全文获取类型
收费全文 | 154515篇 |
免费 | 6551篇 |
国内免费 | 3129篇 |
专业分类
电工技术 | 4640篇 |
技术理论 | 6篇 |
综合类 | 6593篇 |
化学工业 | 23721篇 |
金属工艺 | 8615篇 |
机械仪表 | 7749篇 |
建筑科学 | 7282篇 |
矿业工程 | 2937篇 |
能源动力 | 3302篇 |
轻工业 | 8222篇 |
水利工程 | 2245篇 |
石油天然气 | 5594篇 |
武器工业 | 462篇 |
无线电 | 16622篇 |
一般工业技术 | 25225篇 |
冶金工业 | 6368篇 |
原子能技术 | 1001篇 |
自动化技术 | 33611篇 |
出版年
2024年 | 230篇 |
2023年 | 1201篇 |
2022年 | 2077篇 |
2021年 | 2869篇 |
2020年 | 2148篇 |
2019年 | 1909篇 |
2018年 | 16270篇 |
2017年 | 15511篇 |
2016年 | 11783篇 |
2015年 | 3271篇 |
2014年 | 3638篇 |
2013年 | 4383篇 |
2012年 | 7435篇 |
2011年 | 14066篇 |
2010年 | 12310篇 |
2009年 | 9366篇 |
2008年 | 10488篇 |
2007年 | 11368篇 |
2006年 | 3905篇 |
2005年 | 4626篇 |
2004年 | 3395篇 |
2003年 | 3243篇 |
2002年 | 2389篇 |
2001年 | 1728篇 |
2000年 | 1978篇 |
1999年 | 2095篇 |
1998年 | 1810篇 |
1997年 | 1432篇 |
1996年 | 1441篇 |
1995年 | 1184篇 |
1994年 | 950篇 |
1993年 | 719篇 |
1992年 | 551篇 |
1991年 | 444篇 |
1990年 | 325篇 |
1989年 | 250篇 |
1988年 | 230篇 |
1987年 | 140篇 |
1986年 | 102篇 |
1985年 | 89篇 |
1984年 | 59篇 |
1982年 | 42篇 |
1968年 | 46篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 35篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
Microbiological denitrification of red beet juice 总被引:1,自引:0,他引:1
Dorota Walkowiak-Tomczak 《European Food Research and Technology》2002,215(5):401-406
The purpose of study was the determination of optimal conditions for red beet juice denitrification by Paracoccus denitrificans bacteria as well as the evaluation of the usefulness of microbiologically treated juice for the production of a natural colouring preparation for foods. Total reduction of nitrates was found during bacterial culturing at 25 and 30 °C, at an initial pH of 7.0-8.0 and juice osmotic pressure of 900-1100 mOsm/kg. Microbiological denitrification procedure affected colour, taste and aroma of the juice. However, the use of juice as food colouring and component was made feasible by acidification and partial evaporation of water together with volatile substances. 相似文献
153.
Jin-Wei Shi Chi-Kuang Sun 《Lightwave Technology, Journal of》2002,20(11):1942-1950
We present the theory and design of a tapered line distributed photodetector (TLDP). In the previously demonstrated velocity-matched distributed photodetector (VMDP), high electrical bandwidth is achieved by proper termination in the input end to absorb reverse traveling waves, sacrificing one-half of the quantum efficiency. By utilizing the tapered line structure and phase matching between optical waves and microwaves in our analyzed structure, a traveling-wave photodetector is more realizable and ultrahigh bandwidth can be attained due to removal of the extra input dummy load that sacrifices one-half of the total quantum efficiency. To investigate the advantages of TLDP over VMDP, we calculate their electrical bandwidth performances by using an analytic photodistributed current model. We adopted low-temperature-grown (LTG) GaAs-based metal-semiconductor-metal (MSM) traveling-wave photodetectors as example unit active devices in the analytic bandwidth calculation for their high-speed and high-power performances. Both VMDP and TLDP in our simulation are assumed to be transferred onto glass substrates, which would achieve high microwave velocity/impedance and make radiation loss negligible. The simulated bandwidth of a properly designed LTG GaAs MSM TLDP is /spl sim/325 GHz, which is higher than the simulated bandwidth of the LTG GaAs MSM VMDP with an open-circuit input end (/spl sim/240 GHz) and is almost comparable to the simulated bandwidth of an input-terminated LTG GaAs MSM VMDP (/spl sim/330 GHz). This proposed method can be applied to the design of high-bandwidth distributed photodetectors for radio-frequency photonic systems and optoelectronic generation of high-power microwaves and millimeter waves. 相似文献
154.
155.
156.
157.
George Ter-Stepanian 《Bulletin of Engineering Geology and the Environment》2002,61(3):197-205
The paper discusses the postulated suspension force, by which it is possible to explain some enigmatic phenomena observed
in different types of mass movements. This force is generated in thick suspensions as a result of friction between sinking
solid particles and static water. The suspension force is related to the seepage force but they have opposite directions.
Both forces form flow networks. Having explained the suspension force, the paper describes how this influences the movement
of material, particularly in debris flows. Enigmatic features and the mechanism of debris flows and lahars are explained by
virtue of the suspension force.
Electronic Publication 相似文献
158.
We consider the problem of rescheduling trains in the case where one track of a railway section consisting of two tracks
in opposing directions is closed due to construction activities. After presenting an appropriate model for this situation
we derive a polynomial algorithm for the subproblem of finding an optimal schedule with minimal latenesss if the subsequences
of trains for both directions outside the construction site are fixed. Based on this algorithm we propose a local search procedure
for the general problem of finding good schedules and report test results for some real world instances.
Received: December 8, 1999 / Accepted: May 2, 2001 相似文献
159.
160.