全文获取类型
收费全文 | 2153篇 |
免费 | 80篇 |
国内免费 | 22篇 |
专业分类
化学 | 1394篇 |
晶体学 | 14篇 |
力学 | 78篇 |
数学 | 423篇 |
物理学 | 346篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 45篇 |
2021年 | 45篇 |
2020年 | 53篇 |
2019年 | 58篇 |
2018年 | 57篇 |
2017年 | 40篇 |
2016年 | 76篇 |
2015年 | 76篇 |
2014年 | 93篇 |
2013年 | 143篇 |
2012年 | 169篇 |
2011年 | 234篇 |
2010年 | 113篇 |
2009年 | 100篇 |
2008年 | 152篇 |
2007年 | 126篇 |
2006年 | 131篇 |
2005年 | 104篇 |
2004年 | 91篇 |
2003年 | 76篇 |
2002年 | 53篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 10篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1961年 | 3篇 |
1942年 | 6篇 |
1940年 | 3篇 |
1926年 | 1篇 |
排序方式: 共有2255条查询结果,搜索用时 15 毫秒
991.
David Ropartz Alexandre Giuliani Mathieu Fanuel Cécile Hervé Mirjam Czjzek Hélène Rogniaux 《Analytica chimica acta》2016
The activation of ions by extreme-energy photons (XUV) produced by a synchrotron radiation beamline is a powerful method for characterizing complex glycans using tandem mass spectrometry (MS). As previously described, this activation method leads to rich fragmentation spectra with many structurally valuable cross-ring cleavages while maintaining labile modifications on the glycan structures. However, until now, the tandem MS event was too long to be compatible with liquid chromatography elution times. In this work, the duty cycle of the activation and detection of fragments was shortened, and the background signal on the spectra was drastically reduced. Both improvements allowed, for the first time, the successful coupling of a UHPLC system to XUV-activated tandem MS. The approach was used to characterize a complex mixture of oligo-porphyrans, which are a class of highly sulfated oligosaccharides, in a fully automated way. Due to an enhanced dynamic range and an increased sensitivity, some hypothetical structures of low abundance have been unequivocally confirmed in this study and others have been revised. Some previously undescribed species of oligo-porphyrans that exhibit lateral branching have been fully resolved. This work contributes to the scarce knowledge of the structure of porphyrans in red algae and pushes the current capacities of XUV-activation tandem MS by demonstrating the possibility of a direct coupling with UHPLC. This study will considerably broaden the applicability and practicality of this method in many fields of analytical biology. 相似文献
992.
993.
The thermolysis curves of barbituric acid and some of its derivatives have been determined. Barbituric acid, violuric acid and dilituric acid form hydrates while 1,3-dimethylvioluric acid and barbital are anhydrous. Barbital and 1,3-dimethylvioluric acid sublime before decomposition. The differential thermal analysis for dilituric acid showed a sharp exotherm at 190° indicating a violent explosion. 相似文献
994.
995.
We study some special almost complex structures on strictly pseudoconvex domains in ℝ2
n
. They appear naturally as limits under a nonisotropic scaling procedure and play a role of model objects in the geometry
of almost complex manifolds with boundary. We determine explicitely some geometric invariants of these model structures and
derive necessary and sufficient conditions for their integrability. As applications we prove a boundary extension and a compactness
principle for some elliptic diffeomorphisms between relatively compact domains. 相似文献
996.
Katia NN Lecointre A Regueiro-Figueroa M Platas-Iglesias C Charbonnière LJ 《Inorganic chemistry》2011,50(5):1689-1697
The synthesis of ligand L(P)H(8), based on a 2,6-bispyrazolyl-pyridine scaffold functionalized by iminobismethylenephosphonate functions, is described and its pK values were determined by a combination of pH-spectrophotometric titrations and potentiometry. The interaction of L(P) with Tb(3+) was investigated in water (0.01 M TRIS/HCl pH = 7.0) by means of UV-vis and fluorescence titration experiments and evidenced the formation of at least three species with 1:1; 1:2, and 2:1 M-L ratios, the 1:1 complex appearing as particularly stable under these conditions (log K(cond) > 8). Na(4)[LnL(P)H] complexes (Ln = Eu and Tb) were prepared and characterized by elemental analysis, IR spectroscopy, and electrospray mass spectrometry. Their photophysical properties were investigated in aqueous solutions, revealing an excellent shielding of the Ln cations from the solvent environment (no water molecules in the first coordination sphere), very long luminescence lifetimes (τ(H(2)(O)) = 1.50 and 3.28 ms, respectively, for Eu and Tb) and reasonable luminescent quantum yields (?(H(2)(O)) = 2.4 and 37%, respectively, for Eu and Tb). Using fetal bovine serum as a model for biological media showed the Tb complex to remain luminescent in these conditions. The structure of the europium complex was studied by means of density functional theory (DFT) modeling, confirming the wrapping of the ligand around the cation, and the very good shielding of the coordinated Ln cation. The conditional stability constant for the formation of the Tb complex with L(P) was determined by competition experiments with EDTA and monitored by fluorescence spectroscopy (log K(TbL(P)cond) = 14.1 ± 0.3, 0.01 M TRIS/HCl, pH = 7.4) and was used to determine the thermodynamic constant (log K(TbL(P)) = 20.4 ± 0.4). A systematic comparison with ligand L(C), in which phosphonate functions are replaced by carboxylate ones, is made throughout the study, highlighting the large interest of the introduction of phosphonate moieties to obtain biologically stable luminescent lanthanide complexes. 相似文献
997.
An unprecedented intramolecular Petasis condensation provides a novel approach to biologically important conduramines. The compounds are produced with an exclusive anti stereoselectivity for the newly created β-amino alcohol motif. The stereochemical outcome of the reaction is opposite to the one usually observed in the intermolecular reaction. 相似文献
998.
Vergote T Nahra F Welle A Luhmer M Wouters J Mager N Riant O Leyssens T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(3):793-798
To be or not to bifluoride: Two synthetic pathways to unprecedented N-heterocyclic carbene copper(I) bifluoride complexes have been developed. Catalytic tests demonstrated that copper(I) bifluorides are very efficient catalysts, which do not require any additional activating agent. The first Cu-catalyzed diastereoselective allylation of (R)-N-tert-butanesulfinyl aldimines was also established. The method enables efficient, simple and general synthesis of enantiomerically enriched homoallylic amines at room temperature in high yields. 相似文献
999.
Andr B. Charette Alexandre Gagnon Francine Blanger‐Garipy 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):538-540
The title compound, [Mg2Br2(C14H14NO)2(C4H8O)4]·2C7H8, has been crystallized as a C2‐symmetric dimer and the Mg atom has a distorted octahedral geometry. The metal is chelated by the N atom of the ketiminate and the O atom of the ether moiety, giving a rigid structure. 相似文献
1000.
Arthur J. Schultz Brian N. Figgis Alexandre N. Sobolev 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):1289-1291
The crystal structure of Na2Fe(CN)5(NO)·2D2O, disodium pentacyanonitrosylferrate(III) bis(dideuterium oxide), has been determined by X‐ray diffraction at 11 and 293 K, and by neutron diffraction at 15 K. The accurate and extensive data sets lead to more precise determinations than are available from earlier work. The agreement in atomic positional and displacement parameters between the determinations at low temperature is very good. 相似文献