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   302843篇
  免费   4706篇
  国内免费   817篇
化学   158366篇
晶体学   4351篇
力学   12097篇
综合类   2篇
数学   38962篇
物理学   94588篇
  2021年   2211篇
  2020年   2775篇
  2019年   2846篇
  2018年   3909篇
  2017年   3771篇
  2016年   6198篇
  2015年   4289篇
  2014年   5927篇
  2013年   14384篇
  2012年   11295篇
  2011年   13279篇
  2010年   9040篇
  2009年   8608篇
  2008年   12250篇
  2007年   11990篇
  2006年   11221篇
  2005年   10336篇
  2004年   9229篇
  2003年   8056篇
  2002年   7789篇
  2001年   8373篇
  2000年   6617篇
  1999年   5106篇
  1998年   4304篇
  1997年   4118篇
  1996年   4181篇
  1995年   3731篇
  1994年   3764篇
  1993年   3904篇
  1992年   3926篇
  1991年   3937篇
  1990年   3734篇
  1989年   3576篇
  1988年   3634篇
  1987年   3484篇
  1986年   3300篇
  1985年   4559篇
  1984年   4709篇
  1983年   3815篇
  1982年   4024篇
  1981年   3962篇
  1980年   3794篇
  1979年   3866篇
  1978年   3989篇
  1977年   3890篇
  1976年   3949篇
  1975年   3611篇
  1974年   3624篇
  1973年   3681篇
  1972年   2483篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed.  相似文献   
53.
54.
55.
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   
56.
57.
58.
Development of biocompatible porous supports is a promising strategy in the field of tissue engineering for the repair and regeneration of bone tissues with severe damage. Graphene oxide aerogels (GOAs) are excellent candidates for the manufacture of these systems due to their porosity, ability to imitate bone structure, and mechanical resistance, and according to their surface chemical reactivity, they can facilitate osseointegration, osteogenesis, osteoinduction and osteoconduction. In this review, synthesis of GOAs from the most primary source is described, and recent studies on the use of these functionalized carbonaceous foams as scaffolding for bone tissue regeneration are presented.  相似文献   
59.
60.
New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C2N5]? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C2N5]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries.  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