全文获取类型
收费全文 | 549篇 |
免费 | 29篇 |
专业分类
化学 | 400篇 |
晶体学 | 6篇 |
力学 | 24篇 |
数学 | 43篇 |
物理学 | 105篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 17篇 |
2012年 | 29篇 |
2011年 | 48篇 |
2010年 | 30篇 |
2009年 | 19篇 |
2008年 | 41篇 |
2007年 | 37篇 |
2006年 | 26篇 |
2005年 | 38篇 |
2004年 | 22篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 14篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有578条查询结果,搜索用时 31 毫秒
161.
162.
Interplay between nonlinearity,scan speed,damping, and electronics in frequency modulation atomic-force microscopy 总被引:1,自引:0,他引:1
Numerical simulations of the frequency modulation atomic force microscope, including the whole dynamical regulation by the electronics, show that the cantilever dynamics is conditionally stable and that there is a direct link between the frequency shift and the conservative tip-sample interaction. However, a soft coupling between the electronics and the nonlinearity of the interaction may significantly affect the damping. A resonance between the scan speed and the response time of the system can provide a simple explanation for the spatial shift and contrast inversion between topographical and damping images, and for the extreme sensitivity of the damping to a tip change. 相似文献
163.
164.
The Double‐Bond Configuration of Corynanthean Alkaloids and Its Impact on Monoterpenoid Indole Alkaloid Biosynthesis
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)
Ruben Eckermann Prof. Dr. Tanja Gaich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(16):5749-5755
Experimental evidence is provided for the coherence of the double‐bond geometry and the occurrence of “secondary cyclizations” in the biosynthesis of monoterpenoid indole alkaloids. Biosynthetically, akuammiline, C‐mavacurine, and Strychnos alkaloids are proposed to be derived from the corynanthean alkaloid geissoschizine, a key intermediate in the biosynthetic pathway of these monoterpenoid indole alkaloids. This process occurs by so‐called “secondary cyclizations” from geissoschizine or its derivatives. Although corynanthean alkaloids like geissoschizine incorporate E or Z double bonds located at C19–C20, the alkaloids downstream in the biosynthesis exclusively exhibit the E double bond. This study shows that secondary cyclizations preferentially occur with the E isomer of geissoschizine or its derivatives. This is attributed to the flexibility of the quinolizidine system of the corynanthean alkaloids, which can adopt a cis or trans conformation. For the secondary cyclization to take place, the cis‐quinolizidine conformation is required. Experimental evidence supports the hypothesis that the E double bond of geissoschizine induces the cis conformation, whereas the Z double bond induces the trans conformation, which prohibits secondary cyclization of the Z compounds. 相似文献
165.
Arnaud Boreux Aubin Lambion Dominic Campeau Marina Sanita Ruben Coronel Olivier Riant Fabien Gagosz 《Tetrahedron》2018,74(38):5232-5239
The synthesis of fluorinated synthetic intermediates has become a field of intense research in organic chemistry. In this article, we report the application of a gold-catalyzed rearrangement to the synthesis of β-trifluoromethylated α,β-unsaturated ketones. The scope of the reaction, as well as the valorization of the products in subsequent transformations has been investigated. This study allowed for the preparation of various CF3-substituted enones and fluorinated Diels-Alder adducts from easily accessible starting materials. 相似文献
166.
Vyshnavi Narayanan Petra Lommens Klaartje De Buysser Ruben Hühne Isabel Van Driessche 《Journal of solid state chemistry》2011,184(11):2887-2896
In this work, water-based precursor solutions suitable for dip-coating of thick La2Zr2O7 (LZO) buffer layers for coated conductors on Ni-5%W substrates were developed. The solutions were prepared based on chelate chemistry using water as the main solvent. The effect of polymer addition on the maximum crack-free thickness of the deposited films was investigated. This novel solution preparation method revealed the possibility to grow single, crack-free layers with thicknesses ranging 100–280 nm with good crystallinity and an in-plane grain misalignment with average FWHM of 6.55°. TEM studies illustrated the presence of nanovoids, typical for CSD–LZO films annealed under Ar-5%H2 gas flow. The appropriate buffer layer action of the film in preventing the Ni diffusion was studied using XPS. It was found that the Ni diffusion was restricted to the first 30 nm of a 140 nm thick film. The surface texture of the film was improved using a seed layer. 相似文献
167.
Polarized Neutron Diffraction as a Tool for Mapping Molecular Magnetic Anisotropy: Local Susceptibility Tensors in CoII Complexes
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)
Dr. Karl Ridier Dr. Béatrice Gillon Dr. Arsen Gukasov Dr. Grégory Chaboussant Dr. Alain Cousson Prof. Dominique Luneau Dr. Ana Borta Dr. Jean‐François Jacquot Dr. Ruben Checa Yukako Chiba Prof. Hiroshi Sakiyama Prof. Masahiro Mikuriya 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):724-735
Polarized neutron diffraction (PND) experiments were carried out at low temperature to characterize with high precision the local magnetic anisotropy in two paramagnetic high‐spin cobalt(II) complexes, namely [CoII(dmf)6](BPh4)2 ( 1 ) and [CoII2(sym‐hmp)2](BPh4)2 ( 2 ), in which dmf=N,N‐dimethylformamide; sym‐hmp=2,6‐bis[(2‐hydroxyethyl)methylaminomethyl]‐4‐methylphenolate, and BPh4?=tetraphenylborate. This allowed a unique and direct determination of the local magnetic susceptibility tensor on each individual CoII site. In compound 1 , this approach reveals the correlation between the single‐ion easy magnetization direction and a trigonal elongation axis of the CoII coordination octahedron. In exchange‐coupled dimer 2 , the determination of the individual CoII magnetic susceptibility tensors provides a clear outlook of how the local magnetic properties on both CoII sites deviate from the single‐ion behavior because of antiferromagnetic exchange coupling. 相似文献
168.
169.
In this paper, we analyze an empirical model of viscous fingering for three-component, two-phase, first-contact miscible flows.
We present the complete range of analytical solutions to secondary and tertiary water-alternating-gas (WAG) floods. An important
ingredient in the construction of analytical solutions is the presence of detached (nonlocal) branches of the Hugoniot locus,
that is, curves in composition space that satisfy the Rankine–Hugoniot conditions but do not contain the reference state.
We illustrate how, in water–solvent floods into a medium with mobile water and residual oil (immobile to water), the solvent
front and the water Buckley–Leverett front may interact, resulting in a leading water/solvent shock that is stable to viscous
fingering. The analytical solutions explain why in these miscible tertiary floods, oil and solvent often break through simultaneously.
We discuss the implications of the new solutions in the design of miscible tertiary floods, such as the estimation of the
optimum WAG ratio. 相似文献
170.
Ruben Bartholomäus Fabian Dommershausen Dr. Markus Thiele Narayan S. Karanjule Dr. Klaus Harms Prof. Dr. Ulrich Koert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7423-7436
A total synthesis of the proposed structures of fulicineroside and its aglycone fulicinerine is reported. The tetrasubstituted dibenzofuran substructure was accessible either through a Pd‐mediated ortho‐metalation or by an Ir‐catalyzed meta‐borylation. The synthesis of the β,β,α‐linked trisaccharide consisting of D ‐olivose, L ‐rhodinose, and L ‐rhamnose was challenged by the unprecedented β‐linked rhodinose. A Pd‐catalyzed β‐selective glycosylation of a 4‐epi‐rhodinose and a subsequent Mitsunobu inversion provided selectively the β‐linked L ‐rhodinose‐L ‐rhamnose disaccharide. Comparison with the reported data for the natural product and the aglycone suggests a misassignment of the structure of the natural product. 相似文献