全文获取类型
收费全文 | 339196篇 |
免费 | 5550篇 |
国内免费 | 738篇 |
专业分类
电工技术 | 6657篇 |
综合类 | 641篇 |
化学工业 | 54488篇 |
金属工艺 | 11031篇 |
机械仪表 | 9496篇 |
建筑科学 | 9303篇 |
矿业工程 | 1033篇 |
能源动力 | 9164篇 |
轻工业 | 35499篇 |
水利工程 | 2724篇 |
石油天然气 | 3745篇 |
武器工业 | 8篇 |
无线电 | 41711篇 |
一般工业技术 | 65464篇 |
冶金工业 | 57588篇 |
原子能技术 | 5671篇 |
自动化技术 | 31261篇 |
出版年
2022年 | 2259篇 |
2021年 | 3590篇 |
2020年 | 2330篇 |
2019年 | 2776篇 |
2018年 | 4762篇 |
2017年 | 4507篇 |
2016年 | 4793篇 |
2015年 | 3575篇 |
2014年 | 5678篇 |
2013年 | 16829篇 |
2012年 | 8858篇 |
2011年 | 11849篇 |
2010年 | 9346篇 |
2009年 | 10469篇 |
2008年 | 11031篇 |
2007年 | 10894篇 |
2006年 | 9526篇 |
2005年 | 8662篇 |
2004年 | 8418篇 |
2003年 | 8125篇 |
2002年 | 7938篇 |
2001年 | 8071篇 |
2000年 | 7645篇 |
1999年 | 7945篇 |
1998年 | 18024篇 |
1997年 | 13207篇 |
1996年 | 10381篇 |
1995年 | 8100篇 |
1994年 | 7408篇 |
1993年 | 7082篇 |
1992年 | 5444篇 |
1991年 | 5208篇 |
1990年 | 5055篇 |
1989年 | 4882篇 |
1988年 | 4782篇 |
1987年 | 3983篇 |
1986年 | 4099篇 |
1985年 | 4932篇 |
1984年 | 4484篇 |
1983年 | 4162篇 |
1982年 | 3735篇 |
1981年 | 3915篇 |
1980年 | 3598篇 |
1979年 | 3528篇 |
1978年 | 3339篇 |
1977年 | 3898篇 |
1976年 | 4939篇 |
1975年 | 2874篇 |
1974年 | 2736篇 |
1973年 | 2762篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
RM Bionta G Blewitt CB Bratton D Casper A Ciocio R Claus M Crouch ST Dye S Errede GW Foster W Gajewski KS Ganezer M Goldhaber TJ Haines TW Jones D Kielczewska WR Kropp JG Learned JM LoSecco J Matthews HS Park LR Price F Reines J Schulz S Seidel E Shumard D Sinclair HW Sobel JL Stone L Sulak R Svoboda G Thornton van der Velde JC C Wuest 《Canadian Metallurgical Quarterly》1987,36(1):30-36
992.
KENNETH R. DAVEY 《Journal of texture studies》1985,16(2):143-150
The influence of some factors on the hardness of subcutaneous fat on sides of chilled beef as measured by the average force resisting movement of a cutting pin (Ff) was investigated. Values of Ff determined at a fat temperature of 10°C on grass-fed animals denied water 24 h preslaughter were not significantly influenced by moisture content (5-11%) or fat depth (2-27 mm). There was a quadratic relationship (P<0.001) between the age of animals at slaughter (31-141 months) and Ff, and a linear one (P<0.001) between saturated fatty acid content (35-50%) and Ff. Values of Ffat a fat temperature of 5°C were not significantly related to moisture content (1-22%) but there was a linear relationship (P<0.01) with fat depth (5-13 mm). This had a common slope for the three feeding patterns: (1) grass-fed animals denied water 24 h preslaughter; (2) grass-fed animals given access to water 24 h preslaughter, and; (3) lot-fed animals given access to water 24 h preslaughter. 相似文献
993.
994.
Inverse controller design for fuzzy interval systems 总被引:1,自引:0,他引:1
This paper aims at designing and analyzing an inverse controller for stable inversible (minimum phase) fuzzy interval linear and/or multilinear systems. The controller is designed from the fuzzy interval ranges of the system parameters using an /spl alpha/-cut methodology. Indeed, for a given /spl alpha/-cut of the fuzzy system parameters representing an uncertainty level, the control objective can be viewed as maintaining the system output within a tolerance envelope, around the exact trajectory, specified by the degree of preference /spl alpha/ on the fuzzy trajectory. The stability is ensured in the way that the controller restricts the system output divergence within the tolerance envelope. The validity of the proposed method is illustrated by simulation examples. 相似文献
995.
F. -U. Gast P. S. Dittrich P. Schwille M. Weigel M. Mertig J. Opitz U. Queitsch S. Diez B. Lincoln F. Wottawah S. Schinkinger J. Guck J. Käs J. Smolinski K. Salchert C. Werner C. Duschl M. S. Jäger K. Uhlig P. Geggier S. Howitz 《Microfluidics and nanofluidics》2006,2(1):21-36
We describe a novel microfluidic perfusion system for high-resolution microscopes. Its modular design allows pre-coating of
the coverslip surface with reagents, biomolecules, or cells. A poly(dimethylsiloxane) (PDMS) layer is cast in a special molding
station, using masters made by photolithography and dry etching of silicon or by photoresist patterning on glass or silicon.
This channel system can be reused while the coverslip is exchanged between experiments. As normal fluidic connectors are used,
the link to external, computer-programmable syringe pumps is standardized and various fluidic channel networks can be used
in the same setup. The system can house hydrogel microvalves and microelectrodes close to the imaging area to control the
influx of reaction partners. We present a range of applications, including single-molecule analysis by fluorescence correlation
spectroscopy (FCS), manipulation of single molecules for nanostructuring by hydrodynamic flow fields or the action of motor
proteins, generation of concentration gradients, trapping and stretching of live cells using optical fibers precisely mounted
in the PDMS layer, and the integration of microelectrodes for actuation and sensing. 相似文献
996.
S. Kar T. Searles E. Lee G. B. Viswanathan H. L. Fraser J. Tiley R. Banerjee 《Metallurgical and Materials Transactions A》2006,37(3):559-566
The development of a set of computational tools that permit microstructurally based predictions for the tensile properties
of commercially important titanium alloys, such as Ti-6Al-4V, is a valuable step toward the accelerated maturation of materials.
This paper will discuss the development of neural network models based on a Bayesian framework to predict the yield and ultimate
tensile strengths of Ti-6Al-4V at room temperature. The development of such rules-based model requires the population of extensive
databases, which in the present case are microstructurally based. The steps involved in database development include producing
controlled variations of the microstructure using novel approaches to heat treatments, the use of standardized stereology
protocols to characterize and quantify microstructural features rapidly, and mechanical testing of the heat-treated specimens.
These databases have been used to train and test neural network models for prediction of tensile properties. In addition,
these models have been used to identify the influence of individual microstructural features on the tensile properties, consequently
guiding the efforts toward development of more robust mechanistically based models. Based on the neural network model, it
is possible to investigate the influence of individual microstructural features on the tensile properties, and in certain
cases these dependencies can point toward unrecognized phenomena. For example, the apparently unexpected trend of increase
in tensile strength with increasing prior β-grain size has led to the determination of the pronounced role of the basketweave microstructure in strengthening these alloys,
especially in case of larger prior β grains.
This article is based on a presentation made in the symposium “Computational Aspects of Mechanical Properties of Materials,”
which occurred at the 2005 TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA, under the auspices of the MPMD-Computational
Materials Science & Engineering (Jt. ASM-MSCTS) Committee. 相似文献
997.
Development of a poly-functional catalyst that has higher hydrodealkylation activity based on 15% Cr/γ- Al2 O3 was researched for benzene production from an alkyl-aromatic mixture via hydrodealkylation. For this goal, the effects of the promoters like Fe, Co, or Ni and their concentrations on the activity of a Cr/Al2 O3 catalyst were investigated. Toluene + n-heptane + tetrahydrotiophene (89:10:1 w%) model mixture, which has the same content as industrial aromatics, was used as feedstock. The activities of catalysis in reactions of hydrodealkylation, hydrocracking, and hydrogenolize with respect to conversions of toluene, heptane, and tetrahydrotiophene were tested, respectively. As to the obtained results, the catalyst including 5% Fe has a higher hydrodealkylation activity, compared to the catalyst including Co, and especially to the alumocrom catalyst not including a promoter, while it has a lower coke formation and reduced activity to the catalyst including Ni. 相似文献
998.
999.
A. G. Upolovnikova V. M. Chumarev R. I. Gulyaeva L. Yu. Udoeva 《Russian Metallurgy (Metally)》2007,(1):10-13
The effect of sodium carbonate additions on phase formation during the air oxidation of the sublimates of niobium electron-beam remelting is studied by derivatography, X-ray diffraction analysis, and electron-probe microanalysis. The composition of the oxidation products changes with the heating temperature. The formation of sodium niobates and aluminates is detected by X-ray diffraction analysis at temperatures higher than 600°C. The oxidation of the sublimates is completed by the formation of sodium metaniobate and aluminate. Sodium carbonate additions are shown to accelerate the oxidation of the sublimates. 相似文献
1000.
S A Brantmeier M E Bellin S K Boehm S M Bushmeyer C L Kubajak M R Dentine R R Grummer R L Ax 《Journal of dairy science》1987,70(10):2138-2144
Concentrations of estradiol-17 beta in follicular fluid were correlated to follicular size, stage of estrous cycle, location of corpus luteum, and presence of large follicles. Paired ovaries were obtained from 481 nonpregnant cows at slaughter and follicles were classified as ipsilateral or contralateral to the corpus luteum. Follicular fluid estradiol-17 beta concentrations from 2494 small, 1485 medium, and 396 large follicles were quantified by radioimmunoassay. Stage of estrous cycle was estimated by visual examination of the corpus luteum. Follicles in stage 1 of the estrous cycle (d 1 to 4) had the highest estradiol-17 beta concentration and the smallest mean follicular diameter. Location of follicles relative to the corpus luteum had no influence on estradiol-17 beta concentrations. As follicular size increased, concentration of estradiol-17 beta also increased. The presence of a single large follicle did not affect the concentration of estradiol-17 beta in medium or small follicles. In contrast, if multiple large follicles occurred in the same cow, concentrations of estradiol-17 beta were significantly lower in medium but not small follicles. 相似文献