全文获取类型
收费全文 | 131070篇 |
免费 | 14827篇 |
国内免费 | 9258篇 |
专业分类
电工技术 | 10586篇 |
技术理论 | 1篇 |
综合类 | 14098篇 |
化学工业 | 18272篇 |
金属工艺 | 8243篇 |
机械仪表 | 9169篇 |
建筑科学 | 10276篇 |
矿业工程 | 4899篇 |
能源动力 | 3283篇 |
轻工业 | 15408篇 |
水利工程 | 3660篇 |
石油天然气 | 4721篇 |
武器工业 | 1895篇 |
无线电 | 13953篇 |
一般工业技术 | 11544篇 |
冶金工业 | 4929篇 |
原子能技术 | 1751篇 |
自动化技术 | 18467篇 |
出版年
2024年 | 347篇 |
2023年 | 2151篇 |
2022年 | 4897篇 |
2021年 | 6399篇 |
2020年 | 4644篇 |
2019年 | 3302篇 |
2018年 | 3504篇 |
2017年 | 3991篇 |
2016年 | 3640篇 |
2015年 | 5729篇 |
2014年 | 7411篇 |
2013年 | 8584篇 |
2012年 | 10639篇 |
2011年 | 11265篇 |
2010年 | 10557篇 |
2009年 | 10032篇 |
2008年 | 10311篇 |
2007年 | 9862篇 |
2006年 | 8696篇 |
2005年 | 6969篇 |
2004年 | 4998篇 |
2003年 | 3591篇 |
2002年 | 3546篇 |
2001年 | 3070篇 |
2000年 | 2507篇 |
1999年 | 1306篇 |
1998年 | 647篇 |
1997年 | 487篇 |
1996年 | 449篇 |
1995年 | 361篇 |
1994年 | 241篇 |
1993年 | 198篇 |
1992年 | 150篇 |
1991年 | 124篇 |
1990年 | 97篇 |
1989年 | 99篇 |
1988年 | 72篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 36篇 |
1979年 | 24篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1959年 | 14篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 86 毫秒
11.
Qi Xiao Xinyao Dong Xiumei Yin Hong Wang Hua Zhong Mingming Xing Ying Tian Yao Fu Bin Dong Xixian Luo 《Journal of the American Ceramic Society》2021,104(3):1415-1423
Multicolor upconversion luminescence materials show significantly applications in materials science. In this paper, the novel Yb3+-sensitized Na3La(VO4)2 upconversion luminescence crystals are synthesized by the solid-state reaction method. Three primary colors upconversion luminescence are successfully achieved in Na3La(VO4)2:Yb3+,Tm3+, Na3La(VO4)2:Yb3+,Er3+, and Na3La(VO4)2:Yb3+,Ho3+ crystals excited by the single 980 nm LD. Multicolor upconversion luminescence can be obtained by simply adjusting the combination ratios of these three samples. Luminescence mechanisms of the Yb3+-sensitized system are discussed in detail. In the Na3La(VO4)2 host material, the Yb3+/Ho3+ codoped system exhibits unusual red upconversion luminescence based on the short decay time of Ho3+ ion 5I6 level, which provides the possibility of three primary color luminescence under 980 nm excitation. 相似文献
12.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. 相似文献
13.
14.
15.
Riemann-Liouville分数阶微积分算子是一类带有一个函数的分数阶微积分算子的特殊情形,以Riemann-Liouville分数阶微积分算子的积分中值定理和微分中值定理为基础,我们得到了一类带有一个函数的分数阶微积分算子的积分中值定理和微分中值定理,并给出其在计算方面的一些应用。 相似文献
16.
Yuan-Xia Wang Ying Shi Chen-Chen Wang Jia-Hui Cheng Ying Wang Wen-Jun Shao Li-Zhi Liu 《应用聚合物科学杂志》2021,138(27):50651
Crosslinking of polyolefin elastomer (POE, ENGAGE™ 8480) with Dicumyl Peroxide (DCP) can have effects on its crystallization dynamics, crystal structure, and properties. The POE crosslinked uniformly has significantly lower crystalline ability than the one with only amorphous phase crosslinked, which, in turn, has weaker crystalline ability than neat POE. The crystallinity and melting point depend on how the POE is crosslinked. The neat POE and POE crosslinked in amorphous phase only, are investigated with DSC and in-situ tensile/synchrotron radiation (WAXD/SAXS). In situ tensile/synchrotron X-ray during a uniaxial stretching process indicates that severe crystal fragmentation is observed at a strain around 45%, and with further increase in strain. The stress in the crosslinked POE is significantly larger than neat POE. For both samples, crystal orientation increases sharply within the strain range up to 88% where orientation-induced new crystals aligned in stretching direction are observed. The long period increases more in stretching direction for the crosslinked POE, consistent with larger stress in this sample, and the stress difference is more pronounced at large strains (27.3 vs. 10.9 MPa at a strain 435%). Permanent set of the crosslinked POE is smaller, consistent with less oriented crystals observed after the test for permanent set. 相似文献
17.
基于GA-BP的汽车风振噪声声品质预测模型 总被引:1,自引:1,他引:0
目前对于汽车风振噪声的优化研究主要以声压级(Sound pressure level,SPL)作为单一评价指标,既不能全面反映噪声的物理属性,也无法考虑人耳对噪声的主观认知过程。为准确评价风振噪声,引入声品质,运用大涡模拟(Large eddy simulation,LES)对风振噪声进行数值仿真,根据实车道路试验判断仿真的准确性;对仿真结果进行声品质客观评价与主观评价,综合声品质客观评价参数与声品质主观评价试验结果建立BP神经网络预测模型;利用遗传算法(Genetic algorithm,GA),进一步对BP神经网络的结构参数进行优化,建立GA-BP声品质预测模型。研究结果表明,GA-BP声品质预测模型在训练速度和预测精度上都优于BP神经网络预测模型。预测模型基于声品质主客观评价结果,其预测值可以代替传统的声压级评价指标,为风振噪声提供更为准确合理的评价。 相似文献
18.
19.
Shi-yuan XU Chu-ming LIU Ying-chun WAN Guang ZENG Yong-hao GAO Shu-nong JIANG 《中国有色金属学会会刊》2021,31(5):1291-1302
The corrosion behaviour of Mg-6Gd-3Y-1Zn-0.3Ag (wt.%) alloy components with different sizes after cooling was investigated. The alloys in the small components (SC) cooled fast, which were composed of α-Mg matrix and coarse long-period stacking ordered (LPSO) phases. The alloys in the large components (LC) cooled slowly, and there were thin lamellar LPSO phases precipitating inside the grains, except for α-Mg matrix and coarse LPSO phases. The hydrogen evolution test revealed that the corrosion rate of LC sample was higher than that of SC sample. Electrochemical impedance spectroscopy (EIS) test showed that the surface film on LC alloys provided worse protection. The corrosion morphologies indicated that the precipitation of the thin lamellar LPSO phases in LC sample caused severe micro-galvanic corrosion, which accelerated the rupture of the surface film. 相似文献