全文获取类型
收费全文 | 50547篇 |
免费 | 6239篇 |
国内免费 | 3775篇 |
专业分类
电工技术 | 4953篇 |
技术理论 | 1篇 |
综合类 | 4539篇 |
化学工业 | 6512篇 |
金属工艺 | 3242篇 |
机械仪表 | 3710篇 |
建筑科学 | 3921篇 |
矿业工程 | 1867篇 |
能源动力 | 1425篇 |
轻工业 | 4826篇 |
水利工程 | 1550篇 |
石油天然气 | 1845篇 |
武器工业 | 620篇 |
无线电 | 5809篇 |
一般工业技术 | 4952篇 |
冶金工业 | 2088篇 |
原子能技术 | 705篇 |
自动化技术 | 7996篇 |
出版年
2024年 | 346篇 |
2023年 | 1039篇 |
2022年 | 2118篇 |
2021年 | 3013篇 |
2020年 | 2108篇 |
2019年 | 1504篇 |
2018年 | 1723篇 |
2017年 | 1737篇 |
2016年 | 1697篇 |
2015年 | 2575篇 |
2014年 | 2983篇 |
2013年 | 3651篇 |
2012年 | 4097篇 |
2011年 | 4249篇 |
2010年 | 3856篇 |
2009年 | 3660篇 |
2008年 | 3535篇 |
2007年 | 3416篇 |
2006年 | 3066篇 |
2005年 | 2468篇 |
2004年 | 1745篇 |
2003年 | 1235篇 |
2002年 | 1198篇 |
2001年 | 1040篇 |
2000年 | 895篇 |
1999年 | 397篇 |
1998年 | 227篇 |
1997年 | 173篇 |
1996年 | 147篇 |
1995年 | 129篇 |
1994年 | 71篇 |
1993年 | 64篇 |
1992年 | 62篇 |
1991年 | 30篇 |
1990年 | 39篇 |
1989年 | 53篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 29篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 14篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process. 相似文献
2.
3.
镁钴铝类水滑石催化合成安息香甲醚 总被引:1,自引:0,他引:1
采用共沉淀法制备了镁钴铝类水滑石化合物(MgCoAl-HTLcs),并用 X 射线衍射、扫描电子显微镜、NH_3程序升温脱附等方法对 MgCoAl-HTLcs 进行了表征,并以 MgCoAl-HTLcs 为催化剂催化苯甲醛与甲醇反应合成安息香甲醚,研究了n(Mg):n(Co):n(Al)、催化剂用量、原料配比、反应温度、反应时间对合成反应的影响。表征结果显示,MgCoAl-HTLcs 的晶相完整,表面主要为弱酸、弱碱性。催化合成安息香甲醚的适宜条件为:MgCoAl-HTLcs 催化剂用量0.10 g(约为原料总质量的0.23%),n(Mg):n(Co):n(Al)=0.4:1.6:1.0,V(苯甲醛):V(甲醇)=3:50,反应温度50℃,反应时间150 min。在此条件下,苯甲醛的平衡转化率达77.49%,安息香甲醚选择性接近100%。为洁净合成安息香甲醚开辟了一条新的途径。 相似文献
4.
A 66-kV network generally is grounded through a neutral grounding resistor. In this network a single-phase ground-fault current is limited to as small as 100 to 400 A. There are parallel four-circuit transmission lines mounted on the same tower in the 66-kV network. In such transmission lines, the load and the fault currents could induce circulating current that flows through the lines. Since the circulating current has zero-phase-sequence and negative-phase-sequence components, it could cause unwanted operation of a balance ground relay using zero-phase-sequence current. However, it is difficult to compensate for the circulating current by the conventional vector compensation scheme. This paper presents a new balance ground relay to deal with the circulating current. In the relay from the ground-fault inception until first tripping, the difference current Δ3I2d of negative-phase-sequence current 3I2d of the differential current between two protected lines is used as an input current. The Δ3I2d is the difference current of 3I2d between, before and during faults. After the first tripping, the difference current of positive-phase-sequence load current and zero-phase-sequence current of the forementioned differential current are used as an input current. Consequently, a higher sensitivity of the ground-fault protection for these lines has been achieved. The correct operation of the new balance ground relay was confirmed when a single-phase-ground-fault occurred in the parallel four-circuit transmission lines, to which the relay is applied. 相似文献
5.
Yu Yang Hugo Bender Kai Arstila Bart Swinnen Bert Verlinden Ingrid De Wolf 《Microelectronics Reliability》2008,48(8-9):1517-1520
Focused ion beam (FIB) and nano-probing were applied for failure analysis of three-dimensional stacked circuits with copper through-silicon-vias between the stacked chips. The failure analysis was done after high temperature storage and thermal cycling tests. Passive voltage contrast in FIB allowed to pinpoint the open sites. FIB cross-sections showed the presence of opens at the bottom of the copper vias. The failure cause was suspected to be an interlayer particle, which was confirmed by optical profilometry. Nano-probing was used on another sample to pinpoint the failure location through the measurement of the local resistance within the daisy chains. The failure was traced out to be related with surface contamination. 相似文献
6.
Ben J. A. Kr se Kai M. Compagner Franciscus C. A. Groen 《Robotics and Autonomous Systems》1993,11(3-4):221-230
This paper describes a robust and accurate ultrasonic sensing system for a mobile robot. The system continuously updates a local map of the environment in which obstacles are represented by straight lines or points in a robot centered coordinate frame. The presented algorithms use a Kalman filter for the reduction of the noise in the ultrasonic data and use a systematical error correction (‘bundle correction’) to reduce the uncertainty in obstacle direction. Experiments are carried out in simulation and with a real mobile robot system. Results show that the accuracy with which line parameters can be estimated is in the order of 1 degree for the orientation and about 2 cm for the position. The effect of the bundle correction is significant and maximal when the robot approaches walls under a small angle. 相似文献
7.
本文讨论了用辉光放电法制备氮化硅薄膜时衬底温度、射频功率和气体流量比对薄膜的电导率、介电常数和击穿强度的影响。通过优化生长条件,制备了优质非晶氮化硅薄膜,其介电常数为7.5、击穿强度为5.5MV/cm、电导率为10-13(Ωcm)-1。 相似文献
8.
石油系油浆与煤系闪蒸油的焦化性能——I.热解条件的影响 总被引:3,自引:2,他引:1
通过偏光显微镜观察了石油系油浆(LH)与煤系闪蒸油(SN)焦化后所得焦块的光学结构。结果表明,在较宽条件下两种原料单独焦化均得不到取向度高的流线型结构。将两种原料以一定比例混合后先热解丙焦化所得焦块的光学结构明显好于二者混合后直接焦化所得焦块的光学结构,其中LH和SN以3:2的重量比混合后在440℃、1MPa下热解3.5h然后再在530℃、1MPa下焦化8h所得焦块为具有较高取向度的流线型结构,适合于作为针状焦的起始原料。 相似文献
9.
An 8-valued commutative ring is developed to process colored images. Algebraic operators are defined to perform a number of operations such as the extraction of the primary colors and contours of different colors. 相似文献
10.
The gas flow sputter technique was invented a few years ago particularly for the inexpensive fabrication of sophisticated ceramic layers. Meanwhile, it has matured and become increasingly powerful. Today it is on the verge of being applied in industrial fabrication processes. The present article gives an overview over the method, its characteristics and the numerous applications. 相似文献