全文获取类型
收费全文 | 4191篇 |
免费 | 82篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 37篇 |
综合类 | 1篇 |
化学工业 | 645篇 |
金属工艺 | 126篇 |
机械仪表 | 102篇 |
建筑科学 | 117篇 |
矿业工程 | 5篇 |
能源动力 | 75篇 |
轻工业 | 286篇 |
水利工程 | 19篇 |
石油天然气 | 8篇 |
无线电 | 543篇 |
一般工业技术 | 712篇 |
冶金工业 | 1247篇 |
原子能技术 | 34篇 |
自动化技术 | 324篇 |
出版年
2021年 | 35篇 |
2019年 | 27篇 |
2018年 | 41篇 |
2017年 | 32篇 |
2016年 | 41篇 |
2015年 | 34篇 |
2014年 | 52篇 |
2013年 | 154篇 |
2012年 | 96篇 |
2011年 | 106篇 |
2010年 | 105篇 |
2009年 | 118篇 |
2008年 | 124篇 |
2007年 | 119篇 |
2006年 | 104篇 |
2005年 | 99篇 |
2004年 | 87篇 |
2003年 | 100篇 |
2002年 | 75篇 |
2001年 | 92篇 |
2000年 | 114篇 |
1999年 | 108篇 |
1998年 | 349篇 |
1997年 | 238篇 |
1996年 | 167篇 |
1995年 | 137篇 |
1994年 | 100篇 |
1993年 | 108篇 |
1992年 | 55篇 |
1991年 | 62篇 |
1990年 | 80篇 |
1989年 | 75篇 |
1988年 | 54篇 |
1987年 | 62篇 |
1986年 | 43篇 |
1985年 | 60篇 |
1984年 | 68篇 |
1983年 | 60篇 |
1982年 | 45篇 |
1981年 | 61篇 |
1980年 | 45篇 |
1979年 | 42篇 |
1978年 | 26篇 |
1977年 | 67篇 |
1976年 | 71篇 |
1975年 | 36篇 |
1974年 | 36篇 |
1973年 | 45篇 |
1972年 | 23篇 |
1970年 | 24篇 |
排序方式: 共有4281条查询结果,搜索用时 15 毫秒
1.
R. Morena P. E. Lockwood L. Evans C. W. Fairhurst 《Journal of the American Ceramic Society》1986,69(4):75-C-
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance. 相似文献
2.
As an alternative to surgical splenectomy, partial splenic embolization was performed in seven children for hypersplenism manifested by splenomegaly, thrombocytopenia, leukopenia, and erythrocyte hemolysis. Within a few days, platelet and leukocyte counts rose significantly in all patients and were maintained in six of seven patients during a follow-up period of 9 to 69 months. Spleen size and abdominal distention also decreased significantly in all children. There were no infectious complications. 相似文献
3.
This article is the second of two papers that review the field of spatially sensitive social scientific research into the links between social status and transport disadvantage. The first paper undertook a comprehensive review of the social scientific and transport planning literature to mark the level of development in the field and identify conceptual and methodological issues and constraints in this field of inquiry. The present article supports the advancement of socially and geographically sensitive transport research by opportunities for the development of more sophisticated spatial analytical methodologies. The approach we present is able to account for factors not previously addressed in either social or transport planning research, in particular the temporal dimensions of transport service accessibility. The article articulates the methodology through an empirical case study of socio-spatial transport disadvantage within the Gold Coast City. The article demonstrates that there are important theoretical and practical lessons to be gained for researchers and policy makers in addressing the social dimensions of transport and infrastructure provision. Further, the article argues that an attentiveness to new ways of combining and representing social and transport data-sets can promote policy relevant empirical social inquiry. The article also contributes in a productive way to the empirical knowledge of Australia's sixth-largest metropolitan area, which is often overlooked by urban scholars. 相似文献
4.
H.A.V. Evans 《Food microbiology》1985,2(1):19-22
The growth in beer of 15 brewery strains of Lactobacillus was detected using the automatic conductance measuring technique afforded by the Malthus 8 Growth Analyser. 0·15% ammonium chloride was added to the beer as an electrolyte and sodium acetate was used to raise the pH from ca 4·0 to 4·2 or above. No measurable responses were obtained using unmodified beer. The value of the method for development in routine brewery microbiological control is briefly discussed. 相似文献
5.
Moore J.R. Collings N. Crossland W.A. Davey A.B. Evans M. Jeziorska A.M. Komarcevic M. Parker R.J. Wilkinson T.D. Xu H. 《Photonics Technology Letters, IEEE》2008,20(1):60-62
Polarization-insensitivity is achieved in a reflective spatial light modulator by laying a quarter-wave plate (QWP) at the incident wavelength directly over the mirror pixels of a silicon backplane, and forming a nematic Freedrickcz cell over the QWP to modulate the reflected phase. To achieve the highest drive voltage from the available silicon process, a switched voltage common front electrode design is described, with variable amplitude square wave drive to the pixels to maintain constant root-mean-square drive and minimize phase fluctuations during the dc balance refresh cycle. The silicon has been fabricated and liquid-crystal-on-silicon cells both with and without the QWP assembled; applications include optically transparent switches for optical networks, beam steering for add-drop multiplexers for wavelength-division-multiplexing telecommunications, television multicast, and holographic projection. 相似文献
6.
BACKGROUND: Hydrogen exchange labelling has been a key method in characterizing the structure of transient folding intermediates. In studies of several proteins, however, there has been clear spectroscopic evidence for partial folding of some kind at very early times, before any protection from exchange was measurable. These results, presumably a consequence of limited stability of specific backbone interactions, have made it difficult to assess the extent of native-like folding in the very early intermediates. We have used a variant of the labelling method to investigate marginally stable structures formed within the first few milliseconds of refolding of two such proteins, hen lysozyme and ubiquitin. RESULTS: In lysozyme, population of a subset of native-like secondary structures on this timescale is revealed, thus reconciling the exchange behaviour with circular dichroism measurements and confirming the significance of the rapidly formed embryonic structure as a foundation for the subsequent folding pathway. In the case of ubiquitin, by contrast, no significantly protective structure was detectable, suggesting that here secondary structural elements can be populated only marginally ahead of the major cooperative folding event; this was also supported by stopped-flow circular dichroism measurements. CONCLUSIONS: The hydrogen exchange approach can be extended to probe the formation of native-like structure formed in very early folding intermediates, even when the stability of specific interactions is marginal. In the case of lysozyme, this has provided a new window on an early stage of organization of the alpha-helical domain. 相似文献
7.
8.
9.
10.
Mann-Fu Rau David Rieck James W. Evans 《Metallurgical and Materials Transactions B》1987,18(1):257-278
An “environmental cell” located in a high voltage transmission electron microscope has been used to study the reduction of
single crystal iron oxides by hydrogen and hydrogen-argon mixtures. The cell enables a direct observation of the solid during
reaction, thus permitting the nucleation and growth of solid reaction products to be observed. Hematite was reduced at temperatures
in the range 387 to 610°C with gas pressures up to 5.3 kP. Reduction with pure hydrogen was considerably faster than when
argon was present. Lath magnetite which rapidly transforms to porous magnetite and thence (more slowly) to porous iron was
observed. The reduction of magnetite and of wustite single crystals was observed in the temperature range 300 to 514°C using
both hydrogen and hydrogen-argon mixtures at gas pressures up to 6.6 kP. Incubation periods were found for magnetite reduction;
during these periods faceted pits formed in the oxide. Iron formed in the early stages was epitaxial with the host magnetite;
at later stages the epitaxy was lost and fissures frequently formed in the metal. The morphology of the iron differed between
the gas mixtures. Disproportionation accompanied the reduction of wustite, producing intermediate polycrystalline magnetite
despite reducing conditions. The disproportionation appeared to be promoted by the reduction reaction. For both oxides, reduction
in the hydrogen-argon mixture was slower than in pure hydrogen. 相似文献