全文获取类型
收费全文 | 404篇 |
免费 | 6篇 |
专业分类
化学 | 296篇 |
晶体学 | 5篇 |
力学 | 18篇 |
数学 | 36篇 |
物理学 | 55篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2020年 | 10篇 |
2019年 | 4篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 18篇 |
2012年 | 25篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 10篇 |
2008年 | 30篇 |
2007年 | 29篇 |
2006年 | 25篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 21篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有410条查询结果,搜索用时 31 毫秒
61.
Marco Colella Prof. Dr. Aichiiro Nagaki Prof. Dr. Renzo Luisi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(1):19-32
In the field of organic synthesis, the advent of flow chemistry and flow microreactor technology represented a tremendous novelty in the way of thinking and performing chemical reactions, opening the doors to poorly explored or even impossible transformations using batch methods. In this Concept article, we would like to highlight the impact of flow chemistry for exploiting highly reactive organometallic reagents, and how, alongside the well-known advantages concerning safety, scalability, and productivity, flow chemistry makes possible processes that are impossible to control by using the traditional batch approach. 相似文献
62.
Nogueira Petrnio A. S. Cavalieri Andr V. G. Hanifi Ardeshir Henningson Dan S. 《Theoretical and Computational Fluid Dynamics》2020,34(1):163-176
Theoretical and Computational Fluid Dynamics - The problem of finding optimal forcing and response for unbounded base flows, exemplified by the Blasius boundary layer, is assessed by means of a... 相似文献
63.
64.
A short and efficient synthesis of tetrahydroindenofuranones based on the Michael addition of ortho-lithiated aryloxiranes to alkylidene malonates followed by the nucleophilic oxirane ring-opening and subsequent lactonization is described. The methodology has been applied to the synthesis of a structural analogue of epipodophyllotoxins. 相似文献
65.
Capriati V Florio S Luisi R Mazzanti A Musio B 《The Journal of organic chemistry》2008,73(8):3197-3204
The alpha-lithiation-trapping sequence of trans-N-alkyl-2,3-diphenylaziridines (s-BuLi or s-BuLi/TMEDA), taking place with a stereochemistry which dramatically depends on the solvent coordinating ability (inversion of configuration in THF and retention in toluene), has been carefully investigated. 1H,13C, and 7Li multinuclear NMR investigations at low temperature suggest that two differently configured lithiated aziridines (monomeric cis-1-Li in THF and dimeric trans-1-Li in toluene) are involved. 相似文献
66.
Coasne B Di Renzo F Galarneau A Pellenq RJ 《Langmuir : the ACS journal of surfaces and colloids》2008,24(14):7285-7293
This paper reports a molecular simulation study on the adsorption of simple fluids (argon at 77 K) on hydroxylated silica surfaces and nanopores. The effect of surface chemistry is addressed by considering substrates with either partially or fully hydroxylated surfaces. We also investigate the effect of pore shape on adsorption and capillary condensation by comparing the results for cylindrical and hexagonal nanopores having equivalent sections (i.e., equal section areas). Due to the increase in the polarity of the surface with the density of OH groups, the adsorbed amounts for fully hydroxylated surfaces are found to be larger than those for partially hydroxylated surfaces. Both the adsorption isotherms for the cylindrical and hexagonal pores conform to the typical behavior observed in the experiments for adsorption/condensation in cylindrical nanopores MCM-41. Capillary condensation occurs through an irreversible discontinuous transition between the partially filled and the completely filled configurations, while evaporation occurs through the displacement at equilibrium of a hemispherical meniscus along the pore axis. Our data are also used to discuss the effect of surface chemistry and pore shape on the BET method. The BET surface for fully hydroxylated surfaces is much larger (by 10-20%) than the true geometrical surface. In contrast, the BET surface significantly underestimates the true surface when partially hydroxylated surfaces are considered. These results suggest that the surface chemistry and the choice of the system adsorbate/adsorbent is crucial in determining the surface area of solids using the BET method. 相似文献
67.
Cavalieri F Ashokkumar M Grieser F Caruso F 《Langmuir : the ACS journal of surfaces and colloids》2008,24(18):10078-10083
High-intensity ultrasound induces emulsification and cross-linking of protein molecules in aqueous medium. The stability and the functionality of the resultant protein-coated microbubbles are crucial in many of their applications. For example, the stability of drug-loaded microbubbles should be sufficiently long enough, in vivo, so that they can be ruptured only at specific sites for release of the drugs. In this study, we report the synthesis of stable and functional microbubbles, coated with chemically reduced lysozyme, using high-intensity ultrasound in aqueous solution. In the absence of chemical reduction, stable microbubbles were not produced with native lysozyme, indicating the importance of free -SH functional groups for protein cross-linking. The degree of cross-linking between lysozyme molecules was controlled by manipulating both the extent of chemical reduction of the intramolecular disulfide bonds and sonication time. The lysozyme-coated microbubbles are stable for several months and retain the enzymatic (antimicrobial) activity of lysozyme. The layer-by-layer (LbL) deposition of polyelectrolytes onto the protein-shell air-core template has been used as a versatile procedure to modify the surface properties of the microbubbles, indicating the possibility of adsorbing potential drugs and/or biolabels on the surface of these microbubbles for therapeutic and diagnostic applications. 相似文献
68.
[structure: see text]. The lithiation reaction of cis- and trans-N-alkyl-2,3-diphenylaziridines has been investigated. While cis-diphenylaziridines do not undergo any lithiation upon treatment with organolithiums, the lithiation reaction of the trans counterparts is completely alpha-regioselective and the stereochemical course of the lithiation-trapping sequence is solvent dependent: inversion of configuration in coordinating solvents (THF or toluene/crown ether) and retention in hexane, ether, or toluene. The preparation of stereodefined functionalized N-alkyl-2,3-diphenylaziridines is described. 相似文献
69.
Mariachiara Pastore Celestino Angeli Renzo Cimiraglia 《Theoretical chemistry accounts》2007,118(1):35-46
The vertical electronic spectrum of the thiophene molecule is investigated by means of second and third order multireference
perturbation theory (NEVPT). Single-state and quasi-degenerate NEVPT calculations of more than 25 singlet excited states have
been performed. The study is addressed to the theoretical characterization of the four lowest-energy valence states, as well as the 3s, 3p and 3d Rydberg states. In addition, the excitation energies of two and valence states are also reported. For almost all the excited states, coupled cluster calculations (CCSD and CCSDR(3)) have
been also carried out, using the same geometry and basis set used for the NEVPT ones, in order to make the comparison between
the results of the two methods meaningful. A remarkable accordance between the NEVPT and CC excitation energies is found.
The present results, over all, confirm the experimental assignments but, above all, represent an important contribution to
the assignments of some low-energy states, valence and Rydberg, for which a firm interpretation is not available in the literature. 相似文献
70.
Benedetti M Tamasi G Cini R Marzilli LG Natile G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(11):3131-3142
cis-[PtA2(nucleotide)2] complexes (A2 stands for two amines or a diamine) have been extensively investigated as model compounds for key cisplatin-DNA adducts. All cis-[metal(nucleotide/nucleoside)2] complexes with guanine and related purines characterized in the solid state thus far have the DeltaHT conformation (head-to-tail orientation of the two bases and right-handed chirality). In sharp contrast, the LambdaHT conformation (left-handed chirality) dominates in acidic and neutral aqueous solutions of cis-[PtA2(5'-GMP)2] complexes. Molecular models and solution experiments indicate that the LambdaHT conformer is stabilized by 5'-phosphate/N1H hydrogen-bond interactions between cis nucleotides with the normal anti conformation. However, this evidence, while compelling, is indirect. At last, conditions have been defined to allow crystallization of this elusive conformer. The structure obtained reveals three unique features not present in all other cis-[PtA2(nucleotide)2] solid-state structures: a LambdaHT conformation, very strong hydrogen-bond interactions between the phosphate and N1H of cis nucleotides, and a very small dihedral angle between the planes of the two guanines lying nearly perpendicular to the coordination plane. These new results indicate that, because there are no local base-base repulsions precluding the LambdaHT conformer, global forces rather than local interactions account for the predominance of the DeltaHT conformer over the LambdaHT conformer in the solid state and in both inter- and intrastrand HT crosslinks of oligonucleotides and DNA. 相似文献