全文获取类型
收费全文 | 54082篇 |
免费 | 6069篇 |
国内免费 | 4051篇 |
专业分类
电工技术 | 3237篇 |
综合类 | 5015篇 |
化学工业 | 8991篇 |
金属工艺 | 2822篇 |
机械仪表 | 3163篇 |
建筑科学 | 5737篇 |
矿业工程 | 2450篇 |
能源动力 | 2132篇 |
轻工业 | 3369篇 |
水利工程 | 1869篇 |
石油天然气 | 2841篇 |
武器工业 | 658篇 |
无线电 | 7155篇 |
一般工业技术 | 8173篇 |
冶金工业 | 2443篇 |
原子能技术 | 1118篇 |
自动化技术 | 3029篇 |
出版年
2024年 | 351篇 |
2023年 | 1030篇 |
2022年 | 1699篇 |
2021年 | 2018篇 |
2020年 | 2132篇 |
2019年 | 1906篇 |
2018年 | 1702篇 |
2017年 | 2142篇 |
2016年 | 2097篇 |
2015年 | 2244篇 |
2014年 | 3130篇 |
2013年 | 3345篇 |
2012年 | 3805篇 |
2011年 | 4048篇 |
2010年 | 3021篇 |
2009年 | 3096篇 |
2008年 | 2875篇 |
2007年 | 3442篇 |
2006年 | 3146篇 |
2005年 | 2602篇 |
2004年 | 2243篇 |
2003年 | 1935篇 |
2002年 | 1708篇 |
2001年 | 1334篇 |
2000年 | 1222篇 |
1999年 | 992篇 |
1998年 | 793篇 |
1997年 | 731篇 |
1996年 | 619篇 |
1995年 | 533篇 |
1994年 | 461篇 |
1993年 | 372篇 |
1992年 | 300篇 |
1991年 | 243篇 |
1990年 | 208篇 |
1989年 | 169篇 |
1988年 | 126篇 |
1987年 | 73篇 |
1986年 | 45篇 |
1985年 | 34篇 |
1984年 | 42篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 22篇 |
1979年 | 28篇 |
1965年 | 6篇 |
1963年 | 5篇 |
1959年 | 11篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
振动采油工艺在稠油区的实验研究与应用 总被引:5,自引:2,他引:3
在天然地震的影响下,油井产量发生波动,使人们受到启示,从而引进了振动采油工艺技术。本文对振动增产的机理进行了探讨,指出振动增油机理在于加快地层中流体的流速;改变储集层内油、气、水的重新分布;改变岩石表面润湿性,有利于清除油层堵塞,提高渗透率。通过分析两个试验区的振动采油效果,总结出在不同扰动力、不同激振频率、不同振动周期下的增产效果和规律,对振动采油的实施具有一定的指导意义。 相似文献
43.
A novel approach to the derivation of Bažant’s size effect law is presented. Contrarily to the original Lagrangian derivation
which hinged on energetic consideration, a Newtonian approach based on local stress intensity factors is presented. Through
this approach, it is shown that Bažant’s size effect law is the first (and dominant) term in a series expansion for the nominal
stress. Furthermore, analytical expressions forB are derived for selected specimen geometries. 相似文献
44.
用磁控溅射方法制备了系列 (Fe0 .86 Zr0 .0 33Nb0 .0 33B0 .0 6 8Cu0 .0 1 ) x(Al2 O3) 1 -x颗粒膜样品 ,体积百分比x从 0 .3 3~ 0 .63 ,样品厚度约为10 0nm。室温下在Fe0 .86 Zr0 .0 33Nb0 .0 33B0 .0 6 8Cu0 .0 1 体积百分比x =0 .43时得到 17.5 μΩ·cm的最大饱和霍耳电阻率 ,比纯铁磁金属提高了 3~ 4个量级。对其磁性和微结构进行了研究 ,样品霍耳电阻率随外场的变化曲线 ρxy~H与磁场平行于膜面时的磁化曲线M~H有相似性 ,说明霍尔电阻率 ρxy与磁化强度M相关。样品电阻率 ρxx随金属体积百分比x的减小而增加 ,在x =0 .43附近发生突变 ,从金属导电变为绝缘体。根据微结构和输运性质对可能的机制进行了探讨 相似文献
45.
46.
We derive an effective single-band Hubbard type Hamiltonian for CuO2 planes. The Hamiltonian includes both electron-electron repulsion and electron-phonon coupling to oxygen vibrational modes. We start with first-principles density functional theory parameters and then map onto a single-band model. Unlike previous mappings to a single-band Hamiltonian, ours explicitly preserves the Fermi surface shape and matrix elements of the many-band Hamiltonian. We consider both in-plane oxygen breathing modes as well as out-of-plane tilting modes. The latter modes have a quadratic electron-phonon coupling, and are also highly anharmonic in La2CuO4 based superconductors. The coupling to breathing modes is too small to account for highT
c, while the coupling to quadratic modes is much stronger even though they would be neglected in a standard Migdal-Eliashberg approach to superconductivity. 相似文献
47.
48.
The electroclinic effect in the smectic A phase of ferroelectric liquid crystals is a sensitive probe for measuring the soft
mode response near the A-C* transition point. It is possible to evaluate several coefficients of the Landau theory describing
the A-C* transition by simultaneously measuring the frequency dependence of both the optical signal and the current through
the sample. We have made such measurements on a couple of homologous series [2S,3S]-4′-(2-chloro-3-methyl pentanoyloxy) phenyl-trans-4″-n alkoxy cinnamates synthesized in our labortory. The results show that the Landau meanfield theory is adequate to describe
the A-C* phase transition in these compounds.
Presented at the 15th International Liquid Crystal Conference, Budapest, 3–8 July 1994. 相似文献
49.
The influence of alloying of Pt with 20 at.% of Ni, Co and Fe has been studied in the hydrogenation of 1,3 butadiene. Iron induces the more important modifications, with both higher activity and selectivity. The results are discussed in terms of the surface segregation, the local order in surface and the electronic properties measured by photoemission of core levels. 相似文献
50.
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