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901.
Nobuo Tanaka Hisashi Nagayama Hiroshi Kobayashi Tohru Ikegami Ken Hosoya Norio Ishizuka Hiroyoshi Minakuchi Kazuki Nakanishi Karin Cabrera Dieter Lubda 《Journal of separation science》2000,23(1):111-116
Two types of monolithic silica columns derivatized to form an ODS phase, one prepared in a fused silica capillary (SR‐FS) and the other prepared in a mold and clad with an engineering plastic (poly‐ether‐ether‐ketone) (SR‐PEEK), were evaluated. The column efficiency and pressure drop were compared with those of a column packed with 5‐μm ODS‐silica particles and of an ODS‐silica monolith prepared in a mold and wrapped with PTFE tubing (SR‐PTFE). SR‐FS gave a lower pressure drop than a column packed with 5‐μm particles by a factor of 20, and a plate height of 20 μm at a linear velocity below 1 mm/s. SR‐PEEK showed higher flow‐resistance than the other monolithic silica columns, but they still showed a minimum plate height of 8–10 μm and a lower pressure drop than popular commercial columns packed with 5‐μm particles. The evaluation of SR‐FS columns in a CEC mode showed much higher efficiency than in a pressure‐driven mode. 相似文献
902.
The polarity of poly(ethylene oxide) (PEO) oligomers and PEO/salt mixed system was analyzed as the negative solvatochromism and halochromism of betaine dye, 2,6-diphenyl-4-(2,4,6-triphenylpyridinio) phenolate ( 1 ). The polarity of PEO oligomers, detected as the shift of the absorption maximum of the dye ( 1 ), decreased with increasing PEO chain length, reflecting the terminal hydroxyl group fraction. The polarity of the PEO matrix was the function of both lattice energy and cation radius of the added salt under the same salt concentration. There is a clear relation between the absorption maximum and the lattice energy of a series of salts having the same cation. The lattice energy of most salts was suggested to be estimated empirically by this relation. 相似文献
903.
Tadao Shibutani Hisashi Fujihara Naomichi Furukawa Shigeru Oae 《Heteroatom Chemistry》1991,2(5):521-531
Aryl 3- and 4-pyridyl sulfoxides undergo ligand exchange in reactions with aryl Grignard reagents to generate 3- and 4-pyridyl Grignard reagents, which, upon treatment with aldehydes or ketones, give the corresponding addition products in moderate-to-good yields. The mechanism for the exchange reaction was investigated by treating optically active 3- and 4-pyridyl p-tolyl sulfoxides with a phenyl Grignard reagent. Inversion of the configuration of the sulfur atom was the stereochemical result of the reactions. In the reactions of phenyl 2-pyridyl sulfoxide with Grignard reagents, the leaving ability of the 2-pyridyl group competes with that of the phenyl group. Both the experimental and MO calculated enthalpy values for deprotonation of α-, β-, and γ-protons of pyridine in the gas phase [1] are in accordance with the following order of the leaving abilities of aryl and pyridyl Grignard reagents: 4-PyMgBr > 3-PyMgBr » PhMgBr > p-TolMgBr > 2-PyMgBr. 相似文献
904.
Daiki Fukuhara Masataka Yamauchi Satoru G. Itoh Hisashi Okumura 《Journal of computational chemistry》2023,44(4):534-545
In the replica-permutation method, an advanced version of the replica-exchange method, all combinations of replicas and parameters are considered for parameter permutation, and a list of all the combinations is prepared. Here, we report that the temperature transition probability depends on how the list is created, especially in replica permutation with solute tempering (RPST). We found that the transition probabilities decrease at large replica indices when the combinations are sequentially assigned to the state labels as in the originally proposed list. To solve this problem, we propose to modify the list by randomly assigning the combinations to the state labels. We performed molecular dynamics simulations of amyloid-β(16–22) peptides using RPST with the “randomly assigned” list (RPST-RA) and RPST with the “sequentially assigned” list (RPST-SA). The results show the decreases in the transition probabilities in RPST-SA are eliminated, and the sampling efficiency is improved in RPST-RA. 相似文献
905.
906.
907.
Akinori Takasu Terumi Niwa Hisashi Itou Yoshihito Inai Tadamichi Hirabayashi 《Macromolecular rapid communications》2000,21(11):764-769
A new procedure for chemical modification of poly(vinyl alcohol) (PVA) was established by a glycosidation reaction of hydroxyl groups in PVA with triacetylated sugar oxazoline 1 . 1H and 13C NMR analyses indicated that triacetylated N‐acetyl‐D‐glucosamine (GlcNAc) was introduced onto a PVA backbone selectively via a β‐O‐glycoside linkage. Deacetylation of triacetylated GlcNAc‐substituted PVA 2 resulted in GlcNAc‐substituted PVA 3 in good yield. These modified PVAs 2 and 3 exhibited solubilities and thermal properties different from the original PVA. 相似文献
908.