全文获取类型
收费全文 | 8986篇 |
免费 | 152篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 226篇 |
综合类 | 1篇 |
化学工业 | 2049篇 |
金属工艺 | 263篇 |
机械仪表 | 173篇 |
建筑科学 | 437篇 |
矿业工程 | 88篇 |
能源动力 | 254篇 |
轻工业 | 210篇 |
水利工程 | 49篇 |
石油天然气 | 45篇 |
武器工业 | 1篇 |
无线电 | 1731篇 |
一般工业技术 | 1298篇 |
冶金工业 | 1180篇 |
原子能技术 | 163篇 |
自动化技术 | 977篇 |
出版年
2021年 | 60篇 |
2016年 | 60篇 |
2015年 | 88篇 |
2014年 | 137篇 |
2013年 | 650篇 |
2012年 | 133篇 |
2011年 | 207篇 |
2010年 | 195篇 |
2009年 | 257篇 |
2008年 | 218篇 |
2007年 | 189篇 |
2006年 | 236篇 |
2005年 | 219篇 |
2004年 | 196篇 |
2003年 | 213篇 |
2002年 | 242篇 |
2001年 | 235篇 |
2000年 | 219篇 |
1999年 | 213篇 |
1998年 | 243篇 |
1997年 | 234篇 |
1996年 | 227篇 |
1995年 | 196篇 |
1994年 | 229篇 |
1993年 | 211篇 |
1992年 | 218篇 |
1991年 | 188篇 |
1990年 | 215篇 |
1989年 | 219篇 |
1988年 | 167篇 |
1987年 | 149篇 |
1986年 | 137篇 |
1985年 | 105篇 |
1984年 | 113篇 |
1983年 | 93篇 |
1982年 | 97篇 |
1981年 | 112篇 |
1980年 | 94篇 |
1979年 | 96篇 |
1978年 | 94篇 |
1977年 | 105篇 |
1976年 | 85篇 |
1975年 | 97篇 |
1974年 | 74篇 |
1973年 | 73篇 |
1972年 | 89篇 |
1971年 | 78篇 |
1970年 | 78篇 |
1969年 | 68篇 |
1965年 | 68篇 |
排序方式: 共有9145条查询结果,搜索用时 15 毫秒
91.
The Kirchhoff approximation is used to show that the time domain impulse response of an isolated flat crack can be given a simple geometrical interpretation in terms of the derivative of a projected length function. For an elliptical crack, this derivative can be obtained explicitly to yield the two edge-diffracted waves which originate from the flashpoints of the crack. An explicit coordinate invariant expression is obtained from this elliptical crack solution which relates the time difference, t, between the arrival of these edge-diffracted waves and the crack size and orientation. Previously, we have proposed that this expression, together with t measurements in different scattering directions, could be used in a regression analysis as the basis for performing a constrained inversion of crack scattering data (i.e., where we attempt to obtain the best equivalent flat elliptical crack that fits the scattering measurements). Here we will demonstrate some results of applying the proposed algorithm using noisy synthetic data. The sensitivity of the results to both, number of measurements and transducer orientation, will be discussed. 相似文献
92.
S. Feliu Jr. J. M. Bastidas J. C. Galvan J. Simancas M. Morcillo E. Almeida 《Journal of Applied Electrochemistry》1993,23(2):157-161
The stability of a rusted steel surface exposed to a 0.11 M sodium sulphate solution has been studied. Electrochemical impedance spectroscopy, polarization resistance and atomic absorption analysis techniques were used in conjunction with mild steel specimens rusted in a rural atmosphere and treated with different concentrations of phosphoric acid. Since most of the impedance diagrams obtained differ from the typical semicircle, it is not clear how to obtain kinetic information on the corrosion process. The polarization resistance technique gives more useful data. 相似文献
93.
Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization 总被引:1,自引:0,他引:1
Wayde R. Schmidt Vijay Sukumar William J. Hurley Jr. Roberto Garcia Robert H. Doremus Leonard V. Interrante Gary M. Renlund 《Journal of the American Ceramic Society》1990,73(8):2412-2418
Partially crystalline Si3 N4 , with nanosized crystals and a specific surface area greater than 200 m2 /g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH3 to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si3 N4 proceeds with additional heating above 1400°C under N2 . The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N2 , are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes. 相似文献
94.
The fracture strength of HF-etched samples was measured as a function of field-assisted K-Na ion exchange depth, as well as the severity of abrasion. As expected, the more severe the abrasion, the greater the depth required to make the strength insensitive to abrasion. An abrasion-independent weakening mechanism that increased with exchange depth was also found to be operative. 相似文献
95.
Toughening by Metallic Lamina in Nickel/Alumina Composites 总被引:2,自引:0,他引:2
Tape casting and hot-pressing were used to produce metal/ alumina laminate composites. The mechanical behavior of these laminates was characterized. The strength and toughness of the laminates were greatly improved in comparison to that of monolithic alumina. Indentation strength values of the laminates remained approximately constant for indent loads between 10 and 100 N. Thus, this type of laminate appears to be a good candidate for damage-tolerant composite material design. 相似文献
96.
Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors 总被引:1,自引:0,他引:1
Corinna L. Czekaj Michael L. J. Hackney William J. Hurley Jr. Leonard V. Interrante Gary A. Sigel Paul J. Schields Glen A. Slack 《Journal of the American Ceramic Society》1990,73(2):352-357
Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me3 Si)0.80 ((CH2 =CH)MeSi)1.0 (MeHSi)0.35 ] n (VPS) or [MeHSiCH2 ] n (MPCS) with [R2 AlNH2 ]3 , where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et2 AlNH2 ]3 . In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu2 AlNH2 ]3 yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed. 相似文献
97.
PAUL PREDECKI J. HAAS JOHN FABER Jr. R. L. HITTERMAN 《Journal of the American Ceramic Society》1987,70(3):175-182
The mechanism of lattice thermal expansion in pure hexagonal cordierite prepared by glass devitrification was investigated by time-of-flight neutron powder diffraction at temperatures from 22° to 750°C under vacuum. Full matrix least-squares refinement of the diffraction spectra was carried out in space group P6/mcc using the Rietveld method. The structural data from the refinements were resolved into components parallel and normal to the c axis. The negative c axis expansion results from two effects: (1) increasing distortion of the T2 tetrahedral (ring tetrahedra) with temperature, primarily due to displacement of the T2 cations toward the c-axis channels in the structure; (2) decreasing distortion of the T1 /M tetrahedra/ octahedra with increasing temperature, due to octahedral I (M-O1 ) bond expansion and an associated decrease in torsional distortion of the T1 tetrahedra. 相似文献
98.
Processing and Properties of Particulate Composites from Coated Powders 总被引:13,自引:0,他引:13
Tyrone D. Mitchell Jr. Lutgard C. De Jonghe 《Journal of the American Ceramic Society》1995,78(1):199-204
A method is described for sintering of highly loaded (≤20 vol%) alumina matrix/silicon carbide whisker or platelet composites to closed porosity. The method uses controlled heterogeneous precipitation in a suspension of whiskers or platelets. The suspension-coated particles are calcined to produce a free-flowing composite powder which can be hot-pressed or free-sintered to high density. The results of consolidation and mechanical property testing are reported. 相似文献
99.
Eicosa-5,8,11,14-tetraynoic acid or arachidonic acid or no supplement (controls) was given orally to rats maintained on a
fat free diet and the fatty acid composition of total lipids of several organs determined. No changes were noted in the total
fatty acid concentrations of the organs examined in the various groups. A decrease in the amount of arachidonic acid, 22∶4ω6
and 22∶5ω6 (as percent of total fatty acids), and an increase in the amount of 20∶3ω6 and linoleate were observed in total
lipids of several organs. In the group receiving the arachidonate supplement, there was less linoleate and 20∶3ω6 and more
arachidonate than in the controls. Both eicosa-5,8,11,14-tetraynoic acid and arachidonate supplements resulted in a decrease
in 20∶3ω9 in most organs studied. Generally, the most marked changes were seen in liver but, of the other organs examined
(heart, kidney, testis, brain, and adrenals), only the adrenals failed to show any significant differences between the controls
and each of the two supplemented groups. Although the experimental conditions preclude conclusive interpretation of the changes
observed, it is suggested that eicosa-5,8,11,14-tetraynoic acid was effective in inhibiting the conversion of linoleate to
arachidonate and the conversion of arachidonate to 22∶4 and 22∶5. 相似文献
100.
Thomas J. Brumm C. R. Hurburgh Jr. 《Journal of the American Oil Chemists' Society》1990,67(11):747-749
Drought stress created shriveled and wrinkled (S/W) soybeans in the 1988 soybean crop. Seven lots of 1988 soybeans were examined
to validate the Federal Grain Inspection Service (FGIS) definition of S/W. Lots were subdivided into sized fractions with
both slotted and round-hole screens. Shriveled and wrinkled soybeans were found in all size fractions, whether those fractions
were determined by a slotted or a round-hole screen. None of the size fractions adequately isolated or characterized S/W soybeans.
The FGIS definition of shriveled and wrinkled does not sonsider larger wrinkled soybeans, but only shriveled soybeans passing
through a 10/64″ by 3/4″ slotted screen. The most accurate determination of S/W soybeans can be made by examining the entire
soybean sample, not a sized fraction. 相似文献