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   278141篇
  免费   19757篇
  国内免费   790篇
化学   171601篇
晶体学   3565篇
力学   12042篇
综合类   18篇
数学   31392篇
物理学   80070篇
  2023年   4357篇
  2022年   2635篇
  2021年   4221篇
  2020年   6428篇
  2019年   4414篇
  2018年   5283篇
  2017年   3595篇
  2016年   9797篇
  2015年   8086篇
  2014年   8962篇
  2013年   15580篇
  2012年   11808篇
  2011年   11445篇
  2010年   10307篇
  2009年   9870篇
  2008年   10457篇
  2007年   10239篇
  2006年   9291篇
  2005年   8276篇
  2004年   7590篇
  2003年   6604篇
  2002年   6360篇
  2001年   7201篇
  2000年   5530篇
  1999年   4227篇
  1998年   3428篇
  1997年   3478篇
  1996年   3307篇
  1995年   3154篇
  1994年   2983篇
  1993年   2974篇
  1992年   3284篇
  1991年   3058篇
  1990年   2977篇
  1989年   2782篇
  1988年   2842篇
  1987年   2836篇
  1985年   3489篇
  1984年   3730篇
  1983年   3068篇
  1982年   3276篇
  1981年   3272篇
  1980年   3184篇
  1979年   3228篇
  1978年   3313篇
  1977年   3434篇
  1976年   3522篇
  1975年   3391篇
  1974年   3355篇
  1973年   3276篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
82.
83.
84.
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions.  相似文献   
85.
86.
87.
Journal of Sol-Gel Science and Technology - Multifunctional magnetic mesoporous nanocomposites are promising materials to remove the various pollutants from water due to the remarkable properties...  相似文献   
88.
Herein, we report an addition to the toolbox for the monitoring and quantification of the hydrolytic decay of pentose-1-phosphates, which are known to be elusive and difficult to quantify. This communication describes how apparent equilibrium shifts of a nucleoside phosphorolysis reaction can be employed to calculate hydrolytic loss of pentose-1-phosphates based on the measurement of post-hydrolysis equilibrium concentrations of a nucleoside and a nucleobase. To demonstrate this approach, we assessed the stability of the relatively stable ribose-1-phosphate at 98 °C and found half-lives of 1.8–11.7 h depending on the medium pH. This approach can be extended to other sugar phosphates and related reaction systems to quantify the stability of UV-inactive and hard-to-detect reaction products and intermediates.  相似文献   
89.
We present the fabrication of core-shell-satellite Au@SiO2-Pt nanostructures and demonstrate that LSPR excitation of the core Au nanoparticle can induce plasmon coupling effect to initiate photocatalytic hydrogen generation from decomposition of formic acid. Further studies suggest that the plasmon coupling effect induces a strong local electric field between the Au core and Pt nanoparticles on the SiO2 shell, which enables creation of hot electrons on the non-plasmonic-active Pt nanoparticles to participate hydrogen evolution reaction on the Pt surface. In addition, small SiO2 shell thickness is required in order to obtain a strong plamon coupling effect and achieve efficient photocatalytic activities for hydrogen generation.  相似文献   
90.
Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research.  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