全文获取类型
收费全文 | 244篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学 | 186篇 |
晶体学 | 5篇 |
力学 | 6篇 |
数学 | 49篇 |
物理学 | 14篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 10篇 |
2014年 | 12篇 |
2013年 | 21篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 21篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1965年 | 1篇 |
1870年 | 1篇 |
排序方式: 共有260条查询结果,搜索用时 15 毫秒
251.
The reactions 34S(d,p)35S and 36S(d,p)37S were studied at the incident deuteron energy of 12.3 MeV. Proton groups were analysed using a multi-angle magnetic spectrograph with the resolving power . Precise Q-values corresponding to 13 states of 35S up to the excitation energy of 7483 keV and 22 states of 37S up to the excitation energy of 6406 keV are presented. The ground-state transition Q-value for the reaction 36S(d,p)37S was found to be 2079.12 ± 0.13 keV. Angular distributions of proton groups corresponding to 6 states in 35S and to 11 states in 37S were analysed using DWBA calculations. Transferred orbital angular momenta and spectroscopic factors were deduced. Summed spectroscopic strengths show that substantial parts of single-particle strengths for in both reactions are exhausted b observed transitions. 相似文献
252.
Franc Forstneric 《Journal of Geometric Analysis》1999,9(1):93-117
Let n > 1 and let
C
n
denote the complex n-dimensional Euclidean space. We prove several jet-interpolation results for nowhere degenerate entire
mappings F:C
n →C
n
and for holomorphic automorphisms of
C
n
on discrete subsets of
C
n.We also prove an interpolation theorem for proper holomorphic embeddings of Stein manifolds into
C
n.For each closed complex submanifold (or subvariety) M ⊂
C
n
of complex dimension m < n we construct a domain Ω ⊂C
n
containing M and a biholomorphic map F: Ω →
C
n
onto
C
n
with J F ≡ 1such that F(M) intersects the image of any nondegenerate entire map G:C
n−m →C
n
at infinitely many points. If m = n − 1, we construct F as above such that
C
n ∖F(M) is hyperbolic. In particular, for each m ≥ 1we construct proper holomorphic embeddings F:C
m →C
m−1
such that the complement
C
m+1 ∖F(C
m
)is hyperbolic. 相似文献
253.
Franc G Mazères S Turrin CO Vendier L Duhayon C Caminade AM Majoral JP 《The Journal of organic chemistry》2007,72(23):8707-8715
Two series of phosphorus dendrimers functionalized by maleimide derivatives are synthesized, as well as three new monomeric maleimide derivatives, of which two are characterized by X-ray diffraction. The first series of phosphorus dendrimers possesses maleimide derivatives as end groups (6-48, from generation 0 to generation 3). The second series of dendrimers possesses a single copy of the same maleimide derivative linked "off-center" to a cyclotriphosphazene core, leading to dissymmetrical dendrimers; this series is synthesized from generation 0 to generation 2. The fluorescence properties of both series of dendrimers and of monomers are studied, affording new information. First, the presence of labile hydrogen extinguishes the fluorescence. Second, the grafting of the fluorophore(s) directly to the core affords highly fluorescent compounds. Finally, an original influence of the branches possessing phosphorhydrazone linkages toward the fluorescence properties is shown. 相似文献
254.
255.
256.
Dipl.‐Chem. Yasmin Hemberger Dipl.‐Chem. Kevin Pröpper Birger Dittrich Dipl.‐Chem. Franziska Witterauf Dr. Michael John Prof. Dr. Dr. h.c. mult. Gerhard Bringmann Prof. Dr. Christian Brückner Prof. Dr. Franc Meyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(19):5868-5880
The 3+3‐type synthesis of a pyrazole‐based expanded porphyrin 22 H4 , a hexaphyrin analogue named Siamese‐twin porphyrin, and its homobimetallic diamagnetic nickel(II) and paramagnetic copper(II) complexes, 22 Ni2 and 22 Cu2 , are described. The structure of the macrocycle composed of four pyrroles and two pyrazoles all linked by single carbon atoms, can be interpreted as two conjoined porphyrin‐like subunits, with the two opposing pyrazoles acting as the fusion points. Variable‐temperature 1D and 2D NMR spectroscopic analyses suggested a conformationally flexible structure for 22 H4 . NMR and UV/Vis spectroscopic evidence as well as structural parameters proved the macrocycle to be non‐aromatic, though each half of the molecule is fully conjugated. UV/Vis and NMR spectroscopic titrations of the free base macrocycle with acid showed it to be dibasic. In the complexes, each metal ion is coordinated in a square‐planar fashion by a dianionic, porphyrin‐like {N4} binding pocket. The solid‐state structures of the dication and both metal complexes were elucidated by single‐crystal diffractometry. The conformations of the three structures are all similar to each other and strongly twisted, rendering the molecules chiral. The persistent helical twist in the protonated form of the free base and in both metal complexes permitted resolution of these enantiomeric helimers by HPLC on a chiral phase. The absolute stereostructures of 22 H6 2+, 22 Ni2 , and 22 Cu2 were assigned by a combination of experimental electronic circular dichroism (ECD) investigations and quantum‐chemical ECD calculations. The synthesis of the first member of this long‐sought class of expanded porphyrin‐like macrocycles lays the foundation for the study of the interactions of the metal centers within their bimetallic complexes. 相似文献
257.
Anne Bretschneider Dr. Diego M. Andrada Dr. Sebastian Dechert Steffen Meyer Prof. Dr. Ricardo A. Mata Prof. Dr. Franc Meyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):16988-17000
1,3‐Bis(pentafluorophenyl‐imino)isoindoline (AF) and 3,6‐di‐tert‐butyl‐1,8‐bis(pentafluorophenyl)‐9H‐carbazole (BF) have been designed as preorganized anion receptors that exploit anion–π interactions, and their ability to bind chloride and bromide in various solvents has been evaluated. Both receptors AF and BF are neutral but provide a central NH hydrogen bond that directs the halide anion into a preorganized clamp of the two electron‐deficient appended arenes. Crystal structures of host–guest complexes of AF with DMSO, Cl?, or Br? (AF:DMSO, AF:Cl?, and ${{\rm A}{{{\rm F}\hfill \atop 2\hfill}}}$ :Br?) reveal that in all cases the guest is located in the cleft between the perfluorinated flaps, but NMR spectroscopy shows a more complex situation in solution because of E,Z/Z,Z isomerism of the host. In the case of the more rigid receptor BF, Job plots evidence 1:1 complex formation with Cl? and Br?, and association constants up to 960 M ?1 have been determined depending on the solvent. Crystal structures of BF and BF:DMSO visualize the distinct preorganization of the host for anion–π interactions. The reference compounds 1,3‐bis(2‐pyrimidylimino)isoindoline (AN) and 3,6‐di‐tert‐butyl‐1,8‐diphenyl‐9H‐carbazole (BH), which lack the perfluorinated flaps, do not show any indication of anion binding under the same conditions. A detailed computational analysis of the receptors AF and BF and their host–guest complexes with Cl? or Br? was carried out to quantify the interactions in play. Local correlation methods were applied, allowing for a decomposition of the ring–anion interactions. The latter were found to contribute significantly to the stabilization of these complexes (about half of the total energy). Compounds AF and BF represent rare examples of neutral receptors that are well preorganized for exploiting anion–π interactions, and rare examples of receptors for which the individual contributions to the binding energy have been quantified. 相似文献
258.
Sascha Reith Serhiy Demeshko Beatrice Battistella Alexander Reckziegel Christian Schneider Andreas Stoy Crispin Lichtenberg Franc Meyer Dominik Munz C. Gunnar Werncke 《Chemical science》2022,13(26):7907
Imidyl and nitrene metal species play an important role in the N-functionalisation of unreactive C–H bonds as well as the aziridination of olefines. We report on the synthesis of the trigonal imido iron complexes [Fe(NMes)L2]0,− (L = –N{Dipp}SiMe3); Dipp = 2,6-diisopropyl-phenyl; Mes = (2,4,6-trimethylphenyl) via reaction of mesityl azide (MesN3) with the linear iron precursors [FeL2]0,−. UV-vis-, EPR-, 57Fe Mössbauer spectroscopy, magnetometry, and computational methods suggest for the reduced form an electronic structure as a ferromagnetically coupled iron(ii) imidyl radical, whereas oxidation leads to mixed iron(iii) imidyl and electrophilic iron(ii) nitrene character. Reactivity studies show that both complexes are capable of H atom abstraction from C–H bonds. Further, the reduced form [Fe(NMes)L2]− reacts nucleophilically with CS2 by inserting into the imido iron bond, as well as electrophilically with CO under nitrene transfer. The neutral [Fe(NMes)L2] complex shows enhanced electrophilic behavior as evidenced by nitrene transfer to a phosphine, yet in combination with an overall reduced reactivity.A pair of trigonal imido iron complexes ([Fe(NMes)L2]0,−) in two oxidation states is reported. The anionic complex K{crypt.222}[Fe(NMes)L2] is best described as an iron(ii) imide. 相似文献
259.
260.
Dr. Sheida Rajabi Franziska Rüttger Dr. Jana Lücken Dr. Sebastian Dechert Dr. Michael John Prof. Dr. Franc Meyer 《欧洲无机化学杂志》2023,26(3):e202200597
Two mononuclear ruthenium(II) complexes based on dianionic {N4} ligands and with axial pyridines have been prepared and characterized crystallographically ( 1 ) or by 2D NMR spectroscopy using residual dipolar couplings ( 2 ). The {N4} ligands provide a constrained equatorial coordination with one large N−Ru−N angle, and additional non-coordinating N atoms in case of 2 . Their redox properties have been investigated (spectro)electrochemically, and their potential to serve as water oxidation catalysts has been probed using cerium ammonium nitrate (CAN) at pH 1.0. Complex 1 undergoes rapid degradation, likely via ligand oxidation, whereas 2 is more rugged and exhibits 80 % efficiency in the CeIV-driven water oxidation, with a high initial turnover frequency (TOFi) of 3.07×10−2 s−1 (at 100 equiv. CAN). The initial rate of O2 evolution exhibits 1st order dependence on catalyst concentration, suggesting a water nucleophilic attack mechanism. Repeated addition of CAN and control experiments show that high ionic strength conditions (both NO3− and CeIII) significantly decrease the TOF. 相似文献