全文获取类型
收费全文 | 196730篇 |
免费 | 13308篇 |
国内免费 | 7335篇 |
专业分类
电工技术 | 9162篇 |
技术理论 | 8篇 |
综合类 | 11056篇 |
化学工业 | 28407篇 |
金属工艺 | 11095篇 |
机械仪表 | 10686篇 |
建筑科学 | 11722篇 |
矿业工程 | 4271篇 |
能源动力 | 4569篇 |
轻工业 | 11262篇 |
水利工程 | 3813篇 |
石油天然气 | 6697篇 |
武器工业 | 1263篇 |
无线电 | 23297篇 |
一般工业技术 | 28401篇 |
冶金工业 | 7262篇 |
原子能技术 | 1803篇 |
自动化技术 | 42599篇 |
出版年
2024年 | 636篇 |
2023年 | 2039篇 |
2022年 | 4002篇 |
2021年 | 5617篇 |
2020年 | 4231篇 |
2019年 | 3327篇 |
2018年 | 17717篇 |
2017年 | 17164篇 |
2016年 | 13381篇 |
2015年 | 5819篇 |
2014年 | 6864篇 |
2013年 | 7920篇 |
2012年 | 11858篇 |
2011年 | 18499篇 |
2010年 | 16311篇 |
2009年 | 13083篇 |
2008年 | 14015篇 |
2007年 | 14378篇 |
2006年 | 6282篇 |
2005年 | 6213篇 |
2004年 | 4541篇 |
2003年 | 4097篇 |
2002年 | 3600篇 |
2001年 | 2651篇 |
2000年 | 2249篇 |
1999年 | 2117篇 |
1998年 | 1467篇 |
1997年 | 1254篇 |
1996年 | 1231篇 |
1995年 | 949篇 |
1994年 | 805篇 |
1993年 | 598篇 |
1992年 | 420篇 |
1991年 | 347篇 |
1990年 | 237篇 |
1989年 | 203篇 |
1988年 | 212篇 |
1987年 | 120篇 |
1986年 | 77篇 |
1985年 | 46篇 |
1984年 | 36篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1959年 | 49篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
Variations of Incomplete Open Cubes is the major project by the twentieth-century conceptual artist Sol LeWitt. In this paper we interpret the enumerative component of the project as embeddings of graphs. This formulation permits use of an algorithm to check the completeness of the list of the structures produced by the artist. Our conclusion is that the artist found the correct number of structures (that is, 122), but that his list contains a mistake in the presentation of a pair of incomplete cubes, a discovery that appears not to have been noted before. 相似文献
74.
Zhuo Shi Ningning Dong Dingfeng Zhang Xiaofang Jiang Guanxin Du Shichao Lv Jiejie Chen Jun Wang Shifeng Zhou 《Journal of the American Ceramic Society》2019,102(7):3965-3971
The construction of nonlinear optical materials featuring asymmetric transmission of light is of great technological importance for various applications, including optical switching and optical power limiting. A significant challenge is the scalable fabrication of material candidates with good photochemical stability, high optical transmittance, and excellent optical limiting performance. Here, we present a nanocrystallization avenue for constructing hybrid optical limiting materials that exhibit ultrafast and robust optical limiting performance. The experimental results show that the controllable relaxation of a niobate glass may lead to the clustering of Nb-O units and contracting of the bandgap. It results in the notable improvement in nonlinear optical properties, including the enhanced saturation irradiance (380 GW/cm2), doubly increased nonlinear coefficient, and decreased limiting threshold (200 GW/cm2). Our results suggest a promising material that exhibits promising applications for protecting eyes and sensitive components from laser-induced damage. 相似文献
75.
以2,6-二甲基苯胺为原料,通过重氮化反应制备2,6-二甲基苯腈,经水蒸汽蒸馏法提纯后,采用75%硫酸酸化,再经酸碱法对产物进行脱色和纯化得产物2,6-二甲基苯甲酸,总收率68.4%。工艺简单、操作安全、适合工业化生产。 相似文献
76.
Sumeng Wei Yuling Yang Xiao Feng Shanshan Li Lei Zhou Jingyu Wang Xiaozhi Tang 《International Journal of Food Science & Technology》2020,55(7):2691-2699
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics. 相似文献
77.
Fei Xu Xiangli Shi Qingzhu Zhang Wenxing Wang 《International journal of molecular sciences》2015,16(8):18714-18731
The chlorothiophenoxy radicals (CTPRs) are key intermediate species in the formation of polychlorinated dibenzothiophenes/thianthrenes (PCDT/TAs). In this work, the formation of CTPRs from the complete series reactions of 19 chlorothiophenol (CTP) congeners with H and OH radicals were investigated theoretically by using the density functional theory (DFT) method. The profiles of the potential energy surface were constructed at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) contribution at 600–1200 K. The present study indicates that the structural parameters, thermal data, and rate constants as well as the formation potential of CTPRs from CTPs are strongly dominated by the chlorine substitution at the ortho-position of CTPs. Comparison with the study of formation of chlorophenoxy radicals (CPRs) from chlorophenols (CPs) clearly shows that the thiophenoxyl-hydrogen abstraction from CTPs by H is more efficient than the phenoxyl-hydrogen abstraction from CPs by H, whereas the thiophenoxyl-hydrogen abstraction from CTPs by OH is less impactful than the phenoxyl-hydrogen abstraction from CPs by OH. Reactions of CTPs with H can occur more readily than that of CTPs with OH, which is opposite to the reactivity comparison of CPs with H and OH. 相似文献
78.
Yanlong Shi Xiaojuan Feng Haiyu Guan Jiahua Zhang Zhongai Hu 《International Journal of Hydrogen Energy》2021,46(12):8557-8566
Constructing high-efficient and nonprecious electrocatalysts is of primary importance for improving the efficiency of water splitting. Herein, a novel sunflower plate-like NiFe2O4/CoNi–S nanosheet heterostructure was fabricated via facile hydrothermal and electrodeposition methods. The as-fabricated NiFe2O4/CoNi–S heterostructure array exhibits remarkable bifunctional catalytic activity and stability toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. It presents a small overpotential of 219 mV and 149 mV for OER and HER, respectively, to produce a current density of 10 mA cm?2. More significantly, when the obtained electrodes are used as both the cathode and anode in an electrolyzer, a voltage of 1.57 V is gained at 10 mA cm?2, with superior stability for 72 h. Such outstanding properties are ascribed to: the 3D porous network structure, which exposes more active sites and accelerates mass transfer and gas bubble emission; the high conductivity of CoNi–S, which provides faster charge transport and thus promotes the electrocatalytic reaction of the composites; and the effective interface engineering between NiFe2O4 (excellent performance for OER) and CoNi–S (high activity for HER), which leads to a shorter transport pathway and thus expedites electron transfer. This work provides a new strategy for designing efficient and inexpensive electrocatalysts for water splitting. 相似文献
79.
80.
Xueli Du Yuelong Wang Rongna Shi Zhiyong Mao Zhihao Yuan 《Journal of the European Ceramic Society》2018,38(10):3512-3517
The PbClxS1-x and Pb1-xBixS (x? =?0–0.05) bulks were fabricated with a facile method of hydrothermal synthesis and microwave sintering, and the effect of anionic and cationic donors on the thermoelectric performance of PbS was investigated. Although Cl? and Bi3+ both effectively improved the thermoelectric properties of n-type PbS, more excellent thermoelectric performance was obtained from Cl? doped samples because of higher electrical property and lower thermal conductivity at higher temperature (T? >?600?K). The thermoelectric figure of merit (ZT) reaches 1.04 for PbCl0.015S0.985 at 800?K and increases with temperature increasing without sign of saturation, which is probably the highest value ever reported for single-phase polycrystalline n-type PbS. The results also indicate that the hydrothermal synthesis and microwave sintering can realize anion doping as well as cation doping for n-type PbS at low cost, and PbS should be a robust alternative for PbTe thermoelectric materials. 相似文献