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991.
The Horner–Wadsworth–Emmons (HWE) reaction has become well established among existing methodologies for the highly stereoselective olefination of carbonyl compounds. The reliability of this reaction in terms of its robustness, high stereoselectivity, and broad substrate scope permit retrosynthetic disconnection of the olefin bond in α,β-unsaturated carbonyl intermediates in natural product synthesis. This review discusses recent applications of the HWE reaction in natural product synthesis, highlighting its use for carbon chain elongation, coupling reactions of synthetic segments, ring-closing reactions, tandem reactions including HWE olefination, and asymmetric reactions. 相似文献
992.
Gangfeng Huang Dr. Tristan Wagner Dr. Ulrich Ermler Dr. Eckhard Bill Dr. Kenichi Ataka Dr. Seigo Shima 《Angewandte Chemie (International ed. in English)》2018,57(18):4917-4920
Mono‐iron hydrogenase ([Fe]‐hydrogenase) reversibly catalyzes the transfer of a hydride ion from H2 to methenyltetrahydromethanopterin (methenyl‐H4MPT+) to form methylene‐H4MPT. Its iron guanylylpyridinol (FeGP) cofactor plays a key role in H2 activation. Evidence is presented for O2 sensitivity of [Fe]‐hydrogenase under turnover conditions in the presence of reducing substrates, methylene‐H4MPT or methenyl‐H4MPT+/H2. Only then, H2O2 is generated, which decomposes the FeGP cofactor; as demonstrated by spectroscopic analyses and the crystal structure of the deactivated enzyme. O2 reduction to H2O2 requires a reductant, which can be a catalytic intermediate transiently formed during the [Fe]‐hydrogenase reaction. The most probable candidate is an iron hydride species; its presence has already been predicted by theoretical studies of the catalytic reaction. The findings support predictions because the same type of reduction reaction is described for ruthenium hydride complexes that hydrogenate polar compounds. 相似文献
993.
The geometrical cell structure of the chemically reacting system is discussed. The boundary of the cell uniquely defines the dividing surface between the initial reactant side and the final product side. Introducing the concept of the intrinsic reaction time (IRT) and the accumulation time (AT) of reaction along the meta-IRC (intrinsic reaction coordinate), the intrinsic dynamism in the cell is discussed. Then, the stable limit theorems with respect to the intrinsic nature of the normal vibrations are derived. The theory is elucidated by using a model potential surface. 相似文献
994.
The distribution ratios of TTA and its scandium chelate between aqueous perchlorate solutions (μ=0.1) and 15 ester solvents including ethyl acetate were determined at 25°. A good correlation was found between the distribution coefficients of TTA and the “solubility parameter” of the ester solvents. The relationship between the distribution coefficients of the scandium chelate (PM) and those of TTA (PHA) was shown to be, log PM=n log PHA+ const. The distribution of this chelate into another ester can thus be predicted. 相似文献
995.
Kazuo Ito Kenichi Yakushijin Shigetaka Yoshina Akira Tanaka Katsumi Yamamoto 《Journal of heterocyclic chemistry》1978,15(2):301-305
2-Methylfuro [2,3-c] isoquinolin-5(4H)one (X) and 1-phenylfuro[2,3-c] isoquinolin-5(4H)one (XI) were prepared from thermal cyelization via the Curtius rearrangement of 5-methyl-3-phenyl-2-furoyl azide (VI) and 3,4-diphenyl-2-furoyl azide (VII), respectively. Stability against acid, alkylation and conversion of the NHCO group to a C=N double bond of X and XI, which were synthesized, are described. Also, 5-substituted furo[2,3-c] isoquinolines (XVIIIa-c) and (XIXa-c) were prepared. 相似文献
996.
997.
Yasuo Horiuchi Yoshio Nishi Noburu Sokabe Akira Murai 《International Journal of Infrared and Millimeter Waves》1985,6(9):929-946
Sixty and three absorption transitions in D2CO and H2CO, respectively, have produced a number of far infrared laser lines when they are pumped by an etalon-tuned TE-CO2 laser. Almost all the absorption transitions pumped previously by a free runing TE-CO2 laser have been efficiently pumped by the etalon tuned CO2 laser and found to have offset within ±500 MHz from the line-center of the relevant CO2 pump lines. 22 (1) absorption and 63 (4) emission lines of D2CO (H2CO) are assigned. Some of these lines have generated superfluorescence. In paticular, the D2CO 319-m line pumped by CO2-9P(32) delivered an output energy of approximately one half that of the well-known D2O 66-m. It is shown that a large electric dipole moment and an appreciable amount of fractional population in the lower level of the pump transition of this line are responsible to the superfluorescence. 相似文献
998.
Aoyagi N Rimando AP Izutsu K Katori N Kojima S 《Chemical & pharmaceutical bulletin》2003,51(9):1021-1024
All sugar-coated tablets of chlorpromazine hydrochloride except for those produced by one manufacture showed concave dissolution profiles in water by paddle method at 100 rpm but not at 50 rpm. The study was undertaken to clarify the agitation-dependent abnormal dissolutions. The strange dissolutions were also observed in water at different ionic strengths but not in buffer solutions of pH 1.2, 4.0 and 6.8. When monitored, the pH's of water in dissolution vessels for the abnormal tablets increased with time at 100 rpm and some of them exceeded pH 8 but did not at 50 rpm. The solubility of chlorpromazine hydrochloride decreased with the increase of pH which was too low to dissolve the whole amount of drug contained in a tablet at pH 8. The elevation of pH seemed to be mainly brought about by dissolution of calcium carbonate popularly used for sugar-coated tablets, because larger amount of calcium ion was dissolved out from the abnormal tablets at 100 rpm than from a normal tablet and from them at 50 rpm. These findings indicate that the concave dissolution profiles should be caused by the decrease of drug solubility with increase in pH of water, probably because of dissolution of calcium carbonate. We should pay attention to the change in pH of water which may differ depending on the agitation speed of dissolution tests. 相似文献
999.
Birgit?Heying Ute?Ch. Rodewald Rainer?P?ttgenEmail author Kenichi?Katoh Yuzuru?Niide Akira?Ochiai 《Monatshefte für Chemie / Chemical Monthly》2005,136(5):655-661
Summary. The equiatomic ytterbium–transition metal–germanides YbCuGe and YbIrGe were synthesized in single crystalline form from CuGe and IrGe master alloys and ytterbium via the Bridgman technique and they were characterized through their X-ray powder patterns. The structures were refined from X-ray single crystal diffractometer data: NdPtSb type, P63mc, a=421.36(8), c=703.9(1) pm, wR2=0.0234, 210 F2 values, 11 variable parameters, BASF=0.35(9) for YbCuGe and TiNiSi type, Pnma, a=671.09(6), b=421.55(5), c=757.16(7) pm, wR2=0.0782, 519 F2 values, 20 variable parameters for YbIrGe. The copper (iridium) and germanium atoms build up [CuGe] and [IrGe] networks. In YbCuGe the two-dimensional [CuGe] network consists of puckered layers of Cu3Ge3 hexagons (247pm Cu–Ge) that are charge balanced and separated by the ytterbium atoms. In contrast, the ordered Ir3Ge3 hexagons show a strong orthorhombic distortion and the [IrGe] network is three-dimensional with a distorted tetrahedral germanium coordination around iridium with almost equal Ir–Ge distances (252–259pm). The ytterbium atoms fill cages within this network. The cell volumes of YbCuGe and YbIrGe are indicative for purely trivalent ytterbium. 相似文献
1000.
Y. Nakano S. Murai R. Kani S. Hayase 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3361-3370
Polysilylenes with a phenol group directly bonded to the main chain Si atom were prepared by polymerizing dichlorosilane monomers bearing phenol groups protected by t-butyldimethylsilyl ether, followed by deprotecting the silyl ether. These amphiphilic polysilanes were applied to provide oriented thin films by the Langmuir-Blodgett technique. Stable monolayers were not obtained for polysilylenes having only alkyl and aryl substituents. However, all the polysilylenes with phenol moieties provided monolayers on a water surface. These polysilylene monolayers were transferred to hydrophobic substrates by applying the Langmuir-Blodgett technique. Among these polysilylenes, only poly(n-butyl-3-hydroxyphenylsilylene) provided multilayers in which the Si? Si main chains oriented in the dipping direction. The orientation was determined by polarized UV absorption. The orientation ratio reached 0.45. © 1993 John Wiley & Sons, Inc. 相似文献