全文获取类型
收费全文 | 250911篇 |
免费 | 31252篇 |
国内免费 | 25129篇 |
专业分类
电工技术 | 20047篇 |
技术理论 | 9篇 |
综合类 | 18541篇 |
化学工业 | 58948篇 |
金属工艺 | 9904篇 |
机械仪表 | 13741篇 |
建筑科学 | 17524篇 |
矿业工程 | 2861篇 |
能源动力 | 6758篇 |
轻工业 | 21197篇 |
水利工程 | 3273篇 |
石油天然气 | 6679篇 |
武器工业 | 2321篇 |
无线电 | 36312篇 |
一般工业技术 | 30442篇 |
冶金工业 | 5571篇 |
原子能技术 | 3543篇 |
自动化技术 | 49621篇 |
出版年
2024年 | 618篇 |
2023年 | 3780篇 |
2022年 | 6308篇 |
2021年 | 8464篇 |
2020年 | 8200篇 |
2019年 | 7438篇 |
2018年 | 6935篇 |
2017年 | 9631篇 |
2016年 | 10271篇 |
2015年 | 11876篇 |
2014年 | 12753篇 |
2013年 | 16141篇 |
2012年 | 18902篇 |
2011年 | 20893篇 |
2010年 | 15333篇 |
2009年 | 15470篇 |
2008年 | 16364篇 |
2007年 | 18815篇 |
2006年 | 18117篇 |
2005年 | 15419篇 |
2004年 | 12969篇 |
2003年 | 10382篇 |
2002年 | 8254篇 |
2001年 | 6352篇 |
2000年 | 4898篇 |
1999年 | 4082篇 |
1998年 | 3253篇 |
1997年 | 2584篇 |
1996年 | 2234篇 |
1995年 | 1948篇 |
1994年 | 1766篇 |
1993年 | 1342篇 |
1992年 | 1140篇 |
1991年 | 937篇 |
1990年 | 750篇 |
1989年 | 544篇 |
1988年 | 341篇 |
1987年 | 229篇 |
1986年 | 205篇 |
1985年 | 283篇 |
1984年 | 250篇 |
1983年 | 180篇 |
1982年 | 233篇 |
1981年 | 101篇 |
1980年 | 117篇 |
1979年 | 26篇 |
1978年 | 15篇 |
1977年 | 25篇 |
1976年 | 16篇 |
1959年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
In this study,the low frequency electromagnetic casting(LFEC) technology was adopted to fabricate 2195 Al-Li alloy.The microstructure and solid solubility of as-cast 2195 alloys,as well as the second phase precipitation and tensile properties after aging,were investiagated and compared with the counterpart direct chill casting 2195 alloy.Our results indicate that LFEC can significantly improve the microstructure and metallurgical quality of as-cast alloy,and increase the number density of θ'(Al_2 Cu) and T_1(Al_2 CuLi) phases during aging treatment due to the enhanced solubilities of alloying elements.The tensile properties of 2195 aged alloy cast by LFEC were hence improved evidently. 相似文献
993.
在低平坦化压力下用壳寡糖(COS)环保型络合剂及H2O2氧化剂化学机械抛光铝合金,用原子力显微镜观测抛光后的表面质量,并用X射线光电子能谱仪分析其表面的钝化膜元素,用纳米压痕仪分析钝化膜的力学性能,研究COS及H2O2对铝合金CMP的作用机理。结果表明:H2O2质量分数为2%时,材料去除率随COS含量的增加而增大,当COS质量分数为0.32%时,材料的去除速率达861 nm/min,表面粗糙度最低为2.50 nm;COS质量分数为0.50%时,材料去除率随H2O2含量的增加先增大后减小,当H2O2质量分数为1.2%时,材料的抛光去除速率达840 nm/min,同时其表面粗糙度为3.52 nm。加入COS络合剂会在铝合金表面形成主要成分为Al-COS、Al2O3和Al(OH)3的弱钝化膜。 相似文献
994.
《中国有色金属学会会刊》2020,30(4):982-991
To address the issues of reduced graphene oxide (RGO) dispersion in copper (Cu) matrix and interface bonding between RGO and Cu, an electrostatic adsorption method with interface transition phase design was employed to prepare the RGO/Cu based composites. Cu-Ti alloy powder was employed to improve the combination by forming carbides at the RGO-Cu interface. It was noted that the mechanical property of 0.3wt.%RGO/Cu-Ti composite was increased by 60% compared with that of the matrix. Strengthening mechanism analysis suggested that the enhancement of the mechanical property was ascribed to the load transfer and second phase strengthening which were from the improved dispersion of RGO and the in-situ formed titanium carbide phase. 相似文献
995.
《中国有色金属学会会刊》2020,30(9):2311-2325
A systematical study on the relationship between the amounts of different eutectic phases especially the low-melting-point (LMP) eutectics and the hot tearing susceptibility of ternary Al−Cu−Mg alloys during solidification was performed. By controlling the concentrations of major alloying elements (Cu, Mg), the amounts of LMP eutectics at the final stages of solidification were varied and the corresponding hot tearing susceptibility (HTS) was determined. The results showed that the Al−4.6Cu−0.4Mg (wt.%) alloy, which contained the smallest fraction of LMP eutectics among the investigated alloys, was observed to be the most susceptible to hot tearing. With the amount of total residual liquid being approximately the same in the alloys, the hot tearing resistance is considered to be closely related to the amounts of LMP eutectics. Specifically, the higher the amount of LMP eutectics was, the lower the HTS of the alloy was. Further, the potential mechanism of low HTS for alloys with high amounts of LMP eutectics among ternary Al−Cu−Mg alloys was discussed in terms of feeding ability and permeability as well as total viscosity evolution during solidification. 相似文献
996.
Lili Cai Xiao-Yu Wu Xuefeng Zhu Ahmed F. Ghoniem Weishen Yang 《American Institute of Chemical Engineers》2020,66(7):e16427
Precombustion carbon capture is an effective strategy to reduce large-scale CO2 emissions, which is mainly used in the area of integrated gasification combined cycle (IGCC) power plants. Oxygen transport membranes (OTMs) were suggested as the air separation unit to produce high purity oxygen for the gasifier. However, the improvement in efficiency was limited. Here, a new IGCC process is reported based on a robust OTM reactor, where the OTM reactor is used behind the coal gasifier. This IGCC-OTM process fulfills syngas oxidation, H2 production, and carbon capture in one unit, thus a significant decrease of the energy penalty is expectable. The membrane reactor does not use noble metal components, and exhibits high hydrogen production rates, high hydrogen separation factor (103–104), and stable performance in a gas mixture mimicking real syngas compositions from a coal gasifier with H2S concentrations up to 1,000 ppm. 相似文献
997.
Ho Kim Dan Nguyen Minh Ty Dacheng Zhou Jianbei Qiu Anh-Luan Phan 《Journal of the American Ceramic Society》2020,103(11):6356-6368
In this paper, we study the influence of Cr3+ on yellowish-green upconversion (UC) emission and the energy transfer (ET) of Er3+/Cr3+/Yb3+ tri-doped in SiO2–ZnO–Na2O–La2O3 (SZNL) zinc silicate glasses under excitation of the 980 nm laser diode (LD). The influence of Cr3+ on enhancing the red UC emission of Er3+/Cr3+/Yb3+ tri-doped in SiO2–ZnO–Na2O–La2O3 zinc silicate glasses under the excitation of 980nm LD was also investigated. The ET processes between Yb3+, Cr3+, and Er3+, together with the combination of Yb3+-Cr3+-Er3+, which led to the green UC emission intensity of Er3+/Cr3+/Yb3+ tri-doped in SiO2–ZnO–Na2O–La2O3 zinc silicate glasses bands centered at ~546 nm have been significantly enhanced. By increasing the concentration of Cr3+ from 0 up to 5 mol.%, we can locate the Commission Internationale de l'éclairage (CIE) 1931 (x; y) chromaticity coordinates for UC emissions of Er3+/Cr3+/Yb3+ tri-doped in the central position of the yellowish-green color region of CIE 1931 chromaticity diagram. Besides, the ET processes between the Yb3+, Cr3+, and Er3+ are also proposed and discussed. 相似文献
998.
Peili Luo Ping Huang Jiancheng Wang Chengfang Yao Yuye Zhao Beiying Zhou Qi Zheng Xin Zhang Wan Jiang Lianjun Wang 《Journal of the American Ceramic Society》2020,103(5):3089-3096
Monolithic luminescent glass-ceramic (GC) embedded with fluoride-based nanocrystals (NCs) has drawn much attention as it is stable and possesses long fluorescent lifetime, while only small partial of optically active ions could enter the fluoride NCs prepared by conventional crystallization process. In this work, YF3:Eu3+ embedded GCs have been controllably synthesized by Spark Plasma Sintering at a relatively low sintering temperature (960°C) within 10 minutes. The GC samples show typical sharp reddish-orange emissions peaking at λ = 590 nm and 620 nm, which can be ascribed to the 5D0 → 7Fj transitions of Eu3+ located in the tetrahedral coordination sites of the YF3 NCs. Significantly, a small R/O ratio (photoluminescence intensity ratio of 5D0 → 7F2/5D0 → 7F1) suggests that majority of Eu3+ ions are well preserved in YF3 NCs, which is confirmed by the EDS and TEM results that highly crystallized YF3:Eu3+ NCs are homogeneously dispersed into the silica glass matrix without interfacial reaction. Hence, the lifetime of GC sample is prolonged to 6.8 ms These results demonstrate that Eu3+ could be well protected and resided in YF3 low phonon crystal by this method to fabricate GC composites with high optical performance. 相似文献
999.
Mihail Elisa Lucica Boroica Bogdan Alexandru Sava Stefan Marian Iordache Ana-Maria Iordache Ileana Cristina Vasiliu Raluca Constantina Stefan Aurelian Catalin Galca Victor Kuncser Mihai Eftimie 《Journal of the American Ceramic Society》2020,103(7):3978-3990
This work is focused on investigation of thermal, structural, optical, magnetic, and magneto-optical properties of novel titanium phosphate-tellurite glass applied as Faraday rotators. The glass belonging to the system 35Li2O–10Al2O3–5TiO2–45P2O5–5TeO2 was prepared by a nonconventional wet route of raw materials processing, followed by melting-quenching-annealing steps. Some important physical properties of the investigated glass have been measured and calculated, providing knowledge related to glass compactness, electronic structure, glass forming capability, etc. XRD analysis evidenced an amorphous network structure of the investigated glass. The optical absorption in the Vis domain is mainly due to Ti3+ ions and Te2 clusters formed during the glass melting process. A relatively low optical absorption is noticed over 600 nm that activates a significant Faraday magneto-optical effect. Photoluminescence bands in the blue, red, and infrared domains are observed, caused by Te2 clusters formed during the glass melting process. The magnetization in dependency on applied magnetic field reveals a complex behavior of the glass, depending on temperature. Thus, it is found a ferromagnetic behavior up to 2000 Oe, a paramagnetic component up to 40 000 Oe, followed by a diamagnetic one over 40 000 Oe. Faraday rotation angle and Verdet constant values in the visible domain are correlated with the reduced TeO2 content of the glass. 相似文献
1000.
Kacper Januchta Pengfei Liu Søren R. Hansen Theany To Morten M. Smedskjaer 《Journal of the American Ceramic Society》2020,103(3):1656-1665
Developing less brittle oxide glasses is a grand challenge in the field of glass science and technology, as it would pave the way toward new glass applications and limit the overall raw material usage and energy consumption. However, in order to achieve this goal, more insight into the correlation between the chemical composition and material properties is required. In this work, we focus on the mechanical properties of quaternary sodium aluminoborosilicate glasses, wherein systematic changes in glass chemistry yield different resistances to indentation crack initiation. We discuss the origin of the composition dependence of indentation cracking based on an evaluation of the deformation mechanism taking place during the indentation event. To this end, we use a simple metric, the extent of indent side length recovery upon annealing, to quantify the extent of reversible volume deformation. Finally, we also compare the compositional trend in crack initiation resistance to that in crack growth resistance (fracture toughness), showing no simple correlation among the two. 相似文献