全文获取类型
收费全文 | 7821篇 |
免费 | 191篇 |
国内免费 | 30篇 |
专业分类
电工技术 | 103篇 |
综合类 | 2篇 |
化学工业 | 1404篇 |
金属工艺 | 286篇 |
机械仪表 | 184篇 |
建筑科学 | 103篇 |
矿业工程 | 8篇 |
能源动力 | 309篇 |
轻工业 | 265篇 |
水利工程 | 56篇 |
石油天然气 | 14篇 |
无线电 | 975篇 |
一般工业技术 | 1486篇 |
冶金工业 | 1813篇 |
原子能技术 | 73篇 |
自动化技术 | 961篇 |
出版年
2023年 | 67篇 |
2022年 | 141篇 |
2021年 | 172篇 |
2020年 | 151篇 |
2019年 | 143篇 |
2018年 | 226篇 |
2017年 | 186篇 |
2016年 | 192篇 |
2015年 | 104篇 |
2014年 | 202篇 |
2013年 | 397篇 |
2012年 | 222篇 |
2011年 | 300篇 |
2010年 | 231篇 |
2009年 | 274篇 |
2008年 | 243篇 |
2007年 | 197篇 |
2006年 | 208篇 |
2005年 | 153篇 |
2004年 | 127篇 |
2003年 | 132篇 |
2002年 | 130篇 |
2001年 | 126篇 |
2000年 | 129篇 |
1999年 | 141篇 |
1998年 | 565篇 |
1997年 | 349篇 |
1996年 | 232篇 |
1995年 | 205篇 |
1994年 | 146篇 |
1993年 | 187篇 |
1992年 | 114篇 |
1991年 | 110篇 |
1990年 | 90篇 |
1989年 | 84篇 |
1988年 | 81篇 |
1987年 | 85篇 |
1986年 | 90篇 |
1985年 | 113篇 |
1984年 | 99篇 |
1983年 | 97篇 |
1982年 | 81篇 |
1981年 | 72篇 |
1980年 | 52篇 |
1979年 | 46篇 |
1978年 | 54篇 |
1977年 | 95篇 |
1976年 | 146篇 |
1975年 | 45篇 |
1973年 | 42篇 |
排序方式: 共有8042条查询结果,搜索用时 15 毫秒
61.
In this paper, the authors address the problem of edge-perception for its applications to vision-feedback control in robotic systems.In natural vision, the recognition of objects takes place through the process consisting of eye system, neural networks and cognition. The cognitive process, in turn yields a phenomenon known as perception. This is the phenomenon of perception of physical attributes, such as edges, color and texture, etc., which is responsible for the recognition of objects through the natural vision processes.In this paper, we make an attempt to postulate the theory of perception for gray-level images. The gray-level images, when going through the cognitive and perception processes, are contaminated by the uncertainty; here we call it cognitive uncertainty.The studies in this paper are confined to the phenomenon of edge-perception for two-dimensional gray-level images, however, these studies can be extended to other types of visual attributes both in two-dimensional and three-dimensional spaces. Indeed, the perception of these attributes, which attempts to emulate the human vision system, may help in the design of a truly robust computer vision-feedback control system for robotic applications. 相似文献
62.
Lotka's law and productivity patterns of entomological research in Nigeria for the period, 1900–1973
D. K. Gupta 《Scientometrics》1987,12(1-2):33-46
A bibliography of entomological research in Nigeria, 1900–1973 totally 1720 publications was analysed to study the author productivity patterns and to test the applicability of Lotka's law for the obtained distributions. Four different files were generated, one for the publications of all the authors, second for the publications by first authors, third for single authors and fourth for coauthors. Lotka's law in its original form as inverse square law does not apply to any of the four data sets. However, it does apply in its generalised form with the calculated values of characteristic exponent . The values of were found to be 1.9, 1.8, 2.2 and 2.4 for the four different data sets. K-S statistical test was aplied to test the applicability of generalised form of Lotka's law. The maximum difference in the observed and estimated values of the proportions of authors was found to be highly insignificant at 0.01 level of significance in each of the four cases. 相似文献
63.
R. Gupta G. S. Sekhon K. S. Shishodia 《Journal of Materials Processing Technology》1997,70(1-3):274-278
The grinding operation is considered to be equivalent to a moving band source of heat and mechanical load on the surface of a semi-infinite solid, producing very high temperature on the surface of the workpiece. The resulting temperature may result in high stress in the workpiece. It is thus desirable to be able to predict the stress levels expected during the grinding process. 相似文献
64.
65.
A commonly used energy-efficient nylon 6 reactor is simulated under steady-state conditions. The effects of various operating conditions and parameters, e.g., feed composition, temperature and flow rate, heat transfer coefficients, and reactor dimensions, on the temperature and molecular weight profiles are studied. A temperature maximum is observed in the reactor under usual conditions of operation. The maximum value of the temperature is sensitive to the feed conditions, and one has to ensure that degradation reactions speeded up at high temperatures do not affect product characteristics. The model and the numerical technique used are fairly simple and account for most of the important features of industrial reactors. Hence, these can be used in the development of digital-control algorithms in the future. 相似文献
66.
A. R. Pal D. P. Motiramani S. B. Gupta B. S. Bhargava 《Nutrient Cycling in Agroecosystems》1990,22(3):129-136
Attempts were made to find out the nature and cause of a widespread sugarcane chlorosis in a cane growing area. Soils from chlorotic and nonchlorotic fields did not differ markedly in pH, CaCO3, electrical conductivity, organic C, and soil test P, Zn, Cu, and Mn levels, but the chlorotic field soils had relatively more NH4OAc-extractable K and less clay and DTPA-extractable Fe. Chlorotic and green leaf blades contained about the same concentration of P, S, Mg, Fe, Zn, Cu, and Mo, but the former leaf blades had more K and less Ca and HCl soluble Fe than the green ones. Green leaves of plants that seemed to have naturally recovered in chlorotic fields were higher in Mn. A foliage spray with 2.5% FeSO4.7H2O solution resulted in greening of leaves and a field experiment showed marked crop response to Fe and some response to Mn. The results thus suggest that the chlorosis is due to a lime-induced Fe-deficiency with the possibility of some role of Mn in Fe nutrition in calcareous soil conditions.Deceased 22 September 1988 相似文献
67.
The pyrolysis under nitrogen of salt free and salt treated cellulose was studied by infrared spectroscopy. The results confirm the unzipping mechanism suggested by DTA and TGA studies, and show this mechanism to apply to the untreated and salt treated samples. The results also show the unzipping to stop at the stage of char formation. The onset of this stage was found to occur after the volatilization of only 45–50% of the initial sample of the borax treated cellulose, compared with 65–70% of the KCl treated cellulose and 80–85% of the untreated cellulose. 相似文献
68.
Petr Švec Atul Thakur Eric Raboin Brual C. Shah Satyandra K. Gupta 《Autonomous Robots》2014,36(4):383-405
The capability of following a moving target in an environment with obstacles is required as a basic and necessary function for realizing an autonomous unmanned surface vehicle (USV). Many target following scenarios involve a follower and target vehicles that may have different maneuvering capabilities. Moreover, the follower vehicle may not have prior information about the intended motion of the target boat. This paper presents a trajectory planning and tracking approach for following a differentially constrained target vehicle operating in an obstacle field. The developed approach includes a novel algorithm for computing a desired pose and surge speed in the vicinity of the target boat, jointly defined as a motion goal, and tightly integrates it with trajectory planning and tracking components of the entire system. The trajectory planner generates a dynamically feasible, collision-free trajectory to allow the USV to safely reach the computed motion goal. Trajectory planning needs to be sufficiently fast and yet produce dynamically feasible and short trajectories due to the moving target. This required speeding up the planning by searching for trajectories through a hybrid, pose-position state space using a multi-resolution control action set. The search in the velocity space is decoupled from the search for a trajectory in the pose space. Therefore, the underlying trajectory tracking controller computes desired surge speed for each segment of the trajectory and ensures that the USV maintains it. We have carried out simulation as well as experimental studies to demonstrate the effectiveness of the developed approach. 相似文献
69.
Melt rheological properties of the ternary blend of isotactic polypropylene (PP), styreneethylene–butylene–styrene terpolymer (SEBS), and polycarbonate (PC), PP/SEBS/PC, are studied in a wide range of composition, such that PP is the matrix and SEBS and PC are the minor components, with the proportion of one varying from 0 to 30% at various fixed compositions of the other. The respective binary blends, PP/SEBS and PP/PC, studied as the reference systems for interpretation of results on the ternary blends yielded interesting new information about the morphology development and its correlation with melt rheological properties of these binary blends. The studies include the measurement of melt rheological properties on a capillary rheometer in the shear rate range 101–104 s?1 at a fixed temperature of 240°C. The data presented as conventional flow curves are analyzed for the effect of blend composition and shear rate on pseudoplasticity, melt viscosity, and melt elasticity, and role of each individual component is identified. Morphology of dispersed phases of these blends is studied through scanning electron microscopy of the cryogenically fractured and suitably etched surfaces. Variations of morphology with blend composition and shear rate showed interesting correlation with melt rheological properties, which are discussed in detail. An important finding of the morphological studies is that in the PP/SEBS/PC ternary blend the SEBS phase forms two types of morphologies depending on the blend composition and shear rate: (i) simple droplets and (ii) boundary layer at the surface of the PC droplets. © 1993 John Wiley & Sons, Inc. 相似文献
70.
A cadmium ethylenediamine solvent (cadoxen) of modified composition containing 0.5 M sodium hydroxide, 5% cadmium, and 28–30 % ethylenediamine was found to dissolve high molecular cotton materials even under higher ambient temperature conditions as in India. The stability of cellulose solutions in this solvent was still high enough to enable viscosity measurements without exclusion of air. Intrinsic Viscosity values were determined for a large number of cellulosic materials. A study of the kinetics of degradation of cellulosic solutions in cadoxen gave comparatively higher rate constants in nitrogen atmosphere and a higher energy of activation as compared to other alkaline solvents indicating that degradation in cadoxen cannot be considered primarily oxidative in nature. 相似文献