全文获取类型
收费全文 | 8687篇 |
免费 | 142篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 89篇 |
综合类 | 4篇 |
化学工业 | 1221篇 |
金属工艺 | 162篇 |
机械仪表 | 228篇 |
建筑科学 | 280篇 |
矿业工程 | 55篇 |
能源动力 | 164篇 |
轻工业 | 693篇 |
水利工程 | 69篇 |
石油天然气 | 19篇 |
武器工业 | 1篇 |
无线电 | 747篇 |
一般工业技术 | 1338篇 |
冶金工业 | 2924篇 |
原子能技术 | 81篇 |
自动化技术 | 764篇 |
出版年
2022年 | 48篇 |
2021年 | 54篇 |
2020年 | 40篇 |
2019年 | 55篇 |
2018年 | 78篇 |
2017年 | 72篇 |
2016年 | 84篇 |
2015年 | 78篇 |
2014年 | 99篇 |
2013年 | 354篇 |
2012年 | 193篇 |
2011年 | 250篇 |
2010年 | 252篇 |
2009年 | 237篇 |
2008年 | 254篇 |
2007年 | 250篇 |
2006年 | 213篇 |
2005年 | 237篇 |
2004年 | 177篇 |
2003年 | 191篇 |
2002年 | 189篇 |
2001年 | 158篇 |
2000年 | 172篇 |
1999年 | 157篇 |
1998年 | 780篇 |
1997年 | 555篇 |
1996年 | 400篇 |
1995年 | 307篇 |
1994年 | 259篇 |
1993年 | 277篇 |
1992年 | 116篇 |
1991年 | 111篇 |
1990年 | 122篇 |
1989年 | 127篇 |
1988年 | 121篇 |
1987年 | 93篇 |
1986年 | 83篇 |
1985年 | 113篇 |
1984年 | 113篇 |
1983年 | 86篇 |
1982年 | 75篇 |
1981年 | 71篇 |
1980年 | 82篇 |
1979年 | 79篇 |
1978年 | 90篇 |
1977年 | 141篇 |
1976年 | 231篇 |
1975年 | 60篇 |
1974年 | 63篇 |
1973年 | 57篇 |
排序方式: 共有8839条查询结果,搜索用时 0 毫秒
101.
57Fe Mössbauer spectroscopy has been used to characterize the iron-bearing minerals present in some British Columbia coals. The minerals observed in a range of samples include pyrite/marcasite, siderite, jarosite, rozenite or melanterite, and Fe2+ -bearing clay minerals such as illite. The presence of jarosite is confirmed through the magnetic hyperfine interaction observed at 4.2 K. The absence of magnetic ordering at 4.2 K for the ferrous sulphate component indicates the presence of rozenite, FeS04 · 4H20, or melanterite, FeS04 · 7H20, rather than szomolnokite, FeS04 · H20 or FeS04. The effects of ashing on two of the coals is also studied. 相似文献
102.
G. T. Jones L. A. Glasgow L. E. Erickson S. A. Patel C. H. Lee 《Chemical Engineering Communications》1990,97(1):181-196
Understanding the dynamic phenomena of viability loss of shear sensitive cells and bubble breakage and coalescence within airlift reactors requires knowledge of local, liquid-phase hydrodynamics. The laser-Doppler velocimeter (LDV) is a non-invasive instrument which may be used to obtain this information. Experimental procedures and software were developed to detect and measure Doppler bursts in two-phase flow in a split-cylinder airlift reactor. Off-line analysis of the data indicated a detection rate approximately one order of magnitude greater than that observed using an available commercial frequency tracker. Approximately 400 to 500 observations are needed for the ensemble mean to characterize the local mean velocity to within ±5% for a superficial gas velocity of 10.4 cm/s, the highest superficial gas velocity used in these studies. The limitations, prospects, and signal-processing options for LDV in this application are also discussed 相似文献
103.
Analysis of the carbon disulphide extracts of nine samples of UK coal-maceral concentrates by 1H highresolution n.m.r. spectroscopy, gas-liquid chromatography and field-desorption mass spectrometry indicates the presence of components with a wide molecular weight range extending up to 1200 amu; these are attributed to n-alkanes up to ≈C50 and highly condensed polynuclear aromatic compounds. 相似文献
104.
A method of analysing solids downflow through standpipe and slide valve in the moving bed mode is presented. The method is based on combining Yoon and Kunii equations for moving-bed flow with a proposed modified orifice equation for gas—solid flow. The analysis correctly predicts the observed trend of the effects of gas injection into the standpipe. It also provides quantitative prediction of the conditions for transition from moving-bed flow to dense phase fluidized solids flow and to lean phase “streaming flow”. The latter flow pattern refers to solids streaming down a tube at high voidage typified by the discharge of solid down a tube with no constriction at the lower end of the tube. Further work is required to test the general applicability of the present analysis and to extend the analysis to yield a generalized quantitative flow regime diagram for downflow of solids in a pipe. 相似文献
105.
Murray S. Blum Ray F. Severson Richard F. Arrendale Douglas W. Whitman Pierre Escoubas Olushola Adeyeye Clive G. Jones 《Journal of chemical ecology》1990,16(1):223-244
Adults of a generalist herbivore, the lubber grasshopper,Romalea guttata, can be converted to functional specialists by feeding them exclusively on catnip,Nepeta cataria. No obvious adverse effects on adult development resulted from this enforced monophagy. Notwithstanding the fact thatR. guttata has had no coevolutionary relationship with this Eurasian mint, it readily sequesters compounds that are identical to or derived from the terpenoid lactones that are characteristic ofN. cataria. R. guttata appears to both biomagnify minor allelochemicals and to sequester metabolites of theNepeta terpenes in its paired defensive glands. The levels of autogenously produced phenolics are not affected by feeding onN. cataria and the defensive secretions of catnip-fed grasshoppers are more repellent to ants than those of wild-fed acridids. Metabolites of theN. cataria monoterpenes are sequestered in the defensive glands when catnip is added to the natural diet ofR. guttata. The ability of a generalist,R. guttata, to facilely bioaccumulate a potpourri of foreign allelochemicals when feeding in a specialist mode is analyzed in terms of its biochemical, physiological, and functional significance. Sequestration is examined as a response to the enteric effronteries represented by the phytochemicals that can be characteristic of the overload in a monophagous diet. 相似文献
106.
The skin, skeleton and a fat-filled swim bladder of the orange roughy (Hoplostethus atlanticus) each contained greater than 20% lipid by wet weight which was almost entirely wax esters. These had carbon numbers of 34–40
consistent with the major fatty acid being 18∶1 and the major fatty alcohols being 16∶0, 18∶1, 20∶1 and 22∶1. In contrast,
the liver and the roe contained appreciable quantities of glycerolipids with 18∶1 and 22∶6 as the major fatty acids. 相似文献
107.
A. K. Galwey K. A. Jones R. S. Beckett 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1966,16(5):159-162
It has been observed that concrete containing chalk aggregate had a higher compressive strength than other wise similar concrete which contained basalt aggregate, although the chalk rock had a lower compressive strength than the basalt. Measurements of the rates of development of hardness of concrete containing these aggregates, measurements of the surface areas of these aggregates and X-ray examinations of the crystal phases in the set cement are reported and discussed. It was concluded that the relatively low strength of concrete containing basalt aggregate may be due to development of a phase, not chemically identified in the present work, which had a relatively weak bonding strength to the augite crystals in the basalt concrete. 相似文献
108.
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
109.
The results of conversion determinations on the products from Powhatan No.5 coal liquefied in an autoclave and in a high-pressure, high-temperature e.s.r. cavity are reported. Oil, asphaltene and preasphaltene yields, and overall conversion have been determined for Powhatan No.5 coal samples liquefied in tetralin, SRC-11 heavy distillate, and naphthalene at temperatures from 400 to 480 ° C in both reactor systems. The concept of reaction severity is introduced and used to formalize the relation between the effect of temperature and reaction time on oil yield and conversion. Oil is the predominant product in liquefaction in tetralin or naphthalene, asphaltene is the major product of liquefaction in SRC-II heavy distillate. Retrogressive reaction (THF-insoluble product formation) becomes severe when SRC-II heavy distillate is the liquefaction solvent and residence time of >10 min are used at temperatures >450 °C. Preasphaltenes appear to be the only intermediate species in Powhatan No.5 liquefaction. 相似文献