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   16287篇
  免费   2854篇
  国内免费   3487篇
化学   11852篇
晶体学   408篇
力学   1144篇
综合类   420篇
数学   2265篇
物理学   6539篇
  2024年   49篇
  2023年   288篇
  2022年   520篇
  2021年   612篇
  2020年   662篇
  2019年   661篇
  2018年   548篇
  2017年   606篇
  2016年   735篇
  2015年   774篇
  2014年   919篇
  2013年   1224篇
  2012年   1402篇
  2011年   1327篇
  2010年   1166篇
  2009年   1082篇
  2008年   1227篇
  2007年   1081篇
  2006年   1025篇
  2005年   925篇
  2004年   808篇
  2003年   620篇
  2002年   708篇
  2001年   642篇
  2000年   582篇
  1999年   420篇
  1998年   265篇
  1997年   232篇
  1996年   231篇
  1995年   200篇
  1994年   192篇
  1993年   160篇
  1992年   122篇
  1991年   101篇
  1990年   93篇
  1989年   54篇
  1988年   68篇
  1987年   41篇
  1986年   60篇
  1985年   33篇
  1984年   22篇
  1983年   32篇
  1982年   19篇
  1981年   21篇
  1980年   17篇
  1979年   14篇
  1978年   9篇
  1976年   6篇
  1974年   4篇
  1957年   4篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Despite recent progress in producing perovskite nanowires (NWs) for optoelectronics, it remains challenging to solution-print an array of NWs with precisely controlled position and orientation. Herein, we report a robust capillary-assisted solution printing (CASP) strategy to rapidly access aligned and highly crystalline perovskite NW arrays. The key to the CASP approach lies in the integration of capillary-directed assembly through periodic nanochannels and solution printing through the programmably moving substrate to rapidly guide the deposition of perovskite NWs. The growth kinetics of perovskite NWs was closely examined by in situ optical microscopy. Intriguingly, the as-printed perovskite NWs array exhibit excellent optical and optoelectronic properties and can be conveniently implemented for the scalable fabrication of photodetectors.  相似文献   
82.
Research on Chemical Intermediates - The reaction steps during methanol synthesis from CO2/H2 are influenced by the type of catalysts such as pure Cu and Zn-decorated Cu. In this study, density...  相似文献   
83.
A divergent synthetic approach to six Ganoderma meroterpenoids, namely ganocins A–C, ganocochlearins C and D, and cochlearol T, has been developed for the first time. This synthetic route features a two‐phase strategy which includes early‐stage rapid construction of a common planar tricyclic intermediate followed by highly selective late‐stage transformations into various Ganoderma meroterpenoids. Key to the strategy are a bioinspired intramolecular hetero‐Diels–Alder reaction and Stahl‐type oxidative aromatization, allowing efficient formation of the common tricyclic phenol intermediate. A nucleophilic dearomatization of the phenol unit, combined with a regioselective 1,4‐reduction of the resulting dienone, enabled rapid access to ganocins B and C. Additionally, site‐selective Mukaiyama hydration, followed by an intramolecular oxa‐Michael addition/triflation cascade, served as a key strategic element in the chemical synthesis of ganocin A.  相似文献   
84.
Synthesis of well‐defined atomically mixed alloy nanoparticles on desired substrates is an ultimate goal for their practical application. Herein we report a general approach for preparing atomically mixed AuPt, AuPd, PtPd, AuPtPd NAs(nanoalloys) through single‐atom level manipulation. By utilizing the ubiquitous tendency of aggregation of single atoms into nanoparticles at elevated temperatures, we have synthesized nanoalloys on a solid solvent with CeO2 as a carrier and transition‐metal single atoms as an intermediate state. The supported nanoalloys/CeO2 with ultra‐low noble metal content (containing 0.2 wt % Au and 0.2 wt % Pt) exhibit enhanced catalytic performance towards complete CO oxidation at room temperature and remarkable thermostability. This work provides a general strategy for facile and rapid synthesis of well‐defined atomically mixed nanoalloys that can be applied for a range of emerging techniques.  相似文献   
85.
Wang  Guowei  Yang  Lijian  Zhan  Xuan  Li  Anbang  Jia  Ya 《Nonlinear dynamics》2022,107(4):3945-3962
Nonlinear Dynamics - Chaotic resonance (CR) is the response of a nonlinear system to weak signals enhanced by internal or external chaotic activity (such as the signal derived from Lorenz system)....  相似文献   
86.
Different types of tridimensional polymer networks have been synthetised by photoinitiated cationic polymerisation of vinyl ether and epoxy-functionalised oligomers and polymers. The polymerisation kinetics was followed by real-time infrared (RTIR) spectroscopy, a technique that records directly conversion versus time profiles in a timescale as short as 1 s. The addition of a diacrylate monomer was shown to accelerate the ring-opening polymerisation of epoxidized polyisoprene, with formation of interpenetrating polymer networks having well contrasted properties. A dual polymer network has been generated by photocrosslinking of a polyisoprene functionalised with both epoxy and acrylate groups.  相似文献   
87.
将一种人工合成的无机聚合物——蒙脱石皂石黏土(smectite,Sm)应用于基质辅助激光解吸电离飞行时间质谱分析(matrix-assisted laser desorption/ionization time of flight mass spectrometry, MALDI-TOF-MS),以检测糖类化合物。 将传统的有机基质2,4,6-三羟基苯乙酮(trihydroxyacetophenone, THAP)与阳离子交换后的皂石黏土混合制备成新型复合基质,应用于糖类化合物的检测。通过比较不同的制样方法,测定不同分子直径的糖类化合物,发现由于受复合基质晶面间距的限制,只有小分子糖类化合物能进入晶面间隙充分接触有机基质并被离子化,从而实现对小分子糖类化合物的选择性检测。  相似文献   
88.
The crystal and molecular structures of the title compounds were determined by X-ray diffraction technique from diffractometer intensity measurements. It has been found that two homologous disulfides, bis(dimethoxythiophosphoryl) disulfide 1 and bis(dineopentoxythiophosphoryl) disulfide 2 , form different molecular and crystal structures with space groups C2/c and P&1macr;, respectively. These results were confirmed by 31P CP MAS NMR studies, which showed that under favorable conditions the solid state NMR may lead to determination of the number of crystallographically unique phosphorus atoms. Moreover, the variation of the disulfide S–S bond length versus torsional P–S–S–P angles was observed.  相似文献   
89.
A redox-neutral Fe-catalyzed intramolecular C—H amidation of N-benzoyloxyureas is described.This methodology employs a simple iron complex in situ generated fro...  相似文献   
90.
采用自主设计搭建的雾化辅助化学气相沉积系统设备,开展了Ga2O3薄膜制备及其特性研究工作。通过X射线衍射研究了沉积温度、系统沉积压差对Ga2O3薄膜结晶质量的影响。结果表明,Ga2O3在425~650 ℃温度区间存在物相转换关系。随着沉积温度从425 ℃升高至650 ℃,薄膜结晶分别由非晶态、纯α-Ga2O3结晶状态向α-Ga2O3、β-Ga2O3两相混合结晶状态改变。通过原子力显微镜表征探究了生长温度对Ga2O3薄膜表面形貌的影响,从475 ℃升高至650 ℃时,薄膜表面粗糙度由26.8 nm下降至24.8 nm。同时,高分辨X射线衍射仪测试表明475 ℃、5 Pa压差条件下的α-Ga2O3薄膜样品半峰全宽仅为190.8″,为高度结晶态的单晶α-Ga2O3薄膜材料。  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