首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   24205篇
  免费   3846篇
  国内免费   2651篇
化学   17115篇
晶体学   299篇
力学   1435篇
综合类   242篇
数学   2679篇
物理学   8932篇
  2024年   41篇
  2023年   503篇
  2022年   826篇
  2021年   799篇
  2020年   999篇
  2019年   907篇
  2018年   751篇
  2017年   722篇
  2016年   1100篇
  2015年   1007篇
  2014年   1262篇
  2013年   1644篇
  2012年   2094篇
  2011年   2118篇
  2010年   1436篇
  2009年   1388篇
  2008年   1540篇
  2007年   1412篇
  2006年   1357篇
  2005年   1096篇
  2004年   869篇
  2003年   725篇
  2002年   625篇
  2001年   521篇
  2000年   513篇
  1999年   593篇
  1998年   487篇
  1997年   429篇
  1996年   445篇
  1995年   390篇
  1994年   359篇
  1993年   327篇
  1992年   271篇
  1991年   229篇
  1990年   236篇
  1989年   160篇
  1988年   119篇
  1987年   86篇
  1986年   98篇
  1985年   65篇
  1984年   37篇
  1983年   40篇
  1982年   37篇
  1981年   21篇
  1980年   8篇
  1979年   4篇
  1976年   1篇
  1957年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
Journal of Solid State Electrochemistry - In this work, nanorods like bimetallic Zn/Mn metal–organic-frameworks (MOFs) are proposed as the precursor for preparing MnxOy/porous carbon...  相似文献   
953.
Developing efficient and recyclable heterogeneous catalysts for organic reactions in water is important for the sustainable development of chemical industry. In this work, Pd nanoparticles supported on DABCO-functionalized porous organic polymer was successfully prepared through an easy copolymerization and successive immobilization method. Characterization results indicated that the prepared catalyst featured big surface area, hierarchical porous structure, and excellent surface amphiphilicity. We demonstrated the use of this amphiphilic catalyst in two case reactions, i.e. the aqueous hydrodechlorination and Suzuki-Miyaura coupling reactions. Under mild reaction conditions, the catalyst showed high catalytic activities for the two reactions. In addition, the catalyst could be easily recovered and reused for several times. Also, no obvious Pd leaching and aggregation of Pd nanoparticles occurred up during the consecutive reactions.  相似文献   
954.
Red phosphorus is a promising photocatalyst with wide visible-light absorption up to 700 nm, but the fast charge recombination limits its photocatalytic hydrogen evolution reaction (HER) activity. Now, [001]-oriented Hittorf's phosphorus (HP) nanorods were successfully grown on polymeric carbon nitride (PCN) by a chemical vapor deposition strategy. Compared with the bare PCN and HP, the optimized PCN@HP hybrid exhibited a significantly enhanced photocatalytic activity, with HER rates reaching 33.2 and 17.5 μmol h−1 from pure water under simulated solar light and visible light irradiation, respectively. It was theoretically and experimentally indicated that the strong electronic coupling between PCN and [001]-oriented HP nanorods gave rise to the enhanced visible light absorption and the greatly accelerated photoinduced electron–hole separation and transfer, which benefited the photocatalytic HER performance.  相似文献   
955.
Research on Chemical Intermediates - The low Mg 2p value (47.0 eV) of MgO reported in Res Chem Intermed 44(2018)829 is carefully analyzed and discussed based on a series of X-ray...  相似文献   
956.
957.
958.
2018年和2019年小学期,厦门大学本科生"绿行之踪"社会实践队赴重庆、上海等长江流域主要城市进行社会实践活动,采集了当地的水样,测定了水样中的磷酸根含量和高锰酸盐指数,同时进行了水资源保护的宣传活动和网络问卷调查。  相似文献   
959.
Wang  L. L.  Song  C.  Zhu  J. 《Theoretical and Mathematical Physics》2020,205(1):1303-1317
Theoretical and Mathematical Physics - Using the Riemann–Hilbert approach, we investigate the two-component generalized Ragnisco–Tu equation. The modified equation is integrable in the...  相似文献   
960.
The anion exchange membranes (AEMs) with both high ionic conductivity and alkali stability are always the research focus of the AEM fuel cells. Here, a novel nonplanar polymer for AEMs manufacture, mPBI‐TP‐x‐R, with excellent hydroxide stability and satisfactory processability is reported for the first time. The serial mPBI‐TP‐x resins with steric hindrance were prepared by copolymerization among 3,3′,4,4′‐tetraaminobiphenyl, isophthalic acid and tetraphenyl‐terephthalic acid (TP) in different ratios under microwave condensation. The copolymers mPBI‐TP‐x were quaternized at N1/N3‐sites of benzimidazole unit in backbone with alkyl groups (R?CH3, C2H5, n‐C3H7, or n‐C4H9) to prepare soluble ionomers, and the corresponding membranes in hydroxyl ion form were prepared by a solution casting method and subsequent ion‐exchange process. The chemical structure of all membranes was characterized using FTIR and 1H NMR spectroscopy. The properties of ion exchange capacity, water uptake, swelling ratio, tensile strength, ionic conductivity, and alkaline stability were measured. Among the prepared membranes, the mPBI‐TP‐15%‐(n‐Bu) exhibited the excellent alkaline stability (only degradation ca. 5% under 1M NaOH aqueous solution at 60 °C for 800 h) and satisfactory OH? conductivity (46.66 mS/cm at 80 °C). The current research provides a useful exploration to commercial application of alkaline fuel cell. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1087–1096  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号