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81.
Bis‐, tris‐, and tetrakis‐trimethylgermylpropanoyl esters of p‐tert‐butylcalix[4]arenes 5, 7 , and 8 were synthesized and their conformations in solution were determined by 1H and 13C NMR spectroscopy. The characteristic pair of doublets from the Ar CH2 Ar methylene protons was observed, indicating that all the prepared calixarenes were in the cone conformation. These germylated calixarenes failed to exhibit any appreciable cation‐capturing ability, indicating that further modification is required to make these compounds to be effective ditopic hosts. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:365–373, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10164 相似文献
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85.
Fukuji Higashi Kiyoshi Mitani 《Journal of polymer science. Part A, Polymer chemistry》2000,38(8):1270-1276
A novel synthetic method for the preparation of copolyesters comprised of diols and bisphenols using tosyl chloride (TsCl)/DMF/pyridine (Py) as a condensing agent has been developed. A variety of combinations of monomers could produce relatively high molecular weight copolymers, and better results were obtained by initial oligomerization of diols followed by bisphenols. In order to demonstrate usefulness of this method, copolymers comprised of IPA/TPA (50/50), bis(2‐hydroxyethyl)terephthalate (BHET),and several bisphenols were prepared and compared to the poly(ethylene terephthalate) (PET) modified by TPA and 2,2‐bis(4‐hydroxyphenyl)propane (BPA) diacetate in terms of their thermal properties. The length of mesogenic unit segments in the thermotropic IPA/TPA (50/50)‐BHET/ 4,4′‐dihydroxybenzophenone (4,4′‐DHBP) (50/50) copolymer was changed by initial reaction of BHET followed by dropwise addition of 4,4′‐DHBP in the two‐stage polycondensation and also by varying the amounts of BHET used at the initial and final stages in the three‐stage copolycondensation, and the results were studied by NMR and their thermal properties. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1270–1276, 2000 相似文献
86.
Ren-Hua Jin Suguru Motokucho Yoshito Andou Tadatomi Nishikubo 《Macromolecular rapid communications》1998,19(1):41-46
Hyperbranched and branched polymers were synthesized by one-pot reaction of the AB2 monomer 4-(4′-chloromethylbenzyloxy)phenylacetonitrile (1 ). The polymerization of 1 was controlled by adding a chloromethylarene (A1 comonomer) such as methoxybenzyl chloride and by adding TBAC (tetrabutylammonium chloride). Copolymerization of 1 with A2 comonomers, bis(chloromethyl)arenes, gives the corresponding copolymers. 相似文献
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Thomas G. Minehan Laura Cook-Blumberg Yoshito Kishi Michle R. Prinsep Richard E. Moore 《Angewandte Chemie (International ed. in English)》1999,38(7):926-928
Four monocyclic precursors were assembled in the total synthesis of the proposed structure 1 - A of (+)-tolyporphin A O,O-diacetate (X=Ac). Comparison of the spectroscopic data demonstrated that synthetic tolyporphin O,O-diacetate did not match the O,O-diacetate prepared from natural (+)-tolyporphin A (X=H), calling for a structural revision of this class of natural products. On the basis of a series of NMR experiments including synthetic intermediates, the structure of tolyporphin A is concluded to be 1 - B , in which the configurations of quaternary centers C7 and C17 are opposite to those in the originally proposed structure. 相似文献
89.
We report the basis set dependencies and the basis set superposition errors for the hydrated complexes of K+ and Na+ ions in relation to the recent studies of the KcsA potassium channel. The basis set superposition errors are estimated by the geometry optimizations at the counterpoise-corrected B3LYP level. The counterpoise optimizations alter the hydration distances by about 0.02–0.03 Å. The enthalpies and free energies for K+ + n(H2O) → [K(H2O)n]+ and Na+ + n(H2O) → [Na(H2O)n]+ (n = 1–6) are compared between the theoretical and experimental values. The results show that the addition of diffuse functions to K, Na, and O species are effective. However, it is also found that the counterpoise corrections using diffuse functions work so as to underestimate the free energies for the complexes with increasing the hydration number. The stabilization energies in aqueous solution are larger for a Na+ ion than for a K+ ion, suggesting the contributions of their dehydration processes to the ion selectivity of the KcsA potassium channel. The changes in coordination distance between the isolated [K(H2O)8]+ and the [K(H2O)8]+ in the KcsA potassium channel indicate the importance of hydrogen bondings between the first hydration shell and the outer hydration shells. 相似文献
90.
Integration of knowledge on the sequence-structure correlation of proteins provides a basis for the structural design of artificial
novel proteins. As one of strategies, it is effective to consider a short segment, whose size is in between an amino acid
and a domain, as a correlation unit for exploring the structure-to-sequence relationship. Here we report the development of
a database called ProSeg, which consists of two sub-databases, Segment DB and Cluster DB. Segment DB contains tens of thousands of segments that were
prepared by dividing the primary sequences of 370 proteins using a sliding L-residue window (L = 5, 9, 11, 15). These segments were classified into several thousands of clusters according to their three-dimensional structural
resemblance. Cluster DB contains much cluster-related information, which includes image, rank, frequency, secondary structure
assignment, sequence profile, etc. Users can search for a suitable cluster by inputting an appropriate parameter (i.e., PDB
ID, dihedral angles, or DSSP symbols), which identifies the backbone structure of a query segment. Analogous to a language,
ProSeg could be regarded as a ‘structure-sequence dictionary’ that contains over 10,000 ‘protein words’. ProSeg is freely accessible through the Internet (). 相似文献