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991.
Santos EM Araújo AN Couto CM Montenegro MC 《Analytical and bioanalytical chemistry》2006,384(4):867-875
The construction and general performance of new valproate-selective electrodes based on manganese(III) tetraphenylporphyrin
[Mn(III)TPP-Cl], as an ionophore, are presented. The ionophore was incorporated into PVC and ceramic membranes (sol–gel) based
on methyltriethoxysilane. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives
in PVC membranes were investigated concerning their influence on the slope, response time, selectivity and lifetime of the
electrodes. The PVC membrane without additive and the sol–gel membrane presented slopes and practical limits of detection
of −60.8 mV dec−1 and 5x10−6 mol l−1 and −60.3 mV dec−1 and 1×10−4 mol l−1, respectively. The sol–gel membranes displayed higher selectivity for valproate when compared with PVC membranes. These two
types of electrodes were coupled to a sequential-injection analysis (SIA) system for the direct determination of valproate
in pharmaceutical formulations. The association of Mn(III)TPP-Cl with the sol–gel support inserted in a SIA system provided
potentiometric sensors with an analytical range of 1x10−3–5x10−2 mol l−1, with a sample rate of 55 samples per hour and a sample and carrier consumption of 140 and 2,500 μl per determination, respectively. 相似文献
992.
Pérez-Ruiz T Martínez-Lozano C Martín J García MD 《Analytical and bioanalytical chemistry》2006,384(1):280-285
A very simple, rapid and highly sensitive flow injection fluorimetric method was developed for the determination of phylloquinone.
The assay was based on the on-line reduction of phylloquinone in dodecylsulfate micelles after irradiation with UV light.
The micellar medium enhanced the fluorescence and stability of the reduced phylloquinone. Under optimum experimental conditions,
the range of application of the technique was between 0.09 and 45.0 μg mL−1 and the detection limit was 0.05 μg mL−1. The sample throughput was 90 injections per hour. The reliability of the method for the routine analysis of phylloquinone
in vegetables and fruits is demonstrated. Extractions were made with hexane, and an automated solid phase extraction system
was used to purify the sample extracts prior to injection into the flow injection manifold. 相似文献
993.
Karbass N Sans V Garcia-Verdugo E Burguete MI Luis SV 《Chemical communications (Cambridge, England)》2006,(29):3095-3097
Long-term stable Pd(0) catalysts can be easily supported onto polymeric monoliths containing methyl-imidazole moieties and the corresponding reactors based on these materials can be applied for the continuous Heck reaction in near-critical EtOH. 相似文献
994.
Tortosa-Estorach C Ruiz N Masdeu-Bultó AM 《Chemical communications (Cambridge, England)》2006,(26):2789-2791
High selectivity in acids is obtained in the first example of hydrocarboxylation of 1-octene in supercritical carbon dioxide using a Pd/P(4-C6H4-CF3)3 catalyst system and a perfluorinated surfactant. 相似文献
995.
996.
Galano A Cruz-Torres A Alvarez-Idaboy JR 《The journal of physical chemistry. A》2006,110(5):1917-1924
A theoretical study of the mechanism and kinetics of the OH hydrogen abstraction from isopropylcyclopropane (IPCP) is presented. Optimum geometries, frequencies and gradients have been computed at the BHandHLYP/6-311++G(d,p) level of theory for all stationary points, as well as for additional points along the minimum energy path (MEP). Energies have been improved by single-point calculations at the above geometries using CCSD(T)/6-311++G(d,p) to produce the potential energy surface. The rate coefficients are calculated for the temperature range 260-350 K by using canonical variational theory (CVT) with small-curvature tunneling (SCT) corrections. Our analysis suggests a stepwise mechanism involving the formation of a reactant complex in the entrance channel and a product complex in the exit channel, for all the modeled paths. The reactant complexes are examined in detail, because they exhibit alkene-like structure. The excellent agreement between the overall calculated and experimental rate coefficients at 298 K supports the reliability of the parameters obtained for the temperature dependence and branching ratios of the IPCP + OH reaction, proposed here for the fist time. The expression that best describes the studied reaction is k(overall) = 6.15 x 10(-13)e1747/RT cm3 x molecule(-1) x s(-1). The predicted activation energy is -0.89 kcal/mol. 相似文献
997.
Favero LB Velino B Caminati W Arnason I Kvaran A 《The journal of physical chemistry. A》2006,110(33):9995-9999
The rotational spectra of the main isotopomer, of the (29)Si and of all (13)C isotopologues of axial and equatorial forms of 1-fluoro-silacyclohexane have been measured by conventional (only main species) and molecular beam Fourier transform microwave spectroscopy. r(0) and partial r(s) structures are given separately for the two forms. The main structural differences are discussed. From dipole moments and relative intensity measurements, a slight preference (E(Eq) - E(Ax) = 42 +/- 24 cm(-1)) for the axial conformer was found. The rotational spectra of some, the most intense, vibrational satellites have also been measured. They belong to the ring-puckering motions. 相似文献
998.
Angeles-Beltrán D Lomas-Romero L Lara-Corona VH González-Zamora E Negrón-Silva G 《Molecules (Basel, Switzerland)》2006,11(10):731-738
The catalytic ability of ZrO(2)/SO(4)(2-) to promote solventless three-component condensation reactions of a diversity of aromatic aldehydes, urea or thoiurea and ethyl acetoacetate was studied. Products resulting from Hantzsch and/or Biginelli multi-component reactions are obtained in the presence of solid acid catalysts using the same reactants but different temperature conditions. The sulfated zirconia catalyst can be recovered and recycled in subsequent reactions with a gradual decrease of activity. 相似文献
999.
1000.