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71.
The effect of varying normalising and hardening temperatures on the prior austenite grain size in a low alloy Cr–Mo–Ni–V steel
has been examined. An initial relative insensitivity of grain size to increasing austenitising temperature was observed followed
by a sudden growth of grains at approximately 1000 °C. A detailed study of the precipitates in the steel showed the presence
of a bimodal size distribution of vanadium carbides. The grain size increase is attributed to a decrease in volume fraction
and an increase in size of V4C3 particles with increasing temperature. 相似文献
72.
V. Thomas Paul S. Saroja P. Hariharan A. Rajadurai M. Vijayalakshmi 《Journal of Materials Science》2007,42(14):5700-5713
This paper presents the results of a study on the microstructural and microchemical variations in a multipass Gas Tungsten
Arc weld (GTAW) of modified 9Cr-1Mo steel. The changes brought about in the steel due to the heating and cooling cycles during
welding and the subsequent effects due to reheating effects during multipass welding are described. Detailed analytical transmission
electron microscopy has been carried to study the type and composition of the primary and secondary phases in this steel.
The systematic changes in microstructural parameters such as Prior Austenite Grain Size, martensite lath size, number density,
size and microchemistry of carbides, have been understood based on the different transformations that the steel undergoes
during the heating and cooling process. Based on the observed microstructure, an attempt has been made to identify distinct
microstructural zones and possible thermal cycles experienced by different regions of the weldment. 相似文献
73.
I. A. Ovid’ko 《Journal of Materials Science》2007,42(5):1694-1708
An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is
presented. The key experimentally detected facts on ductile and brittle fracture processes are discussed. Special attention
is paid to computer simulations and theoretical models of nucleation and growth of nanocracks and nanopores in deformed nanocrystalline
materials. Also, we discuss mechanisms for fracture suppression in such materials showing good ductility or superplasticity. 相似文献
74.
This article will review the development of the Fe–Ga (Galfenol) alloy system for magnetostriction applications including
work on substitutional ternary alloying additions for magnetic property enhancement. A majority of the alloying addition research
has focused on substitutional ternary elements in Bridgman grown single crystals with the intent of improving the magnetostrictive
capability of the Galfenol system. Single crystals provide the ideal vehicle to assess the effectiveness of the addition on
the magnetostrictive properties by eliminating grain boundary effects, orientation variations, and grain-to-grain interactions
that occur when polycrystals respond to applied magnetic fields. In almost all cases, ternary additions of transition metal
elements have decreased the magnetostriction values from the binary Fe–Ga alloy. Most of the ternary additions are known to
stabilize the D03 chemical order and could be a primary contribution to the observed reduction in magnetostriction. In contrast, both Sn and
Al are found to substitute chemically for Ga. For Sn additions, whose solubility is limited, no reduction in magnetostriction
strains are observed when compared to the equivalent binary alloy composition. Aluminum additions, whose effect on the magnetoelastic
coupling on Fe is similar to Ga, result in a rule of mixture relationship. The reviewed research suggests that phase stabilization
of the disordered bcc structure is a key component to increase the magnetostriction of Fe–Ga alloys. 相似文献
75.
Nina Georgieva Kostova Elka Kraleva Alla A. Spojakina Erika Godocikova Peter Balaz 《Journal of Materials Science》2007,42(10):3321-3325
The Al-MCM-41 has been used as support to prepare Mo-containing catalysts. The 12- molybdophosphoric heteropoly acid (HPMo)
is used as initial compound. The catalysts are synthesized by two different methods: incipient impregnation with aqueous solution
of the acid and mechanochemical synthesis. The samples were tested in the reaction of the thiophene hydrodesulfurization after
activation with mixture H2 + H2S. The effect of the preparation method of the catalysts on their physicochemical and catalytic properties has been studied.
A partial destruction of the loaded compound is observed in mechanochemically treated sample whereas the aggregates are formed
from the particles of different size in the impregnated sample. The specific surface area of the sample prepared by mechanical–chemical
treatment decreases 2–3 times, while the total pore volume is about four times lower. The HDS activity is higher on the impregnated
sample than on the mechanochemically treated one. 相似文献
76.
On structural and high temperature electrochemical properties of ZrO2 thin film coating on Zr metal produced by carbonate melt 总被引:1,自引:0,他引:1
Melt of NaCO3 can favor oxidation of Zr to form ZrO2 thin film on Zr surface, which is used to make Zr/ZrO2 oxidation/reduction electrode of pH sensor for testing elevated temperature aqueous solutions. Using SEM, EPMA, XPS, EXAFS
and HRTEM, we found that ZrO2 film is tightness and solid with 20 μm thickness composed by nanometer-sized monoclinic crystals. Zr/ZrO2 interface is characterized of zoning structure according to topography and chemical composition in five zones: oxygen-rich
ZrO2, ZrO2, oxygen-rich Zr metal, oxygen-bearing Zr and Zr from outmost to center. Melt oxidation process of Zr involved oxidation time,
air and temperature. The air is important effect on structural and electrochemical properties of ZrO2 thin film for making elevate temperature electrochemical sensor. If oxygen air largely presented in carbonate melting process,
ZrO2 thin film is not tightness and not for oxidation/reduction electrode. 相似文献
77.
Prabhakar R. Bandaru 《Journal of Materials Science》2007,42(5):1809-1818
A review on the syntheses and electrical characterization of Y-shaped multi-walled carbon nanotube morphologies is presented.
Modified thermal CVD processes, using Ti precursors, are used to grow Y-junctions of different geometries and distribution
of catalyst particles. It has been established that novel electrical switching behavior is feasible, where any one of the
three branches of the Y-junction can be used for modulating the electrical current flow through the other two branches. Current
blocking behavior, leading to perfect rectification, is seen which could be related to the interplay of the carrier lifetime
and the transit time. The overall goal is to investigate the possibility of obtaining novel functionality at the nanoscale,
which can lead to new device paradigms. 相似文献
78.
Z. Ferhat-Hamida H. Phuong-Nguyen P. Bernazzani A. Haine G. Delmas 《Journal of Materials Science》2007,42(9):3138-3154
LLDPE samples synthesized with Ziegler–Natta (ZN) and Metallocene (MT) catalysts have been analyzed to investigate a potential
catalyst-dependent morphology and to find an explanation for the difficult processing of MT. Slow calorimetry at v = 0.02 K/min and IR at RT and in the melt are used. The differences between MT and ZN are assigned to their different composition,
MT not having the linear segments, which are present in ZN. Slow calorimetry is effectively a drawing process of the melt
with chain orientation followed by decay. The later event, characterized by an endotherm, ΔH
network, occurs at higher temperatures for MT, the presence of a regular distribution of methyl groups slowing down the process.
The rocking, gauche, bending and stretching regions of the IR spectra are analyzed. The nascent MT has more strained bands
in the rocking region. The wagging region reveals the more homogeneous environment of MT through the maximum absorbance at
1,368 cm−1. Decomposition of bands is made for the rocking and wagging regions. The orthorhombic crystallinity, αc (FTIR), measures the sum of long- and short-range orthorhombic order, the latter being obtained by αc (FTIR)-αc (X-rays). The values of αc (FTIR) for MT and ZN are very similar in conditions of equilibrium. The justifications for the molecular origin of ΔH
network are presented: (i) the slow relaxation of long chains strained and oriented in the melt measured by other techniques, (ii)
The correlation, for gels of a linear sample, made in different solvents, between the maximum drawability, λmax, and ΔH
network in a slow T-ramp. The range is 80–270 for λmax and 40–120 J/g for ΔH
network. (iii) The comparison of two traces of the same sample, between 140 °C and 270 °C, show that comparable events in the melt
appear in the integrated absorbance and in the slow calorimetry signal. Analysis on thin films of the little-studied CH2 stretching region reveals that their extinction coefficient, ε, and the shape of the bands are highly sensitive to the sample
history, ε diminishing by a large factor in slowly crystallized samples. Events in the slow T-ramp, followed by a fast crystallization, on the other hand, leads to materials with standard characteristics. Slow calorimetry
traces display more events (endothermic and exothermic) for MT than for ZN, a finding consistent with more flow irregularities
during processing. Equilibrium conditions and better processing could be reached for MT by extending time in the melt or using
higher temperatures. 相似文献
79.
Dielectric relaxation behaviour of (1 − x)PMN − xPZ, for x = 0.10, 0.30 and 0.40 have been studied. The nature of relaxational behaviour was found to change with PZ concentration.
A crossover from a static freezing to critical slowing down like behaviour is observed with increase in Zr4+ concentration. We have used Glazounov and Tangastev criterion to distinguish freezing and critical slowing down like behaviour. 相似文献
80.
Daniel X. Gouveia Odair P. Ferreira Antonio G. Souza Filho M. G. da Silva J. A. C. de Paiva Oswaldo L. Alves Josué Mendes Filho 《Journal of Materials Science》2007,42(2):534-538
The thermal decomposition properties of Mg–Fe hydrotalcites were studied through in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. Abrupt changes in the quadrupolar splitting measured in the Mössbauer spectra revealed a phase transition from the starting lamellar structure to a new crystalline arrangement. By analyzing the Mössbauer parameters we show that the material is highly disordered in the 300–400 °C temperature range. This hypothesis is confirmed by the X-ray results whose diffractograms indicated the collapse of the lamellar structure and the formation of a solid solution. 相似文献