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   50520篇
  免费   8589篇
  国内免费   6672篇
化学   36265篇
晶体学   653篇
力学   3084篇
综合类   509篇
数学   6263篇
物理学   19007篇
  2024年   55篇
  2023年   980篇
  2022年   1223篇
  2021年   1608篇
  2020年   2041篇
  2019年   2029篇
  2018年   1778篇
  2017年   1777篇
  2016年   2433篇
  2015年   2391篇
  2014年   2972篇
  2013年   3885篇
  2012年   4622篇
  2011年   4804篇
  2010年   3483篇
  2009年   3325篇
  2008年   3576篇
  2007年   3207篇
  2006年   2969篇
  2005年   2436篇
  2004年   1796篇
  2003年   1431篇
  2002年   1270篇
  2001年   1102篇
  2000年   1017篇
  1999年   1056篇
  1998年   829篇
  1997年   790篇
  1996年   697篇
  1995年   691篇
  1994年   604篇
  1993年   505篇
  1992年   418篇
  1991年   382篇
  1990年   354篇
  1989年   268篇
  1988年   210篇
  1987年   169篇
  1986年   149篇
  1985年   142篇
  1984年   80篇
  1983年   67篇
  1982年   70篇
  1981年   28篇
  1980年   18篇
  1979年   10篇
  1971年   4篇
  1959年   2篇
  1957年   11篇
  1936年   5篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
The large-scale production of ammonia mainly depends on the Haber–Bosch process, which will lead to the problems of high energy consumption and carbon dioxide emission. Electrochemical nitrogen fixation is considered to be an environmental friendly and sustainable process, but its efficiency largely depends on the activity and stability of the catalyst. Therefore, it is imperative to develop highefficient electrocatalysts in the field of nitrogen reduction reaction (NRR). In this paper, we developed a BiVO4/TiO2 nanotube (BiVO4/TNT) heterojunction composite with rich oxygen vacancies as an electrocatalytic NRR catalyst. The heterojunction interface and oxygen vacancy of BiVO4/TNT can be the active site of N2 dynamic activation and proton transition. The synergistic effect of TiO2 and BiVO4 shortens the proton transport path and reduces the over potential of chemical reaction. BiVO4/TNT has high ammonia yield of 8.54 μg·h−1·cm−2 and high Faraday efficiency of 7.70% in −0.8 V vs. RHE in 0.1 M Na2SO4 solution.  相似文献   
62.
International Journal of Theoretical Physics - A new quantum watermark algorithm is presented by combining maximum pixel difference partitioning with the least significant bit substitution...  相似文献   
63.
Zhou  Yan  Yan  Xiang-Ping  Zhang  Cun-Hua 《Nonlinear dynamics》2021,105(4):3731-3747
Nonlinear Dynamics - This article considers a reaction–diffusion predator–prey model with schooling behavior both in predator and prey species and subject to the homogeneous Neumann...  相似文献   
64.
为探究加强型Bi-2212超导股线的力学性能以及不锈钢包带对超导股线力学性能的影响,运用Ansys软件建立加强型Bi-2212超导股线的三维模型,采用有限元分析方法,对其机械结构进行仿真,模拟高温高压热处理后轴向受拉形变量和应力应变分布情况。仿真结果显示,在同样施加100 N拉力的情况下,与超导原线(Bi-2212超导线)相比,密绕Ni80Cr20包带后的加强型Bi-2212超导股线轴向受拉形变程度减小,约10%;应力应变均降低,约30%。采用Ni80Cr20作为外包带制成的加强型Bi-2212超导股线力学性能显著,是未来超导线发展方向之一。  相似文献   
65.
Covalent organic frameworks(COFs), as a class of crystalline porous materials with periodic lattices and porous structures, have received extensive attention in the fields of gas storage and separation, energy storage, catalysis and optoelectronics and so on. However, COFs are still in their infancy in the field of nuclear waste treatment, especially for sequestration of long-live problematic radionuclides, such as 99Tc. Battle of decontamination of pertechnetate(TcO4), a main existence of 99Tc under aerobic environments, is far from finished. In this review, recent progresses of COFs and some relative materials in the sequestration of pertechnetate, and perspective on surmounting the unmet issues are elucidated.  相似文献   
66.
Molecular interactions are crucial in diverse fields of protein folding,material science,nanotechnology,and life origins.Although mounting experimental research controls luminescent behavior by adjusting molecular interactions in light-emitting materials,it remains elusive to correlate microscopic molecular interactions with macroscopic luminescent behavior directly.Here,we synthesized three red luminogens with subtle structural variation and investigated the influence of molecular interactions on their luminescent behavior in solution and aggregate states.Our results indicate that strongπ-πand D-A interactions in both dilute solution(between luminogen and solvent molecules)and aggregate(between luminogens)states cause the redshift in emission,while weak interactions(e.g.,Van der Waals,C–H…π,and C–H…F interactions)enhance the quantum yield.This work provides a thoughtful investigation into the complicated influence of various molecular interactions on luminescent behavior.  相似文献   
67.
68.
Journal of Radioanalytical and Nuclear Chemistry - Prostate-specific membrane antigen (PSMA)-targeted radiolabeled agents have been developed to diagnose and treat prostate cancer. In this study,...  相似文献   
69.
Cellulose - It is important to design gas separation membrane from natural resources such as clay and cellulose. In this work, natural clay attapulgite (ATP) nanorods were integrated into cellulose...  相似文献   
70.
Cubic-like CaTaO2N photocatalysts with high crystallinity and uniform particle size were successfully prepared by the flux-assisted nitridation method. The growth of CaTaO2N single crystals under different synthesis conditions was systematically investigated to understand the effects of the crystallinity and optical property on photocatalytic performance of CO2 reduction. Moreover, the modification of CaTaO2N single crystals with core-shell Ni−Ag bicomponent cocatalyst by two-step decoration process gave a 2.4 times higher amount of CO evolution than the deposition of sole Ag cocatalyst, because of the synergistic effects of bicomponent cocatalyst on the interfacial electron transfer and surface catalytic process. This study provides a valuable way to construct high-crystalline photocatalysts with effective bicomponent cocatalyst for visible-light-driven CO2 reduction with H2O.  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