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991.
A full account of stereoselective total synthesis of a novel glycolipid, acremomannolipin A (1), the potent calcium signal modulator isolated from Acremonium strictum, by employing the stereoselective β-mannosylation of 4,6-O-benzylidene-protected mannosyl sulfoxide with d-mannitol as the key reaction is described. The α-anomer (epi-1) of 1 was also synthesized selectively. The calcium modulating activity was reduced upon inversion of the configuration at the anomeric center, indicating that the β-configuration of the mannose moiety is preferable for the activity. 相似文献
992.
The first ferrocenecarboselenoic acid was synthesized and characterized. The existence of tautomeric equilibrium between the selenol (FcCOSeH) and selenoxo forms (FcCSeOH) in polar solvents was proven by 1H‐, 13C‐ and 77Se‐NMR spectra. The selenoxo form exists predominantly in a polar solvent at low temperature below –70 °C. Treatment of this acid with lithium, sodium, and potassium hydrides and with rubidium and cesium fluorides gave the corresponding alkali metal ferrocenecarboselenoates in quantitative yields. Treatment with 4‐methylphenyl isocyanate at room temperature led to ferrocenoyl 4‐methylphenylcarbamoyl selenide FcCOSeC(O)NHC6H4Me‐4 in high yield. A similar reaction with phenyl isothiocyanate formed a mixture of FcCOSeC(S)NHPh and FcCOSeC(SH)=NPh in moderate to good yield. The carboselenoic acid readily reacted with piperidine to give piperidinium ferrocenecarboselenoate in good yield. Air oxidation of this selenoic acid afforded diferrocenoyl selenide as a major product along with diferrocenoyl diselenide. The structures of the selenide (FcCO)2Se and diselenide (FcCOSe)2 were examined by single‐crystal X‐ray analysis. 相似文献
993.
The ion transport current was clearly observed across a bilayer lipid membrane (BLM) between two aqueous phases (W1, W2) containing 0.1 M CsCl. This indicates that Cs+ can spontaneously penetrate the BLM in the absence of any kind of transporter. In addition, the current density at a given potential between W1 and W2 increased using I? instead of Cl? as the counter ion. Our results strongly suggest that the cell membrane transport is partially responsible for the internal exposure of 134Cs and 137Cs. 相似文献
994.
Kenji Nomura Kazuko Hirayama Takeo Ohsaka Masahiro Nakanishi Osamu Hatozaki Noboru Oyama 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(2-3):593-608
The electrochemical and electrochromic properties of polymer films containing a conductive powder (SnO2/TiO2) have been investigated. The films are complexes of polytetramethyleneviologen and poly(p-styrenesulfonic acid). It was found that the coloration (purple) and bleaching rates of the composite films increase markedly with increasing conductive powder content(x). The coloring and bleaching of the composite film with x = 95 wt% were about 7 and 44 times faster, respectively, than those for an equivalent film without conductive powder. This increase in the rate of color change by introduction of a conductive powder was found to be correlated with the apparent diffusion coefficient (D app) for the diffusionlike charge-transport process within the composite films which increases with increasing x. The D app for the reduction process of the film with x = 95 wt% was larger by about 3 orders of magnitude than that for the unfilled film. 相似文献
995.
Pierre Thuéry Martine Nierlich Zouhair Asfari Jacques Vicens Osamu Morikawa Hisatoshi Konishi 《Supramolecular chemistry》2013,25(4):521-527
Abstract The crystal structures of the all-cis epimer of C-(n-propyl)calix[4]resorcinarene (1) and its caffeine complex are reported. 1 · CH3CN · H2O (2) crystallizes in the tetragonal space group P4, a = 14.3645(9), c = 9.3344(8) Å, V = 1926(2) Å3. Refinement led to a final conventional R 1 value of 0.047 for 3406 reflections and 236 parameters. The caffeine complex 1 · C8H10N4O2 · CH3OH · H2O (3) crystallizes in the triclinic space group P1, a = 11.2892(4), b = 13.0367(8), c = 16.9700(11) Å, α = 82.902(2), β = 79.713(3), γ = 88.053(2)°, V = 2438(2) Å3. Refinement led to a final conventional R 1 value of 0.067 for 6393 reflections and 641 parameters. The resorcinarene displays the usual bowl shape in both compounds. The caffeine molecule in 3 is hydrogen bonded to two resorcinarene and one water molecules and one of its methyl groups is included in the cavity of a third macrocycle, suggesting CH3…π interactions. Extended hydrogen bonding patterns involving phenolic protons and solvent molecules are also present in both compounds. 相似文献
996.
Tisato Kajiyama Osamu Yonekura Jun-Ichiro Nishiwaki Hirotsugu Kikuchi 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1847-1865
Polymer/liquid crystal composite films were prepared from a solution of polymer and nematic liquid crystal (LC) by a solvent casting method. The phase-separated structure of the composite film was controlled by the solvent evaporation rate. The light-scattering profile of a poly(diisopropyl fumarate)/LC: 40/60 w/w solution during solvent evaporation exhibited a periodic structure, indicating that the phase-separated structure was formed by spinodal decomposition. The aggregation structure of the composite film was investigated with a scanning electron microscope (SEM). SEM observation of the composite film suggested the presence of periodicity and dual connectivity of polymer and LC phases. The faster the solvent was evaporated, the smaller the LC channel (domain) size in the composite film. The composite film, composed of poly(methyl methacrylate) (PMMA) and a nematic LC (E44) with a positive dielectric anisotropy, exhibited remarkable and reversible light-scattering-light-transmission switching, under the modulation of an ac electric field. The light-scattering state was dependent on such optical heterogeneities as spatial distribution of the nematic directors and/or mismatching in the refractive indices of the components. The electrooptical behavior of the composite film was strongly dependent on the LC channel (domain) size in the composite film. The transmittance increased and the rise and decay response times (τR and τD), decreased and increased, respectively, with an increase in the size of the LC channel (domain). The electrooptical switching properties for the polymer/LC composite film should be influenced by miscibility between the polymer and the LC phases. The miscibility between both phases was evaluated from a distribution of relaxation time for interfacial polarization. The anchoring effect was also investigated by measuring the nonlinearity of the dielectric constant for the composite system. 相似文献
997.
Takumi Nakanishi Yuta Hori Shuqi Wu Hiroyasu Sato Atsushi Okazawa Norimichi Kojima Yusuke Horie Hajime Okajima Akira Sakamoto Yoshihito Shiota Kazunari Yoshizawa Osamu Sato 《Angewandte Chemie (International ed. in English)》2020,59(35):14781-14787
A proton–electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi‐step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric‐like arrangement. 相似文献
998.
The expression mechanism of permselectivity through a gramicidin A (gA) channel between two aqueous phases (W1 and W2) was investigated. When the concentration of CsCl or CsBr in W1 was equivalent to that in W2, the single‐channel current was proportional to the absolute value of the applied membrane potential. Although the single‐channel current linearly increased with increasing electrolyte concentration in W1 and W2 until about 0.1 M (mol dm?3), it began to level off around 0.1 M, indicating that ion permeation across the channel pore is the rate‐determining step and that the saturation of the transporting ion within the channel pore provokes the leveling off. In the case of asymmetric composition of the electrolyte in W1 and W2, the monovalent cation and the counter anion were transported in the opposite direction through the gA channel pore or the bilayer lipid membrane around the gA channel. Finally, the experimental data was fitted using the Goldman‐Hodgkin‐Katz equation based on the relationship between the membrane potential and the single‐channel current to define the ratio of the diffusion coefficients of Cs+, Cl?, and Br? as 5.7 : 1.0 : 0.26. 相似文献
999.
Abstract 1, 2, 3-Tri-O-acetyl-6-O-benzyl-4-O-chloroacetyl-α- and -β-D-glucopyranose (4α β)were derived from 1, 2, 3-tri-O-acetyl-4, 6- O -benzyl-idehe-β-D-giucopyranose (1) in two steps. Compound 1, 1, 2, 3-tri-O -acetyl-β-D-glucopyranose (2), and 4α,β were subjected to the cyclization reaction using Lewis acids ( SnCl4 and BF3-etherate), to give corresponding 1, 6-anhydro derivatives. 相似文献
1000.
Abstract Recently, great interest has been focussed on the synthesis of oligosaccharides containing N-acetylneuraminic acid (Neu5Ac) because of its important roles in a variety of biological recognitions.2 However, many difficulties in the synthesis of naturally occurring α-glycosides still remained.3 We have recently reported the stereo-selective synthesis of a series of α- and β-2-thio-neuraminyl glycosides.1-4 In the meantime, the utility of thioglycosides in oligosaccharide synthesis has been widely developed.5 Particularly noteworthy is the dimethyl(methylthio)sulfonium triflate (DMTST) promoted glyco-sylation method5k.1 because excellent yields are achieved due to the high thiophilicity of this reagent. 相似文献