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   3270篇
  免费   233篇
  国内免费   19篇
电工技术   30篇
综合类   8篇
化学工业   913篇
金属工艺   94篇
机械仪表   96篇
建筑科学   98篇
矿业工程   4篇
能源动力   256篇
轻工业   425篇
水利工程   34篇
石油天然气   38篇
武器工业   1篇
无线电   299篇
一般工业技术   642篇
冶金工业   146篇
原子能技术   26篇
自动化技术   412篇
  2024年   8篇
  2023年   76篇
  2022年   97篇
  2021年   229篇
  2020年   152篇
  2019年   178篇
  2018年   187篇
  2017年   180篇
  2016年   188篇
  2015年   139篇
  2014年   210篇
  2013年   329篇
  2012年   212篇
  2011年   275篇
  2010年   161篇
  2009年   122篇
  2008年   94篇
  2007年   77篇
  2006年   64篇
  2005年   40篇
  2004年   38篇
  2003年   43篇
  2002年   40篇
  2001年   30篇
  2000年   33篇
  1999年   19篇
  1998年   40篇
  1997年   21篇
  1996年   20篇
  1995年   17篇
  1994年   19篇
  1993年   14篇
  1992年   5篇
  1991年   16篇
  1990年   10篇
  1989年   7篇
  1988年   13篇
  1987年   8篇
  1986年   12篇
  1985年   10篇
  1984年   9篇
  1983年   12篇
  1982年   9篇
  1981年   7篇
  1978年   6篇
  1977年   9篇
  1976年   7篇
  1975年   4篇
  1974年   6篇
  1971年   3篇
排序方式: 共有3522条查询结果,搜索用时 171 毫秒
991.
The increasing demand for storage, networking and computation has driven intensification of large complex data centers that run many of today's Internet, financial, commercial and business applications. A data center comprises of many thousands of servers and can use as much energy as small city. Massive amount of computation power is required to drive and run these server farms resulting in many challenging like huge energy consumptions, emission of green house gases, backups and recovery; This paper proposes energy efficiency and low carbon enabler green IT framework for these large and complex server farms to save consumption of electricity and reduce the emission of green house gases to lower the effects of global warming. The framework uses latest energy saving techniques like virtualization, cloud computing and green metrics to achieve greener data centers. It comprises of five phase to properly implement green IT techniques to achieve green data centers. The proposed framework seamlessly divides data center components into different resource pools and then applies green metrics like Power Usage Effectiveness, Data Center Effectiveness and Carbon Emission Calculator to measure performance of individual components so that benchmarking values can be achieved and set as standard to be followed by data centers.  相似文献   
992.
The development and introduction of injectable biomaterials and the identification of methods through which materials may form in situ are currently the topics of interest in materials science, specifically in the field of biomaterials. Over the last few decades, hydrogels which refers to the swellable polymeric matrices have gained wide attention due to their excellent characteristics such as swelling in different media, pH and temperature sensitivity, and sensitivity to other stimuli. Nowadays, injectable hydrogels have widely been studied due to their excellent insitu gelation at body temperature. These injectable insitu gels serve as depot system which ensures the local and systemic drug and gene delivery. These insitu gels also protect the proteins and peptide drugs invivo from environmental effect. The current review is made to report latest extensive literature regarding hydrogels, their classification, synthesis methods, structure of hydrogel network, methods of crosslinking, environment-sensitive hydrogel system, drug loading, and release, hydrogels as biosensors and applications of hydrogels.  相似文献   
993.
This paper studies optimization of three design parameters (mass ratio, frequency ratio and damping ratio) of multiple tuned mass dampers MTMDs that are applied in a cable stayed bridge excited by a strong wind using minimax optimization technique. ABAQUS finite element program is utilized to run numerical simulations with the support of MATLAB codes and Fast Fourier Transform FFT technique. The optimum values of these three parameters are validated with two benchmarks from the literature, first with Wang and coauthors and then with Lin and coauthors. The validation procedure detected a good agreement between the results. Box-Behnken experimental method is dedicated to formulate the surrogate models to represent the control efficiency of the vertical and torsional vibrations. Sobol’s sensitivity indices are calculated for the design parameters in addition to their interaction orders. The optimization results revealed better performance of the MTMDs in controlling the vertical and the torsional vibrations for higher mode shapes. Furthermore, the calculated rational effects of each design parameter facilitate to increase the control efficiency of the MTMDs in conjunction with the support of the surrogate models.  相似文献   
994.
We present the design analysis of a point focused electron beam emitter using numerical techniques. Simulation and modeling were performed followed by the calculation of emission parameters using programming codes EGUN and CST-PS. Beam emittance, average current density and perveance were calculated and are in agreement with the experimental values obtained at 10 kV acceleration potential. The emission parameters were evaluated up to 110 kV. This confirms possibilities of potential application of emitter for a linear accelerator.  相似文献   
995.
The purpose of this study was to investigate the effect of packaging film on physicochemical properties, microbial profile, and biogenic amines content of barramundi (Lates calcarifer Bloch) fillets packed in polyamide, polypropylene, and low-density polyethylene films and kept at 8°C more than 20 days under modified atmosphere packaging. Putrescine and cadaverine were the most abundant amines, whereas the concentration of histamine ranged from less than 0.5 (not detected) to 198.0, 264.3, and 308.5 mg/kg for polyamide, polypropylene, and polyethylene (low-density polyethylene) films, respectively. Among the three, the psychrotrophic bacteria count was initially 4.26 log colony forming units/g and exceeded the acceptable limit of 7 log colony forming units/g on the 16th day of storage for polyamide and on 12th day of storage for polypropylene and polyethylene. However, the total plate count, among the three packaging films, was initially 3.54 log colony forming units/g and exceeded the acceptable limit of 6 log colony forming units/g on the 12th day of storage. The histamine-forming bacteria count was significantly (p < 0.05) lower in barramundi fillets packaged with polyamide compared to polypropylene and polyethylene. The significant difference (p < 0.05) was observed between the concentration of amines in polyamide as compared with polypropylene and polyethylene. Among the three packaging materials, polyamide was found to be the best for prolonging the storage of barramundi fillets.  相似文献   
996.
997.
This study investigated the probiotic characteristics of lactic acid bacteria (LAB) isolated from 14 Malaysian fermented food or milk products. In total, 22.3% (121 of 542) of the LAB isolated from the local fermented products exhibited antibacterial activity against Micrococcus luteus. Twelve LAB that demonstrated better antibacterial activity against M. luteus as compared to a commercial strain Lactobacillus casei strain Shirota (LABPC) were selected for further characterisation. Based on 16S rRNA gene sequence, the LAB were identified as pediococci (seven) and lactobacilli (five). All 12 LAB showed bile tolerance, but only eight were acid tolerant at pH ≥ 3.0. The highest level of adhesion to HT‐29 cells was observed among the Lactobacillus sp. LAB 1 and 10. The LAB also showed antimicrobial activity against Escherichia coli and Staphylococcus aureus through the production of organic acids. LAB isolated from Malaysian fermented food and milk products, especially fermented tapioca, contains potential probiotic candidates.  相似文献   
998.
Temperature distribution, velocity and pressure profiles during high pressure compression (500 MPa) of liquid food (water) and solid–liquid food mixture (beef fat and water), within a three dimensional cylinder basket is simulated. The computations domain in both cases was performed for a cylinder with a diameter of 38 mm and height of 290 mm, which are the same dimensions of the high pressure unit “FOOD-LAB model S-FL-850-9-W” available at the University of Auckland, New Zealand. The governing equations for continuity, momentum and energy conservation are solved using a commercial computational fluid dynamics (CFD) package (PHOENICS), version 3.5, which is based on a finite volume method of solution. The simulation for liquid food only shows the effect of forced and free convection flow on the temperature distribution in the liquid at the early stages of compression. This is due to the difference between the velocity of the pumping fluid as it enters the cylinder inlet hole (10−2–10−3) m s−1 and the velocity in the treatment chamber (10−8–10−9) m s−1. The simulation for the solid–liquid mixture shows as well, the temperature distribution in the solid and liquid at different stages of compression. It shows that the solid pieces are more heated than the liquid, which is due to the difference in their compression heating coefficient. Validation of the computed temperature in both cases is found to be in an agreement with those measured experimentally and reported in the literature.  相似文献   
999.
The focus in Uzbekistan on cotton and its irrigation led to large increases in water use with significant downstream impacts, particularly on the Aral Sea. While agriculture is still heavily influenced by the state, Uzbekistan has become more integrated in the global economy since its independence. The major goal of this paper is to examine the interrelationship between agricultural policies and water use during the last 15 years and how moves towards freer markets, such as those which might occur under the World Trade Organization, may impact Uzbekistan's water resources in the future. The results show that partial or full market liberalization may result in an increase in water use. However, the greater message is that non-water policies can have a major impact on water outcomes and therefore should be considered in any discussions of water sector reform.  相似文献   
1000.
A study on development of Fourier-transform infrared spectrophotometric method combined with principle component analysis as well as real-time polymerase chain reaction for determination of pork–beef mixture in meatballs has been performed. A lipid component extracted from pork and beef in meatballs is analyzed using Fourier-transform infrared spectroscopy, while DNA extracted from meatball was analyzed using real-time polymerase chain reaction. The correlation between actual and predicted concentration of lard using Fourier-transform infrared spectroscopy was performed by aid of partial least squares, while grouping of lard and beef fat components in meatball was carried out by Fourier-transform infrared spectra coupled with principle component analysis. The results showed that Fourier-transform infrared spectra at wavenumbers of 1000–1200 cm?1 coupled with partial least square and principle component analysis are successfully used for quantification and classification of pork in beef meatballs. The relationship between actual value and predicted value of lard (lipid fraction obtained from meatballs containing pork) with Fourier-transform infrared spectrophotometric method revealed good correlation, with coefficient determination (R2) value of 0.997 and standard error of calibration of 0.04%. Principle component analysis is able to classify samples containing pork and beef meatballs. Fourier-transform infrared spectroscopy using normal spectra is fast technique for identification and quantification of lard extracted from pork in meatball. In addition, real-time polymerase chain reaction using Leptin Primer–AJ 865080 can be used for amplification of pork DNA specifically in meatballs containing pork.  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