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991.
Kohji Tashiro Kazuhiro Takeuchi Yasuaki Ohta Makoto Hanesaka Tomoko Hashida Yayoi Yoshioka Chellaswami Ramesh 《Macromolecular Symposia》2006,242(1):250-256
Structural changes occurring in the high temperature region of doubly-oriented nylon 10/10 sample have been investigated through the temperature-dependent simultaneous measurements of wide-angle and small-angle X-ray scatterings, and the results were compared with the infrared spectral data as well as the molecular dynamics simulation results. In the Brill transition region of 150–180 °C the methylene segments are conformationally disordered with keeping the intermolecular hydrogen bonds. During this phase transition the stacked lamellar structure did not change very much: the lamellae are tilted by ca. 34° from the draw axis and the long period is almost 160 Å. In the temperature region immediately below the melting point the molecular chains were found to be contracted by ca. 10% the original repeating period and the intermolecular hydrogen bonds were almost broken, causing the violent rotational and translational motions of the chains around the chain axis. At the same time the long period increased remarkably from 160 Å to 410 Å and the originally tilted lamellae stood up in parallel to the draw axis. 相似文献
992.
Miyake Masato Takase Kazuya Narato Midori Khatipov Emir Schnackenberg Joerg Shirai Makoto Kurane Ryuichiro Asada Yasuo 《Applied biochemistry and biotechnology》2000,84(1-9):991-1002
Genetic characterization and enhancement of polyhydroxybutyrate (PHB) accumulation in cyanobacteria were investigated for
efficient PHB production from CO2. The genome DNAs in the PHB-accumulating strains Synechococcus sp. MA19 and Spirulina platensis NIES46 retained the highly homologous region to phaC of Synechocystis PCC6803, whereas low homology was detected in the nonaccumulating strains Synechococcus sp. PCC7942 and Anabaenacylindrica NIES19. Synechococcus sp. MA19, which accumulates PHB up to 30% of dry cell weight from CO2 as the sole carbon source, was mutated by insertion of transposon Tn5 to enhance the PHB accumulation. Genetic and physiological
analysis of the mutant indicated that decreased phosphotransacetylase activity could trigger an increase of acetyl coenzyme
A leading to enhancement of PHB accumulation. PHB synthase in Synechococcus sp. MA19 was probably attached to thylakoid membrane since PHB granules were associated with pigments. A genetically engineered
cyanobacteria retaining soluble PHB synthase from Ralstonia eutropha accumulated pigment-free PHB granules, which is an advantage for the purification of PHB. 相似文献
993.
Alexander G. O'Brien Akinobu Maruyama Yasuhide Inokuma Makoto Fujita Phil S. Baran Donna G. Blackmond 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(44):12062-12065
Electrochemical reactions are shown to be effective for the C H functionalization of a number of heterocyclic substrates that are recalcitrant to conventional peroxide radical initiation conditions. Monitoring reaction progress under electrochemical conditions provides mechanistic insight into the C H functionalization of a series of heterocycles of interest in medicinal chemistry. 相似文献
994.
Vera Yu. Mishina Irina V. Abrashina Andrei T. Teleshev Larisa K. Vasyanina Eduard E. Nifant'ev 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2425-2434
Interaction between the equimolecular amounts of glycols (diatomic phenols) and phosphorous acid triamides in diglyme or without solvent gives phosphorus-bearing polyamidophosphites. The structure of these compounds was studied by NMR spectroscopy, and it was shown that a partial disproportionation of amidophosphite fragments into phosphite ones can occur in the course of their synthesis. The chemical properties of the obtained compounds are being studied. First rhodium complexes with polyamidophosphite ligands were obtained. These complexes are shown to be more active hydrogenation catalysts than the corresponding low-molecular complexes. 1 相似文献
995.
996.
Makoto Oba Atsushi Shimabukuro Miyako Ono Mitsunobu Doi Masakazu Tanaka 《Tetrahedron: Asymmetry》2013,24(8):464-467
A method of synthesizing an optically active cyclic methionine analogue, 3-aminotetrahydrothiophene-3-carboxylic acid (At5c), is described. A Bucherer–Bergs reaction of 4,5-dihydro-3(2H)-thiophenone and the subsequent alkaline hydrolysis of a hydantoin, followed by Cbz protection of the amine, afforded racemic Cbz-At5c (±)-3 in excellent yield. Diastereomeric esters derived from Cbz-At5c (±)-3 and (R)-BINOL could be separated by column chromatography to give both diastereomers with >99% de. X-ray crystallographic analysis revealed the absolute configuration of the synthesized amino acid derived from the less polar diastereomeric ester to be (S). 相似文献
997.
Total Synthesis and Complete Stereostructure of a Marine Macrolide Glycoside, (−)‐Lyngbyaloside B 下载免费PDF全文
Prof. Dr. Haruhiko Fuwa Naoya Yamagata Yuta Okuaki Yuya Ogata Asami Saito Prof. Dr. Makoto Sasaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6815-6829
We have described in detail the total synthesis of both the proposed and correct structures of (?)‐lyngbyaloside B, which facilitated the elucidation of the complete stereostructure of this natural product. Our study began with the total synthesis of 13‐demethyllyngbyaloside B, in which an esterification/ring‐closing metathesis (RCM) strategy was successfully used for the efficient construction of the macrocycle. We also established reliable methods for the introduction of the conjugated diene side chain and the l ‐rhamnose residue onto the macrocyclic framework. However, the esterification/RCM strategy proved ineffective for the parent natural product because of the difficulties in acylating the sterically encumbered C‐13 tertiary alcohol; macrolactionization of a seco‐acid was also extensively investigated under various conditions without success. We finally completed the total synthesis of the proposed structure of (?)‐lyngbyaloside B by means of a macrolactonization that involves an acyl ketene as the reactive species. However, the NMR spectroscopic data of our synthetic material did not match those of the authentic material, which indicated that the proposed structure must be re‐examined. Inspection of the NMR spectroscopic data of the natural product and molecular mechanics calculations led us to postulate that the configuration of the C‐10, C‐11, and C‐13 stereogenic centers had been incorrectly assigned in the proposed structure. Finally, our revised structure of (?)‐lyngbyaloside B was unambiguously verified through total synthesis. 相似文献
998.
999.
Coupling Reaction of Enol Derivatives with Silyl Ketene Acetals Catalyzed by Gallium Trihalides 下载免费PDF全文
Dr. Yoshihiro Nishimoto Yuji Kita Hiroki Ueda Hiroto Imaoka Kouji Chiba Prof. Dr. Makoto Yasuda Prof. Dr. Akio Baba 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11837-11845
A cross‐coupling reaction between enol derivatives and silyl ketene acetals catalyzed by GaBr3 took place to give the corresponding α‐alkenyl esters. GaBr3 showed the most effective catalytic ability, whereas other metal salts such as BF3?OEt2, AlCl3, PdCl2, and lanthanide triflates were not effective. Various types of enol ethers and vinyl carboxylates as enol derivatives are amenable to this coupling. The scope of the reaction with silyl ketene acetals was also broad. We successfully observed an alkylgallium intermediate by using NMR spectroscopy, suggesting a mechanism involving anti‐carbogallation among GaBr3, an enol derivative, and a silyl ketene acetal, followed by syn‐β‐alkoxy elimination from the alkylgallium. Based on kinetic studies, the turnover‐limiting step of the reaction using a vinyl ether and a vinyl carboxylate involved syn‐β‐alkoxy elimination and anti‐carbogallation, respectively. Therefore, the leaving group had a significant effect on the progress of the reaction. Theoretical calculations analysis suggest that the moderate Lewis acidity of gallium would contribute to a flexible conformational change of the alkylgallium intermediate and to the cleavage of the carbon?oxygen bond in the β‐alkoxy elimination process, which is the turnover‐limiting step in the reaction between a vinyl ether and a silyl ketene acetal. 相似文献
1000.