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排序方式: 共有1319条查询结果,搜索用时 500 毫秒
121.
Annemarie Huijser Dr. Alessandro Pezzella Dr. Jonas K. Hannestad Lucia Panzella Dr. Alessandra Napolitano Prof. Marco d'Ischia Prof. Villy Sundström Prof. 《Chemphyschem》2010,11(11):2424-2431
The UV‐dissipative mechanisms of the eumelanin building block 5,6‐dihydroxyindole‐2‐carboxylic acid (DHICA) and the 4,7‐dideutero derivative (DHICA‐d2) in buffered H2O or D2O have been characterized by using ultrafast time‐resolved fluorescence spectroscopy. Excitation of the carboxylate anion form, the dominating state at neutral pH, leads to dual fluorescence. The band peaking at λ=378 nm is caused by emission from the excited initial geometry. The second band around λ=450 nm is owed to a complex formed between the mono‐anion and specific buffer components. In the absence of complex formation, the mono‐anion solely decays non‐radiatively or by emission with a lifetime of about 2.1 ns. Excitation of the neutral carboxylic acid state, which dominates at acidic pH, leads to a weak emission around λ=427 nm with a short lifetime of 240 ps. This emission originates from the zwitterionic state, formed upon excitation of the neutral state by sub‐ps excited‐state intramolecular proton transfer (ESIPT) between the carboxylic acid group and the indole nitrogen. Future studies will unravel whether this also occurs in larger building blocks and ESIPT is a built‐in photoprotective mechanism in epidermal eumelanin. 相似文献
122.
J. Pablo Lamas Lucia Sanchez-PradoMarta Lores Carmen Garcia-JaresMaria Llompart 《Journal of chromatography. A》2010,1217(33):5307-5316
Exposure to fragrance substances is exponentially increasing in our daily life due to the enhanced use of scented products. Some fragrances are known to be important sensitizers, inhalation being an important exposure pathway in indoor environments. A simple and sensitive method based on solid-phase enrichment and solid-phase microextraction (SPME) followed by gas chromatography–mass spectrometry (GC–MS) has been developed for the analysis of 24 volatile fragrance allergens in indoor air. Suspected allergens present in the air (0.2 m3) were adsorbed onto a very small quantity of florisil (25 mg) and then transferred to a SPME fiber in the headspace mode (HS). To the best of our knowledge, this paper describes the first application of SPME for the determination of these compounds in air samples. The experimental parameters affecting the microextraction process have been optimized using a multifactor experimental design strategy. Accuracy, linearity, precision and detection limits (LODs) were evaluated to assess the performance of the proposed method. External calibration, using spiked sorbent standards, and not requiring the complete sampling process (only the SPME step), demonstrated to be suitable for the quantification of all suspected allergens. Recovery studies were performed at three concentration levels (0.04, 1.00 and 50 μg m−3), obtaining quantitative recoveries (≥85%) in most cases. LOD values at the low ng m−3 level were achieved for all the target compounds. The application of the method to daily home air samples demonstrated the ubiquity of this kind of fragrance ingredients in quotidian indoor environments, finding 18 of the 24 considered compounds in concentrations ranging from 0.01 to 56 μg m−3. Benzyl alcohol, linalool, citronellol, ionone and lilial were found in most analyzed samples. 相似文献
123.
A reversed-phase high-performance liquid chromatographic method for the determination of benzydamine hydrochloride and its impurities 3-dimethylaminopropyl 2-benzylaminobenzoate, 3-dimethylaminopropyl-2-aminobenzoate,1-benzyl-1H-indazol-3-ol, 1-benzyl-2-(3-dimethylaminopropyl)-1,2-dihydro-3H-indazol-3-one, and 1-benzyl-3-(3-(3-dimethylaminopropyl)-3-methylamino)propoxy-(1)H-indazole in a collutory formulation is developed. The separation is carried out on a Gemini C(18) (250 × 4.6 mm, 5 μm) column using acetonitrile-methanol-ammonium carbonate buffer (10 mM; pH 10.5) (37.5:37.5:25, v/v/v) as mobile phase at a flow rate of 1.0 mL/min, column temperature 30°C, and UV detection at 218 nm. Famotidine is used as an internal standard. The total run-time is less than 15 min. The analytical curves present coefficients of correlation greater than 0.99, and detection limits are calculated for all analytes. Excellent accuracy and precision are obtained for benzydamine hydrochloride. Recoveries vary from 98.25 to 102.8%, and intra- and inter-day precisions, calculated as the percent relative standard deviation, are lower than 2.2%. Specificity and robustness for benzydamine hydrochloride are also determined. The method allows the quantitative determination of benzydamine hydrochloride and its impurities, and it is suitable for routine analysis in quality control laboratories. 相似文献
124.
Lamas JP Sanchez-Prado L Garcia-Jares C Lores M Llompart M 《Journal of chromatography. A》2010,1217(52):8087-8094
A new method based on solid phase dispersion-pressurized liquid extraction (PLE) followed by gas chromatography-mass spectrometry (GC-MS) has been developed for the determination of 26 suspected fragrance allergens (all the regulated in the EU Cosmetics Directive amenable by GC, as well as pinene and methyleugenol) in cosmetic samples. The effects of the temperature, extraction time and solvent, and dispersing sorbent, affecting the whole proposed procedure, have been evaluated using a multifactor strategy. The optima conditions after the analysis of main and second order effects entailed the extraction at 120°C for 15 min, using hexane/acetone as solvent, and florisil as dispersing sorbent. The method performance has been studied, showing good linearity (R≥0.996) as well as good precision (RSD≤10%). Detection limits (S/N=3) ranged from 0.000001 to 0.0002% (w/w), values far below the established restrictions as regard labelling in the European Cosmetics Regulation. Reliability was demonstrated through the quantitative recoveries of all the studied compounds. The absence of matrix effects allowed quantification of the compounds by calibration with standard solutions. The analysis of 10 samples (several moisturizing and anti-wrinkle creams and lotions, hand creams, and sunscreen and after-sun creams), covering very different matrices, showed the presence of suspected allergens in all the analyzed samples; in fact, half of the samples contained an elevated number of them. Although the ubiquity of these compounds was demonstrated, labelling was in all cases in consonance with the European Cosmetics Regulation. 相似文献
125.
Rosa IL Filho PC Neri CR Serra OA de Figueiredo AT Varela JA Longo E 《Journal of fluorescence》2011,21(4):1575-1583
This work reports on the synthesis and characterization of a new complex of Eu3+ with the 3-hydroxypicolinamide ligand (Hhpa). Here we present an approach for obtaining bis[2-carbamoyl(κO)pyridin-3-olato(κO’)]
lanthanide complexes, which were characterized through elemental analysis, thermal analysis, infrared and photoluminescence
spectroscopies (emission, excitation, luminescence lifetimes, quantum efficiencies, Judd-Ofelt parameters and quantum yields).
Although hpa can act as a bidentate ligand in different conformations, the results attest for the occurrence of a unique coordination
site of low symmetry for the Eu3+ ions, in which two anionic hpa ligands coordinate the cations through an O/O chelating system. The phosphorescence of the
synthesized gadolinium complex provides the energy of the triplet state, which is determined to be at 20,830 cm-1 over the ground state. This makes the Hhpa ligand very adequate for sensitizing the Eu3+ luminescence, which leads to a very efficient antenna effect and opens a wide range of applications for the complex in light
emitting organic-inorganic devices. 相似文献
126.
Marcolan M Martins PA Pedrosa VA Rodrigues MR de Oliveira HP Codognoto L 《Journal of fluorescence》2011,21(2):733-738
A simple, rapid and effective analytical method based on fluorescence spectroscopy for the determination of coumarin in pharmaceutical
formulations without pre-treatment or pre-concentration step was development. Coumarin had maximum excitation and emission
at 310 nm and 390 nm, respectively. Optimum conditions for the detection of coumarin were investigated. Under optimized conditions,
we observed a linear behavior for the sign of coumarin in the concentration range of 2.5 × 10−6 to 1.0 × 10−4 mol L−1, with linearity of 0.998 and sensitivity of 2.9 × 1010 u.a/mol L−1. The proposed method was validated in terms of accuracy, precision and specificity of coumarin using the standard addition
and external calibration. It was noted that the results support (P < 0.05), indicating that the matrices were not an interference in the determination of coumarin by fluorescence spectroscopy.
The results were favorable compared with those obtained by reference chromatographic methods. 相似文献
127.
Ana Paula A. Marques Marcos Takashi S. Tanaka Elson Longo Edson R. Leite Ieda Lucia Viana Rosa 《Journal of fluorescence》2011,21(3):893-899
SrMoO4 doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating
materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr1−xEuxMoO4 powders, where x = 0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical
properties of the SrMoO4:Eu3+ were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent
Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800 °C for 2 h,
2θ = 27.8° (100% peak). The excitation spectra of the SrMoO4:Eu3+ (λEm. = 614 nm) presented the characteristic band of the Eu3 + 5L6 transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d)
one in the SrMoO4 matrix. The emission spectra of the SrMoO4:Eu3+ powders (λExc. = 394 and 288 nm) show the group of sharp emission bands among 523–554 nm and 578–699 nm, assigned to the 5D1→7F0,1and 2 and 5D0→7F0,1,2,3 and 4, respectively. The band related to the 5D0→7F0 transition indicates the presence of Eu3+ site without inversion center. This hypothesis is strengthened by the fact that the band referent to the 5D0→7F2 transition is the most intense in the emission spectra. 相似文献
128.
Ofelia T. Alas Lucia R. Junqueira Jan van Mill Vladimir V. Tkachuk Richard G. Wilson 《Central European Journal of Mathematics》2011,9(3):603-615
For a topological property P, we say that a space X is star Pif for every open cover Uof the space X there exists Y ? X such that St(Y,U) = X and Y has P. We consider star countable and star Lindelöf spaces establishing, among other things, that there exists first countable pseudocompact spaces which are not star Lindelöf. We also describe some classes of spaces in which star countability is equivalent to countable extent and show that a star countable space with a dense σ-compact subspace can have arbitrary extent. It is proved that for any ω 1-monolithic compact space X, if C p (X)is star countable then it is Lindelöf. 相似文献
129.
130.
The methods of theoretical chemistry have been used to elucidate molecular properties of selected and novel antiangiogenic
agents (semaxanib, sunitinib, N-methylsunitinib, sorafenib, motesanib, ABT-869, vatalanib, vandetanib, AEE 788, CP-547632, A-1, A-2, A-3, and A-4). The geometries
and energies of these drugs have been computed using HF/6-31G(d), Becke3LYP/6-31G(d) and Becke3LYP/6-31++G(d,p) model chemistries.
Wherever possible the most stable conformations of inhibitors studied are stabilized by means of intramolecular hydrogen bonds.
Water has a remarkable effect on the geometry of the antiangiogenic agents studied. Computed partition coefficients (ALOGPS
method) varied between 2.3 and 5. Compounds studied are described as lipophilic inhibitors. Semaxanib is inhibitor with lowest
lipophilicity. The antiangiogenic agents studied are only slightly soluble in water; their computed solubility (log S) from interval between −3.4 and −5.4 is sufficient for fast absorption. Selection criteria for drug-like properties of VEGFR2
inhibitors investigated were designed. Based on these criteria, three compounds (A-2, A-3, and A-4) were selected for synthesis
and biological testing for antianiogenic activity on VEGFR2 receptor. 相似文献