首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2749篇
  免费   179篇
  国内免费   25篇
电工技术   41篇
综合类   15篇
化学工业   705篇
金属工艺   83篇
机械仪表   125篇
建筑科学   135篇
矿业工程   4篇
能源动力   105篇
轻工业   248篇
水利工程   39篇
石油天然气   24篇
武器工业   3篇
无线电   326篇
一般工业技术   442篇
冶金工业   113篇
原子能技术   19篇
自动化技术   526篇
  2024年   19篇
  2023年   46篇
  2022年   82篇
  2021年   156篇
  2020年   169篇
  2019年   166篇
  2018年   209篇
  2017年   161篇
  2016年   159篇
  2015年   100篇
  2014年   207篇
  2013年   275篇
  2012年   179篇
  2011年   204篇
  2010年   139篇
  2009年   108篇
  2008年   95篇
  2007年   58篇
  2006年   53篇
  2005年   40篇
  2004年   24篇
  2003年   23篇
  2002年   7篇
  2001年   17篇
  2000年   12篇
  1999年   11篇
  1998年   28篇
  1997年   23篇
  1996年   25篇
  1995年   20篇
  1994年   12篇
  1993年   13篇
  1992年   8篇
  1991年   12篇
  1990年   7篇
  1989年   4篇
  1988年   7篇
  1987年   9篇
  1986年   10篇
  1985年   6篇
  1984年   5篇
  1982年   3篇
  1980年   3篇
  1979年   3篇
  1975年   3篇
  1973年   5篇
  1972年   2篇
  1971年   6篇
  1970年   8篇
  1969年   4篇
排序方式: 共有2953条查询结果,搜索用时 15 毫秒
71.
72.
Efforts have been done to recover proteins from waste liquors rich in protein in a soluble form. Cheese whey and animal bloods are byproducts from the manufacture of cheese and meat. It contains a variety of proteins which can be reclaimed. The efficiency of protein precipitation from the sweet-cheese whey by the use of hydroxyethyl cellulose (HEC) was similar to that precipitated by the use of carboxymethyl cellulose (CMC). Both are greater than that precipitated by trichloro acetic acid. The same results of the efficiency of precipitation were attained when the plasma protein was precipitated. It was found that cheesewhey protein-HEC-complex and plasms protein-HEC-complex contain a large amount of essential amino acids. Electrophoretic separation of whey protein complex showed that β-Lactoglobulin forms the major fraction while in case of plasma protein complex albumin forms the major fraction. The fractionation patterns of different complexes with HEC, CMC or TCA gave the same components and about the same ratio. It appears from these results that HEC-protein complexes are preferable than CMC-protein complexes or proteins precipitated by TCA. Chemical analysis of whey protein complexes revealed that lactose content of whey protein-HEC-complex was higher than that of CMC-complex or protein precipitated by TCA. Elemental analysis of protein complexes showed that the level of sodium, phosphorus, and potassium was increased while that of copper or zinc decreased. Cellulose derivative protein complexes showed no significant effects on the liver or kindney function of albino rat and these results indicated that no toxic effect was observed from the uses of these protein complexes in feeding.  相似文献   
73.
ABSTRACT:  Free radical scavenging activity of 21 tropical plant extracts was evaluated using 1,1-diphenyl-2-picrylhydrazyl assay (DPPH). Total phenolic compounds and flavonoids were determined using Folin–Ciocalteu and HPLC, respectively. Results of the study revealed that all the plants tested exhibited excellent antioxidant activity with IC50 in the range of 21.3 to 89.6 μg/mL. The most potent activity was demonstrated by  Cosmos caudatus  (21.3 μg/mL) and  Piper betle  (23.0 μg/mL) that are not significantly different than that of     -tocopherol or BHA.  L. inermis  extract was found to consist of the highest concentration of phenolics, catechin, epicatechin, and naringenin. High content of quercetin, myricetin, and kaempferol were identified in  Vitex negundo ,  Centella asiatica , and  Sesbania grandiflora  extracts, respectively. Luteolin and apigenin, on the other hand, were found in  Premna cordifolia  and  Kaempferia galanga  extracts. Strong correlation ( R  = 0.8613) between total phenolic compounds and total flavonoids ( R  = 0.8430) and that of antioxidant activity of the extracts were observed. The study revealed that phenolic, in particular flavonoids, may be the main contributors to the antioxidant activity exhibited by the plants.
Practical Application: Potent antioxidant from natural sources is of great interest to replace the use of synthetic antioxidants. In addition, some of the plants have great potential to be used in the development of functional ingredients/foods that are currently in demand for the health benefits associated with their use.  相似文献   
74.
Microencapsulation is a process of building a functional barrier between the core and wall material to avoid chemical and physical reactions and to maintain the biological, functional, and physicochemical properties of core materials. Microencapsulation of marine, vegetable, and essential oils has been conducted and commercialized by employing different methods including emulsification, spray‐drying, coaxial electrospray system, freeze‐drying, coacervation, in situ polymerization, melt‐extrusion, supercritical fluid technology, and fluidized‐bed‐coating. Spray‐drying and coacervation are the most commonly used techniques for the microencapsulation of oils. The choice of an appropriate microencapsulation technique and wall material depends upon the end use of the product and the processing conditions involved. Microencapsulation has the ability to enhance the oxidative stability, thermostability, shelf‐life, and biological activity of oils. In addition, it can also be helpful in controlling the volatility and release properties of essential oils. Microencapsulated marine, vegetable, and essential oils have found broad applications in various fields. This review describes the recognized benefits and functional properties of various oils, microencapsulation techniques, and application of encapsulated oils in various food, pharmaceutical, and even textile products. Moreover, this review may provide information to researchers working in the field of food, pharmacy, agronomy, engineering, and nutrition who are interested in microencapsulation of oils.  相似文献   
75.
This study aimed to develop a nanoliposomal formulation containing α‐tocopherol loaded with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and to characterise the formulation by its physical stability. For this purpose, different nanoliposomal formulations with dipalmitoyl phosphocholine were prepared using a modified thin‐film hydration method and evaluated by particle size, polydispersity index (PDI), transmission electron microscopy, differential scanning calorimetry and determining the encapsulation efficiencies of DHA and EPA. A physical stability study was conducted by investigating the change in the vesicle encapsulation efficiency, particle size, PDI and shape when stored at 4, 30 and 40 °C for 3 months. High encapsulation efficiency of DHA and EPA (89.1% ± 0.6% and 81.9% ± 1.4%) and appropriate particle size (82 ± 0.8 nm) were obtained for liposomes composed of α‐tocopherol. The optimum formulation was stable for 90 days when kept at 4 °C. This study demonstrated that α‐tocopherol had a protective effect on the physical stability of the nanoliposomes containing DHA and EPA.  相似文献   
76.
Old oil palm trunks that had been felled for replanting were found to contain large quantities of high glucose content sap. Notably, the sap in the inner part of the trunk accounted for more than 80% of the whole trunk weight. The glucose concentration of the sap from the inner part was 85.2 g/L and decreased towards the outer part. Other sugars found in relatively low concentrations were sucrose, fructose, galactose, xylose, and rhamnose. In addition, oil palm sap was found to be rich in various kinds of amino acids, organic acids, minerals and vitamins. Based on these findings, we fermented the sap to produce ethanol using the sake brewing yeast strain, Saccharomyces cerevisiae Kyokai no.7. Ethanol was produced from the sap without the addition of nutrients, at a comparable rate and yield to the reference fermentation on YPD medium with glucose as a carbon source. Likewise, we produced lactic acid, a promising material for bio-plastics, poly-lactate, from the sap using the homolactic acid bacterium Lactobacillus lactis ATCC19435. We confirmed that sugars contained in the sap were readily converted to lactic acid with almost the same efficiency as the reference fermentation on MSR medium with glucose as a substrate. These results indicate that oil palm trunks felled for replanting are a significant resource for the production of fuel ethanol and lactic acid in palm oil-producing countries such as Malaysia and Indonesia.  相似文献   
77.
Food Science and Biotechnology - Exopolysaccharide (EPS), as potential microbial base polysaccharide source, has plenty of applications due to its unique physicochemical structure. A Pantoea sp....  相似文献   
78.
The chemical composition of the hydrodistillate of aerial parts of Cymbopogon jawarancusa, a natural grass considered as major forage for animal nutrition, used in food because of the presence of sufficient concentration of minerals like calcium and potassium was analysed by capillary GC–FID, GC–MS and 13C NMR. Seventeen constituents representing 97.8% of the total oil with piperitone (58.6%) and elemol (18.6%) as major constituents were identified. In vitro cytotoxicity of the oil and its constituents on human cancer cell lines THP-1 (leukemia), A-549 (lung), HEP-2 (liver) and IGR-OV-1 (ovary) was evaluated by Sulphorhodamine-B assay. The oil was found to be more potent than its components against cancer cell lines tested with IC50 of 6.5 μg/ml (THP-1), 6.3 μg/ml (A-549), 7.2 μg/ml (HEP-2) and 34.4 μg/ml (IGR-OV-1). Antioxidant activity of oil and its constituents was evaluated by DPPH assay. In conclusion, the results demonstrate potent cytotoxic and antioxidant effects of oil, and its components like piperitone, α-pinene, β-caryophyllene and β-elemene.  相似文献   
79.
The essential oils obtained by hydrodistilation of the leaves and rhizomes of Zingiber officinale var. rubrum Theilade were analysed by capillary GC and GC–MS. Forty-six constituents were identified in the leaf oil, while 54 were identified in the oil from the rhizomes. The leaf oil was clearly dominated by β-caryophyllene (31.7%), while the oil from the rhizomes was predominantly monoterpenoid, with camphene (14.5%), geranial (14.3%), and geranyl acetate (13.7%) the three most abundant constituents. The evaluation of antibacterial activities using the micro-dilution technique revealed that both the leaf and rhizome oils were moderately active against the Gram-positive bacteria Bacilluslicheniformis, Bacillus spizizenii and Staphylococcus aureus, and the Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae and Pseudomonas stutzeri.  相似文献   
80.
Fat, alkaloid and polyphenol contents of two clones of cocoa (UIT1 and PBC 140) were removed and the remaining powder was autolyzed at pH 3.5 and 5.2. Based on the results, autolysates of UIT produced at pH 3.5 exhibited the highest ability to inhibit α-amylase activity. However, no α-glucosidase inhibition activity was observed under the conditions specified. Autolysates produced under pH 3.5 caused the highest amount of insulin secretion. In streptozotocin-diabetic rats, all cocoa autolysates significantly decreased blood glucose at 4 h. To assure that the results from the assays were not due to the polyphenols of cocoa autolysates qualitative and quantitative tests were applied. According to their results cocoa autolysates were found to be free from polyphenols. Analysis of amino acid composition revealed that cocoa autolysates were abundant in hydrophobic amino acids. It can be suggested that besides other compounds of cocoa, its peptides and amino acids could contribute to its health benefits.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号