全文获取类型
收费全文 | 4440篇 |
免费 | 333篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 31篇 |
综合类 | 2篇 |
化学工业 | 1269篇 |
金属工艺 | 44篇 |
机械仪表 | 79篇 |
建筑科学 | 167篇 |
矿业工程 | 8篇 |
能源动力 | 166篇 |
轻工业 | 1003篇 |
水利工程 | 45篇 |
石油天然气 | 11篇 |
无线电 | 217篇 |
一般工业技术 | 648篇 |
冶金工业 | 97篇 |
原子能技术 | 18篇 |
自动化技术 | 975篇 |
出版年
2024年 | 5篇 |
2023年 | 51篇 |
2022年 | 141篇 |
2021年 | 256篇 |
2020年 | 151篇 |
2019年 | 192篇 |
2018年 | 196篇 |
2017年 | 178篇 |
2016年 | 199篇 |
2015年 | 154篇 |
2014年 | 231篇 |
2013年 | 379篇 |
2012年 | 327篇 |
2011年 | 379篇 |
2010年 | 263篇 |
2009年 | 240篇 |
2008年 | 221篇 |
2007年 | 218篇 |
2006年 | 140篇 |
2005年 | 130篇 |
2004年 | 124篇 |
2003年 | 97篇 |
2002年 | 82篇 |
2001年 | 46篇 |
2000年 | 45篇 |
1999年 | 42篇 |
1998年 | 53篇 |
1997年 | 40篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有4780条查询结果,搜索用时 203 毫秒
191.
Francisco Lara-Ochoa Juan Antonio Cogordan Ioan Silaghi-Dumitrescu 《Fullerenes, Nanotubes and Carbon Nanostructures》2013,21(5):887-896
Abstract The interaction of tBu-calix[8]arene with C60 and C70 in the 1:1 and 1:2 models have been investigated by means of molecular dynamics and molecular mechanics (CVFF91 force field) calculations. The results reveal that one C60 molecule can be encapsulated in the cavity of the calixarene which adopts a conformation with six phenyl groups oriented upward and the other two (1 and 5) outward. The relatively weak bonded 1:1 C60-calixarene system is a result of attractive π…H(C-tBu. C-methylene) and repulsive π…π interactions. C70, more voluminous than C60 can not be accommodated in the cavity of the calixarcnc and forces it to a relatively opened conformation where the number of atractive interactions is less than in the C60-calixarene system. This conformation allows however the interaction with a second molecule and thus 1:2 adducts are formed. Thus, if proper substituents are on the calixarene and the fullerene size permite the encapsulation, 1:1 complexes are obtainable while if the fullerene size is larger than the cavity of the calixarene can cope with, only the 1:2 adducts can be separated. 相似文献
192.
Aída R. Callejas-Cárdenas Irma Caro Carolina Blanco Luz H. Villalobos-Delgado Nuria Prieto Raúl Bodas Francisco J. Giráldez Javier Mateo 《Meat science》2014
The effects of vacuum ageing on the quality changes of lamb steaks during retail display were assessed. Biceps femoris and Quadriceps femoris muscles from thirty early fattening lambs fed barley straw and concentrate or alfalfa and concentrate were used. Half of the muscles were vacuum aged for three weeks (VA), and the other half were not aged (control). Control and VA muscles were sliced and aerobically displayed. Weight loss, pH, aldehyde contents, instrumental color characteristics and color acceptance were measured at display days 1, 3, 7 and 14. At day 1 redness was higher in VA lamb. However, redness of VA lamb decreases more rapidly during further storage. Redness and color acceptance decreased in VA lamb from day 3, whereas in not-aged lamb the decrease was observed from day 7 onwards. From days 7 to 14 a drop of color acceptance accompanied by an increase in pH and a decrease in lightness was observed in control and VA lamb. 相似文献
193.
Fernando Araya Robert Dell Pedro Donoso Vladimir Marianov Francisco Martínez Andrés Weintraub 《International Transactions in Operational Research》2012,19(5):695-710
The Chilean Ministry of Education oversees preschool, primary, and secondary education in both urban and rural areas. Many parts of Chile are sparsely populated and there are currently over 4,000 rural schools (almost 38% of all schools in Chile) educating 9.5% of the students in the country. Many of the rural schools are small with only one teacher responsible for instruction of all local students (multigrade schools). The geographical distribution of the rural schools has not been coordinated and this has resulted in unequal utilization of existing schools and some unreasonably long travel distances by students. Good management of the rural schools is fundamental to meeting Chile's goal of providing quality education to its citizens. Seeking to improve the situation, the Ministry of Education ordered a study of the optimal location and size of rural schools with the general goals of reducing the number of lesser quality multigrade schools and reducing student travel distances while maintaining reasonable costs. This paper presents results of this study obtained using an integer linear program that has been embedded in a geographical information system. We present computational results for the entire country. Recommendations include where to open new rural schools as well as where to expand, reduce, close, or leave unchanged existing schools. We show how recommendations are sensitive to key parameters such as the cost of transportation. 相似文献
194.
195.
Aguayo-Canela Francisco José Alaiz-Moretón Héctor García-Ordás María Teresa Benítez-Andrades José Alberto Benavides Carmen García-Rodríguez Isaías 《The Journal of supercomputing》2021,77(11):13046-13068
The Journal of Supercomputing - The increasing number of connected devices and the complexity of Internet of Things (IoT) ecosystems are demanding new architectures for managing and securing these... 相似文献
196.
The demonstrated existence of vast brine pools in a number of places in the ocean basin around the world offers an interesting opportunity to the production of power from ocean, which has not been yet considered. The attractiveness of these vast deposits of brine lie in the fact that can be readily dissolved with the surrounding top waters extracting the spontaneous osmotic mixing energy released. In addition, osmotic engines can pumped out the brackish streams by buoyancy without the add of pressure exchangers (PEXs) as is required in current pressure retarded osmosis (PRO) technology and then simplifying significatively the overall process. Utilizing a simplified physical model, a first estimation for the density of power per unit of membrane area was calculated. 相似文献
197.
198.
Elton Joao Zierhut Rodrigo Battisti Ricardo Antonio Francisco Machado Cintia Marangoni 《化学工程与技术》2020,43(9):1884-1896
Intrinsic characteristics of distillation such as dead time and high nonlinearities do not allow the complete elimination of transient times when any external disturbance or set-point change occurs. Thus, aiming at the use of easy-tuning systems, a distributed-action control in trays of a diabatic distillation unit with Smith's predictor was implemented in the Simulink environment to further reduce transient times and out-of-specification product. The distributed-action strategy with Smith's predictor led to a reduction of 33.3 min (33 %) in the transient time of the top temperature control loop and 66 % in out-of-specification product, when compared with the conventional strategy, and thus is shown to be an efficient approach to increasing the productivity of distillation plants. 相似文献
199.
In this brief note, a first assessment on the possibilities for thermal osmotic storage by harnessing the thermal dependence of the solubility of common salts as an alternative method to sensible heat storage is discussed. In a recent study it was found that such a dependence could be used to run a heat powered cycle (osmotic heat engine). The question raised then is whether that approach could be suitable for thermal energy storage as well. The attractiveness of such a possibility lies in the capability to store energy for an indefinite period of time without using expensive isolation systems if one considers that osmotic energy only is released when both streams with different salinities are brought together. Utilizing a simplified model, a comparative study with sensible heat storage was performed. It is shown that thermal osmotic storage via thermal precipitation of common salts could be an attractive option when long thermal storage (days) and compactness is desired. 相似文献