全文获取类型
收费全文 | 3632篇 |
免费 | 224篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 65篇 |
综合类 | 13篇 |
化学工业 | 882篇 |
金属工艺 | 124篇 |
机械仪表 | 95篇 |
建筑科学 | 77篇 |
矿业工程 | 16篇 |
能源动力 | 84篇 |
轻工业 | 351篇 |
水利工程 | 20篇 |
石油天然气 | 5篇 |
无线电 | 276篇 |
一般工业技术 | 665篇 |
冶金工业 | 585篇 |
原子能技术 | 14篇 |
自动化技术 | 591篇 |
出版年
2023年 | 43篇 |
2022年 | 83篇 |
2021年 | 153篇 |
2020年 | 105篇 |
2019年 | 94篇 |
2018年 | 131篇 |
2017年 | 123篇 |
2016年 | 172篇 |
2015年 | 114篇 |
2014年 | 180篇 |
2013年 | 257篇 |
2012年 | 213篇 |
2011年 | 205篇 |
2010年 | 142篇 |
2009年 | 166篇 |
2008年 | 166篇 |
2007年 | 143篇 |
2006年 | 101篇 |
2005年 | 70篇 |
2004年 | 81篇 |
2003年 | 70篇 |
2002年 | 43篇 |
2001年 | 56篇 |
2000年 | 26篇 |
1999年 | 56篇 |
1998年 | 165篇 |
1997年 | 111篇 |
1996年 | 81篇 |
1995年 | 52篇 |
1994年 | 44篇 |
1993年 | 47篇 |
1992年 | 21篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 11篇 |
1985年 | 23篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 36篇 |
1974年 | 5篇 |
1932年 | 4篇 |
排序方式: 共有3863条查询结果,搜索用时 11 毫秒
101.
Grégory Chatelain Micaël Ripert Carole Farre Salomé Ansanay-Alex Carole Chaix 《Electrochimica acta》2012
We report the use of a four-ferrocene modified oligonucleotide as a probe for DNA detection with a gold electrode microsystem. This oligonucleotide is synthesized by automated solid-phase synthesis with four successive ferrocene moieties at the 5′-end and a C6-thiol modifier group at the 3′-end. The grafting of this 4Fc-DNA probe on a gold electrode microsystem results in the appearance of the ferrocene redox couple in cyclic voltammetry. The probe sequence is a stem-loop structure that folds efficiently on the electrode, thus optimizing electron transfer. Such architecture serves as sensor for DNA detection which is based on hybridization. The resulting disposable voltammetric sensor allowed direct, reagentless DNA detection in a small volume (20 μL). Electrochemical response upon hybridization with complementary short sequence (30-base length) and long sequence (50-base length) strands was observed by differential pulse voltammetry. Current variations were compared. The longer the sequence, the greater the decrease in current. The system's detection limit was estimated at 3.5 pM (0.07 fmol in 20 μL) with the 50-base length target and provided a dynamic detection range between 3.5 pM and 5 nM. Single mismatch detection showed a good level of sensitivity. The system was regenerated twice with no significant loss of Fc signal. Finally, 1 pM sensitivity was reached with a long chain analog of DNA PCR products of Influenza virus. 相似文献
102.
Fabrice Roussière Christophe Baley Grégory Godard Dominique Burr 《Applied Composite Materials》2012,19(2):171-188
Nowadays, the ecological footprint of a material is becoming tremendously important. The Poly l-Lactide Acid (PLLA) matrix
composites reinforced by randomly scattered flax fibres have mechanical properties similar to polyester/glass composites [1], lower environmental impacts and can be compost at the end of their lives. In this study, the mechanical characterization
of biocomposites has been pushed further with the determination of the compressive and tensile properties. Furthermore, the
mechanical properties of single flax fibres have been measured and implemented in a micro-mechanical estimation of the composite
elastic modulus. Tensile and compressive stiffness determined by the mechanical analyses show very good correlations with
the mathematical estimation. 相似文献
103.
To exploit spectrum resources on a secondary basis, a Sensor Network Aided Cognitive Radio Network uses a wireless sensor network that assists a secondary cognitive radio network by providing information about the current primary spectrum occupancy. In this paper we determine the performance for different cell sizes when considering the costs for deployment of base stations in a secondary network that exploits spectrum holes identified by the wireless sensor network. The secondary base station is deployed co-located with a mobile primary network that uses a cellular reuse pattern with seven frequencies. Performance of the secondary system and impact on the primary system are mainly studied in terms of throughput, packet loss and coverage when using spectrum holes in the space, time and frequency domains. Especially, we find that the cell size and configured transmit powers for the secondary system are important for optimal system performance, and that smaller cell sizes and less expensive base stations for the secondary system are beneficial. The impact on primary system performance was found to be low, but that optimal tuning of the sensor network is important. 相似文献
104.
Eric Chin David Chieng Victor Teh Marek Natkaniec Krzysztof Loziak Janusz Gozdecki 《Wireless Networks》2014,20(3):379-396
Through time domain observation, typical wireless signal strength values seems to exhibit some forms of mean-reverting and discontinuous “jumps” behaviour. Motivated by this fact, we propose a wireless link prediction and triggering (LPT) technique using a modified mean-reverting Ornstein–Uhlenbeck (OU) jump diffusion process. The proposed technique which we refer as OU-LPT is an integral component of wireless mesh network monitoring system developed by ICT FP7 CARrier grade wireless MEsh Network project. In particular, we demonstrate how this technique can be applied in the context of wireless mesh networks to support link switching or handover in the event of predicted link degradation or failure. The proposed technique has also been implemented and evaluated in a real-time experimental testbed. The results show that OU-LPT technique can significantly enhance the reliability of wireless links by reducing the rate of false triggers compared to a conventional linear prediction technique and therefore offers a new direction on how wireless link prediction, triggering and switching process can be conducted in the future. 相似文献
105.
106.
Krzysztof Witek Tadeusz Piotrowski Agata Skwarek 《Materials Science and Engineering: B》2012,177(15):1373-1377
Infrared radiation as a heat source is used in many fields. In particular, the positive effect of far-infrared radiation on living organisms has been observed. This paper presents two technological solutions for infrared heater production using polymer-silver and polymer-carbon pastes screenprinted on foil substrates. The purpose of this work was the identification of polymer layers as a specific frequency range IR radiation sources. The characterization of the heaters was determined mainly by measurement of the surface temperature distribution using a thermovision camera and the spectral characteristics were determined using a special measuring system. Basic parameters obtained for both, polymer silver and polymer carbon heaters were similar and were as follows: power rating of 10–12 W/dm2, continuous working surface temperature of 80–90 °C, temperature coefficient of resistance (TCR) about +900 ppm/K for polymer-carbon heater and about +2000 ppm/K for polymer-silver, maximum radiation intensity in the wavelength range of 6–14 μm with top intensity at 8.5 μm and heating time about 20 min. For comparison purposes, commercial panel heater was tested. The results show that the characteristics of infrared polymer heaters are similar to the characteristics of the commercial heater, so they can be taken into consideration as the alternative infrared radiation sources. 相似文献
107.
P. Balasubramanian L. Hupa B. Jokic R. Detsch A. Grünewald Aldo R. Boccaccini 《Journal of Materials Science》2017,52(15):8785-8792
Boron-containing bioactive glasses (BGs) are being extensively researched for the treatment and regeneration of bone defects because of their osteostimulatory and neovascularization potential. In this study, we report the effects of the ionic dissolution products (IDPs) of different boron-doped, borosilicate, and borate BG scaffolds on mouse bone marrow stromal cells in vitro, using an angiogenesis assay. Five different BG scaffolds of the system SiO2–Na2O–K2O–MgO–CaO–P2O5–B2O3 (with varying amounts of SiO2 and B2O3) were fabricated by the foam replication technique. Bone marrow stromal cells were cultivated in contact with the IDPs of the boron-containing BG scaffolds at different concentrations for 48 h. The expression and secretion of vascular endothelial growth factor (VEGF) from the cultured cells was measured quantitatively using the VEGF ELISA Kit. Cell viability and cell morphology were determined using WST-8 assay and H&E staining, respectively. The cellular response was found to be dependent on boron content and the B release profile from the glasses corresponded to the positive or negative biological activity of the BGs. 相似文献
108.
109.
Martti Heinonen Miltiadis Anagnostou Stephanie Bell Mark Stevens Robert Benyon Reidun Anita Bergerud Jovan Bojkovski Rien Bosma Jan Nielsen Norbert B?se Plunkett Cromwell Aliye Kartal Dogan Seda Aytekin Ali Uytun Vito Fernicola Krzysztof Flakiewicz Bertrand Blanquart Domen Hudoklin Per Jacobson Anders Kentved Isabel Lóio George Mamontov Alexandra Masarykova Helmut Mitter Regina Mnguni Jan Otych Anton Steiner Nagyné Szilágyi Zsófia Davor Zvizdic 《International Journal of Thermophysics》2012,33(8-9):1422-1437
In the field of humidity quantities, the first CIPM key comparison, CCT-K6 is at its end. The corresponding European regional key comparison, EUROMET.T-K6, was completed in early 2008, about 4?years after the starting initial measurements in the project. In total, 24 NMIs from different countries took part in the comparison. This number includes 22 EURAMET countries, and Russia and South Africa. The comparison covered the dew-point temperature range from ?50?°C to +20?°C. It was carried out in three parallel loops, each with two chilled mirror hygrometers as transfer standards in each loop. The comparison scheme was designed to ensure high quality results with evenly spread workload for the participants. It is shown that the standard uncertainty due to the long-term instability was smaller than 0.008?°C in all loops. The standard uncertainties due to links between the loops were found to be smaller than 0.025?°C at ?50?°C and 0.010?°C elsewhere. Conclusions on the equivalence of the dew-point temperature standards are drawn on the basis of calculated bilateral degrees of equivalence and deviations from the EURAMET comparison reference values (ERV). Taking into account 16 different primary dew-point realizations and 8 secondary realizations, the results demonstrate the equivalence of a large number of laboratories at an uncertainty level that is better than achieved in other multilateral comparisons so far in the humidity field. 相似文献
110.
Beatriz Gutiérrez‐Rivera Krzysztof Waliszewski‐Kubiak Octavio Carvajal‐Zarrabal Maria Guadalupe Aguilar‐Uscanga 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(2):263-270
BACKGROUND: Efficient conversion of glucose/xylose mixtures from lignocellulose is necessary for commercially viable ethanol production. Oxygen and carbon sources are of paramount importance for ethanol yield. The aim of this work was to evaluate different glucose/xylose mixtures for ethanol production using S. cerevisiae ITV‐01 (wild type yeast) and P. stipitis NRRL Y‐7124 and the effect of supplying oxygen in separate and co‐culture processes. RESULTS: The complete conversion of a glucose/xylose mixture (75/30 g L?1) was obtained using P. stipitis NRRL Y‐7124 under aerobic conditions (0.6 vvm), the highest yield production being Yp/s = 0.46 g g?1, volumetric ethanol productivity Qpmax = 0.24 g L?1 h?1 and maximum ethanol concentration Pmax = 34.5 g L?1. In the co‐culture process and under aerobic conditions, incomplete conversion of glucose/xylose mixture was observed (20.4% residual xylose), with a maximum ethanol production of 30.3 g L?1, ethanol yield of 0.4 g g?1 and Qpmax = 1.26 g L?1 h?1. CONCLUSIONS: The oxygen present in the glucose/xylose mixture promotes complete sugar consumption by P. stipitis NRRL Y‐7124 resulting in ethanol production. However, in co‐culture with S. cerevisiae ITV‐01 under aerobic conditions, incomplete fermentation occurs that could be caused by oxygen limitation and ethanol inhibition by P. stipitis NRRL Y‐7124; nevertheless the volumetric ethanol productivity increases fivefold compared with separate culture. Copyright © 2011 Society of Chemical Industry 相似文献