全文获取类型
收费全文 | 2936篇 |
免费 | 65篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 16篇 |
综合类 | 1篇 |
化学工业 | 386篇 |
金属工艺 | 43篇 |
机械仪表 | 44篇 |
建筑科学 | 79篇 |
矿业工程 | 9篇 |
能源动力 | 47篇 |
轻工业 | 486篇 |
水利工程 | 25篇 |
石油天然气 | 10篇 |
无线电 | 201篇 |
一般工业技术 | 249篇 |
冶金工业 | 1074篇 |
原子能技术 | 9篇 |
自动化技术 | 324篇 |
出版年
2021年 | 33篇 |
2020年 | 29篇 |
2019年 | 31篇 |
2018年 | 34篇 |
2017年 | 32篇 |
2016年 | 31篇 |
2015年 | 32篇 |
2014年 | 47篇 |
2013年 | 106篇 |
2012年 | 79篇 |
2011年 | 110篇 |
2010年 | 92篇 |
2009年 | 79篇 |
2008年 | 110篇 |
2007年 | 127篇 |
2006年 | 103篇 |
2005年 | 107篇 |
2004年 | 83篇 |
2003年 | 91篇 |
2002年 | 87篇 |
2001年 | 72篇 |
2000年 | 67篇 |
1999年 | 67篇 |
1998年 | 147篇 |
1997年 | 110篇 |
1996年 | 102篇 |
1995年 | 77篇 |
1994年 | 61篇 |
1993年 | 66篇 |
1992年 | 54篇 |
1991年 | 31篇 |
1990年 | 51篇 |
1989年 | 59篇 |
1988年 | 46篇 |
1987年 | 55篇 |
1986年 | 57篇 |
1985年 | 43篇 |
1984年 | 34篇 |
1983年 | 42篇 |
1982年 | 30篇 |
1981年 | 43篇 |
1980年 | 32篇 |
1979年 | 34篇 |
1978年 | 27篇 |
1977年 | 17篇 |
1976年 | 37篇 |
1975年 | 10篇 |
1974年 | 14篇 |
1973年 | 7篇 |
1970年 | 7篇 |
排序方式: 共有3003条查询结果,搜索用时 31 毫秒
61.
62.
Lyndsay A. Cartwright Sue Hayes Douglas C. Tozer Dan Clayton Mary-Ann Burns Dena Lewis Noah Gaetz Namrata Shrestha 《Journal of Great Lakes research》2021,47(2):273-282
Beneficial use impairments (BUIs) under the Great Lakes Water Quality Agreement identify environmental issues requiring remedial action within the Great Lakes Areas of Concern (AOCs). We conducted this study to support the assessment of the wildlife component of BUI 3: degradation of fish and wildlife populations. We compared bird and amphibian (frogs and toads) data from the Toronto and Region Conservation Authority’s Terrestrial Long-term Monitoring Program in the Toronto and Region AOC to an adjacent, but otherwise similar, reference watershed, Duffins Creek. Twelve of 13 targets were met within the AOC for forest bird, wetland bird, meadow bird and amphibian populations based on averages of mean annual values at sites within the AOC that were within two standard deviations of averages at sites in the Duffins Creek reference watershed between 2008 and 2017. Even though wildlife populations within the AOC were within the normal range of variability expected from a reference watershed, they were often at lower levels than within the Duffins Creek reference watershed. In addition, forest bird and amphibian populations were negatively affected by urbanization within the AOC and meadow bird indices declined. We conclude that while wildlife populations within the AOC currently meet targets for BUI 3, they continue to be negatively impacted by numerous stressors that are primarily related to past and ongoing urbanization. Thus, continued restoration of wildlife habitat and protection of existing habitat within the AOC is highly recommended. 相似文献
63.
Boreham CJ Fookes CJ Popp BN Hayes JM 《Energy & fuels : an American Chemical Society journal》1990,4(6):658-661
Compared with the carbon-13 isotopic composition of the ubiquitous C32DPEP (DPEP, deoxophylloerythroetioporphyrin) the heavy but equivalent carbon-13 isotopic composition for the porphyrin structures 15(2)-methyl-15,17-ethano-17-nor-H-C30DPEP and 15,17-butano-, 13,15-ethano-13(2),17-propano-, and 13(1)-methyl-13,15-ethano-13(2),17-propanoporphyrin suggests a common precursor, presumably chlorophyll c, for these petroporphyrins isolated from the marine Julia Creek oil shale and the lacustrine Condor oil shale. Similarly, the heavy but variable carbon-13 isotopic composition of 7-nor-H-C31DPEP compared with C32DPEP is consistent with an origin from both chlorophyll b and chlorophyll c3. The equivalent carbon-13 isotopic composition for 13(2)-methyl-C33DPEP compared with C32DPEP suggests a common origin resulting from a weighted average of chlorophyll inputs. 相似文献
64.
To extend R. E. Fancher's (see record 1987-31600-001) review of claims that photographs of the Kallikak family in H. H. Goddard's (1912) study had been retouched to make them look more menacing and retarded, 29 Ss (aged 18–69 yrs) were surveyed for their impressions of the photographs. Overall, Ss were strongly inclined to view the photographed individuals as "kind" and "very bright." (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
65.
66.
67.
Atmospheric degradation of volatile organic compounds 总被引:19,自引:0,他引:19
68.
C. Flötgen M. Pawlak E. Pabo H. J. van de Wiel G. R. Hayes V. Dragoi 《Microsystem Technologies》2014,20(4-5):653-662
Wafer-level Cu–Sn intermetallic bonding is an interesting process for advanced applications in the area of MEMS and 3D interconnects. The existence of two intermetallic phases for Cu–Sn system makes the wafer bonding process challenging. The impact of process parameters on final bonding layer quality have been investigated for transient liquid phase wafer-level bonding based on the Cu–Sn system. Subjects of this investigation were bonding temperature profile, bonding time and contact pressure as well as the choice of metal deposition method and the ratio of deposited metal layer thicknesses. Typical failure modes in intermetallic compound growth for the mentioned process and design parameters have been identified and were subjected to qualitative and quantitative analysis. The possibilities to avoid abovementioned failures are indicated based on experimental results. 相似文献
69.
The processing of carbon-ceramic composites by utilizing the unique sintering ability of mesocarbon microbeads (MCMB) is reported. The ceramic constituents (silicon nitride and silicon carbide) are formed in situ by reactions between MCMB and silicon in different atmospheres. In comparison with direct addition of ceramic (SiC, Si3N4) phases, in situ formation shows several appealing features. By inducing the reaction of silicon with MCMB, the sintering ability of the composite is enhanced via reaction bonding mechanisms. Similarly, it is demonstrated that composite porosity is limited owing to silicon reaction with nitrogen. The reactive formation of nanoscale ceramic reinforcements via decomposition of the silicon-containing polymer (e.g. poly-carbomethyl-silane) is also reported. This approach results in formation of uniform nanosized (>100 nm) SiC layers strongly bonded to the surface of the carbon particles. The presented results contribute to the development of carbon-ceramic materials with high-operational properties. 相似文献
70.
Douglas G. Hayes Robert Kleiman 《Journal of the American Oil Chemists' Society》1995,72(11):1309-1316
Eight lipases were screened for their ability to synthesize estolides from a mixture that contained lesquerolic (14-hydroxy-11-eicosenoic)
acid and octadecenoic acid. With the exception ofAspergillus niger lipase, all 1,3-specific enzymes (fromRhizopus arrhizus andRhizomucor miehei lipases) were unable to synthesize estolides.Candida rugosa andGeotrichum lipases catalyzed estolide formation at >40% yield, with >80% of the estolide formed being monoestolide from one lesquerolic
and one octadecenoic acyl group:Pseudomonas sp. lipase synthesized estolides at 62% yield, but the product mixture contained significant amounts of monoestolide with
two lesquerolic acyl groups as well as diestolide. ImmobilizedR. miehei lipase was chosen to catalyze the esterification of mono-and polyestolide, derived synthetically from oleic acid, with fatty
alcohols or α,ω-diols. Yields were >95% for fatty alcohol reactions and >60% for diol reactions. In addition, the estolide
linkage remained intact through the course of the esterification process. Esterification of estolides improved the estolide’s
properties—for example, lower viscosity and higher viscosity index—but slightly raised the melting point. Estolides and, particularly,
estolide esters may be suitable as lubricants or lubricant additives. 相似文献