全文获取类型
收费全文 | 50483篇 |
免费 | 15103篇 |
国内免费 | 51篇 |
专业分类
电工技术 | 921篇 |
综合类 | 20篇 |
化学工业 | 19936篇 |
金属工艺 | 828篇 |
机械仪表 | 1778篇 |
建筑科学 | 1905篇 |
矿业工程 | 5篇 |
能源动力 | 1403篇 |
轻工业 | 8226篇 |
水利工程 | 370篇 |
石油天然气 | 61篇 |
无线电 | 8908篇 |
一般工业技术 | 13925篇 |
冶金工业 | 1291篇 |
原子能技术 | 218篇 |
自动化技术 | 5842篇 |
出版年
2024年 | 21篇 |
2023年 | 204篇 |
2022年 | 277篇 |
2021年 | 707篇 |
2020年 | 1698篇 |
2019年 | 3391篇 |
2018年 | 3401篇 |
2017年 | 3767篇 |
2016年 | 4271篇 |
2015年 | 4242篇 |
2014年 | 4390篇 |
2013年 | 5762篇 |
2012年 | 3594篇 |
2011年 | 3434篇 |
2010年 | 3386篇 |
2009年 | 3327篇 |
2008年 | 2829篇 |
2007年 | 2474篇 |
2006年 | 2178篇 |
2005年 | 1841篇 |
2004年 | 1784篇 |
2003年 | 1695篇 |
2002年 | 1651篇 |
2001年 | 1383篇 |
2000年 | 1326篇 |
1999年 | 706篇 |
1998年 | 431篇 |
1997年 | 296篇 |
1996年 | 220篇 |
1995年 | 153篇 |
1994年 | 143篇 |
1993年 | 111篇 |
1992年 | 83篇 |
1991年 | 82篇 |
1990年 | 68篇 |
1989年 | 68篇 |
1988年 | 34篇 |
1987年 | 48篇 |
1986年 | 30篇 |
1985年 | 35篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 4篇 |
1970年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The corrosion behavior of Cr-N coated steels with different phases (-Cr, CrN and Cr2N) deposited by cathodic arc deposition on AISI H13 steel was investigated in a 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization tests than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the Cr2N coating than in the other Cr-N coated steels. EIS measurements showed, for most of the Cr-N coated steels, that the Bode plot presented two time constants. Also, the Cr2N coating represented the characteristic of Warburg behavior after 72 h of immersion. The coating morphologies were examined in planar view and cross-section by SEM analysis and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, it is concluded that the CrN coating provided a better corrosion protection than the other Cr-N coated steels. 相似文献
942.
The texture of cold rolled aluminum sheet has been known to vary through the thickness due to inhomogeneous deformation during rolling. The copper texture is obtained in the center layer that is plane strain compressed while the shear texture in the surface layer, which is approximated by major 001 011 and minor 111 112 and 111 110 components. The stability condition of these components was calculated based on the full constraint Taylor-Bishop-Hill theory and could be described by a parameterdɛ13/dɛ11 with the suffixes 1 and 3 indicating the rolling and thickness directions, respectively. 相似文献
943.
Chan-Yeol Seo Seung-Jun Choi Jeon Choi Choong-Nyeon Park Paul. S. Lee Jai-Young Lee 《Journal of Alloys and Compounds》2003,350(1-2):324-331
AB5-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi3.6Al0.4Co0.7Mn0.3 with a hexagonal CaCu5 structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi3.6Al0.4Co0.7Mn0.3Tiy, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi3.6Al0.4Co0.7Mn0.3Tiy (y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (P–C–T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test. 相似文献
944.
Sang Chul Seo Hyun Jung Kim Byung Ho Park Kwang Suk Son Sung Keun Lee Sun Bae Kang Donggyu Kim 《Metals and Materials International》2006,12(3):273-277
In a continuous casting steelmaking operation, the surface of a slab is under a condition that can be characterized as high-temperature,
low-cycle fatigue in which the tensile and compressive stress is repeatedly developed. For this reason, for the evaluation
of the hot ductility of a slab, considering the fatigue deformation is more feasible before a tensile or compressive test.
In this study, the effects of low-cycle fatigue on the hot ductility of steels with a carbon content of 0.06–0.8 wt.% are
investigated at various temperatures. For a carbon content of 0.06%, there were no significant differences between the RA
values from a simple tensile test and those from a tensile test after fatigue deformation. The tendency of ductility deterioration
with fatigue deformation is evident in 0.1 %C steel, and is due to the deformation-induced ferrite film that forms around
the prior austenite grain. Conversely, high carbon steel containing 0.8 %C did not show a recovery of hot ductility in a low
temperature region, and the specimen on which the tensile was measured after fatigue showed a higher hot ductility in the
low temperature region, which is thought to result from the pearlite refinement effects. As the results obtained in this work
showed noticeable differences in the hot ductility of carbon steel through the test conditions, it is suggested that for more
accurate data, fatigue deformation be adopted in which the temperature range in an unbending operation is determined in the
steelmaking factory. 相似文献
945.
This paper examines a new concept of corrosion surface damage analysis by using the digital image processing. Corrosion phenomena are analyzed using a digital value for morphological surface damages instead of electrochemical methods. Initial images are characterized by three categories: color, texture and shape features. To calculate corrosion surface damages color we use the interpretation of HIS model. For the texture attributes, the method of co-occurrence matrix is used. Five types of corrosion damage are examined. Multidimensional scaling procedure is used to define the classification plane. This study suggests a probabilistic method of decision-making. This analysis develops a method for automated identification system of corrosion damages and is supposed to be more advantageous than that of electrochemical techniques. 相似文献
946.
Yoon -Suk Choi Sung -Joon Kim Ik -Min Park Kwang -Woo Kwon In -Suk Yoo 《Metals and Materials International》1997,3(2):118-124
Boron distribution in a low-alloy steel (15B26:0.25C-0.29Cr-0.03Ti-0.028Al-0.0016B) has been characterized employing Fission
Track Etching (FTE) method. The characteristics of boron distribution with variation of cooling rate after austenitization
and through case-hardened depth after carburization were analyzed. Hardenability of 15B26 steel was also evaluated through
Jominy-end-quench test and the results are as follows: It was observed that, in austenitized 15B26 steel, boron was distributed
uniformly over the whole area of specimen with a little segregation along the austenite grain boundaries at higher cooling
rates and boron precipitates were formed in the intergranular as well as transgranular regions at lower cooling rates. Jominy
equivalents (HRC 35) of 15B26 steel were fairly increased between the Jominy temperatures of 820°C and 850°C, which might
result from the increase of the amount of soluble boron in austenite due to the dissolution of borocarbides between 820°C
and 850°C. In carburized 15B26 steel, the different through thickness features of boron distribution from the carburized surface
were found; coarse nodular boron precipitates up to the depth of 150 μm; uniform distribution of dissolved boron between 150~650
μm; and segregation of boron atoms along grain boundaries in the regions deeper than 650 μm. 相似文献
947.
Galvanic coupling effect on the corrosion of SiC-reinforced aluminum alloy-matrix composites was investigated in a sodium chloride solution. The potentiodynamic polarization measurement indicated that pitting potentials of metal matrix composites (MMCs) and AA2124 matrix alloy were similar, and pitting potential of MMCs was almost same as corrosion potential, while pitting susceptibility of MMCs was higher than that of AA2124 alloy. Galvanic current by formation of galvanic couple between SiCw and matrix reveals very low value because of large cathodic polarization of SiC. However, by increasing potential of matrix to pitting potential by this galvanic couple and thus, forming pits easily at the weak passive film near SiC reinforcing phase preferentially, it is concluded that pitting susceptibility of MMCs increases highly than AA2124 alloy of matrix composition. 相似文献
948.
Y.?S.?HanEmail author J.?O.?Choi C.?O.?Choi D.?G.?McCartney 《Metals and Materials International》2004,10(1):27-32
The present study has been undertaken to better understand the solidification behavior of Al−Si−Fe alloys containing 7wt.%
Si and 0.9wt.% Fe, with particular regard to the formation of phase during controlled solidification and influence of growth
rates on intermetallic phase selection. The alloys studied were Al-7Si-0.9Fe alloys, which were produced by a modified Bridgman
solidification arrangement. These alloys were solidified unidirectionally with different growth rates (1–30mm/min). The solidified
microstructure of these alloys consists of the growth of primary aluminum and multiple second phase reactions. 相似文献
949.
Young Suk Kim Sang Bok Ahn Dong Joon Oh Sung Soo Kim Yong Moo Cheong 《Metals and Materials International》2002,8(3):241-246
With the aim of assessing the degradation of Zr−2.5Nb pressure tubes operating in the Wolsong unit-1 nuclear power plant, characterization tests are being conducted on irradiated Zr−2.5Nb tubes removed after 10-year operation. The examined tube had been exposed to temperatures ranging from 264 to 306°C and a neutron fluence of 8.9×1021 n/cm2 (E>1 MeV) at the maximum. Tensile tests were carried out at temperatures ranging from RT to 300°C. The density of a-type and c-type dislocations was examined on the irradiated Zr-2.5Nb tube using a transmission electron microscope. Neutron irradiation up to 8.9×1021 n/cm2 (E>1 MeV) yielded an increase in a-type dislocation density of the Zr−2.5Nb pressure tube to 7.5×1014 m−2, which was highest at the inlet of the tube exposed to the low temperature of 275°C. In contranst, the c-component dislocation density did not change with irradiation, keeping an initial dislocation density of 0.8×1014 m−2 over the whole length of the tube. As expected, the neutron irradiation increased mechanical strength by about 17–26% in the transverse direction and by 34–39% in the longitudinal direction compared to that of the unirradiated tube at 300°C. The change in the mechanical properties with irradiation is discussed in association with the microstructural change as a function of temperature and neutron fluence. 相似文献
950.
Jong-Young?Park Young-Soo?No Byung-Jun?Park Hyun-Woo?Lee Ji-Won?Choi Jin-Sang?Kim Y.?Ermakov Seok-Jin?Yoon Young-Jei?Oh Won-Kook?ChoiEmail author 《Metals and Materials International》2004,10(4):351-355
A low energy N2 ? ion beam impinged on a α-Al2O3(0001) single crystal surface in the range of fluence 5×1015/cm2?1×1018/cm2 at room temperature. After ion bombardment, chemical bonding on the modified sapphire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×1015/cm2, only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×1017/cm2 induced Al?O?N bonding at around 403 eV. The occurrence of Al?N bonding was identified at ion fluence higher than 5×1017/cm2 at 396.6 eV. II–VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al?O?N bonding only, and both Al?O?N and Al?N bonding showed a significant reduction of the peak related to deep-level defects in photoluminescence. These results are explained in terms of the formation of Al?N?O and Al?O?N layers and relaxation of the interfacial strain between Al2O3 and ZnO. 相似文献