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101.
Christoph Gutsche Andrey Lysov Ingo Regolin Kai Blekker Werner Prost Franz-Josef Tegude 《Nanoscale research letters》2011,6(1):65
In this letter, n-type doping of GaAs nanowires grown by metal–organic vapor phase epitaxy in the vapor–liquid–solid growth mode on (111)B
GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of
doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily
n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane.
Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires
from the same run, the donor concentrations N
D of GaAs nanowires are found to vary from 7 × 1017 cm-3 to 2 × 1018 cm-3. The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal–insulator-semiconductor field-effect
transistor devices. 相似文献
102.
Yixun Liu Panagiotis Foteinos Andrey Chernikov Nikos Chrisochoides 《Engineering with Computers》2012,28(4):305-318
Multi-tissue meshing is necessary for the realistic building of a biomechanical model of the brain, which has been widely used in brain surgery simulation, brain shift, and non-rigid registration. A two step multi-tissue mesher is developed. First, a coarse multi-tissue mesh is generated by redistributing labels of a body-centered cubic (BCC) mesh. Second, all the surfaces of the submeshes are deformed to their corresponding tissue boundaries. To deform the mesh, two strategies are developed. One is based on a point-based registration (PBR) and the other is based on a robust point matching (RPM). The PBR method explicitly calculates the correspondence, which takes both smoothing and quality into account, then resolves the displacement vector by minimizing an energy function. Unlike PBR method, RPM does not require the correspondence between the source points and the target points to be known in advance. To simultaneously resolve the displacement vector and the correspondence, the Expectation and Maximization optimization is employed to alternately estimate the correspondence and the displacement vector. To effectively cope with outliers, least trimmed square, a robust regression technique, is employed to correct the regression bias induced by outliers. Both methods are effective in deforming the multi-tissue mesh. However, the PBR method favors quality and smoothing, and the RPM method favors fidelity. The resulting mesh is characterized by its flexible control of four mesh properties: (1) tissue-dependent resolution, (2) fidelity to tissue boundaries, (3) smoothness of mesh surfaces, and (4) element quality. Each mesh property can be controlled on a tissue level. Our experiments conducted on synthetic data, clinic MRI, visible human data, and brain atlas effectively demonstrate these features of this multi-tissue mesher. 相似文献
103.
104.
Valentina E. Smirnova Iosif V. Gofman Vladimir E. Yudin Irina P. Dobrovolskaya Alexander N. Shumakov Andrey L. Didenko Valentine M. Svetlichnyi Ellen Wachtel Rinat Shechter Hannah Harel Gad Marom 《Polymer Engineering and Science》2009,49(2):217-222
The solid state crystallization in drawn thermoplastic polyimide films is studied as a function of draw ratio (DR) under the effect of vapor grown carbon fiber nanoinclusions. The nucleating effect of the nanoinclusions coupled with the orientation effect of drawing generates a unique orientated layered lamellar structure, characteristic of smectic‐like mesophase. The degree of draw induced orientated crystallization increases with the content of nanoinclusions and with the DR, and is reflected in the mechanical behavior of the film. Generally, the Young's modulus and the yield point of the drawn crystalline films in the drawing direction are significantly higher compared with the noncrystalline counterparts. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers 相似文献
105.
Vladimir Ivanovich Lysenko Sergey Bardakhanov Alexey Korchagin Nikolay Kuksanov Alexander Lavrukhin Rustam Salimov Sergey Fadeev Vladislav Cherepkov Mikhail Veis Andrey Nomoev 《Bulletin of Materials Science》2011,34(4):677-681
Electron-beam evaporation of various natural and industrial materials in the atmosphere of different gases at atmospheric
pressure can be used for the synthesis of nanosize powders. These powders are characterized by high purity and may exhibit
unusual properties. In particular, nanopowders of silicon dioxide and oxide (SiO2, SiO), magnesia (MgO), alumina (Al2O3), titania (TiO2), gadolinium oxide (Gd2O3), various metals (tantalum, molybdenum, nickel, aluminium, copper, silver), semiconductor (Si), nitrides (AlN, TiN), and
some other substances had been produced. The process of nanopowder synthesis is highly effective; in particular, the yield
of oxides can exceed ten kilograms per hour. 相似文献
106.
Abstract The distribution of anionic groups in fibres, fines, the colloidal fraction, and the dissolved fraction of thermomechanical pulp (TMP) suspensions was determined. The influence of extraction, alkaline treatment, and peroxide bleaching of spruce TMP were also studied. Spruce TMP was extracted with hexane, treated with alkali, or bleached with peroxide. Suspensions were made at pH 5.5 or 8, and fractionated into long fibres, large fines, small fines, a colloidal fraction, and a dissolved fraction. The surface and total charge of the fractions were determined separately by polyelectrolyte titration. To determine the origin of the charges, the contents of fatty acids, resin acids, and acidic units in polysaccharides in the different fractions were determined by gas chromatography. Extraction of TMP with hexane prior to fractionation increased the measured total and surface charge of the fibres. The removal of wood resin probably uncovered some anionic groups on the fibre surface, or improved the penetration of the polymers into the pores of the fibres. The total charge, determined with polybrene titration, of the fines and the colloidal fraction was lower when the resin had been removed, while the surface charge, determined with poly-DADMAC, was not greatly affected. Alkaline treatment of the TMP increased both the total charge and the surface charge of the fibres and fines, mainly because of demethylation of pectins. Alkaline treatment also increased the total and surface charge of the dissolved substances, due to the release of pectic acids into the water phase. Alkaline peroxide bleaching further increased the total and surface charge of fibres and dissolved substances, most likely due to oxidation of lignin. The total charge and the surface charge of the colloidal substances, consisting mainly of wood resin, were only slightly affected by alkaline treatment and peroxide bleaching. The anionic charge in TMP suspensions originated mainly from free uronic acids in the xylans, arabinogalactans, and pectic acids. The contribution from the fatty and resin acids was substantial only for the colloidal fraction. 相似文献
107.
Jie Duanmu E. Kristofer Gamstedt Andrey Pranovich Ari Rosling 《Composites Part A》2010,41(10):1409-1418
In a previous work we introduced a new family of thermoset composites of softwood fiber and allylglycidyl ether modified potato starch (AGE-starch with a degree of substitution of 1.3 and 2.3) prepared by hot pressing. To improve the processability of AGE-starch with a DS = 1.3 (LDS-3) and to increase hygromechanical properties, the LDS-3 matrix has now been partially degraded by α-amylase at 45 °C (pH 6) for 0.5, 6 and 18 h. The study shows that already a 30 min enzymatic hydrolysis has a marked effect on the modified starch molecular weight and its thermal properties. The new composites with enzyme hydrolyzed AGE-starch, generically named D-LDS-3, showed good fiber dispersion and excellent interface between the fiber and matrix as studied by SEM. Premixes of D-LDS-3 matrix and fiber showed improved processability. The water vapor absorption was evaluated at 43.2% and 82.2% RH and the stiffness and strength properties were measured. The water uptake was shown to be reduced. The strength of neat matrix D-LDS-3-6 at ambient 68% RH reached 63 MPa and Young’s modulus 3200 MPa and with 40 wt.% wood fiber reinforcement impressive 128 MPa and 4500 MPa, respectively. 相似文献
108.
109.
Andrey V. Boiko Kwang Hyo Jung Ho Hwan Chun Inwon Lee 《Journal of Mechanical Science and Technology》2007,21(1):196-206
In this study, experimental investigations were made regarding the effect of riblets on the streak instability in boundary
layer. The streak instability is now regarded as a major source of the self-regeneration mechanism for the hairpin type coherent
structures in turbulent boundary layer flow. Thus, it is important to control the instability to suppress the drag-inducing
vortical structure in terms of drag reduction. Toward enhancing the measurement accuracy and spatial resolution, an enlarged
version of riblets was applied to a streak which was artificially induced by a microwing in a laminar boundary layer. It is
found that the riblets have attenuation effect on the streak instability, i.e., to reduce the spanwise velocity gradient of
the quasi-streamwise streak in boundary layer. 相似文献
110.
Andrey V. Pyatigorets Joseph F. Labuz Sofia G. Mogilevskaya Henryk K. Stolarski 《Journal of Materials Science》2010,45(4):936-945
A new approach is proposed for the experimental study of the effective shear modulus of porous elastic materials using the
uniaxial tension test. The idea is to measure strains at a few points surrounding a cluster of holes that represents the structure
of the material. The representative cluster is placed in the material with the same elastic properties as those of the matrix.
The measured strains lead to the properties of the equivalent circular inhomogeneity, which would produce the same elastic
fields as from the cluster. An aluminum plate containing a cluster of seven circular or hexagonal holes was used. The effective
shear modulus obtained from the strain data was compared with theoretical predictions and various bounds, and it was shown
that the laboratory estimated values are quite accurate. The experimental technique can be used for the determination of the
effective Poisson’s ratio of porous media and/or cellular solids if more detailed strain data are obtained. 相似文献