全文获取类型
收费全文 | 121869篇 |
免费 | 16005篇 |
国内免费 | 5161篇 |
专业分类
电工技术 | 7722篇 |
技术理论 | 13篇 |
综合类 | 7734篇 |
化学工业 | 29095篇 |
金属工艺 | 3010篇 |
机械仪表 | 3986篇 |
建筑科学 | 8279篇 |
矿业工程 | 18877篇 |
能源动力 | 5908篇 |
轻工业 | 8192篇 |
水利工程 | 3818篇 |
石油天然气 | 14316篇 |
武器工业 | 391篇 |
无线电 | 6833篇 |
一般工业技术 | 7813篇 |
冶金工业 | 5799篇 |
原子能技术 | 980篇 |
自动化技术 | 10269篇 |
出版年
2024年 | 375篇 |
2023年 | 1799篇 |
2022年 | 5291篇 |
2021年 | 6083篇 |
2020年 | 4225篇 |
2019年 | 3718篇 |
2018年 | 3804篇 |
2017年 | 4406篇 |
2016年 | 5972篇 |
2015年 | 6564篇 |
2014年 | 8698篇 |
2013年 | 8418篇 |
2012年 | 9039篇 |
2011年 | 8202篇 |
2010年 | 6336篇 |
2009年 | 6257篇 |
2008年 | 5829篇 |
2007年 | 7388篇 |
2006年 | 7226篇 |
2005年 | 6133篇 |
2004年 | 4486篇 |
2003年 | 4248篇 |
2002年 | 3348篇 |
2001年 | 2745篇 |
2000年 | 2430篇 |
1999年 | 1798篇 |
1998年 | 1174篇 |
1997年 | 1110篇 |
1996年 | 969篇 |
1995年 | 815篇 |
1994年 | 677篇 |
1993年 | 426篇 |
1992年 | 366篇 |
1991年 | 292篇 |
1990年 | 270篇 |
1989年 | 211篇 |
1988年 | 162篇 |
1987年 | 142篇 |
1986年 | 110篇 |
1985年 | 274篇 |
1984年 | 304篇 |
1983年 | 214篇 |
1982年 | 188篇 |
1981年 | 67篇 |
1980年 | 64篇 |
1966年 | 26篇 |
1965年 | 23篇 |
1964年 | 34篇 |
1962年 | 64篇 |
1959年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene. 相似文献
54.
55.
56.
煤炭作为山西经济发展的支柱产业,在实现全面建设小康社会的奋斗目标过程中,要做出突出贡献,任务非常艰巨,要实现这一奋斗目标,2003年要努力做好6个方面的工作,在新型煤炭工业化道路上迈出更大步伐。 相似文献
57.
As a result of shrinking fossil fuels, biomass as a regenerative energy source gains importance. To realize biomass projects it is essential to investigate in convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses are indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available, it will be shown, which biomass is suitable for fixed bed or fluidized bed gasifiers. 相似文献
58.
Vatroslav Bubalo Vjekoslav Jerolimov Ivo Bau
i Mladen Andreis Zorica Veksli 《Polymer International》2005,54(5):848-853
The electron‐spin‐resonance (ESR) spin‐probe method, was used to study the heterogeneity of denture resins based on poly(methyl methacrylate). Results for three resins processed by microwave energy, conventional curing and cold curing (depending on the curing procedure and exposed to ageing in various environmental conditions) were compared. All three cured resins were stored over the same time (1200 h) in distilled water at ambient temperature and in artificial saliva at 348 K. The temperature‐dependent ESR spectra of a spin probe dispersed in the denture resins are analyzed in terms of line‐shapes and line‐widths. The appearance of two spectral components was taken as an indication of resin heterogeneity. The results reveal that the cold‐cured resin has a lower local density in comparison with microwave and conventionally cured resin. The amount of residual monomer also contributes to the local motion of polymer segments. The change of denture resins exposed to ageing is influenced both by the structure of the original resin and the ageing conditions. Restricted motion of a spin probe incorporated into the acrylic resins exposed to accelerated ageing suggests additional crosslinking of polymer chains. The differences are observed for all the investigated resins, but the highest change is observed with the cold‐cured resin. The ESR results are accompanied by Tg and Tm measurements. Copyright © 2005 Society of Chemical Industry 相似文献
59.
A set of six coals ranging in rank from lignite to hvA bituminous was swollen with a series of alkyl-substituted pyridines and a smaller set of 4-alkylanilines. The size and branching of the alkyl groups was varied and the effect of this variation on the dissolution of the amines in the coal and the resulting coal swelling was measured volumetrically. In a few cases, substituents which hindered the amine nitrogen were studied. The lignite and subbituminous coal have a much higher tolerance to branched, bulky groups than do the bituminous coals. The presence of tertiary groups in a solute strongly inhibits their dissolution in bituminous coals. Bituminous coals behave as if extensive parallel packing of structures occurs. Often, they can accept very large planar groups but have a low capacity for branched groups. 相似文献
60.
Two lignite samples, Beulah No. 3 and Big Brown No. 1, were liquefied at 420 °C using H2 and synthesis gas to determine the optimum beneficial amount of H2S in the batch autoclave reactor. Under the conditions employed, 50–100 psi partial pressure of H2S, nominally 4–10 wt% of daf lignite, was optimum for both samples. Synthesis gas outperformed H2 with and without H2S for the liquefaction of the two coals. 相似文献