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71.
Angelo C. Pinto Susan K. Do Prado Raimundo Braz Filho William E. Hull Andras Neszmelyi Gabor Lukacs 《Tetrahedron letters》1982,23(50):5267-5270
With the help of Natural Abundance 13C - 13C Coupling Constants, observed via double quantum coherence, the structural determination of VELLOZIOLONE (1), a new diterpene, has been carried out. 相似文献
72.
73.
The composition of a (μ-oxo)diiron(III) complex coordinated by tris[(3,5-dimethyl-4-methoxy)pyridyl-2-methyl]amine (R(3)TPA) ligands was investigated. Characterization using a variety of spectroscopic methods and X-ray crystallography indicated that the reaction of iron(III) perchlorate, sodium hydroxide, and R(3)TPA affords [Fe(2)(μ-O)(μ-OH)(R(3)TPA)(2)](ClO(4))(3) (2) rather than the previously reported species [Fe(2)(μ-O)(OH)(H(2)O)(R(3)TPA)(2)](ClO(4))(3) (1). Facile conversion of the (μ-oxo)(μ-hydroxo)diiron(III) core of 2 to the (μ-oxo)(hydroxo)(aqua)diiron(III) core of 1 occurs in the presence of water and at low temperature. When 2 is exposed to wet acetonitrile at room temperature, the CH(3)CN adduct is hydrolyzed to CH(3)COO(-), which forms the compound [Fe(2)(μ-O)(μ-CH(3)COO)(R(3)TPA)(2)](ClO(4))(3) (10). The identity of 10 was confirmed by comparison of its spectroscopic properties with those of an independently prepared sample. To evaluate whether or not 1 and 2 are capable of generating the diiron(IV) species [Fe(2)(μ-O)(OH)(O)(R(3)TPA)(2)](3+) (4), which has previously been generated as a synthetic model for high-valent diiron protein oxygenated intermediates, studies were performed to investigate their reactivity with hydrogen peroxide. Because 2 reacts rapidly with hydrogen peroxide in CH(3)CN but not in CH(3)CN/H(2)O, conditions that favor conversion to 1, complex 1 is not a likely precursor to 4. Compound 4 also forms in the reaction of 2 with H(2)O(2) in solvents lacking a nitrile, suggesting that hydrolysis of CH(3)CN is not involved in the H(2)O(2) activation reaction. These findings shed light on the formation of several diiron complexes of electron-rich R(3)TPA ligands and elaborate on conditions required to generate synthetic models of diiron(IV) protein intermediates with this ligand framework. 相似文献
74.
An E Jeong CB Cha C Kim do H Lee H Kong H Kim J Kim JW 《Langmuir : the ACS journal of surfaces and colloids》2012,28(9):4095-4101
Corneocytes represents the main water reservoir of stratum corneum, and that ability intimately arises from their architecture and total composition. Here we describe a novel method for fabricating a microgel-in-liposome (M-i-L) structure consisting of a sodium hyaluronate microgel and a lipid membrane envelop in order to mimic corneocyte cell structures. The essence of our approach is to use a lecithin-based microemulsion with a very low interfacial tension between the water droplet and oil continuous phase. Using this emulsion enables us to stabilize a dispersion of microgel particles without phase separation or aggregation. The addition of excess water produced single-core or multicore microgel particles enveloped in a lipid layer. To demonstrate the applicability of this unique vesicle system, we encapsulated a high concentration of natural moisturizing factor (NMF) in the microgel core and investigated how the M-i-L structure affected the water retention in comparison with other control systems. We have observed that our M-i-L particles with the NMF in the core, which mimicked the corneocyte cell structure, showed an excellent ability to retain water in the system. This experimental result inspired us to investigate how corneocyte cells, which feature a lipid-enveloped hydrogel structure, provide such long-lasting hydration to the skin. 相似文献
75.
76.
A short, 4-step route to the scaffold of frondosin A and B is reported. The [1-methoxycarbonyl-5-(2',5'-dimethoxyphenyl)pentadienyl]Fe(CO)(3)(+) cation was prepared in two steps from (methyl 6-oxo-2,4-hexadienoate)Fe(CO)(3). Reaction of this cation with isopropenyl Grignard or cyclohexenyllithium reagents affords (2-alkenyl-5-aryl-1-methoxycarbonyl-3-pentene-1,5-diyl)Fe(CO)(3) along with other addition products. Oxidative decomplexation of these (pentenediyl)iron complexes, utilizing CuCl(2), affords 6-aryl-3-methoxycarbonyl-1,4-cycloheptadienes via the presumed intermediacy of a cis-divinylcyclopropane. 相似文献
77.
E. F. Keskenler S. Doğan B. Diyarbakır S. Duman B. Gürbulak 《Journal of Sol-Gel Science and Technology》2011,60(1):66-70
ZnO thin films were deposited onto glass subsrates by a Sol-gel spin coating method. The structural and optical properties
of ZnO thin films were investigated. The molar ratios of the zinc acetate dihydrate to Monoethanolamine were maintained 1:1.
The as-grown film was sintered 250 °C for 10 min, then annealed in air at 500 °C for 30 min. The XRD results indicate that
ZnO films were strongly oriented to the c-axis of the hexagonal nature. Absorption measurements were carried out as a function
of temperature with 10 K steps in the range 10–320 K. The band gap energy was measured 3.275 and 3.267 eV for 0.5 and 1.0
molarity (M) ZnO thin films at 300 K. The steepness parameters were observed between 10 and 320 K and their extrapolations
converged at (E0, α0) = 3.65 eV, 172,819 cm−1 and 3.70 eV, 653,436 cm−1 for 0.5 and 1.0 M ZnO thin films, respectively. 相似文献
78.
The present paper deals with the electrokinetic characterization of sepiolite. A series of systematic zeta potential measurements have been carried out to determine the isoelectric point (iep) and potential-determining ions (pdi), and the effect of mono-, di-, and trivalent electrolytes such as NaCl, KCl, LiCl, NaNO(3), NaCH(3)COO, MgCl(2), CaCl(2), BaCl(2), CoCl(2), CuCl(2), Pb(NO(3))(2), Na(2)CO(3), Na(2)SO(4), AlCl(3), FeCl(3), and Na(3)PO(4) on the zeta potential of sepiolite. Zeta potential has been calculated with the aid of Smoluchowski's equation. Sepiolite yields an isoelectric point at pH 6.6. The zeta potential for the sepiolite has ranged from +23.3 mV at pH approximately 2 to -22.4 mV at pH approximately 8 at 20 +/- 2 degrees C in water. The valency of the ions have proven to have a great influence on the electrokinetic behavior of the suspension. Monovalent cations were found to have a weak effect, while di- and trivalent cations made the zeta potential positive. Charge reversal was observed for divalent cations at 1 x 10(-2) M and for trivalent cations at 3 x 10(-4) M. As a result, it can be said that monovalent cations are indifferent ions when di- and trivalent cations are potential-determining ions. 相似文献
79.
A new borate ion selective electrode using solid salts of Ag3BO3, Ag2S and Cu2S has been developed. Detailed information is provided concerning the composition, working pH and conditioning of the electrode. An analytically useful potential change occurred from 1 × 10−6 to 1 × 10−1 M borate ion. The slope of the linear portion was 31 ± 2 mV/10-fold changes in borate concentration. The measurements were made at constant ionic strength (0.1 M NaNO3) and at room temperature. The effect of Cl−, Br−, NO3−, SO=4, H2PO4− anions and K+, Na+, Cu2+, Ag+, Ca2+ cations on borate response is evaluated and it was found that only Ag+ had a small interference effect. The lifetime of the electrode was more than two years, when used at least 4-5 times a day, and the response time was about 20-30 s. Borate content in waste water of borax factory, tap water of a town situated near to the borax factory and city tap water far from these mines were also determined. The validation was made with differential pulse polarography for the same water sample, and high consistency was obtained. 相似文献
80.
Do C Hatfield J Patel S Vasudevan D Tirla C Mills NS 《The Journal of organic chemistry》2011,76(1):181-187
Oxidation of m- and p-substituted benzylidene fluorenes to antiaromatic dications was attempted by electrochemical and chemical means. Electrochemical oxidation to dications was successful for benzylidene fluorenes with p-methoxy, p-methyl, p-fluoro, and unsubstituted phenyl rings in the 3-position; attempts to oxidize the m-substituted derivatives via electrochemistry were unsuccessful. Chemical oxidation with SbF(5)/SO(2)ClF gave the dication of 9-[(4-methoxyphenyl)methylene]-9H-fluorene cleanly; oxidation of all other substituted benzylidene fluorenes resulted in mixtures of products. The excellent linear relationship between the chemical shifts calculated by the GIAO method and the experimental shifts for the p-methoxy-substituted benzylidene fluorene dication suggests that the calculations satisfactorily reflect the magnetic properties of this dication and potentially those of the other dications studied. The redox potentials from electrochemical oxidation, a measure of the stability of the dications, showed a good linear relationship with another measure of stability, the calculated difference in energy between each dication and its neutral precursor. The dications of benzylidene fluorenes were less stable than the dications of diphenylmethylidene fluorenes; within each type of compound, dications with p-substituted phenyl rings were more stable than dications with m-substituted phenyl rings and dications with phenyl rings substituted with electron-donating groups were more stable than dications with phenyl rings substituted with electron-withdrawing groups. The antiaromaticity of the fluorenyl system was assessed through the nucleus-independent chemical shift (NICS) that was also calculated by the GIAO method. The plot of the NICS values per square area versus the calculated energy difference for the dications showed a moderate degree of linearity; the plot of NICS values per square area versus the oxidation potentials was less linear. Thus, a suggestive, but not conclusive, relationship between magnetic and energetic measures of antiaromaticity was observed. 相似文献