全文获取类型
收费全文 | 3359篇 |
免费 | 112篇 |
国内免费 | 7篇 |
专业分类
化学 | 2356篇 |
晶体学 | 10篇 |
力学 | 43篇 |
数学 | 641篇 |
物理学 | 428篇 |
出版年
2021年 | 36篇 |
2020年 | 43篇 |
2019年 | 43篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 85篇 |
2015年 | 72篇 |
2014年 | 81篇 |
2013年 | 110篇 |
2012年 | 143篇 |
2011年 | 163篇 |
2010年 | 91篇 |
2009年 | 101篇 |
2008年 | 124篇 |
2007年 | 113篇 |
2006年 | 119篇 |
2005年 | 85篇 |
2004年 | 103篇 |
2003年 | 69篇 |
2002年 | 78篇 |
2001年 | 47篇 |
2000年 | 52篇 |
1999年 | 51篇 |
1998年 | 51篇 |
1997年 | 40篇 |
1996年 | 40篇 |
1995年 | 56篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 39篇 |
1991年 | 43篇 |
1990年 | 39篇 |
1989年 | 52篇 |
1988年 | 47篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 50篇 |
1984年 | 39篇 |
1983年 | 46篇 |
1982年 | 31篇 |
1981年 | 25篇 |
1980年 | 40篇 |
1979年 | 30篇 |
1978年 | 29篇 |
1977年 | 40篇 |
1976年 | 24篇 |
1975年 | 20篇 |
1971年 | 21篇 |
1934年 | 27篇 |
1933年 | 20篇 |
排序方式: 共有3478条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
135.
136.
Frank W. Vergeer Taasje Mahabiersing Enrique Lozano Diz Georg Süss-Fink František Hartl 《Journal of Cluster Science》2004,15(1):47-59
Electrochemical and photochemical properties of the tetrahedral cluster [Ru3Ir(
3-H)(CO)13] were studied in order to prove whether the previously established thermal conversion of this cluster into the hydrogenated derivative [Ru3Ir(-H)3(CO)12] also occurs by means of redox or photochemical activation. Two-electron reduction of [Ru3Ir(
3-H)(CO)13] results in the loss of CO and concomitant formation of the dianion [Ru3Ir(
3-H)(CO)12]2–. The latter reduction product is stable in CH2Cl2 at low temperatures but becomes partly protonated above 283K into the anion [Ru3Ir(-H)2(CO)12]– by traces of water. The dianion [Ru3Ir(
3-H)(CO)12]2– is also the product of the electrochemical reduction of [Ru3Ir(-H)3(CO)12] accompanied by the loss of H2. Stepwise deprotonation of [Ru3Ir(-H)3(CO)12] with Et4NOH yields [Ru3Ir(-H)2(CO)12]– and [Ru3Ir(
3-H)(CO)12]2–. Reverse protonation of the anionic clusters can be achieved, e.g., with trifluoromethylsulfonic acid. Thus, the electrochemical conversion of [Ru3Ir(
3-H)(CO)13] into [Ru3Ir(-H)3(CO)12] is feasible, demanding separate two-electron reduction and protonation steps. Irradiation into the visible absorption band of [Ru3Ir(
3-H)(CO)13] in hexane does not induce any significant photochemical conversion. Irradiation of this cluster in the presence of CO with
irr>340nm, however, triggers its efficient photofragmentation into reactive unsaturated ruthenium and iridium carbonyl fragments. These fragments are either stabilised by dissolved CO or undergo reclusterification to give homonuclear clusters. Most importantly, in H2-saturated hexane, [Ru3Ir(
3-H)(CO)13] converts selectively into the [Ru3Ir(-H)3(CO)12] photoproduct. This conversion is particularly efficient at
irr
>340nm. 相似文献
137.
Emission of volatile sesquiterpenes and monoterpenes in grapevine genotypes following Plasmopara viticola inoculation in vitro
下载免费PDF全文
![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alberto Algarra Alarcon Valentina Lazazzara Luca Cappellin Pier Luigi Bianchedi Rainer Schuhmacher Georg Wohlfahrt Ilaria Pertot Franco Biasioli Michele Perazzolli 《Journal of mass spectrometry : JMS》2015,50(8):1013-1022
The grapevine (Vitis vinifera) is one of the most widely cultivated fruit crops globally, and one of its most important diseases in terms of economic losses is downy mildew, caused by Plasmopara viticola. Several wild Vitis species have been found to be resistant to this pathogen and have been used in breeding programs to introduce resistance traits to susceptible cultivars. Plant defense is based on different mechanisms, and volatile organic compounds (VOCs) play a major role in the response to insects and pathogens. Although grapevine resistance mechanisms and the production of secondary metabolites have been widely characterized in resistant genotypes, the emission of VOCs has not yet been investigated following P. viticola inoculation. A Proton Transfer Reaction‐Time of Flight‐Mass Spectrometer (PTR‐ToF‐MS) was used to analyze the VOCs emitted by in vitro‐grown plants of grapevine genotypes with different levels of resistance. Downy mildew inoculation significantly increased the emission of monoterpenes and sesquiterpenes by the resistant SO4 and Kober 5BB genotypes, but not by the susceptible V. vinifera Pinot noir. Volatile terpenes were implicated in plant defense responses against pathogens, suggesting that they could play a major role in the resistance against downy mildew by direct toxicity or by inducing grapevine resistance. The grapevine genotypes differed in terms of the VOC emission pattern of both inoculated and uninoculated plants, indicating that PTR‐ToF‐MS could be used to screen hybrids with different levels of downy mildew resistance. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
138.
139.
140.
Will R. Gutekunst Athina Anastasaki Sungbaek Seo Alaina J. McGrath David J. Lunn Paul G. Clark Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2017,55(5):801-807
A new di‐tert‐butyl acrylate (diTBA) monomer for controlled radical polymerization is reported. This monomer complements the classical use of tert‐butyl acrylate (TBA) for synthesis of poly(acrylic acid) by increasing the density of carboxylic acids per repeat unit, while also increasing the flexibility of the carboxylic acid side‐chains. The monomer is well behaved under Cu(II)‐mediated photoinduced controlled radical polymerization and delivers polymers with excellent chain‐end fidelity at high monomer conversions. Importantly, this new diTBA monomer readily copolymerizes with TBA to further the potential for applications in areas such as dispersing agents and adsorbents. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 801–807 相似文献