全文获取类型
收费全文 | 539930篇 |
免费 | 8024篇 |
国内免费 | 1856篇 |
专业分类
电工技术 | 10156篇 |
综合类 | 503篇 |
化学工业 | 82764篇 |
金属工艺 | 21140篇 |
机械仪表 | 17589篇 |
建筑科学 | 12479篇 |
矿业工程 | 2525篇 |
能源动力 | 14717篇 |
轻工业 | 45533篇 |
水利工程 | 5301篇 |
石油天然气 | 8478篇 |
武器工业 | 24篇 |
无线电 | 65212篇 |
一般工业技术 | 107489篇 |
冶金工业 | 98851篇 |
原子能技术 | 11035篇 |
自动化技术 | 46014篇 |
出版年
2021年 | 4839篇 |
2020年 | 3705篇 |
2019年 | 4813篇 |
2018年 | 7964篇 |
2017年 | 7957篇 |
2016年 | 8514篇 |
2015年 | 5647篇 |
2014年 | 9126篇 |
2013年 | 26415篇 |
2012年 | 14716篇 |
2011年 | 19500篇 |
2010年 | 15513篇 |
2009年 | 17451篇 |
2008年 | 18107篇 |
2007年 | 18066篇 |
2006年 | 16045篇 |
2005年 | 14479篇 |
2004年 | 13834篇 |
2003年 | 13615篇 |
2002年 | 13049篇 |
2001年 | 12845篇 |
2000年 | 12106篇 |
1999年 | 12571篇 |
1998年 | 30732篇 |
1997年 | 21567篇 |
1996年 | 16853篇 |
1995年 | 12714篇 |
1994年 | 11240篇 |
1993年 | 11183篇 |
1992年 | 8353篇 |
1991年 | 7902篇 |
1990年 | 7859篇 |
1989年 | 7553篇 |
1988年 | 7122篇 |
1987年 | 6321篇 |
1986年 | 6185篇 |
1985年 | 7046篇 |
1984年 | 6502篇 |
1983年 | 5969篇 |
1982年 | 5509篇 |
1981年 | 5517篇 |
1980年 | 5106篇 |
1979年 | 4991篇 |
1978年 | 4900篇 |
1977年 | 5680篇 |
1976年 | 7340篇 |
1975年 | 4274篇 |
1974年 | 3952篇 |
1973年 | 4066篇 |
1972年 | 3381篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Incorporation of silicon species from an alloy substrate into anodic titania is shown to stabilise the structure of the film, facilitating investigation of the ionic transport processes in amorphous titania grown at high efficiency. Thus, an amorphous anodic film developed on a sputtering-deposited Ti-6 at.%Si alloy formed to 100 V in phosphoric acid electrolyte in contrast to a partially crystalline film developed on relatively pure titanium at <20 V. Silicon species, which are immobile and act as marker species in the growing film, are present in the inner 58% of the film thickness. Evidently, the film material forms simultaneously at the film/electrolyte and alloy/film interfaces by co-operative transport of cations and anions, as is usual in amorphous anodic oxides. The phosphate anions incorporated from the electrolyte migrate inward at 0.34 times the rate of O2− ions and hence are present in the outer 62% of the film thickness. 相似文献
932.
By using mathematical formulae developed in previous studies, certain pollution parameters of dye effluent obtained from reactive dyeing with a single dye can be predicted with good accuracy. In this study, the degree of pollution of reactive dyeing effluent using dye mixtures was also predicted by other approaches, such as linear and non-linear regression. The prediction accuracy was found to be satisfactory. 相似文献
933.
Letters to the editor 总被引:6,自引:0,他引:6
934.
935.
The Kerendan carbonate platform (Oligocene Berai Limestone) covers a subsurface area measuring approximately 11 by 16 km in the westernmost Kutei Basin, Central Kalimantan. Aggradation of the Kerendan platform occurred during a major Oligocene transgression, and is contemporaneous with aggradation and backstepping of the Barito shelf margin which was located approximately 30 km to the south. The Kerendan platform is approximately 1,000 m thick, and comprises three aggrading seismic sequences identified by the downlap of basinal strata at the platform margin and downlap of transgressive strata within the platform. Carbonate deposition started in the Late Eocene, and ended when the upper limestone sequence drowned and was covered with shale in the Late Oligocene (approximately 28.6 Ma). Three depositional areas can be distinguished in seismic sections: (1) a platform interior (lagoon); (2) a slightly raised platform rim (1–2 km wide); and (3) a basinward‐dipping platform margin and slope. The margin of the platform is identified by inflections on the seismic profiles where the relatively flat platform top begins to slope basinward. Depositional models from outcrops combined with core from three Kerendan wells were used to extrapolate depositional facies onto the seismically‐defined platform. Platform‐interior (lagoon) facies consist largely of fossiliferous wackestones and packstones, and porosities are generally lower than 5%. The platform rim is characterized by interbedded bioclastic wackestones, packstones, grainstones and boundstones, with grainstones increasing toward the platform margin. Porosity preferentially occurs in packstones, grainstones and boundstones. The platform‐rim deposits have greater porosity (5–13%) than the platform interior because the platform run is more grainstone‐rich, and because acidic waters compacting out of basinal shales concentrated dissolution near the platform margin. Pore types include vuggy porosity, microporosity within grains, and intercrystalline porosity in dolomite in the upper part of the platform rim. Different pore types have resulted in variable but locally very high permeabilities (greater than 100 mD). Permeabilities decrease with depth as vuggy pores decrease, and microporosity becomes dominant. 相似文献
936.
Calum MacNeil Jaimie T A Dick Ewan Bigsby Robert W Elwood W Ian Montgomery Chris N Gibbins David W Kelly 《Water research》2002,36(1):75-84
In freshwaters. Gammarus spp. are more sensitive to organic pollution than Asellus spp. and the relative abundance of the two taxa has been proposed as a pollution index. We tested the validity of this by examining the relationship between the Gammarus: Asellus (G : A) ratio and (1) a suite of physico-chemical variables. (2) established biotic (average score per taxon, ASPT) and richness (species richness (S) and Ephemeroptera, Plecoptera and Trichoptera families richness (EPT family richness)) indices generated from the macroinvertebrate community. In addition, we investigated a suspected biotic interaction, predation, between Gammarus and Asellus. Both univariate and multivariate analyses showed that the G: A ratio was sometimes responsive to changes in parameters linked to organic pollution, such as BOD5 and nitrate levels. However, the G : A ratio also appeared responsive to variables not directly linked to organic pollution, such as conductivity and distance from source. There were significant positive correlations among the G : A ratio and the ASPT, S and EPT, indicating that changes in the relative abundances of Gammarus and Asellus were reflected in changes in the pollution sensitivity and richness of the wider macroinvertebrate community. A laboratory experiment revealed significant predation of Asellus aquaticus juveniles by Gammarus duebeni celticus adults, but no reciprocal predation. We propose that the G: A ratio may be useful as a crude measure of organic pollution that could supplement more complex indices in a multimetric approach to pollution monitoring or be used for monitoring individual sites, where a simple technique is required for monitoring purposes over a period of time. Also, we urge recognition of the possible role of biotic interactions among taxa used in the generation of pollution indices. 相似文献
937.
Magnetic Acoustic Emission in Ferromagnetic Materials. 3: Effect of Structural Changes on Magnetic Acoustic Emission (Review Article) 总被引:1,自引:0,他引:1
Gorkunov E. S. Ul'yanov A. I. Khamitov V. A. 《Russian Journal of Nondestructive Testing》2002,38(5):376-397
This part of the review is devoted to effects of structural changes in multiply alloyed ferromagnetic materials on parameters of magnetoelastic acoustic emission. 相似文献
938.
A previously proposed model of strain in ceria–zirconia-encapsulated precious-metal particles is revised to reflect several new observations: encapsulation of unstrained Pt particles, quantitative relation between partial reduction and the change in ceria–zirconia cell parameters, temperature/time dependence of strain relaxation/imposition in encapsulated Pd and Rh particles, and strained PdO. According to the revised model, the main cause of strain is partial oxidation of the precious metal (rather than the change in oxygen content of ceria–zirconia, as originally suggested). 相似文献
939.
ABSTRACT: This study investigated the effects of 10% (w/v) salt, trisodium phosphate (TSP), sodium tripolyphosphate (STPP), and tetrapotassium pyrophosphate (TKPP) washes on removal of attached Salmonella typhimurium from sterile chicken breast patties, as well as on their injury and survival in a refrigerator for 16 d, in a –20 °C freezer for 10 mo, and after 3 freeze-thaw cycles. S. typhimurium were grown on chicken patties at 20 °C for 20 h, washed, and enumerated by plating on selective and nonselective media. Salt and phosphates washing significantly lowered the survival populations of attached S. typhimurium on patties, but did not cause any significant sublethal injury of attached S. typhimurium , irrespective of storage treatments. The TSP washes showed superior effects of removing and inactivating S. typhimurium compared to other washing treatments. 相似文献
940.
A.S. Fraser 《Journal of Great Lakes research》1980,6(1):83-87
An apparent decrease in total phosphorus concentrations of approximately 4.l μgP/L has been reported recently for the spring values of 1977 and 1978 in Lake Ontario. Investigation of the loading reduction for this period independent of sedimentation factors can account for only 10% of the change. The results indicate that changes in the sedimentation rate of total phosphorus during this period offer an explanation for the majority of the change in concentration. 相似文献