全文获取类型
收费全文 | 33090篇 |
免费 | 934篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 366篇 |
综合类 | 35篇 |
化学工业 | 6795篇 |
金属工艺 | 858篇 |
机械仪表 | 624篇 |
建筑科学 | 1839篇 |
矿业工程 | 247篇 |
能源动力 | 1016篇 |
轻工业 | 2762篇 |
水利工程 | 339篇 |
石油天然气 | 207篇 |
武器工业 | 2篇 |
无线电 | 2168篇 |
一般工业技术 | 5229篇 |
冶金工业 | 6642篇 |
原子能技术 | 322篇 |
自动化技术 | 4639篇 |
出版年
2022年 | 196篇 |
2021年 | 386篇 |
2020年 | 333篇 |
2019年 | 399篇 |
2018年 | 488篇 |
2017年 | 508篇 |
2016年 | 523篇 |
2015年 | 466篇 |
2014年 | 742篇 |
2013年 | 2142篇 |
2012年 | 1243篇 |
2011年 | 1591篇 |
2010年 | 1169篇 |
2009年 | 1262篇 |
2008年 | 1440篇 |
2007年 | 1473篇 |
2006年 | 1256篇 |
2005年 | 1174篇 |
2004年 | 1054篇 |
2003年 | 1026篇 |
2002年 | 1031篇 |
2001年 | 635篇 |
2000年 | 616篇 |
1999年 | 577篇 |
1998年 | 599篇 |
1997年 | 503篇 |
1996年 | 608篇 |
1995年 | 547篇 |
1994年 | 533篇 |
1993年 | 537篇 |
1992年 | 489篇 |
1991年 | 325篇 |
1990年 | 439篇 |
1989年 | 425篇 |
1988年 | 387篇 |
1987年 | 425篇 |
1986年 | 382篇 |
1985年 | 515篇 |
1984年 | 491篇 |
1983年 | 444篇 |
1982年 | 464篇 |
1981年 | 446篇 |
1980年 | 356篇 |
1979年 | 365篇 |
1978年 | 329篇 |
1977年 | 308篇 |
1976年 | 268篇 |
1975年 | 318篇 |
1974年 | 243篇 |
1973年 | 279篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
For users of an executive information system (EIS), the EIS interface is the system and is crucial to the EIS's success. These guidelines for designing EIS interfaces are based on studies of actual EIS interfaces that meet the unique information needs of executives. 相似文献
32.
33.
John Bensted 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(4):181-184
Characterisation of raw materials for Portland cement manufacture by use of the methylene blue adsorption method is discussed. The method is shown to be a simple, convenient ‘rule of thumb’ procedure. It provides a guide to the quantity and type of argillaceous minerals present in a given raw material sample. 相似文献
34.
Experiments showing the frequency and amplitude of the flow induced motion of the gate for a 2- and a 4-in. swing check valve have been performed. The gate motion is due to turbulence in approach flow. We have found the dominant turbulent frequency of the approach flow is about half the natural frequency of the valves. The valves appear to be almost critically damped. Because of this, the valves respond almost as they would to a static force of the magnitude characteristic of the turbulent fluctuation in the flow. Both the dimensionless exciting force and the damping ratio have been found to be independent of valve size so the above statements are true for larger valves also. The recommended valve oscillation amplitudes and frequencies are used to calculate the wear at the shaft and at the stop. For an unpegged check valve, such as one of the 10-in. valves which was used at the San Onofre Nuclear Generation Station, it was found that shaft bearing wear would amount to 0.27 in.3/year and stop wear to 0.03 in.3/year. 相似文献
35.
36.
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
37.
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
38.
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
39.
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
40.
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