全文获取类型
收费全文 | 916篇 |
免费 | 16篇 |
专业分类
电工技术 | 26篇 |
化学工业 | 235篇 |
金属工艺 | 10篇 |
机械仪表 | 16篇 |
建筑科学 | 15篇 |
能源动力 | 7篇 |
轻工业 | 54篇 |
水利工程 | 4篇 |
石油天然气 | 1篇 |
无线电 | 83篇 |
一般工业技术 | 102篇 |
冶金工业 | 269篇 |
原子能技术 | 9篇 |
自动化技术 | 101篇 |
出版年
2020年 | 8篇 |
2017年 | 12篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 23篇 |
2012年 | 15篇 |
2011年 | 22篇 |
2010年 | 20篇 |
2009年 | 13篇 |
2008年 | 12篇 |
2007年 | 17篇 |
2006年 | 9篇 |
2005年 | 10篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 20篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 28篇 |
1998年 | 90篇 |
1997年 | 55篇 |
1996年 | 52篇 |
1995年 | 36篇 |
1994年 | 16篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1985年 | 13篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1970年 | 11篇 |
1969年 | 9篇 |
1968年 | 12篇 |
1967年 | 7篇 |
1966年 | 12篇 |
1965年 | 6篇 |
1962年 | 8篇 |
1960年 | 10篇 |
排序方式: 共有932条查询结果,搜索用时 0 毫秒
61.
62.
Effects of dietary trielaidin upon the alkenyl chain profile of plasmalogens were studied using heart mitochondria of rats
fed a semi-purified diet containing 10% of fat supplement in which elaidic acid accounted for 69% of total fatty acids. Alkyl
substituted dioxane (ASD) derivatives of the alkenyl groups of plasmalogens were prepared and analyzed by silver nitrate TLC
and by GLC on different phases (BDS and OV-275). After two months of feeding the experimental diet, 40% of the ASD contained
atrans-octadecenyl chain, suggesting that dietary elaidic acid was reduced in vivo to the corresponding alcohol and incorporated
into plasmalogens. There was a simultaneous decrease in the percentage of ASD containing saturated chains, but the percentage
of ASD substituted withcis-octadecenyl chains was not significantly affected. These observations suggested that elaidic acid may compete with saturated
fatty acids, but not withcis-octadecenoic acids during the plasmalogen biosynthesis. Feeding trielaidin did not seem to have any significant influence
on the relative proportions of plasmalogens, which accounted for 11–12%, on a phosphorus basis, of total heart mitochondria
phospholipids. 相似文献
63.
Robert L. Wolff Olivier Lavialle Frédérique Pédrono Elodie Pasquier Laurent G. Deluc Anne M. Marpeau Kurt Aitzetmüller 《Lipids》2001,36(5):439-451
Following our previous review on Pinus spp. seed fatty acid (FA) compositions, we recapitulate here the seed FA compositions of Larix (larch), Picea (spruce), and Pseudotsuga (Douglas fir) spp. Numerous seed FA compositions not described earlier are included. Approximately 40% of all Picea taxa and one-third of Larix taxa have been analyzed so far for their seed FA compositions. Qualitatively, the seed FA compositions in the three genera studied here are the same as in Pinus spp., including in particular the same Δ5-olefinic acids. However, they display a considerably lower variability in Larix and Picea spp. than in Pinus spp. An assessment of geographical variations in the seed FA composition of P. abies was made, and intraspecific dissimilarities in this species were found to be of considerably smaller amplitude than interspecific dissimilarities among other Picea species. This observation supports the use of seed FA compositions as chemotaxonomic markers, as they practically do not depend on edaphic or climatic conditions. This also shows that Picea spp. are coherently united as a group by their seed FA compositions. This also holds for Larix spp. Despite a close resemblance between Picea and Larix spp. seed FA compositions, principal component analysis indicates that the minor differences in seed FA compositions between the two genera are sufficient to allow a clear-cut individualization of the two genera. In both cases, the main FA is linoleic acid (slightly less than one-half of total FA), followed by pinolenic (5,9,12-18:3) and oleic acids. A maximum of 34% of total Δ5-olefinic acids is reached in L. sibirica seeds, which appears to be the highest value found in Pinaceae seed FA. This apparent limit is discussed in terms of regio- and stereospecific distribution of Δ5-olefinic acids in seed triacylglycerols. Regarding the single species of Pseudotsuga analyzed so far (P. menziesii), its seed FA composition is quite distinct from that of the other two genera, and in particular, it contains 1.2% of 14-methylhexadecanoic (anteiso-17:0) acid. In the three genera studied here, as well as in most Pinus spp., the C18Δ5-olefinic acids (5,9-18:2 and 5,9,12-18:3 acids) are present in considerably higher amounts than the C20Δ5-olefinic acids (5,11-20:2 and 5,11,14-20:3 acids). 相似文献
64.
Dibutyroyl derivatives of monoacylglycerols (DBMAG) from conifer seed oil triacylglycerols (TAG) were prepared by partial deacylation of TAG with ethylmagnesium bromide followed by diesterification with n-butyryl chloride. The resulting mixtures were analyzed by gas-liquid chromatography (GCL) with 65% phenylmethyl silicon open tubular fused-silica capillary column operated under optimal conditions and separated according to both their fatty acid structures and their regiospecific distribution. Seed oils of 18 species from 5 conifer families (Pinaceae, Taxaceae, Cupressaceae, Cephalotaxaceae, and Podocarpaceae) were analyzed. The chromatograms showed a satisfactory resolution of DBMAG containing palmitic (16∶0) stearic (18∶0), taxoleic (cis-5, cis-9 18∶2), oleic (cis-9 18∶1), cis-vaccenic (cis-11 18∶1), pinolenic (cis-5, cis-9, cis-12 18∶3), linoleic (cis-9, cis-12 18∶2), α-linolenic (cis-9 cis-12, cis-15 18∶3), and an almost baseline resolution of DBMAG containing gondoic (cis-11 20∶1), cis-5, cis-11 20∶2, sciadonic (cis-5, cis-11, cis-14 20∶3), dihomolinoleic (cis-11 cis-14 20∶2), juniperonic (cis-5, cis-11, cis-14, cis-17 20∶4), and dihomo-α-linolenic (cis-11, cis-14, cis-17 20∶3) acids. We have observed that results for Pinus pinaster and P. koraiensis seed oils obtained with this new simple method compared favorably with literature data established with other usual regiospecific analytical techniques. Δ5-Olefinic acids are esterified mainly at the external positions of the glycerol backbone in all cases, in agreement with data obtained by other methodologies allowing validation of the GLC regiospecific method. To date, 45 gymnosperm species (mostly Coniferophytes) from 21 genera belonging to 9 families have been analyzed, all of them showing a definite enrichment of Δ5-olefinic acids in the external positions of TAG. These fatty acids (FA), with one exception only, represent between-2 and 8% of FA esterified to the internal positions. For some species, i.e., P. koraiensis and P. pinaster, this asymmetrical distribution was established by at least three analytical procedures and confirmed by stereospecific analysis of their seed TAG. 相似文献
65.
The authors describe the Kontek HVDC cable link connecting Denmark and Germany which has been in commercial operation since 1996, and, with a total length of 172 km and a transmission capacity of 600 MW at 400 kV, the cable link is still unique worldwide. In addition, the 120 km of land cable is the world's longest continuous length of underground cable for HVDC application. The objective of this grand project was to enable the export of electric power from efficient Danish power generating stations, combined with an eventual transmission link between Sweden and the eastern part of Germany 相似文献
66.
The proposed method is based on spline functions, takes into account thermal and noise effects, allows a scaling of different FET device geometries, and is available in commercial CAD software like Agilents Series IV or ADS 相似文献
67.
68.
69.
Optical InP-GaInAsP directional coupler switches with a total length of 2 mm have been fabricated and operated by carrier injection. Switching is achieved at a very low injection current of 4 mA. For both switching states a crosstalk suppression exceeding 20 dB is obtained. In addition, the insertion loss estimated from the loss contributions of waveguides, bends and free carriers is as low as 1.3 dB.<> 相似文献
70.
- Alcoholysis of triglycerides by methylglucoside gave an impure reaction mixture containing from 60–70% of glucoside-monoesters.
- The mono-, di-, and trioleoyl methylglucosides were prepared by alcoholysis of methyloleate with α-methylglucoside.
- Hydrolysis of the glucoside esters of fatty acids to dextrose esters could not be achieved. The ester linkage hydrolyzed in preference to the acetal linkage.