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91.
Dr. Koichi Nagata Takahiro Murosaki Prof. Dr. Tomohiro Agou Prof. Dr. Takahiro Sasamori Prof. Dr. Tsukasa Matsuo Prof. Dr. Norihiro Tokitoh 《Angewandte Chemie (International ed. in English)》2016,55(41):12877-12880
Activation of dihydrogen by masked dialumenes (Al=Al doubly bonded species) is reported. Reactions of barrelene‐type dialumanes, which have the reactivity as masked equivalents of 1,2‐diaryldialumenes ArAl=AlAr, with H2 afforded dihydroalumanes ArAlH2 at room temperature (Ar: bulky aryl groups). These dihydroalumanes form hydrogen‐bridged dimers [ArHAl(μ‐H)]2 in the crystalline state, while a monomer–dimer equilibrium was suggested in solution. The 1,2‐diaryldialumenes generated from the barrelene‐type dialumanes are the putative active species in the cleavage of H2. 相似文献
92.
High‐Density Liquid‐Crystalline Polymer Brushes Formed by Surface Segregation and Self‐Assembly 下载免费PDF全文
Koji Mukai Dr. Mitsuo Hara Prof. Shusaku Nagano Prof. Takahiro Seki 《Angewandte Chemie (International ed. in English)》2016,55(45):14028-14032
High‐density polymer brushes on substrates exhibit unique properties and functions stemming from the extended conformations due to the surface constraint. To date, such chain organizations have been mostly attained by synthetic strategies of surface‐initiated living polymerization. We show herein a new method to prepare a high‐density polymer brush architecture using surface segregation and self‐assembly of diblock copolymers containing a side‐chain liquid‐crystalline polymer (SCLCP). The surface segregation is attained from a film of an amorphous base polymer (polystyrene, PS) containing a minor amount of a SCLCP‐PS diblock copolymer upon annealing above the glass‐transition temperature. The polystyrene portion of the diblock copolymer can work as a laterally mobile anchor for the favorable self‐assembly on the polystyrene base film. 相似文献
93.
Iwasaki Y Matsui R Suzuki T Nakazaki A Kobayashi S 《Chemical & pharmaceutical bulletin》2011,59(4):522-524
We have developed a high-yielding and stereoselective vinylogous Mukaiyama aldol reaction (VMAR) of α-haloenals. Contrary to the simple α,β-unsaturated aldehyde, α-haloenals were found to be reactive affording the corresponding VMAR adducts in excellent yields. Some transformations of VMAR adducts by Pd-mediated cross-coupling were also examined in order to demonstrate the synthetic utility of VMAR of α-haloenals. 相似文献
94.
Imada Y Iida H Kitagawa T Naota T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(21):5908-5920
A versatile reducing agent, diimide, can be generated efficiently by the aerobic oxidation of hydrazine with neutral and cationic synthetic flavin catalysts 1 and 2. This technique provides a convenient and safe method for the aerobic reduction of olefins, which proceeds with 1 equiv of hydrazine under an atmosphere of O(2) or air. The synthetic advantage over the conventional gas-based method has been illustrated through high hydrazine efficiency, easy and safe handling, and characteristic chemoselectivity. Vitamin B(2) derivative 6 acts as a highly practical, robust catalyst for this purpose because of its high availability and recyclability. Association complexes of 1b with dendritic 2,5-bis(acylamino)pyridine 15 exhibit unprecedented catalytic activities, with the reduction of aromatic and hydroxy olefins proceeding significantly faster when a higher-generation dendrimer is used as a host pair for the association catalysts. Contrasting retardation is observed upon similar treatment of non-aromatic or non-hydroxy olefins with the dendrimer catalysts. Control experiments and kinetic studies revealed that these catalytic reactions include two independent, anaerobic and aerobic, processes for the generation of diimide from hydrazine. Positive and negative dendrimer effects on the catalytic reactions have been ascribed to the specific inclusion of hydrazine and olefinic substrates into the enzyme-like reaction cavities of the association complex catalysts. 相似文献
95.
Yoshinari Sawama Takahiro Imanishi Ryosuke NakataniYuta Fujiwara Yasunari MonguchiHironao Sajiki 《Tetrahedron》2014
While gem-dichloromethyl groups can be directly synthesized by the mono-dechlorination of the corresponding trichloromethyl groups, the suppression control of the over-reduction to form chloromethyl or methyl functionalities is quite difficult. We have established the efficient and widely applicable mono-dechlorination method of the trichloromethyl groups to form the corresponding gem-dichloromethyl groups using platinum on carbon in dimethylacetamide as a specific solvent at 25 °C under a hydrogen atmosphere. The mono-dechlorination of the α,α,α-trichloromethylcarbonyl groups smoothly proceeded by the use of platinum on carbon as a catalyst in a highly chemoselective manner, while the efficient mono-dechlorination of the alkyl- and aryl-trichloromethyl groups required the combined use of Bu3SnH. 相似文献
96.
Tubiferal A, a triterpenoid isolated from myxomycete Tubifera dimorphotheca, exhibits a reversal effect of vincristine (VCR) resistance against VCR-resistant KB cell lines. The compound possesses a complex structure involving the 6-7-6-5 polycyclic carbon framework with various functional groups. The stereoselective synthesis of the right-hand segment of tubiferal A was achieved on the basis of the cyclopentene annulation method and the semi-pinacol rearrangement reaction of an epoxy alcohol for constructing the trans-fused 6-5 bicyclic skeleton possessing two quaternary carbon atoms at the angular positions. 相似文献
97.
A diphenylanthracene-based diamidine (1a) fluorescent probe for the detection of dicarboxylic acids has been designed and synthesized, which has an extended π-conjugation rather than a simple anthracene ring, in order to observe highly different fluorescence wavelengths after complex formation with dicarboxylic acids. The fluorescence spectra of the mixed solution of the diamidine 1a and carboxylic acids showed two different fluorescence bands, which corresponded to the complex formation (amidinium-carboxylate formation, λem?=?450?nm, light blue color) and dissociated amidinium formation (λem?=?510?nm as a broad band, green color). The complexed and dissociated states were confirmed by DOSY NMR and TD-DFT calculations. These different fluorescence wavelengths may come from the differences in the dihedral angles between the phenyl rings at the 1,8-position and anthracene ring (difference in π-conjugation) of 1a under complex formation and dissociated amidinium formation. The proposed mechanism for the observation of the different fluorescence wavelengths (complex formation and amidinium formation) was also confirmed by the fluorescence study of diamidine 1b which causes restricted rotation of the phenyl rings by substitution of the steric methyl groups, and observed the same fluorescence spectra for the complex formation and amidinium formation (400, 420, 450?nm as a vibrational structure of anthracene ring). These fluorescence characteristics of the diamidine 1a are also applicable for the detection of α,ω?dicarboxylic acids. 相似文献
98.
Yasuo Saegusa Takahiro Kato Hirotaka Oshiumi Shigeo Nakamura 《Journal of polymer science. Part A, Polymer chemistry》1992,30(7):1401-1406
Novel polyaryloxydiphenylsilanes with reduced viscosities of 0.31–0.65 dL/g were obtained by the melt polycondensation of dianilinodiphenylsilane with three bisphenols, 2,2-bis (4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane, 3 (4-hydroxyphenyl)-1,1,3-trimethyl-5-indanol, and 9,9-bis (4-hydroxyphenyl) fluorene, at 200–320°C in vacuo. These polymers are all amorphous and readily soluble in a wide variety of organic solvents such as chlorinated and aromatic hydrocarbons, cyclic ethers, and polar aprotic solvents. Because of their bulky and/or rigid ring structures, polyaryloxydiphenylsilanes containing diphenylhexafluoropropane, phenylindane, and diphenylfluorene units in the main chain have high glass transition temperatures of 106, 112, and 172°C, respectively. They are thermally stable showing almost no weight loss up to 350°C in air. Colorless, transparent, but brittle films are obtained from these polymers by solution casting. Ultraviolet transmission is sharply cut off by these polyaryloxydiphenylsilane films at ca. 300 nm, and the cut-off wavelength depends on the bisphenols used. 相似文献
99.
Takahiro Hosokawa Takanori Kono Toru Shinohara Shun-Ichi Murahashi 《Journal of organometallic chemistry》1989,370(1-3):C13-C16
The oxidative cyclization of 2-(3-pentenyl)phenol catalyzed by [(η3-pinene)PdOAc]2 gives optically active (+)-2-vinylchroman (25% e.e.), while (−)-2-(1-hydroxyethyl)chroman (56% e.e.) is formed as a single diastereomer upon treatment with t-BuOOH in the presence of Ti(OiPr)4 and
-(+)-diethyl tartrate. 2-(2-Butenyl)phenol also undergoes the Ti-promoted asymmetric cyclization to give (2S,1′R)-(−)-2-(1-hydroxyethyl)-2,3-dihydrobenzofuran (29% e.e.). 相似文献
100.
Chiral‐Substrate‐Assisted Stereoselective Epoxidation Catalyzed by H2O2‐Dependent Cytochrome P450SPα
Dr. Takashi Fujishiro Dr. Osami Shoji Dr. Norifumi Kawakami Takahiro Watanabe Dr. Hiroshi Sugimoto Dr. Yoshitsugu Shiro Prof. Dr. Yoshihito Watanabe 《化学:亚洲杂志》2012,7(10):2286-2293
The stereoselective epoxidation of styrene was catalyzed by H2O2‐dependent cytochrome P450SPα in the presence of carboxylic acids as decoy molecules. The stereoselectivity of styrene oxide could be altered by the nature of the decoy molecules. In particular, the chirality at the α‐positions of the decoy molecules induced a clear difference in the chirality of the product: (R)‐ibuprofen enhanced the formation of (S)‐styrene oxide, whereas (S)‐ibuprofen preferentially afforded (R)‐styrene oxide. The crystal structure of an (R)‐ibuprofen‐bound cytochrome P450SPα (resolution 1.9 Å) revealed that the carboxylate group of (R)‐ibuprofen served as an acid–base catalyst to initiate the epoxidation. A docking simulation of the binding of styrene in the active site of the (R)‐ibuprofen‐bound form suggested that the orientation of the vinyl group of styrene in the active site agreed with the formation of (S)‐styrene oxide. 相似文献