首页 | 官方网站   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   2591篇
  免费   88篇
  国内免费   362篇
数理化   3041篇
  2024年   4篇
  2023年   77篇
  2022年   55篇
  2021年   73篇
  2020年   103篇
  2019年   84篇
  2018年   94篇
  2017年   135篇
  2016年   135篇
  2015年   82篇
  2014年   151篇
  2013年   463篇
  2012年   253篇
  2011年   155篇
  2010年   131篇
  2009年   137篇
  2008年   142篇
  2007年   150篇
  2006年   142篇
  2005年   124篇
  2004年   128篇
  2003年   79篇
  2002年   18篇
  2001年   11篇
  2000年   7篇
  1999年   13篇
  1998年   12篇
  1997年   11篇
  1996年   8篇
  1995年   7篇
  1994年   9篇
  1993年   8篇
  1992年   6篇
  1991年   12篇
  1990年   5篇
  1989年   2篇
  1988年   5篇
  1987年   2篇
  1984年   3篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
排序方式: 共有3041条查询结果,搜索用时 15 毫秒
81.
《Analytical letters》2012,45(9):775-783
Abstract

A modification of a fluorescence assay method for β-cyanoalanine synthase has been described which involves the direct coupling of the product of cyanide and cysteine to resazurin, to produce the fluorescent resosurfin, The fluorescence produced was found to be directly proportional to the rate of the reaction.  相似文献   
82.
The molecular and crystal structures of chlorine-, bromine-, and nitro-substituted chromium(III) acetylacetonate are determined. Connecting the substituent to the central atom does not change bond lengths and valence angles in metal chelate rings. Studied chromium complexes are characterized by greater intermolecular interactions compared with analogous metal acetylacetonates. In some cases, intermolecular interactions increase the bend of chelate rings along the O?O line. Substituents do not interact with chromium ions of neighboring molecules because metal is blocked by three ligands.  相似文献   
83.
Synthesis of β-bromostyrenes from styrene bromohydrins using H-β-zeolite as catalyst under moderate conditions is reported. The catalyst could be regenerated and reused up to three consecutive cycles.  相似文献   
84.
Use of the calcium-ethylenediamine and sodium-liquid ammonia reduction systems for the ring opening of dihydropyran derivatives was studied. (Z)-Alkenyl alcohols and (E)-alkenyl alcohols were stereoselectively synthesized respectively.  相似文献   
85.
  相似文献   
86.
  相似文献   
87.
In this paper,we propose a near-infrared p-type β-FeSi2/n-type 4H-SiC heterojunction photodetector with semiconducting silicide(β-FeSi2) as the active region for the first time.The optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature.The results show that the photodetector has a good rectifying character and a good response to near-infrared light.Interface states should be minimized to obtain a lower reverse leakage current.The response spectrum of the β-FeSi2/4H-SiC detector,which consists of a p-type β-FeSi2 absorption layer with a doping concentration of 1×1015cm-3 and a thickness of 2.5 μm,has a peak of 755 mA/W at 1.42 μm.The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi2 side.The results illustrate that the β-FeSi2/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.  相似文献   
88.
A series of random polyesteramides (PEAs) within a range of molar composition from 90/10 to 10/90 were synthesized by a direct melt polycondensation of lactic acid and β-alanine. Their structures were fully characterized by NMR spectroscopy. The resulting copolymers are amorphous; they are thermally stable to temperatures up to 254°C, and present increasing glass transition temperatures at increasing amide content. The copolymers were also characterized by FTIR and viscosimetry measurements.  相似文献   
89.
Phthalimide derivatives as nitrogen nucleophiles with α,β‐unsaturated aldehydes for asymmetric aza‐Michael additions have been reported. The reactions proceed smoothly to afford corresponding Michael adducts in good yields (up to 98%) and enantioselectivities (up to 95% ee).  相似文献   
90.
Abstract

The extraction properties of a series of carbamoylmethylphosphine oxides and β-aminophosphine oxides with lanthanide metal ions is presented. Tris[bis(2-diphenyl- phosphorylethyl)-aminoethyl]amine is shown to be highly effective for extraction of Re(VII).  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-23

京公网安备 11010802026262号