全文获取类型
收费全文 | 252322篇 |
免费 | 29317篇 |
国内免费 | 26609篇 |
专业分类
电工技术 | 20914篇 |
技术理论 | 8篇 |
综合类 | 15506篇 |
化学工业 | 57945篇 |
金属工艺 | 10886篇 |
机械仪表 | 14175篇 |
建筑科学 | 9446篇 |
矿业工程 | 3243篇 |
能源动力 | 18899篇 |
轻工业 | 17932篇 |
水利工程 | 2549篇 |
石油天然气 | 6035篇 |
武器工业 | 2212篇 |
无线电 | 35326篇 |
一般工业技术 | 29469篇 |
冶金工业 | 7176篇 |
原子能技术 | 5247篇 |
自动化技术 | 51280篇 |
出版年
2024年 | 1254篇 |
2023年 | 4870篇 |
2022年 | 8984篇 |
2021年 | 10539篇 |
2020年 | 9428篇 |
2019年 | 8644篇 |
2018年 | 7899篇 |
2017年 | 10157篇 |
2016年 | 10791篇 |
2015年 | 11796篇 |
2014年 | 12678篇 |
2013年 | 16778篇 |
2012年 | 18022篇 |
2011年 | 21340篇 |
2010年 | 15422篇 |
2009年 | 15047篇 |
2008年 | 15956篇 |
2007年 | 17422篇 |
2006年 | 16334篇 |
2005年 | 13921篇 |
2004年 | 11736篇 |
2003年 | 9398篇 |
2002年 | 7392篇 |
2001年 | 5726篇 |
2000年 | 4850篇 |
1999年 | 3959篇 |
1998年 | 3300篇 |
1997年 | 2673篇 |
1996年 | 2167篇 |
1995年 | 1774篇 |
1994年 | 1566篇 |
1993年 | 1181篇 |
1992年 | 1007篇 |
1991年 | 790篇 |
1990年 | 672篇 |
1989年 | 509篇 |
1988年 | 383篇 |
1987年 | 241篇 |
1986年 | 221篇 |
1985年 | 286篇 |
1984年 | 242篇 |
1983年 | 163篇 |
1982年 | 231篇 |
1981年 | 122篇 |
1980年 | 124篇 |
1979年 | 41篇 |
1978年 | 23篇 |
1977年 | 29篇 |
1959年 | 33篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
981.
982.
Hwar-Ching Ku Bala Ramaswamy 《International journal for numerical methods in engineering》1995,38(4):667-683
A new multi-grid (two-grid) pseudospectral element method has been carried out for solution of incompressible flow in terms of primitive variable formulation. The main objective of the proposed method is to apply the multi-grid technique solving the incompressible flow problems associated with three commonly encountered multi-grid environments. In domain decomposition terminology, it includes (I) partially overlapped subdomains, each of which has same types of grids; (II) partially overlapped subdomains, each of which has different types of grids; (III) local adaptive subdomains fully overlapped with the original computational domain (composite grids). The approach for flow problems, complex geometry or not, is to first divide the computational domain into a number of subdomains with the inter-overlapping area (partially or fully overlapped). In categories I and II, the fine-grid or coarse-grid subdomains can be defined by their representation, while in category III the fine-grid or coarse-grid subdomains are defined as usual. Next, implement the Schwarz Alternating Procedure (SAP) to exchange the data among subdomains, where the coarse-grid correction is used to remove the high frequency error that occurs when the data interpolation from the fine-grid subdomain to the coarse-grid subdomain is conducted. The strategy behind the coarse-grid correction is to adopt the operator of the divergence of velocity field, which intrinsically links the pressure equation, into this process. The solution of each subdomain can be efficiently solved by the direct (or iterative) eigenfunction expansion technique or preconditioned method with the least storage requirement, i.e. O(N2) in 2-D. Numerical results of (i) driven cavity flow (Re = 100,400) with Cartesian grids (category I) in each subdomain, (ii) driven cavity flow (Re = 3200) with local adaptive grids (category III) in each subdomain, and (iii) flow over a cylinder (Re = 250) with ‘O’ grids in one subdomain and Cartesian grids in another (category II) will be presented in the paper to account for the versatility of the proposed multi-grid method. 相似文献
983.
广州市住宅直饮水设计定额的确定 总被引:1,自引:0,他引:1
对住宅直饮水系统的实际运营情况进行了分析,运营中出现的销售水量低于直饮水定额、制水设备实际工作时间低于额定时间及水表工作不正常等现象都反映了现行直饮水设计定额的不合理性,建议将用水量定额定为5~8L/(户·d),既符合实际情况又能满足居民远期需求。 相似文献
984.
985.
986.
Titipong Issariyakul Mangesh G. KulkarniAjay K. Dalai Narendra N. Bakhshi 《Fuel Processing Technology》2007
Transesterification of waste fryer grease (WFG) containing 5–6 wt.% free fatty acid (FFA) was carried out with methanol, ethanol, and mixtures of methanol/ethanol maintaining the oil to alcohol molar ratio of 1:6, and initially with KOH as a catalyst. Mixtures of methanol and ethanol were used for transesterification in order to use the better solvent property of ethanol and rapid equilibrium using methanol. Formation of soap by reaction of FFA present in WFG with KOH instigated difficulty in the separation of glycerol from biodiesel ester. To untangle this problem, two-stage (acid and alkali catalyzed) method was used for biodiesel synthesis. More than 90% ester was obtained when two-stage method was used compared to ∼ 50% ester in single stage alkaline catalyst. In the case of mixed alcohol, a relatively smaller amount of ethyl esters was formed along with methyl esters. Acid value, viscosity, and cetane number of all the esters prepared from WFG were within the range of the ASTM standard. Esters obtained from WFG showed good performance as a lubricity additive. 相似文献
987.
U(Ⅳ)-U(Ⅵ)同位素交换反应动力学研究 Ⅰ.Fe~(2+)对U(Ⅳ)-U(Ⅵ)同位素交换反应的催化作用 总被引:1,自引:0,他引:1
一、前言由于U(IV)-U(VI)同位素交换体系具有相当大的同位素效应和很好的稳定性,并且容易实现两相回流,这对于分离U同位素的工业应用都是十分有利的。但是,U(IV)-U(VI)同位素交换反应速度非常慢,常温下H~+浓度为1.0—4.0 mol/l时,速度常数为1.0×10~(-4)l~2/mol·s。因此要用U(IV)-U(VI)交换体系浓缩铀同位素,必须研究U(IV)-U(VI)交换反应动力学,找到加快交换反应的方法。 相似文献
988.
989.
990.
This study has explored the potential energy surface on the chemical reaction of CH2OH with NO by using ab initio calculation. We have found the new reaction pathway producing N-hydroxy formamide, which can further decompose to generate isocyanic acid as a reducing agent of hydrocarbons selective catalytic reduction. 相似文献