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   4266篇
  完全免费   548篇
  轻工业   4814篇
  2019年   60篇
  2018年   240篇
  2017年   374篇
  2016年   210篇
  2015年   180篇
  2014年   253篇
  2013年   526篇
  2012年   318篇
  2011年   375篇
  2010年   254篇
  2009年   221篇
  2008年   245篇
  2007年   268篇
  2006年   139篇
  2005年   101篇
  2004年   89篇
  2003年   73篇
  2002年   80篇
  2001年   69篇
  2000年   57篇
  1999年   55篇
  1998年   21篇
  1997年   20篇
  1996年   20篇
  1995年   21篇
  1994年   26篇
  1993年   28篇
  1992年   26篇
  1991年   19篇
  1990年   37篇
  1989年   44篇
  1988年   37篇
  1987年   30篇
  1986年   25篇
  1985年   19篇
  1984年   20篇
  1983年   25篇
  1982年   23篇
  1981年   32篇
  1980年   20篇
  1979年   23篇
  1978年   15篇
  1977年   9篇
  1976年   4篇
  1975年   6篇
  1974年   6篇
  1973年   2篇
  1972年   5篇
  1971年   11篇
  1970年   9篇
  1969年   5篇
  1968年   2篇
  1967年   4篇
  1966年   5篇
  1965年   2篇
  1964年   1篇
  1963年   4篇
  1962年   1篇
  1961年   6篇
  1960年   1篇
  1959年   1篇
  1957年   1篇
  1956年   3篇
  1955年   2篇
  1954年   3篇
  1953年   1篇
  1952年   1篇
  1951年   1篇
排序方式: 共有4814条查询结果,搜索用时 31 毫秒
1.
Chitin--the undisputed biomolecule of great potential   总被引:23,自引:0,他引:23  
Of the truly abundant polysaccharides in Nature, only chitin has yet to find utilization in large quantity. Chitin is the second most abundant natural biopolymer derived from exoskeletons of crustaceans and also from cell walls of fungi and insects. Chitin is a linear beta 1,4-linked polymer of N-acetyl-D-glucosamine (GlcNAc), whereas chitosan, a copolymer of GlcNAc (approximately 20%) and glucosamine (GlcN, 80%) residues, is a product derived from de-N-acetylation of chitin in the presence of hot alkali. Chitosan is, in fact, a collective name representing a family of de-N-acetylated chitins deacetylated to different degrees. Both chitin/chitosan and their modified derivatives find extensive applications in medicine, agriculture, food, and non-food industries as well. They have emerged as a new class of physiological materials of highly sophisticated functions. Their application versatility is a great challenge to the scientific community and to industry. All these are the result of their versatile biological activity, excellent biocompatibility, and complete biodegradability in combination with low toxicity. Commercial availability of high-purity forms of chitin/chitosan and the continuous appearance of new types of chitin/chitosan derivatives with more and more useful and specific properties have led to an unlimited R&D efforts on this most versatile amino polysaccharide, chitin to find new applications, which are necessary to realize its full potential. Incidentally, this too has become an environmental priority. No doubt, chitin is surely an undisputed biomolecule of great potential.  相似文献
2.
A review on biological control and metabolism of aflatoxin   总被引:14,自引:0,他引:14  
The series of events that led to the discovery of aflatoxin as a potent carcinogen, its biosynthesis, mechanism of action, structure-function relationship provide interesting insight into the economical and technological factors involved in the development of an effective control measure for the toxin. Scientists all over the world are making continuous efforts to explore a generalized process of detoxification, which can bring down the toxin content in heterogenous commodities to a threshold level. In this article biological control methods with special emphasis on in vivo and in vitro enzymatic detoxification of aflatoxin have been reviewed. Future areas of research involving large-scale enzymatic detoxification and modified atmosphere storage are also discussed.  相似文献
3.
Monitoring of black tea fermentation process using electronic nose   总被引:14,自引:0,他引:14  
Black tea fermentation is essentially an oxidation process. After the plucked tea leaves are treated by series of processes called withering (removal of moisture by air flow), pre-conditioning and CTC (essentially maceration and cutting of leaves), the leaves are subjected to the process of fermentation by exposing them to air by laying the cut tea leaves on floor, trough or moving conveyor under controlled temperature, humidity and air-flow conditions. During this process, the leaves change colour from green to coppery brown and the grassy smell gets transformed to floral smell. It is critical that the leaves be allowed to ferment only up to the desired limit and both under and over fermentation result in deteriorated quality of black tea. Out of the two detectable parameters (colour and smell), smell is very important since a strong, very specific fragrance emanates from the leaves once leaves are optimally fermented. A new electronic nose-based approach for monitoring of tea aroma during fermentation is proposed. Two methods namely the 2-Norm method (2NM) and the Mahalanobis distance method (MDM) were tested and the results were correlated with the results of colorimetric tests and human expert evaluation.  相似文献
4.
5.
Removal of chlorophenols using industrial wastes   总被引:13,自引:0,他引:13  
Development of inexpensive adsorbents from industrial wastes for the treatment of wastewaters is an important area in environmental sciences. Blast furnace slag, dust and sludge from steel plants, and carbon slurry from fertilizer plants after their treatment have been utilized as inexpensive adsorbents for the removal of phenols, which are an important class of pollutants as they are highly toxic. The characterization of the four adsorbents prepared has shown that the carbonaceous adsorbent prepared from carbon slurry possesses high porosity and maximum surface area (380 m2/g) as compared to the other three adsorbents (4-28 m2/g). The adsorption of four phenols (phenol, 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol) on these adsorbents is parallel to their porosity and surface area order. The uptake of the phenols on carbonaceous adsorbent is substantial and found to be 17.2, 50.3, 57.4, and 132.5 mg/g for phenol, 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol, respectively. The detailed adsorption studies on carbonaceous adsorbent have indicated that the adsorption process follows the Langmuir isotherm, is first order, and is pore diffusion controlled. As adsorption of phenols on prepared carbonaceous adsorbent is significant, its performance has been evaluated with respect to standard activated charcoal. The results indicate that the phenols removal efficiency of carbonaceous adsorbent is about 45% to that of a standard activated charcoal sample. Thus, the carbonaceous adsorbent can be used for the removal of phenols as a low-cost alternative (approximately 0.1 U.S. dollars/kg) to activated charcoal.  相似文献
6.
Sandhya 《LWT》2010,43(3):381-392
Fresh produce is more susceptible to disease organisms because of increase in the respiration rate after harvesting. The respiration of fresh fruits and vegetables can be reduced by many preservation techniques. Modified atmosphere packaging (MAP) technology is largely used for minimally processed fruits and vegetables including fresh, “ready-to-use” vegetables. Extensive research has been done in this research area for many decades. Oxygen, CO2, and N2, are most often used in MAP. The recommended percentage of O2 in a modified atmosphere for fruits and vegetables for both safety and quality falls between 1 and 5%. Although other gases such as nitrous and nitric oxides, sulphur dioxide, ethylene, chlorine, as well as ozone and propylene oxide have also been investigated, they have not been applied commercially due to safety, regulatory, and cost considerations. Successful control of both product respiration and ethylene production and perception by MAP can result in a fruit or vegetable product of high organoleptic quality; however, control of these processes is dependent on temperature control.  相似文献
7.
Solubilization and refolding of bacterial inclusion body proteins   总被引:9,自引:0,他引:9  
Inclusion bodies produced in Escherichia coli are composed of densely packed denatured protein molecules in the form of particles. Refolding of inclusion body proteins into bioactive forms is cumbersome, results in poor recovery and accounts for the major cost in production of recombinant proteins from E. coli. With new information available on the structure and function of protein aggregates in bacterial inclusion bodies, it has been possible to develop improved solubilization and refolding procedures for higher recovery of bioactive protein. Inclusion bodies are formed from partially folded protein intermediates and are composed of aggregates of mostly single types of polypeptide. This helps to isolate and purify the protein aggregates to homogeneity before solubilization and refolding. Proteins inside inclusion body aggregates have native-like secondary structures. It is assumed that restoration of this native-like secondary structure using mild solubilization conditions will help in improved recovery of bioactive protein in comparison to solubilization using a high concentration of chaotropic agent. Analysis of the dominant forces causing aggregation during inclusion body formation provides information to develop suitable mild solubilization procedures for inclusion body proteins. Refolding from such solubilized protein will be very high due to restoration of native-like secondary structure. Human growth hormone inclusion bodies were purified to homogeneity from E. coli cells before solubilization and refolding. Pure inclusion bodies were solubilized at alkaline pH in the presence of 2 M urea solution. The solubilized proteins were refolded using a pulsatile renaturation process and subsequently purified using chromatographic procedures. More than 40% of the inclusion body proteins could be refolded back to the bioactive native conformation. Mild solubilization is thus the key for high recovery of bioactive protein from inclusion bodies.  相似文献
8.
High pressure pretreatment (100–700 MPa) was applied to enhance mass transfer rates during osmotic dehydration of pineapples and accelerate the process. Experimentally determined diffusivity values, based on a Fickian model, increased fourfold for water and twofold for sugar. Diffusivity values were correlated with pretreatment pressure by an equation of the form D=A exp(–B/P), which suggests that diffusivity would level after an initial increase in pressure. The increase was attributed to breaking-up of cells walls which facilitated the transport of water. Evidence for the extent of cell wall break-up with applied pressure was based on differential interference contrast microscopic examination of tissue. Preliminary experiments on rehydration characteristics showed high pressure pretreated samples did not absorb as much water as controls.  相似文献
9.
The present study was carried out to assess levels of different heavy metals like iron, manganese, copper and zinc, in vegetables irrigated with water from different sources. The results indicated a substantial build-up of heavy metals in vegetables irrigated with wastewater. The range of various metals in wastewater-irrigated plants was 116–378, 12–69, 5.2–16.8 and 22–46 mg/kg for iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn), respectively. The highest mean levels of Fe and Mn were detected in mint and spinach, whereas the levels of Cu and Zn were highest in carrot. The present study highlights that both adults and children consuming vegetables grown in wastewater-irrigated soils ingest significant amount of these metals. However, the values of these metals were below the recommended maximum tolerable levels proposed by the [Joint FAO/WHO Expert Committee on Food Additives (1999). Summary and conclusions. In 53rd Meeting, Rome, June 1–10, 1999]. However, the regular monitoring of levels of these metals from effluents and sewage, in vegetables and in other food materials is essential to prevent excessive build-up of these metals in the food chain.  相似文献
10.
Anti-oxidant activity and total phenolic content of some Asian vegetables   总被引:8,自引:0,他引:8  
The anti-oxidant activity of extracts from 36 vegetables was evaluated by using a model system consisting of β-carotene and linoleic acid. The total phenolics of the extracts was determined spectrophotometrically according to the Folin–Ciocalteau procedure and ranged from 34 to 400 mg (100 g)−1 on a fresh weight basis. Mint, aonla, black carrots, chenopodium, fenugreek, kachnar and ginger had high phenolic contents. The anti-oxidant activity expressed as per percent inhibition of oxidation ranged from a high of 92% in turmeric extracts to a low of 12.8% in long melon. Other vegetables found to have high anti-oxidant activity (>70%) were kachnar, aonla, ginger, fenugreek, mint, beetroot, black carrots, Brussels sprouts, broccoli, lotus stem, yam, coriander and tomato. Anti-oxidant activity correlated significantly and positively with total phenolics ( r 2=0.6578, P  < 0.05). The results indicate that vegetables containing high phenolics may provide a source of dietary anti-oxidants.  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