全文获取类型
收费全文 | 34660篇 |
免费 | 4703篇 |
国内免费 | 793篇 |
专业分类
电工技术 | 2354篇 |
技术理论 | 2篇 |
综合类 | 2401篇 |
化学工业 | 7873篇 |
金属工艺 | 663篇 |
机械仪表 | 591篇 |
建筑科学 | 1458篇 |
矿业工程 | 16771篇 |
能源动力 | 2487篇 |
轻工业 | 110篇 |
水利工程 | 203篇 |
石油天然气 | 989篇 |
武器工业 | 11篇 |
无线电 | 239篇 |
一般工业技术 | 546篇 |
冶金工业 | 1929篇 |
原子能技术 | 40篇 |
自动化技术 | 1489篇 |
出版年
2024年 | 50篇 |
2023年 | 172篇 |
2022年 | 718篇 |
2021年 | 1162篇 |
2020年 | 1323篇 |
2019年 | 739篇 |
2018年 | 806篇 |
2017年 | 759篇 |
2016年 | 1034篇 |
2015年 | 1248篇 |
2014年 | 2564篇 |
2013年 | 2212篇 |
2012年 | 3768篇 |
2011年 | 3102篇 |
2010年 | 2189篇 |
2009年 | 2199篇 |
2008年 | 2027篇 |
2007年 | 2185篇 |
2006年 | 1894篇 |
2005年 | 1606篇 |
2004年 | 1246篇 |
2003年 | 1211篇 |
2002年 | 933篇 |
2001年 | 911篇 |
2000年 | 729篇 |
1999年 | 593篇 |
1998年 | 399篇 |
1997年 | 391篇 |
1996年 | 326篇 |
1995年 | 267篇 |
1994年 | 206篇 |
1993年 | 113篇 |
1992年 | 108篇 |
1991年 | 60篇 |
1990年 | 42篇 |
1989年 | 29篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 187篇 |
1984年 | 223篇 |
1983年 | 169篇 |
1982年 | 145篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
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
15.
Blended SRC-II process streams, representing a full boiling range distillate material, were fractionally distilled into non-overlapping 50 °F cuts with boiling points between 300 and 850 °F. Another set of 18 distillate cuts were obtained with boiling points ranging between 138 and 1055 °F. Distillate cuts were assayed for mutagenic activity using the histidine reversion assay with Salmonella typhimurium strains TA98, TA100, TA1535 and TA1537, as well as for mammalian-cell transformation activity in the Syrian hamster embryo test, and DNA damage in the prophage induction assay. Samples were also separated into chemical class fractions by alumina column chromatography and analysed by high resolution gas chromatography so that the chemical composition of the cuts could be related to their relative activity in the different assays. In the mammalian cell transformation and microbial mutagenicity assays, significant activity was found almost exclusively in distillate cuts with components boiling > 700 °F, with the highest activity in the transformation assay observed for cuts > 800 °F. All of the distillate cuts showed increased levels of DNA damage as expressed by lambda prophage induction in Escherichia coli 8177. However, the greatest activity was associated with distillate cuts with boiling points in the 800 °F + range. Chemical analysis of the 50 °F distillate cuts showed a variety of polycyclic aromatic hydrocarbons (PAH) and amino-PAH compounds to be present in the distillate cuts boiling > 700 °F and essentially absent from cuts boiling < 700 °F. The sample set of non-overlapping (50 °F) cuts were reblended according to the proportions of each cut found in the original blend material. These reblended composites were then assayed to compare their activity with that predicted from the activities of the component distillate cuts. The reblending experiments indicated the microbial mutagenicity response was essentially additive. Mammalian cell transformation activities were non-additive, indicating a compositional effect on the expression of transforming agents in the complex mixture. 相似文献
16.
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
17.
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
18.
Erv J. Kuhlmann Dick Y. Jung Richard P. Guptill Charles A. Dyke Hyung K. Zang 《Fuel》1985,64(11):1552-1557
The presence of hydroaromatic, hydrogen donor components in a coal-derived solvent is one of the more important factors in the successful operation of a non-catalytic coal liquefaction process. Various hydrogen donor species present in a hydrogenated creosote oil have been identified. Their rate of disappearance under conditions that are consistent with a short residence time coal liquefaction process has been used to rank the reactivities of the various hydrogen donors. 1,2,3,10b-Tetrahydrofluoranthene was found to be an exceptional donor while 4,5-dihydropyrene, the hexahydropyrenes and 9,10-dihydrophenanthrene were found to be quite active. Sym.-octahydrophenanthrene and 2a,3,4,5-tetrahydroacenaphthene exhibited moderate activity. Tetralin and the four methyltetralin isomers were found to be unreactive under the coal liquefaction conditions employed. 相似文献
19.
The new structure of fibre glass reinforced plastics bolt 总被引:4,自引:0,他引:4
The develop actuality and direction of FRP (fibre glass reinforced plastics) bolt in the world are analyzed. The new type structure of FRP bolt was designed. Trial data indicate that, all kinds of capability target of this FRP bolt all achieve and exceed the country stand-ard, substitute present metal bolt, wood bolt and bamboo bolt and other side bolt, it can gain magnitude technology and economy benefit. FRP bolt mechanization product line produce ef-ficiency is high, its throughput a day are 750 base, this can meet demand of hit-small mining company. 相似文献
20.
针对朱仙庄矿 84 15工作面切眼特殊的地质条件 ,介绍了高强锚杆 (索 )支护技术成功应用于特厚极软煤层的经验 ,并对巷道支护成本进行了分析 相似文献