全文获取类型
收费全文 | 110621篇 |
免费 | 12161篇 |
国内免费 | 7905篇 |
专业分类
电工技术 | 8530篇 |
技术理论 | 6篇 |
综合类 | 10814篇 |
化学工业 | 15500篇 |
金属工艺 | 6602篇 |
机械仪表 | 7318篇 |
建筑科学 | 8368篇 |
矿业工程 | 3624篇 |
能源动力 | 2966篇 |
轻工业 | 13020篇 |
水利工程 | 3314篇 |
石油天然气 | 4430篇 |
武器工业 | 1483篇 |
无线电 | 12231篇 |
一般工业技术 | 10342篇 |
冶金工业 | 3800篇 |
原子能技术 | 1662篇 |
自动化技术 | 16677篇 |
出版年
2024年 | 581篇 |
2023年 | 1939篇 |
2022年 | 4126篇 |
2021年 | 5344篇 |
2020年 | 4126篇 |
2019年 | 2977篇 |
2018年 | 3186篇 |
2017年 | 3556篇 |
2016年 | 3195篇 |
2015年 | 5136篇 |
2014年 | 6539篇 |
2013年 | 7685篇 |
2012年 | 9228篇 |
2011年 | 9665篇 |
2010年 | 8818篇 |
2009年 | 8185篇 |
2008年 | 8252篇 |
2007年 | 7912篇 |
2006年 | 6970篇 |
2005年 | 5416篇 |
2004年 | 3910篇 |
2003年 | 2954篇 |
2002年 | 2900篇 |
2001年 | 2595篇 |
2000年 | 1777篇 |
1999年 | 1134篇 |
1998年 | 528篇 |
1997年 | 404篇 |
1996年 | 374篇 |
1995年 | 254篇 |
1994年 | 197篇 |
1993年 | 162篇 |
1992年 | 162篇 |
1991年 | 101篇 |
1990年 | 71篇 |
1989年 | 69篇 |
1988年 | 38篇 |
1987年 | 30篇 |
1986年 | 32篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 36篇 |
1979年 | 14篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1959年 | 10篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
12.
目的:研究抗坏血酸(ascorbic acid,AsA)-还原型谷胱甘肽(reduced glutathione,GSH)循环代谢在水杨酸处理采后甜瓜诱导的过量H2O2清除过程中的作用。方法:用4 mmol/L水杨酸浸泡‘玉金香’厚皮甜瓜10 min,测定处理后果实常温贮藏过程中丙二醛(malondialdehyde,MDA)含量,分析活性氧的积累水平、超氧化物歧化酶(superoxide dismutase,SOD)和过氧化氢酶(catalase,CAT)活力,以及AsA-GSH循环过程相关酶活力及产物和底物含量。结果:水杨酸处理降低了果实MDA含量,第10天处理组MDA含量较对照组降低14.6%;显著提高了果实O2-·的产生速率和H2O2含量(P<0.05),其中处理后第2天O2-·的产生速率高出同期对照组的1.9 倍,第6天H2O2含量高出对照组果实29.7%;提高了果实SOD活力,但抑制了CAT活力,说明H2O2的清除可能是依赖于除酶促系统外的其他系统。此外,水杨酸处理提高了果实抗坏血酸过氧化物酶、单脱氢抗坏血酸过氧化物酶、脱氢抗坏血酸还原酶和谷胱甘肽还原酶的活力,增加了AsA和氧化型谷胱甘肽的含量,降低了脱氢抗坏血酸和GSH的含量。结论:水杨酸处理诱导了厚皮甜瓜果实的氧爆,抑制了MDA产生,由水杨酸诱导产生的过量H2O2主要依靠AsA-GSH循环系统清除。 相似文献
13.
14.
Jieyun Tu Xinghui Shi Yuanrong Jing Huimin Zou Jakub Kadlcak Zhanfu Yong Susu Liu Guangyong Liu 《Polymer Engineering and Science》2021,61(8):2213-2221
Equilibrium swelling and rheological tests were adopted to systematically investigate the effects of softener type and dosage on the crosslink densities. The results turned out that the chemical crosslink density could be distinguished from the physical crosslink density by comparing the results of equilibrium swelling and rheological tests. The liquid butadiene (LB) as a softener leads to the greatest reduction in crosslink density, followed by polyethylene wax (PW) and paraffinic oil (PO). The tensile strength decreases with increasing PO content while shows peak values with increase of LB and PW contents. The dependencies of chemical crosslink density on the aging time under 150°C are quite different for the three softeners, which can be expected from the double crosslinking networks consisting of small softener and large main crosslinking networks. Further investigation has been performed to correlate the tensile strength with chemical crosslink density of ethylene propylene diene monomer elastomer vulcanizates. Three different linear relationships can be obtained for the softeners independent of the aging time. It can now be expected from this study that the role of some new softeners in rubber compounds is not only confined to plasticization but also forms crosslinking networks in the peroxide-cured rubbers. 相似文献
15.
16.
Sheng Mingming Yang Rongkun Gong Hongyu Zhang Yujun Lin Xiao Jing Jie 《Journal of Materials Science》2022,57(10):5805-5824
Journal of Materials Science - With the extensive use of high-power electronic appliances, polymer-based thermal insulation composites with excellent thermal properties are utilized in the field of... 相似文献
17.
Jinshuang Wang Luyao Chen Mengdi Chen Yuyang Wu Yinghui Wang Yongsheng Yu Junbin Sun Bing Liu Qiangshan Jing 《Ceramics International》2021,47(16):22965-22975
In this study, the destabilization resistance of Sc2O3 and CeO2 co-stabilized ZrO2 (SCZ) ceramics was tested in Na2SO4 + V2O5 molten salts at 750°C–1100 °C. The phase structure and microstructure evolution of the samples during the hot corrosion testing were analyzed with X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). Results showed that the destabilization of SCZ ceramics at 750 °C was the result of the chemical reaction with V2O5 to produce m-ZrO2 and CeVO4, and little ScVO4 was detected in the Sc2O3-rich SCZ ceramics. The primary corrosion products at 900 °C and 1100 °C were CeO2 and m-ZrO2 due to the mineralization effect. The Sc2O3-rich SCZ ceramics exhibited excellent degradation resistance and phase stability owing to the enhanced bond strength and the decreased size misfit between Zr4+ and Sc3+. The destabilization mechanism of SCZ ceramic under hot corrosion was also discussed. 相似文献
18.
Hongli Liu Peng Wang Bo Zhang Hongyan Li Jing Li Yajing Li Zhong Chen 《Ceramics International》2021,47(5):6487-6495
A novel carbon/m-HNTs composite aerogel was synthesized by introducing the modified halloysite nanotubes (m-HNTs) into phenolic (PR) aerogels through chemical grafting, followed with carbonization treatment. In order to explore the best proportion of HNTs to phenolic, the micromorphology of PR/m-HNTs were investigated by SEM before carbonization, confirming 10 wt% of m-HNTs is most beneficial to the porous network of aerogels. The interaction between PR and HNTs was studied by FTIR spectra, and microstructure evolution of the target product-carbon/m-HNTs composite aerogel were illustrated by SEM and TEM techniques. SEM patterns indicated that the carbon/m-HNTs aerogels maintain a stable porous structure at 1000 °C (carbonization temperature), while a ~20 nm carbon layer was formed around m-HNTs generating an integral unit through TEM analysis. Specific surface area and pore size distribution of composite aerogels were analyzed based on mercury intrusion porosimetry and N2 adsorption–desorption method, the obtained results stayed around 500 m2g?1 and 1.00 cm3g?1 (pore volume) without significant discrepancy, compared with pure aerogel, showing the uniformity of pore size. The weight loss rate (26.76%) decreased greatly compared with pure aerogel, at the same time, the best volumetric shrinkage rate was only 30.83%, contributed by the existence of HNTs supporting the neighbor structure to avoid over-shrinking. The highest compressive strength reached to 4.43 MPa, while the data of pure aerogel was only 1.52 MPa, demonstrating the excellent mechanical property of carbon/m-HNTs aerogels. 相似文献
19.
美军将网络空间视为继陆、海、空、天外的第五大作战域,并将其列为国防部11项现代化优先事项之一,在美国等军事大国推动下,网络空间成为国家安全竞争和军事斗争的新疆域.文中对近年美国联邦政府、各部门及各军种发布的网络空间领域主要战略政策、规划计划进行梳理,研究其主要战略思想;分析美军2022财年国防预算、研究经费投向投量及重点项目的 研发情况.形成的研究成果将对我国网络空间安全领域研究提供技术支撑. 相似文献
20.
Li Qian Chen Yan Sun Shikun Zhu Muyuan Xue Jing Gao Zihan Zhao Jinfeng Tang Yihe 《Water Resources Management》2022,36(12):4799-4817
Water Resources Management - Increasing water consumption in agriculture due to global climate change has posed considerable challenges to food security, thus improving the efficiency of water... 相似文献