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   2623篇
  免费   65篇
  国内免费   4篇
电工技术   32篇
综合类   10篇
化学工业   495篇
金属工艺   76篇
机械仪表   53篇
建筑科学   49篇
能源动力   89篇
轻工业   136篇
水利工程   4篇
石油天然气   4篇
无线电   437篇
一般工业技术   438篇
冶金工业   469篇
原子能技术   16篇
自动化技术   384篇
  2023年   10篇
  2022年   38篇
  2021年   55篇
  2020年   20篇
  2019年   23篇
  2018年   33篇
  2017年   32篇
  2016年   49篇
  2015年   55篇
  2014年   79篇
  2013年   172篇
  2012年   116篇
  2011年   144篇
  2010年   139篇
  2009年   166篇
  2008年   136篇
  2007年   144篇
  2006年   102篇
  2005年   77篇
  2004年   82篇
  2003年   59篇
  2002年   71篇
  2001年   48篇
  2000年   44篇
  1999年   45篇
  1998年   192篇
  1997年   96篇
  1996年   78篇
  1995年   42篇
  1994年   54篇
  1993年   32篇
  1992年   26篇
  1991年   31篇
  1990年   22篇
  1989年   18篇
  1988年   11篇
  1987年   10篇
  1986年   12篇
  1985年   16篇
  1984年   16篇
  1983年   8篇
  1982年   11篇
  1981年   12篇
  1980年   10篇
  1979年   8篇
  1978年   5篇
  1977年   9篇
  1976年   8篇
  1975年   5篇
  1973年   5篇
排序方式: 共有2692条查询结果,搜索用时 109 毫秒
101.
This paper addresses the architecture and implementation of a medical drawing management system. The system enables physicians to draw directly on a patient picture or built-in anatomical templates of a body part. It contains modules for querying patient data and managing associated drawings including sketching, uploading, and sharing features. The system adapts to embed Windows-based applications into web pages; the web-based applications contain Windows-based graphical tools and enable seamlessly incorporating necessary drawing modules into the web-based healthcare information system at National Taiwan University Hospital. The system provides a web-based sketching capability that effectively support practitioners’ daily operations, as well as the use of paperless, digitizing patient records, and ultimately, will improve the overall quality of healthcare.  相似文献   
102.
Summary Syntheses of potential initiators N-(O-(1-phenylethyl)oxy)phthalimide, N-(O-(1-phenylmethyl)oxy)phthalimide (POP), cyclohexanone-O-(1-phenylethyl)oxime, and cyclohexanone-O-(1-phenylmethyl)oxime (CHPO) are described. Bulk polymerization of styrene in the presence of POP or CHPO and molecular weight measurement by GPC indicate that the polymerization is not a living process. Ab initio calculations show that the C-O or O-N bond cleavage energies of POP and CHPO are close to each other (3: C-O: 46.4, O-N: 47.3 kcal/mol; 1: C-O: 46.9, O-N: 63.0 kcal/mol) and much higher than the similar analogs of 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) (C-O: 20.9, O-N: 34.4 kcal/mol). The similar C-O and O-N bond cleavage energies of the synthesized initiators (POP/CHPO) indicate two possible cleavage pathways and may explain the non-living nature of the polymerization. These results may be helpful in finding future reversible terminator compounds for living polymerization. Received: 28 August 2000/Revised version: 5 December 2000/Accepted: 7 December 2000  相似文献   
103.
At least 44,000 people die in hospitals each year as a result of medical errors, and these deaths are becoming the eighth-leading cause of death in the United States. Thus, medical providers have the responsibility to pay attention for reducing avoidable medical errors and improve patient safety as best as they can. It requires the rapid evaluation and prioritisation of life threatening injuries in the primary survey followed by a detailed secondary survey in the emergency room. However, time is always valuable and limited such that some important vital signs may be delayed and ignored. This research explores delayed diagnosis problem and uses the affinity set by Topology concept to classify/focus on key attributes causing delayed diagnosis (missed injury) in order to reduce error risk. Results interestingly indicate that when a patient can breathe normally, but his (or her) blood-pressure or pulse is abnormal, a high probability of delayed diagnosis exists. This affinity work also compares the performance with the model of rough set (Rosetta), neural network, support vector machine and logistic regression. And our affinity model shows its advantage by prediction accuracy and explanation power.  相似文献   
104.
Chitosan has received extensive attention as a biomedical material; however, the poor solubility of chitosan is the major limiting factor in its utilization. In this study, chitosan‐based biomaterials with improved aqueous solubility were synthesized. Two molecular weights (750 Da and 2000 Da) of methoxypoly(ethylene glycol) (mPEG) were grafted onto chitosan (mPEG‐g‐chitosan) to form a ~100‐μm‐thick plastic film as a wound dressing. The chemical structures of the mPEG‐g‐chitosan copolymers were confirmed using Fourier transform infrared spectroscopy (FTIR), and the thermal properties were characterized using thermogravimetry analysis (TGA). Their microstructures were observed using scanning electron microscopy (SEM). The other properties were analyzed via the swelling ratio, tensile strength, elongation, and water vapor transmission rate (WVTR). Biocompatibility evaluations through biodegradability, cytotoxicity, and antimicrobial effect studies were also performed. The obtained mPEG‐g‐chitosan copolymers were soluble in slightly acidic aqueous solutions (pH~6.5) at a concentration of 10 wt %. The optimal mPEG‐g‐chitosan hydrogels had swelling ratios greater than 100% and WVTRs greater than 2000 g/m2/day. Their performance against Staphylococcus aureus will be subjected to further improvements with respect to medical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42340.  相似文献   
105.
Journal of Mechanical Science and Technology - The predictive maintenance of wind turbines has become a critical issue with the rapid development of wind power generation. The early detection of...  相似文献   
106.
It is customary to assume a frequency distribution in flood frequency analysis. The parameters of the distribution are estimated by using observed or transformed data. The fitted distribution is then used to estimate the magnitudes of floods of different frequencies.

The maximum entropy (ME) probability distribution is defined as the 'minimally prejudiced probability distribution which maximizes the entropy subject to constraints supplied by the given information'. In spite of many attractive features of the ME distribution, it has not been used in its general form in practice. The main reason for not using the ME distribution in its general form is that the parameter estimation problem associated with the ME distribution is not easy. Recently this problem has been solved and an algorithm has been developed to estimate the parameters of the ME distribution.

The objective of the research reported in the present paper is to fit ME distributions to flood data. The ME distributions are compared with other well known distributions. The computational aspects and selection of orders of distributions are also discussed. The ME distribution is shown to be versatile and fits a variety of flood data very well.  相似文献   
107.
This article discusses the appropriate dispersant for titania (TiO2) nanopowder in organic‐based suspensions. Four types of oleyl‐based dispersants, namely, oleyl alcohol, oleic acid, oleylamine, and oleyl phosphate, which have the functional groups hydroxyl (–OH), carboxyl (–COOH), amino (–NH2), and phosphorous [–P(=O)(OH)2], respectively, were compared for their ability to disperse TiO2. Experimental results for zeta potential, adsorption, FT‐IR spectroscopy, and rheology, as well as theoretical calculations, indicate that dispersants with –P(=O)(OH)2 and –NH2 were more efficient than those with –COOH or –OH. The primary reason for this difference is related to the different interactions of TiO2 with various dispersants and to different dispersion mechanisms. In addition to the major functional groups, –OH in the chemical structure of dispersants was important, as it might have other effects such as destabilization of the suspensions.  相似文献   
108.
This study uses the solution mixing method to combine plasticized polyvinyl alcohol (PVA) as a matrix, and multiwalled carbon nanotubes (MWCNTs) as reinforcement to form PVA/MWCNTs films. The films are then laminated and hot pressed to create PVA/MWCNTs composites. The control group of PVA/MWCNTs composites is made by incorporating the melt compounding method. Diverse properties of PVA/MWCNTs composites are then evaluated. For the experimental group, the incorporation of MWCNTs improves the glass transition temperature (Tg), crystallization temperature, Tc), and thermal stability of the composites. In addition, the test results indicate that composites containing 1.5 wt % of MWCNTs have the maximum tensile strength of 51.1 MPa, whereas composites containing 2 wt % MWCNTs have the optimal electrical conductivity of 2.4 S/cm, and electromagnetic shielding effectiveness (EMI SE) of ?31.41 dB. This study proves that the solution mixing method outperforms the melt compounding method in terms of mechanical properties, dispersion, melting and crystallization behaviors, thermal stability, and EMI SE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43474.  相似文献   
109.
The organic ionic exchange intercalation of smectite clays is conventionally performed in water swelling conditions. Here we report a different mechanism for modifying the smectite clays in alcohol solvents. The modification of sodium montmorillonite with poly(oxyethylene-oxypropylene)-amines (POA-amine) were compared for the differences between in water and in alcohol. In water, the intercalation of hydrophobic poly(oxypropylene)-rich amines in the silicate galleries expands the interlayer spacing up to 10 nm and even to exfoliation (featureless in X-ray diffraction pattern) with over 5 amine equivalents, where as hydrophilic poly(oxyethylene)-rich amines could only intercalate in a low spacing of 1.8 nm. On the other hand, all of the POA-amines in isopropanol afford the exfoliation with over, 3 amine equivalents. The mechanism of this unexpected exfoliation is explained by the thermodynamic formations of an imaginary membrane surrounding the clay units, followed by amine diffusion from the solvent into the clay galleries.  相似文献   
110.
Blends of polylactide (PLA) and recycled polypropylene (rPP) were prepared by melt-processing using a corotating twin-screw extruder and subsequent pelletizing of the extrudates for injection molding. The PLA/rPP blends were characterized by Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), rheometer (MCR-102), scanning electron microscopy(SEM), tensile tests, and impact measurements. The results indicate that the PLA/rPP blend is immiscible and has a two-phase structure. TGA revealed enhancement of the thermal stability of the blends upon addition of rPP. The storage modulus, loss modulus, and complex viscosity of the blends increased with rPP concentration. Mechanical studies showed that introduction of rPP results in a decrease in tensile strength and modulus and enhancement of the impact strength of PLA in the blends. The effects of a silane coupling agent on the morphology and on the tensile and impact properties of the rPP blends of silane-modified PLA were also examined. SEM studies suggest that silane is an effective interfacial modifier. Thus, better interfacial adhesion was observed with silane-modified blends as compared with unmodified blends. Silane also improved the mechanical properties of the modified blends. The blends reached maximum tensile strength at 1.5 wt.% silane (relative to modified PLA content), and impact strength increased with increasing silane concentration. These results confirm the enhancing effect of silane on modified PLA/rPP blends.  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