全文获取类型
收费全文 | 1707篇 |
免费 | 40篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 50篇 |
综合类 | 20篇 |
化学工业 | 413篇 |
金属工艺 | 20篇 |
机械仪表 | 23篇 |
建筑科学 | 108篇 |
矿业工程 | 10篇 |
能源动力 | 32篇 |
轻工业 | 175篇 |
水利工程 | 20篇 |
石油天然气 | 18篇 |
无线电 | 130篇 |
一般工业技术 | 293篇 |
冶金工业 | 262篇 |
原子能技术 | 17篇 |
自动化技术 | 158篇 |
出版年
2023年 | 15篇 |
2021年 | 22篇 |
2020年 | 17篇 |
2019年 | 18篇 |
2018年 | 22篇 |
2016年 | 16篇 |
2015年 | 25篇 |
2014年 | 38篇 |
2013年 | 88篇 |
2012年 | 58篇 |
2011年 | 85篇 |
2010年 | 51篇 |
2009年 | 65篇 |
2008年 | 69篇 |
2007年 | 71篇 |
2006年 | 60篇 |
2005年 | 48篇 |
2004年 | 55篇 |
2003年 | 34篇 |
2002年 | 43篇 |
2001年 | 20篇 |
2000年 | 28篇 |
1999年 | 21篇 |
1998年 | 28篇 |
1997年 | 25篇 |
1996年 | 19篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 31篇 |
1990年 | 23篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 23篇 |
1975年 | 19篇 |
1974年 | 27篇 |
1973年 | 20篇 |
1972年 | 26篇 |
1970年 | 20篇 |
1968年 | 13篇 |
1967年 | 14篇 |
1966年 | 15篇 |
排序方式: 共有1749条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
The fracture strength of HF-etched samples was measured as a function of field-assisted K-Na ion exchange depth, as well as the severity of abrasion. As expected, the more severe the abrasion, the greater the depth required to make the strength insensitive to abrasion. An abrasion-independent weakening mechanism that increased with exchange depth was also found to be operative. 相似文献
5.
Karin Yaccato Alfred Hagemeyer Andreas Lesik Anthony Volpe Henry Weinberg 《Topics in Catalysis》2004,(1):127-132
High-throughput synthesis and screening methods have been developed for the discovery of highly active lead compounds for the selective catalytic reduction as well as direct decomposition of NO in the temperature range 200–300 °C. The discovery libraries for primary screening consisted of 16 × 16 catalyst arrays on 4in. square quartz wafers. Catalysts were prepared by robotic liquid dispensing techniques and screened for catalytic activity in Symyx' scanning mass spectrometer. The scanning mass spectrometer is a fast serial screening tool that uses flat wafer catalyst surfaces, local laser heating, a scanning/sniffing nozzle and a quadrupolar mass spectrometer to compare relative catalytic activities. The feed consisted of NO/NH3 mixtures with optional O2 cofeed and Kr as the internal standard in Ar carrier gas. QMS detection allowed for tracking of H2O, N2, NO, O2, N2O and Kr. Screening protocols for catalytic materials encompassed metal precursors and carriers for supported vanadia systems, extensive doping of V2O5/TiO2, and broad screening of mixed redox metal oxides and supported base and noble metal systems. More than 500 samples could be screened in a single day. Active hits (high NO consumption accompanied by corresponding N2 production) identified in discovery libraries were re-synthesized as focus libraries for lead confirmation and further optimization. These libraries used shallower compositional gradients, for example 56 points (compositions) per ternary, with four 56-point ternaries per 4in. wafer. Broad screening ternaries were generally 8 or 15 points. The focus libraries more clearly reveal the trends and provide guidelines for secondary screening and scale-up. High conversions were achieved in scanning mass spectrometer so the scalability risk is small for the short contact time reactions. 相似文献
6.
Zvi Mendel Lev Zegelman Alfred Hassner Fabienne Assael Miriam Harel Shlomo Tam Ezra Dunkelblum 《Journal of chemical ecology》1995,21(3):331-341
The active component of the sex pheromone ofMatsucoccus josephi is (2E,6E,8E)-5,7-dimethyl-2,6,8-decatrien-4-one; the chemical is also a powerful kairomone of adult males and females of the bugElatophilus hebraicus the principal predator ofM. josephi. The presence of theZ isomer (2E,6Z,8E)-5,7-dimethyl-2,6,8-decatrien-4-one does not interfere with the attractancy of the activeE component forM. josephi males or the bug. Our results show a clear dose-response between trap catch ofM. josephi males andE. hebraicus. Conversely, increasing amounts of theZ isomer in the mixture did not affect the attraction of the scale insect males or the bug. The catch ofM. josephi males did not differ significantly among traps of different color, and was significantly higher with traps attached to the tree trunk than those suspended between trees. Comparison of the catch ofM. josephi among the three forests and between pine species suggests that the level of infestation ofPinus halepepsis andPinus brutia ssp.brutia is similar, despite the fact that the latter pine is resistant to the scale insect. Both sexes ofE. hebraicus were trapped in much lower numbers at the more infested sites. This may be related to interference with the activity ofE. hebraicus due to deterioration and drying of parts of the tree crowns and heavy colonization by generalist predators in injured trees. 相似文献
7.
Various reactions occur between pyrite (FeS2) in coal and CaO to form CaS when a finely pulverized intimate mixture of coal and CaO is coked at 900 °C in an inert atmosphere. The effectiveness of lime and calcined dolomite (CaO.MgO) in promoting this reaction has been evaluated; calcined dolomite is somewhat more effective than lime over coal/ oxide weight ratios from 2.8 to 14. The degree of conversion of pyrite to calcium sulphide at a coal/calcined dolomite weight ratio of 7 has been determined as a function of time at 900 °C; coking time in excess of 2.5 h does not have a significant effect. It has been shown that the total sulphur lost on coking coal/lime mixtures decreases and the percentage of FeS, originating from the dissociation of pyrite, converted to CaS increases as the amount of lime added increases. But although the total sulphur content of coke produced in the presence of CaO is then higher than when the coal is coked without lime, the pyritic sulphur has been converted to CaS which is more amenable to chemical conversion to H2S. A method is outlined for determining CaS in the coked mixture in the presence of FeS. 相似文献
8.
9.
Alfred Hermida Seth C. Lewis Rodrigo Zamith 《Journal of Computer-Mediated Communication》2014,19(3):479-499
News sourcing practices are critical as they shape from whom journalists get their information and what information they obtain, mostly from elite sources. This study evaluates whether social media platforms expand the range of actors involved in the news through a quantitative content analysis of the sources cited by NPR's Andy Carvin on Twitter during the Arab Spring. Results show that, on balance, nonelite sources had a greater representation in the content than elite sources. Alternative actors accounted for nearly half of the messages. The study points to the innovative forms of production that can emerge with new communication technologies, with the journalist as a central node trusted to authenticate and interpret news flows on social awareness streams. 相似文献
10.
In a previous study on the basis of reaction equilibrium, it was demonstrated that the synthesis of fatty acids esters of heavy alcohols by catalytic reactive distillation (RD) is basically feasible. Presently, the analysis is expanded to the kinetics-based design applied to the synthesis of 2-ethylhexyl dodecanoate. Experimental data for a super-acidic sulphated zirconia catalyst are employed. It is shown that this catalyst is highly selective even for the high alcohol/acid ratios as prevail in a RD column. To avoid catalyst deactivation, liquid-liquid segregation into an organic and an aqueous phase must be prevented, and operating temperatures beyond must be chosen. A kinetic model based on liquid activities is proposed, with parameters determined from both kinetic and equilibrium measurements. A typical column design has 13 reactive stages with a catalyst loading of , temperature profile of 400-, and a space velocity of for 99.9% purity product ester. A modified Damköhler number is proposed. 相似文献