全文获取类型
收费全文 | 3031篇 |
免费 | 10篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 39篇 |
金属工艺 | 1篇 |
机械仪表 | 5篇 |
建筑科学 | 12篇 |
矿业工程 | 1篇 |
能源动力 | 6篇 |
轻工业 | 60篇 |
水利工程 | 1篇 |
石油天然气 | 2篇 |
无线电 | 17篇 |
一般工业技术 | 56篇 |
冶金工业 | 2830篇 |
自动化技术 | 9篇 |
出版年
2021年 | 10篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 11篇 |
2013年 | 9篇 |
2012年 | 6篇 |
2011年 | 7篇 |
2010年 | 5篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 9篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 15篇 |
2002年 | 4篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 89篇 |
1998年 | 932篇 |
1997年 | 495篇 |
1996年 | 343篇 |
1995年 | 189篇 |
1994年 | 148篇 |
1993年 | 153篇 |
1992年 | 19篇 |
1991年 | 44篇 |
1990年 | 35篇 |
1989年 | 33篇 |
1988年 | 35篇 |
1987年 | 44篇 |
1986年 | 36篇 |
1985年 | 23篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 58篇 |
1976年 | 138篇 |
1975年 | 6篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有3041条查询结果,搜索用时 724 毫秒
141.
Experimental observation of rainbow scattering by a coated cylinder: twin primary rainbows and thin-film interference 总被引:1,自引:0,他引:1
We experimentally examine the primary rainbow created by the illumination of a coated cylinder. We present a simple technique for varying the coating thickness over a wide range of values, and we see evidence for two different scattering regimes. In one, where the coating thickness is large, twin rainbows are produced. In the second, where the coating is thin enough to act as a thin film, a single rainbow is produced whose intensity varies periodically as the coating thickness varies. We find good agreement with previous theoretical predictions. 相似文献
142.
Graphene oxide (GO) was controllably reduced using electron beam generated plasmas produced in methane/argon mixtures. Operating parameters including, total pressure, duty factor (the ratio of the pulse duration to the pulse period), treatment time, and methane flow rate were varied to determine their impact on the reduction process. The resulting surface chemistry, topography and crystallinity of the reduced graphene oxide (r-GO) was determined with X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectroscopy. Oxygen concentration could be tuned to values between 43 at.% and 5 at.%, and under certain operating conditions the sp2 cluster size grows. System diagnostics identified the critical operating parameters for the reduction of oxygen in GO. 相似文献
143.
J A Lock 《Journal of the Optical Society of America. A, Optics, image science, and vision》2001,18(12):3085-3097
Semiclassical scattering phenomena appearing in the far-zone scattered intensity of a point source of electromagnetic radiation inside a spherical particle are examined in the context of both ray theory and wave theory, and the evolution of the phenomena is studied as a function of source position. A number of semiclassical effects that do not occur for plane-wave scattering by the sphere appear prominently for scattering by an interior source. These include a series of scattering resonances and a new family of rainbows in regions of otherwise total internal reflection. Diffractive effects accompanying the semiclassical phenomena are also examined. 相似文献
144.
145.
146.
147.
R Ramasamy R Kanagaratnam PD Chandanie K Kulachelvy MS Ramasamy PM Dharmasena 《Canadian Metallurgical Quarterly》1999,1453(1):115-125
We describe here a new type of mitochondrial mutation (dum24; for dark uniparental minus inheritance) of the unicellular photosynthetic alga Chlamydomonas reinhardtii. The mutant fails to grow under heterotrophic conditions and displays reduced growth under both photoautotrophic and mixotrophic conditions. In reciprocal crosses between mutant and wild-type cells, the meiotic progeny only inherit the phenotype of the mating-type minus parent, indicating that the dum24 mutation exclusively affects the mitochondrial genome. Digestion with various restriction enzymes followed by DNA gel blot hybridizations with specific probes demonstrated that dum24 cells contain four types of altered mitochondrial genomes: deleted monomers lacking cob, nd4, and the 3' end of the nd5 gene; deleted monomers deprived of cob, nd4, nd5, and the 5' end of the cox1 coding sequence; and two types of dimers produced by end-to-end fusions between monomers similarly or differently deleted. Due to these mitochondrial DNA alterations, complex I activity, the cytochrome pathway of respiration, and presumably, the three phosphorylation sites associated with these enzyme activities are lacking in the mutant. The low respiratory rate of the dum24 cells results from the activities of rotenone-resistant NADH dehydrogenase, complex II, and alternative oxidase, with none of these enzymes being coupled to ATP production. To our knowledge, this type of mitochondrial mutation has never been described for photosynthetic organisms or more generally for obligate aerobes. 相似文献
148.
Infants today lose maternal measles antibody sooner than in the past. This is related to demographic changes in maternal immunization. Data for rates of decay of maternal antibody and seroconversion after measles vaccination for infants born to naturally immune (Group 1) or vaccinated (Group 2) mothers have been used to evaluate two vaccination schedules: Regime 1, measles-mumps-rubella (MMR) at 1 year of age and Regime 2, monovalent measles at 6 months followed by MMR at 15 months of age. Regime 2 costs less because MMR can be administered at 15 months with the last pentavalent booster. Months of protection/1000 children aged 0-15 months (child-months of protection) were estimated for infant populations ranging from 0 to 100% Group 1 for Regimes 1 and 2. Regime 1 provides more child-months of protection only for 100% Group 1 populations. For the study population Regime 2 provided at least 17% more child-months of protection than Regime 1. Regime 2 provides increased medical and financial benefits in proportion to the number of Group 2 infants in the population and thus is ever more advantageous for today's increasingly vaccinated populations. 相似文献
149.
150.
PM Napoli 《The Journal of communication》1999,49(4):7-34
This article presents an examination of the diversity principle in communications policy. Given the Federal Communication Commission's recent emphasis on diversity as a policy objective, diversity assessments must return to the forefront of communications policy analysis. To provide an analytical framework for such research, the diversity principle is broken into three distinct components (source, content, and exposure diversity), and multiple subcomponents. In the spirit of the FCC's empirical commitment to the diversity principle, this analysis focuses on diversity as a measurable concept, with potentially interacting dimensions and numerous means of assessment. 相似文献