全文获取类型
收费全文 | 8799篇 |
免费 | 411篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 118篇 |
综合类 | 38篇 |
化学工业 | 2251篇 |
金属工艺 | 226篇 |
机械仪表 | 184篇 |
建筑科学 | 601篇 |
矿业工程 | 20篇 |
能源动力 | 281篇 |
轻工业 | 844篇 |
水利工程 | 87篇 |
石油天然气 | 43篇 |
武器工业 | 1篇 |
无线电 | 658篇 |
一般工业技术 | 1448篇 |
冶金工业 | 548篇 |
原子能技术 | 58篇 |
自动化技术 | 1815篇 |
出版年
2023年 | 85篇 |
2022年 | 202篇 |
2021年 | 333篇 |
2020年 | 184篇 |
2019年 | 200篇 |
2018年 | 270篇 |
2017年 | 233篇 |
2016年 | 314篇 |
2015年 | 233篇 |
2014年 | 337篇 |
2013年 | 624篇 |
2012年 | 482篇 |
2011年 | 614篇 |
2010年 | 426篇 |
2009年 | 491篇 |
2008年 | 453篇 |
2007年 | 410篇 |
2006年 | 341篇 |
2005年 | 291篇 |
2004年 | 269篇 |
2003年 | 258篇 |
2002年 | 189篇 |
2001年 | 137篇 |
2000年 | 137篇 |
1999年 | 114篇 |
1998年 | 128篇 |
1997年 | 128篇 |
1996年 | 96篇 |
1995年 | 79篇 |
1994年 | 79篇 |
1993年 | 83篇 |
1992年 | 58篇 |
1991年 | 60篇 |
1990年 | 62篇 |
1989年 | 68篇 |
1988年 | 49篇 |
1987年 | 47篇 |
1986年 | 51篇 |
1985年 | 55篇 |
1984年 | 63篇 |
1983年 | 45篇 |
1982年 | 38篇 |
1981年 | 37篇 |
1980年 | 39篇 |
1979年 | 32篇 |
1978年 | 34篇 |
1977年 | 33篇 |
1976年 | 39篇 |
1975年 | 40篇 |
1973年 | 36篇 |
排序方式: 共有9221条查询结果,搜索用时 0 毫秒
991.
Jan Brückner Sören Thieme Falko Böttger‐Hiller Ingolf Bauer Hannah Tamara Grossmann Patrick Strubel Holger Althues Stefan Spange Stefan Kaskel 《Advanced functional materials》2014,24(9):1284-1289
The lithium sulfur battery system has been studied since the late 1970s and has seen renewed interest in recent years. However, even after three decades of intensive research, prolonged cycling can only be achieved when a large excess of electrolyte and lithium is used. Here, for the first time, a balanced and stable lithium sulfur full cell is demonstrated with silicon–carbon as well as all‐carbon anodes. More than 1000 cycles, a specific capacity up to 1470 mAh g?1 sulfur (720 mAh g?1 cathode), and a high coulombic efficiency of over 99% even with a low amount of electrolyte are achieved. The alternative anodes do not suffer from electrolyte depletion, which is found to be the main cause of cell failure when using metallic lithium anodes. 相似文献
992.
Wang Z Yang C Fingas M Hollebone B Peng X Hansen AB Christensen JH 《Environmental science & technology》2005,39(22):8700-8707
Biomarkers have become increasingly important for identifying the source of spilled oil, due to their specificity and high resistance to biodegradation. The biomarkers most commonly used in forensic investigations are the high molecular weight (MW) tri- and pentacyclic terpanes and steranes. For lighter petroleum products such as jet fuels and diesels, the refining processes remove most high MW biomarkers from the original crude oil feedstock. The smaller bicyclic sesquiterpanes, however, are concentrated in these products. Sesquiterpanes are ubiquitous components of crude oils and ancient sediments. Examination of GC-MS chromatograms of these bicyclic biomarkers using their characteristic fragment ions (m/z 123, 179, 193, and 207) provides a highly diagnostic means for identifying spilled oil, particularly for lighter refined product samples that are difficult to identify by current techniques. In this work, sesquiterpanes in crude oils and petroleum products are identified and characterized, distributions of sesquiterpanes in oils and refined products are compared, the effects of evaporative weathering on sesquiterpane distributions are examined, and a methodology using diagnostic indices of sesquiterpanes is developed for oil correlation and differentiation. Finally, two case studies are presented to illustrate the unique utility of sesquiterpanes for fingerprinting and identifying unknown diesel spills. 相似文献
993.
Marta Jaczak-Pieniek Dagmara Migut Tomasz Piechowiak Jan Buczek Maciej Balawejder 《International journal of molecular sciences》2021,22(13)
Quercetin, classified as a flavonoid, is a strong antioxidant that plays a significant role in the regulation of physiological processes in plants, which is particularly important in the case of biotic and abiotic stresses. The study investigated the effect of the use of potassium quercetin solutions in various concentrations (0.5%, 1.0%, 3.0% and 5.0%) on the physiological and biochemical properties of wheat seedlings. A pot experiment was carried out in order to determine the most beneficial dose of this flavonoid acting as a bio-stimulant for wheat plants. Spraying with quercetin derivative solutions was performed twice, and physiological measurements (chlorophyll content and fluorescence as well as gas exchange) were carried out on the first and seventh days after each application. The total phenolic compounds content and the total antioxidant capacity were also determined. It was shown that the concentrations of potassium quercetin applied have a stimulating effect on the course of physiological processes. In the case of most of the tested physiological parameters (chlorophyll content and fluorescence and gas exchange) and the total antioxidant capacity, no significant differences were observed in their increase as a result of application with concentrations of 3.0 and 5.0%. Therefore, the beneficial effect of quercetin on the analysed parameters is already observed when spraying with a concentration of 3.0%. 相似文献
994.
We present new methods for building the polynomial-regression based nodal nuclear data models. The data models can reflect dependences on a large number of state variables, and they can consider various history effects. Suitable multivariate polynomials that approximate the nodal data dependences are identified efficiently in an iterative manner. The history effects are analysed using a new sampling scheme for lattice calculations where the traditional base burnup and branch calculations are replaced by a large number of diverse burnup histories. The total number of lattice calculations is controlled so that the data models are built to a required accuracy. 相似文献
995.
Dmitry A. Zaitsev Tatiana R. Shmeleva Jan Friso Groote 《IEEE/CAA Journal of Automatica Sinica》2019,6(3):733-742
A model of a hypertorus communication grid has been constructed in the form of an infinite Petri net. A grid cell represents either a packet switching device or a bioplast cell. A parametric expression is obtained to allow a finite specification of an infinite Petri net. To prove properties of an ideal communication protocol, we derive an infinite Diophantine system of equations from it, which is subsequently solved. Then we present the programs htgen and ht-mcrl2-gen, developed in the C language, which generate Petri net and process algebra models of a hypertorus with a given number of dimensions and grid size. These are the inputs for the respective modeling tools Tina and mCRL2, which provide model visualization, step simulation, state space generation and reduction, and structural analysis techniques. Benchmarks to compare the two approaches are obtained. An ad-hoc induction-like technique on invariants, obtained for a series of generated models, allows the calculation of a solution of the Diophantine system in a parametric form. It is proven that the basic solutions of the infinite system have been found and that the infinite Petri net is bounded and conservative. Some remarks regarding liveness and liveness enforcing techniques are also presented. 相似文献
996.
电信级以太网在电力通信网络建设中的应用 总被引:4,自引:0,他引:4
随着电力工业的不断发展,电力通信网所承载的业务越来越多地呈现出业务类型多样化和业务流向不确定性的特点。文章分析了满足电力通信网建设的4种技术,介绍了邢台供电公司采用电信级以太网技术建设电力通信网络的方案,分析了电信级以太网解决方案的特点以及方案实施后的效果,为电力通信网络的建设探索了一种新方式。 相似文献
997.
Masood Jan Zhixin Liu Chenxi Guo Yaping Zhou Xuwu Sun 《International journal of molecular sciences》2022,23(9)
Cotton refers to species in the genus Gossypium that bear spinnable seed coat fibers. A total of 50 species in the genus Gossypium have been described to date. Of these, only four species, viz. Gossypium, hirsutum, G. barbadense, G. arboretum, and G. herbaceum are cultivated; the rest are wild. The black dot-like structures on the surfaces of cotton organs or tissues, such as the leaves, stem, calyx, bracts, and boll surface, are called gossypol glands or pigment glands, which store terpenoid aldehydes, including gossypol. The cotton (Gossypium hirsutum) pigment gland is a distinctive structure that stores gossypol and its derivatives. It provides an ideal system for studying cell differentiation and organogenesis. However, only a few genes involved in the process of gland formation have been identified to date, and the molecular mechanisms underlying gland initiation remain unclear. The terpenoid aldehydes in the lysigenous glands of Gossypium species are important secondary phytoalexins (with gossypol being the most important) and one of the main defenses of plants against pests and diseases. Here, we review recent research on the development of gossypol glands in Gossypium species, the regulation of the terpenoid aldehyde biosynthesis pathway, discoveries from genetic engineering studies, and future research directions. 相似文献
998.
999.
Two types of montmorillonite (MMT), natural sodium montmorillonite (Na-MMT) and organically modified montmorillonite (OMMT), in different amounts of 1, 2, 5, 10 and 25 phr (parts per hundred resin), were dispersed in rigid poly (vinyl chloride) by two different methods: solution blending and solution blending + melt compounding. The effects on morphology, thermal and mechanical properties of the PVC/MMT nanocomposites were studied by varying the amount of Na-MMT and OMMT in both methods. SEM and XRD analysis revealed that possible intercalated and exfoliated structures were obtained in all of the PVC/MMT nanocomposites. Thermogravimetric analysis revealed that PVC/Na-MMT nanocomposites have better thermal stability than PVC/OMMT nanocomposites and PVC. In general, PVC/MMT nanocomposites prepared by solution blending + melt compounding revealed improved thermal properties compared to PVC/MMT nanocomposites prepared by solution blending. Vicat tests revealed a significant decrease in Vicat softening temperature of PVC/MMT nanocomposites prepared by solution blending + melt compounding compared to unfilled PVC. 相似文献
1000.
Andrzej Taube Robert Mroczyński Katarzyna Korwin-Mikke Sylwia Gierałtowska Jan Szmidt Anna Piotrowska 《Materials Science and Engineering: B》2012,177(15):1281-1285
In this work, we report on effects of post-deposition annealing on electrical characteristics of metal–insulator–semiconductor (MIS) structures with HfO2/SiO2 double gate dielectric stacks. Obtained results have shown the deterioration of electro-physical properties of MIS structures, e.g. higher interface traps density in the middle of silicon forbidden band (Ditmb), as well as non-uniform distribution and decrease of breakdown voltage (Ubr) values, after annealing above 400 °C. Two potential hypothesis of such behavior were proposed: the formation of interfacial layer between hafnia and silicon dioxide and the increase of crystallinity of HfO2 due to the high temperature treatment. Furthermore, the analysis of conduction mechanisms in investigated stacks revealed Poole–Frenkel (P–F) tunneling at broad range of electric field intensity. 相似文献