全文获取类型
收费全文 | 32820篇 |
免费 | 1412篇 |
国内免费 | 120篇 |
专业分类
电工技术 | 428篇 |
综合类 | 229篇 |
化学工业 | 6121篇 |
金属工艺 | 702篇 |
机械仪表 | 759篇 |
建筑科学 | 1145篇 |
矿业工程 | 102篇 |
能源动力 | 1080篇 |
轻工业 | 4522篇 |
水利工程 | 287篇 |
石油天然气 | 175篇 |
武器工业 | 6篇 |
无线电 | 2525篇 |
一般工业技术 | 4753篇 |
冶金工业 | 6396篇 |
原子能技术 | 256篇 |
自动化技术 | 4866篇 |
出版年
2024年 | 59篇 |
2023年 | 204篇 |
2022年 | 647篇 |
2021年 | 964篇 |
2020年 | 670篇 |
2019年 | 758篇 |
2018年 | 854篇 |
2017年 | 914篇 |
2016年 | 905篇 |
2015年 | 718篇 |
2014年 | 1066篇 |
2013年 | 1821篇 |
2012年 | 1579篇 |
2011年 | 1964篇 |
2010年 | 1449篇 |
2009年 | 1465篇 |
2008年 | 1336篇 |
2007年 | 1171篇 |
2006年 | 943篇 |
2005年 | 961篇 |
2004年 | 1001篇 |
2003年 | 912篇 |
2002年 | 869篇 |
2001年 | 738篇 |
2000年 | 583篇 |
1999年 | 558篇 |
1998年 | 2079篇 |
1997年 | 1345篇 |
1996年 | 950篇 |
1995年 | 626篇 |
1994年 | 489篇 |
1993年 | 545篇 |
1992年 | 227篇 |
1991年 | 290篇 |
1990年 | 234篇 |
1989年 | 201篇 |
1988年 | 211篇 |
1987年 | 161篇 |
1986年 | 167篇 |
1985年 | 186篇 |
1984年 | 131篇 |
1983年 | 97篇 |
1982年 | 120篇 |
1981年 | 129篇 |
1980年 | 119篇 |
1979年 | 93篇 |
1978年 | 76篇 |
1977年 | 145篇 |
1976年 | 229篇 |
1975年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
J. C. Gasparetto F. S. F. Smolarek T. M. G. de Francisco L. C. Miranda R. Pontarolo P. F. Siqueira 《Journal of the American Oil Chemists' Society》2012,89(7):1211-1222
In this study, a new HPLC method was developed and validated for the determination of daidzin, genistin, glycitin, and their respective aglycones daidzein, genistein and glycitein in extracts from different stages of soy processing. The chromatographic separation was achieved using a Bonus RP 100 × 3.0 mm (3.5-μm particle size) column maintained at 35 °C. The mobile phase consisted of a gradient of water and acetonitrile both containing 0.1% formic acid. Analyses were conducted at a flow rate of 1.0 mL min−1 and the detector was set at 254 nm. Validation parameters indicated that the method has high selectivity and is linear over a range of 1.5–150 μg mL−1 for all compounds. The range of recovery was 95–102% with a RSD% <5% for intra-day and inter-day precision. The robustness study indicated that the flow rate was the only critical factor. The new HPLC–DAD method was successfully applied to real samples and excellent separation was achieved without the need of any sample pretreatment. 相似文献
982.
983.
984.
985.
Moisés Frías Holmer Savastano Ernesto Villar M. Isabel Sánchez de Rojas Sergio Santos 《Cement and Concrete Composites》2012,34(9):1019-1023
The worldwide production of bamboo generates large volumes of leaf wastes, which are deposited in landfills or burned in an uncontrolled manner, with negative effects in the environment. The ash obtained by calcining of the bamboo leaf waste, shows good qualities as supplementary cementing material for the production of blended cements.The current paper shows a detailed scientific study of a Brazilian bamboo leaf ash (BLA) calcined at 600 °C in small scale condition, by using different techniques (XRF, XRD, SEM/EDX, FT–IR, TG/DTG) and technical study in order to analyse the behaviour of this ash in blended cements elaborated with 10% and 20% by mass of BLA. The results stated that this ash shows a very high pozzolanic activity, with a reaction rate constant K of the order of 10?1/h and type I CSH gel was the main hydrated phase obtained from pozzolanic reaction. The BLA blended cements (10% and 20%) complied with the physical and mechanical requirements of the existing European standards. 相似文献
986.
Marta C. Picardo José Luiz de Medeiros Juliana Garcia M. Monteiro Ricardo Moreira Chaloub Mario Giordano Ofélia de Queiroz Fernandes Araújo 《Clean Technologies and Environmental Policy》2013,15(2):275-291
The increasing interest for biotechnological use of microalgae demands a methodology for selection of species suitable to support the development of technologies based on the use of such non-conventional renewable raw material, i.e., green industrial applications. The vast and expanding collection of experimental data on both cell growth and biomass composition available in the literature can be used to reduce the cost of the experimental investigations required to support process engineering and optimization. Selecting the appropriate organism requires extracting useful information from such data, a cumbersome task since various multidisciplinary factors must be considered. This paper presents a computer-aided methodology for selecting appropriate algal species given an energy or green chemical process application employing microalgae as a renewable raw material. The approach is “system oriented”, based on biomass composition and chemical processing of the biomass downstream of the CO2 biofixation and harvesting operations. Quantitative performance results are supported by professional process simulation. Besides comparison of a set of species performances, the proposed methodology also allows the discrimination among distinct algal compositions resulting from different growth conditions for a given species. Furthermore, three categories of screening metrics are proposed to be maximized by the decision making procedure in order to elicit the relevant information. To demonstrate the potential of the proposed methodology, a databank of both biochemical and elemental compositions of microalgal biomass was used in three green applications: Assessment of biomass heating value; production of syngas by gasification of the biomass; and production of Bio-H2. Within the accuracy of the databank employed to illustrate the procedure, the methodology selected Botryococcus braunii and Isochrysis galbana as potential promising candidates, for the three examined applications. 相似文献
987.
Nair do Amaral Sampaio Neta José Cleiton Sousa dos Santos Soraya de Oliveira Sancho Sueli Rodrigues Luciana Rocha Barros Gonçalves Ligia R. Rodrigues José A. Teixeira 《Food Hydrocolloids》2012
Sugar esters are compounds with surfactant properties (biosurfactants), i.e., capable of reducing the surface tension and promote the emulsification of immiscible liquids. On the other hand, as with all emulsions, coconut milk is not physically stable and is prone to phase separation. Therefore, the aim of this work was to evaluate the synthesis of fructose, sucrose and lactose esters from the corresponding sugars using Candida antarctica type B lipase immobilized in two different supports, namely acrylic resin and chitosan, and evaluate its application in the stabilization of coconut milk emulsions. The enzyme immobilized on chitosan showed the highest yield of lactose ester production (84.1%). Additionally, the production of fructose ester was found to be higher for the enzyme immobilized on the acrylic resin support (74.3%) as compared with the one immobilized on chitosan (70.1%). The same trend was observed for the sucrose ester, although with lower percentage yields. Sugar esters were then added to samples of fresh coconut milk and characterized according to their surface tension, emulsification index and particle size distribution. Although the microscopic analysis showed similar results for all sugar esters, results indicated lactose ester as the best biosurfactant, with a surface tension of 38.0 N/m and an emulsification index of 54.1%, when used in a ratio of 1:10 (biosurfactant:coconut milk, v/v) for 48 h experiments. 相似文献
988.
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
989.
Francieli Tiecher Denise Carpena Coitinho Dal Molin Márcia Elisa Boscato Gomes Nicole Pagan Hasparyk Paulo José Meleragno Monteiro 《Cement and Concrete Composites》2012,34(10):1130-1140
Mesostasis material present in the interstices of volcanic rocks is the main cause of the alkali-aggregate reaction (AAR) in concretes made with these rock aggregates. Mesostasis often is referred to as volcanic glass, because it has amorphous features when analyzed by optical microscopy. However, this study demonstrates that mesostasis in the interstitials of volcanic rocks most often consists of micro to cryptocrystalline mineral phases of quartz, feldspars, and clays. Mesostasis has been identified as having different characteristics, and, thus, this new characterization calls for a re-evaluation of their influence on the reactivity of the volcanic rocks. The main purpose of this study is to correlate the characteristics of mesostasis with the AAR in mortar bars containing basalts and rhyolites. 相似文献
990.
R. M. J. Janssen A. Endo J. J. A. Baselmans P. J. de Visser R. Barends T. M. Klapwijk 《Journal of Low Temperature Physics》2012,167(3-4):354-359
The sensitivity of microwave kinetic inductance detectors (MKIDs) based on coplanar waveguides (CPWs) needs to be improved by at least an order of magnitude to satisfy the requirements for space-based terahertz astronomy. Our aim is to investigate if this can be achieved by reducing the width of the CPW to much below what has typically been made using optical lithography (>1?μm). CPW resonators with a central line width as narrow as 300?nm were made in NbTiN using electron beam lithography and reactive ion etching. In a systematic study of quarter-wave CPW resonators with varying widths it is shown that the behavior of responsivity, noise and power handling as a function of width continues down to 300?nm. This encourages the development of narrow KIDs using Al in order to improve their sensitivity. 相似文献