全文获取类型
收费全文 | 734739篇 |
免费 | 31266篇 |
国内免费 | 13643篇 |
专业分类
电工技术 | 25440篇 |
技术理论 | 56篇 |
综合类 | 20010篇 |
化学工业 | 117381篇 |
金属工艺 | 31958篇 |
机械仪表 | 32744篇 |
建筑科学 | 37200篇 |
矿业工程 | 11818篇 |
能源动力 | 20560篇 |
轻工业 | 61958篇 |
水利工程 | 8514篇 |
石油天然气 | 24707篇 |
武器工业 | 2612篇 |
无线电 | 90472篇 |
一般工业技术 | 113645篇 |
冶金工业 | 92235篇 |
原子能技术 | 8678篇 |
自动化技术 | 79660篇 |
出版年
2023年 | 5880篇 |
2022年 | 10247篇 |
2021年 | 15005篇 |
2020年 | 11490篇 |
2019年 | 10255篇 |
2018年 | 12827篇 |
2017年 | 14066篇 |
2016年 | 13186篇 |
2015年 | 15456篇 |
2014年 | 21326篇 |
2013年 | 37866篇 |
2012年 | 29936篇 |
2011年 | 36535篇 |
2010年 | 30056篇 |
2009年 | 30748篇 |
2008年 | 31391篇 |
2007年 | 31132篇 |
2006年 | 30641篇 |
2005年 | 27709篇 |
2004年 | 21571篇 |
2003年 | 20105篇 |
2002年 | 18822篇 |
2001年 | 18353篇 |
2000年 | 18060篇 |
1999年 | 20178篇 |
1998年 | 31742篇 |
1997年 | 24066篇 |
1996年 | 19967篇 |
1995年 | 16111篇 |
1994年 | 13969篇 |
1993年 | 12280篇 |
1992年 | 9511篇 |
1991年 | 8666篇 |
1990年 | 7808篇 |
1989年 | 7269篇 |
1988年 | 6821篇 |
1987年 | 5540篇 |
1986年 | 5341篇 |
1985年 | 6298篇 |
1984年 | 5822篇 |
1983年 | 5023篇 |
1982年 | 4676篇 |
1981年 | 4567篇 |
1980年 | 4325篇 |
1979年 | 4134篇 |
1978年 | 3798篇 |
1977年 | 4577篇 |
1976年 | 6139篇 |
1975年 | 3132篇 |
1974年 | 3020篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
203.
204.
三元复合驱油体系中驱油剂的协同效应,会使油水间的界面张力大幅度下降,原油采收率大幅度提高;但三元复合驱油体系的色谱分离现象也会破坏其协同效应和完整性,揭示色谱分离现象及其影响因素对于改善三元复合驱油效果具有十分重要意义。以油藏工程和分析化学理论为指导,以化学分析和物理模拟为技术途径,并以大庆喇嘛甸油田典型区块地质特征和流体性质为研究对象,开展强碱三元复合驱色谱分离现象及其影响因素研究。结果表明,采用前置高浓度聚合物段塞后,可以有效扩大波及体积,但表面活性剂与碱和聚合物之间无因次等浓距增加,色谱分离现象加剧。大庆油区喇嘛甸油田不同区块油水性质差异对色谱分离现象存在影响,原因在于部分重烷基苯石油磺酸进入油相,影响水相中浓度检测值。强碱三元复合驱油体系中表面活性剂与碱和聚合物之间色谱分离程度比较严重,碱与聚合物之间较弱。 相似文献
205.
206.
Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
207.
208.
Lei He Yan Xuan Feng Zhang Xue Wang Huaqing Pan Junfeng Ren Meina Chen 《International Journal of Hydrogen Energy》2021,46(1):1096-1105
Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains. 相似文献
209.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
210.
Theoretical investigation of solvent effects on the selective hydrogenation of furfural over Pt(111)
Jian Wang Cun-Qin Lv Jian-Hong Liu Rong-Rong Ren Gui-Chang Wang 《International Journal of Hydrogen Energy》2021,46(2):1592-1604
It was well known that solvent effect plays a very important role in the catalytic reaction. There are many theoretical studies on the solvent effect in homogeneous catalysis while there are few theoretical studies on the solvent effect in the heterogeneous catalytic reaction and there has been no work to investigate the solvent effect on furfural transformation in heterogeneous catalysis. In the present work, both the density functional calculations and the microkinetic analysis were performed to study the selective hydrogenation of furfural over Pt(111) in the presence of methanol as well as toluene and compared with that in the gas condition. The present results indicated that the methanol can enhance the adsorption strength of furfural and other oxygen-containing reaction species due to its relatively strong polarity properties and this can be a main reason for solvent-induced high activity and selectivity. Another reason is that reaction paths study showed that the presence of methanol solvent makes the dehydrogenation of furfural less thermochemical due to the fact that furfural is more stabilized than that of dehydrogenation species, and methanol also has an inhibition effect on the dehydrogenation of furfural in the kinetic aspect, and further energetic span theory proves highest activity and selectivity for hydrogenation in methanol solvent of vapor, methanol and toluene. Moreover, microkinetic model simulation demonstrated that the activity and selectivity of hydrogenation in methanol is both higher than that in vapor and toluene. The much higher activity in methanol is due to the stabilized adsorbed reactants in the surface, which leads to a higher surface coverage of furfural. It might be proposed based on the present work that a solvent with relatively strong polarity may be favorable for the high selective hydrogenation of furfural. 相似文献