全文获取类型
收费全文 | 3763篇 |
免费 | 175篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 59篇 |
综合类 | 7篇 |
化学工业 | 912篇 |
金属工艺 | 67篇 |
机械仪表 | 70篇 |
建筑科学 | 104篇 |
矿业工程 | 21篇 |
能源动力 | 117篇 |
轻工业 | 301篇 |
水利工程 | 28篇 |
石油天然气 | 21篇 |
无线电 | 377篇 |
一般工业技术 | 702篇 |
冶金工业 | 418篇 |
原子能技术 | 36篇 |
自动化技术 | 706篇 |
出版年
2023年 | 43篇 |
2022年 | 122篇 |
2021年 | 140篇 |
2020年 | 83篇 |
2019年 | 100篇 |
2018年 | 111篇 |
2017年 | 103篇 |
2016年 | 134篇 |
2015年 | 90篇 |
2014年 | 150篇 |
2013年 | 249篇 |
2012年 | 201篇 |
2011年 | 250篇 |
2010年 | 176篇 |
2009年 | 155篇 |
2008年 | 157篇 |
2007年 | 155篇 |
2006年 | 143篇 |
2005年 | 116篇 |
2004年 | 109篇 |
2003年 | 99篇 |
2002年 | 94篇 |
2001年 | 54篇 |
2000年 | 52篇 |
1999年 | 66篇 |
1998年 | 76篇 |
1997年 | 68篇 |
1996年 | 56篇 |
1995年 | 47篇 |
1994年 | 30篇 |
1993年 | 37篇 |
1992年 | 27篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 33篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 29篇 |
1984年 | 17篇 |
1983年 | 22篇 |
1982年 | 24篇 |
1981年 | 12篇 |
1980年 | 20篇 |
1979年 | 22篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 24篇 |
1975年 | 18篇 |
1973年 | 12篇 |
排序方式: 共有3946条查询结果,搜索用时 15 毫秒
81.
We present specific new expressions for thermal stresses as Green's functions for a plane boundary value problem of steady-state thermoelasticity for a semi-layer. We also obtain new integration formulas of Green's type, which determine the thermal stresses in the form of integrals of the products of the given distributed internal heat source, boundary temperature, and heat flux and derived kernels. Elementary functions results obtained are formulated in a theorem, which is proved using the harmonic integral representations method to derive thermal stresses Green's functions, which are written in terms of Green's functions for Poisson's equation. A new solution to particular two-dimensional boundary value problem for a semi-layer under a boundary constant temperature gradient is obtained in explicit form. Graphical presentations for thermal stresses Green's functions created by a unit heat source (line load in out-of-plane direction) and by a temperature gradient are also included. 相似文献
82.
Chi Zhang P.R. Shukla David G. Victor Thomas C. Heller Debashish Biswas Tirthankar Nag 《Energy Policy》2006
The study examines the dynamics of carbon emissions baselines of electricity generation in Indian states and Chinese provinces in the backdrop of ongoing electricity sector reforms in these countries. Two Indian states—Gujarat and Andhra Pradesh, and three Chinese provinces–Guangdong, Liaoning and Hubei have been chosen for detailed analysis to bring out regional variations that are not captured in aggregate country studies. The study finds that fuel mix is the main driver behind the trends exhibited by the carbon baselines in these five cases. The cases confirm that opportunities exist in the Indian and Chinese electricity sectors to lower carbon intensity mainly in the substitution of other fuels for coal and, to a lesser extent, adoption of more efficient and advanced coal-fired generation technology. Overall, the findings suggest that the electricity sectors in India and China are becoming friendlier to the global environment. Disaggregated analysis, detailed and careful industry analysis is essential to establishing a power sector carbon emissions baseline as a reference for CDM crediting. However, considering all the difficulties associated with the baseline issue, our case studies demonstrate that there is merit in examining alternate approaches that rely on more aggregated baselines. 相似文献
83.
OH Perez R Aznar LM Ballesteros JD Mendez A Rosado 《Canadian Metallurgical Quarterly》1976,14(4):421-433
Ribonucleic acid (RNA) metabolism of the normal and copper-treated ( Cu-T200 IUD) human endometrium was investigated. The relative concentration of total, messenger, ribosomal and transfer RNA was measured in normal and Cu-treated endometrium using the technique of affinity chromatography in polysepharose. The transition from the proli ferative to the secretory endometrium in normal women was accompanied by significant increases (p less than .05) in total RNA, messenger RNA and in ribosomal RNA. The relative proportions of bound and free messenger RNA were also modified by endometrial maturation changing from 70% bound messenger RNA in the proliferative to 83% in the secretory phase. Cu-T200 Cu release appeared to particularly affect RNA metabolism in the secretory phase. During the proliferative phase only the concentration of transfer RNA and the proportion of bound to free messenger RNA were modified by the Cu-T200. The Cu-T200 induced significant decreases (p less than .01 and p less than .05) in all RNA parameters, with the exception of the RNA/deoxyribonucleic acid ratio. 相似文献
84.
Nikolaos Kontoudakis Mireia Esteruelas Francesca Fort Joan Miquel Canals Victor De Freitas Fernando Zamora 《Food chemistry》2011
Nowadays, consumers demand red wines with deep colour, soft tannins and fruit scents, but these wines can only be obtained from grapes with complete phenolic maturity. Diverse methods have been proposed for measuring phenolic maturity. However, all these methods only provide the average value and do not consider any possible heterogeneity. Throughout ripening, grapes were separated according to their density, which revealed the existence of a large heterogeneity. Grapes at harvest were also separated by density in three groups. The higher the density of the grapes the higher ethanol content, pH, colour intensity, total phenolic index and anthocyanin and proanthocyanidin concentrations, and the lower the titratable acidity and bitterness of the wines. When the grapes were denser the wines were also better balanced in flavour and mouthfeel sensation. These results suggest that grape heterogeneity may influence the final wine composition and quality and therefore it should be considered at harvest. 相似文献
85.
Virgínia C. Fernandes Valentina F. Domingues Victor de Freitas Cristina Delerue-Matos Nuno Mateus 《Food chemistry》2012
Consumer awareness, pesticide and fertilizer contaminations and environmental concerns have resulted in significant demand for organically grown farm produce. Consumption of berries has become popular among health-conscious consumers due to the high levels of valuable antioxidants, such as anthocyanins and other phenolic compounds. The present study evaluated the influence that organic farming (OF) and integrated pest management (IPM) practise exert on the total phenolic content in 22 strawberry samples from four varieties. Postharvest performance of OF and IPM strawberries grown in the same area in the centre of Portugal and harvested at the same maturity stage were compared. Chemical profiles (phenolic compounds) were determined with the aid of HPLC-DAD/MS. Total phenolic content was higher for OF strawberry extracts. This study showed that the main differences in bioactive phytochemicals between organically and IPM grown strawberries concerned their anthocyanin levels. Organically grown strawberries were significantly higher in antioxidant activity than were the IPM strawberries, as measured by DPPH and FRAP assays. 相似文献
86.
AbstractDigitisation of historical costumes is an actual multidisciplinary area of research that uses science-based methods of reconstruction in virtual reality. The main aim of this study was to create a method for generating numerical replicas of skirts of the late 1850?s and the1860s. We applied two-dimensional and three-dimensional software to parameterise all the elements of the skirts and recreate them layer by layer. Computer modelling allowed us to gain insight into the interrelation between the parameters of cage crinolines, skirt construction and the behaviour of textile materials on the crinoline’s surface. A replica of a historical costume was generated and the similarity between the historical prototype and its replica was proved. The application of computer graphics tools for the reconstruction of the visible and invisible elements of historical costumes can advance their scientific study. The reconstructions can be an effective instrument for teaching, enriching museum collections and producing online presentations. 相似文献
87.
Victor Ladero Esther Sánchez‐Llana María Fernández Miguel A. Alvarez 《International Journal of Food Science & Technology》2011,46(3):516-521
Biogenic amines (BAs) are low molecular weight organic bases with biological activity, synthesised by the microbial decarboxylation of precursor amino acids such as histidine, tyrosine or arginine. The consumption of food and beverages containing large amounts of BA can have toxicological effects. This paper reports the resistance of aminogenic lactic acid bacteria strains to pasteurisation (63 °C for 30 min). Skimmed milk inoculated with histamine‐ and tyramine‐producing strains of Enterococcus and Lactobacillus was subjected to pasteurisation. The viable number of Enterococcus durans IPLA 655 was reduced by 1 log, while that of Enterococcus faecalis BA64 was reduced by 3 logs. Lactobacillus brevis CECT 3810 did not survive pasteurisation, while the other Lactobacillus strains examined were more resistant; their viable numbers were reduced by about 2 logs. The two most resistant strains, E. durans IPLA 655 and Lactobacillus curvatus VI6, were subjected to higher temperatures. Enterococcus durans was completely inactivated at 78 °C, while some live cells of Lb. curvatus were observed. These results show that some native, metabolically active BA producers could be found in pasteurised milk owing to their resistance to the thermal treatment; their presence could have a negative impact on the final content of BAs in dairy products made from such milk. 相似文献
88.
Joo Pissarra Sandra Loureno Jos Maria Machado Nuno Mateus David Guimaraens Victor de Freitas 《Journal of the science of food and agriculture》2005,85(7):1091-1097
The commercial wine spirit used for this study revealed that the aldehyde content mainly comprises acetaldehyde but other aldehydes such as propionaldehyde, 2‐methylbutyraldehyde, isovaleraldehyde, methylglyoxal, benzaldehyde and others are also present in significant amounts. A typical grape must was used to assess the influence of wine spirit in the analytical and sensorial characteristics of fortified wines. Decreasing levels of anthocyanins, as well the increase in the red colour and tanning capacity, were observed, and seem to be positively correlated with the increase of the aldehyde content present in the wine spirits used to fortify the must. Using the CIE L*a*b* system, this aldehyde content present in the spirit used seemed to be correlated with the decrease of the wines' lightness (darkening effect), the displacement of the hue angle to higher values (yellowing effect) and the increase of the chromaticity (colour saturation) of the wines. Copyright © 2005 Society of Chemical Industry 相似文献
89.
Real time quantitative PCR detection of histamine-producing lactic acid bacteria in cheese: Relation with histamine content 总被引:1,自引:0,他引:1
Victor Ladero Daniel M. Linares María Fernndez Miguel A. Alvarez 《Food research international (Ottawa, Ont.)》2008,41(10):1015-1019
Biogenic amines (BAs) are low molecular weight organic bases with biological activity, mainly formed by the microbial decarboxylation of amino acids. The consumption of food containing large amounts of some BAs can have toxicological consequences. Histamine is the most active BA and the most frequently involved in food-borne intoxications. This article reports the concentrations of histamine found in 80 cheeses made from different types of milk and subjected to different ripening periods. Histamine was detected in 41.25% of the samples, with values ranging from 20 to over 1000 mg per Kg of cheese. The highest histamine concentrations were recorded in long ripening cheeses made from raw milk. The presence and quantification of histamine-producing lactic acid bacteria was determined by RT-qPCR, and a good association was obtained between the Ct values and histamine concentrations determined by HPLC. 相似文献
90.
Victor Enujiugha Collins Amadi Tajudeen Sanni 《European Food Research and Technology》2002,214(6):497-500
The !-amylases of raw and fermented seeds of African oil bean (Pentaclethra macrophylla Benth) were isolated, partially purified (tenfold) and subjected to different thermal and pH conditions. The specific activities of the purified enzyme from raw and fermented seeds were 0.037 ml-1 min-1 and 0.88 ml-1 min-1 respectively. The !-amylase from fermented seeds was more thermostable with optimum activity at 70 °C, compared to the optimum temperature of 60 °C obtained for the raw seed enzyme. The assayed !-amylases were stable over a wide range of pH (3.0-7.0), with optimum activity found at pH 6.0 and pH 5.0 for raw and fermented seeds respectively. The results show that the !-amylase of Pentaclethra macrophylla complements the microbial amylases in the mainly bacterial fermentation of African oil bean seeds to 'ugba', a highly nutritious food condiment. While the !-amylase in the raw seeds was basically the plant enzyme, that isolated from the fermented seeds was a combination of plant and microbial !-amylases. 相似文献