全文获取类型
收费全文 | 11963篇 |
免费 | 1117篇 |
国内免费 | 313篇 |
专业分类
电工技术 | 54篇 |
综合类 | 328篇 |
化学工业 | 4014篇 |
金属工艺 | 701篇 |
机械仪表 | 196篇 |
建筑科学 | 396篇 |
矿业工程 | 34篇 |
能源动力 | 147篇 |
轻工业 | 4810篇 |
水利工程 | 21篇 |
石油天然气 | 372篇 |
武器工业 | 50篇 |
无线电 | 337篇 |
一般工业技术 | 1412篇 |
冶金工业 | 270篇 |
原子能技术 | 100篇 |
自动化技术 | 151篇 |
出版年
2024年 | 107篇 |
2023年 | 265篇 |
2022年 | 466篇 |
2021年 | 601篇 |
2020年 | 473篇 |
2019年 | 515篇 |
2018年 | 489篇 |
2017年 | 506篇 |
2016年 | 557篇 |
2015年 | 445篇 |
2014年 | 594篇 |
2013年 | 810篇 |
2012年 | 684篇 |
2011年 | 921篇 |
2010年 | 576篇 |
2009年 | 635篇 |
2008年 | 601篇 |
2007年 | 544篇 |
2006年 | 519篇 |
2005年 | 373篇 |
2004年 | 355篇 |
2003年 | 380篇 |
2002年 | 356篇 |
2001年 | 230篇 |
2000年 | 185篇 |
1999年 | 142篇 |
1998年 | 188篇 |
1997年 | 132篇 |
1996年 | 99篇 |
1995年 | 96篇 |
1994年 | 69篇 |
1993年 | 62篇 |
1992年 | 54篇 |
1991年 | 58篇 |
1990年 | 49篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 26篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 37篇 |
1983年 | 17篇 |
1982年 | 32篇 |
1980年 | 19篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Polycrystalline Ag treated with O2 at pressures up to 1 bar and at temperatures up to 920 K was examined by TDS. It was found that the peak commonly observed at 595±25 K and assigned to adsorbed atomic oxygen (Oa) is shifted to higher desorption temperatures with rising dosing temperatures. Since saturation of the uptake was not possible either, this peak was identified as dissolved atomic oxygen (Od). The existence of a maximum for the O2 uptake after exposure at 820 K was found. Hence, under conditions of formaldehyde synthesis ( 920 K) the ability of the catalyst to dissolve oxygen is near its maximum. 相似文献
92.
Kaiguang Yang 《Desalination》2005,175(3):297-304
DNA-encapsulated polyethersulfone (PES) hollow microspheres are fabricated by means of a liquid-liquid phase separation technique; the hollow microspheres are then used to remove environmental pollutant organic compounds and heavy metal ions. The amounts of DNA encapsulated in the microspheres are dependent on the PES concentration, the DNA concentration used to prepare the particles, and the diameter of the syringe needle. The hollow microspheres can be used to remove harmful organic compounds including ethidium bromide (EB), acridine orange (AO) and endocrine disruptors. With the increase of the DNA amount encapsulated into the hollow microspheres, the removal ratios of these compounds increased. Additionally, the DNA-encapsulated PES hollow microspheres can selectively accumulate and remove heavy metal ions such as Ag+, Cu2+ and Zn2+ These results suggested that the DNA-encapsulated PES hollow microspheres have a potential to be used in environmental applications. 相似文献
93.
Model compound studies were carried out to elucidate the reaction mechanisms taking place during the liquefaction of coal with the hydrogen produced from the reaction of zinc and water. In compounds of the type Ph-(CH2)n-Ph the splitting of the aliphatic bridge was easier with higher n values. Ether type compounds such as diphenylether were unreactive although the C-O bond in dibenzylether was easily cleaved. Condensed ring aromatic compounds gave low conversion with hydrogenation being facilitated by an increase in ring number. Phenolic compounds such as phenol did not react well, but the reactivity increased with increase in aromatic ring size. The cleavage of the aliphatic bridge was accelerated by the OH group, for example, in the case of 4-hydroxydiphenylmethane bond scission was about 15 times higher than that of diphenylmethane. Heterocyclic compounds were unreactive. 相似文献
94.
95.
96.
New organodilithium initiators were prepared in a hydrocarbon solvent in the absence of any polar additive. Although these initiators are insoluble when they are synthesized, they may be easily purified and reacted with dienes to give perfectly telechelic polydienes having unimodal distributions and low dispersity. A good agreement between experimental and theoretical molecular weights was observed. The polymer microstructures were similar to those of polymers initiated by butyllithium in the same solvent. Triblock thermoplastic elastomers were also prepared, the characteristics of which are given. The mechanical properties of a S.B.S. sample support also the claim of a good initiating ability and difunctionality of these initiators. 相似文献
97.
An infra-red spectroscopic investigation of the poly(tetramethylene terephthalate) model compounds butyl-dibenzoate: C6H5COO(CH2)4OCOC6H5 (i), 1,4-bis-butyl terephthalate: HO(CH2)4-OCO6H4COO(CH2)4-OH (ii), α-butyl-ω-butoxyterephthalaoyl-di-(tetramethylene terephthalate): H(CH2)4(OCOC6H4COO-(CH2)4-)3-OH (iii), and α-butyl-ω-butoxyterephthalaoyl-tetra-(tetra-methylene terephthalate): HO(CH2)4-(OCOC6H4COO(CH2)4-)5-OH (iv) is presented. The synthesis of (i) is also described. Spectroscopic evidence indicates that the crystal conformations of the aliphatic segments in (i) and (ii) closely resemble the extended all trans beta form of PTMT. Oligomers (iii) and (iv), however, are found to be more similar to the crumpled alpha crystal phase of PTMT. 相似文献
98.
本文综术了杂多化合物作为酸催化剂,催化烷基化和去烷基化反应、缩聚反应、水合和失水、酯化和醚化反应;以及作为氧化催化剂,在烯烃、芳烃、酚的氧化和环氧化反应中的应用。表面杂多化合物作为催化剂在合成精细化学中有广泛的应用价值。 相似文献
99.
Ccile Donze Pavel Korovchenko Pierre Gallezot Michle Besson 《Applied catalysis. B, Environmental》2007,70(1-4):621-629
The synthesis of substituted benzaldehydes, benzoic acids, heterocyclic aromatic aldehydes and acids has been studied via the oxidation of the aromatic alcohols with air under mild pressure (<20 bar) at 100 °C, in the presence of a 1.95 wt.% Pt/C catalyst. The solvent was found to play the most important role in determining the selectivity of the oxidation products. Changing the solvent enabled tuning the reaction either to the aldehyde (pure dioxane), or the carboxylic acid (dioxane/aqueous solution without or with addition of sodium hydroxide). This oxidation method allowed to effectively oxidize many substituted benzylalcohols with various electron-releasing or -attracting groups (NO2, Me, OMe, Cl, Br, OH, phenyl, …) and heterocyclic alcohols including nitrogen and sulphur atoms (2-thiophenemethanol, 2- and 4-pyridine methanol compounds). 相似文献
100.
国外农药开发现状与中间体需求(2)刘长令(化工部沈阳化工研究院,沈阳110021)三、新近开发的农药及中间体需求近几年新出现的农药类型很多,本文仅对部分类型(文献较多或参与公司较多的)予以介绍。1.吡啶系列农药吡啶类杀菌剂有已知的啶斑肟及新近开发的I... 相似文献