全文获取类型
收费全文 | 10433篇 |
免费 | 906篇 |
国内免费 | 635篇 |
专业分类
电工技术 | 237篇 |
综合类 | 854篇 |
化学工业 | 4773篇 |
金属工艺 | 683篇 |
机械仪表 | 317篇 |
建筑科学 | 1005篇 |
矿业工程 | 147篇 |
能源动力 | 210篇 |
轻工业 | 911篇 |
水利工程 | 146篇 |
石油天然气 | 509篇 |
武器工业 | 42篇 |
无线电 | 526篇 |
一般工业技术 | 992篇 |
冶金工业 | 222篇 |
原子能技术 | 56篇 |
自动化技术 | 344篇 |
出版年
2024年 | 50篇 |
2023年 | 121篇 |
2022年 | 243篇 |
2021年 | 281篇 |
2020年 | 296篇 |
2019年 | 285篇 |
2018年 | 267篇 |
2017年 | 374篇 |
2016年 | 422篇 |
2015年 | 380篇 |
2014年 | 490篇 |
2013年 | 660篇 |
2012年 | 789篇 |
2011年 | 754篇 |
2010年 | 522篇 |
2009年 | 562篇 |
2008年 | 526篇 |
2007年 | 578篇 |
2006年 | 650篇 |
2005年 | 546篇 |
2004年 | 490篇 |
2003年 | 383篇 |
2002年 | 365篇 |
2001年 | 311篇 |
2000年 | 300篇 |
1999年 | 263篇 |
1998年 | 190篇 |
1997年 | 160篇 |
1996年 | 137篇 |
1995年 | 103篇 |
1994年 | 102篇 |
1993年 | 75篇 |
1992年 | 65篇 |
1991年 | 40篇 |
1990年 | 33篇 |
1989年 | 31篇 |
1988年 | 23篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
为了探究不同油浸变压器受火情况下的火灾动力学过程,搭建了全尺度变压器火灾实验平台,分别针对基于RAPO天然酯植物油和25号变压器油的10 kV油浸变压器开展了外部热源耐火实验。研究结果表明,在同一外部热源条件下,矿物油变压器在受火状态下9 min左右即出现猛烈的喷射火灾现象,喷射出的矿物油品同时导致了大面积的池火和流淌火灾,使得火灾进一步加剧。相比而言,植物油变压器燃烧相对平缓,在24 min左右才出现轻微的喷射火现象,但并未造成明显的火灾加剧,且实验结束后变压器周边残存大量未燃植物油。在燃烧实验中,植物油的温升速率约为0.18 ℃/s,显著低于矿物油的0.24 ℃/s,也进一步说明了植物绝缘油的安全性。从消防安全角度,植物油变压器的火灾安全性远胜于矿物油变压器,具有较好的应用前景。 相似文献
952.
介绍采用低品位磷矿生产湿法磷酸中通过改善磷矿萃取率和磷石膏洗涤率来提高磷得率的措施。措施实施后,磷得率由90.0%提高至94.3%,年创造效益5 200万元。 相似文献
953.
Qing-Wei Tan Fang-Luan Gao Fu-Rong Wang Qi-Jian Chen 《International journal of molecular sciences》2015,16(3):5750-5761
Plant-associated microorganisms are known to produce a variety of metabolites with novel structures and interesting biological activities. An endophytic fungus FJBJ11, isolated from the plant tissue of Brucea javanica (L.) Merr. (Simaroubaceae), was proven to be significantly effective in producing metabolites with anti-Tobacco mosaic virus (TMV) activities. The isolate was identified as Aspergillus tubingensis FJBJ11 based on morphological characteristics and ITS sequence. Bioassay-guided isolation led to the identification of a cycli penta-peptide, malformin A1, along with two cyclic dipeptides, cyclo (Gly-l-Pro) and cyclo (Ala-Leu). Malformin A1 showed potent inhibitory effect against the infection and replication of TMV with IC50 values of 19.7 and 45.4 μg·mL−1, as tested using local lesion assay and leaf-disc method, respectively. The results indicated the potential use of malformin A1 as a leading compound or a promising candidate of new viricide. 相似文献
954.
为了研究预制拼装桥墩与整体现浇桥墩抗震性能方面的差异,以常见城市高架桥为工程背景,制作完成了3个缩尺比为1∶3.5的试件模型,进行了整体现浇桥墩和无粘结预应力钢绞线预制拼装桥墩拟静力循环加载试验。通过给墩顶施加强迫往复位移,从5个方面研究了预制拼装桥墩与整体现浇桥墩抗震性能的差别,并对试验结果进行了纤维模型计算分析。结果表明:无粘结预应力预制拼装混凝土桥墩混凝土破坏轻微,耗能能力较弱,残余位移小,适合低烈度地区;无粘结预应力带耗能钢筋预制拼装混凝土桥墩墩底混凝土有明显压碎,耗能能力强,残余位移相对于钢筋混凝土现浇桥墩较小,适合中高烈度地区。 相似文献
955.
Do‐Hyun Kim Chang‐Hwan Lee Young K. Ju Sang‐Dae Kim 《The Structural Design of Tall and Special Buildings》2015,24(4):243-256
In this study, a subassemblage test was performed using buckling‐restrained braces with an H‐shaped core element, which have been proven in a previous uniaxial component test to have good performance. The loading protocol prescribed the quasi‐static cyclic pattern with stepwise incremental displacement amplitude. Two different end connections (bolted connection and pin connection) and two different buckling‐restrained mechanisms (concrete‐filled tube and hollow steel tube) were examined as the test parameters. The performance of the specimen was evaluated by comparing the test results with the recommended provisions for buckling‐restrained braces. The test results showed that the compression strength capacity of buckling‐restrained brace (BRB) with in‐filled concrete increased by about 10% compared with BRB without in‐filled concrete. According to test result at same story drift of 2Dbm, structural performance of pin connection specimen without bolt slippage is superior to bolted connection specimen. Also, bolted connection specimens showed similar performance for total energy dissipation and cumulative plastic ductility, regardless of the connection types and the existence of concrete filling. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
956.
957.
Guangni Ding Chengjun Li Yifan Shen Bin Lu Zhaoguo Zhang Xiaomin Xie 《Advanced Synthesis \u0026amp; Catalysis》2016,358(8):1241-1250
Potassium hydroxide‐catalyzed hydrosilylation exhibits excellent activity and chemoselectivity for the reduction of cyclic imides under mild reaction conditions. The chemoselectivity of the reduction system may be readily tuned by changing the identity and stoichiometry of the hydrosilanes: a polymethylhydrosiloxane (PMHS)/potassium hydroxide reduction system resulted in the reduction of various cyclic imides to the corresponding ω‐hydroxylactams in 70–94% yield, while the diphenylsilane (Ph2SiH2)/potassium hydroxide reduction system selectively afforded the aryl lactams in 33–95% yield. These catalytic protocols tolerate diverse functional groups and are easy to scale up.
958.
Concepts to facilitate the conversion of epoxides with carbon dioxide to the corresponding cyclic carbonates commonly focus on the activation of the epoxide. Herein we report a catalytic system which allows the simultaneous activation of carbon dioxide and the epoxide. This convergent activation concept is realized by combining a suitable carbene as catalyst for the carbon dioxide activation with a second catalytic system based on potassium iodide for epoxide activation. Initial experiments showed synergistic effects and thus proving the feasibility of this activation concept. Moreover a standard protocol was developed and the substrate scope under these conditions has been studied. Under mild and solvent‐free conditions 14 epoxides could be converted. The respective cyclic carbonates were obtained in good to excellent yields with selectivities ≥ 99 % after simple filtration.
959.
Lu‐Jia Zhou Yu‐Chen Zhang Fei Jiang Guofeng He Jingjing Yan Han Lu Shu Zhang Feng Shi 《Advanced Synthesis \u0026amp; Catalysis》2016,358(19):3069-3083
The first catalytic asymmetric construction of the cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindole scaffold with potential bioactivity has been developed via chiral phosphoric acid‐catalyzed enantioselective addition reactions of cyclic enaminones to isatin‐derived imines, which afforded a series of cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindoles in high yields and excellent enantioselectivities (up to 99% yield, 97% ee). The investigation of the reaction mechanism suggested that it was facilitated by a dual hydrogen‐bonding activation mode between the two substrates and the chiral phosphoric acid. Besides, this method could be utilized for a large‐scale synthesis with maintained enantioselectivity. This approach will not only offer a useful method for enantioselective construction of the cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindole scaffold, but also enrich the research on catalytic asymmetric addition reactions of isatin‐derived imines by using electron‐rich olefins as nucleophiles. More importantly, a preliminary evaluation on the cytotoxicity of some selected products revealed that two of the enantio‐pure compounds exhibited moderate to strong cytotoxicity to A549, 786‐0, ECA109 and BT474 cancer cell lines.
960.