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21.
A first-derivative spectrophotometric (1D) method and a derivative-ratio zero-crossing spectrophotometric (1DD) method were used to determine pyritinol dihydrochloride (I) in the presence of its precursor (II) and its degradation product (III) with 0.1N hydrochloric acid as a solvent. Linear relationships were obtained in the ranges of 6-22 microg/mL for the (1D) method and 6-20 microg/mL for the (1DD) method. By applying the proposed methods, it was possible to determine pyritinol dihydrochloride in its pure powdered form with an accuracy of 100.36 +/- 1.497% (n = 9) for the (1D) method and an accuracy of 99.92 +/- 1.172% (n = 8) for the (1DD) method. Laboratory-prepared mixtures containing different ratios of (I), (II), and (III) were analyzed, and the proposed methods were valid for concentrations of < or = 10% (II) and < or = 50% (III). The proposed methods were validated and found to be suitable as stability-indicating assay methods for pyritinol in pharmaceutical formulations. 相似文献
22.
Quinazolin-4(3H)-one derivatives were synthesized successfully via a one-pot, three component reaction of isatoic anhydride and an orthoester with ammonium acetate or a primary amine catalyzed by silica sulfuric acid under solvent-free conditions. This is the first report on the synthesis of 2-substituted quinazolin-4(3H)-ones by this procedure. 相似文献
23.
The present work is dedicated to the XRD, ED and HREM characterization of a new bismuth copper oxyphosphate Bi∼6.2Cu∼6.2O8(PO4)5 (a=11.599(2)Å, , c=37.541(5)Å, R1=0.0755, Rw2=0.174, G.S Pn21a). The relatively long size of its c parameter is due to the arrangement along this direction of two kinds of ribbon-like polycations formed by edge sharing O(Bi, Cu)4 tetrahedra. The existence of such cations is characterized by the b∼5.2 Å value intrinsic to the ribbons structure and commonly found in bismuth oxyphosphate materials. In the title compound, 2-tetrahedra wide [Bi∼2.4Cu∼3.6O4]6.4+ and 3-tetrahedra wide [Bi∼5Cu∼3O6]9+ ribbons are isolated by phosphate groups and alternate along c. The interstitial site created between two different sizes ribbons is occupied by Cu2+ cations disordered over several close crystallographic sites. The mixed Bi3+/Cu2+ nature of certain edge-of-ribbons positions induces a disorder over several configurations of the phosphate groups. The concerned oxygen atoms form the environment of the disordered interstitial Cu2+ cations which occupy tunnels formed by the phosphate anions. The high-resolution electron microscope study enables a precise correlation between the observed images and the refined crystal structure, evidencing the polycations visualization. Furthermore, this material being the second example of partially disordered compound similar chemical system, some topological rules can be deduced. The b-axis doubling was observed by ED and HREM and is assigned to the ordering of interstitial Cu2+ within tunnels cations. A partial intra-tunnel ordering was also observed. 相似文献
24.
Panda M Das S Mostafa G Castineiras A Goswami S 《Dalton transactions (Cambridge, England : 2003)》2005,(7):1249-1255
2-(Arylazo)pyridine ligands, L1a-1c react with the salt K2[PtCl4] to give the mononuclear complexes [PtCl2(L1)](1), which readily react with ArNH2 to yield the monochloro complexes of type [PtCl(L2)](HL2= 2-[(2-(arylamino)phenyl)azo]pyridine)(2) via regioselective ortho-amine fusion at the pendent aryl ring of coordinated L1. Oxidative addition of the electrophiles Y2(Y = Cl, Br, I) to the square-planar platinum(II) complex, has led to syntheses of the corresponding octahedral platinum(IV) complexes, [PtY3(L2)](3) in high yields. Ascorbate ion reductions of the platinum(IV) complexes, , resulted in reductive halogen elimination to revert to the platinum(II) complexes almost quantitatively. Isolation of products and X-ray structure determination of the representative complexes followed all these chemical reactions. In crystal packing, the compound [PtCl2(L1c)](1c) forms dimeric units with a Pt...Pt distance of 3.699(1) A. In contrast, the crystal packing of 2b revealed that the molecules are arranged in an antiparallel fashion to form a noncovalent 1D chain to accommodate pi(aryl)-pi(pyridyl) and Pt-pi(aryl) interactions. Notably, the oxidation of [Pt(II)Cl(L2a)](2a) by I2 produced a mixed halide complex [Pt(IV)ClI2(L2a)](5), which, in turn, is reduced by ascorbate ion to produce [Pt(II)I(L2a)] with the elimination of ClI. All the platinum(II) complexes are brown, the platinum(IV) complexes, on the other hand, are green. Low-energy visible range transitions in the complexes of the extended ligand [L2]- are ascribed to ligand basedpi-pi* transitions. Cyclic voltammetric behaviour of the complexes is reported. 相似文献
25.
Huang X El-Sayed IH Yi X El-Sayed MA 《Journal of photochemistry and photobiology. B, Biology》2005,81(2):76-83
Nicotinamide adenine dinucleotide is an important coenzyme involved in the production of ATP, the fuel of energy, in every cell. It alternates between the oxidized form NAD(+) and the reduced form dihydronicotinamide adenine dinucleotide (NADH) and serves as a hydrogen and electron carrier in the cellular respiratory processes. In the present work, the catalytic effect of gold nanoparticles on the oxidization of NADH to NAD(+) was investigated. The addition of gold nanoparticles was found to quench the NADH fluorescence intensities but had no effect on the fluorescence lifetime. This suggested that the fluorescence quenching was not due to coupling with the excited state, but due to changing the ground state of NADH. The intensity of the 340 nm absorption band of NADH was found to decrease while that of the 260 nm band of NAD(+) was found to increase as the concentration of gold nanoparticles increased. This conversion reaction was further supported by nuclear magnetic resonance and mass spectroscopy. The effect of the addition of NADH was found to slightly red shift and increase the intensity of the surface plasmon absorption band of gold nanoparticles at 520 nm. This gives a strong support that the conversion of NADH to NAD(+) is occurring on the surface of the gold nanoparticles, i.e. NADH is surface catalyzed by the gold nanoparticles. The catalytic property of this important reaction might have important future applications in biological and medical fields. 相似文献
26.
G.A.E. Mostafa 《Talanta》2007,71(4):1449-1454
The construction and general performance characteristics of two novel potentiometric carbon paste electrodes (CPE) responsive to antimony are described. These sensors are based on the use of the ion associate complexes of tetraiodoantimonate (TIA) anion with cetylpyridinium (CP) and triphenyl tetrazolium (TPT) counter cations as ion exchange site in a carbon paste matrix. The two sensors exhibits fast, stable and near-Nernstian for the mono charged TIA anion over the concentration range 1 × 10−3 to 10−6 M at 25 °C in the pH range 4-10 with anionic slope of 58.0 ± 0.5 and 55.0 ± 0.7 per concentration decade for TIA-CP and TIA-TPT, respectively. The lower detection limits are 4 and 5 × 10−6 M and response time are 20 and 30 s in the same order of both electrodes. Selectivity coefficients for antimony relative to a number of different cations and anions were investigated. There is negligible interference from many inorganic cation and anion except for Hg2+, Cd2+, and Bi3+; however, their effect were eliminated by EDTA. The determination of 1.0-120.0 μg/ml of antimony in aqueous solutions shows an average recovery of 99.0 and 97.5% with relative standard deviation of 2.0% for both electrodes at 40 μg/ml. The determination of antimony in wastewater and some antibilharzial compounds using the proposed electrodes gave results that compare favorably with those obtained by the atomic absorption spectrometric method. Precipitation titrations involving cetylpyridinium chloride as titrant are monitored with both electrodes with inflection point of 180 and 100 mV for TIA-CP and TIA-TPT, respectively. 相似文献
27.
Lamia T. Abou El-Kassem Usama W. Hawas Mohamed S. Abdelfattah Ayat A. Mostafa 《Natural product research》2020,34(5):613-620
AbstractA new rotenoid named 12-O-methylrotenolol along with five known rotenoid and isoflavone metabolites were isolated from the seeds of Dalbergia lanceolaria subsp. paniculata, collected from Egypt. The structures of these compounds were identified by physical and spectroscopic data measurements ([α]D, UV, 1D- and 2D-NMR and MS). The methanol extract of the seeds exhibited strong antioxidant activity with IC50 value 0.7?µg/µl against DPPH radical, in respect to quercetin as antioxidant reference (IC50 1.5?μM), while the tested compounds from this extract showed weak activities with IC50 values ranged from 19.6 to 33.0?µM. 相似文献
28.
Farajollah?MohanazadehEmail author Mostafa?Hosini Mahmoud?Tajbakhsh 《Monatshefte für Chemie / Chemical Monthly》2005,136(12):2041-2043
Summary. Reduction of aldehydes and ketones to the corresponding alcohols was achieved in a simple procedure using the system sodium
borohydride and ammonium carbonate. This system needs lower excesses of reducing agent and leads to significantly shortened
reaction times. 相似文献
29.
The influence of group 15 various substituents and effect of metal centers on metal-borane interactions and structural isomers of transition metal-borane complexes W(CO)5(BH3 · AH3) and M(CO)5(BH3 · PH3) (A = N, P, As, and Sb; M = Cr, Mo, and W), were investigated by pure density functional theory at BP86 level. The following results were observed: (a) the ground state is monodentate, η1, with C1 point group; (b) in all complexes, the η1 isomer with CS symmetry on potential energy surface is the transition state for oscillating borane; (c) the η2 isomer is the transition state for the hydrogens interchange mechanism; (d) in W(CO)5(BH3 · AH3), the degree of pyramidalization at boron, interaction energy as well as charge transfer between metal and boron moieties, energy barrier for interchanging hydrogens, and diffuseness of A increase along the series A = Sb < As < P < N; (e) in M(CO)5(BH3 · PH3), interaction energy is ordered as M = W > Cr > Mo, while energy barrier for interchanging hydrogens decreases in the order of M = Cr > W > Mo. 相似文献
30.
The photoluminescence (PL) of CdSe quantum dots (QD) in aqueous media has been studied in the presence of gold nanoparticles (NP) with different shapes. The steady state PL intensity of CdSe QD (1.5-2 nm in size) is quenched in the presence of gold NP. Picosecond bleach recovery and nanosecond time-resolved luminescence measurements show a faster bleach recovery and decrease in the lifetime of the emitting states of CdSe QD in the presence of quenchers. Surfactant-capped gold nanorods (NR) with aspect ratio of 3 and surfactant-capped and citrate-capped nanospheres (NS) of 12 nm diameter were used as quenchers in order to study the effect of shape and surface charge on the quenching rates. The Stern-Volmer kinetics model is used to examine the observed quenching behavior as a function of the quencher concentration. It was found that the quenching rate of NR is more than 1000 times stronger than that of NS with the same capping material. We also found that the quenching rate decreases as the length of the NR decreases, although the overlap between the CdSe emission and the NR absorption increases. This suggests that the quenching is a result of electron transfer rather than long-range (Forster-type) energy transfer processes. The quenching was attributed to the transfer of electron with energies below the Fermi level of gold to the trap holes of CdSe QD. The observed large difference between NR and NS quenching efficiencies was attributed to the presence of the [110] facets only in the NR, which have higher surface energy. 相似文献