全文获取类型
收费全文 | 1943篇 |
免费 | 48篇 |
国内免费 | 6篇 |
专业分类
化学 | 1185篇 |
晶体学 | 9篇 |
力学 | 45篇 |
数学 | 237篇 |
物理学 | 521篇 |
出版年
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2017年 | 14篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 25篇 |
2013年 | 77篇 |
2012年 | 75篇 |
2011年 | 84篇 |
2010年 | 41篇 |
2009年 | 38篇 |
2008年 | 86篇 |
2007年 | 87篇 |
2006年 | 76篇 |
2005年 | 87篇 |
2004年 | 86篇 |
2003年 | 66篇 |
2002年 | 63篇 |
2001年 | 49篇 |
2000年 | 54篇 |
1999年 | 39篇 |
1998年 | 32篇 |
1997年 | 19篇 |
1996年 | 46篇 |
1995年 | 35篇 |
1994年 | 32篇 |
1993年 | 32篇 |
1992年 | 44篇 |
1991年 | 23篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 33篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 29篇 |
1984年 | 19篇 |
1983年 | 29篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 26篇 |
1978年 | 20篇 |
1977年 | 20篇 |
1976年 | 27篇 |
1975年 | 25篇 |
1974年 | 21篇 |
1973年 | 16篇 |
1972年 | 9篇 |
1970年 | 14篇 |
排序方式: 共有1997条查询结果,搜索用时 15 毫秒
101.
102.
Oxidative Addition of Haloheteroarenes to Palladium(0): Concerted versus SNAr‐Type Mechanism
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Bert U. W. Maes Dr. Stefan Verbeeck Dr. Tom Verhelst Audrey Ekomié Niklas von Wolff Dr. Guillaume Lefèvre Dr. Emily A. Mitchell Prof. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7858-7865
The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd0(PPh3)2] (generated from [Pd0(PPh3)4]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2‐halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented SNAr‐type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies. 相似文献
103.
Journal of Nonlinear Science - We compare one-dimensional representations for the isotopy stable dynamics of homeomorphisms in two dimensions. We consider the skeleton graph representative, which... 相似文献
104.
S.L. Mitchell 《Applied Mathematical Modelling》2012,36(1):127-138
In this paper the combined integral method is applied to a simple one-dimensional ablation problem. One of the drawbacks of heat balance integral methods is how to choose the approximating function. It is common to use a polynomial form but even then it is not clear what the power of the highest order term should be. Previous studies have determined exponents either from exact solutions or from expansions valid over short time scales; neither approach is satisfactory nor very accurate for larger times. We combine the heat balance and refined integral methods to determine this exponent as part of the solution process, and conclude that it is in fact time-dependent in the ablation stage. From comparing the approximate solutions with numerical and exact analytical solutions whenever possible, we show that this new method greatly improves the accuracy on standard methods, without overcomplicating the method. 相似文献
105.
106.
Abstract The family Anacardiaceae consists of 76 genera and about 600 species. A comparison of the species of Anacardiaceae is discussed with special emphasis on the importance of the exudates, the so-called sap, for their importance as lacquer to produce lacquer ware. Many exudates are poisonous. The individual chemical compounds which constitute the active ingredients of the oleoresin part of the sap and their function are described based on space-filling molecular models. Emphasis is also given to the organic components of lacquer trees of the South East Asian region, which is compared to other species of the Anacardiaceae family. 相似文献
107.
Robert G. Gilbert Alex C. Wu Mitchell A. Sullivan Gonzalo E. Sumarriva Natascha Ersch Jovin Hasjim 《Analytical and bioanalytical chemistry》2013,405(28):8969-8980
Two highly branched glucose polymers with similar structures—starch and glycogen—have important relations to human health. Slowly digestible and resistant starches have desirable health benefits, including the prevention and alleviation of metabolic diseases and prevention of colon cancer. Glycogen is important in regulating the use of glucose in the body, and diabetic subjects have an anomaly in their glycogen structure compared with that in healthy subjects. This paper reviews the biosynthesis–structure–property relations of these polymers, showing that polymer characterization produces knowledge which can be useful in producing healthier foods and new drug targets aimed at improving glucose storage in diabetic patients. Examples include mathematical modeling to design starch with better nutritional values, the effects of amylose fine structures on starch digestibility, the structure of slowly digested starch collected from in vitro and in vivo digestion, and the mechanism of the formation of glycogen α particles from β particles in healthy subjects. A new method to overcome a current problem in the structural characterization of these polymers using field-flow fractionation is also given, through a technique to calibrate evaporative light scattering detection with starch. Figure
? 相似文献
108.
The reaction of N-methoxy-derivatives of pyridines in methanol with ammonium persulphate gives improved yields of mono-hydroxymethylated products. In contrast to the original Minisci procedure the reaction requires only catalytic amounts of ammonium persulphate. Evidence is presented which establishes that the reaction does not proceed via an intramolecular pathway. 相似文献
109.
Dr. Laia Vilà‐Nadal Dr. Scott G. Mitchell Dr. Stanislav Markov Dr. Christoph Busche Dr. Vihar Georgiev Prof. Asen Asenov Prof. Leroy Cronin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16502-16511
We explore the concept that the incorporation of polyoxometalates (POMs) into complementary metal oxide semiconductor (CMOS) technologies could offer a fundamentally better way to design and engineer new types of data storage devices, due to the enhanced electronic complementarity with SiO2, high redox potentials, and multiple redox states accessible to polyoxometalate clusters. To explore this we constructed a custom‐built simulation domain bridge. Connecting DFT, for the quantum mechanical modelling part, and mesoscopic device modelling, confirms the theoretical basis for the proposed advantages of POMs in non‐volatile molecular memories (NVMM) or flash‐RAM. 相似文献
110.
Haitao Wu Vincent Coble Olga Vasalatiy Rolf E. Swenson Murali C. Krishna James B. Mitchell 《Tetrahedron letters》2014
Nitroxides can ameliorate the toxic effects of radiation during cancer therapy. Nitroxides are paramagnetic and can be used in magnetic resonance imaging (MRI) and electron paramagnetic resonance imaging (EPRI) to monitor in vivo oxidative stress status. Compound 5 (3-(N-piperidinemethyl)-2,2,5,5-tetramethyl-1-oxy-3-pyrroline) was found to be the most effective nitroxide radioprotector. An efficient synthesis for this promising radioprotector was developed. 相似文献