全文获取类型
收费全文 | 85833篇 |
免费 | 6236篇 |
国内免费 | 2909篇 |
专业分类
电工技术 | 4372篇 |
技术理论 | 9篇 |
综合类 | 4649篇 |
化学工业 | 14987篇 |
金属工艺 | 4506篇 |
机械仪表 | 5266篇 |
建筑科学 | 6994篇 |
矿业工程 | 1997篇 |
能源动力 | 2490篇 |
轻工业 | 4943篇 |
水利工程 | 1448篇 |
石油天然气 | 4481篇 |
武器工业 | 492篇 |
无线电 | 10418篇 |
一般工业技术 | 11209篇 |
冶金工业 | 4632篇 |
原子能技术 | 828篇 |
自动化技术 | 11257篇 |
出版年
2024年 | 149篇 |
2023年 | 1254篇 |
2022年 | 1764篇 |
2021年 | 2996篇 |
2020年 | 2314篇 |
2019年 | 2007篇 |
2018年 | 2227篇 |
2017年 | 2490篇 |
2016年 | 2341篇 |
2015年 | 2953篇 |
2014年 | 4037篇 |
2013年 | 5099篇 |
2012年 | 5292篇 |
2011年 | 5555篇 |
2010年 | 4936篇 |
2009年 | 4747篇 |
2008年 | 4503篇 |
2007年 | 4427篇 |
2006年 | 4675篇 |
2005年 | 4165篇 |
2004年 | 2793篇 |
2003年 | 2518篇 |
2002年 | 2203篇 |
2001年 | 2030篇 |
2000年 | 2289篇 |
1999年 | 2570篇 |
1998年 | 2390篇 |
1997年 | 1841篇 |
1996年 | 1710篇 |
1995年 | 1438篇 |
1994年 | 1213篇 |
1993年 | 881篇 |
1992年 | 657篇 |
1991年 | 539篇 |
1990年 | 404篇 |
1989年 | 364篇 |
1988年 | 312篇 |
1987年 | 168篇 |
1986年 | 156篇 |
1985年 | 103篇 |
1984年 | 91篇 |
1983年 | 59篇 |
1982年 | 57篇 |
1981年 | 50篇 |
1980年 | 39篇 |
1979年 | 32篇 |
1978年 | 13篇 |
1977年 | 33篇 |
1976年 | 16篇 |
1975年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
82.
Wax deposit properties are a significant concern in pipeline pigging during waxy crude oil transportation. In the present work, the impacts of flow conditions and oil properties on the wax precipitation characteristics of wax deposits are investigated. A flow loop apparatus was developed to conduct wax deposition experiments using four crude oils collected from different field pipes. The differential scanning calorimetry (DSC) technique was employed to observe the wax precipitation characteristics of crude oil and wax deposit. The results show that the wax content and the wax appearance temperature (WAT) of the deposits increase with shear stress and radial temperature gradient, and decrease with radial wax molecule concentration gradient near the pipe wall. The DSC tests on the wax deposits revealed that the deposit wax content is strongly correlated to the oil wax content. Furthermore, an empirical correlation was developed to predict the wax content and the WAT of the wax deposit. Verification of the empirical correlation using the different oils indicated that the average relative error of the wax content prediction and average absolute error of WAT prediction were 13.2% and 3.6°C, respectively. 相似文献
83.
86.
87.
Hai Huang Haichao An Haibo Ma Shenyan Chen 《International journal for numerical methods in engineering》2019,117(3):291-315
This work presents an engineering method for optimizing structures made of bars, beams, plates, or a combination of those components. Corresponding problems involve both continuous (size) and discrete (topology) variables. Using a branched multipoint approximate function, which involves such mixed variables, a series of sequential approximate problems are constructed to make the primal problem explicit. To solve the approximate problems, genetic algorithm (GA) is utilized to optimize discrete variables, and when calculating individual fitness values in GA, a second-level approximate problem only involving retained continuous variables is built to optimize continuous variables. The solution to the second-level approximate problem can be easily obtained with dual methods. Structural analyses are only needed before improving the branched approximate functions in the iteration cycles. The method aims at optimal design of discrete structures consisting of bars, beams, plates, or other components. Numerical examples are given to illustrate its effectiveness, including frame topology optimization, layout optimization of stiffeners modeled with beams or shells, concurrent layout optimization of beam and shell components, and an application in a microsatellite structure. Optimization results show that the number of structural analyses is dramatically decreased when compared with pure GA while even comparable to pure sizing optimization. 相似文献
88.
Jianmou Lu Yanli Huang Shunyan Ren 《International Journal of Control, Automation and Systems》2020,18(5):1250-1263
This paper investigates the general decay synchronization and general decay H∞ synchronization problems of multi-weighted coupled reaction-diffusion 相似文献
89.
采用大气熔炼铸造及热变形方法制备了Al-4.5Cu-1Li-0.7Mg-1Zn-0.3Ag-0.3Mn-0.2Zr新型铝锂合金板材。通过维氏硬度、拉伸性能、扫描电镜、透射电镜等方法,研究了固溶后不同冷轧预变形量对显微组织和力学性能影响。结果表明,时效前的冷轧预变形量有效促进了新型铝锂基体合金中T1(Al2CuLi)相的析出与均匀分布,减少了θ′(Al2Cu)相的体积分数。冷轧预变形量的增加,缩短了峰时效时间,晶界析出相由连续析出变为非连续析出,无沉淀析出区宽度变小。当冷轧预变形量为15%时,时效态合金的屈服强度与抗拉强度分别达到了668 MPa、690 MPa,延伸率保持在7.9%。 相似文献
90.
The in-situ fabrication of an electron-blocking layer between the Ba-containing anode and the ceria-based electrolyte is an effective approach in suppressing the internal electronic leakage in ceria-based solid oxide fuel cell (SOFC). To improve the thickness of the electron-blocking layer and to research the effect of the layer thickness on the improvement of SOFC, a Ba-containing compound (0.6NiO-0.4BaZr0.1Ce0.7Y0.2O3-δ) modified by Y stabilized zirconia (YSZ) was employed as a composite anode in this research. SEM analyses demonstrated that the thickness of the interlayer can be simply controlled by regulating the proportion of YSZ at anode. The in-situ formed interlayer in the cell with the anode modified by 20?mol% YSZ possesses a thickness of 0.9?µm which is more suitable for the cell achieving an enhanced performance. 相似文献