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101.
Combination of an ultrasonic nebulizer and plasma excitation sources for spectrochemical analysis offers desirable features of low detection limits, high sample throughput, wide dynamic range of operation, acceptable precision and accuracy, and simultaneous quantitative analytical capabilities. Moreover, the ultrasonic nebulizer does not require sample preconcentration. Recently we have developed a three-phase plasma arc (TPPA) for atomic emission spectrochemical analysis. In the present work, to increase the analytical utility of the three-phase plasma system, an ultrasonic nebulizer was used for sample introduction. The effects of the argon gas flow rate, current, excitation temperature have been studied. The analytical calibration curves are obtained for Ca, Cr, Fe, Mg and Mn, and detection limits have been calculated. The present technique is used to determine the concentration of the elements Ca, Cr, Fe, Mg and Mn in airborne samples. 相似文献
102.
The conversion of amorphous tricalcium phosphate with different hydration ratio into apatite in water at 25 °C has been studied by microcalorimetry and several physical-chemical methods. The hydrolytic transformation was dominated by two strong exothermic events. A fast, relatively weak, wetting process and a very slow but strong heat release assigned to a slow internal rehydration and the crystallization of the amorphous phase into an apatite. The exothermic phenomenon related to the rehydration exceeded the crystalline transformation enthalpy. Rehydration occurred before the conversion of the amorphous phase into apatite and determined the advancement of the hydrolytic reaction. The apatitic phases formed evolved slightly with time after their formation. The crystallinity increased whereas the amount of HPO42− ion decreased. These data allow a better understanding of the behavior of biomaterials involving amorphous phases such as hydroxyapatite plasma-sprayed coatings. 相似文献
103.
Soot deep oxidation catalyzed by molybdena and molybdates: a thermogravimetric investigation 总被引:2,自引:0,他引:2
Molybdena (MoO3) and molybdates of bismuth (Bi2Mo3O12), chromium (Cr2Mo3O12), barium (BaMoO4), manganese (MnMoO4) and copper (Cu3Mo2O9) were synthesized and characterized by X-ray powder diffractometry and infrared spectroscopy. They were then assessed as ‘loose contact' catalysts for soot deep oxidation (combustion) in air by thermogravimetry. A similar assessment was carried out on commercial chromia (Cr2O3) and tungsta (WO3). Observed high oxidation activity of MoO3, as compared to both Cr2O3 and WO3, is attributed to the higher volatility (mobility) of MoOx species. On similar grounds, observed high activity of MoO3 and Cu3Mo2O9, as compared to the other test molybdates, is explained. Relatively speaking, however, a higher activity was observed for Cu3Mo2O9 than MoO3, whereby soot ignition temperature decreased from 571°C (uncatalyzed oxidation) to 430°C, to occur within the temperature range of diesel exhaust (200–450°C). This observation is ascribed to copper-promoted redox conduct of Mo(VI) in the oxidation reaction of soot. Kinetics of the reaction was studied non-isothermally, and the kinetic parameters (A, k, ΔE and the reaction order) were calculated. 相似文献
104.
Mohamed S. A. El‐Gaby Ahmed M. Sh El‐Sharief Ahmed A. Atalla Abu‐Bakr A. A. M. El‐Adasy 《中国化学会会志》2004,51(2):327-333
The novel cyanothioformamides 2a‐d were prepared by treatment of isothiocyanatosulfonamides 1a‐d with potassium cyanide at room temperature. Cyclocondensation of compounds 2b,c with phenyl isocyanate as electrophile furnished the corresponding imidazolidines 3a,b . The reactivity of compound 3a towards some nitrogen nucleophiles was investigated. Thus, the thiosemicarbazone 4 and imidazo[4,5‐b]quinoxaline 6 were synthesized by condensation of compound 3a with thiosemicarbazide and o‐phenylenediamine, respectively. Treatment of 3a with hydrochloric acid afforded compound 7 . Our investigation was extended to include the reactivity of cyanothioformamide 2 towards o‐aminophenol, anthranilic acid, and o‐phenylenediamine and yielded the corresponding heterocycles 9 , 11 and 13 derivatives, respectively. Structures of the synthesized compounds were established by their elemental analysis and spectral data. 相似文献
105.
Namita Singh Sana Ahmed Aliyah Fakim Somayah Qutub Othman Alahmed Omar El Tall Osama Shekhah Mohamed Eddaoudi Niveen M. Khashab 《Chemical science》2020,11(41):11280
Assembling well-defined MOF superstructures remains challenging as it requires easily removable hard templates or readily available immiscible solutions for an emulsion-based soft-template approach. In this work, a single-step emulsion-free soft templating approach is reported to spontaneously prepare hollow ZIF-8 and ZIF-67 colloidosomes with no further purification. These superstructures can load different enzymes regardless of the size and charge with a high encapsulation efficiency of 99%. We envisage that this work will expand the repertoires of MOF superstructures by the judicious selection of precursors and the reaction medium.An emulsion-free approach for the preparation of hollow ZIF-8 superstructures in a single step is established based on metal sulfate hydrates in methanol. 相似文献
106.
Smaali M. Issam Gargouri Mohamed Legoy Marie Dominique Maugard Thierry Limam Farid Marzouki Nejib 《Applied biochemistry and biotechnology》2004,112(2):63-77
The filamentous fungus Sclerotinia sclerotiorum, grown on a xylose medium, was found to excrete one β-glucosidase (β-glu x). The enzyme was purified to apparent homogeneity
by ammonium sulfate precipitation, gel filtration, anion-exchange chromatography, and high-performance liquid chromatography
(HPLC) gel filtration chromatography. Its molecular mass was estimated to be 130 kDa by HPLC gel filtration and 60 kDa by
sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that β-glu x may be a homodimer. For p-nitrophenyl β-d-glucopyranoside hydrolysis, apparent K
m and V
max values were found to be 0.09 mM and 193 U/mg, respectively, while optimum temperature and pH were 55–60°C and pH 5.0, respectively. β-Glu x was strongly
inhibited by Fe2+ and activated about 35% by Ca2+. β-Glu x possesses strong transglucosylation activity in comparison with commercially available β-glucosidases. The production
rate of total glucooligosaccharides (GOSs) from 30% cellobiose at 50°C and pH 5.0 for 6 h with 0.6 U/mL of enzyme preparation
was 80 g/L. It reached 105 g/L under the same conditions when using cellobiose at 350 g/L (1.023 M). Finally, GOS structure was determined by mass spectrometry and 13C nuclear magnetic resonance spectroscopy. 相似文献
107.
Masoud MS Abou El-Enein SA Ayad ME Goher AS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(1-2):77-87
Complexes of Co(II), Ni(II) and Cu(II) with substituted phenylazo-6-aminouracils containing (-H, p-OH, p-CH(3), p-OCH(3) p-COOH) have been synthesized and characterized by elemental analysis, magnetic measurements and spectral measurements (IR, UV-Vis, ESR). Infrared spectra assigned the fundamental bands of the major groups, O-H, N-H, C-H, C=O, C=N, N=N, C-N and C-O (nu, delta and gamma modes of vibrations). The absence of nu(OH) and the appearance of nu(C=O) in the infrared spectra of the free ligands of 5-(p-tolyl and p-anisylazo)-6-aminouracil, assigned the keto structure, whereas in cases of 5-(phenyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracil ligands, the data showed strong nu(OH) and nu(C=O) bands to assign keto-enol tautomerisms. The modes of interactions between the ligands and the metals were discussed, where oxygen and nitrogen atoms (of amino-amide groups) are involved in chelation. The azo group was not involved in chelation for all the prepared complexes except those of copper complexes derived from 5-(phenyl, p-tolyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracils. The room temperature effective magnetic moment values, the Nujol mull spectra and ESR proved that all the prepared complexes were of octahedral geometry, except the nickel complex derived from 5-(phenylazo)-6-aminouracil and cobalt complex derived from 5-(p-carboxy-phenylazo)-6-aminouracil were square planar. 相似文献
108.
Mohamed Mongi Ftini Mohamed Krifa Haddad Amor 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):i106-i108
The title compounds, potassium pentamolybdenum oxide, KMo5O13, and potassium niobate antimonate or potassium niobium antimony oxide (1/1.76/3.24), KNb1.76Sb3.24O13, were synthesized by solid‐state reactions and are isomorphous in space group Cmcm. The structure of the Mo complex has three unique Mo atoms and consists of MoO6 octahedra sharing edges to form Mo2O6 pairs and Mo3O9 triplets, which, in turn, form layers by sharing corners. These layers are linked together in the [100] direction, yielding a three‐dimensional network similar to that of KSb5O13. This framework delimits interconnected tunnels, running approximately along the [110] and [10] directions, in which K+ ions are located. In the isomorphous KNb1.76Sb3.24O13 structure, one of the Mo sites in KMo5O13 is replaced by Sb and the other two Mo sites have been replaced by Nb/Sb. 相似文献
109.
Based on the reaction with p-aminophenol, a series of procedures have been developed for the spectrophotometric determination of phenol and resorcinol. Three basic approaches have been studied: (i) a batch procedure, using the dissolved oxygen as oxidant, (ii) a stopped-flow procedure by use of KIO(4) as oxidant and (iii) a flow injection (FI) procedure developed in the presence of KIO(4). Phenol can be accurately determined at 626 nm, in the stopped-flow mode, after a reaction time of 45 min in 0.005M NaOH, 0.004M KIO(4) and 500 mug/ml of PAP. The development of a manifold, which incorporates a sample parking, is a convenient approach which makes it possible to measure, in the stopped-flow mode, four solutions in one hour. The limit of detection of this method corresponds to 64 ng/ml of phenol Resorcinol can be determined by FI at 540 nm in 0.006M NaOH, 0.0002M KIO(4) and 50 mug/ml PAP with a limit of detection of 6.6 ng/ml and a sample throughput of 300 injections per hour. A combination between the FI procedure for the determination of resorcinol and the stopped-flow procedure for phenol determination provides accurate results in the analysis of spiked samples containing both phenol and resorcinol. 相似文献
110.
Hamza A. S. Abujabal Mahmoud M. El-Borai 《Journal of Applied Mathematics and Computing》1996,3(2):279-290
In the present paper, we study the Cauchy problem in a Banach spaceE for an abstract nonlinear differential equation of form $$\frac{{d^2 u}}{{dt^2 }} = - A\frac{{du}}{{dt}} + B(t)u + f(t,W)$$ whereW = (A 1(t)u,A 2(t)u,?,A ?(t)u), (A i (t),i = 1, 2, ?,?), (B(t),t ∈I = [0,b]) are families of closed operators defined on dense sets inE intoE, f is a given abstract nonlinear function onI ×E ? intoE and ?A is a closed linear operator defined on dense set inE intoE, which generates a semi-group. Further, the existence and uniqueness of the solution of the considered Cauchy problem is studied for a wide class of the families (A i(t),i = 1, 2, ?,?), (B(t),t ∈I). An application and some properties are also given for the theory of partial diferential equations. 相似文献