全文获取类型
收费全文 | 233361篇 |
免费 | 1500篇 |
国内免费 | 244篇 |
专业分类
电工技术 | 3938篇 |
综合类 | 206篇 |
化学工业 | 34553篇 |
金属工艺 | 15552篇 |
机械仪表 | 10159篇 |
建筑科学 | 4259篇 |
矿业工程 | 2519篇 |
能源动力 | 3320篇 |
轻工业 | 9983篇 |
水利工程 | 3699篇 |
石油天然气 | 9658篇 |
武器工业 | 12篇 |
无线电 | 20503篇 |
一般工业技术 | 55265篇 |
冶金工业 | 32797篇 |
原子能技术 | 7756篇 |
自动化技术 | 20926篇 |
出版年
2018年 | 10365篇 |
2017年 | 10912篇 |
2016年 | 7655篇 |
2015年 | 2150篇 |
2014年 | 3041篇 |
2013年 | 6398篇 |
2012年 | 6588篇 |
2011年 | 12645篇 |
2010年 | 11530篇 |
2009年 | 10769篇 |
2008年 | 10820篇 |
2007年 | 12556篇 |
2006年 | 4208篇 |
2005年 | 6795篇 |
2004年 | 5440篇 |
2003年 | 5071篇 |
2002年 | 4077篇 |
2001年 | 3530篇 |
2000年 | 3504篇 |
1999年 | 3242篇 |
1998年 | 7031篇 |
1997年 | 5156篇 |
1996年 | 3836篇 |
1995年 | 2929篇 |
1994年 | 2633篇 |
1993年 | 2746篇 |
1992年 | 2273篇 |
1991年 | 2330篇 |
1990年 | 2411篇 |
1989年 | 2317篇 |
1988年 | 2324篇 |
1987年 | 2194篇 |
1986年 | 2248篇 |
1985年 | 2298篇 |
1984年 | 2207篇 |
1983年 | 2137篇 |
1982年 | 1987篇 |
1981年 | 2200篇 |
1980年 | 2057篇 |
1979年 | 2276篇 |
1978年 | 2437篇 |
1977年 | 2438篇 |
1976年 | 3101篇 |
1975年 | 2247篇 |
1974年 | 2310篇 |
1973年 | 2346篇 |
1972年 | 2159篇 |
1971年 | 1916篇 |
1970年 | 1704篇 |
1969年 | 1689篇 |
排序方式: 共有10000条查询结果,搜索用时 906 毫秒
121.
V. M. Bozrov 《Journal of Machinery Manufacture and Reliability》2018,47(3):213-220
A methodology for estimation of the limit energy characteristics of volumetric pneumatic motors based on the Parameter Space Investigation method and a generalized mathematical model in dimensionless (normalized) form taking into account the dynamics of working processes is proposed. A calculated example is presented. The methodology is applicable for determination of the limit energy characteristics of newly created design solutions, of prospects to improve the known designs of pneumatic motors, of evaluation of energy capacity of several pneumatic motors supplied from a single source of compressed air, and of the initial data preparation for parametric synthesis of rotational pneumatic drives for two or more robots taking into account their interaction. 相似文献
122.
Konstantin V. Dergilev Evgeny K. Shevchenko Zoya I. Tsokolaeva Irina B. Beloglazova Ekaterina S. Zubkova Maria A. Boldyreva Mikhail Yu. Menshikov Elizaveta I. Ratner Dmitry Penkov Yelena V. Parfyonova 《International journal of molecular sciences》2020,21(24)
Cell therapy of the post-infarcted myocardium is still far from clinical use. Poor survival of transplanted cells, insufficient regeneration, and replacement of the damaged tissue limit the potential of currently available cell-based techniques. In this study, we generated a multilayered construct from adipose-derived mesenchymal stromal cells (MSCs) modified to secrete stem cell factor, SCF. In a rat model of myocardium infarction, we show that transplantation of SCF producing cell sheet induced activation of the epicardium and promoted the accumulation of c-kit positive cells in ischemic muscle. Morphometry showed the reduction of infarct size (16%) and a left ventricle expansion index (0.12) in the treatment group compared to controls (24–28%; 0.17–0.32). The ratio of viable myocardium was more than 1.5-fold higher, reaching 49% compared to the control (28%) or unmodified cell sheet group (30%). Finally, by day 30 after myocardium infarction, SCF-producing cell sheet transplantation increased left ventricle ejection fraction from 37% in the control sham-operated group to 53%. Our results suggest that, combining the genetic modification of MSCs and their assembly into a multilayered construct, we can provide prolonged pleiotropic effects to the damaged heart, induce endogenous regenerative processes, and improve cardiac function. 相似文献
123.
124.
125.
The dynamic interaction between the mechanical and electrical drive parameters when damage suddenly appears in the mechanical part of a conveyer belt is investigated. The possibility of using the change in the motor’s electrical parameters as a diagnostic signal is assessed. A model for investigating the dynamic processes in the system consisting of the grid, the induction motor, and the conveyer belt is proposed. The grid and induction motor are described by a model of fourth-order state space, whose output is the torque at the motor shaft. The moments of inertia and pliability of the links between the elements in the mechanical part of the conveyer belt are determined. By gradually identifying the elements with the minimum moment of inertia and distributing their moments of inertia and pliabilities among the adjacent elements, we obtain a three-mass system simulating the mechanical part of the conveyer belt. This dynamic model is solved by means of Matlab Simulink software. The energy characteristics of the drive are determined in dynamic processes following a mechanical accident. 相似文献
126.
127.
An agriglass composition containing different oxides acts as a slow release for macro and micro nutrients and was chosen to improve maize yield under most important abiotic stresses which affecting agriculture development; salinity and drought. A field experiment was performed in salt affected soil (EC =?7.5 dSm??1) by using different water deficit rates (I1 = 100, I2 = 85 and I3 = 70% of maize water requirements). Irrigation levels were located in main plots. Every main-plot divided into six sub-plots contained glassy fertilizer treatments [F1 = 55 kg fed?1 with 1/2 mm diameter of agriglass (fed. =?4200 m2), F2 = 55 kg fed?1 with 1 mm diameter, F3 = 80 kg fed?1 with 1/2 mm diameter, F4 = 80 kg fed?1 with 1 mm diameter, F5 = Recommendations of Ministry of Agriculture and F6 = control]. The experimental results demonstrated that, ears, straw, grains and biological yields increased with increasing both water and agriglass rates. Application of agriglass as a slow release fertilizer improved yield more than mineral fertilizer. Some growth parameters, water use efficiency (IWUE), macronutrients concentration and their relations were included. Other studies on residual effect of agriglass and the annual application rates to withstand salinity and drought stress by strategic crops are required. 相似文献
128.
Advanced technologies and modern high-production machines for underground mining of thick gently dipping coal demand strict adherence to technological discipline, reduction in operational loss and selection of optimized ventilation modes. The authors analyze ventilation schemes used in working areas in thick gently dipping seams in order to reveal influence exerted by the schemes, methods and parameters of ventilation on distribution of air loss in mined-out areas. 相似文献
129.
Semiconductors - The optical properties of dielectric nanostructures strongly depend on dielectric nanoparticles (NP) polarizability which can take the high values even interacting with... 相似文献
130.
Ahmed Obaid M. Alzahrani M. Sh. Abdel-wahab Meshari Alayash M. S. Aida 《Journal of Materials Science: Materials in Electronics》2018,29(19):16317-16324
In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector. 相似文献