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   1423篇
  免费   79篇
  国内免费   16篇
电工技术   27篇
综合类   7篇
化学工业   381篇
金属工艺   41篇
机械仪表   61篇
建筑科学   51篇
矿业工程   14篇
能源动力   96篇
轻工业   105篇
水利工程   10篇
石油天然气   41篇
无线电   133篇
一般工业技术   259篇
冶金工业   58篇
原子能技术   4篇
自动化技术   230篇
  2024年   3篇
  2023年   28篇
  2022年   65篇
  2021年   89篇
  2020年   65篇
  2019年   87篇
  2018年   123篇
  2017年   90篇
  2016年   82篇
  2015年   50篇
  2014年   76篇
  2013年   162篇
  2012年   90篇
  2011年   98篇
  2010年   65篇
  2009年   72篇
  2008年   37篇
  2007年   25篇
  2006年   24篇
  2005年   19篇
  2004年   14篇
  2003年   16篇
  2002年   12篇
  2001年   10篇
  2000年   3篇
  1999年   6篇
  1998年   12篇
  1997年   5篇
  1996年   2篇
  1995年   12篇
  1994年   3篇
  1993年   5篇
  1992年   8篇
  1991年   9篇
  1990年   4篇
  1989年   2篇
  1988年   4篇
  1987年   3篇
  1986年   2篇
  1985年   6篇
  1984年   2篇
  1983年   2篇
  1981年   4篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1976年   5篇
  1975年   4篇
  1974年   6篇
  1973年   2篇
排序方式: 共有1518条查询结果,搜索用时 62 毫秒
91.
Milk of high conjugated linoleic acid (CLA) level (1.25 g per 100 g milk fat) was produced by inclusion of fish oil and rousted soy bean in the ration of Holstein cows as compared to 0.55 g per 100 g milk fat in the milk of animals receiving control diet. Milk of normal (control) and high CLA content (treatment) was spray‐dried. Labneh was made from 20 g L?1 reconstituted milk using 3 mL per 100 mL yoghurt starter and 2 mL per 100 mL of probiotic cultures of Lactobacillus casei or Lactobacillus acidophilus. The control (C) and high CLA (T) labneh were analysed chemically and microbiologically, and their viscosities were determined during cold storage for 15 days. The fat content of labneh of high CLA was less than that of the control, but the total solids (TS) were unaffected by the CLA level. Labneh made with Lb. acidophilus had lower TS and higher acidity, exopolysaccharides and acetaldehyde contents and viscosity than that made with the use of Lb. casei. Labneh from the different treatments retained high counts of the added probiotic (>108 cfu g?1) throughout the storage period. The storage period had significant effects on all parameters determined.  相似文献   
92.
The mechanical performance of cemented paste backfill (CPB) placed in underground openings (e.g., mine stopes) often differs from laboratory-predicted performance, even under the same atmospheric curing conditions (ambient temperature and relative humidity). This is probably due to the specific self-weight consolidation, different drainage conditions and confinement pressures encountered in the paste backfilled stopes. A new test system named CUAPS (Curing Under Applied Pressure System) was designed at the Université du Québec en Abitibi-Témiscamingue (UQAT) to assess the hydro-mechanical performance of in situ CPB samples at laboratory scale. The CUAPS apparatus allows the effective curing of CPB samples subjected to an assortment of vertical pressure applications (curing under stresses) that can mimic in situ placement and consolidation conditions. The compressive strength development of CPB samples prepared from sulphide-rich mine tailings from Garpenberg polymetallic mine (Sweden) was investigated using CUAPS apparatus and conventional plastic moulds (unconsolidated undrained samples) in parallel. The effect of curing stress (i.e. simulating different consolidation conditions) on resultant geotechnical index parameters and hydromechanical properties of CPB samples was analyzed. The primary observation is the confirmation that the compressive strength development of the consolidated CPB samples is higher than that of unconsolidated undrained ones. It could be attributed to the removal of excess pore water mainly due to the applied pressure during the effective curing process, which seems to improve consolidation process of the CPB material. The results also account for the differences in the CPB strength observed between laboratory samples and in situ samples. Thus, CUAPS would be more suitable than conventional plastic moulds to collect data for preliminary and final design of CPB systems.  相似文献   
93.
The aim of this work is to study the effect of phase composition and microstructure of cordierite-based co-clinkers on the electrical properties and coefficient of thermal expansion of cordierite briquettes. To achieve this aim talc and kaolinite samples were collected from quarries in the Egyptian desert. The samples are characterized using XRD, XRF, polarized light, cathodoluminescence and SEM microscopy attached with EDAX, in addition to X-ray micro-computed tomography (3D- µXCT). The electrical properties and coefficient of thermal expansion of the cordierite briquettes are determined using HiTESTER instrument and automatic Netzsch DIL402 PC dilatometer, respectively.Five talc-based batches were shaped and fired in the temperature range 1000–1350 °C for 2 h. The microstructural and physical characteristics of the resulted cordierite-based co-clinkers depend mainly on the viscosity of the liquid phase developed during firing. The microchemistry of the cordierite briquettes confirms their enrichment of both cordierite and ferroan-cordierite crystallized directly from locally developed melts. The dielectric constant and loss factor values for cordierite briquettes allow their possible use as insulator components in electronic applications.  相似文献   
94.
This study investigates the efficiency of top Arab banks using two quantitative methodologies: data envelopment analysis and neural networks. The study uses a probabilistic neural network (PNN) and a traditional statistical classification method to model and classify the relative efficiency of top Arab banks. Accuracy indices are used to assess the classification accuracy of the models. Results indicate that the predictive accuracy of NN models is quite similar to that of traditional statistical methods. The study shows that the NN models have a great potential for the classification of banks’ relative efficiency due to their robustness and flexibility of modeling algorithms. From a policy perspective, this study highlights the economic importance of encouraging increased efficiency throughout the banking industry in the Arab world.  相似文献   
95.
The impact of induced lipolysis on the composition of plasma lipids is analyzed by proton magnetic resonance spectroscopy (MRS) in humans. The variations of the methylene and methyl resonances from lipids in lipoproteins are studied under two sets of lipolytic conditions: acute endovascular lipolysis induced by an intravenous injection of heparin and subacute lipolysis induced by short fasting. During acute lipolysis, the degradation of the very low density lipoproteins structures is well correlated to the modifications observed in the areas of CH2 and CH3 MRS signals. The comparison of regular spectra, spectra with water signal suppression, and spectra recorded with a spin-echo sequence provides information on the behavior of the different parts of the lipoproteins, that is, the neutral core, little affected by heparine-induced lipoprotein lipase (LPL) activation, and the surface layer supplying substrates to LPL. During 48 h of fasting, only limited modifications occur on the MR spectra, and lipolysis cannot be documented in details.Address for correspondence: CRMBM-CNRS, Faculté de Médecine, 27, bd Jean Moulin, 13005 Marseille, France.  相似文献   
96.
Vibro-acoustography is a method that produces images of the acoustic response of a material to a localized harmonic motion generated by ultrasound radiation force. The low-frequency, oscillatory radiation force (e.g., 10 kHz) is produced by amplitude modulating a single ultrasound beam, or by interfering two beams of slightly different frequencies. Proper beam forming for the stress field of the probing ultrasound is very important because it determines the resolution of the imaging system. Three beam-forming geometries are studied: amplitude modulation, confocal, and x-focal. The amplitude of radiation force on a unit point target is calculated from the ultrasound energy density averaged over a short period of time. The profiles of radiation stress amplitude on the focal plane and on the beam axis are derived. The theory is validated by experiments using a small sphere as a point target. A laser vibrometer is used to measure the velocity of the sphere, which is proportional to the radiation stress exerted on the target as the transducer is scanned over the focal plane or along the beam axis. The measured velocity profiles match the theory. The theory and experimental technique may be useful in future transducer design for vibro-acoustography.  相似文献   
97.
Mobile computing systems provide users with access to information regardless of their geographical location. In these systems, Mobile Support Stations (MSSs) play the role of providing reliable and uninterrupted communication and computing facilities to mobile hosts. The failure of a MSS can cause interruption of services provided by the mobile system. Two basic schemes for tolerating the failure of MSSs exist in the literature. The first scheme is based on the principle of checkpointing used in distributed systems. The second scheme is based on state information replication of mobile hosts in a number of secondary support stations. Depending on the replication scheme used, the second approach is further classified as a pessimistic or an optimistic technique. In this paper, we propose a hybrid scheme which combines the pessimistic and the optimistic replication schemes. In the proposed scheme, an attempt is made to strike a balance between the long delay caused by the pessimistic and the high memory requirements of the optimistic schemes. In order to find the best ratio between the number of pessimistic to the number of optimistic secondary stations in the proposed scheme, we used fuzzy logic. We also used simulation to compare the performance of the proposed scheme with those of the optimistic and the pessimistic schemes. Simulation results showed that the proposed scheme performs better than either schemes in terms of delay and memory requirements.  相似文献   
98.
ABSTRACT

The present study is an investigation to demonstrate the effectiveness of in situ approach in the synthesis of hydroxyapatite-grafted titanium nanotube composite (HA-TNT). This method involves combining the process of HA sol–gel and rapid breakdown anodisation of titanium in a novel solution consisting of NaCl and N3PO4. This new synthesis approach produced a uniform dispersion of Anatase and Rutile phases of TiO2 nanotubes with minimal agglomeration in the matrix of crystalline HA. The characterisation of homogenised HA-TNT composite was investigated via field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD). FESEM and TEM images indicated the nanostructure of composite with TiO2 nanotube diameter of approximately 10 nm. XRD and EDS analyses confirmed the formation of HA crystalline with the Ca/P ratio of 1.58 and formation of Anatase and Rutile phase of TiO2 nanotubes.  相似文献   
99.
Sorption of Mo(VI) from aqueous nitrate solutions onto zirconium molybdosilicate (ZrMoSi) gel was studied using 99Mo radiotracer. The acid–base titration curve showed that the prepared ZrMoSi gel was an amphoteric material with the point of zero charge (PZC) at pH 2.5. The highest distribution coefficient (600 mL g–1) of 99Mo(VI) on ZrMoSi from nitrate media was achieved at pH 2.1. The sorption kinetics of 99Mo(VI) onto ZrMoSi obeyed the pseudo-second-order model. The breakthrough sorption capacity of ZrMoSi gel was found to be 4.25 × 10–2 [mmol Mo(VI)] g–1. The prepared 99Mo/99mTc chromatographic column generator showed a good performance: The 99mTc elution yield was 87.7%, pH of the eluate ranged from 5.6 to 7.2, and the radionuclidic purity of the eluted 99mTc was >99.99% with a radiochemical purity of 98.31% (as 99mTcO4).  相似文献   
100.
This article presents a numerical formulation and experimental implementation for the dynamics behavior verification of the nonlinear piezoelectric beam through harmonic excitation. The nonlinear piezoelectric beam dynamic analysis program is developed with MATLAB software. To verify the nonlinear piezoelectric beam dynamic analysis results, the experimental results are used for the vibration analysis of a piezoelectric beam to the harmonic excitation of the base of the beam. Then, the piezoelectric effect on the output voltage, velocity, acceleration values, and the time response are obtained. Afterwards, the effects of the excitation velocity and the position of concentrated mass on the output voltage are verified.  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