全文获取类型
收费全文 | 32815篇 |
免费 | 996篇 |
国内免费 | 65篇 |
专业分类
电工技术 | 361篇 |
综合类 | 35篇 |
化学工业 | 6669篇 |
金属工艺 | 854篇 |
机械仪表 | 618篇 |
建筑科学 | 1839篇 |
矿业工程 | 247篇 |
能源动力 | 1031篇 |
轻工业 | 2757篇 |
水利工程 | 337篇 |
石油天然气 | 187篇 |
武器工业 | 2篇 |
无线电 | 2141篇 |
一般工业技术 | 5202篇 |
冶金工业 | 6648篇 |
原子能技术 | 324篇 |
自动化技术 | 4624篇 |
出版年
2021年 | 387篇 |
2020年 | 337篇 |
2019年 | 407篇 |
2018年 | 496篇 |
2017年 | 510篇 |
2016年 | 526篇 |
2015年 | 468篇 |
2014年 | 742篇 |
2013年 | 2147篇 |
2012年 | 1248篇 |
2011年 | 1593篇 |
2010年 | 1174篇 |
2009年 | 1262篇 |
2008年 | 1437篇 |
2007年 | 1470篇 |
2006年 | 1257篇 |
2005年 | 1174篇 |
2004年 | 1052篇 |
2003年 | 1023篇 |
2002年 | 1032篇 |
2001年 | 637篇 |
2000年 | 615篇 |
1999年 | 576篇 |
1998年 | 603篇 |
1997年 | 501篇 |
1996年 | 607篇 |
1995年 | 548篇 |
1994年 | 520篇 |
1993年 | 521篇 |
1992年 | 468篇 |
1991年 | 311篇 |
1990年 | 427篇 |
1989年 | 420篇 |
1988年 | 376篇 |
1987年 | 416篇 |
1986年 | 376篇 |
1985年 | 512篇 |
1984年 | 488篇 |
1983年 | 441篇 |
1982年 | 464篇 |
1981年 | 444篇 |
1980年 | 352篇 |
1979年 | 364篇 |
1978年 | 329篇 |
1977年 | 307篇 |
1976年 | 270篇 |
1975年 | 318篇 |
1974年 | 242篇 |
1973年 | 277篇 |
1972年 | 153篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
52.
53.
The major results reported by R. A. Carlson et al (see record 1989-24864-001) confirm predictions of J. R. Anderson's (1983) ACT* theory. In particular, ACT* predicts the detrimental effects of the transition to randomized practice because of the need to learn new productions, the complexity effect of gate and judgment type because of more complex production conditions, the effects of practice and its interaction with complexity because of the strengthening mechanisms, and the effects of memory load because of the need to hold information active in working memory so that it can be matched by production conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
54.
Significant increases in the activity of vanadium(III) amidinate catalysts for ethylene polymerization have been obtained by immobilization on a MgCl2‐based support prepared by reaction of AlEt3 with a MgCl2/ethanol adduct. Catalyst immobilization and activation on this type of support prevents the rapid decay in activity observed under homogeneous polymerization conditions with unsupported catalysts. Stable polymerization activity is also observed with analogous titanium(III) complexes. Polyethylene with narrow molecular weight distribution and spherical particle morphology is obtained without reactor fouling. Copyright © 2005 Society of Chemical Industry 相似文献
55.
Wladek T. Sobol L.John SchreinerLjubis̆a Miljković Maria E. Marcondes-HeleneLeonard W. Reeves M.Mik Pintar 《Fuel》1985
The first results of the analysis of bitumen and oil sands using the recently developed n.m.r. spingrouping technique are presented. The n.m.r. relaxation experiments were carried out on bitumen, and on natural and dried oil sands samples. The results indicate that the spin-grouping can resolve and quantify several components of the samples studied. The bitumen and bitumen fraction of the oil sands are resolved according to their spin-spin relaxation times into three major groups: solid-like (rigid), solid-like (mobile) and semi-liquid. The water in the oil sands exists in two different environments. Tentatively one environment is assigned to be the bridges between the sand grains, while the other is assigned to be the clay surface. One can conclude that with spin grouping of complex mixtures the decomposition (in which components are resolved according to their dynamic state) is possible. The accuracy of such resolution is of the order of a few per cent. 相似文献
56.
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
57.
The reaction of lignite in a slagging gasifier produces reactants which in turn form 5,5-dimethylhydantoin (DMH) as a major constituent in the condensate water. Variations in plant operating conditions made it impossible to accurately study the kinetics of formation of DMH in the actual gasifier water, and thus a model system was chosen. The reaction of acetone cyanohydrin in the presence of excess ammonium carbonate at concentrations approaching those obtained in the condensate water were studied at 50,70, and 90 °C. Secondorder kinetics were obeyed, and the pseudo second-order rate constants at the respective temperatures were 1.86, 3.6, and 4.62 dm3 mol? 1 h? 1. Independent variation of the concentration of either acetone, cyanide, ammonia or carbonate gave results consistent with the interpretation that the formation of DMH is first order in all reactants: rate of formation of DMH = k[acetone][HCN][NH3][CO2]. The pseudo second-order rate constant is a complex rate constant including several rapid equilibria. A mechanism consistent with the kinetic data is presented. 相似文献
58.
Mathematical models have been developed which predict the composition, molecular weight, and melt rheological properties for vinyl chloride/vinyl acetate copolymers of inherent viscosity range 0.4–0.7 dL/g and bound vinyl acetate levels of 3.8–17.4%. The effect of polymer long chain branching on the viscous/elastic moduli ratio is discussed as well as the comparison of Tinius–Olsen melt index measurements vs. mechanical spectrometer results. The reactivity ratio for vinyl chloride/vinyl acetate comonomer pairs was remeasured and found to be significantly different from literature values. 相似文献
59.
The effects of monomer refluxing on both resin properties and reactor fouling of suspension PVC have been studied in a laboratory-scale 14-L reactor. Process control equations were developed which related the particle properties to the reflux condenser operation by controlling the parameters of (1) the time at which refluxing is begun and (2) the rate profile of heat removal from the condenser. An operating envelope has been developed for laboratory scale operations which optimizes the cycle time of polymerization while minimizing the adverse effects on particle properties. These operating conditions may have application to production scale operations when the proper scaling factors are employed. 相似文献
60.
John R. Grace 《加拿大化工杂志》1986,64(3):353-363
An attempt is made to extend schemes for classifying the behaviour of gas—solid contacting modes and other two-phase systems. The regime diagram approach of Reh (1971) is modified and extended to cover the operating regions of common reactors and contactors where a gas flows upwards through a bed of solids including fixed and moving packed beds, conventional fluidized beds, circulating beds, spouted beds, and pneumatically conveyed suspensions. New boundaries are proposed between groups A and B and between groups B and D of the Geldart (1972, 1973) powder classification scheme. These boundaries reflect more recent data and allow the classification scheme to be used for gases other than air and for temperatures and pressures other than atmospheric. 相似文献