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   3945篇
  免费   71篇
  国内免费   3篇
电工技术   32篇
综合类   2篇
化学工业   936篇
金属工艺   78篇
机械仪表   84篇
建筑科学   154篇
矿业工程   12篇
能源动力   155篇
轻工业   293篇
水利工程   43篇
石油天然气   11篇
无线电   320篇
一般工业技术   790篇
冶金工业   484篇
原子能技术   22篇
自动化技术   603篇
  2024年   65篇
  2023年   64篇
  2022年   126篇
  2021年   182篇
  2020年   117篇
  2019年   121篇
  2018年   128篇
  2017年   116篇
  2016年   137篇
  2015年   109篇
  2014年   164篇
  2013年   260篇
  2012年   226篇
  2011年   286篇
  2010年   206篇
  2009年   168篇
  2008年   173篇
  2007年   184篇
  2006年   121篇
  2005年   103篇
  2004年   103篇
  2003年   87篇
  2002年   83篇
  2001年   43篇
  2000年   41篇
  1999年   37篇
  1998年   72篇
  1997年   72篇
  1996年   36篇
  1995年   36篇
  1994年   27篇
  1993年   25篇
  1992年   24篇
  1991年   17篇
  1990年   29篇
  1989年   18篇
  1988年   11篇
  1987年   9篇
  1986年   11篇
  1985年   17篇
  1984年   9篇
  1983年   13篇
  1982年   9篇
  1981年   13篇
  1980年   11篇
  1979年   10篇
  1977年   9篇
  1976年   21篇
  1975年   8篇
  1974年   9篇
排序方式: 共有4019条查询结果,搜索用时 0 毫秒
81.
82.
ABSTRACT

An experimental study was conducted to apply the jet spouted bed (JSB) dryer with inert bodies for drying of fodder antibiotic; (zinc-salt bacitracin and tylosin) and baker's yeast which are extracted from fermentation broth. After establishing the drving properties of these products (e.g. sorption isotherm, water activity and thermostability), the influence of basic drying parameters (temperature of drying agent, bed loading, gas flow rate) on drying characteristics and quality of the products was determined. The results proved that a JSB dryer may be successfully applied to fodder antibiotics; especially to Zn-bacitracin; however, for a highly labile live organism like baker's yeast, this method cannot be used. The optimal parameters for drying of Zn-bacitracin have been presented.  相似文献   
83.
An inter-comparison study of instruments designed to measure the microphysical and optical properties of soot particles was completed. The following mass-based instruments were tested: Couette Centrifugal Particle Mass Analyzer (CPMA), Time-of-Flight Aerosol Mass Spectrometer—Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Soot Particle-Aerosol Mass Spectrometer (SP-AMS) and Photoelectric Aerosol Sensor (PAS2000CE). Optical instruments measured absorption (photoacoustic, interferometric, and filter-based), scattering (in situ), and extinction (light attenuation within an optical cavity). The study covered an experimental matrix consisting of 318 runs that systematically tested the performance of instruments across a range of parameters including: fuel equivalence ratio (1.8 ≤ φ ≤ 5), particle shape (mass-mobility exponent ( D fm ), 2.0 D fm ≤ 3.0), particle mobility size (30 d m ≤ 300 nm), black carbon mass (0.07 ≤ m BC ≤ 4.2 fg) and particle chemical composition. In selected runs, particles were coated with sulfuric acid or dioctyl sebacate (DOS) (0.5 ≤ Δ r ve ≤ 201 nm) where Δ r ve is the change in the volume equivalent radius due to the coating material. The effect of non-absorbing coatings on instrument response was determined. Changes in the morphology of fractal soot particles were monitored during coating and denuding processes and the effect of particle shape on instrument response was determined. The combination of optical and mass based measurements was used to determine the mass specific absorption coefficient for denuded soot particles. The single scattering albedo of the particles was also measured. An overview of the experiments and sample results are presented.  相似文献   
84.
The effect of scale, processing conditions, interfacial tension and viscosity of the dispersed phase on power draw and drop size distributions in three in-line Silverson rotor–stator mixers was investigated with the aim to determine the most appropriate scaling up parameter. The largest mixer was a factory scale device, whilst the smallest was a laboratory scale mixer. All the mixers were geometrically similar and were fitted with double rotors and standard double emulsor stators. 1 wt.% silicone oils with viscosities of 9.4 mPa s and 339 mPa s in aqueous solutions of surfactant or ethanol were emulsified in single and multiple pass modes. The effect of rotor speed, flow rate, dispersed phase viscosity, interfacial tension and scale on drop size distributions was investigated.  相似文献   
85.
Thyroid hormones play a critical role in the growth and development of the alimentary tract in vertebrates. Their effects are mediated by nuclear receptors as well as the cell surface receptor integrin αVβ3. Systemic thyroid hormone levels are controlled via activation and deactivation by iodothyronine deiodinases in the liver and other tissues. Given that thyroid hormone signaling has been characterized as a major effector of digestive system growth and homeostasis, numerous investigations have examined its role in the occurrence and progression of cancers in various tissues of this organ system. The present review summarizes current findings regarding the effects of thyroid hormone signaling on cancers of the esophagus, stomach, liver, pancreas, and colon. Particular attention is given to the roles of different thyroid hormone receptor isoforms, the novel integrin αVβ3 receptor, and thyroid hormone-related nutrients as possible protective agents and therapeutic targets. Future investigations geared towards a better understanding of thyroid hormone signaling in digestive system cancers may provide preventive or therapeutic strategies to diminish risk, improve outcome and avert recurrence in afflicted individuals.  相似文献   
86.
A new group of nonionic dicephalic saccharide amides, N-dodecyl-N,N-bis[(3-d-gluconylamido)propyl]-amine, N-dodecyl-N,N-bis[(3-d-glucoheptonylamido)propyl]-amine, and N-alkyl-N,N-bis[(3-lactobionylamido)propyl]amines (alkyl: n-C12H25′ n-C16H33′, n-C18H37) were synthesized and characterized. Their structure and purity were confirmed by means of 1H and 13C nuclear magnetic resonance analysis and electrospray ionization mass spectrometry. Carbon spectra were verified using a DEPT experiment. The surface and interfacial properties such as critical micelle concentration (CMC), standard free energy of micellization, ΔG CMC, surface excess concentration, ΓCMC, and surface area demand per molecule, A CMC, were determined. The tertiary nitrogen atom seems to have a surprising effect on surfactnat packing at the interface.  相似文献   
87.
88.
89.
The article presents the results of research on the use of the new technology of friction welding with a non-wearing tool for welding pipe ends with lids. The pipes and lids were made of aluminium alloy EN AW 2017A, non-weldable by conventional methods. The aim of the study was to verify the possibility of welding the lid to the pipe using the FSW method as well as a new method with a tool with specially profiled friction surface. The article presents the results of structural tests and strength tests of the weld joints obtained using the new technique.  相似文献   
90.
This paper presents results of analyses of water in the river Ma?a Panew in South West Poland flowing through a rural area with some chemical industry developed. The aims of the work were to investigate the pollutants level in the river, compare the obtained results with obligatory drinking water standards and determine possible health effects when using the river as a source for drinking water production. Attention was given to nitrogen compounds as nitrate(V) ions (NO(3-)) and nitrite(III) ions (NO(2-)), mostly of anthropogenic origin, were detected in the monitored water. The average concentrations of NO(3-) and NO(2-) were 3.54 and 0.286 mg/dm(3), respectively. The chances for non-carcinogenic effects, namely methemoglobinemia, resulting from possible exposure to the examined chemicals were determined based on the analytical and toxicological data. As infants are the sub-population most susceptible to nitrate-induced methemoglobinemia, the assessment was limited to children aged 0-3 years. The determined values expressed by hazard quotient (HQ) and hazard index (HI) indicate that the water pollutants and their concentrations do not exceed unity; however, in the case of infants, the other nitrate sources should be controlled.  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