全文获取类型
收费全文 | 1538篇 |
免费 | 34篇 |
专业分类
电工技术 | 15篇 |
化学工业 | 285篇 |
金属工艺 | 25篇 |
机械仪表 | 30篇 |
建筑科学 | 79篇 |
矿业工程 | 17篇 |
能源动力 | 36篇 |
轻工业 | 133篇 |
水利工程 | 7篇 |
石油天然气 | 9篇 |
武器工业 | 1篇 |
无线电 | 109篇 |
一般工业技术 | 187篇 |
冶金工业 | 388篇 |
原子能技术 | 11篇 |
自动化技术 | 240篇 |
出版年
2022年 | 9篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 19篇 |
2015年 | 26篇 |
2014年 | 29篇 |
2013年 | 90篇 |
2012年 | 46篇 |
2011年 | 71篇 |
2010年 | 50篇 |
2009年 | 73篇 |
2008年 | 56篇 |
2007年 | 63篇 |
2006年 | 72篇 |
2005年 | 66篇 |
2004年 | 64篇 |
2003年 | 48篇 |
2002年 | 54篇 |
2001年 | 45篇 |
2000年 | 33篇 |
1999年 | 33篇 |
1998年 | 43篇 |
1997年 | 43篇 |
1996年 | 42篇 |
1995年 | 25篇 |
1994年 | 30篇 |
1993年 | 28篇 |
1992年 | 31篇 |
1991年 | 12篇 |
1990年 | 29篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 15篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 21篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有1572条查询结果,搜索用时 397 毫秒
901.
902.
Hanwen Wu Terry Haig Jim Pratley Deirdre Lemerle Min An 《Journal of chemical ecology》2000,26(9):2141-2154
Wheat allelopathy has potential for weed suppression. Allelochemicals were identified in wheat seedlings, and they were exuded from seedlings into agar growth medium. p-Hydroxybenzoic, trans-p-coumaric, cis-p-coumaric, syringic, vanillic, trans-ferulic, and cis-ferulic acids and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) were identified in both the shoots and roots of 17-day-old wheat seedlings and their associated agar growth medium. Wheat accessions with previously identified allelopathic activity tended to contain higher levels of allelochemicals than poorly allelopathic ones. The allelopathic compounds present in the shoots generally also were identified in the roots and in the agar medium. Allelochemicals were distributed differentially in wheat, with roots normally containing higher levels of allelochemicals than the shoots. When the eight allelochemicals were grouped into benzoic acid and cinnamic acid derivatives, DIMBOA, total coumaric, and total ferulic acids, the amount of each group of allelochemicals was correlated between the roots and the shoots. Most of the allelochemicals identified in the shoots and roots could be exuded by the living roots of wheat seedling into the agar growth medium. However, the amounts of allelochemicals in the agar growth medium were not proportional to those in the roots. Results suggest that wheat plants may retain allelochemicals once synthesized. The presence of allelochemicals in the agar growth medium demonstrated that wheat seedlings were able to synthesize and to exude phytotoxic compounds through their root system that could inhibit the root growth of annual ryegrass. 相似文献
903.
Oleg S. Alexeev Sundaram Krishnamoorthy Michael S. Ziebarth George Yaluris Terry G. Roberie Michael D. Amiridis 《Catalysis Today》2007,127(1-4):176-188
Pdn+/Cen+/Na+/γ-Al2O3-type materials used as FCC additives for CO/NOx control were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy and in situ FTIR. The EXAFS data indicate that in freshly prepared samples palladium is present in the form of highly dispersed PdO species. Reduction with H2 at 500 °C leads to the formation of small Pd clusters incorporating on average approximately six to eight metal atoms at a Pd−Pd bond distance of 2.76 Å. All components of these materials can interact with NO and promote the formation of nitrate/nitrite species, essentially “trapping” NOx species on the catalyst surface. However, the Na+ species dominate the surface chemistry and readily form sodium nitrates with a characteristic IR band at 1370–1385 cm−1. Finally, hydroxyls from the support are also actively participating in the formation of HNOx type compounds with characteristic stretching vibrations in the 3500–3572 cm−1 region. 相似文献
904.
Melissa S. Mund Terry A. Isbell 《Journal of the American Oil Chemists' Society》1999,76(10):1189-1200
Chloroalkoxy substituted C20 and C22 fatty acids can be synthesized from the unsaturated fatty acids in meadow-foam oil by reaction of the fatty acids with primary
or secondary alcohols and an aqueous sodium hypochlorite solution (commercial bleach). The reactions are conducted at room
temperature for 3 h. Chlorohydroxy fatty acid derivatives are formed as by-products owing to the presence of water in the
reaction mixture. Chlorinated δ-lactones are also produced by direct reaction of sodium hypochlorite with the Δ5 unsaturated
fatty acids present in meadowfoam or by ring closure of the 6-chloro-5-hydroxy fatty acids. The product yield of chloroalkoxy
fatty acids is dependent on the nature and volume of the alcohol used in the reaction, as well as the concentration and pH
of the sodium hypochlorite solution. Primary alcohols such as methanol and butanol produce maximal yields (50–60%) of chloroalkoxy
fatty acids whereas the secondary alcohol 2-propanol gives a 30% yield. Chloroalkoxy fatty acid yields can be increased to
75–80% by elimination of water from the reaction mixture through a procedure that partitions sodium hypochlorite from water
into hexane/ethyl acetate mixtures. All of the reaction products were fully characterized using nuclear magnetic resonance
and gas chromatography-mass spectrometry. 相似文献
905.
Kenneth D. Carlson Bliss S. Phillips Terry A. Isbell Terry C. Nelsen 《Journal of the American Oil Chemists' Society》1998,75(10):1429-1436
As part of a program to improve meadowfoam seed processing, the authors examined the effects of seed moisture, seed temperature,
and flaking roll opening on oil extraction efficiency in meadowfoam flakes. Flakes were prepared using a Wolf Mill with dual
horizontal, unheated 12-in. diameter rolls. Roll openings of 0.005, 0.013, and 0.020 in. (0.127, 0.330, and 0.508 mm, respectively)
gave average flake thicknesses of 0.013, 0.021, and 0.031 in., respectively (0.330, 0.533, and 0.787 mm). Seed moistures of
9, 12, and 15% and seed temperatures of 65, 190, and 210°F (18, 88, and 99°C) chosen for flaking were known to provide a range
of conditions suitable for enzyme inactivation during seed cooking prior to flaking. Experimental flakes were examined for
extractable oil content (petroleum ether extraction); this was compared to total oil content (31.5%) determined on finely
ground flakes. Roll opening was the dominant variable determining flake thickness, the primary parameter affecting oil extraction
efficiency. Thus, the thinnest flakes at 0.013 in. were only slightly less extractable (29.8%) than finely ground flakes (31.5%),
but intermediate (0.021 in.) and thick (0.031 in.) flakes were significantly less extractable (28.0 and 26.0%, respectively).
There was a slight but significant (P<0.01) trend toward thicker flakes with increasing seed moisture (15>12>9%) during flaking. A similar trend to thicker flakes
with increasing temperature was significant (P<0.01) only for the thickest flakes produced at the largest roll opening (0.020 in.). Lower seed moisture and higher seed
temperature significantly impacted extractable oil content of the thickest flakes, but negligibly affected extractability
of the thinnest flakes. The authors conclude that meadowfoam flakes must be as thin as possible (e.g., <0.015 in.) for efficient
oil extraction. Further, seed cooking temperatures >190°F at moistures >10% and <15% that are adequate for efficient enzyme
inactivation in the whole seed are also suitable for seed flaking. 相似文献
906.
This paper considers the gradual re‐emergence of urban food production initiatives in the local authorities of England and Wales. A typology of local authority actions is constructed which links urban food initiatives to broader Local Agenda 21 processes and community participation initiatives. Several key dimensions are identified which need to be assembled in local authorities if urban food production is to become more widespread. These include: the development of the enabling role of local authorities, the commitment of member involvement, seeing urban food production as a central element in progressing sustainable and community development, developing a more proactive and integrated planning policy which develops capacity and reverses the steady decline in allotment provision. Making the links between food production, community involvement and effective land‐use planning strategies is a key element in progressing food production and reducing the conception of urban food production as simply a contradiction in terms. This will involve the engagement of local authorities, and particularly planning in the broader aspects of the politics and local economy of food currently emerging amongst urban consumers. 相似文献
907.
Taylor H. Gerry; Yeates Keith Owen; Wade Shari L.; Drotar Dennis; Klein Susan K.; Stancin Terry 《Canadian Metallurgical Quarterly》1999,13(1):76
This study examined recovery over the first year following traumatic brain injury (TBI) in children 6–12 years of age. Forty-two children with severe TBI and 52 with moderate TBI were compared to 58 children with orthopedic injuries. The children and their families were evaluated at a baseline assessment and at 6- and 12-month follow-ups. Findings documented cognitive, achievement, and behavioral sequelae of TBI, with only limited evidence for recovery over the first year postinjury. Outcomes were predicted by preinjury factors, TBI severity, and measures of the postinjury family environment. Some of the sequelae of severe TBI were more marked in the context of higher compared with lower levels of family burden or dysfunction. The findings confirm the need to consider environmental contributions to outcomes of TBI in children. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
908.
David J. Sessa Terry C. Nelsen Janet M. Snyder 《Journal of the American Oil Chemists' Society》1998,75(8):911-916
The primary objective was to determine whether salts will stabilize soy storage proteins against the denaturing effects of
alcohols or the heat and pressure used in supercritical CO2 during the defatting process. Nitrogen solubility index (NSI) and differential scanning calorimetry (DSC) were used to monitor
the denaturation of proteins. A variety of salt solutions used to hydrate full-fat soy grits increased the thermal stability
of both 7S and 11S storage proteins. DSC was used to monitor their denaturation temperature. Neutral salt hydrations followed
the lyotropic series for protein stabilization. Of the salts evaluated, the test results indicate that the reducing salt,
sodium sulfite, and the neutral salt, sodium sulfate, when used to steep beans, yielded significantly higher NSI than did
the water-steeped controls or other salt treatments after partial defatting with absolute isopropanol or ethanol and supercritical
CO2. However, these same salt treatments did not as effectively stabilize the proteins against the denaturing effects of ethanol
more aqueous than 84% when these alcohols were used as the defatting medium. 相似文献
909.
The dispersion of nanotubes in polymer matrices has been investigated as a means of deriving new and advanced engineering materials. These composite materials have been formed into fibers and thin films and their mechanical and electrical properties determined. The nanotube concentration at which conductivity was initiated (the percolation threshold) varied with host polymer. In poly(propylene), this was as low as 0.05 vol.‐%, while higher concentrations were required for polystyrene and particularly for ABS. There was a small increase in elastic modulus and decrease in tensile strength at low nanotube loading, but as the concentration was increased there was a progressive increase in both strength and stiffness. 相似文献
910.