全文获取类型
收费全文 | 833篇 |
免费 | 112篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 338篇 |
金属工艺 | 23篇 |
机械仪表 | 34篇 |
建筑科学 | 10篇 |
能源动力 | 34篇 |
轻工业 | 212篇 |
水利工程 | 4篇 |
石油天然气 | 8篇 |
无线电 | 30篇 |
一般工业技术 | 98篇 |
冶金工业 | 55篇 |
原子能技术 | 1篇 |
自动化技术 | 93篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 38篇 |
2021年 | 62篇 |
2020年 | 38篇 |
2019年 | 51篇 |
2018年 | 48篇 |
2017年 | 51篇 |
2016年 | 55篇 |
2015年 | 30篇 |
2014年 | 50篇 |
2013年 | 57篇 |
2012年 | 55篇 |
2011年 | 61篇 |
2010年 | 52篇 |
2009年 | 41篇 |
2008年 | 41篇 |
2007年 | 23篇 |
2006年 | 30篇 |
2005年 | 21篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1969年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有945条查询结果,搜索用时 15 毫秒
61.
R. A. C. Santana S. Prasad A. R. N. Campos F. O. Araújo G. P. da Silva P. de Lima-Neto 《Journal of Applied Electrochemistry》2006,36(1):105-113
Electrodeposition of Ni–W–B alloys from plating baths containing ammonia and citrate is reported. Optimum conditions for plating
including current density, temperature, mechanical agitation and pH were studied. The corrosion resistance and amorphous character
were also evaluated. The operational conditions for depositing the alloy with good corrosion resistance were: current density
35 mA cm−2, bath temperature 40 °C, pH 9.0 and cathode rotation at 90 rpm. The alloy was deposited at 38% current efficiency, with an
average composition of 73 wt% Ni, 27 wt% W and traces of boron and with E
corr −0.300 V and R
p 3.369×104 Ω. The deposit obtained under these conditions had an amorphous character with the presence of some microcracks on its surface
reaching down to the copper substrate. Electrochemical corrosion tests verified that the Ni–W–B alloy had better corrosion
resistance than Co–W–B. 相似文献
62.
González-Coloma A Reina M Medinaveitia A Guadaño A Santana O Martínez-Díaz R Ruiz-Mesía L Alva A Grandez M Díaz R Gavín JA De la Fuente G 《Journal of chemical ecology》2004,30(7):1393-1408
We have tested the insect antifeedant and toxic activity of 43 norditerpenoid alkaloids on Spodoptera littoralis and Leptinotarsa decemlineata including eserine (physostigmine), anabasine, and atropine. Antifeedant effects of the test compounds were structure- and species-dependent. The most active antifeedants to L. decemlineata were 1,14-diacetylcardiopetaline (9) and 18-hydroxy- 14-O-methylgadesine (33), followed by 8-O-methylconsolarine (12), 14-O-acetyldelectinine (27), karakoline (7), cardiopetaline (8), 18-O-demethylpubescenine (13), 14-O-acetyldeltatsine (18), takaosamine (21), ajadine (24), and 8-O-methylcolumbianine (6) (EC50 < 1 microg/cm2). This insect showed a moderate response to atropine. S. littoralis had the strongest antifeedant response to 24, 18, 14-O-acetyldelcosine (19), and delphatine (29) (EC50 < 3 microg/cm2). None of the model substances affected the feeding behavior of this insect. The most toxic compound to L. decemlineata was aconitine (1), followed by cardiopetalidine (10) (% mortality > 60), 14-deacetylpubescenine (14), 18-O-benzoyl-18-O-demethyl-14-O-deacetylpubescenine (17), 14-O-acetyldelcosine (19), 14-deacetylajadine (25) and methyllycaconitine (30) (% mortality > 45). Orally injected S. littoralis larvae were negatively affected by 1, cardiopetaline (8), 10, 1,14-O-acetylcardiopetalidina (11), 12, 14, 1,18-O-diacetyl-19-oxo-gigactonine (41), olivimine (43), and eserine in varying degrees. Their antifeedant or insecticidal potencies did not parallel their reported nAChR binding activity, but did correlate with the agonist/antagonist insecticidal/antifeedant model proposed for nicotininc insecticides. A few compounds [14, tuguaconitine (38), 14-demethyldelboxine (40), 19, dehydrodelsoline (36), 18-O-demethylpubescenine (13), 41, 9, and delcosine (23)] had selective cytotoxic effects to ward insect-derived Sf9 cells. None were cytotoxic to mammalian CHO cells and none increased Trypanosoma cruzi mortality. The selective cytotoxic effects of some structures indicate that they can act on biological targets other than neuroreceptors. 相似文献
63.
Aline Olivier Leila Benkhaled Tadeusz Pakula Bernd Ewen Andreas Best Mustapha Benmouna Ulrich Maschke 《大分子材料与工程》2004,289(12):1047-1052
Summary: This paper discusses static and dynamic mechanical properties of electron beam‐cured mixtures made of the nematic liquid crystal (LC) E7 and either tripropyleneglycol diacrylate (TPGDA) or propoxylated glycerol triacrylate (GPTA) as monomers differing essentially by their functionality. Dilution of the initial mixture with LC leads to a significant weakening of the film mechanical strength. Strong effects were found on Young modulus and rubbery state modulus. As the concentration of LC increases, these mechanical parameters drop significantly together with the glass transition temperature of the polymer showing a plasticizing effect. The results for the glass transition temperatures for the polymer and the LC were confirmed by thermograms obtained by differential scanning calorimetry.
64.
E. Y. A. Okino D. E. Teixeira M. R. de Souza M. A. E. Santana M. E. de Sousa 《Holz als Roh- und Werkstoff》2004,62(3):221-224
This research is part of a general study on the properties of oriented strandboard (OSB) using wood strands of species from Brazilian planted forests. The OSB industry is the latest wood related activity established in Brazil. In this particular part of the study, 80 mm long strands of Pinus taeda L. were bonded using two resin types (urea-formaldehyde and phenol-formaldehyde) at two levels of resin content (5% and 8%) to produce three-layer cross-aligned OSB to a face to core layer ratio of 1:2 and target density of 0.75 g/cm3. Physical and mechanical properties of the boards were evaluated according to ASTM standard D 1037-96a (1997) and the results compared to standards available as requirements for commercial structural panels. The results indicate that all the mechanical properties evaluated were above the requirements set forth by the Canadian standard CSA O437.0 (1993) for structural panels. The results of Janka hardness were in average 4 folds higher than the minimal requirements for Grade R-1 waferboard. Screw withdrawal values were also above the minimum required by grade M-3 of ANSI A208.1 standard (1993). Nevertheless, values of thickness swelling and water absorption were very high. The low dimensional stability may be related to the high density of the boards (“springback” effect) and also to the fact that no wax was used. 相似文献
65.
L. M. Santana 《International journal of remote sensing》2013,34(19):4225-4242
Latin American cities have witnessed rapid and unplanned growth causing social, economic and environmental problems. To solve these problems, urban planners require information and indicators that normally are not available. In this study, the applicability of remote sensing data to extract environmental data was examined. A Landsat Enhanced Thematic Mapper (ETM+) image was used to gather information about land surface temperature (Ts) and its relationship with the Normalized Difference Vegetation Index (NDVI) and the Leaf Water Content Index (LWC). A strong negative relationship between Ts and NDVI and between Ts and LWC was observed. Analysis of variance points out statistically significant differences in the averages of Ts, NDVI, and LWC among neighbourhoods. Areas with high density housing, with a deficient urban design and those with commercial establishments had the lowest means of NDVI and LWC, and higher means of Ts. On the other hand, neighbourhoods with a higher proportion of trees and green zones had higher NDVI and LWC, and lower Ts. Finally, all neighbourhoods were classified into those that have lower to higher Ts. Therefore, the greening campaigns and new landscape design of the city should be directed specifically at neighbourhoods with the lowest level of NDVI or LWC. 相似文献
66.
The main purpose of this work is to show the ability of the TCS (task configuration system) to perform both the design and the operation optimization of power plants. The TCS is a module that permits to set the main task of each one of the equipments of the system and consequently setting how they respond to variable loads. In this work, the TCS was applied to a micro cogeneration plant of 60 kW in which both the electrical and the thermal loads were variable. Primarily, the design optimization of the nominal power of the equipments and of the TCS configuration was performed for the loads and electricity/fuel costs assumed in the design. After this operational optimizations in cases where the loads and electricity/fuel costs were doubled and then halved in relation to the standard case were performed. The results presented the TCS in a very robust way in most of the cases even the operational conditions being very different from the originally assumed. Based on the results, it is possible to defend the use of the TCS to decrease the risk of high initial investments made in cogeneration systems. 相似文献
67.
Alisa Schnellbaecher Anton Lindig Maxime Le Mignon Tim Hofmann Brit Pardon Stephanie Bellmaine Aline Zimmer 《International journal of molecular sciences》2021,22(12)
Biomanufacturing processes may be optimized by storing cell culture media at room temperature, but this is currently limited by their instability and change in color upon long-term storage. This study demonstrates that one of the critical contributing factors toward media browning is tryptophan. LC-MS technology was utilized to identify tryptophan degradation products, which are likely formed primarily from oxidation reactions. Several of the identified compounds were shown to contribute significantly to color in solutions but also to exhibit toxicity against CHO cells. A cell-culture-compatible antioxidant, a-ketoglutaric acid, was found to be an efficient cell culture media additive for stabilizing components against degradation, inhibiting the browning of media formulations, and decreasing ammonia production, thus providing a viable method for developing room-temperature stable cell culture media. 相似文献
68.
C.M.A. Rodrigues C.M. Della Lucia R.M.C. Azeredo A.M. Cota A.M.C. Santana H.M. Pinheiro-SantAna 《Food Control》2010,21(3):264-271
This study aimed to elaborate a set of measures to control vitamin C losses in vegetables prepared at a food service (FS). Vegetables were randomly selected for vitamin C analysis by high performance liquid chromatography (HPLC) after delivery of raw material and during distribution for consumption of the food prepared. Some principles underlying the Hazards Analysis and Critical Control Points (HACCP) were applied to identify the Nutritional Control Points (NCP) for vitamin C losses. A Nutritional Control Measure (NCM) was adopted for each NCP as well as the monitoring criteria. The vegetables were again collected for vitamin C analysis after adoption of the NCMs. The results indicated reduction of vitamin C losses with NCM adoption. 相似文献
69.
Aline M. C. Racanicci Bente Danielsen Leif H. Skibsted 《European Food Research and Technology》2008,227(1):255-260
Aqueous extract of mate, made from dried leaves of Ilex paraguariensis, St. Hilaire, was shown to be effective during chilled
storage for up to 10 days in protecting lipids and vitamin E against oxidation in pre-cooked meat balls made from chicken
breast added 0.5% salt and packed in atmospheric air. Extracts made with water, methanol, ethanol or 70% aqueous acetone were
evaluated by comparing (1) total phenolic content, (2) radical scavenging capacity, (3) effect on lipid oxidation in a food
emulsion model, and in liposomes. Based on the three-step evaluation, aqueous mate extract was preferred for food use. Dried
leaves were further compared to dried rosemary leaves in chicken meat balls, and mate (0.05 and 0.10%) found to yield equal
or better protection than rosemary at the same concentration against formation of secondary lipid oxidation products. 相似文献
70.