全文获取类型
收费全文 | 2025篇 |
免费 | 39篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 17篇 |
综合类 | 2篇 |
化学工业 | 388篇 |
金属工艺 | 20篇 |
机械仪表 | 30篇 |
建筑科学 | 69篇 |
矿业工程 | 16篇 |
能源动力 | 26篇 |
轻工业 | 131篇 |
水利工程 | 10篇 |
石油天然气 | 4篇 |
无线电 | 147篇 |
一般工业技术 | 276篇 |
冶金工业 | 703篇 |
原子能技术 | 29篇 |
自动化技术 | 210篇 |
出版年
2021年 | 23篇 |
2019年 | 18篇 |
2018年 | 26篇 |
2016年 | 22篇 |
2014年 | 18篇 |
2013年 | 107篇 |
2012年 | 45篇 |
2011年 | 86篇 |
2010年 | 46篇 |
2009年 | 34篇 |
2008年 | 61篇 |
2007年 | 74篇 |
2006年 | 60篇 |
2005年 | 58篇 |
2004年 | 35篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 27篇 |
2000年 | 41篇 |
1999年 | 25篇 |
1998年 | 79篇 |
1997年 | 55篇 |
1996年 | 50篇 |
1995年 | 46篇 |
1994年 | 37篇 |
1993年 | 56篇 |
1992年 | 37篇 |
1991年 | 19篇 |
1990年 | 32篇 |
1989年 | 42篇 |
1988年 | 34篇 |
1987年 | 37篇 |
1986年 | 37篇 |
1985年 | 30篇 |
1984年 | 43篇 |
1983年 | 39篇 |
1982年 | 31篇 |
1981年 | 36篇 |
1980年 | 26篇 |
1979年 | 25篇 |
1978年 | 38篇 |
1977年 | 32篇 |
1976年 | 43篇 |
1975年 | 31篇 |
1974年 | 24篇 |
1973年 | 17篇 |
1972年 | 19篇 |
1971年 | 15篇 |
1970年 | 21篇 |
1964年 | 17篇 |
排序方式: 共有2078条查询结果,搜索用时 15 毫秒
11.
Stanley M. Howard 《Metallurgical and Materials Transactions B》1989,20(6):845-852
The primary objective of this investigation was to demonstrate a new method of measuring activities. The mass spectrometric
analysis of effusates from a unique valved Knudsen cell was used to determine the activity of Ag in the liquid Ag−Cu system
at 1400 K. The alloy compositions were varied from one composition extreme to the otherin situ. The system exhibits positive deviation from ideal behavior, and the results are in agreement with previous investigations
and are summarized by the equation
相似文献
12.
The attrition mill is a device for mechanically reducing solid particle size by intense agitation of a slurry of material being milled and coarse milling media. For example, in 10 hours of milling, specific surfaces of 40 and 25 m2/g were obtained for alumina and barite, corresponding to 38 and 56 nm equivalent spherical diameter, respectively. Size reduction rates for relatively coarse particles were first-order and increased linearly with power input to the mill. Optimum milling medium concentration corresponded to medium particles moving a distance of approximately 0.7 of their diameter before collision with another such particle. Power characteristics of the attrition mill were essentially the same as those of a radial flow turbine mixer. Laminar flow became disrupted at NRe ≈ 200, while turbulent flow was established at NRe > 8000. Slurries of fine powders exhibited the same linear power-average density dependence as single-phase liquids. However, a different dependence was observed with large particles. 相似文献
13.
The reactions of a variety of activated vinyl compounds with cotton cellulose fabric containing quaternary ammonium hydroxide substituents were explored. Each reaction, catalyzed by the basic groups in the cellulose, was followed to or near the point of leveling off. The results are analyzed and discussed in terms of accessibility of the cellulosic compositions and in terms of the efficiency of the quaternary ammonium substituents as catalysts for the addition reactions. Estimates of relative forward rate constants (kf) and equilibrium constants (K) for the reactions were made. The values of kf for reactions of the vinyl compounds with the quaternary ammonium celluloses show a relative order which is similar to that for the reactions of the vinyl compounds with simple alcohols. Evidence is presented to indicate that, in some cases, the addition of vinyl compounds is accompanied by anionic-catalyzed graft polymerization. 相似文献
14.
Frank N. Jones Weidian Shen Stanley M. Smith Zhihua Huang Rose A. Ryntz 《Progress in Organic Coatings》1997,34(1-4):119-129
Scanning probe microscopy (SPM) is in a period of rapid development. It shows great promise for characterizing coating surfaces. This paper describes modification of an SPM so that it can be used to mar the surfaces of coatings under controlled conditions and to characterize the mars. Mar resistance of coatings is analyzed in terms of a ‘three response, two mechanism model.' The three responses (fracture, elastic, and plastic) can be measured quantitatively using the SPM. Of the three responses, only two (fracture and plastic deformation) are marring mechanisms – elastic deformations recover instantaneously. In some cases mars resulting from plastic deformation may recover slowly with time or with immersion in water; this phenomenon is attributed to viscoelastic creep. Microhardness is also measured with the modified SPM. Some thermoset coatings appear to be substantially harder near their surfaces than in the mass of material, and such materials may respond quite differently to stress applied at different levels near the surface. This finding has important implications for all coating properties that are strongly influenced by the surface. A quantity called ‘micro mar resistance' is defined. It may be useful for comparing different coatings under specified conditions of marring. However, there can be no single quantity that expresses ‘mar resistance' of a coating under all conditions. 相似文献
15.
Chul Kwak Stanley I. Sandler Hun-Soo Byun 《Korean Journal of Chemical Engineering》2006,23(6):1016-1022
The correlation of vapor-liquid equilibrium data for high-pressure carbon dioxide systems is of interest in a number of industrial
applications, including supercritical extraction. Here, we consider the correlation of data for 12 binary systems of carbon
dioxide separately with alcohols, with hydrocarbons, and with acetone, benzene, and water. The Wong-Sandler (W-S) and modified
Huron — Vidal first order (MHV1) free energy-based equation of state mixing rules (the W-S and MHV1 models) were used in the
calculations. Both combined equation of state+free energy models generally resulted in good correlations of the experimental
data over wide ranges of temperature and pressure with temperature — independent parameters. However, for the carbon dioxide+water
system, the W-S model produced an 11% average absolute deviation in pressure, while no parameter that resulted in an AAD in
pressure of less than 20% could be found for the MHV1 model. 相似文献
16.
Effects of crack depth on elastic-plastic fracture toughness 总被引:1,自引:1,他引:0
William A. Sorem Robert H. Dodds Jr. Stanley T. Rolfe 《International Journal of Fracture》1991,47(2):105-126
Short crack test specimens (a/W 0.50) are frequently employed when conventional deep crack specimens are either inappropriate or impossible to obtain, for example, in testing of particular microstructures in weldments and in-service structures containing shallow surface flaws. Values of elastic-plastic fracture toughness, here characterized by the crack tip opening displacement (CTOD), are presented for square (cross-section) three-point bend specimens with a/W ratios of 0.15 and 0.50 throughout the lower-shelf and lower-transition regions. Three dimensional, finite-element analyses are employed to correlate the measured load and crack mouth opening displacement (CMOD) values to the corresponding CTOD values, thus eliminating a major source of experimental difficulty in previous studies of shallow crack specimens. In the lower-transition region, where extensive plasticity (but no ductile crack growth) precedes brittle fracture, critical CTOD values for short crack specimens are significantly larger (factor of 2–3) than the CTOD values for deep crack specimens at identical temperatures. Short crack specimens are shown to exhibit increased toughness at the initiation of ductile tearing and decreased brittle-to-ductile transition temperatures. Numerical analyses for the two a/W ratios reveal large differences in stress fields ahead of the crack tip at identical CTOD levels which verify the experimentally observed differences in critical CTOD values. Correlations of the predicted stresses with measured critical CTOD values demonstrate the limitations of single-parameter fracture mechanics (as currently developed) to characterize the response. 相似文献
17.
Clarke DT Botchway SW Coles BC Needham SR Roberts SK Rolfe DJ Tynan CJ Ward AD Webb SE Yadav R Zanetti-Domingues L Martin-Fernandez ML 《The Review of scientific instruments》2011,82(9):093705
Optics clustered to output unique solutions (OCTOPUS) is a microscopy platform that combines single molecule and ensemble imaging methodologies. A novel aspect of OCTOPUS is its laser excitation system, which consists of a central core of interlocked continuous wave and pulsed laser sources, launched into optical fibres and linked via laser combiners. Fibres are plugged into wall-mounted patch panels that reach microscopy end-stations in adjacent rooms. This allows multiple tailor-made combinations of laser colours and time characteristics to be shared by different end-stations minimising the need for laser duplications. This setup brings significant benefits in terms of cost effectiveness, ease of operation, and user safety. The modular nature of OCTOPUS also facilitates the addition of new techniques as required, allowing the use of existing lasers in new microscopes while retaining the ability to run the established parts of the facility. To date, techniques interlinked are multi-photon/multicolour confocal fluorescence lifetime imaging for several modalities of fluorescence resonance energy transfer (FRET) and time-resolved anisotropy, total internal reflection fluorescence, single molecule imaging of single pair FRET, single molecule fluorescence polarisation, particle tracking, and optical tweezers. Here, we use a well-studied system, the epidermal growth factor receptor network, to illustrate how OCTOPUS can aid in the investigation of complex biological phenomena. 相似文献
18.
Favaro P Soatto S Burger M Osher SJ 《IEEE transactions on pattern analysis and machine intelligence》2008,30(3):518-531
Defocus can be modeled as a diffusion process and represented mathematically using the heat equation, where image blur corresponds to the diffusion of heat. This analogy can be extended to non-planar scenes by allowing a space-varying diffusion coefficient. The inverse problem of reconstructing 3-D structure from blurred images corresponds to an "inverse diffusion" that is notoriously ill-posed. We show how to bypass this problem by using the notion of relative blur. Given two images, within each neighborhood, the amount of diffusion necessary to transform the sharper image into the blurrier one depends on the depth of the scene. This can be used to devise a global algorithm to estimate the depth profile of the scene without recovering the deblurred image, using only forward diffusion. 相似文献
19.
Mosaic organization of DNA nucleotides 总被引:23,自引:0,他引:23
CK Peng SV Buldyrev S Havlin M Simons HE Stanley AL Goldberger 《Canadian Metallurgical Quarterly》1994,49(2):1685-1689
Long-range power-law correlations have been reported recently for DNA sequences containing noncoding regions. We address the question of whether such correlations may be a trivial consequence of the known mosaic structure ("patchiness") of DNA. We analyze two classes of controls consisting of patchy nucleotide sequences generated by different algorithms--one without and one with long-range power-law correlations. Although both types of sequences are highly heterogenous, they are quantitatively distinguishable by an alternative fluctuation analysis method that differentiates local patchiness from long-range correlations. Application of this analysis to selected DNA sequences demonstrates that patchiness is not sufficient to account for long-range correlation properties. 相似文献
20.
|