全文获取类型
收费全文 | 405684篇 |
免费 | 87272篇 |
国内免费 | 56086篇 |
专业分类
电工技术 | 42157篇 |
技术理论 | 21篇 |
综合类 | 37393篇 |
化学工业 | 58284篇 |
金属工艺 | 36658篇 |
机械仪表 | 21357篇 |
建筑科学 | 30661篇 |
矿业工程 | 20030篇 |
能源动力 | 14552篇 |
轻工业 | 36638篇 |
水利工程 | 12006篇 |
石油天然气 | 24281篇 |
武器工业 | 5960篇 |
无线电 | 54301篇 |
一般工业技术 | 53175篇 |
冶金工业 | 17188篇 |
原子能技术 | 4213篇 |
自动化技术 | 80167篇 |
出版年
2024年 | 3696篇 |
2023年 | 7955篇 |
2022年 | 12084篇 |
2021年 | 15350篇 |
2020年 | 15779篇 |
2019年 | 23095篇 |
2018年 | 25141篇 |
2017年 | 27240篇 |
2016年 | 26270篇 |
2015年 | 28086篇 |
2014年 | 29487篇 |
2013年 | 30767篇 |
2012年 | 32069篇 |
2011年 | 29396篇 |
2010年 | 26914篇 |
2009年 | 22907篇 |
2008年 | 20757篇 |
2007年 | 19607篇 |
2006年 | 18034篇 |
2005年 | 15765篇 |
2004年 | 14943篇 |
2003年 | 12316篇 |
2002年 | 12095篇 |
2001年 | 10530篇 |
2000年 | 9509篇 |
1999年 | 9075篇 |
1998年 | 7355篇 |
1997年 | 6441篇 |
1996年 | 6205篇 |
1995年 | 5633篇 |
1994年 | 4616篇 |
1993年 | 3924篇 |
1992年 | 3556篇 |
1991年 | 2631篇 |
1990年 | 2051篇 |
1989年 | 1841篇 |
1988年 | 1483篇 |
1987年 | 569篇 |
1986年 | 464篇 |
1985年 | 322篇 |
1984年 | 216篇 |
1983年 | 161篇 |
1982年 | 210篇 |
1981年 | 191篇 |
1980年 | 158篇 |
1976年 | 229篇 |
1975年 | 203篇 |
1972年 | 237篇 |
1971年 | 128篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
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
22.
23.
24.
Yude Ji Yanping Guo Yuejuan Liu Yun Tian 《International Journal of Adaptive Control and Signal Processing》2020,34(3):283-297
This article focuses on the consensus problem of leader-following fractional-order multi-agent systems (MASs) with general linear and Lipschitz nonlinear dynamics. First, the distributed adaptive protocols for linear and nonlinear fractional-order MASs are constructed, respectively. We allow the control coupling gains to be time varying for each agent. Moreover, the adaptive modification schemes for the control gain are designed, which renders smaller control gains and thus requires smaller amplitude on the control input without sacrificing consensus convergence. Second, based on fractional-order Lyapunov stability theorem and Barbalat's lemma, two novel sufficient conditions in terms of linear matrix inequalities are provided to ensure that the leader-following consensus can be obtained in the case for any undirected connected communication graph. Furthermore, we show that the proposed algorithm also works for consensus of agents with intrinsic Lipschitz nonlinear dynamics. As a result, the proposed framework requires no global information and thus can be implemented in a fully distributed manner. Finally, the numerical simulations are given to demonstrate the effectiveness of obtained the theoretical results. 相似文献
25.
26.
27.
Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface. 相似文献
28.
29.
陕南山地烟田不同植烟年限土壤养分的变化 总被引:1,自引:0,他引:1
为给陕南山地烟草生产布局及有针对性的施肥措施提供依据,分析了陕南山地烟田不同植烟年限(0~15年)与土壤养分含量的关系。结果表明:随着植烟年限延长,有机质线性下降,全氮和速效钾显著上升,有效磷先上升后下降;氯、有效铁、有效锰、有效硼和有效铜无显著变化或变化很小,有效锌则在第1年急剧下降,之后保持稳定,10年后再次显著下降。认为陕南山地烟区烟叶生产中应适当增加有机肥的施用而合理控制氮肥、磷肥和钾肥的施用,并要注意锌肥的补充。 相似文献
30.
Weikang Dong Ruishi Qi Tiansheng Liu Yi Li Ning Li Ze Hua Zirui Gao Shuyuan Zhang Kaihui Liu Jiandong Guo Peng Gao 《Advanced materials (Deerfield Beach, Fla.)》2020,32(46):2002014
Hyperbolic phonon polaritons (HPhPs) in orthorhombic-phase molybdenum trioxide (α-MoO3) show in-plane hyperbolicity, great wavelength compression, and ultralong lifetime, therefore holding great potential in nanophotonic applications. However, its polaritonic response in the far-infrared (FIR) range remains unexplored due to challenges in experimental characterization. Here, monochromated electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) is used to probe HPhPs in α-MoO3 in both mid-infrared (MIR) and FIR frequencies and correlate their behaviors with microstructures and orientations. It is found that low structural symmetry leads to various phonon modes and multiple Reststrahlen bands (RBs) over a broad spectral range (over 70 meV) and in different directions (55–63 meV and 119–125 meV along the b-axis, 68–106 meV along the c-axis, and 101–121 meV along the a-axis). These HPhPs can be selectively excited by controlling the direction of swift electrons. These findings provide new opportunities in nanophotonic and optoelectronic applications, such as directed light propagation, hyperlenses, and heat transfer. 相似文献