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   528篇
  免费   12篇
  国内免费   2篇
电工技术   38篇
综合类   2篇
化学工业   155篇
金属工艺   11篇
机械仪表   8篇
建筑科学   7篇
矿业工程   2篇
能源动力   15篇
轻工业   30篇
石油天然气   1篇
武器工业   1篇
无线电   33篇
一般工业技术   117篇
冶金工业   86篇
原子能技术   15篇
自动化技术   21篇
  2023年   3篇
  2022年   3篇
  2021年   6篇
  2019年   4篇
  2018年   2篇
  2017年   10篇
  2016年   10篇
  2015年   5篇
  2014年   10篇
  2013年   38篇
  2012年   21篇
  2011年   31篇
  2010年   19篇
  2009年   22篇
  2008年   14篇
  2007年   23篇
  2006年   13篇
  2005年   19篇
  2004年   15篇
  2003年   17篇
  2002年   13篇
  2001年   7篇
  2000年   18篇
  1999年   19篇
  1998年   31篇
  1997年   22篇
  1996年   17篇
  1995年   12篇
  1994年   18篇
  1993年   12篇
  1992年   4篇
  1991年   9篇
  1990年   7篇
  1989年   10篇
  1988年   5篇
  1986年   3篇
  1985年   7篇
  1984年   2篇
  1983年   5篇
  1982年   3篇
  1981年   6篇
  1980年   6篇
  1979年   4篇
  1978年   3篇
  1977年   1篇
  1976年   5篇
  1975年   2篇
  1974年   1篇
  1972年   2篇
  1966年   1篇
排序方式: 共有542条查询结果,搜索用时 218 毫秒
51.
ABSTRACT

Superheated steam drying of sintered spheres of glass beads with different diameters is investigated to reveal the effects of the gravitational force on drying rates. In a previous study, the drying rate curves of small samples with coarse glass beads in which the frictional resistance to flow of water and the effect of the gravitational force are negligible, were predicted by an evaporation zone model.In the present investigation, the drying rate curves of sintered spheres of glass beads with diameters ranging from 1.53×10-2m to 4.99×lO-2m are experimentally and theoretically obtained, and also the capillary pressure curves are measured by use of Haines' apparatus. The drying rate curves of large samples in which the effect of the gravitational force can not be negligible, are compared with those for small samples and the difference among these curves is discussed in terms of the moisture distributions which are estimated from the evaporation zone model with the observed capillary pressure curves.  相似文献   
52.
53.
54.
Sintered spheres(made of glass beads) were simply produced with a definite diameter, with a precision of ±0·5 mm in diameter, for a wide range of sintered angles (0-27°). The experimental values of the porosity of the sintered spheres were consistent with the calculated results for the coordination number N ≠ 8. The residual equilibrium saturation, as one of the basic physical properties of sintered glass beads was investigated experimentally and theoretically, resulting in the presence of a distribution in the angle of pendular ring.  相似文献   
55.
A microscopic chromatography has been developed where nanometer-size molecules or particles are separated according to their size by the laser-induced shockwave in a water-filled capillary. As the shockwave passed through the mixture of molecules/particles in solution, they move to the direction of the propagation of the shockwave. The distance from the point of shockwave generation depends on the particle size or molecular weight. This technique has some advantages compared to conventional chromatography, in terms of quick analysis of molecular weight and applicability to sticky and adsorbing polymers. Experimental results obtained for proteins, their aggregates, and inorganic nanoparticles are presented.  相似文献   
56.
BACKGROUND: The granaticins are members of the benzoisochromanequinone class of aromatic polyketides, the best known member of which is actinorhodin made by Streptomyces coelicolor A3(2). Genetic analysis of this class of compounds has played a major role in the development of hypotheses about the way in which aromatic polyketide synthases (PKSs) control product structure. Although the granaticin nascent polyketide is identical to that of actinorhodin, post-PKS steps involve different pyran-ring stereochemistry and glycosylation. Comparison of the complete gene clusters for the two metabolites is therefore of great interest. RESULTS: The entire granaticin gene cluster (the gra cluster) from Streptomyces violaceoruber T-22 was cloned on either of two overlapping cosmids and expressed in the heterologous host, Streptomyces coelicolor A3(2), strain CH999. Chemical analysis of the recombinant strains demonstrated production of granaticin, granaticin B, dihydrogranaticin and dihydrogranaticin B, which are the four known metabolites of S. violaceoruber. Analysis of the complete 39,250 base pair sequence of the insert of one of the cosmids, pOJ466-22-24, revealed 37 complete open reading frames (ORFs), 15 of which resemble ORFs from the act (actinorhodin) gene cluster of S. coelicolor A3(2). Among the rest, nine resemble ORFs potentially involved in deoxysugar metabolism from Streptomyces spp. and other bacteria, and six resemble regulatory ORFs. CONCLUSIONS: On the basis of these resemblances, putative functional assignments of the products of most of the newly discovered ORFs were made, including those of genes involved in the PKS and tailoring steps in the biosynthesis of the granaticin aglycone, steps in the deoxy sugar pathway, and putative regulatory and export functions.  相似文献   
57.
A simple analytical model is proposed here that captures to a large extent the kinematic structure of rat exploratory behavior. Previous studies have shown that such behavior consists of regular excursions into the environment from a preferred place termed a home base. In the first part of this study, we showed that with time and repeated exposure to the same large environment, there is a gradual increase in the length of excursions. Concurrently, the rat's velocity pattern changes in a complex yet structured way, which is correlated with the exposure (= familiarity) to places. In this part, we show that the complex pattern described there might be explained by an analytic model, in terms of a simple dynamical system, with few assumptions concerning motivation and learning. The model is studied both by analysis and simulation. The theoretical examination of the dynamics of excursion length suggests that excursion length increases as a linear function of two system parameters, one governing the rate of motivation loss, and the other the rate of (location-specific) familiarization. Combining this theoretical finding with the empirical results suggests that the two theoretical parameters are linearly related: the less confident the rat, the slower its familiarization rate, and thus differences in patterns of movement between rats can be explained using one rat-specific parameter. Furthermore, the more complex velocity pattern of the rat can then be easily captured by the same model. The analyzed behavior of the rat suggests that the locale sensory information that the rat collects has a gradient towards the home base, with decreasing information input away from home base. This sensory pattern emerges from the simple set of rules and restrictions on the rat's exploratory behavior. Thus, instead of imposing a set of ad hoc restrictions on a simulated rat so that its spatial learning is similar to that of a real rat, the model suggests a set of simple intrinsic constraints to govern the exploratory behavior.  相似文献   
58.
A laser-guided BTA tool has been developed to prevent axial hole deviations. Four kinds of experiments were conducted to examine the performance of this tool in detail and to determine its practical application using a duralumin (A2017-T4) workpiece with a prebored 108-mm diameter hole. The first experiment was performed to examine the conditions of the hole deviation in the case of normal deep-hole boring. The second was to examine whether the tool corrects for the stated hole deviation. The third was to examine whether the tool can go straight through to the target without shifting toward a thin wall (t = 0.7 mm) on one side of the workpiece. The fourth was to examine whether the tool can be guided toward the target without affecting a prebored hole, which was inclined to radial direction at 100 μm for a hole length of 100 mm. The experiments were performed with a rotating tool-stationary workpiece system. Rotational speed was 270 rpm and feed ws 0.125 mm/rev. Tool diameter was 110 mm. The results show that the tool can be guided to go straight through toward the target despite the disturbances.  相似文献   
59.
A simple and rapid chromatographic method has been developed for the determination of 2,2,2-trichloroethanol (TCEOH) and its glucuronide in plasma and urine. A glass column (150 x 6.6 mm i.d.) packed with Aminex A-5 cation-exchange resin (potassium form) following the slurry method was used as the analytical column, and an admixture of 10 mmol l-1 potassium sulfate and 10 mmol l-1 potassium hydroxide solution as the eluent (pH 12.2). Diluted plasma samples and urine samples were directly injected into the chromatograph through a 0.45 micron membrane filter without deproteinization. The amount of TCEOH conjugated to glucuronide was determined following treatment with beta-glucuronidase (200 U) for 30 min at 37 degrees C. This allowed the concentration of free, total, and conjugated TCEOH to be determined. The calibration graph was rectilinear from 5 to 500 mg l-1 of TCEOH, with a detection limit of 3 mg l-1, 2 sigma, being the signal-to-noise ratio. The analytical recovery of TCEOH, obtained by analysing spiked plasma and urine samples, was in the range 98.4-102% and the relative standard deviation was less than 3.5%.  相似文献   
60.
The concentration distribution of an antioxidant 2,6-di-tert-butyl-p-cresol (BHT) in the polypropylene (PP) after heating the film containing BHT for a long period of time in succession was studied with use of the rolled film method. The film of 0.003 cm in thickness containing uniformly 710 mg kg?1 of BHT was wound tightly around a glass tube. At the beginning, BHT was distributed uniformly in all layers, and after a given time of the heat treatment at 70–100°C, a remarkable alteration of the concentration distribution of BHT in PP took place. The relations between BHT concentration and the distance from the surface were shown by parabolic curves after heating. The BHT concentration was always kept at almost zero concentration at the surface layer of the rolled film. Assuming that the diffusion obeys Fick's law, the diffusion coefficients at 70, 80, 90, and 100°C were estimated to be 1.05, 4.17, 8.69, and 24.7 × 10?9 cm2 s?1, respectively. The activation energy was calculated as 105 kJ mol?1.  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