全文获取类型
收费全文 | 2771篇 |
免费 | 54篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 42篇 |
综合类 | 3篇 |
化学工业 | 556篇 |
金属工艺 | 162篇 |
机械仪表 | 70篇 |
建筑科学 | 149篇 |
矿业工程 | 10篇 |
能源动力 | 98篇 |
轻工业 | 225篇 |
水利工程 | 26篇 |
石油天然气 | 62篇 |
武器工业 | 1篇 |
无线电 | 207篇 |
一般工业技术 | 690篇 |
冶金工业 | 206篇 |
原子能技术 | 80篇 |
自动化技术 | 250篇 |
出版年
2021年 | 30篇 |
2020年 | 21篇 |
2019年 | 23篇 |
2018年 | 66篇 |
2017年 | 53篇 |
2016年 | 55篇 |
2015年 | 42篇 |
2014年 | 45篇 |
2013年 | 105篇 |
2012年 | 102篇 |
2011年 | 158篇 |
2010年 | 130篇 |
2009年 | 131篇 |
2008年 | 94篇 |
2007年 | 111篇 |
2006年 | 113篇 |
2005年 | 63篇 |
2004年 | 64篇 |
2003年 | 84篇 |
2002年 | 79篇 |
2001年 | 90篇 |
2000年 | 61篇 |
1999年 | 51篇 |
1998年 | 94篇 |
1997年 | 89篇 |
1996年 | 59篇 |
1995年 | 48篇 |
1994年 | 50篇 |
1993年 | 54篇 |
1992年 | 38篇 |
1991年 | 41篇 |
1990年 | 30篇 |
1989年 | 35篇 |
1988年 | 34篇 |
1987年 | 38篇 |
1986年 | 44篇 |
1985年 | 31篇 |
1984年 | 35篇 |
1983年 | 14篇 |
1982年 | 19篇 |
1981年 | 26篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 14篇 |
1977年 | 21篇 |
1976年 | 32篇 |
1975年 | 14篇 |
1974年 | 18篇 |
1973年 | 16篇 |
1971年 | 14篇 |
排序方式: 共有2837条查询结果,搜索用时 31 毫秒
121.
Ch.F. Markides D.N. Pazis S.K. Kourkoulis 《International Journal of Rock Mechanics and Mining Sciences》2010,47(2):227-237
The Brazilian disk test, namely the diametric compression of a circular disk by radial loads that are uniformly distributed along two symmetric arcs of its periphery, is studied using the method of complex potentials introduced by Kolosov and Muskhelishvili. The rock is assumed to be linear elastic. Closed form full-field solutions are obtained for both the stress and the displacement fields, assuming either plane-stress or plane-strain conditions. The theoretical analysis highlights some critical features of the stresses and the displacements immediately adjacent to the load contact areas, revealing the limitations of the linear elastic solutions. The problem is also studied experimentally by carrying out a series of Brazilian disk tests, according to the ISRM suggestions, with specimens mainly made from Dionysos marble. In addition, a limited number of tests are carried using specimens made from porous natural building stones or from PMMA. The results of the theoretical solution are compared with those of the experiments, and the agreement is satisfactory, at least in the regions of the disk where the stresses developed during loading remain below the linearity limit of the materials. 相似文献
122.
Different acid solids loaded with 1 wt.% of Pt have been studied in n-heptane hydroisomerization in order to determine the influence of porosity and acidity (considered measured by the activity) on selectivities. The open solids like Y and β zeolites and a pillared clay present different activities towards n-C7 conversion but similar selectivities. Consequently, acidity seems to be a less important parameter in n-C7 isomerization than porosity. Very different results were obtained as a function of the solid structure and so n-heptane hydroconversion appears to be a simple and rapid method to obtain data concerning the porosity of unknown zeolite structures. The highest content of multibranched isomers was obtained on open solids but the value predicted by the thermodynamic was never reached due to the fact that cracking of multibranched isomers is initiated quickly. 相似文献
123.
C. A. Christodoulou L. Ekonomou K. A. Stefanou G. P. Fotis D. Ch. Karamousantas D. S. Oikonomou N. Harkiolakis G. E. Chatzarakis I. A. Stathopulos 《Canadian Metallurgical Quarterly》2009,23(5):314-319
The Hellenic electrical distribution lines have been basically supported with the use of wood poles. Outages due to aging, degradation, or broken wood poles may infer significant costs due to repair and loss of energy to consumers. Lifetime estimation of wood poles is significant for maintenance and replacement decisions at the power utility. The paper presents a methodology, based on a statistical analysis, for the evaluation of the life expectancy and the production of a survival curve of a typical Hellenic distribution wood pole in-service. The proposed methodology intends to minimize the life-cycle cost of inspection and refurbishment of wood poles in the distribution network of Hellas, something that is really important in the new competitive and liberating Hellenic electrical energy market. 相似文献
124.
125.
Bit error probability (BEP) and word error probability (WEP) are used as reliability-based retransmission criteria in conjunction with hybrid ARQ (HARQ) protocols. Instead of exploiting an error-detecting code, the decision for a retransmission is based on the error probability of the decoded word, which can be calculated in or after the decoding process. 相似文献
126.
Ch. Alk. Apostolopoulos V. P. Pasialis 《Journal of Materials Engineering and Performance》2010,19(3):385-394
The results of an experimental study for assessing the degradation of the fatigue properties of reinforcing steel bars grade
S400 caused by exposure to laboratory salt spray corrosion environment are presented. For this purpose, low cycle fatigue
(LCF) tests were carried out. Furthermore, the effect of ribs on the fatigue strength was recorded. Results are indicative
of the catalytic impact of corrosion on LCF behavior. Since two important degradation factors such as corrosion and LCF are
functions of time, it appears that the reliability of steel S400 is also time dependant. Additionally, the presence of ribs
on material’s surface affects significantly the fatigue behavior by reducing energy dissipation and duration of test. 相似文献
127.
G. Avramovic-Cingara Ch.A.R. Saleh M.K. Jain D.S. Wilkinson 《Metallurgical and Materials Transactions A》2009,40(13):3117-3127
Commercial dual-phase (DP) steel in sheet form and comprised of ferrite, martensite, and bainite was subjected to uniaxial
tension up to fracture. The damage characteristics were studied through extensive quantitative metallography and scanning
electron microscope (SEM) observations of polished sections and fracture surfaces of failed specimens. The observed void nucleation
mechanisms include nucleation at the martensite/ferrite interface or triple junction (most predominant), nucleation due to
the cracking of martensite particles, and nucleation at the inclusions. The void characteristics in terms of area fraction,
void density, void size ranges, and void orientations were analyzed as a function of thickness strain from various regions
of the different uniaxial tensile test specimens taken to fracture. The damage analysis suggests that the void nucleation
occurs during the entire deformation process with an almost constant rate and this rate reduces before fracture. A nucleation
strain of 0.15 has been estimated for this material. 相似文献
128.
129.
Catalytic packed bed non‐thermal plasma reactor for the extraction of hydrogen from hydrogen sulfide
The decomposition of hydrogen sulfide (H2S) to hydrogen and sulfur with Al2O3, MoOx/Al2O3, CoOx/Al2O3 and NiO/Al2O3 packed non‐thermal plasma dielectric barrier discharge reactor was studied. The reaction was carried out with 5‐mm discharge gap during the decomposition of 5 vol.% H2S at 150 ml/min (STP) flow rate. Typical results indicated the conversion of ~50% at a specific input energy of ~0.92 kJ/l H2S and 10% (in length) packed reactor showed the best conversion. Among the catalysts studied, MoOx and CoOx supported on Al2O3 showed high performance, which may be caused by synergy between plasma excitation of the carrier gas molecules and catalytic behaviour of MoOx and CoOx. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
130.
C. Schmetterer H. Flandorfer Ch. Luef A. Kodentsov H. Ipser 《Journal of Electronic Materials》2009,38(1):10-24
Being the most complex constituent of the quaternary system Ag-Cu-Ni-Sn, the ternary system Cu-Ni-Sn is the key system for
the investigation of the interactions of Ag-Cu-Sn solder alloys with Ni as a contact material. Although this system has been
thoroughly studied in the literature, there are still many uncertainties left. In the present work, a study of the phase equilibria
in four isothermal sections at 220, 400, 500, and 700°C of the Cu-Ni-Sn system was carried out following a comprehensive literature
study. The methods employed were x-ray diffraction (XRD), metallography, and scanning electron microscopy including electron
probe microanalysis. The ternary solubilities of the Ni3Sn2-Cu6Sn5 and Ni3Sn-Cu3Sn fields were characterized in detail. So far no continuous solubility between the respective phases has been found. At 25 at.%
Sn the existence of two ternary compounds formed from the BiF3-type (Cu,Ni)3Sn phase and reported in literature could be confirmed. On the other hand, our results differ significantly from the very
recent literature related to lead-free soldering. 相似文献