全文获取类型
收费全文 | 266609篇 |
免费 | 3220篇 |
国内免费 | 823篇 |
专业分类
电工技术 | 5140篇 |
综合类 | 331篇 |
化学工业 | 37639篇 |
金属工艺 | 10299篇 |
机械仪表 | 8511篇 |
建筑科学 | 6149篇 |
矿业工程 | 1078篇 |
能源动力 | 6404篇 |
轻工业 | 23449篇 |
水利工程 | 2562篇 |
石油天然气 | 3910篇 |
武器工业 | 68篇 |
无线电 | 34770篇 |
一般工业技术 | 50250篇 |
冶金工业 | 51576篇 |
原子能技术 | 5425篇 |
自动化技术 | 23091篇 |
出版年
2021年 | 2057篇 |
2019年 | 2043篇 |
2018年 | 3476篇 |
2017年 | 3548篇 |
2016年 | 3744篇 |
2015年 | 2339篇 |
2014年 | 4069篇 |
2013年 | 11371篇 |
2012年 | 6601篇 |
2011年 | 8908篇 |
2010年 | 7017篇 |
2009年 | 7878篇 |
2008年 | 8709篇 |
2007年 | 8643篇 |
2006年 | 7831篇 |
2005年 | 7178篇 |
2004年 | 6911篇 |
2003年 | 6755篇 |
2002年 | 6389篇 |
2001年 | 6477篇 |
2000年 | 6190篇 |
1999年 | 6393篇 |
1998年 | 15705篇 |
1997年 | 11108篇 |
1996年 | 8692篇 |
1995年 | 6754篇 |
1994年 | 6019篇 |
1993年 | 5900篇 |
1992年 | 4613篇 |
1991年 | 4310篇 |
1990年 | 4122篇 |
1989年 | 3879篇 |
1988年 | 3734篇 |
1987年 | 3276篇 |
1986年 | 3155篇 |
1985年 | 3667篇 |
1984年 | 3407篇 |
1983年 | 3062篇 |
1982年 | 2902篇 |
1981年 | 3004篇 |
1980年 | 2826篇 |
1979年 | 2683篇 |
1978年 | 2553篇 |
1977年 | 3108篇 |
1976年 | 3919篇 |
1975年 | 2367篇 |
1974年 | 2355篇 |
1973年 | 2346篇 |
1972年 | 1887篇 |
1971年 | 1789篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The main goal of this work is to find the best way to represent the equilibrium conditions between soybean and air. The experimental study was based on the static method using saturated salt solutions in order to regulate the vapour pressure of the air surrounding the grains. We developed a discrimination study among some ensting equations used for grains. To discriminate these equations we explored some non-linearity measures. The obtained results showed that the Halsey modified equation was the best model in terms of nonsignifiance for bias and non-linearity measures. The distribution for the estimated parameters. using simulation procedures, also showed good normal behavior for the Halsey equation. 相似文献
992.
D. A. Ivashintsov D. V. Stefanishin A. B. Veksler 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1995,29(4):227-234
Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 4, pp. 30–35, April, 1995. 相似文献
993.
994.
Air entrainment in fresh concrete with PFA 总被引:6,自引:0,他引:6
D.S. Zhang 《Cement and Concrete Composites》1996,18(6):409-416
The results of a study into the influence of PFA on air entrainment in fresh concrete are discussed It is shown that the required dosage of AEA to produce an air content of 5.5 ± 0.5% in a PFA modified concrete mix is two-six times that required in the corresponding neat OPC concrete mix. The dosage of a vinsol based air entraining agent (AEA) required appears to be directly related to the PFA content of the mix. Similar direct relationships were obtained with a range of different PFAs. The dosage of an AEA based on the salt of a fatty acid appears to be sensitive to both PFA and OPC contents. For the type of PFA used, the variability of measured air content or the amount of air retained after continued agitation both indicated that vinsol based AEAs show the highest variability whilst fatty acid based AEAs show low variability. The between batch variability of air content was significantly improved by the addition of PFA regardless of the AEA used. 相似文献
995.
L. D. Monti P. E. Sandoli S. Costa V. C. Phan P. M. Piatti 《Journal of Automated Methods and Management in Chemistry》1993,15(5):177-181
Intermediate products of the metabolism of glucose, fat and amino-acid are important in the evaluation of such metabolic disorders as diabetes mellitus, liver disease and metabolic acidosis. In the present study, methods for the measurement of intermediate metabolites (lactate, pyruvate, alanine, β-hydroxybutyrate and glycerol) have been adapted to a fast centrifugal analyzer: the COBAS FARA. Correlation coeffcients rangedfrom 0.90 to 0.99, compared to established manual spectrophotometric methods. Within-run coeffcients of variation (CVs) ranged between 2.9 and 8.8% at low levels, between 1.5 and 5.7% at medium levels and between 1.2 and 5.6% at high levels. Between-run CVs were between 4.0 and 15.0% at low levels, between 1.7 and 7.0% at medium levels and between 1.3 and 2.7% at high levels. These fluorimetric assays for the determination of intermediate metabolites on COBAS FARA (Roche) have a good sensitivity and precision, are less costly than manual methods and can be used on a routine basis. 相似文献
996.
997.
The authors demonstrate, for the first time, a three node optically time division multiplexed network with a maximum capacity of 40 Gbit/s. Electro-optical switches were used for both `drop and insert' and demultiplexing, and electronic clock recovery provided synchronisation throughout the network 相似文献
998.
B D Butler 《Medical instrumentation》1985,19(2):59-62
The widespread use of bubble oxygenators during cardiopulmonary bypass has raised questions concerning the production and introduction of gaseous microemboli (GME) into patients. An understanding of the complications associated with GME requires awareness of the biophysical and biochemical responses that occur between bubbles and blood. The production of GME as well as their interactions with each other and with blood products are examined. These interactions can influence the data collected from Doppler ultrasound devices and the development of organ dysfunction. 相似文献
999.
The characteristics of SF6/He plasmas which are used to etch Si3N4 have been examined with experimental design and modeled empirically by response-surface methodology using a Lam Research Autoetch 480 single-wafer system. The effects of variations of process gas flow rate (20-380 sccm), reactor pressure (300-900 mtorr). RF power (50-450 W at 13.56 MHz), and interelectrode spacing (8-25 mm) on the etch rates of LPCVD (low-pressure chemical vapor deposition) Si3N4, thermal SiO2, and photoresist were examined at 22±2°C. Whereas the etch rate of photoresist increases with interelectrode spacing between 8 and 19 mm and then declines between 19 and 25 mm, the etch rate of Si3N 4 increases smoothly from 8 to 25 mm, while the etch rate of thermal SiO2 shows no dependence on spacing between 8 and 25 mm. The etch rates of all three films decrease with increasing reactor pressure. Contour plots of the response surfaces for etch rate and etch uniformity of Si3N4 as a function of spacing and flow rate at constant RF power (250 W) display complex behavior at fixed reactor pressures. A satisfactory balance of etch rate and etch uniformity for Si3N4 is predicted at low reactor pressure (~300 mtorr), large electrode spacing (12-25 mm), and moderate process gas flow rates (20-250 sccm) 相似文献
1000.
D.S. Horschel 《Nuclear Engineering and Design》1987,104(3)
This paper discusses the features and construction of a
reinforced-concrete containment model that has been built at Sandia National Laboratories in Albuquerque, New Mexico. The model Light-Water-Reactor (LWR) containment building was designed and built to the American Society of Mechanical Engineers (ASME) code by United Engineers and Constructors, Inc. The containment model will be tested to failure to determine its response to static internal overpressurization. The results from testing the heavily instrumented containment will be used to assess the capability of analytical methods for predicting the performance of containments subject to severe accident loads as part of the US Nuclear Regulatory Commission's program on containment integrity.The scaled dimensions of the cylindrical wall and hemispherical dome are typical of a full-size containment. Features representative of a prototypical containment and included in the heavily reinforced model are equipment hatches, personnel airlocks, several small piping penetrations, and a thin steel liner attached to the concrete by headed studs. 相似文献