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1.
2.
Two monophagous sawflies,Neodiprion dubiosus andN. rugifrons, actively avoid feeding on the current season's needles of jack pine,Pinus banksiana, while the polyphagousN. lecontei feeds indiscriminately on foliage of all age classes. Bioassay studies with needle extracts indicate thatN. dubiosus andN. rugifrons larval feeding preference is governed by a group of tricyclic diterpene resin acids. Resin acids commonly occur in needles of all ages; however, levopimaric, palustric, dehydroabietic, and neoabietic acids were at higher concentrations in the new needles.N. dubiosus was significantly deterred from feeding on 1-year-old foliage when treated with the pure resin acids, palustric and levopimaric, at 0.5 and 1.0 mg/ml MeOH.N. rugifrons larvae were deterred from feeding by pure dehydroabietic, neoabietic, and palustric acids at 1.0 mg/ml MeOH. 相似文献
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B. Y. C. Wu C. A. Schuh P. J. Ferreira 《Metallurgical and Materials Transactions A》2005,36(7):1927-1936
We present an experimental approach to systematically produce nanostructures with various grain sizes and twin densities in
the Ni-Co binary system. Using electrodeposition with various applied current densities and organic additive contents in the
deposition bath, we synthesize nanostructured fcc and hcp solid solutions with a range of compositions. Due to the low stacking
fault energy (SFE) of these alloys, growth twins are readily formed during deposition, and by adjusting the deposition conditions,
a range of twin boundary densities is possible. The resulting nanostructured alloys cannot be described by a single characteristic
length scale, but instead must be characterized in terms of (1) a true grain size pertaining to general high-angle grain boundaries
and (2) an effective grain size that incorporates twin boundaries. Analysis of Hall-Petch strength scaling for these materials
is complicated by their dual length scales, but the hardness trends found in Ni-80Co are found to be roughly in line with
those seen in pure nanocrystalline nickel. 相似文献
5.
Eva Hoch Christian Schuh Thomas Hirth Günter E. M. Tovar Kirsten Borchers 《Journal of materials science. Materials in medicine》2012,23(11):2607-2617
Gelatin is a very promising matrix material for in vitro cell culture and tissue engineering, e.g. due to its native RGD content. For the generation of medical soft tissue implants chemical modification of gelatin improves the mechanical properties of gelatin hydrogels and the viscous behavior of gelatin solutions for liquid handling. We present a systematic study on the influence of high degrees of methacrylation on the properties of gelatin solutions and photo-chemically crosslinked hydrogels. Changes from shear thinning to shear thickening behavior of gelatin solutions were observed depending on mass fraction and degree of methacrylation. Degrees of swelling of crosslinked hydrogels ranged from 194 to 770?% and storage moduli G′ from 368 to 5?kPa, comparable to various natural tissues including several types of cartilage. Crosslinked gels proofed to be cytocompatible according to extract testings based on DIN ISO 10933-5 and in contact with porcine chondrocytes. 相似文献
6.
Stian M. UelandChristopher A. Schuh 《Acta Materialia》2012,60(1):282-292
In oligocrystalline shape memory alloys, the total grain boundary area is smaller than the surface area of the specimen, leading to significant effects of free surfaces on the martensitic transformation and related shape memory and superelastic properties. Here we study sample size effects upon the superelastic characteristics of oligocrystalline microwires after one loading cycle and after many. Cu-Zn-Al wires with diameters ranging from ∼100 down to ∼20 μm are fabricated by the Taylor liquid processing technique and characterized through both uniaxial cyclic tensile testing and mechanically constrained thermal cycling. The energy dissipated per superelastic cycle increases with decreasing wire diameter, and this size effect is preserved after extensive cycling despite a significant transient evolution of the superelastic response for early cycles. We also present fatigue and fracture data, indicating that oligocrystalline wires of this normally brittle alloy can exhibit fatigue lifetimes two orders of magnitude improved over conventional polycrystalline Cu-Zn-Al. 相似文献
7.
Cenk Aktas Eva Dörrschuck Cathrin Schuh Marina Martinez Miró Juseok Lee Norbert Pütz Gunther Wennemuth Wolfgang Metzger Martin Oberringer Michael Veith Hashim Abdul-Khaliq 《Materials science & engineering. C, Materials for biological applications》2012,32(5):1017-1024
The effect of the micro- and nanotopography on vascular cell-surface interaction is investigated using nano- and microstructured Al2O3 as model substrate. Two different nanostructured Al2O3 surfaces composed of low density (LD) and high density (HD) nanowires (NWs) were synthesized by chemical vapour deposition (CVD) and commercially available microstructured Al2O3 plates were used for comparison. A clear diverging response of human umbilical vein endothelial cells (HUVEC) and human umbilical vein smooth muscle cells (HUVSMC) was observed on these nano- and microstructured surfaces. LD Al2O3 NWs seem to enhance the proliferation of HUVECs selectively. This selective control of the cell-surface interaction by topography may represent a key issue for the future stent material design. 相似文献
8.
Silicides, intermetallic compounds formed by the reaction of a metal and Si, have long been used as contacts for metal oxide
semiconductor (CMOS) transistors and have more become interesting for other Si nanowire (SiNW) devices. In the following,
experimental results for the Ti, V, Pt, Pd, Fe, and Ni–Si systems are reported and placed in the context of prior work on
silicide formation from metal films on Si wafers. For the early transition metals Ti and V, the silicide is formed only underneath
the contact pad and is Si-rich (MSi2). For the middle transition metal Fe and late transition metals Pt and Pd, a metal-rich silicide was the first phase observed
to form, but poor morphologies were common, making it a challenge to incorporate these contacts into nanowire devices. Nickel
contacts were the only ones with well-behaved axial silicide growth away from the contact pad, and silicide formation was
strongly dependent on the original SiNW orientation. These findings are discussed in terms of kinetic features of the metal-SiNW
systems. 相似文献
9.
In the analysis of crystallographic texture, the orientation distribution function (ODF) of the grains is generally expressed
as a linear combination of the generalized spherical harmonics. Recently, an alternative expansion of the ODF, as a linear
combination of the hyperspherical harmonics, has been proposed, with the advantage that this is a function of the angles that
directly describe the axis and angle of each grain rotation, rather than of the Euler angles. This article provides the formulas
required to convert between the generalized spherical harmonics and the hyperspherical harmonics, and between the coefficients
appearing in their respective expansions of the ODF. A short discussion of the phase conventions surrounding these expansions
is also presented. 相似文献
10.
Beschreibung der Versuchsapparatur zur Messung der Thermospannung der Kette Rh |T + Δ AIN |T Rh für Temperatur-differenzen bis zu ± 60 °C zwischen 1350 und 1650 °C. Ermittlung der Thermokraft und ihres homogenen Anteils. Berechnung der Überführungswärme der wandernden Ionen aus der homogenen Thermokraft. Erörterung zum Leitungsmechanismus im Aluminiumnitrid AlN. 相似文献