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961.
D. Galvan V. Ocelík Y. Pei B. J. Kooi Jeff Th. M. De Hosson E. Ramous 《Journal of Materials Engineering and Performance》2004,13(4):406-412
TiB/Ti-6Al-4V metal-matrix composite (MMC) layers were produced on Ti-6Al-4V substrates by laser cladding. A TiB2/Ti powder mixture was used as a precursor to obtain a dispersion of TiB needles in the Ti alloy matrix, with the aid of an
exothermic reaction between TiB2 and Ti. A eutectic microstructure was obtained that consisted of an extremely homogeneous dispersion of TiB eutectic needles
in the Ti alloy matrix, having a volume fraction as high as 0.33. Also, an equilibrium-like microstructure was found, consisting
of a dispersion of both primary and eutectic TiB needles inside the Ti alloy matrix. An analysis of the geometry of the layers
was performed and proved successful in determining the percentage of B. Further, it correctly predicted the variation of atomic
B content as a function of laser power. The relative wear resistance coefficient, defined as the wear coefficient of the uncoated
matrix divided by that of coating, shows an improvement by a factor as high as 1500 for the eutectic microstructure.
This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September
15–17, 2003, in Indianapolis, Indiana, and appeared on pp. 411–18 of the Proceedings. 相似文献
962.
Lars Arnberg Ragnvald H. Mathiesen 《JOM Journal of the Minerals, Metals and Materials Society》2007,59(8):20-26
The directional solidification of thin alloy sheets in a Bridgman furnace has been studied by x-radiography using high-brilliance
synchrotron x-radiation in combination with a low-noise, fast-readout camera. Spatial resolutions down to 1.5 μm and a temporal
resolution of about 0.15 s have permitted real-time video microscopy of microstructural evolution during columnar and equiaxed
dendrite growth and eutectic and monotectic growth. The technique has also allowed for direct observations of important solidification
phenomena such as dendrite fragmentation and porosity formation, primarily in aluminium alloys. As a result, insights have
been gained into mechanisms of dendrite fragmentation, criteria for dendrite tip kinetics and interface stability during transient
growth, and microstructure formation mechanisms during monotectic solidification. The results are expected to be important
for validation of dendrite growth models. This paper presents a review of the technique as well as examples of images obtained
during solidification of aluminum alloys. 相似文献
963.
The effects of joint design on the mechanical properties of AL7075-T6 aluminum sheet were studied on the latest automated
gas-tungsten arc-welding system. Using ER5356 filler metal, full-penetration welds were made on workpieces with various included
joint angles. Testing of the mechanical properties of the joints was done in the as-welded, naturally aged, and postweld heat-treated
conditions. The results show that by using crack-resistant filler, and by selecting the proper joint design and postweld heat
treatment, strong, dependable welds can be produced on thin AL7075 sheet material. An elasticity model of the weld joint was
established to help understand the mechanical behavior of the joints. An undermatched joint design is shown to be capable
of achieving a joint strength that matches the strength of the base alloy. 相似文献
964.
Kyung-Man Moon Hwang-Rae Cho Myung-Hoon Lee Sung-Kyu Shin Sung-Cheol Koh 《Metals and Materials International》2007,13(3):211-216
The differences between the general corrosion and microbiologically influenced corrosion (MIC) of steels were investigated
in terms of its electrochemical behavior and surface phenomena. The corrosion potential of steels in the absence of SRB (sulfate-reducing
bacteria) shifted to a negative value with the immersion time. However, the potential of the presence of SRB shifted to a
positive value after 30 days' incubation, indicating the growth of SRB biofilms on the test metal specimens and the formation
of corrosion products. In addition, the color of a medium inoculated with SRB changed from gray to black. The change in color
appeared to be caused by the formation of pyrites (FeS) as a corrosion product, while no significant change in color was observed
in a medium without SRB inoculation. Moreover, corrosion rates of various steels tested for MIC were higher compared to those
of steels in the absence of SRB. In particular, the corrosion current density of TMCP steels in the presence of SRB was larger
than that of other steels. Pitting corrosion was also observed at the surface of all steels in the SRB-inoculated medium.
The pitting corrosion likely occurred due to SRB that was associated with the increasing corrosion rates through increasing
cathodic reactions, which caused a reduction of sulfate to sulfide as well as the formation of an oxygen concentration cell. 相似文献
965.
Joon-Ho Shin Jong-Hwa Kim Ki-Won Kim Hyo-Jun Ahn 《Metals and Materials International》2002,8(4):417-422
Lead acid batteries have had restricted applications because of relatively low energy density below 50Wh/kg. Many efforts have achieved lighter battery components such as separators, connections and containers etc. Thus, the most important problem of the lead acid battery is to improve the low capacity of the active material in the positive electrode. The purpose of this study is to improve the utilization of the active material in the lead dioxide electrode for the lead acid battery through the production of lead oxide with better physicochemical characteristics through cementation. A cementation reaction was performed in 1.0wt.%HCl solution using pure magnesium plate as the reductant. We investigated the utilization of the active material and discharge characteristics of the positive electrode with a current density ranging from 3.4 to 108.8mAcm−2. As a result, the active material utilization was about 72% at 3.48 mAcm−2 and increased with decreasing current density. The discharge characteristics according to current density are especially very good at high current density 相似文献
966.
Grain coarsening tests were carried out on Al-4.5 pct Cu and Al-4.5 pct Si alloys. The effects of three variables, melt composition, pour temperature, and mold temperature, were determined. It was found that the macrostructure generally coarsened with increased pour and mold temperatures. Coarsening was extreme in the unrefined alloys but was retarded by the active grain refiners like titanium and columbium. The effect of boron was spectacular in suppressing coarsening tendencies. The results of the investigation support the carbide theory of nucleation as opposed to the peritectic theory. 相似文献
967.
Satyam S. Sahay B. V. Harish Kumar Sangeetha J. Krishnan 《Journal of Materials Engineering and Performance》2003,12(6):701-707
Design of industrial annealing cycles requires recrystallization and grain growth studies, which are typically carried out
under isothermal laboratory condition. The kinetics coefficients of these phase transformations are obtained from such studies,
which are subsequently used in designing the industrial nonisothermal cycles using the additivity principles. However, the
strong heating rate effects on the grain growth kinetics necessitate such kinetics studies using industrial thermal profiles.
In the present work, the hot and cold spot cycles of an industrial batch annealing cycle for AIK grade steel have been simulated
in a programmable laboratory furnace. Subsequently, the effect of annealing temperature, soaking time, and heating rate on
the microstructural features, such as grain size distribution, grain shape anisotropy, and grain orientation, have been investigated
through extensive quantitative microscopy. The implications of these results on the design of industrial batch annealing cycles
have been discussed. 相似文献
968.
Gordon D. Gemmell Nicholas J. Grant 《JOM Journal of the Minerals, Metals and Materials Society》1957,9(4):417-423
The effects of solid solution alloying on the creep-rupture properties, deformation characteristics, ductility, and fracture of pure aluminum were studied by means of creep-rupture tests on polished specimens of three alloys each of Al-Cu (0.24, 0.79, and 2.05 pct Cu), Al-Zn (4.93, 9.89, and 19.78 pct Zn), and Al-Mg (0.94, 1.92, and 5.10 pct Mg) at 500°, 700°, and 900°F. 相似文献
969.
Bob R. Powell Vadim Rezhets Michael P. Balogh Richard A. Waldo 《JOM Journal of the Minerals, Metals and Materials Society》2002,54(8):34-38
The micro structural analysis of die-cast AE42 reveals a correlation between micro structure and creep strength. A lamellar-phase
Al11RE3, which dominates the interdendritic microstructure of the alloy, partly decomposes above 150‡C into Al2RE and Al (forming Mg17Al12). The increased solubility of aluminum in magnesium at higher temperatures may also promote the decomposition of Al11RE3. The creep strength decreases sharply with these phase changes. A mechanism for the decrease in creep strength of AE42 is
proposed whereby the reduced presence of lamellar Al111RE3 and/or the presence of Mg17Al12 contribute to the observed poor creep strength at higher temperatures. 相似文献
970.
Nicholas J. Grant Earl C. Roberts John Chipman 《JOM Journal of the Minerals, Metals and Materials Society》1954,6(2):145-149
An equilibrium study was made of the distribution of chromium and oxygen between liquid iron, containing less than 1 pct Cr, and simple slags of the CaO(MgO)-SiO2-FeO-Cr2O3 type in the temperature range 1526° to 1734°C The effects of slag oxidation, temperature, and basicity were observed. 相似文献