liver tumor cell lines examined. The results of the present study have verified the presence of a liver tumor suppressor locus within human 11p11.2-p12, and have identified a substantial number of microsatellite markers that are closely linked to this tumor suppressor region. These chromosomal markers will facilitate positional cloning of candidate genes from this region, and may prove useful for determining the involvement of this locus in the pathogenesis of human liver cancer. 相似文献
996.
Linus M. Perander Zoran D. Zujovic Tom F. Kemp Mark E. Smith James B. Metson 《JOM Journal of the Minerals, Metals and Materials Society》2009,61(11):33-39
Fines in smelter-grade aluminas are recognized as a significant process problem in aluminum smelting. However, understanding
the nature of this fine material and how it impacts the reduction process are less clearly understood. The combination of
new analytical methods such as variable pressure scanning electron microscopy and very high field solid state nuclear magnetic
resonance provide new insights into the phases present and their spatial distribution within aluminas, and suggest how such
fine materials are generated, particularly during calcination in the alumina refinery. 相似文献
997.
Xuefeng Zhang Kenneth A. Smith Douglas R. Worsnop Jose L. Jimenez John T. Jayne Charles E. Kolb 《Aerosol science and technology》2013,47(6):619-638
As a sequel to our previous effort on the modeling of particle motion through a single lens or nozzle, flows of gas–particle suspensions through an integrated aerodynamic-lens–nozzle inlet have been investigated numerically. It is found that the inlet transmission efficiency (ηt) is unity for particles of intermediate diameters (Dp ~ 30–500 nm). The transmission efficiency gradually diminishes to ~40% for large particles (Dp > 2500 nm) because of impact losses on the surface of the first lens. There is a catastrophic reduction of ηt to almost zero for very small particles (Dp ≤ 15 nm) because these particles faithfully follow the final gas expansion. We found that, for very small particles, particle transmission is mainly controlled by nozzle geometry and operating conditions. A lower upstream pressure or a small inlet can be used to improve transmission of very small particles, but at the expense of sampling rate, or vice versa. Brownian motion exacerbates the catastrophic reduction in ηt for small particles; we found that the overall particle transmission efficiency can be roughly calculated as the product of the aerodynamic and the purely Brownian efficiencies. For particles of intermediate diameters, Brownian motion is irrelevant, and the modeling results show that the transmission efficiency is mainly controlled by the lenses. Results for an isolated lens or nozzle are used to provide guidance for the design of alternative inlets. Several examples are given, in which it is shown that one can configure the inlet to preferentially sample large particles (with ηt > 50% for Dp = 50–2000 nm) or ultrafine particles (with ηt > 50% for Dp = 20–1000 nm). Some of the results have been compared with experimental data, and reasonable agreement has been demonstrated. 相似文献
998.
999.
Samples of Mimolette (France) and Milbenkase (Germany) cheeses traditionally ripened by mites were analyzed to determine the mite species present on each sample. Scientific literature was reviewed to understand which mite species most commonly infest cheese. Morphological features possessed by mites were then studied to understand what unique characteristics are required to ensure accurate identification. After identification and compilation of a detailed key of stored food mites (subclass Acari, order Astigmata) and their delineating features, the mites were viewed through a cryogenic scanning electron microscope. It was determined that Mimolette cheese is inoculated with Acarus siro L. The features studied to identify this mite species included idiosomal length and shape, setae length and arrangement, leg size, placement of anus and genitals, and solenidia shape. The Milbenkase cheese is inoculated with Tyrolichus casei Oudemans, which was evident after viewing the same features used to identify A. siro and the supracoxal seta shape. With this knowledge, further research can be conducted on the 2 cheese varieties to understand what chemical, physical, and microbial changes occur within the cheeses because of mites. It is important to identify the mite species present on each cheese variety to improve our understanding of their role in creating the distinctive characteristics that set these cheeses apart from others. 相似文献
1000.