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   85530篇
  免费   987篇
  国内免费   238篇
电工技术   785篇
综合类   2325篇
化学工业   11857篇
金属工艺   4858篇
机械仪表   3050篇
建筑科学   2224篇
矿业工程   564篇
能源动力   1165篇
轻工业   3713篇
水利工程   1285篇
石油天然气   345篇
无线电   9335篇
一般工业技术   16596篇
冶金工业   2844篇
原子能技术   263篇
自动化技术   25546篇
  2023年   26篇
  2022年   53篇
  2021年   50篇
  2020年   49篇
  2019年   68篇
  2018年   14478篇
  2017年   13408篇
  2016年   9997篇
  2015年   639篇
  2014年   299篇
  2013年   282篇
  2012年   3200篇
  2011年   9500篇
  2010年   8348篇
  2009年   5595篇
  2008年   6832篇
  2007年   7836篇
  2006年   179篇
  2005年   1265篇
  2004年   1170篇
  2003年   1219篇
  2002年   568篇
  2001年   118篇
  2000年   198篇
  1999年   81篇
  1998年   99篇
  1997年   66篇
  1996年   77篇
  1995年   37篇
  1994年   31篇
  1993年   27篇
  1992年   32篇
  1991年   31篇
  1990年   21篇
  1969年   27篇
  1968年   45篇
  1967年   34篇
  1966年   43篇
  1965年   45篇
  1963年   28篇
  1962年   22篇
  1960年   31篇
  1959年   35篇
  1958年   37篇
  1957年   36篇
  1956年   35篇
  1955年   65篇
  1954年   68篇
  1951年   18篇
  1950年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Indian Punjab, a strategically important region from India’s national food security standpoint, is increasingly the focus of attention for academics and policymakers because of serious concerns about over-exploitation of its groundwater resources. Currently, policy makers and agricultural researchers/scientists in India are in a fix to prescribe an alternative, probably more sustainable, crop-mix to farmers that can save water while maintaining farm incomes. Using primary data from 120 farmers, this paper evaluates the current situation of groundwater resources in Punjab, and outlines the major socio-economic factors that have a significant association with the change in the groundwater depth in this region. General ANOVA regression results suggest that groundwater depth varied significantly with respect to agro-climatic regions, crop diversity, and farmer education. Crop diversity had an inverse relationship with groundwater depth whereas the association between farmer education and groundwater depth was non-linear although in the case of Gurdaspur, they showed a direct relationship. In the central zone of Indian Punjab, groundwater level on 92% of the farms had depleted by more than 0.60 m annually between 2000 and 2010, while the current state of groundwater resources in the other two regions was not so serious and are manageable for the time being. However, if the existing policy framework for groundwater resources in the state, which allows the state government to release 0.11 million more connections to farmers, putting much pressure not only on the groundwater resources but also burdening the state exchequer, continues, Punjab may end up losing all its groundwater resources for ever. Considering this alarming situation, one-fifth of the farmers surveyd agreed to delay the sowing of rice by another 2 weeks i.e. up to 30 June which could save the fast depleting groundwater resources in Punjab.  相似文献   
993.
Food fraud is an intentional act for economic gain. It poses a risk to food integrity, the economy, public health and consumers’ ethics. Seafood is one commodity which has endured extensive fraudulent activity owing to its increasing consumer demand, resource limitations, high value and complex supply chains. It is essential that these fraudulent opportunities are revealed, the risk is evaluated and countermeasures for mitigation are assigned. This can be achieved through mapping of the seafood supply chains and identifying the vulnerability analysis critical control points (VACCP), which can be exposed, infiltrated and exploited for fraudulent activity. This research systematically maps the seafood supply chain for three key commodities: finfish, shellfish and crustaceans in the United Kingdom. Each chain is comprised of multiple stakeholders across numerous countries producing a diverse range of products distributed globally. For each supply chain the prospect of fraud, with reference to species substitution, fishery substitution, illegal, unreported and unregulated substitution, species adulteration, chain of custody abuse, catch method fraud, undeclared product extension, modern day slavery and animal welfare, has been identified and evaluated. This mapping of the fraudulent opportunities within the supply chains provides a foundation to rank known and emerging risks and to develop a proactive mitigation plan which assigns control measures and responsibility where vulnerabilities exist. Further intelligence gathering and management of VACCPs of the seafood supply chains may deter currently unknown or unexposed fraudulent opportunities.  相似文献   
994.
Carvacrol is a monoterpenic phenol present in Thymus quinquecostatus Celak. The protective effects of carvacrol against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage were investigated in human Chang cells. Cells treated with carvacrol extracts promoted Chang cell survival and protection was associated with stabilization of the mitochondrial membrane potential (MMP), prevention of oxidative stress-triggered reactive oxygen species (ROS), and lipid peroxidation (MDA production). In addition, Annexin V/PI, observed using Hoechst staining, indicated that carvacrol inhibited t-BHP-induced cell damage and stimulated the antioxidant capability of Chang cells due to elevation of glutathione (GSH) levels, which were reduced by t-BHP treatment. Carvacrol prevented oxidative stress-induced Chang cell damage via suppression of ROS and MDA levels, and increased GSH levels.  相似文献   
995.
Instrumental analyses were used to evaluate the rheological properties of regular (10%), reduced-fat (6%) and low-fat (3%) ice cream mixes and frozen ice creams stored at −18 °C. The reduced-fat and low-fat ice creams were prepared using 4% whey protein isolate (WPI) or 4% inulin as the fat replacement ingredient. The composition, colour, apparent viscosity, consistency coefficient, flow behaviour index, hardness and melting characteristics were measured. No effect of WPI or inulin was obtained on the colour values. Compared with regular ice cream, WPI changed rheological properties, resulting in significantly higher apparent viscosities, consistency indices and greater deviations from Newtonian flow. In addition, both hardness and melting resistance significantly increased by using WPI in reduced-fat and low-fat ice creams. Inulin also increased the hardness in comparison to regular ice cream, but the products made with inulin melted significantly faster than the other samples.  相似文献   
996.
The objectives of this study were to identify the potential function of microwave-discharged cold plasma (MCP) treatment in preparing starch citrate (SC) non-thermally and to investigate the physicochemical properties of MCP-induced starch citrates. SCs were prepared by either dry heating in a convection oven (as a reaction control; COV) or MCP treatment using N2 (N2-MCP) and N2–O2 (N2/O2-MCP). Fourier transform-infrared spectra of the MCP-induced SCs revealed new peaks indicating ester bonds. The molar degree of substation was 0.013–0.015 depending on the reaction conditions. The plasma-formed dents were observed more on the surfaces of granular starch citrates (GSCs) treated with N2/O2-MCP than N2-MCP. Relative to COV, MCP-induced GSCs possessed lower resistant starch content, solubility, and gelatinization temperatures and higher swelling power. The pasting viscosities were higher with N2-MCP GSCs and lower with N2/O2-MCP GSCs. The results suggest that MCP can be used as a novel catalyst for non-thermal starch citration.  相似文献   
997.
The effect of fermented red beet (FRB) on shelf-life of low-salt frankfurters stored for 4 weeks was investigated. The pH, volatile basic nitrogen (VBN), lightness, and yellowness of frankfurters decreased with increasing levels of FRB, whereas the redness of frankfurters increased with increasing levels of FRB. The VBN, thiobarbituric acid reactive substance values, total viable count, and redness of all treatments decreased with increasing period of refrigeration storage. The appearance, color, and juiciness scores of the control and treatments decreased with increasing period of refrigeration storage. However, there was no significant (p > 0.05) difference among the treatments except for the color of T3 (3.0% FRB) and juiciness of T4 (5.0% FRB). The flavor, tenderness, and overall acceptability scores of all the treatments decreased with increasing storage periods. These results demonstrated that FRB can be added to low-salt frankfurters to maintain their qualities and extend the shelf-life of refrigerated storage.  相似文献   
998.
The objective of this study was to select and identify yeasts and molds isolated from traditional nuruk and to investigate their brewing characteristics for Cheongju production. The yeast strains Y190 (Accession ID-KACC 93251P), Y263 (Accession ID-KACC 93252P), and Y270 (Accession ID-KACC 93253P) showing high alcohol and flavor productivity were isolated and identified by phylogenetic inference based on an internal transcribed spacer 2 region sequence analysis. In addition, Aspergillus oryzae 83-10 (Accession ID-KACC 93254P) showing the highest enzyme activity was isolated. This study provides basic data for the production of Korean Cheongju and assesses the applicability of these three yeast strains and A. oryzae 83-10 isolated from traditional nuruk.  相似文献   
999.
Vaccinium bracteatum Thunb, have been widely used in various traditional medicines and food products. The narrow and uniform particle size distribution in V. bracteatum Thunb leaves (VBTL) can be achieved through a new emerging type of foodstuff processing and superfine grinding. The VBTL powders were subjected to four particle sizes as followed: 300–125, 125–75, 75–40, and <40 μm. The VBTL powders were observed to be with smaller size and bulk density, greater surface area, tapped density and the angle of repose. Water solubility index, water holding capacity and total flavonoid extraction increased slightly with the decrease in particle size. Differential scanning calorimetry showed that the VBTL exhibiting particle size of <40 μm had the lowest peak temperature; whereas, powder with a particle size of 125–300 μm displayed the largest endothermic enthalpy. Our results of the properties of VBTL superfine powder supplied the basis for VBTL in potential industrial applications of foods.  相似文献   
1000.
The ability of lactic acid bacterial starter cultures to produce gamma-aminobutyric acid (GABA) during sausage fermentation was studied. Among 305 strains of lactic acid bacteria isolated from kimchi samples, 11 strains were selected as starter candidates based on the following criteria: growth speed, pH lowering ability, and biogenic amine productivity including GABA-producing activity. During in vitro tests, the Y8 (Lactobacillus brevis), O52, and KA20 strains produced 39.00 ± 1.36, 49.73 ± 3.80, and 64.59 ± 0.61 mg/kg of GABA, respectively. Interestingly, although isolate Y8 showed low productivity in vitro, the GABA content it produced during in situ tests (61.30 ± 2.61 mg/kg) was similar to that produced by isolate PM3 (L. brevis) used as positive control (69.64 ± 2.20 mg/kg). Therefore, isolate Y8 was selected as the best functional starter culture for the production of fermented sausage because it exhibited rapid growth, safety, and abundant GABA productivity.  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