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991.
M.D. Carvalho L.P. Ferreira J.C. Waerenborgh A.B. Lopes 《Journal of solid state chemistry》2008,181(9):2530-2541
Ca2Fe1−xMnxAlO5 (0?x?1) compounds were prepared by a self-combustion method under air (x=0, 0.1, 0.2 and 0.3) and nitrogen (x=0.5, 0.7 and 1.0). The samples prepared under nitrogen were successfully oxidized after short annealing under air. Both X-ray powder diffraction (XRD) Rietveld analysis and electron diffraction revealed that all compounds adopt the brownmillerite-type structure. All samples present an overall antiferromagnetic behaviour and data from magnetic measurements and Mössbauer spectroscopy allowed to conclude that the transition temperature decreases as Mn content increases for x?0.3 and increases in the case of the x?0.5 compounds. Except for x=1, chemical disorder due to the occupancy of both octahedral and tetrahedral sites by different metals as well as the competition between different moments’ orientation induce a complex magnetic behaviour characterized by magnetic frustration and canted antiferromagnetism. Mössbauer spectroscopy and chemical titrations also allowed to conclude about the preferential oxidation of Mn3+ over Fe3+, obtained by thermal treatment under air of the x=0.5 and 0.7 compositions. 相似文献
992.
Elvira M. Bauer Carlo Bellitto Guido Righini 《Journal of solid state chemistry》2008,181(5):1213-1219
A new Ni(II) layered hybrid organic-inorganic compound of formula Ni2[(NDI-BP)(H2O)2]·2H2O has been prepared in very mild conditions from N,N′-bis(2-phosphonoethyl)napthalene-1,4:5,8-tetracarboximide (NDI-BP ligand) and NiCl2. The X-ray powder structure characterization of the title compound suggests a pillared layered organic-inorganic hybrid structure. The distance between the organic and inorganic layers has been found to be 17.8 Å. The inorganic layers consist of corner sharing [NiO5(H2O)] octahedra and they are pillared by the diphosphonate groups. DC and AC magnetic measurements as a function of temperature and field indicate the presence of 2D antiferromagnetic exchange interactions between the nearest-neighbor Ni(II) ions below 100 K. A long-range magnetic ordering at Tc∼21 K has been established and is attributed to the presence of spin canting. AC magnetic measurements as a function of temperature at different frequencies confirm the occurrence of the magnetic ordering temperature at T=21 K and the presence of a slight structural disorder in the title compound. 相似文献
993.
Capillary electrophoresis is one of the separation tools commonly used in conjugation with mass spectrometry. Its primary purpose is to resolve the components in a sample mixture prior to mass spectral identification. Moreover, an increasing number of applications reported in the literature involve the use of CE for additional purposes, such as sample preparation and derivatization, and the study of biochemical properties. This review provides an overview on the various roles of CE beyond that of a simple separation tool. While the scope focuses on the area of interest rather than a predefined time period, the majority of the references highlighted were initially published within the past five years. 相似文献
994.
Sofianos ZD Katsila T Kostomitsopoulos N Balafas V Matsoukas J Tselios T Tamvakopoulos C 《Journal of mass spectrometry : JMS》2008,43(10):1381-1392
The study of pharmacologically active peptides is central for the understanding of cancer and the development of novel therapeutic approaches. In this context, both qualitative and quantitative determination of bioactive peptides in biological fluids/tissues and their effect on endogenous factors (e.g. hormones) are of great importance. A mass spectrometry-based approach was developed and applied towards the measurement of leuprolide, a peptide drug for the treatment of prostate cancer, in mouse plasma. High-pressure liquid chromatography coupled to a hybrid quadrupole linear ion trap (QqLIT) mass spectrometer, a platform that combines the benefits of triple QqLIT instruments, was employed for the study. Using the described methodology, we established that picomolar concentrations of leuprolide could be measured in mouse plasma (limit of quantification of 0.1 ng/ml). In order to optimize pharmacokinetic properties of analogs of leuprolide, a facile in vivo mouse model was developed and leuprolide concentrations were determined in mouse plasma following intraperitoneal administration. In the same animal model, we demonstrated the versatility of the described MS-based approach by the determination of plasma concentrations of testosterone, an established biomarker for the treatment of prostate cancer. Following dosing with leuprolide, circulating testosterone was increased significantly in comparison to vehicle-treated mice. Finally, in vitro metabolism of leuprolide was evaluated by incubation of leuprolide with mouse kidney membranes, followed by identification of major metabolites by MS. Such studies provide the framework for future evaluation of novel leuprolide analogs with potential therapeutic advantages. 相似文献
995.
R.?G.?Rodríguez?Avenda?oEmail author J.?A.?de?los?Reyes J.?A.?Montoya T.?Viveros 《Journal of Sol-Gel Science and Technology》2005,33(1):133-138
An experimental strategy was developed to obtain mesoporous SiO2-ZrO2 mixed oxides via a sol–gel process, which involved the use of tetraethylorthosilicate (TEOS) and an inorganic Zr-containing salt. The effects of key process parameters on the properties of the materials were investigated, including the choice of Zr(IV) source (zirconium oxychloride or nitrate), the ZrO2 content and the synthesis pressure (i.e. ambient pressure or hydrothermal conditions). The resulting solids were dried, calcined at 500 °C, and characterized by nitrogen physisorption, pyridine chemisorption, 29Si Nuclear Magnetic Resonance and X-ray diffraction. The data revealed that mesoporous materials with very narrow pore diameter distribution were obtained when using the autoclave procedure from both zirconium nitrate and oxychloride salts. The surface areas and pore size distributions were a function of ZrO2 content. Differences in acidity, as determined by pyridine adsorption, were observed depending on the synthesis parameters. 相似文献
996.
Nemkovich NA Pivovarenko VG Baumann W Rubinov AN Sobchuk AN 《Journal of fluorescence》2005,15(1):29-36
Electrooptical absorption measurements (EOAM) were used to measure the dipole moments of the normal form of 4-(dimethylamino)-3-hydroxyflavone (FME), and 4 N-(15-azacrown-5)-3-hydroxyflavone (FCR) in 1,4-dioxane, toluene, and cyclohexane. With these probes excited-state intramolecular proton transfer (ESIPT) takes place. For comparison, the dipole moments of 4-(dimethylamino)-3-metoxyflavone (FME3ME), for which ESIPT is lacking, were measured, too. For all three probes the ground (g) and excited Franck-Condon state (eFC) electrical dipole moments are parallel to each other and also parallel to the transition dipole moment. The electrical dipole moments of FCR, FME, and FME3ME in their ground state have values within the range (12.0–17.7) × 10–30 C m. Upon optical excitation, the dipole moments increase by (41.9–52.9) ×10–30 C m. The value of the change of the dipole moment vector a with excitation to the Franck-Condon state and the value of the vector eFC for FCR and FME are practically independent on the solvent polarity. From this point of view and due to large values of the dipole moments FCR and FME are very promising probes for the investigation of the distribution of the local polarity in biological systems using site-selective excitation of the different sites. Our steady-state fluorescence studies on FME and FCR have demonstrated a high spectral sensitivity of the normal form to such solvent characteristics as polarity. 相似文献
997.
A liquid foam in contact with a solid surface forms a two-dimensional foam on the surface. We derive the equilibrium equations for this 2D foam when the solid surface is curved and smooth, generalising the standard case of flat Hele-Shaw cells. The equilibrium conditions at the vertices in 2D, at the edges in 3D, are invariant by conformal transformations. Regarding the films, conformal invariance only holds with restrictions, which we explicit for 3D and flat 2D foams. Considering foams confined in thin interstices between two non-parallel plates, normal incidence and Laplace’s law lead to an approximate equation relating the plate profile to the conformal map. Solutions are given for the logarithm and power laws in the case of constant pressure. The paper concludes on a comparison with available experimental data. 相似文献
998.
Mandeep?Singh?BakshiEmail author Rohit?Sood Radha?Ranganathan Paul?Shin 《Colloid and polymer science》2005,284(1):58-65
The electron paramagnetic resonance (EPR) study has been carried out for the micellar solutions of various ionic surfactant solutions as well as various generations of aqueous dendrimer both in their respective presence as well as their absence at 25°C and in different media. From these measurements, the rotation correlation time (τB) have been calculated for all the ionic surfactant + PAMAM + water system. A variation in the τBvalue remains mostly constant for the dodecyltrimethyammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) + PAMAM + water ternary mixtures. The τBvalue shows an increase with the increase in the amount of PAMAM for SDS in basic medium and for 12-2-12 in acidic medium. It has been concluded from these results that SDS undergo complexation with all generations of PAMAM in basic medium and 12-2-12 in acidic medium and produce stronger hydrophobic environment. The nuclear magnetic resonance study (NMR) allowed us to evaluate the spin–spin relaxation (T1) times of SDS in the presence of all generations of PAMAM. The T1 values for all the tail protons of SDS showed a slight decrease with the increase in the constant amount of PAMAM suggesting the adsorption of PAMAM molecules on the micelle surface. 相似文献
999.
Keita?Suzuki Jun-ichi?Oku Kenichi?Izawa Hiro-Fumi?OkabayashiEmail author Isao?Noda Charmian?J.?O’Connor 《Colloid and polymer science》2005,283(5):551-558
A set of time resolved gel-permeation chromatography (GPC) profiles, for the reaction mixture of a well-defined polymeric silane coupling agent, triethoxysilyl-terminated polystyrene with molecular weight equal to 8000 (TESi-PS (8000)), catalyzed by HCl (0.1 mol/kg) in tetrahydrofuran (THF), was measured over a long time scale (1–768 h). The GPC profiles were then converted to two-dimensional (2D) correlation spectra. The 2D GPC correlation spectra were compared with those for the CH3SO3H (0.1 mol/kg)-catalyzed TESi-PS (8000)-THF system. It has been demonstrated that predominant production of less-reactive oligomers in the HCl-catalyzed system hinders further growth of the oligomer, while formation of reactive oligomers leads to further growth of polymeric precursors in the CH3SO3H-catalyzed system. 相似文献
1000.
Blackmond DG 《Angewandte Chemie (International ed. in English)》2005,44(28):4302-4320
Reaction progress kinetic analysis to obtain a comprehensive picture of complex catalytic reaction behavior is described. This methodology employs in situ measurements and simple manipulations to construct a series of graphical rate equations that enable analysis of the reaction to be accomplished from a minimal number of experiments. Such an analysis helps to describe the driving forces of a reaction and may be used to help distinguish between different proposed mechanistic models. This Review describes the procedure for undertaking such analysis for any new reaction under study. 相似文献