全文获取类型
收费全文 | 1698篇 |
免费 | 61篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 18篇 |
综合类 | 3篇 |
化学工业 | 451篇 |
金属工艺 | 102篇 |
机械仪表 | 35篇 |
建筑科学 | 74篇 |
矿业工程 | 15篇 |
能源动力 | 23篇 |
轻工业 | 185篇 |
水利工程 | 1篇 |
石油天然气 | 11篇 |
无线电 | 89篇 |
一般工业技术 | 357篇 |
冶金工业 | 199篇 |
原子能技术 | 14篇 |
自动化技术 | 188篇 |
出版年
2021年 | 20篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 34篇 |
2017年 | 20篇 |
2016年 | 36篇 |
2015年 | 33篇 |
2014年 | 44篇 |
2013年 | 67篇 |
2012年 | 57篇 |
2011年 | 76篇 |
2010年 | 67篇 |
2009年 | 66篇 |
2008年 | 57篇 |
2007年 | 51篇 |
2006年 | 49篇 |
2005年 | 36篇 |
2004年 | 45篇 |
2003年 | 24篇 |
2002年 | 33篇 |
2001年 | 30篇 |
2000年 | 35篇 |
1999年 | 38篇 |
1998年 | 47篇 |
1997年 | 42篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 34篇 |
1993年 | 26篇 |
1992年 | 33篇 |
1991年 | 24篇 |
1989年 | 25篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 26篇 |
1983年 | 29篇 |
1982年 | 27篇 |
1980年 | 28篇 |
1979年 | 24篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1976年 | 30篇 |
1975年 | 37篇 |
1974年 | 19篇 |
1973年 | 26篇 |
1972年 | 15篇 |
1971年 | 20篇 |
1970年 | 21篇 |
排序方式: 共有1765条查询结果,搜索用时 15 毫秒
61.
Ilse Bacaloglu Truong The Ky Carmen Boeriu Hans Horst Glatt Radu Bacaloglu Dieter Martin Heinz Graubaum 《Advanced Synthesis \u0026amp; Catalysis》1982,324(5):803-808
Acylation of Heterocycles with Carbonic Acid Derivatives. I. Kinetics and Mechanism of the Reaction of 2-Aminobenzimidazoles with Aryl Cyanates The second order rate constants for the reaction of 2-amino-benzimidazoles (2-ABI) with aryl cyanates forming 2-amino-benzimidazole aryl ester imide 3 have been determined in dependence on substituent effects by u. v. measurements. The results are interpreted by a six-membered cyclic transition state in which the electrophilic attack of the cyanate on the endocyclic N atom is catalyzed by an H bridge interaction of the exocyclic amino group of 2-ABI with the OCN group. 相似文献
62.
Linxing Yao Tong Wang Michael Persia Ronald L. Horst Mallory Higgins 《Journal of food science》2013,78(2):C178-C183
A 40‐wk experiment was conducted using Hy‐Line W‐36 laying hens (19‐wk old) to investigate the impact of feeding cholecalciferol‐enriched diets on egg yolk quality. Feeds were enriched with 4 cholecalciferol levels, 9700 (diet 2), 17200 (diet 3), 24700 (diet 4), and 102200 (diet 5) IU/kg feed. The control (diet 1) contained 2200 IU cholecalciferol/kg feed. Eggs from each replicate group of enriched diets were collected daily and the yolks were pooled into 2‐d period during the first 2 wk. During weeks 3, 4, 6, 8, 12, 16, 20, 24, 28, 32, 36, and 40, pooled samples were generated by daily collection of 3 consecutive days of egg production. The cholecalciferol content of egg yolk from the enriched diets increased rapidly during the first 3 wk. The peak cholecalciferol concentrations in egg yolk that occurred at week 3 were 865, 1641, 2411, and 34815 IU/100 g egg yolk (wet basis) from diet 2 to 5. The average cholecalciferol concentration in yolk during weeks 3 to 40 and the deposition rate of cholecalciferol during the first 3 wk were both linearly increased with the dietary cholecalciferol level when the feed contained no more than 24700 IU/kg cholecalciferol. Egg yolk lipid profile (total lipid content, fatty acid composition, phospholipid composition, and unsaponifiables), physical and functional properties (yolk viscosity and emulsifying property), and sensory quality of hard‐boiled egg yolk were not affected by the cholecalciferol enrichment in the feed. Practical Application: A linear dose‐response relationship between dietary vitamin D3 level and egg yolk vitamin D3 content was established at relatively low enrichment levels. Such relationship can be used to formulate feed to achieve a target egg vitamin D level. High vitamin D yolk showed no difference from the conventional yolk in other compositional, functional, and sensory properties. 相似文献
63.
Rolf Sommer Paul L.G. Vlek Tatiana Deane de Abreu Sá Konrad Vielhauer Roberta de Fátima Rodrigues Coelho Horst Fölster 《Nutrient Cycling in Agroecosystems》2004,68(3):257-271
For over a hundred years shifting cultivation with slash-and-burn land preparation has been the predominant type of land use by smallholders in the Bragantina region of the Brazilian Eastern Amazon. This study contrasts the nutrient balance of slash-and-burn agriculture with a fire-free cultivation. Therefore, one half of a 3.5-year-old (28.7 t DM ha–1) and a 7-year-old woody fallow vegetation (46.5 t DM ha–1) was burnt and the other half mulched, leaving the biomass as a surface residue. Subsequently, a sequence of maize, beans and cassava was cropped for 1.5 year. Burning the 3.5- and 7-year-old fallow removed 97 and 94% of the C, 98 and 96% of the N, 90 and 63% of the P-stocks, and between 45 and 70% of the cations K, Mg and Ca of the aboveground biomass by volatilization or ash-particle transfer. These losses were avoided with the slash-and-mulch land preparation. Mulching did not increase the losses of nutrients by leaching, despite the high amount of rapidly decomposing surface mulch. Also the length of preceding fallow had no significant influence on leaching losses. At a depth of 3 m, leached nutrients were quantitatively negligible in both treatments. Comparing the nutrient fluxes at soil depths of 0.9 m, 1.8 m and 3 m, the amounts of all mobile nutrients, and also of chloride and sodium were markedly reduced during percolation and must have been retained. It is likely that nutrient retention in the subsoil layer is only temporary, emphasizing the need for a rapid re-establishment of the naturally deep-rooting secondary vegetation after abandonment of sites to enable uptake of these nutrients. The overall nutrient balance was highly negative for slash-and-burn. 291 and 403 kg N ha–1, 21 and 18 kg P ha–1, and 70 and 132 kg K ha–1 were removed from the burnt plots with a preceding fallow of 3.5 and 7 years, respectively. A reduced fallow period (3.5 years), which is a common trend in the region, resulted in a higher mean annual rate of nutrient loss averaged over the duration of the cycle than a fallow period of 7 years. Eliminating the burning losses by mulching brought the agricultural system back to an equilibrated or even slightly positive nutrient balance, even after a reduced fallow period. Thus, slash-and-mulch is a viable alternative to maintain agricultural productivity and ecosystem functioning. 相似文献
64.
原材料成本推动Autocoro纺纱工艺发展.最近几年纱线生产成本在总成本中的份额不断地在增加.以前纱线生产成本也许占总成本的一半,目前已达75%.介绍了纺纱厂应对这种趋势的方法. 相似文献
65.
66.
67.
Michael Horst Andrea L. Welker Robert G. Traver 《Canadian Metallurgical Quarterly》2011,137(6):352-358
The use of infiltration storm-water best management practices (BMPs) has become a more commonly used approach as a means of reducing postdevelopment runoff volumes in many areas throughout the United States. Although studies regarding the performance of infiltration BMPs are emerging, much remains to be learned about their design, construction, and operation. The increase in knowledge will improve the performance and longevity of these BMPs. The performance of one such infiltration basin over a 2-year cycle is presented in this paper. The study site is a pervious concrete infiltration basin BMP built in 2002 in a courtyard common area at Villanova University. The system consists of three linked infiltration beds lined with geotextile filter fabric, filled with coarse aggregate, and overlaid with pervious concrete. The natural soil beneath the infiltration BMP is a silty sand. The BMP is extensively instrumented to facilitate water quantity and quality research. Both water-quantity and -quality results are presented. The water-quantity analysis showed that the performance of the basin was directly related to its infiltration characteristics. The infiltration rate of the silty sand is cyclic, with higher rates during warmer periods and lower rates during colder periods. The water quality analysis investigated the pollutant reduction for chloride, copper, nitrogen, and phosphorus from the inlet to the surface-water outlet of the structure, as well as differences in pollutant concentration levels between the basin, surrounding ground, and varying soil layer elevations beneath the basin. In general, the pollutant reduction to the surface waters was greater than 90% from inlet to outlet, primarily influenced by the infiltration of the storm water into the natural soils below the BMP. The pollutant concentration of the infiltrating runoff was found to be higher than expected in the area adjacent to the bed when compared to concentration levels found at a similar depth beneath the infiltration bed. Comparison of pollutant concentration levels, as the water moved from within the storage bed to the soil beneath the bed, were shown to vary, with statistical differences found for mean concentration levels of both pH and copper levels; and no statistical differences were found for conductivity, total phosphorous, and chloride at each elevation. 相似文献
68.
Marc Blumenau Afrooz Barnoush Ingo Thomas Harald Hofmann Horst Vehoff 《Surface & coatings technology》2011,205(2-3):542-552
The present study discusses the impact of selective oxidation during in-line annealing of Fe–23%Mn–0.6%C–0.3%Si steel on surface and sub-surface properties and is focused on hot-dip galvanizability and susceptibility to hydrogen-induced delayed cracking. Annealing temperature (700–1100 °C) and dewpoint DP (? 15/?30/?50 °C) of the 5%H2–N2 annealing atmosphere were varied in order to investigate Zn wetting in dependence on selective oxidation of Mn and Si. Sub-surface microplasticity (hardness, pop-in frequency, pop-in activation load) was examined by electrochemical nanoindentation in-situ to hydrogen charging (ECNI) to assess hydrogen/material interactions. Zn wetting fails if external Mn and Si oxidation is not avoided by performing high reductive bright annealing (1100 °C/DP ? 50 °C). Zn wetting will however turn to increase if a roughly globular MnO layer appears and Si is internally oxidized (700–900 °C/DP ? 15 °C). Selective oxidation further affects hydrogen/material interactions by influencing the local distribution of solid-soluted Mn: ECNI results indicate hydrogen-induced dislocation demobilization (HEDE mechanism) or dislocation mobilization (HELP mechanism) in dependence on the local amount of solid-soluted Mn within the sub-surface. Macroscopic delayed cracking seems to occur earlier if HELP is predominating. The gained results benefit understanding the impact of selective oxidation on galvanizability and susceptibility to hydrogen-induced failure of austenitic FeMnC steel and advance further developments in processing high Mn alloyed steels. 相似文献
69.
A. M. Al-Mukhtar H. Biermann P. Hübner S. Henkel 《Journal of Materials Engineering and Performance》2010,19(9):1225-1234
In this work, the parameters stress intensity factor (SIF), initial and final crack lengths (a
i and a
f), crack growth parameters (C and m), and fatigue strength (FAT) are investigated. The determination of initial crack length seems to be the most serious factor
in fatigue life and strength calculations for welded joints. A fracture mechanics approach was used in these calculations
based on SIF which was calculated with the finite element method (FEM). The weld toe crack was determined to be equal to 0.1 mm,
whereas the weld root crack’s length was varied depending on the degree of the weld penetration. These initial crack length
values are applicable for all types of joints which have the same crack phenomenon. As based on the above calculated parameters,
the new limits of FAT for new geometries which are not listed yet in recommendations can be calculated according to the current
approach. 相似文献
70.
Marta Lubary Theo W. de LoosJoop H. ter Horst Gerard W. Hofland 《The Journal of Supercritical Fluids》2011,55(3):1079-1088
The ScMM (Supercritical Melt Micronization) process was applied for the production of microparticles from anhydrous milk fat (AMF) and a diacylglycerol-based modified milk fat (D-AMF). Both fats were able to dissolve ca. 30 wt% CO2 in the studied pressure and temperature ranges, being the CO2 amount slightly higher for AMF. A melting point depression was observed in both systems in the presence of CO2. Two powder morphologies were obtained (spherical hollow particles and a mass sponge-like broken particles) depending on the ScMM process conditions. The concentration of CO2 in the fat melt was the main process variable affecting the particle morphology, followed by the temperature of the melt. The small broken particles originated from the breakage of spherical fat particles that solidified before all CO2 could escape from the atomized droplets. While the hollow spheres had a tendency to agglomerate, the broken microparticles constituted a free-flowing powder as long as they were stored at low temperatures (up to −18 °C). Both types of particles have a potential for being incorporated in refrigerated or frozen food products as a structuring agent. 相似文献