全文获取类型
收费全文 | 1814篇 |
免费 | 107篇 |
国内免费 | 1篇 |
学科分类
工业技术 | 1922篇 |
出版年
2024年 | 6篇 |
2023年 | 17篇 |
2022年 | 29篇 |
2021年 | 59篇 |
2020年 | 47篇 |
2019年 | 40篇 |
2018年 | 70篇 |
2017年 | 59篇 |
2016年 | 64篇 |
2015年 | 52篇 |
2014年 | 75篇 |
2013年 | 124篇 |
2012年 | 101篇 |
2011年 | 120篇 |
2010年 | 80篇 |
2009年 | 79篇 |
2008年 | 82篇 |
2007年 | 73篇 |
2006年 | 62篇 |
2005年 | 43篇 |
2004年 | 37篇 |
2003年 | 35篇 |
2002年 | 37篇 |
2001年 | 23篇 |
2000年 | 27篇 |
1999年 | 24篇 |
1998年 | 64篇 |
1997年 | 50篇 |
1996年 | 29篇 |
1995年 | 40篇 |
1994年 | 27篇 |
1993年 | 29篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 6篇 |
排序方式: 共有1922条查询结果,搜索用时 15 毫秒
71.
K.S. Mohandas N. Sanil M. Noel P. Rodriguez 《Journal of Applied Electrochemistry》2001,31(9):997-1007
The anodic behaviour of compacted graphite, graphite powder, glassy carbon and reticulated vitreous carbon electrodes in basic sodium chloroaluminate melt in the temperature range 428–573 K was studied using cyclic voltammetry. Chlorine evolution (> + 2.1 V vs Al) alone was the predominant reaction on the compact glassy carbon and fresh RVC electrodes. On compacted graphite, chlorine-assisted chloroaluminate intercalation was found to be a competitive process to the chlorine evolution. At high sweep rates, intercalation/deintercalation near the graphite lattice edges occur faster than chlorine evolution. Subsequent intercalation, however, is a slow process. Chlorine evolution predominates at higher temperatures and at higher anodic potentials. On graphite powders, a more reversible free radical chlorine adsorption/desorption process also occurs in the potential region below chlorine evolution. The process occurs at the grain boundaries, edges and defects of the graphite powder material. Intercalation/deintercalation processes are mainly responsible for the disintegration of graphitic materials in low-temperature chloroaluminate melts. Repeated intercalation/deintercalation cycles result in the irreversible transformation of the electrode surface and electrode characteristics. The surface area of the electrode is increased substantially on cycling. Electrode materials and operating conditions suitable for chlorine generation, intercalation/deintercalation and chlorine adsorption/desorption and power sources based on these processes are identified in this work. 相似文献
72.
73.
Sergio Neves Monteiro Felipe Perissé Duarte Lopes Anderson Paula Barbosa Alice Barreto Bevitori Isabela Leão Amaral Da Silva Lucas Lopes Da Costa 《Metallurgical and Materials Transactions A》2011,42(10):2963-2974
Recent investigations on the tensile properties of natural cellulose-based fibers revealed an increasing potential as engineering
materials. This is particularly the case of very thin fibers of some species such as sisal, ramie, and curaua. However, several
other commonly used fibers such as flax, jute, hemp, coir, cotton, and bamboo as well as less known bagasse, piassava, sponge
gourde, and buriti display tensile properties that could qualify them as engineering materials. An overview of the strength
limits attained by these fibers is presented. Based on a tensile strength vs density chart, it is shown that natural fibers stand out as a relevant class of engineering materials. 相似文献
74.
Isabel Lopes Fernando Gonçalves Antonio Nogueira Amadeu M. V. M. Soares Rui Ribeiro 《The International journal of environmental studies》2013,70(1):3-20
Acid mine drainage (AMD) is characterised by very low pH and high heavy metal concentrations. Serious ecotoxicological effects, often leading to the complete disruption of the ecosystem, can be observed at the regions suffering this kind of contamination. Those effects can be caused either by low pH itself or by other contaminants that emerge with water acidification (mobilisation and increased solubility of heavy metals). The discrimination between the toxicity due to each of these two factors is not possible with the existing toxicity tests; the addition of chelating agents or serial dilution methods seriously alter the chemical and physical properties of the effluent. A toxicity test, based on the survival time of Ceriodaphnia dubia (Crustacea, Cladocera) neonates exposed to the unchanged effluent, was developed and field validated, on an AMD contaminated site. 相似文献
75.
This paper describes an active compensation technique which is readily applicable to all active-RC networks, independently of the circuit topology. This procedure considers the network in its totality and derives general active compensation conditions for a generic active-RC network employing 2 or 3 operational amplifiers. Furthermore, the remaining degrees of freedom of the circuits are used to optimize the performance of the actively compensated circuits to further extend its operating frequency range. Simulation and experimental results are also reported. 相似文献
76.
Odilia I Bermudez Claire Toher Gabriela Montenegro-Bethancourt Marieke Vossenaar Paul Mathias Colleen Doak Noel W Solomons 《Nutrition journal》2010,9(1):20
Background
Consumption of healthy diets that contribute with adequate amounts of fat and fatty acids is needed for children. Among Guatemalan children, there is little information about fat intakes. Therefore, the present study sought to assess intakes of dietary fats and examine food sources of those fats in Guatemalan children. 相似文献77.
Fernanda Lopes Aldina Santiago Luís Simões da Silva Tim Heistermann Milan Veljkovic José Guilherme da Silva 《钢结构国际杂志》2013,13(3):459-472
The reverse channel connection appears to have the best combination of desirable features under fire loading: moderate construction cost, ability to develop catenary action and extremely high ductility through deformation of the web channel (Ding and Wang, 2007). This paper presents the results of an experimental investigation of a reverse channel component conducted at the University of Coimbra as part of the European RFCS COMPFIRE Project, the main focus of which is to characterise the behaviour of steel joints that connect steel beams to concrete-filled tubular columns under natural fire loading. A series of tensile and compressive tests at ambient and elevated temperatures was conducted. The purposes of the experimental tests were to characterise the strength, stiffness and ductility of this joint component and to establish a relationship between force, displacement and temperature. 相似文献
78.
Fernande G. Honfo Anita R. Linnemann Noel Akissoe Mohamed M. Soumanou Martinus A. J. S. van Boekel 《International Journal of Food Science & Technology》2013,48(8):1714-1721
The traditional production of shea butter requires a heat treatment of the nuts. This study compared the end products derived by two commonly used heat treatments, namely smoking and boiling followed by sun‐drying. Neither treatment influenced the moisture content of the kernels (8–10%), but the boiling treatment resulted in more free fatty acids (FFA) (6%) and a higher fat content (41%) of kernels. A sensory panel preferred shea butter from boiled kernels because of its soft texture and intense smell. This butter also had the highest values for moisture content (2%), unsaponifiable matter (7%), tocopherol compounds (125 mg g?1), peroxide value (8 meq O2 kg?1), iodine value (53 mg I2 100 g?1) and FFA (2%). Minor variations were noticed in the fatty acid profile. Aside from the use of butter from both boiled and smoked kernels in cosmetics, the butter from smoked kernels will be more suitable for food purposes. 相似文献
79.
Lenine Campos Miranda Fabio Cavalcanti Lopes Andre Galembeck Eduardo Padron Hemaindez 《化学与化工:英文版》2013,(12):1149-1155
This paper presents a study of the relationship between the magnetic properties and microstructure of nanocomposite Ni/MnO, Ni/CoO, Co/MnO, Co/CoO. The objective is to understand how the coupling interface FM/AFM (ferromagnetic/anti-ferromagnetic) manifests itself in magnetic response of these materials to an applied field. Sample preparation was performed using mechanochemical synthesis by means of a ball mill planetary type high power at normal atmosphere. The characterization was done by XRD (X-ray diffraction), SEM (scanning electron microscopy) and VSM (vibrating sample magnetometry). Analyzing the XRD peaks of the samples studied, there was a decrease in the average particle diameter with increasing milling time, which is important in the magnetic interactions of the atoms of the surface. In addition, the diffraction pattern showed formation of new phases by oxidation interfering with the magnetic measurements. Analyses by SEM show chipboard multiform nano- and micrometer-sized grains on the surface of the clusters being responsible for the interaction. The magnetic measurements show a strong coupling between the phases present in nanocomposites showing once again that the MS (mechanosynthesis) is a powerful technique for this kind of purpose. The effect of the decrease in crystallite size leads to large variations of magnetic properties of the material which have been specifically observed changes in HC (coercive field) in the RM (remanent magnetization) and SM (saturation magnetization). The decrease in crystallite size in the course of grinding intensifies the effects that depend on the surface-to-volume ratio of the material. M vs. T measures were taken for different values of applied field and found a jump in the moment of the sample near the N6el temperature of the antiferromagnetic. 相似文献
80.
Tony Minoru Tamura Lopes Andre Augusto Ciré Cid Carvalho de Souza Arnaldo Vieira Moura 《Constraints》2010,15(2):151-189
Brazilian petrobras is one of the world largest oil companies. Recurrently, it faces a very difficult planning and scheduling problem: how to
operate a large pipeline network in order to adequately transport oil derivatives and biofuels from refineries to local markets.
In spite of being more economical and environmentally safer, the use of a complex pipeline network poses serious operational
difficulties related to resource allocation and temporal constraints. The current approaches known from the literature only
consider a few types of constraints and restricted topologies, hence they are far from being applicable to real instances
from petrobras. We propose a hybrid framework based on a two-phase problem decomposition strategy. A novel Constraint Programming (CP) model
plays a key role in modelling operational constraints that are usually overlooked in literature, but that are essential in
order to guarantee viable solutions. The full strategy was implemented and produced very adequate results when tested over
large real instances. 相似文献