全文获取类型
收费全文 | 756篇 |
免费 | 18篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 111篇 |
金属工艺 | 6篇 |
机械仪表 | 13篇 |
建筑科学 | 40篇 |
能源动力 | 4篇 |
轻工业 | 85篇 |
水利工程 | 8篇 |
无线电 | 66篇 |
一般工业技术 | 135篇 |
冶金工业 | 230篇 |
原子能技术 | 1篇 |
自动化技术 | 71篇 |
出版年
2023年 | 5篇 |
2021年 | 12篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 14篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 51篇 |
2012年 | 24篇 |
2011年 | 40篇 |
2010年 | 22篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 24篇 |
2006年 | 17篇 |
2005年 | 20篇 |
2004年 | 17篇 |
2003年 | 17篇 |
2002年 | 8篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 61篇 |
1997年 | 49篇 |
1996年 | 26篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 19篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1972年 | 4篇 |
1970年 | 7篇 |
1938年 | 3篇 |
1937年 | 5篇 |
排序方式: 共有774条查询结果,搜索用时 31 毫秒
721.
722.
723.
724.
Fatty acid content of marine oil capsules 总被引:2,自引:0,他引:2
Kew M. Chee Jun Xian Gong Deirdre M. Good Rees Mohsen Meydanl Lynne Ausman Julia Johnson Edward N. Siguel Ernst J. Schaefer 《Lipids》1990,25(9):523-528
The use of dietary ω3 fatty acid capsules has been associated with a decrease in plasma triglyceride levels. In addition,
populations consuming diets rich in fish appear to have a decreased incidence of cardiovascular disease. Eicosapentaenoic
acid (EPA, 20∶5ω3) and docosahexaenoic acid (DHA, 22∶6ω3) are major fatty acids in fish oils. It is believed that fish oils
exert their biolotic effect through these fatty acids. Many individuals are currently taking fish oil capsules to lower lipids,
increase bleeding time, and possibly decrease cardiovascular risk. These capsules also have been classified as food additives
with less stringent controls on content. We assessed the fatty acid, cholesterol, and vitamin A and E content of eight commercially
available capcules along with cod liver oil. The content of EPA was found to range from 8.7–26.4% (wt%) with a mean of 17.3%
(82.4% of labeled content), and that of DHA from 8.9–17.4% with a mean of 11.5% (90.0% of labeled content) as assessed by
capillary column gas-liquid chromatography. The mean content of the polyunsaturated ω3 fatty acids was 31.9%, and that of
the ω6 fatty acids was 1.4%. The content of saturated fatty acids was 32,0%, and that of monounsaturated fatty acids was 25.1%.
Cholesterol content was low, with a range of 0.7–8.3 mg/g, the α-tocopherol range was 0.62–2.24 mg/g, and the range of retinyl
esters was 0.4–298.4 μg/g. Cod liver oil had substantially more retinyl esters (2450.1 μg/g) than did fish oil capsules. Our
data serve as an independent guide to fish oil capsule fatty acid content upon single lot analysis, and indicate that these
capsules contain as much saturated fat as they contain ω3 fatty acids. 相似文献
725.
Stanley S Percival CJ Auer M Braithwaite A Newton MI McHale G Hayes W 《Analytical chemistry》2003,75(7):1573-1577
A chemically coated piezoelectric sensor has been developed for the determination of PAHs in the liquid phase. An organic monolayer attached to the surface of a gold electrode of a quartz crystal microbalance (QCM) via a covalent thiol-gold link complete with an ionically bound recognition element has been produced. This study has employed the PAH derivative 9-anthracene carboxylic acid which, once bound to the alkane thiol, functions as the recognition element. Binding of anthracene via pi-pi interaction has been observed as a frequency shift in the QCM with a detectability of the target analyte of 2 ppb and a response range of 0-50 ppb. The relative response of the sensor altered for different PAHs despite pi-pi interaction being the sole communication between recognition element and analyte. It is envisaged that such a sensor could be employed in the identification of key marker compounds and, as such, give an indication of total PAH flux in the environment. 相似文献
726.
Allelochemicals in Wheat (Triticum aestivum L.): Variation of Phenolic Acids in Shoot Tissues 总被引:9,自引:0,他引:9
Seven known phenolic acids implicated in wheat allelopathy were analyzed in a worldwide collection of 58 wheat accessions by gas chromatography and tandem mass spectrometry (GC-MS-MS). Chemical analysis showed that accessions differed significantly in the production of p-hydroxybenzoic, vanillic, syringic, trans-p-coumaric, cis-p-coumaric, trans-ferulic, and cis-ferulic acids in the shoots of 17-day-old wheat seedlings. The concentrations of p-hydroxybenzoic, vanillic, cis-p-coumaric, and cis-ferulic acids were normally distributed in the 58 accessions. A binormal distribution was found for syringic and trans-ferulic acids and a skewed normal distribution for trans-p-coumaric acid. The concentration of each compound also varied with phenolic acids. The relative abundance of each phenolic acid was ordered decreasingly as trans-ferulic, vanillic, trans-p-coumaric, p-hydroxybenzoic, syringic, cis-ferulic, and cis-p-coumaric acids. The concentration of total identified phenolic acids varied from 93.2 to 453.8 mg/kg in the shoots of 58 accessions. The content of each phenolic acid or group was highly associated with others in the shoots of wheat seedlings. Wheat accessions with high levels of total identified phenolic acids in the shoots are generally strongly allelopathic to the growth of annual ryegrass. 相似文献
727.
728.
An algorithm to recover bit timing is proposed which maximises a quadratic polynomial approximation to the log-likelihood function. The exact equation for the mean of the log-likelihood function derivative, i.e. the S-curve, is derived and shown to have a sine form. In each time interval the S-curve has two zeros. The zero corresponding to the maximum of the likelihood function is resolved using quadratic interpolation based on four samples per period. The resulting timing synchroniser has a simple open loop feedforward structure which has effectively no acquisition period. Receiver performances in terms of rms timing jitter and bit error rate (BER) are analysed and shown to agree closely with theoretical results. 相似文献
729.
TA Elhadd A Bancroft M McLaren RW Newton JJ Belch 《Canadian Metallurgical Quarterly》1997,90(7):461-464
Having previously shown an increase in white blood cell (WBC) aggregation in groups known to have a high incidence of cardiovascular events, we compared 28 patients with diabetes mellitus and no history or clinical evidence of macrovascular disease with 28 age- and sex-matched normal controls. Patients and controls had blood taken in the morning and analysed for WBC aggregation in vitro using a whole blood technique. WBC aggregation was significantly higher in the diabetic group compared with the normal controls (mean +/- SD 31.10 +/- 10.26% vs. 25.7 +/- 9.38%; p < 0.04, Student t-test). WBC aggregation predates the appearance of clinical symptoms of macrovascular disease in diabetes. 相似文献
730.
JA Newton Bishop 《Canadian Metallurgical Quarterly》1997,16(1-2):141-154
There has long been a clinical need for improved molecular pathology in melanoma, particularly in the histopathology laboratory where the differentiation of melanoma from its benign counterparts is commonly difficult. The need for improved molecular pathology has recently increased as immunotherapeutic options for the treatment of the tumour evolve. It seems likely that in the relatively near future tumour typing before and during immunotherapy will be needed. The identification of the tumour suppressor gene coding for the protein p16 as an important gene in the pathogenesis of melanoma is of great interest but the identification of oncogenes having a significant role in melanoma carcinogenesis has been slow. 相似文献