全文获取类型
收费全文 | 25613篇 |
免费 | 1597篇 |
国内免费 | 60篇 |
专业分类
电工技术 | 374篇 |
综合类 | 27篇 |
化学工业 | 5940篇 |
金属工艺 | 1024篇 |
机械仪表 | 1559篇 |
建筑科学 | 465篇 |
矿业工程 | 8篇 |
能源动力 | 1002篇 |
轻工业 | 2103篇 |
水利工程 | 101篇 |
石油天然气 | 16篇 |
无线电 | 4308篇 |
一般工业技术 | 5563篇 |
冶金工业 | 1745篇 |
原子能技术 | 349篇 |
自动化技术 | 2686篇 |
出版年
2024年 | 25篇 |
2023年 | 330篇 |
2022年 | 451篇 |
2021年 | 785篇 |
2020年 | 551篇 |
2019年 | 619篇 |
2018年 | 821篇 |
2017年 | 825篇 |
2016年 | 939篇 |
2015年 | 742篇 |
2014年 | 1145篇 |
2013年 | 1619篇 |
2012年 | 1720篇 |
2011年 | 2093篇 |
2010年 | 1499篇 |
2009年 | 1558篇 |
2008年 | 1414篇 |
2007年 | 1092篇 |
2006年 | 934篇 |
2005年 | 814篇 |
2004年 | 758篇 |
2003年 | 698篇 |
2002年 | 696篇 |
2001年 | 584篇 |
2000年 | 512篇 |
1999年 | 495篇 |
1998年 | 789篇 |
1997年 | 488篇 |
1996年 | 450篇 |
1995年 | 293篇 |
1994年 | 207篇 |
1993年 | 192篇 |
1992年 | 148篇 |
1991年 | 132篇 |
1990年 | 96篇 |
1989年 | 100篇 |
1988年 | 89篇 |
1987年 | 69篇 |
1986年 | 60篇 |
1985年 | 69篇 |
1984年 | 47篇 |
1983年 | 31篇 |
1982年 | 36篇 |
1981年 | 33篇 |
1980年 | 41篇 |
1979年 | 23篇 |
1977年 | 27篇 |
1976年 | 41篇 |
1975年 | 23篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Fatigue growth of multiple-cracks near a row of fastener-holes in a fuselage lap-joint 总被引:4,自引:0,他引:4
The fatigue growth of multiple cracks, of arbitrary lengths, emanating from a row of fastener holes in a bonded, riveted, lap joint in a pressurized aircraft fuselage is studied. The effects of residual stresses due to a rivet misfit, and of plastic deformation near the hole, are included. A Schwartz-Neumann alternating method which uses the analytical solution for a row of multiple colinear cracks in an infinite sheet (the crack-faces being subject to arbitrary tractions), is developed to analyze this MSD problem on a personal computer. It is found that for a range of crack lengths, a phenomena wherein the shorter cracks may grow faster than longer cracks may exist. 相似文献
103.
Sang‐Heung Lee Seung‐Yun Lee Hyun‐Cheol Bae Ja‐Yol Lee Sang‐Hoon Kim Bo Woo Kim Jin‐Yeong Kang 《ETRI Journal》2005,27(5):569-578
The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on‐chip 1 to 6 GHz up‐conversion and 1 to 8 GHz down‐conversion mixers using a 0.8 µm SiGe hetero‐junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up‐conversion mixer was implemented on‐chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up‐conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down‐conversion mixer was implemented on‐chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down‐conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz. 相似文献
104.
The effects of α‐form and β‐form nuclei on polymorphic morphology of poly(butylene adipate) (PBA) upon recrystallization from the molten state up to various Tmax values were examined by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and polarized light microscopy (PLM). In this study, PBA with complex melting and polymorphism behaviour was used as a model for examining different types and extents of residual nuclei. As the PBA initially containing the sole α‐crystal was brought to a molten state of various Tmax, the extents of trace α‐form crystal nuclei varied and were dependent on Tmax. Furthermore, it did not matter whether, initially, the PBA contained α‐ or β‐form crystals (or both) because only a single type of α‐nuclei could be left upon treatment to the molten liquid state at Tmax. Therefore, only the α‐crystal in PBA had ‘memory capacity’ in the molten liquid state while the β‐crystal did not. This was so because the latter had been completely transformed into the solid state prior to being heated into a liquid. PBA crystallized before α‐nuclei could be packed into α‐crystal, regardless of the crystallization temperature (Tc). For recrystallization from molten PBA without any nuclei, the crystalline polymorphism was correspondingly influenced by Tc. Copyright © 2005 Society of Chemical Industry 相似文献
105.
Microwave induced plasma processing was used to sinter synthetic Idaho Chemical Processing Plant (ICPP) alumina and zirconia based high level nuclear waste calcines in a nitrogen atmosphere. The microwave densification behaviour of these nuclear waste calcines was observed parallel with identification of the phases formed after sintering. Sintered densities of > 3.20 g cm–3 were obtained within 10 min of microwave sintering of pure calcines. Glass frit containing calcines showed lower sintering densities (< 2.0 g cm–3) due to reactions between the frit and volatile substances in both zirconia based and alumina based calcines; prior removal of frit volatiles increased the sintered density. Phases formed in the microwave sintered calcines were identified by X-ray diffraction. 相似文献
106.
Seoijin Park R. Leavitt R. Enck V. Luciani Y. Hu P.J.S. Heim D. Bowler M. Dagenais 《Photonics Technology Letters, IEEE》2005,17(5):980-982
A semiconductor optical amplifier was developed for coarse wavelength-division-multiplexing (CWDM) operating over 1540-1620 nm (C-L band). A unique quantum-well structure was designed to meet the requirements for the CWDM operation such as wide bandwidth, low polarization-dependent gain, and high-saturation power at the short wavelength end of the band (1540 nm). Over the band, 24-dB maximum chip gain was obtained with less than 4.3-dB gain flatness and more than 14.6-dBm saturation power. 相似文献
107.
The notion of pseudorandomness is the theoretical foundation on which to consider the soundness of a basic structure used in some block ciphers. We examine the pseudorandomness of the block cipher KASUMI, which will be used in the next‐generation cellular phones. First, we prove that the four‐round unbalanced MISTY‐type transformation is pseudorandom in order to illustrate the pseudorandomness of the inside round function FI of KASUMI under an adaptive distinguisher model. Second, we show that the three‐round KASUMI‐like structure is not pseudorandom but the four‐round KASUMI‐like structure is pseudorandom under a non‐adaptive distinguisher model. 相似文献
108.
In this work, five branched polyethylenes with different branching units were synthesized using bidentate nickel (II) catalyst containing -diimine ligands. For comparison, one linear polyethylene was also prepared using tridentate iron (II) catalyst containing -diimine ligand. The crystalline structure of the polyethylenes was investigated using X-ray diffraction (XRD) and polarized optical microscope. The crystalline properties were also measured by differential scanning calorimeter (DSC). Viscoelastic properties of the polyethylenes were investigated using rheometric dynamic analyzer. The DSC and XRD results showed that highly branched polyethylenes exhibit no melting points and no predominating crystalline forms, while the linear polyethylene exhibits clear orthorhombic (110) and (200) reflections on XRD pattern and a clear melting point at 118 °C. The viscoelastic properties of the branched polyethylenes were very complicated due to the combined effect of the molecular weight difference and the degree of chain branching as well as the branching structure. 相似文献
109.
Deborah C. Blaine John D. Gurosik Seong Jin Park Randall M. German Donald F. Heaney 《Metallurgical and Materials Transactions A》2006,37(3):715-720
Sintering experiments with various molybdenum powders are rationalized using a master sintering curve concept that collapses
density, grain size, or other parameters onto a single curve. In this case, the integral work of sintering is developed and
customized for different green densities. Construction of the master sintering curve is described to show how the curve can
be normalized with respect to green density effects. Various grades of molybdenum for metal injection molding and die compaction
are included in the analysis, processed over a range of heating cycles. Die-compacted samples of varying green densities are
used to illustrate the efficacy of the new, normalized master sintering curve concept. Sintering cycle optimization is one
possible outcome from this analysis. 相似文献
110.