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   24644篇
  免费   4060篇
  国内免费   3966篇
化学   18313篇
晶体学   508篇
力学   1455篇
综合类   384篇
数学   2969篇
物理学   9041篇
  2024年   38篇
  2023年   365篇
  2022年   663篇
  2021年   780篇
  2020年   904篇
  2019年   871篇
  2018年   714篇
  2017年   820篇
  2016年   1062篇
  2015年   1112篇
  2014年   1315篇
  2013年   1807篇
  2012年   2130篇
  2011年   2239篇
  2010年   1707篇
  2009年   1612篇
  2008年   1815篇
  2007年   1582篇
  2006年   1568篇
  2005年   1392篇
  2004年   1041篇
  2003年   887篇
  2002年   998篇
  2001年   759篇
  2000年   662篇
  1999年   558篇
  1998年   401篇
  1997年   353篇
  1996年   363篇
  1995年   319篇
  1994年   275篇
  1993年   248篇
  1992年   226篇
  1991年   190篇
  1990年   181篇
  1989年   137篇
  1988年   120篇
  1987年   82篇
  1986年   77篇
  1985年   83篇
  1984年   41篇
  1983年   41篇
  1982年   31篇
  1981年   31篇
  1980年   15篇
  1979年   12篇
  1978年   6篇
  1973年   3篇
  1971年   4篇
  1957年   8篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
Kahweol, a compound from Coffea arabica, possesses antioxidant, anti-inflammatory, and antitumour properties. However, an anti-adipogenic effect has not yet been reported. In this study, we have shown that kahweol has an anti-adipogenic effect on 3T3-L1 adipocytes. Kahweol significantly inhibited the differentiation of intracellular lipid accumulation in 3T3-L1 adipocytes, without being cytotoxic. It also downregulated the expression of adipogenesis-related gene, including an adipocytokine, adiponectin. This anti-adipogenic effect stems from an ability to inhibit key adipogenic regulators, including PPARγ and C/EBPα. These results demonstrate that kahweol significantly inhibits the differentiation of 3T3-L1 cells, and suggest that it has potential as a novel anti-obesity treatment.  相似文献   
992.
993.
994.
Four Zn(II) complexes, [Zn L 2(SO4)]n ( 1 ), [Zn L 4(H2O)2]?2(NO3)?4EtOH ( 2 ), [Zn L 2Cl2]? L ( 3 ), and [Zn L 2Br2]? L ( 4 ) ( L  = uniconazole), were synthesized using a hydrothermal method and characterized by elemental analysis, FT‐IR spectroscopy, and single‐crystal XRD. Complex 1 formed a one‐dimensional polymer chain. However, complexes 2 ‐ 4 were obtained as zero‐dimensional mononuclear coordination compounds. The antifungal activities of these complexes were then evaluated against four selected fungi using the mycelial growth rate method. The resulting data indicate that all complexes show better antifungal activities than their ligands and mixtures. In addition, the interactions between the metal salts of complexes 1 ‐ 4 and uniconazole seem to be synergistic. Furthermore, the polymer chain structure of complex 1 significantly enhanced the bioactivity, especially against Botryosphaeria ribis ( I ). Density functional theory (DFT) calculations were carried out to help explain the enhanced bioactivity after the formation of Zn(II) complexes. The resulting data show that the HOMO–LUMO energy gaps of complexes 1 ‐ 4 (0.0578, 0.0946, 0.1053, and 0.1245 eV) are smaller than that of the free ligand (0.1247 eV) and correlate with the antifungal activity of the zinc complexes.  相似文献   
995.
Azulenesulfonium salts may be readily prepared from the corresponding azulenes by an SEAr reaction. These azulene sulfonium salts are bench‐stable species that may be employed as pseudohalides for cross‐coupling. Specifically, their application in Suzuki–Miyaura reactions has been demonstrated with a diverse selection of coupling partners. These azulenesulfonium salts possess significant advantages in comparison with the corresponding azulenyl halides, which are known to be unstable and difficult to prepare in pure form.  相似文献   
996.
We report on the fabrication of efficient annealing-free organic solar cells using co-solvent solution considered as a promising method for low-cost and time-saving manufacturing. Higher device efficiency could be obtained compared to the pure solvent casted device, resulting from the improved crystallinity, optical absorption and transport properties. The power conversion efficiency of 2.8% was obtained, demonstrating the feasibility of achieving low-cost and high-efficiency organic solar cells without any additional treatment and processing additives.  相似文献   
997.
Multifunctional nanomaterials with task-specific physicochemical properties, especially core?Cshell nanostructures with Fe3O4 core and NH2-functional shells (Fe3O4@SiO2?CNH2), have been extensively investigated as high-performance adsorbents, catalysts and catalyst supports; and in most cases the controllable sol?Cgel technique is the choice for fabrication of this kind of widely applied materials. Herein, we demonstrated that mono-dispersed and spherical Fe3O4@SiO2?CNH2 nanomaterials with magnetic response core, NH2-functional shell structure can be facilely prepared by co-condensation of TEOS with APTMS using a versatile sol?Cgel process. It was shown that the proper usage of APTMS and appropriate pre-hydrolysis time of TEOS were crucial and key steps for formation of highly uniform and desirable amino loading Fe3O4@SiO2?CNH2 materials. The TEOS pre-hydrolysis and the critical time (around 90?min) before the addition of APTMS prove to be vital for uniform structure evolution, while the appropriate concentration of APTMS (~2.28?mmol?L?1 in our system) leads to well-dispersed materials with relatively high loading of amino functionality. The as-prepared Fe3O4@SiO2?CNH2 magnetic nanoparticles prepared under optimum conditions possessing superparamagnetic behavior, uniform core?Cshell structure (~200?nm in diameter), relatively large BET surface area (~138?m2/g) and high incorporation of amino-functionality (~2.90?wt?%).  相似文献   
998.
999.
1000.
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