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   24260篇
  免费   2316篇
  国内免费   1117篇
电工技术   1677篇
技术理论   5篇
综合类   3739篇
化学工业   3022篇
金属工艺   637篇
机械仪表   889篇
建筑科学   2531篇
矿业工程   853篇
能源动力   829篇
轻工业   4065篇
水利工程   652篇
石油天然气   883篇
武器工业   145篇
无线电   1372篇
一般工业技术   1895篇
冶金工业   770篇
原子能技术   259篇
自动化技术   3470篇
  2024年   66篇
  2023年   281篇
  2022年   533篇
  2021年   658篇
  2020年   768篇
  2019年   675篇
  2018年   625篇
  2017年   728篇
  2016年   791篇
  2015年   949篇
  2014年   1462篇
  2013年   1521篇
  2012年   1855篇
  2011年   1869篇
  2010年   1456篇
  2009年   1439篇
  2008年   1394篇
  2007年   1660篇
  2006年   1508篇
  2005年   1204篇
  2004年   1004篇
  2003年   890篇
  2002年   741篇
  2001年   523篇
  2000年   494篇
  1999年   378篇
  1998年   363篇
  1997年   293篇
  1996年   261篇
  1995年   228篇
  1994年   220篇
  1993年   142篇
  1992年   166篇
  1991年   121篇
  1990年   85篇
  1989年   75篇
  1988年   63篇
  1987年   44篇
  1986年   26篇
  1985年   29篇
  1984年   23篇
  1983年   7篇
  1982年   5篇
  1981年   9篇
  1980年   9篇
  1964年   5篇
  1961年   4篇
  1960年   5篇
  1955年   7篇
  1954年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Although hydrogen automobile has attracted increasing attention in recent years, previous studies did not extensively investigate customers' purchase intention for hydrogen automobile, as well as the factors that might affect their purchase intention. The present study therefore investigated whether customers' environmental concern and perceived social value of green buying would affect their purchase intention for hydrogen automobile. Customers' green buying behavior was included as a mediator, and their monthly income and gender were included as moderators. Data from 300 adults in China were collected. Results from structural equation modeling showed that customers’ green buying behavior fully mediated the positive association between perceived social value and purchase intention for hydrogen automobile. Further multi-group analysis found that monthly income and gender had moderating effects on the associations between some of the study variables. Based on these findings, possible explanation and practical implications were discussed.  相似文献   
33.
We designed and fabricated non-precious and highly efficient electrocatalysts of nickelmolybdenum/copper-nanosheets/nickel-foam composites (NiMo/Cu-NS/NF) by step electrodepositions, combining with chemical oxidation method. The catalysts were charaterized by means of SEM, XRD and XPS spectra. Their electrocatalytic activities were assessed by hydrogen evolution reactions (HER) over a wide pH range, where acidic, neutral and alkaline electrolytes were used, respectively. Benefiting from the unique midlayer Cu nanosheets (NS) architecture and optimum Mo–Ni composition at the surface layer which led to high electronic conductivity and large electrochemically active surface area (ECSA), the NiMo/Cu-NS/NF-2 catalyst displayed superior electrocatalytic activities with low overpotentials of η10 = 43, 86 and 89 mV in 0.5 M H2SO4, 1.0 M PBS and 1.0 M KOH electrolyte, respectively. Especially in the acidic condition, it exhibited the best electrocatalytic activity with smaller Tafel slope of 54 mV dec?1 and higher exchange current density of 1.93 mA cm?2.  相似文献   
34.
This study aimed to evaluate the influence of plasma treatment time, bacterial exposure time to PAW and bacterial species on the inactivation efficacy of plasma-activated water (PAW), with additional investigation of the inactivation mechanisms of PAW. Six bacterial species, including Listeria innocua, Staphyloccus aureus, Escherichia coli, Pseudomonas fluorescens, Shewanella putrefaciens and Aeromonas hydrophila were selected as the representative bacteria. The initial bacterial concentration was around 7 log CFU ml−1 after mixing with PAW, and the inactivation efficacy was measured after different exposure times during the 4 °C storage. Scanning electron microscopy (SEM) images of the bacteria after PAW treatment were carried out to inspect the cell structure damage, and physicochemical properties of PAW, including pH, conductivity and long-living reactive species of H2O2, , and , were examined. The results showed that the inactivation efficacy of PAW was positively correlated with plasma treatment time and bacterial exposure time, and for the species examined in this study, the Gram-negative species were more sensitive to PAW than the Gram-positive species. Cell structure damage, including shrinkage, distortion, or holes, was observed after PAW treatment. The pH of PAW was acidified to 2.5–2.9, and conductivity was significantly increased to 518.0 μs cm−1. and H2O2 were reduced during the 48 h storage, while an increased concentration was observed for . This study demonstrated that the processing parameters of plasma treatment time, exposure time and characteristics of bacteria can significantly affect the inactivation efficacy of PAW.  相似文献   
35.
Hydrogels with environment‐sensitive properties have great potential applications in the controlled drug release field. In this paper, hybrid hydrogels with semi‐interpenetrating polymer networks (semi‐IPNs), composed of poly(N‐isopropylacrylamide) (PNIPAM) as the thermo‐sensitive component by in situ polymerization and self‐assembled collagen nanofibrils as the pH‐sensitive framework, were prepared for controlled release of methyl violet as a model drug. From Fourier transform infrared spectroscopy and scanning electron microscopy, it was indicated that the crosslinking of PNIPAM in the presence of collagen nanofibrils led to the formation of semi‐IPNs with homogeneous porous structure, and the semi‐IPNs showed improved thermal stability and elastic properties compared with the native collagen as determined using differential scanning calorimetry and rheologic measurements. Furthermore, the semi‐IPNs possessed swelling behaviors quite different from those of neat collagen or PNIPAM hydrogel under various pH values and temperatures. Correspondingly, as expected, the drug release behavior in vitro for semi‐IPNs performed variously compared with that for single‐component semi‐IPNs, which revealed the tunable performance of semi‐IPNs for release ability. Finally the thermo‐ and pH‐responsive mechanism of the semi‐IPNs was illuminated to provide guidance for the application of the thermo‐ and pH‐sensitive collagen‐based hybrid hydrogels in controlled drug delivery systems. © 2019 Society of Chemical Industry  相似文献   
36.
A novel process for the production of superabsorbent materials (hydrogels) from bacterial cellulose (BC) was developed. Prior to crosslinking with a water‐soluble polyethylene glycol diacrylate (PEGDA), BC was first carboxymethylated and functionalized with glycidyl methacrylate. The degree of crosslinking influenced the swelling properties of the hydrogels. The use of greater amounts of PEGDA enhanced the formation of a thicker macromolecular network containing fewer capillary spaces in the crosslinked gel. The maximum water retention value of the hydrogels containing 2.5–3.5 mmol of carboxyl groups per gram of gel reached 125 g g?1 in distilled water, and 29 g g?1 in saline (0.9% NaCl solution). The highly porous hydrogel architecture with a pore size of 350–600 µm created a high specific surface area. This enables rapid mass penetration in superabsorbent applications. The superabsorbent hydrogels reached 80% of their maximum water absorption capacity in 30 min. © 2018 Society of Chemical Industry  相似文献   
37.
This paper presents part of the work ComEd and Quanta Technology have performed to quantify the locational and temporal value of DER to avoid distribution grid upgrade investments. It focuses on the formulation of a robust and efficient algorithm for DER optimal dispatch on a distribution feeder to mitigate the violation of current and voltage limits using the allocated cost of capacity and locational marginal value of real and reactive DER injection/withdrawal.  相似文献   
38.
《Planning》2019,(1)
伴随着医疗体系的改革,放射科医生的工作模式正在发生变化,由既往仅书写大量的放射影像报告转变为多学科诊疗团队的核心成员,在患者安全和医疗质量、教育、科普宣传、临床科学研究及卫生经济学等层面均发挥着重要作用。多学科诊疗模式为放射科医生提供了向临床各科室、患者、医疗机构和社会展现自我价值的重要机会。  相似文献   
39.
BackgroundAvocado (Persea americana Mill.) is a tropical and subtropical fruit that is native to Mexico and Central America; avocado is gaining increasing worldwide acceptance and has received extensive marketing and a wide distribution due to its relevant nutritional benefits for human health. Mexico harvests more than 30% of avocados worldwide, representing the main producer and exporter of avocado, which has become a crop of high interest and has great economic impact on Mexico.Scope and approachIn this paper, we describe relevant information on the production, composition and application of avocado, with an emphasis on its by-products, focusing on the proper use of waste and the possibility of monetizing waste for nutritional and environmental purposes. The entire avocado is rich in biocompounds (pulp, seed and peel) and has many health benefits, such as antimicrobial, antioxidant and anticancer activities, as well as dermatological uses and others. In this paper, we demonstrate the current panorama of production, exportation and uses of avocado in Mexico.Key findings and conclusionsSeveral food grade ingredients can be obtained from avocado wastes, particularly premium-grade fats or extracts with a high functional power. Studies should continue to identify the profiles and phytochemicals available to the business sector, which can also be implemented to valorize the nutritional and functional potential of avocado seeds and peels.  相似文献   
40.
《Oil and Energy Trends》2020,45(2):47-51
Values of net oil imports(-)/exports for Austria, Belgium, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, Japan, Canada, the United States and Australia. Updated on a monthly basis. Number of imports for Belgium, France, Germany, Greece, Republic of Ireland, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, and Other EU-15 (EU-15), Norway, Poland, Switzerland, Turkey, and Other Europe (OECD Europe), Canada, Chile, Mexico, and the United States (OECD Western Hemisphere), and Australia, Japan, Republic of Korea, New Zealand, (OECD Asia-Pacific), and Total OECED. Current data for Austria, Belgium, Finland, France, Germany, Greece, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, Other EU-15 (EU-15), Czech Republic, Hungary, Poland, Slovakia, Turkey, and Other Europe (OECD Europe), Canada, Mexico, and the United States (OECD Western Hemisphere), Australia, Japan, Republic of Korea, and New Zealand (OECD Asia-Pacific). Updated on a monthly basis. Current data for principal importers of natural gas and the amount in which they import from United States, Republic of Korea, United Kingdom, France, Japan, Italy, Germany and Spain (Table 19.1). Current data for principal exporters of natural gas and the amount they export to Canada, Trinidad and Tobago, the United States, Netherlands, Norway, Russia, Turkmenistan, Qatar, Algeria, Nigeria, Indonesia, Malaysia and Australia (Table 19.2). Updated on a monthly basis.  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