全文获取类型
收费全文 | 4081篇 |
免费 | 438篇 |
国内免费 | 68篇 |
专业分类
电工技术 | 19篇 |
综合类 | 309篇 |
化学工业 | 1283篇 |
金属工艺 | 45篇 |
机械仪表 | 200篇 |
建筑科学 | 896篇 |
矿业工程 | 26篇 |
能源动力 | 58篇 |
轻工业 | 1109篇 |
水利工程 | 71篇 |
石油天然气 | 342篇 |
无线电 | 6篇 |
一般工业技术 | 153篇 |
冶金工业 | 48篇 |
原子能技术 | 8篇 |
自动化技术 | 14篇 |
出版年
2024年 | 20篇 |
2023年 | 82篇 |
2022年 | 144篇 |
2021年 | 163篇 |
2020年 | 203篇 |
2019年 | 139篇 |
2018年 | 154篇 |
2017年 | 172篇 |
2016年 | 188篇 |
2015年 | 179篇 |
2014年 | 272篇 |
2013年 | 283篇 |
2012年 | 276篇 |
2011年 | 281篇 |
2010年 | 214篇 |
2009年 | 244篇 |
2008年 | 169篇 |
2007年 | 193篇 |
2006年 | 200篇 |
2005年 | 130篇 |
2004年 | 117篇 |
2003年 | 111篇 |
2002年 | 85篇 |
2001年 | 64篇 |
2000年 | 63篇 |
1999年 | 42篇 |
1998年 | 47篇 |
1997年 | 49篇 |
1996年 | 41篇 |
1995年 | 32篇 |
1994年 | 41篇 |
1993年 | 39篇 |
1992年 | 37篇 |
1991年 | 35篇 |
1990年 | 10篇 |
1989年 | 16篇 |
1988年 | 1篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有4587条查询结果,搜索用时 15 毫秒
21.
综述了在成品油市场竞争日趋激烈的形势下,做好成品油销售工作的经验和体会,介绍了领导带上,上下剂心协力,分析用户的需求和用油规律,抓住商机,以适合市场规律的营销策略和热情周到的服务,现固已有市场,并开拓了新市场的做法。 相似文献
22.
通过小偏心受压性能试验对比研究3根的天然骨料混凝土柱和3根同强度全再生砖混骨料混凝土柱,强度分别为C25、C30和C35. 对6根柱进行加载试验,分析再生砖混骨料混凝土柱相比于同强度天然骨料混凝土柱在受力过程、破坏特征、变形能力与承载力等方面的差异. 试验发现,再生砖混骨料混凝土柱在小偏心加载至破坏的过程中,具有与天然骨料混凝土柱相似的3个受力阶段,且符合平截面假定. 与同强度的天然骨料混凝土柱相比,变形较大,但再生砖混骨料混凝土柱的极限承载力略高,原因可能在于两者轴心抗压强度的差异. 相似文献
23.
By the virtue of their olfactory, physicochemical, and biological characteristics, essential oils (EOs) have drawn wide attention as additives in daily chemicals like perfume or personal care products. Nevertheless, they are physicochemically unstable and susceptible to degradation or loss. Microencapsulation offers a feasible strategy to stabilize and prolong release of EO. This review summarizes the recognized benefits and functional properties of various preparation and characterization methods, wherein innovative fabrication strategies and their formation mechanisms are especially emphasized. Progress in combining detecting/measuring technologies with kinetic modelling are discussed, to give an integral approach of controlling the dynamic release of encapsulated EOs. Moreover, new development trends of EOs capsules are also highlighted. 相似文献
24.
Raffaele Sacchi Isabel Medina Santiago P. Aubourg Francesco Addeo Livio Paolillo 《Journal of the American Oil Chemists' Society》1993,70(3):225-228
Based on proton nuclear magnetic resonance (1H-NMR) spectroscopy, a rapid and structure-specific method for the determination of ω-3 polyunsaturated fatty acids (PUFAs)
in fish lipids is presented. The different chemical shift observed for the methyl resonance of ω-3 PUFAs (δ=0.95 ppm) with
respect to the methyl resonance of all other fatty acids (δ=0.86 ppm) has provided the possibility of proposing a new and
rapid method for the determination of ω-3 PUFA content. Twenty-four fish lipid samples (raw, cooked and canned albacore tuna)
produced results that showed good agreement between1H-NMR analysis and gas chromatographic determination. Raw and cooked samples showed significantly higher levels of ω-3 PUFA
than canned tuna. 相似文献
25.
Paresh Chandra Dutta 《Journal of the American Oil Chemists' Society》1997,74(6):659-666
Hydrogenated rapeseed oil/palm oil blend, sunflower oil and high-oleic sunflower oil, and French fries fried in these oils
were assessed for contents of sterol oxidation products. Different oxidation products of phytosterols (7α- and 7β-hydroxy-sito-and
campesterol, 7-ketosito- and 7-ketocampesterol, 5α,6α-epoxy-sito- and campesterol, 5β,6β-epoxy-sito-and campesterol, dihydroxysitosterol
and dihydroxycampesterol) were identified and quantiated by gas chromatography (GC) and GC-mass spectroscopy. Rapeseed oil/palm
oil blend contained 41 ppm total sterol oxides before frying operations. After two days of frying, this level was increased
to 60 ppm. Sunflower oil and high-oleic sunflower oil had 40 and 46 ppm sterol oxides, respectively, before frying operations.
After two days of frying operations, these levels increased to 57 and 56 ppm, respectively. In addition to campesterol and
sitosterol oxidation products, small amounts of 7α- and 7β-hydroxystigmasterol were detected in the oil samples. Total sterol
oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower
oil were 32, 37, and 54 ppm, respectively. The levels of total oxidized sterols, calculated per g sample, ranged from 2.4
to 4.0 ppm. In addition to the content of phytosterol oxides, full scan mass spectra of several oxidation products of stigmasterol
are reported for the first time.
Part of these results were presented at the 86th Annual Meeting of the AOCS, May 7–11, 1995, San Antonio, TX. 相似文献
26.
Dorota Johansson Björn Bergenståhl 《Journal of the American Oil Chemists' Society》1992,69(8):728-733
The influence of water on the interactions between fat and sugar crystals dispersed in triglyceride (vegetable) oils was qualitatively
estimated from sedimentation and rheological experiments. The experiments were performed both with and without food emulsifiers
(monoglycerides and lecithins) present in the oil. The effects of minor natural oil components (nontriglycerides) on the interactions
and on emulsifier adsorption to the crystals were examined by comparing a commercial refined oil and a chromatographically
purified oil. The results show that water generally increases the adhesion between fat and sugar crystals in oils and also
increases the surface activity of the oil-soluble food emulsifiers. Minor oil components give a small increase in the adhesion
between fat and sugar crystals in oils, but do not influence the adsorption of food emulsifiers in any systematic way. 相似文献
27.
Sajid Husain M. Kifayatullah G. S. R. Sastry N. Prasada Raju 《Journal of the American Oil Chemists' Society》1993,70(12):1251-1254
Application of13C nuclear magnetic resonance (NMR) spectroscopy for detection of castor oil (CO) in various edible oils, such as coconut oil,
palm oil, groundnut oil and mustard oil, is described. Characteristic signals observed at δ 132.4, δ 125.6, δ 71.3, δ 36.8
and δ 35.4 ppm, due to C10, C9, C12, C13 and C11 carbons of ricinoleic acid (RA) in CO, were selected for distinguishing it
from edible oils. Quantitative13C NMR spectra of oils were recorded in CDCl3 with a gated decoupling technique. The minimum detection limits for qualitative and quantitative analyses were 2.0 and 3.0%,
respectively. The proposed method is simple, nondestructive and requires no sample pretreatment. Its application to heat-abused
oils has also been demonstrated successfully without any of the interferences observed in most other methods. 相似文献
28.
M.?MelgosaEmail author R.?Huertas E.?Hita J.?M.?Roa F.?J.?Heredia J.?Alba M.?J.?Moyano 《Journal of the American Oil Chemists' Society》2004,81(4):323-330
A new color scale was developed from a broad data set of 1700 virgin olive oil samples over four crop seasons, which can be
considered highly representative of the whole color range of virgin olive oils available in Spain. This color scale provides
a new set of 60 color standards, improving the results achieved by the old 60-color standards proposed by the bromthymol blue
method. Seeking the greatest possibility of including a near match between colors of virgin olive oils and proposed standards,
we developed our new color scale using a recent uniform color space, with standards placed in a regular rhombohedral lattice
like the one employed by the Uniform Color Scales of the Optical Society of America. The average color difference between
each of the 1700 virgin olive oils and its nearest standard is reduced from 8.17 CIELAB units, using the bromthymol blue standards,
to 3.99 CIELAB units using the new standards. Within a color tolerance of 7.0 CIELAB units, 93.2% of our virgin olive oils
can be classified with the new standards, but only 59.1% with the bromthymol blue ones. In the interest of future adoption,
the performance of the new color standards should be tested by industry and researchers. 相似文献
29.
O'Reilly-Wapstra JM Potts BM McArthur C Davies NW Tilyard P 《Journal of chemical ecology》2005,31(3):519-537
Hybridization in plants provides an opportunity to investigate the patterns of inheritance of hybrid resistance to herbivores, and of the plant mechanisms conferring this resistance such as plant secondary metabolites. We investigated how inter-race differences in resistance of Eucalyptus globulus to a generalist mammalian herbivore, Trichosurus vulpecula, are inherited in their F1 hybrids. We assessed browsing damage of three-year-old trees in a common environment field trial on four hybrid types of known progeny. The progency were artificial intra-race crosses and reciprocal inter-race F1 hybrids of two geographically distinct populations (races) of E. globulus; north-eastern Tasmania and south-eastern Tasmania. Populations of trees from north-eastern Tasmania are relatively susceptible to browsing by T. vulpecula, while populations from south-eastern Tasmania are more resistant. We assessed the preferences of these trees in a series of paired feeding trials with captive animals to test the field trial results and also investigated the patterns of inheritance of plant secondary metabolites. Our results demonstrated that the phenotypic expression of resistance of the inter-race F1 hybrids supported the additive pattern of inheritance, as these hybrids were intermediate in resistance compared to the pure parental hybrids. The expression of plant secondary metabolites in the F1 hybrids varied among groups of individual compounds. The most common pattern supported was dominance towards one of the parental types. Together, condensed tannins and essential oils appeared to explain the observed patterns of resistance among the four hybrid types. While both chemical groups were inherited in a dominant manner in the inter-race F1 hybrids, the direction of dominance was opposite. Their combined concentration, however, was inherited in an additive manner, consistent with the phenotypic differences in browsing. 相似文献
30.
A novel bio‐based composite material, suitable for electronic as well as automotive and aeronautical applications, was developed from soybean oils and keratin feather fibers (KF). This environmentally friendly, low‐cost composite can be a substitute for petroleum‐based composite materials. Keratin fibers are a hollow, light, and tough material and are compatible with several soybean (S) resins, such as acrylated epoxidized soybean oil (AESO). The new KFS lightweight composites have a density ρ ≈ 1 g/cm3, when the KF volume fraction is 30%. The hollow keratin fibers were not filled by resin infusion and the composite retained a significant volume of air in the hollow structure of the fibers. Due to the retained air, the dielectric constant, k, of the composite material was in the range of 1.7–2.7, depending on the fiber volume fraction, and these values are significantly lower than the conventional silicon dioxide or epoxy, or polymer dielectric insulators. The coefficient of thermal expansion (CTE) of the 30 wt % composite was 67.4 ppm/°C; this value is low enough for electronic application and similar to the value of silicon materials or polyimides used in printed circuit boards. The water absorption of the AESO polymer was 0.5 wt % at equilibrium and the diffusion coefficient in the KFS composites was dependent on the keratin fiber content. The incorporation of keratin fibers in the soy oil polymer enhanced the mechanical properties such as storage modulus, fracture toughness, and flexural properties, ca. 100% increase at 30 vol %. The fracture energy of a single keratin fiber in the composite was determined to be about 3 kJ/m2 with a fracture stress of about 100–200 MPa. Considerable improvements in the KFS composite properties should be possible by optimization of the resin structure and fiber selection. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1524–1538, 2005 相似文献