全文获取类型
收费全文 | 2722篇 |
免费 | 110篇 |
国内免费 | 21篇 |
专业分类
化学 | 1765篇 |
晶体学 | 15篇 |
力学 | 54篇 |
数学 | 513篇 |
物理学 | 506篇 |
出版年
2023年 | 17篇 |
2021年 | 25篇 |
2020年 | 43篇 |
2019年 | 42篇 |
2018年 | 36篇 |
2017年 | 34篇 |
2016年 | 81篇 |
2015年 | 74篇 |
2014年 | 95篇 |
2013年 | 116篇 |
2012年 | 149篇 |
2011年 | 189篇 |
2010年 | 115篇 |
2009年 | 103篇 |
2008年 | 153篇 |
2007年 | 173篇 |
2006年 | 159篇 |
2005年 | 145篇 |
2004年 | 145篇 |
2003年 | 75篇 |
2002年 | 75篇 |
2001年 | 42篇 |
2000年 | 38篇 |
1999年 | 29篇 |
1998年 | 25篇 |
1997年 | 34篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 35篇 |
1993年 | 24篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 24篇 |
1982年 | 29篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 20篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1974年 | 20篇 |
1973年 | 25篇 |
1972年 | 13篇 |
排序方式: 共有2853条查询结果,搜索用时 31 毫秒
1.
2.
Erik Fooladi Bjrn Dalhus Christian Rmming Mats Tilset 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(12):m567-m569
In the title compound, [Rh(CH3)2(C2H3N)(C9H21N3)](C24H20B), the geometry around the RhIII centre is distorted octahedral, with elongated Rh—N bonds trans to the metal‐bonded methyl groups. The metal‐containing cations are located in channels formed by an anionic supramolecular mesh, in which aromatic π–π interactions between anionic [B(Ph)4]? units play a major role. 相似文献
3.
The aim of this Note is to give explicit limit expressions, for diffusion equations involving a small parameter ε, describing both nonperiodic homogenization and reduction of dimension. We consider two kinds of reduction of dimension: the case of plates and the case of thin cylinders. In particular, we give the limit diffusion equation for stratified plates. This is completely explicit and requires no special assumption, except stratification. In the case of thin cylinders, the formulae are less explicit, but we also indicate some simple applications to fibered materials. To cite this article: B. Gustafsson, J. Mossino, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 977–982. 相似文献
4.
5.
6.
Christoph Elschenbroich Jrn Plackmeyer Klaus Harms Olaf Burghaus Jürgen Pebler 《无机化学与普通化学杂志》2006,632(5):819-827
Trovacene Chemistry. 13 [1] On Being Lead and Mislead in the Synthesis of Di([5]trovacenyl)ketone Di([5]trovacenyl)ketone ( 3¨ ) has been prepared from lithio‐[5]trovacene and dimethylcarbamoyl chloride and studied by X‐ray diffraction, cyclic voltammetry, magnetic susceptometry and EPR spectroscopy. Slight variation of the synthetic protocol affords an unusual trinuclear complex 5 ? that is also fully characterized. Spin‐spin exchange interaction is smaller in 3¨ than in 1,1‐di([5]trovacenylethene ( 2¨ ), which differs from 3¨ by a replacement of O for CH2. The novel trinuclear complex 5 ? , however, displays exchange coupling very similar to that observed in 1‐methoxy‐2,5,6‐tri([5]trovacenyl)benzene ( 7 ? ). In both cases, an unsymmetrical triangular arrangement of S = 1/2 centers is encountered. These findings are discussed in terms of the nature of the respective spacers. 相似文献
7.
The synthesis of unsaturated unnatural amino acids according to the Heck-Jeffery protocol using a ball-milling procedure is presented. NOE data recorded on the products confirm that the Z-isomer is formed. This type of mechano-chemistry provides an efficient, “solvent free” and reliable method for the synthesis of substituted dehydroalanines. These conditions provide patterns of reactivity complementary to conventional procedures. 相似文献
8.
Örn Helgason Haraldur P. Gunnlaugsson Siguröur Steinthorsson Steen Mørup 《Hyperfine Interactions》1992,70(1-4):981-984
Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (JS-T) curves with Curie temperatures of about 580°C, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability, of maghemite at temperatures above 350°C, this reversibility is rather surprising. Here we report Mössbauer studies on heated lava samples, showing high content of maghemite. The samples were kept at 600°C in oxidizing, reducing, and inactive atmospheres, respectively, for different lengths of time, and then analyzed with Mössbauer spectroscopy at room temperature. The Mössbauer spectra showed that maghemite is stable in the oxidizing atmosphere for at least several hours. In the inactive atmosphere a considerable amount of maghemite still exists after two hours heating. In the reducing atmosphere maghemite had transformed to magnetite after only 30 minutes. 相似文献
9.
10.
Björn Wängler Carmen Beck Esther Schirrmacher Frank Rösch Michael Eisenhut 《Tetrahedron letters》2006,47(33):5985-5988
The synthesis of tris-allyl-DOTA starting from cyclen and its application in the preparation of DOTA-peptide conjugates is reported. Clinically important conjugates such as DOTA-Tyr3-octreotide (DOTA-TOC), DOTA-Tyr3-octreotate (DOTA-TATE) as well as a DOTA-RGD peptide were synthesized in high yields with Fmoc solid phase peptide synthesis. The final, extremely reliable de-allylation was achieved on solid phase by different methods identifying morpholine/Pd(0) as the most suitable one obtaining all DOTA peptide conjugates in high yields. All DOTA-peptides were purified by reversed phase HPLC and structural identity was proved using MALDI-TOF mass spectrometry. 相似文献