全文获取类型
收费全文 | 8680篇 |
免费 | 112篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 98篇 |
综合类 | 2篇 |
化学工业 | 1018篇 |
金属工艺 | 103篇 |
机械仪表 | 300篇 |
建筑科学 | 229篇 |
矿业工程 | 28篇 |
能源动力 | 130篇 |
轻工业 | 873篇 |
水利工程 | 107篇 |
石油天然气 | 15篇 |
无线电 | 864篇 |
一般工业技术 | 1022篇 |
冶金工业 | 3154篇 |
原子能技术 | 108篇 |
自动化技术 | 750篇 |
出版年
2021年 | 68篇 |
2020年 | 53篇 |
2019年 | 62篇 |
2018年 | 64篇 |
2017年 | 85篇 |
2016年 | 67篇 |
2015年 | 48篇 |
2014年 | 104篇 |
2013年 | 321篇 |
2012年 | 160篇 |
2011年 | 241篇 |
2010年 | 213篇 |
2009年 | 232篇 |
2008年 | 261篇 |
2007年 | 240篇 |
2006年 | 246篇 |
2005年 | 218篇 |
2004年 | 181篇 |
2003年 | 199篇 |
2002年 | 200篇 |
2001年 | 162篇 |
2000年 | 160篇 |
1999年 | 198篇 |
1998年 | 762篇 |
1997年 | 482篇 |
1996年 | 420篇 |
1995年 | 298篇 |
1994年 | 252篇 |
1993年 | 254篇 |
1992年 | 113篇 |
1991年 | 129篇 |
1990年 | 138篇 |
1989年 | 134篇 |
1988年 | 136篇 |
1987年 | 137篇 |
1986年 | 108篇 |
1985年 | 127篇 |
1984年 | 94篇 |
1983年 | 100篇 |
1982年 | 70篇 |
1981年 | 88篇 |
1980年 | 70篇 |
1979年 | 79篇 |
1978年 | 70篇 |
1977年 | 110篇 |
1976年 | 198篇 |
1975年 | 72篇 |
1974年 | 71篇 |
1973年 | 63篇 |
1972年 | 54篇 |
排序方式: 共有8801条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
105.
Laura M. Russell Lloyd F. Johnson D. P. H. Hasselman Robert Ruh 《Journal of the American Ceramic Society》1987,70(10):226-C
The thermal conductivity and diffusivity of silicon carbide whisker reinforced mullite was shown to increase with whisker content. This effect was much greater for vapor-liquid-solid (VLS) whiskers than for rice-hull (RH) whiskers. This suggests that the thermal conductivity for the VLS whiskers was significantly higher than for the RH whiskers. Due to preferred orientation of the whiskers, thermal conductivity and diffusivity of the composite samples exhibited significant anisotropy. 相似文献
106.
A. R. Johnson A. C. Fogerty Judith A. Pearson F. S. Shenstone Audrey M. Bersten 《Lipids》1969,4(4):265-269
Hen liver preparations which desaturate stearic acid at the 9,10 position to form oleic acid have been found to desaturate
other saturated fatty acids of carbon chain length from 12 to 20 and 22. The 9,10-monoenoic fatty acid of the same chain length
as the substrate fatty acid is the major product formed. Minor amounts of the 10,11- and 11, 12-monoenoic acids are also formed.
Maximum desaturation occurred with the C14 fatty acid substrate and with the fatty acids C17 and C18, suggesting the presence of at least two desaturating systems. The cyclopropene fatty acids, sterculic and malvalic acids,
inhibited the desaturation of all thefatty acids at the 9,10 position but desaturation at the 10,11 and 11, 12 positions was
affected only slightly. The effect is not due to inhibition of the primary activating enzyme, the long chain acyl CoA synthetase.
Sterculic acid is a more effective inhibitor than either malvalic acid or sterculyl alcohol, probably because these cyclopropene
compounds do not block the desaturating site of the enzyme as completely as sterculic acid. 相似文献
107.
Raman spectra of Graphon carbon black 总被引:1,自引:0,他引:1
The Raman spectrum of Graphon carbon black has been recorded using rotating cell techniques. Angular dependence of scattering at 1360, 1580 and 2700 cm?1 are reported and these data suggest that the 1360 cm?1 line is associated with non-planar microstructure distortions. The excitation frequency dependence of the intensity ratio of the bands at 1360 (D) and 1580 cm?1 (G) is interpreted in terms of resonance (vibronic) interaction. This dependence is primarily the result of an increase in the intensity of the 1360 cm ?1 line. The disorder-associated line (D) exhibits a significant excitation-dependent shift from 1378 cmi?1 (457.9 nm Ar+) to 1330 cm?1 (647.1 nm Kr+). The “graphite” (G) line position is less sensitive to changes in excitation frequency. The spectral features are discussed in terms of factor group, C6v4, and layer site symmetry, C3v. Also the possible role of localized alkene-like structure in zones of structural distortion is considered. 相似文献
108.
H. J. Dutton S. B. Johnson F. J. Pusch M. S. F. Lie Ken Jie F. D. Gunstone R. T. Holman 《Lipids》1988,23(5):481-489
An approach to the analysis of 55 possible nonconjugated positional isomers of octadecadienoic acid is described and tested
with mixtures of individual synthetic methyl esters. In the first example, by ozonolysis a sevencomponent mixture consisting
ofcis,cis 5,12-, 6,10-, 6,11-, 6,12-, 7,12-, 8,12-, and 9,12-octadecadienoates was converted to aldehydes, aldehyde-esters and dialdehydes.
These fragments were separated on a 50 m×0.2 mm free fatty acid phase (FFAP) vitreous silica capillary column. Equations for
an arbitrarily restricted 12×15 matrix of linear simultaneous equations and a computer solution of the matrix provided the
composition of the initial methyl octadecadienoate mixture. The power and significance of this method became apparent with
the observation that only two of the seven isomers in the known mixture were resolved as single peaks by state-of-the-art
capillary gas chromatography, but all seven were identified and estimated with acceptable error by the ozonolysis-capillary
gas chromatography-computer procedure. In a generalized approach to the analysis of the 55 possible nonconjugated isomers,
a computer program selects the appropriate matrix of linear simultaneous equations based on the aldehyde data supplied by
the analyst. Twenty of 21 combinations of seven isomeric esters taken five at a time have been analyzed to assess the efficiency
of the method. To illustrate applicability at this stage of development, the method has been used to analyze the diene products
of the hydrazine reduction of γ-linolenic acid and the diene products from the biological desaturation of isomeric monoenes.
The possibility of distinguishing geometric and positional isomers of 18∶2 has been opened by the observed separation ofcis-andtrans-unsaturated aldehydes and aldehyde-esters.
Presented in part at the 16th World Congress of the International Society for Fat Research, October 4–7, 1983, in Budapest,
Hungary, and at the American Oil Chemists' Society Meeting, May 15, 1986, in Honolulu, Hawaii. 相似文献
109.
The volatile products from the thermal degradation of poly(vinyl chloride) (PVC) resins and compounds are shown to contain trace amounts of vinyl chloride. Data presented show the effect of temperature and resin type on the amount of vinyl chloride formed. At the maximum temperatures involved in PVC processing which may reach 210°C, vinyl chloride monomer (VCM) evolution amounts to less than 1 ppm (resin basis). A technique employing a thermogravimetric balance and charcoal adsorption of volatiles is described for studying thermal degradation of PVC. The volatiles are analyzed for vinyl chloride by gas chromatography. Peak identity was confirmed by mass spectrometry. 相似文献
110.
Flaking and extrusion as mechanical treatments for enzyme-assisted aqueous extraction of oil from soybeans 总被引:6,自引:7,他引:6
B. P. Lamsal P. A. Murphy L. A. Johnson 《Journal of the American Oil Chemists' Society》2006,83(11):973-979
Flaking and extruding dehulled soybeans were evaluated as a means of enhancing oil extraction efficiency during enzyme-assisted
aqueous processing of soybeans. Cellulase, protease, and their combination were evaluated for effectiveness in achieving high
oil extraction recovery from extruded flakes. Aqueous extraction of extruded full-fat soy flakes gave 68% recovery of the
total available oil without using enzymes. A 0.5% wt/wt protease treatment after flaking and extruding dehulled soybeans increased
oil extraction recovery to 88% of the total available oil. Flaking and extruding enhanced protease hydrolysis of proteins
freeing more oil. Treating extruded flakes with cellulase, however, did not enhance oil extraction either alone or in combination
with protease. Discrepancies in oil extraction recoveries were encountered when merely considering crude free fat because
some oil became bound to denatured protein during extrusion and/or sample drying. Bound fat was unavailable for determination
by using the hexane extraction method, but was accounted for by using the acid hydrolysis method for total oil determination.
Oil extraction recovery from extruded soybean flakes was affected by oil determination methods, which was not the case for
unextruded full-fat soy flour. 相似文献