全文获取类型
收费全文 | 18488篇 |
免费 | 777篇 |
国内免费 | 388篇 |
专业分类
电工技术 | 5120篇 |
技术理论 | 1篇 |
综合类 | 604篇 |
化学工业 | 1178篇 |
金属工艺 | 436篇 |
机械仪表 | 927篇 |
建筑科学 | 759篇 |
矿业工程 | 203篇 |
能源动力 | 1776篇 |
轻工业 | 456篇 |
水利工程 | 802篇 |
石油天然气 | 173篇 |
武器工业 | 65篇 |
无线电 | 1994篇 |
一般工业技术 | 743篇 |
冶金工业 | 231篇 |
原子能技术 | 1960篇 |
自动化技术 | 2225篇 |
出版年
2024年 | 25篇 |
2023年 | 140篇 |
2022年 | 248篇 |
2021年 | 350篇 |
2020年 | 381篇 |
2019年 | 257篇 |
2018年 | 243篇 |
2017年 | 426篇 |
2016年 | 524篇 |
2015年 | 485篇 |
2014年 | 909篇 |
2013年 | 879篇 |
2012年 | 877篇 |
2011年 | 1458篇 |
2010年 | 1000篇 |
2009年 | 1022篇 |
2008年 | 951篇 |
2007年 | 1015篇 |
2006年 | 1070篇 |
2005年 | 1368篇 |
2004年 | 1125篇 |
2003年 | 784篇 |
2002年 | 513篇 |
2001年 | 382篇 |
2000年 | 375篇 |
1999年 | 432篇 |
1998年 | 385篇 |
1997年 | 302篇 |
1996年 | 314篇 |
1995年 | 277篇 |
1994年 | 226篇 |
1993年 | 248篇 |
1992年 | 157篇 |
1991年 | 110篇 |
1990年 | 84篇 |
1989年 | 76篇 |
1988年 | 51篇 |
1987年 | 25篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 40篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
介绍了万家寨水电站 1号水轮机、 2号水轮机在设计和制造过程中采用的抗磨蚀措施 ,对机组经过运行后 ,抗磨涂层尤其是耐而久涂层的应用现状及涂层破坏原因作了探讨 相似文献
993.
For an internal fire analysis, fire scenarios are developed carefully and quantified in a sequential and iterative way in a traditional fire Probabilistic Safety Assessment (PSA). However, there has been no proven explicit method to avoid these iterative quantifications till now. This study presents the Jung's Single Top And Run (JSTAR) method that facilitates a simultaneous single quantification of all fire scenarios. The JSTAR method could be employed at the fire PSA phases of a quantitative screening or detailed analysis. Using the JSTAR method, accurate fire risks of a fault tree that has many negates could be calculated by avoiding the frequent house event propagations of the fire scenario conditions. Furthermore, the proposed JSTAR method is a simple and explicit method to build a single-top external event PSA model for a risk-monitoring system.The JSTAR method could be implemented easily by developing a small automatic conversion tool. Depending on the maintenance policy of a fire PSA model, a single-top fire PSA model that is created by the conversion tool could be maintained permanently or it could be temporarily generated and discarded. The use of the JSTAR method is recommended for all external event PSAs such as an internal flooding risk analysis. 相似文献
994.
The power spectral density of a signal can be estimated most accurately by using a window with a narrow bandwidth and large sidelobe attenuation. Conventional windows generally control these characteristics by only one parameter, so there is a trade-off problem: if the bandwidth is reduced, the sidelobe attenuation is also reduced. To overcome this problem, we propose using a Butterworth window with two control parameters for power spectral density estimation and analyze its characteristics. Simulation results demonstrate that the sidelobe attenuation and the 3 dB bandwidth can be controlled independently. Thus, the trade-off problem between resolution and spectral leakage in the estimated power spectral density can be overcome. 相似文献
995.
996.
接地的内涵不仅包括需要接地的电气回路导体或电气设备金属外壳与大地的连接,还包括它们与替代大地的某些导体的连接,即等电位联结。对工频而言,接地回路起主导作用的是电阻;对高频而言,起主导作用的则是电抗。 相似文献
997.
This paper treats the control of multilevel rectifier by applying the soft computing technique represented by the fuzzy logic. This latest, provides an inexpensive solution for controlling the ill-known complex systems, while relying on the imitation of human reasoning. In our case, the proposed intelligent controller aims at eliminating the current line harmonics, guaranteing an improved power factor, reducing the output voltage ripple and ensuring the balance between the two voltages across the two capacitors of Vienna rectifier. In order to evaluate the performance of the proposed control for Vienna rectifier, a comparative study in real time via the dSPACE card 1104 has been carried out between the traditional approach based on the conventional controllers and the new method using an intelligent controller. The experimental results confirm that the modified control approach has guaranteed a good quality of source currents in phase with the grid voltages and operation of the studied system with a power factor very close to unity. Furthermore, only one fuzzy controller used has ensured the regulation of the DC bus voltage, the minimization of the undulations for the two partial voltages and the improvement of the error of the voltage balance for the Vienna rectifier. 相似文献
998.
A N,N-dimethylamino substituted tetraphenylethylene derivative (TPE-NMe) was synthesized and characterized, and was successfully applied as hole transport material (HTM) in perovskite solar cells. The methoxy-substituted analogue TPE-4DPA was also studied for comparison. The effect of replacing the para-methoxy substituent with N,N-dimethylamino on photophysical properties, energy levels, and hole transport properties is investigated. Photovoltaic performances of the corresponding devices using the two HTMs are studied. Compared to the methoxy substituent, the N,N-dimethylamino groups in TPE-NMe generates a lower Voc (0.87 V), yet it provides higher Jsc (21.69 mA/cm2) and FF (0.73) values, resulting in an overall power conversion efficiency of 13.78%. 相似文献
999.
The life table parameters and digestive enzymatic activity of Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae), an important insect pest of grains, were studied under laboratory conditions (25 ± 1 °C, relative humidity of 65 ± 5% and a photoperiod of 16: 8 (L: D) h). Seeds of ten barley cultivars including Bahman, CB-84-10, Fajr30, Makuyi, Nosrat, Yousof, 12A1, 13A1, 18A1 and 19A1 were used as host diet. S. cerealella showed the shortest developmental time and the highest survival and fecundity after feeding on cultivar 19A1. The longest developmental time and the lowest fecundity were on cultivars Bahman and Fajr30, respectively. The gross and net reproductive rates and intrinsic rate of increase were the highest when S. cerealella was reared on cultivar 19A1. However, a corresponding decrease in these parameters was observed on cultivar Fajr30. Fourth instar larvae fed on cultivar 19A1 showed higher α-amylase activity than those fed on other barley cultivars. However, S. cerealella larvae exhibited no significant difference in proteolytic activity among barley cultivars. Correlation analyses showed that high correlations existed between the life table parameters and α-amylase activity on one side and particle size index on the other. It is suggested that nutritional quality, especially seed hardness, may be the major factor responsible for the susceptibility of barley cultivars to S. cerealella. 相似文献
1000.
Unstructured and multi-objective task arrangement in radiation field is a complicating problem decision-makers are most concerned about. Proper task arrangement is helpful to improve efficiency of engineering and reduce hazard. The goal of this work is to discuss some criteria of task, build task hierarchy structure model, and then propose a task analytic method in radiation field based on analytic hierarchy process (AHP). The proposed method is useful for selection of schemes to reduce hazard and increase efficiency of task. In addition, we use this proposed method solve a hypothetical case, which is utilized to explain how the method works and to prove the method effective. 相似文献