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991.
Duarte P Ferreira DP Ferreira Machado I Vieira Ferreira LF Rodríguez HB San Román E 《Molecules (Basel, Switzerland)》2012,17(2):1602-1616
The photophysical behaviour of phloxine B adsorbed onto microcrystalline cellulose was evaluated by reflectance spectroscopy and laser induced time-resolved luminescence in the picosecond-nanosecond and microsecond-millisecond ranges. Analysis of the absorption spectral changes with concentration points to a small tendency of the dye to aggregate in the range of concentrations under study. Prompt fluorescence, phosphorescence and delayed fluorescence spectral decays were measured at room temperature and 77 K, without the need of sample degassing because cellulose protects triplet states from oxygen quenching. In all cases, spectral changes with time and lifetime distribution analysis were consistent with the dye coexisting in two different environments: dyes tightly entrapped between polymer chains in crystalline regions of cellulose showed longer fluorescence and phosphorescence lifetimes and more energetic triplet states, while dyes adsorbed in more amorphous regions of the support showed shorter lifetimes and less energetic triplet states. This behaviour is discussed in terms of the different dye-support interactions in both kinds of adsorption sites. 相似文献
992.
Paulo C. Carrião Patrícia L. Cunha Olímpio H. Miyagaki 《Nonlinear Analysis: Theory, Methods & Applications》2012
This paper deals with the Klein–Gordon–Maxwell system when the nonlinearity exhibits critical growth. We prove the existence of positive ground state solutions for this system when a periodic potential V is introduced. The method combines the minimization of the corresponding Euler–Lagrange functional on the Nehari manifold with the Brézis and Nirenberg technique. 相似文献
993.
Rmulo A. Ando Deborah R. C. Matazo Paulo S. Santos 《Journal of Raman spectroscopy : JRS》2010,41(7):771-775
Although the amine sulfur dioxide chemistry was well characterized in the past both experimentally and theoretically, no systematic Raman spectroscopic study describes the interaction between N,N‐dimethylaniline (DMA) and sulfur dioxide (SO2). The formation of a deep red oil by the reaction of SO2 with DMA is an evidence of the charge transfer (CT) nature of the DMA–SO2 interaction. The DMA–SO2 normal Raman spectrum shows the appearance of two intense bands at 1110 and 1151 cm−1, which are enhanced when resonance is approached. These bands are assigned to νs(SO2) and ν(ϕ N) vibrational modes, respectively, confirming the interaction between SO2 and the amine via the nitrogen atom. The dimethyl group steric effect favors the interaction of SO2 with the ring π electrons, which gives rise to a π–π* low‐energy CT electronic transition, as confirmed by time‐dependent density functional theory (TDDFT) calculations. In addition, the calculated Raman DMA–SO2 spectrum at the B3LYP/6‐311 + + g(3df,3pd) level shows good agreement with the experimental results (vibrational wavenumbers and relative intensities), allowing a complete assignment of the vibrational modes. A better understanding of the intermolecular interactions in this model system can be extremely useful in designing new materials to absorb, detect, or even quantify SO2. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
994.
Douglas José AlemJr. Pedro Augusto MunariJr. Marcos Nereu Arenales Paulo Augusto Valente Ferreira 《Annals of Operations Research》2010,179(1):169-186
This paper addresses the one-dimensional cutting stock problem when demand is a random variable. The problem is formulated
as a two-stage stochastic nonlinear program with recourse. The first stage decision variables are the number of objects to
be cut according to a cutting pattern. The second stage decision variables are the number of holding or backordering items
due to the decisions made in the first stage. The problem’s objective is to minimize the total expected cost incurred in both
stages, due to waste and holding or backordering penalties. A Simplex-based method with column generation is proposed for
solving a linear relaxation of the resulting optimization problem. The proposed method is evaluated by using two well-known
measures of uncertainty effects in stochastic programming: the value of stochastic solution—VSS—and the expected value of perfect information—EVPI. The optimal two-stage solution is shown to be more effective than the alternative wait-and-see and expected value approaches,
even under small variations in the parameters of the problem. 相似文献
995.
Eduardo Sobarzo‐Sánchez Eugenio Uriarte Lourdes Santana Ricardo A. Tapia Paulo Pérez Lourido 《Helvetica chimica acta》2010,93(7):1385-1394
2,3‐Dihydro‐6‐hydroxy‐5‐methoxy‐7H‐dibenzo[de,h]quinolin‐7‐one, 6‐hydroxy‐5‐methoxy‐7H‐dibenzo[de,h]quinolin‐7‐one, and 2‐(6,7‐dimethoxy‐3,4‐dihydroisoquinolin‐1‐yl)benzyl benzoate, easily available by a Bischler–Napieralski cyclization, were used as starting materials to afford 6‐oxoisoaporphine and 2,3‐dimethoxy‐5,6,8,12b‐tetrahydroisoindolo[1,2‐a]isoquinoline as the main products. However, the catalytic hydrogenation of the benzyl benzoate derivative afforded, under mild conditions, 1,2,3,4‐tetrahydro‐6,7‐dimethoxy‐1‐(2‐methylphenyl)isoquinoline. 相似文献
996.
Simionato AV Simó C Cifuentes A Lacava PT Araújo WL Azevedo JL Carrilho E 《Electrophoresis》2006,27(13):2567-2574
CE-ESI-MS with a liquid sheath interface and IT mass analyzer was used for analysis of siderophores from different strains of Methylobacterium spp. citrus endophyte extracts. Three Methylobacterium strains were investigated according to positive bioassay tests. Bacteria cultures were grown under Fe(III) absence (siderophore producing cultures) and under Fe(III) presence (control cultures). Siderophores were extracted from culture supernatant with polystyrene resins. BGE and sheath-liquid composition were optimized, respectively, in order to assure both, best peak resolution and ESI-MS sensitivity. The best analysis conditions were obtained with 100 mmol/L ammonium bicarbonate at pH 8 as BGE and methanol:H(2)O 25:75 + 0.05% formic acid as sheath liquid. CZE-ESI-MS analysis revealed two possible siderophores, according to bacterium species, presenting M(r) of 1004.3 and 798.3 Da. 相似文献
997.
A multivariate calibration model (PLS) was developed for the simultaneous spectrophotometric determination of Al(III) and Fe(III) in post-hemodialysis fluids with pyrocathecol violet (PCV) as chromogenic reagent. The analytes build stable complexes with PCV in presence of hexamine buffered medium at pH 6.1. The complexes show overlapped absorption bands in the spectral range of 220-800 nm so that absorptions of 580 wavelengths were necessary for the calibrations. Determinations of Al(III) and Fe(III) were done without masking agents. The best calibration model was obtained by using PLS-1 regression with three components after data mean centering. The spectrophotometric method applied to assay the analytes in real post-hemodialysis samples containing no desferrioxamine B presented good agreement with voltammetric measurements used as reference. Concentrations ranging from 0.20 to 0.60 mg L−1 for Al(III) and for Fe(III) were determined in real samples. The multivariate detection limits for Al(III) and Fe(III) were 0.044 and 0.052 mg L−1, respectively, and the calculated values of sensitivity were 6.33 for Al(III) and 3.44 for Fe(III). The proposed method showed to be straightforward and useful to follow the hemodialysis progress for patients under treatment. Interferents were also investigated. 相似文献
998.
Rodrigo S. Bitzer Ana Maria Rocco Paulo Sérgio Santos Carlos A.L. Filgueiras 《Journal of organometallic chemistry》2006,691(9):2005-2013
The reaction between cis-[Mo(CO)4(piperidine)2] and 2,3,5,6-tetrakis(α-pyridyl)pyrazine (TPP) in the 3:1 (Mo:TPP) stoichiometric ratio afforded the organobimetallic compound {[Mo(CO)4]2(μ-TPP)} (1) in 89% yield. This complex has been characterized by elemental and thermogravimetric analyses, vibrational (FT-IR and FT-Raman) and electronic spectroscopy, and 1H and 13C-CP/MAS NMR spectroscopy. NMR data have revealed that TPP coordinates to each metal at two adjacent pyridine nitrogen atoms, according to a rare bis-bidentate chelating mode. The cyclic voltammogram of 1 in DMF has shown an irreversible metal-based oxidation at +0.77 V versus SCE. A DFT/B3LYP study of two plausible molecular structures for 1 has been carried out in vacuum using the LACV3P(d,p) and LACV3P++(d,p) basis sets. This theoretical study has pointed to the structure with the Mo(CO)4 moieties on opposite sides with respect to the pyrazine ring (trans isomer - C2h symmetry) as the most stable one. The vibrational frequencies of the trans structure have been calculated at the B3LYP/LACV3P(d,p) level and compared with the FT-IR and FT-Raman spectra of 1. An excellent agreement between experimental and calculated frequencies was obtained. 相似文献
999.
1000.
Paulo L Freitas AA da Silva PF Shimizu K Quina FH Maçanita AL 《The journal of physical chemistry. A》2006,110(6):2089-2096
Synthetic and natural hydroxyflavylium salts are super-photoacids, exhibiting values of the rate constant for proton transfer to water in the excited state as high as 1.5 x 10(11) s(-1). The synthetic flavylium salt 4-carboxy-7-hydroxy-4'-methoxyflavylium chloride (CHMF) has an additional carboxyl group at the 4-position of the flavylium cation that deprotonates in the ground state at a lower pH (pK(a1) = 0.73; AH2+ --> Z) than the 7-hydroxy group (pK(a2) = 4.84; Z --> A-). Ground-state deprotonation of the carboxyl group of the acid (AH2+) to form the zwitterion (Z) is too fast to be detected by nanosecond laser flash perturbation of the ground-state equilibrium, while deprotonation of the hydroxyl group of Z to form the anionic base (A-) occurs in the microsecond time range (k(d2) = 0.6 x 10(6) s(-1) and k(p2) = 4.2 x 10(10) M(-1) x s(-1)). In the excited state, the cationic form (AH2+) deprotonates in approximately 9 ps, resulting in the excited neutral base form (AH), which is unstable in the ground state. Deprotonation of Z occurs in 30 ps (k(d2) = 2.9 x 10(10) s(-1)), to form excited A-, which either reprotonates (k(p3)* = 3.7 x 10(10) M(-1) x s(-1)) or decays in 149 ps, and shows an important contribution from geminate recombination to give the excited neutral base (AH). Predominant reprotonation of A- at the carboxylate group reflects both the presence of the negative charge on the carboxylate and the increase in the excited-state pK(a) of the carboxyl group. Thus, while the hydroxyl pK(a) decreases by approximately 5 units upon going from the ground state (pK(a) = 4.84) to the excited state (pK(a) = -0.2), that of the carboxyl group increases by at least this much. Consequently, the excited state of the Z form of CHMF acts as a molecular proton transporter in the picosecond time range. 相似文献