全文获取类型
收费全文 | 1106篇 |
免费 | 96篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 21篇 |
综合类 | 2篇 |
化学工业 | 229篇 |
金属工艺 | 38篇 |
机械仪表 | 79篇 |
建筑科学 | 10篇 |
矿业工程 | 3篇 |
能源动力 | 41篇 |
轻工业 | 53篇 |
水利工程 | 9篇 |
无线电 | 181篇 |
一般工业技术 | 279篇 |
冶金工业 | 127篇 |
原子能技术 | 12篇 |
自动化技术 | 121篇 |
出版年
2023年 | 16篇 |
2022年 | 23篇 |
2021年 | 41篇 |
2020年 | 29篇 |
2019年 | 30篇 |
2018年 | 35篇 |
2017年 | 41篇 |
2016年 | 41篇 |
2015年 | 32篇 |
2014年 | 47篇 |
2013年 | 62篇 |
2012年 | 79篇 |
2011年 | 86篇 |
2010年 | 49篇 |
2009年 | 57篇 |
2008年 | 48篇 |
2007年 | 35篇 |
2006年 | 37篇 |
2005年 | 28篇 |
2004年 | 36篇 |
2003年 | 25篇 |
2002年 | 36篇 |
2001年 | 22篇 |
2000年 | 23篇 |
1999年 | 16篇 |
1998年 | 46篇 |
1997年 | 50篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 3篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1205条查询结果,搜索用时 15 毫秒
1.
Golam Haider Krishna Sampathkumar Tim Verhagen Lukáš Nádvorník Farjana J. Sonia Václav Valeš Jan Sýkora Peter Kapusta Petr Němec Martin Hof Otakar Frank Yang-Fang Chen Jana Vejpravová Martin Kalbáč 《Advanced functional materials》2021,31(29):2102196
Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability. 相似文献
2.
Mani Balamurugan Hui‐Yun Jeong Venkata Surya Kumar Choutipalli Jung Sug Hong Hongmin Seo Natarajan Saravanan Jun Ho Jang Kang‐Gyu Lee Yoon Ho Lee Sang Won Im Venkatesan Subramanian Sun Hee Kim Ki Tae Nam 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(25)
The electrochemical reduction of carbon dioxide (CO2) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO2 to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO2 to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO2 in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions. 相似文献
3.
The three-dimensional structure of glutathione S-transferase from Arabidopsis thaliana has been solved at 2.2 A resolution (Reinemer et al., 1996). The enzyme forms a dimer of two identical subunits. The structure shows a new G-site architecture and a novel and unique dimer interface. Each monomer of the protein forms a separate G-site. Therefore, the requirements on the dimer interface are reduced. As a consequence, the interactions between the monomers are weaker and residues at the dimer interface are more variable. Thus, the dimer interface looses its relevance for a classification of plant glutathione S-transferases and the formation of heterodimers becomes even more difficult to predict. 相似文献
4.
5.
EJ Velthuis-te Wierik H van den Berg JA Weststrate KH van het Hof C de Graaf 《Canadian Metallurgical Quarterly》1996,50(4):214-219
Plasma levels of fibrinogen, factor VIIc and prothrombin fragment F1 + 2, a marker of thrombin generation in vivo, were studied in 68 subjects with serum total cholesterol (TC) levels between 135 and 349 mg/dl but without clinical evidence of cardiovascular disease and other atherosclerotic risk factors. F1 + 2 plasma levels were directly correlated with TC (p < 0.0004), low-density lipoprotein cholesterol (LDL-C; p < 0.0018) and factor VIIc (p < 0.024). Thirty-five subjects with TC greater than 249 mg/dl (median value of the whole group) showed higher levels of F1 + 2 (p < 0.0001) and fibrinogen (p < 0.0015) than those with TC lower than 249 mg/dl. In subjects with TC > 249 mg/dl and F1 + 2 > 1.2 nM (median value of the whole group), a cholesterol-lowering drug (simvastatin) was able to reduce F1 + 2 (p < 0.009) as well as TC and LDL-C. This study shows a relationship between serum cholesterol and the rate of thrombin generation supporting the hypothesis that a hypercoagulable state may occur in hypercholesterolemic subjects before the onset of clinical evidence of atherosclerotic cardiovascular disease. 相似文献
6.
The purpose of this work is to study the effects of specularly reflecting wall under the combined radiative and laminar free
convective heat transfer in an infinite square duct. An absorbing and emitting gray medium is enclosed by the opaque and diffusely
emitting walls. The walls may reflect diffusely or specularly. Boussinesq approximation is used for the buoyancy term. The
radiative heat transfer is evaluated using the direct discrete ordinates method. The parameters under considerations are Rayleigh
number, conduction to radiation parameter, optical thickness, wall emissivity and reflection mode. The differences caused
by the reflection mode on the stream line, and temperature distribution and wall heat fluxes are studied. Some differences
are observed for the categories mentioned above if the order of the conduction to radiation parameter is less than order of
10-3 for the range of Rayleigh number studied. The differences at the side wall heat flux distributions are observed as long as
the medium is optically thin. As the top wall emissivity decreases, the differences between these two modes are increased.
As the optical thickness decreases at the fixed wall emissivity, the differences also increase. The difference of the streamlines
or the temperature contours is not as distinct as the side wall heat flux distributions. The specular reflection may alter
the fluid motion. 相似文献
7.
Sangho Kim Young-Roc Im Sunghak Lee Hu-Chul Lee Sung-Joon Kim Jun Hwa Hong 《Metallurgical and Materials Transactions A》2004,35(7):2027-2037
This study is concerned with the effects of alloying elements on fracture toughness in the transition temperature region of
base metals and heat-affected zones (HAZs) of Mn-Mo-Ni low-alloy steels. Three kinds of steels whose compositions were varied
from the composition specification of SA 508 steel (grade 3) were fabricated by vacuum-induction melting and heat treatment,
and their fracture toughness was examined using an ASTM E1921 standard test method. In the steels that have decreased C and
increased Mo and Ni content, the number of fine M2C carbides was greatly increased and the number of coarse M3C carbides was decreased, thereby leading to the simultaneous improvement of tensile properties and fracture toughness. Brittle
martensite-austenite (M-A) constituents were also formed in these steels during cooling, but did not deteriorate fracture
toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated HAZs also had sufficient
impact toughness after postweld heat treatment. These findings indicated that the reduction in C content to inhibit the formation
of coarse cementite and to improve toughness and the increase in Mo and Ni to prevent the reduction in hardenability and to
precipitate fine M2C carbides were useful ways to improve simultaneously the tensile and fracture properties of the HAZs as well as the base
metals. 相似文献
8.
Failure analysis of hollow glasses The failure analysis is very important to clarify damages of hollow glasses. Damages of glass bottle through over pressure are very often linked with damages to persons. This is the reason why the causal research is from particular importance. Different surface characteristics of glass fragments as well as the fracture pattern give hints to the direction of the crack, the stress just before breakage and the reason of stress. A reconstruction of the bottle is a further helpful instrument for cause studies. The difference of the various characteristics of the surface will be explained. Further on there will be discussed different reasons and mechanism of fracture. 相似文献
9.
Kyungyong Choi Maesoon Im Ji-Min Choi Yang-Kyu Choi 《Microfluidics and nanofluidics》2012,12(5):821-827
A new droplet-driving scheme for digital microfluidics termed the “pre-charging of a droplet” is demonstrated. In this method,
a droplet is initially charged by applying “pre-charging” voltage between the droplet and an electrode buried under dielectric
layers. The droplet is then driven to the next electrode by applying “driving” voltage between two adjacent buried electrodes.
The concept of pre-charging was proved by the polarity of the charge stored in the droplet. When the droplet is pre-charged
with positive voltage, it is driven with negative voltage and vice versa. Therefore, the magnitudes of the pre-charging and
driving voltages are identical, but only with the opposite polarity. A 2.5-μL deionized water droplet is pre-charged and driven
at a minimal voltage of 12 V. The charge stored in the droplet by this pre-charging method remained for more than 2 min, and
the driving actuation could be repeated more than 150 times while the droplet remained its charged state. This method suggests
a new means of driving a droplet for digital microfluidics at a relatively low voltage by utilizing both the electrostatic
and dielectrophoretic force in the droplet transport process with a simpler structure compared to other single-plate structured
devices. 相似文献
10.
Microstructures and properties of sintered CdS films on glass substrates and sintered CdTe films on polycrystal CdS substrates have been investigated. The CdS films, which contained 9 wt % CdCl2 as a sintering aid and were sintered at 650° C for 1 h in nitrogen, are transparent and have an average grain size of 15m and an electrical resistivity of 0.5cm. The CdTe films, which were coated on the sintered CdS substrate and were sintered above 610° C for 1 h in nitrogen, have a dense structure with an average grain size larger than 5m. All polycrystal CdS/CdTe solar cells were fabricated by this successive coating and sintering method. The sintering temperature of CdTe films on the sintered CdS films was varied from 585 to 700° C. Compositional interfaces and p-n juctions are formed during sintering. The highest solar efficiency (7.18%) was found in a solar cell made by sintering the composite layer of glass-CdS-CdTe at 625° C for 1 h. A fabrication temperature below 610° C resulted in poor solar cell efficiencies due to the porous structure of the CdTe films and above 650° C also resulted in poor efficiencies due to the formation of a CdS1-x
Tex layer at the interface and a large p-n junction depth. 相似文献