全文获取类型
收费全文 | 4676篇 |
免费 | 984篇 |
国内免费 | 694篇 |
专业分类
化学 | 5673篇 |
晶体学 | 11篇 |
力学 | 87篇 |
综合类 | 10篇 |
数学 | 170篇 |
物理学 | 403篇 |
出版年
2024年 | 4篇 |
2023年 | 55篇 |
2022年 | 98篇 |
2021年 | 131篇 |
2020年 | 268篇 |
2019年 | 122篇 |
2018年 | 184篇 |
2017年 | 129篇 |
2016年 | 269篇 |
2015年 | 351篇 |
2014年 | 335篇 |
2013年 | 436篇 |
2012年 | 382篇 |
2011年 | 356篇 |
2010年 | 334篇 |
2009年 | 343篇 |
2008年 | 403篇 |
2007年 | 332篇 |
2006年 | 311篇 |
2005年 | 284篇 |
2004年 | 259篇 |
2003年 | 319篇 |
2002年 | 86篇 |
2001年 | 85篇 |
2000年 | 80篇 |
1999年 | 53篇 |
1998年 | 37篇 |
1997年 | 72篇 |
1996年 | 69篇 |
1995年 | 59篇 |
1994年 | 20篇 |
1993年 | 18篇 |
1992年 | 23篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有6354条查询结果,搜索用时 15 毫秒
971.
George Pitsevich Elena Shalamberidze Alex Malevich Valdas Sablinskas Vytautas Balevicius Lars G. M. Pettersson 《Molecular physics》2017,115(20):2605-2613
The frequencies and intensities of vibration–rotational transitions of water molecules in an argon matrix were calculated for temperatures of 6 and 30 K. The rigid asymmetric top approximation was used with available literature values of the effective rotational constants in the ground and excited vibrational states. The calculations were carried out by taking into account the existence of a non-equilibrium population distribution between the rotational levels of ortho- and para-water isomers. It was assumed that the temperature relaxation of the population of rotational levels is independent of the ortho- and para-isomers. Comparison of the results of the theoretical calculations with experimental literature data shows good agreement for the majority of the rotational structure lines for symmetric and antisymmetric stretching vibrations both in the frequency values and in the values of the relative intensities. 相似文献
972.
《Angewandte Chemie (International ed. in English)》2017,56(7):1704-1718
Since the pioneering days of total synthesis and retrosynthetic analysis, the community has embraced guiding principles for planning synthetic approaches towards complex natural products. These guideposts have enabled the community to synthesize ever more complex compounds by applying prior knowledge gained in new settings. The recently isolated schinortriterpenoid family of natural products has attracted considerable synthetic attention and provided a rich opportunity to evaluate the lessons learned in the construction of complex, polycyclic scaffolds. In this Minireview, a detailed discussion of the synthetic work within this family is provided, including the six reported total syntheses, as well as a comparative analysis of the approaches utilized in their construction. 相似文献
973.
《Angewandte Chemie (International ed. in English)》2017,56(18):4936-4940
Herein, we describe the first catalytic asymmetric intramolecular [4+2] cycloaddition of in situ generated ortho‐quinone methides. In the presence of a confined chiral imidodiphosphoric acid catalyst, various salicylaldehydes react with dienyl alcohols to give transient ortho ‐quinone methide intermediates, which undergo an intramolecular [4+2] cycloaddition to provide highly functionalized furanochromanes and pyranochromanes in excellent diastereoselectivity and enantioselectivity. 相似文献
974.
Dr. Bo Chen Cheng Fang Prof. Peng Liu Prof. Joseph M. Ready 《Angewandte Chemie (International ed. in English)》2017,56(30):8780-8784
We describe the synthetically useful enantioselective addition of Br−CX3 (X=Cl or Br) to terminal olefins to introduce a trihalomethyl group and generate optically active secondary bromides. Computational and experimental evidence supports an asymmetric atom-transfer radical addition (ATRA) mechanism in which the stereodetermining step involves outer-sphere bromine abstraction from a [(bisphosphine)RhIIBrCl] complex by a benzylic radical intermediate. This mechanism appears unprecedented in asymmetric catalysis. 相似文献
975.
Enantioselective total synthesis of anti HIV-1 active (+)-calanolide A was achieved by a quinine-catalyzed asymmetric intramolecular oxo-Michael addition as a key step. 相似文献
976.
977.
978.
Several key problems involved in the analyses of spectra of asymmetric top molecules, i.e., the effective Hamiltonian, the representation and basis vector, identification of energy levels, the selection rules, the relative intensity, and Zeeman tuning rate, were elucidated systematically. Introducing the high-order centrifugal distortion terms into the effective Hamiltonian, the precision for calculation has been improved substantially, which allows us to analyze the high-lying rotational transitions. A global analysis of all available spectra of 14N16O2 in the ground vibronic state has been made to obtain a set of molecular constants of 14N16O2 in the ground vibronic state which is the most precise and extensive so far. Using the improved parameters, some FIR LMR lines left unassigned hitherto have been identified successfully. 相似文献
979.
980.
Eugene R. Speer 《Journal of statistical physics》1997,89(1-2):169-175
Abstruct The algebra describing a shock measure in the asymmetric simple exclusion model, seen from a second class particle, has finite-dimensional
representations if and only if the asymmetry parameterp of the model and the left and right asymptotic densitiesp
± of the shock satisfy [(1−p)/p]
r
=p
−(1−p
+)/p
+(1−p
−) for some integerr≥1; the minimal dimension of the representation is then 2r. These representations can be used to calculate correlation functions
in the model. 相似文献