全文获取类型
收费全文 | 115972篇 |
免费 | 10272篇 |
国内免费 | 6985篇 |
专业分类
电工技术 | 19107篇 |
技术理论 | 2篇 |
综合类 | 7993篇 |
化学工业 | 20184篇 |
金属工艺 | 6692篇 |
机械仪表 | 8607篇 |
建筑科学 | 3062篇 |
矿业工程 | 1873篇 |
能源动力 | 4111篇 |
轻工业 | 6532篇 |
水利工程 | 765篇 |
石油天然气 | 4524篇 |
武器工业 | 972篇 |
无线电 | 14502篇 |
一般工业技术 | 11000篇 |
冶金工业 | 4385篇 |
原子能技术 | 1271篇 |
自动化技术 | 17647篇 |
出版年
2024年 | 181篇 |
2023年 | 1511篇 |
2022年 | 2085篇 |
2021年 | 3209篇 |
2020年 | 3051篇 |
2019年 | 2844篇 |
2018年 | 2656篇 |
2017年 | 3613篇 |
2016年 | 3916篇 |
2015年 | 4140篇 |
2014年 | 5986篇 |
2013年 | 6488篇 |
2012年 | 7427篇 |
2011年 | 8715篇 |
2010年 | 6996篇 |
2009年 | 7663篇 |
2008年 | 7489篇 |
2007年 | 8254篇 |
2006年 | 7916篇 |
2005年 | 6499篇 |
2004年 | 5535篇 |
2003年 | 5067篇 |
2002年 | 4099篇 |
2001年 | 3289篇 |
2000年 | 2795篇 |
1999年 | 2190篇 |
1998年 | 1539篇 |
1997年 | 1268篇 |
1996年 | 1187篇 |
1995年 | 1190篇 |
1994年 | 1018篇 |
1993年 | 856篇 |
1992年 | 679篇 |
1991年 | 409篇 |
1990年 | 267篇 |
1989年 | 263篇 |
1988年 | 181篇 |
1987年 | 124篇 |
1986年 | 116篇 |
1985年 | 86篇 |
1984年 | 71篇 |
1983年 | 48篇 |
1982年 | 52篇 |
1981年 | 58篇 |
1980年 | 29篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1977年 | 20篇 |
1976年 | 26篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
91.
不同含量低污染水对人工湿地中细菌的影响研究 总被引:1,自引:0,他引:1
探究水平流人工湿地(HFCW)系统处理低污染水过程中,相同COD/ρ(TN)下不同碳氮含量对细菌群落结构的影响。结果表明,进水为较高碳氮含量的HFCW(HF1)和进水为较低碳氮含量的HFCW(HF2)对COD和TN的去除效率具有一定的差异,HF1和HF2对COD的去除效率分别为48.26%和28.89%,对TN的去除率分别为79.06%和81.87%。HF1中细菌的丰富度和多样性均高于HF2,HF1中富集的优势细菌为Chloroflexaceae、Comamonadaceae和Rhodocyclaceae,均具有异养反硝化功能,HF2中富集的优势细菌为Xanthomonadaceae和Rhodocyclaceae,其中Xanthomonadaceae具有自养反硝化功能。COD、NH4^+-N和NO3^--N对HF1中细菌群落的影响大于对HF2中细菌群落的影响,HF1中COD对细菌群落的影响大于NH4^+-N和NO3^--N。 相似文献
92.
采用酸处理方法对CoPd/TiO2催化剂进行改性,并将酸改性催化剂用于温和条件下CH4-CO2梯阶转化直接合成C2含氧化合物(乙酸和乙醇)的反应。在150~300℃考察了浸酸方式和不同种类酸处理对催化剂活性和选择性的影响。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、NH3程序升温脱附(NH3-TPD)和N2吸附对催化剂进行了表征。结果表明,酸改性明显提高了CoPd/TiO2上C2含氧化合物的生成速率和选择性。浸酸方式对催化剂性能和结构有显著影响,先用酸浸渍载体然后再浸渍活性金属所得催化剂具有更高的活性。在H3PO4、HNO3和HCl中,H3PO4浸渍的催化剂活性最佳,在150℃时C2含氧化合物(乙酸和乙醇)的生成速率为3365 μg/(g·h),选择性达到91%。 相似文献
93.
Meiling He Yinzi Cheng Linli Shen Huiling Zhang Chenyang Shen Weidong Xiang Xiaojuan Liang 《Journal of the American Ceramic Society》2019,102(3):1090-1100
CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) represent bright and tunable photoluminescence, it is regrettable that the air instability and poor water resistant properties prevent their application in optoelectronic devices. At the same time, the toxicity of lead is also a major factor restricting its development. As a consequence, we demonstrate the partial replacement of Pb with Mn through conventional melt-quenching and heat-treatment method preparation of Mn-doped CsPb(Cl/Br)3 QD glass. Mn-doped CsPb(Cl/Br)3 QD glass exhibits high luminescent intensity like QDs. It is important that Mn-doped CsPb(Cl/Br)3 QD glass with Dual-Color maintained the same lattice structure like Mn-doped CsPb(Cl/Br)3 QDs, and highly homogeneous spectral characteristics of Mn luminescence. The intensity and position of this Mn-related emission are also tunable by altering the experimental parameters, such as the Pb-to-Mn feed ratio, annealing temperature. More importantly, the as-prepared orange Mn-doped CsPb(Cl/Br)3 QD glass was employed to fabricate white LEDs combined with a commercial Ce3+:Y3Al5O12 phosphor-in-glass (Ce-PiG) on top of a InGaN blue chip. And the constructed WLEDs generate a warm white with an optimal luminous efficacy (LE) of 67.00 lm/W, a high CRI of 81.4, and a low CCT of 4902 K. 相似文献
94.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
95.
96.
Ismail Seçkin Çardaklı Ali Kalkanlı 《International Journal of Cast Metals Research》2019,32(3):145-153
In this study, as alternative methods to conventional production methods involving thin section copper permanent mould casting (fast solidification) and water atomization (rapid solidification) of AISI DC 53 cold work tool steel have been investigated. Thin slabs obtained by copper mould casting was homogenized at 1150 °C for one hour and then hot rolling was be applied. After hot rolling, conventional heat treatment have been applied to thin slabs. The same heat treatment procedure have been performed for a commercially available AISI DC 53 which is manufactured by thick section ingot casting and rolling. In order to investigate also the effect of rapid solidification on AISI DC 53 tool steel, steel powder was produced by water atomization technique. Experiments have revealed that thin steel slabs in permanent copper mould and rapidly solidified tool steel powder by water atomization have a more refined primary M7C3 carbides than commercially available steel. 相似文献
97.
Guoqiang Yu Xiguang Gao Chuyang Xie Yingdong Song 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(2):454-465
Understanding the in‐plane shear behaviour of composites is essential to establish the design basis for practical applications. This study aims to investigate the shear damage behaviours of 2D needled C/SiC composites by various characterization techniques. The effect of layer arrangement on shear modulus and strength was discussed via shear stress‐strain responses. The shear strain field evolution and uniformity variation were studied by digital image correlation. It shows that the uniformity of shear strain field changes with the shear load, and the shear strain field evolution consist of 5 stages. The electrical resistivity measurement results indicate that structural deformation and damage evolution caused the electrical resistivity change. Furthermore, the damage evolution has a double effect on the electrical resistivity variation. The acoustic emission monitoring shows that the shear damage evolution is a 3‐stage nonlinear process before failure. The shear damages were categorized via acoustic characteristics. Besides, the postfailure behaviours were also discussed in this study. 相似文献
98.
Multiple degrees‐of‐freedom (multi‐DOF) cell orientation control is a vital important technique involved in single cell surgery applications. Currently, few studies have been performed toward automation of multi‐DOF cell orientation control using robotically controlled optical tweezers. In this paper, a robust control framework is developed to perform multi‐DOF cell rotational control with consideration of model uncertainties and external disturbances. Both simulation and experimental studies are presented to illustrate the performance of the proposed control strategy. The main contributions of this work lie in that this is the first time to develop a unified framework to achieve multi‐DOF cell orientation control without the need for accurate dynamic model parameters and/or any knowledge about uncertainty characteristic, which greatly enhances the robustness of the overall system. 相似文献
99.
Sandrine Hönig Dietmar Koch Steffen Weber Simon Etzold Thorsten Tonnesen Rainer Telle Nicolas Traon 《International Journal of Applied Ceramic Technology》2019,16(5):1723-1733
The determination of elastic properties at application temperature is fundamental for the design of fibre reinforced ceramic composite components. An attractive method to characterize the flexural modulus at room and high temperature under specific atmosphere is the nondestructive Resonant Frequency Damping Analysis (RFDA). The objective of this paper was to evaluate and validate the modulus measurement via RFDA for orthotropic C/C-SiC composites at the application temperature. At room temperature flexural moduli of C/C-SiC with 0/90° reinforcement were measured under quasi-static 4-point bending loads and compared with dynamic moduli measured via RFDA longitudinally to fibre direction. The dynamic modulus of C/C-SiC was then measured via RFDA up to 1250°C under flowing inert gas and showed an increase with temperature which fitted with literature values. The measured fundamental frequencies were finally compared to those resulting from numerical modal analyses. Dynamic and quasi-static flexural moduli are comparable and the numerical analyses proved that bending modes are correctly modeled by means of dynamic modulus measured via RFDA. The nondestructive RFDA as well as the numerical modeling approach are suitable for evaluation of C/C-SiC and may be transferred to other fibre reinforced ceramic composite materials. 相似文献
100.
Ichiro Fujii Saki Nakashima Takahiro Wada 《Journal of the American Ceramic Society》2019,102(3):1240-1248
0.24Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 transparent ceramics were fabricated by a conventional sintering technique. Through optimization of sintering conditions of calcination and sintering temperatures and time, the obtained ceramics showed high optical transmittance of 53% and 71% at light wavelengths of 1300 and 2000 nm, respectively. The ceramics showed a rhombohedral to tetragonal phase transition at ~120°C and a tetragonal to cubic phase transition at 222°C. These transition temperatures were higher than those of 0.67Pb(Mg1/3Nb2/3)-0.33PbTiO3 ceramics. In addition, the ceramics had a ferroelectric hysteresis loop, a large piezoelectric constant d33 of 407 pC/N, and a planar electromechanical coupling factor kp of 52%. These results suggest that the transparent ceramics may be used as a temperature-stable, linear electro-optic material. 相似文献