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91.
A selection of amino-substituted 1,1,2,2,9,9,10,10 octafluoro[2.2]paracyclophanes were tested for enantiodiscrimination by 1H and 19F NMR spectroscopy via their interaction with different lanthanide tris β-diketonate chiral shift reagents. The amino-, and the pseudo-ortho di-amino substituted octafluoro[2.2]paracyclophanes, both of which exhibit planar chirality, revealed significant shifts and splittings of various 1H and 19F NMR signals upon the addition of the chiral shift reagents, which allowed the easy determination of the enantiomeric purity. When the chiral shift reagent was added to an inseparable mixture of the (chiral) pseudo-meta, and (achiral) pseudo-para diamino analogues, both the chiral and achiral molecules revealed NMR doubling. In the case of the achiral molecule, this NMR behavior is due to the meso nature of the pseudo-para species. 相似文献
92.
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
93.
Alex H. F. Lee Jian Chen Albert S. C. Chan Tianhu Li 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):1163-1174
5-(7-Hydroxyheptyl)-1,2-dithiolan-3-one 1-oxide was designed and synthesized in our laboratories that contain the heterocycle of 1,2-dithiolan-3-one 1-oxide, a reactive core of antibiotic leinamycin. In addition, the activated ester of 5-(7-hydroxyheptyl)-1,2-dithiolan-3-one 1-oxide was prepared, which presumably is useful for coupling this DNA-cleaving functionality to certain DNA-binding agents. 相似文献
94.
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96.
árpád Somogyi Alex G. Harrison Béla Paizs 《Journal of the American Society for Mass Spectrometry》2012,23(12):2055-2058
Middle-sized b n (n????5) fragments of protonated peptides undergo selective complex formation with ammonia under experimental conditions typically used to probe hydrogen?Cdeuterium exchange in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Other usual peptide fragments like y, a, a*, etc., and small b n (n????4) fragments do not form stable ammonia adducts. We propose that complex formation of b n ions with ammonia is characteristic to macrocyclic isomers of these fragments. Experiments on a protonated cyclic peptide and N-terminal acetylated peptides fully support this hypothesis; the protonated cyclic peptide does form ammonia adducts while linear b n ions of acetylated peptides do not undergo complexation. Density functional theory (DFT) calculations on the proton-bound dimers of all-Ala b 4 , b 5 , and b 7 ions and ammonia indicate that the ionizing proton initially located on the peptide fragment transfers to ammonia upon adduct formation. The ammonium ion is then solvated by N+-H??O H-bonds; this stabilization is much stronger for macrocyclic b n isomers due to the stable cage-like structure formed and entropy effects. The present study demonstrates that gas-phase guest?Chost chemistry can be used to selectively probe structural features (i.e., macrocyclic or linear) of fragments of protonated peptides. Stable ammonia adducts of b 9 , b 9 -A, and b 9 -2A of A8YA, and b 13 of A20YVFL are observed indicating that even these large b-type ions form macrocyclic structures. 相似文献
97.
Sean Ekins Alex M. Clark S. Joshua Swamidass Nadia Litterman Antony J. Williams 《Journal of computer-aided molecular design》2014,28(10):997-1008
Over the past decade we have seen a growth in the provision of chemistry data and cheminformatics tools as either free websites or software as a service commercial offerings. These have transformed how we find molecule-related data and use such tools in our research. There have also been efforts to improve collaboration between researchers either openly or through secure transactions using commercial tools. A major challenge in the future will be how such databases and software approaches handle larger amounts of data as it accumulates from high throughput screening and enables the user to draw insights, enable predictions and move projects forward. We now discuss how information from some drug discovery datasets can be made more accessible and how privacy of data should not overwhelm the desire to share it at an appropriate time with collaborators. We also discuss additional software tools that could be made available and provide our thoughts on the future of predictive drug discovery in this age of big data. We use some examples from our own research on neglected diseases, collaborations, mobile apps and algorithm development to illustrate these ideas. 相似文献
98.
The Newton radius of a code is the largest weight of a uniquely correctable error. We establish a lower bound for the Newton radius in terms of the rate. In particular we show that in any family of linear codes of rate below one half, the Newton radius increases linearly with the codeword length. 相似文献
99.
100.
Monique A. Mballa Mballa Johan P. A. Heuts Alex M. van Herk 《Colloid and polymer science》2013,291(6):1419-1427
The effect of montmorrilonite clay (MMT) platelets on the morphology of polystyrene/poly(methyl methacrylate) (PMMA) composite latex particles prepared via PMMA-seeded (semi-) batch emulsion polymerization of styrene was studied. It was found that the particle morphology obtained greatly depended on the ability of the clay platelets to diffuse through the polymer particle. Indeed, when the reactions were strictly under kinetic control, i.e., where the clay platelets were unable to diffuse during polymerization, anisotropic core-shell-like morphologies with split core were observed. A better mobility of the clay platelets could more or less restrict the diffusion of the second-stage polymers within the host polymer, leading to original kinetically controlled morphologies. In the case of a full migration of the clay platelets to the particle surface, the penetration of the second-stage polymer species in the seed latex was found to be more limited, enhancing the formation of secondary particles. 相似文献