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991.
Contreras Ricardo R. Fontal Bernardo Bahsas Alí Suárez Trino Reyes Marisela Bellandi Fernando Nava Flor Cancines Pedro 《Transition Metal Chemistry》2004,29(1):51-55
The synthesis of [benzyl-N,N-alkylbis(2-amino-1-cyclopentencarbodithioate)]MII [alkyl = ethene (L2) and propene, (L3) and M = Cu, Ni and Co] complexes and their characterization (u.v.–vis., FT-IR, 1H-n.m.r., mass spectra and cyclic voltametry) are reported. 相似文献
992.
Trace elements in small sample volumes of saliva were determined by coupling a high efficiency direct injection nebulizer to inductively coupled plasma mass spectrometry and employing quantification by isotope dilution. Aliquots of 0.4 ml of human saliva were mixed with 0.1 ml of concentrated nitric acid and diluted to 2 ml with water. Sample solutions were spiked with an isotopic solution enriched in 135Ba, 112Cd, 65Cu, 206Pb and 66Zn. The amount of each isotope added to the samples and the measurement procedure were adjusted to attain precise analytical results calculated from the isotope ratios 135Ba/138Ba, 112Cd/114Cd, 65Cu/63Cu, 206Pb/208Pb and 66Zn/68Zn. Data acquisition for Ba, Cu and Zn isotopes was performed for a single sample injection of 50 microl and in another sample injection the Cd and Pb isotopes were measured. Concentrations ranging from 5.0 to 16 microg l(-1) for Ba, from 0.50 to 1.1 microg l(-1) for Cd, from 6.0 to 50 microg l(-1) for Cu, from 0.8 to 18.8 microg l(-1) for Pb and from 46.0 to 230 microg l(-1) for Zn were found in saliva samples. Detection limits of 0.11, 0.03, 0.40, 0.05 and 0.59 microg l(-1) were determined for Ba, Cd, Cu, Pb and Zn, respectively. The concentrations found by isotope dilution were in agreement with those of the completely digested samples quantified by external calibration. The direct analysis of 30 samples per hour was attained with the proposed procedure, avoiding time-consuming digestion steps, contamination risks and matrix effects. 相似文献
993.
M. S. Rahman M. Parre?o R. Bossi A. B. Payá-Pérez B. Larsen 《Fresenius' Journal of Analytical Chemistry》1998,360(5):556-563
Six extraction methods for the analysis of PCBs (CB-28, CB-52, CB-101, CB-118, CB-138, CB-153 and CB-180) in sewage sludge
were tested. A certified reference material (CRM 392) was used for the evaluation of the performance of the methods. Soxhlet-Dean-Starch
with toluene as solvent, Soxhlet with hexane:acetone (2:3), cold digestion/saponification with 2 mol/L KOH in methanol followed
by partition with hexane, and sonicated liquid-solid extraction with hexane:acetone (1:1) produced accurate results (97%,
93%, 104%, and 88%, respectively) with acceptable precisions (6.2%, 6.8%, 15% and 12%, respectively). Results in close agreement
with the certified value for all congeners were obtained by treatment with BF3-methanol prior to partition with dichloromethane. However, this is a tedious procedure and involves the use of hazardous
compounds. Cyclic steam distillation produced results with an accuracy of around 80% and a good precision (5.2%). The very
low consumption of solvents and other expensive chemicals by this technique and the possibility of analyzing the extract directly
without clean-up make it an interesting alternative to the more sophisticated methods. Column elution with dichloromethane
was found to be less efficient (61%), but it is a rapid, direct method with a low consumption of solvents and it may therefore
serve as screening method.
Received: 29 April 1997 / Revised: 30 July 1997 / Accepted: 6 August 1997 相似文献
994.
Prásilová J 《Talanta》1966,13(11):1567-1571
A substoichiometric method for the determination of heavy rare earths (holmium, thulium) has been developed. After the addition of a substoichiometric amount of EDTA to the test sample of rare earth labelled with its radioactive isotopes, the negatively charged complex formed was separated by passage through a column of Dowex 50 x 8. Interfering metals can be removed by preliminary cupferron and diethylammonium diethyldithiocarbamate extraction. Concentrations of rare earth down to 4 x 10(-7)g 5 ml have been determined. 相似文献
995.
In this work we present a study of the F+CH(4)-->HF+CH(3) reaction (DeltaHdegrees(298 K)=-32.0 kcal mol(-1)) using different methods of the chemical reaction theory. The ground potential energy surface (PES) is characterized using several ab initio methods. Full-dimensional rate constants have been calculated employing the variational transition state theory and using directly ab initio data. A triatomic analytical representation of the ground PES was derived from ab initio points calculated at the second- and fourth-order M?ller-Plesset levels with the 6-311+G(2df,2pd) basis set, assuming the CH(3) fragment to be a 15 a.m.u. pseudoatom in the fitting process. This is suggested from experiments that indicate that the methyl group is uncoupled to the reaction coordinate. A dynamics study by means of the quasiclassical trajectory (QCT) method and employing this analytical surface was also carried out. The experimental data available on the HF internal states distributions are reproduced by the QCT results. Very recent experimental information about the reaction stereodynamics is also borne out by our QCT calculations. Comparisons with the benchmark F+H(2) and analogous Cl+CH(4) reactions are established throughout. 相似文献
996.
Monooctyl--(4-carboxyanilino)benzylphosphonic acid (H2L) was investigated as a novel reagent for the extraction and separation of lead(II) and bismuth(III) from nitrate solutions. Stoichiometric ionization constants of H2L in ethanol — water mixtures determined by potentiometric NaOH titration had values pKa1 2.25 and pKa2 4.33. Ethanol and chloroform solutions of H2L followed Beer's law at 300 nm and 296 nm, molar absorptivities being 2.94·104 mol–1·l·cm–1 and 2.85·104 mol–1·l·cm–1, respectively. HNO3 and HCl were also extracted into chloroform solutions containing H2L. Bismuth(III) was quantitatively transferred into the chloroform H2L solution at pH 1, and lead(II) at 3.5. The value of the separation factor DBi/DPb is 160 at pH 1. 相似文献
997.
New improved types of analytical columns Zorbax Eclipse XDB-C18 (75 mm x 4.6 mm i.d., 3.5 microm) and Zorbax Eclipse XDB-C18 (50 mm x 4.6 mm i.d., 1.8 microm) have been tested for determination of estradiol (active substance), methylparaben, propylparaben (preservatives) and estrone (degradation product) and compared with the conventional C18 columns (250 mm x 3.0 mm i.d., 5.0 microm). The Zorbax columns differ with their particle size, column length and ODS (octadecylsilica) type as well. Higher flow-rates (up to about 2.5 ml min(-1)) could be applied regardless to back-pressure. The analysis - previously done at 40 degrees C - could be performed even at ambient temperature. Analytical run was shortened to 3.5 min (from 12 min used for the conventional C18 column) with the same or better retention characteristics. System suitability data for all Zorbax columns show the advantages of these columns for the practical use in routine quality control of pharmaceuticals, particularly from the point of view of speed of analysis and solvent consumption. 相似文献
998.
Comparison
of the fragility index of different eudragit polymers determined by activation
enthalpies
Gabriella Csóka A. Gelencsér Dorottya Kiss Eszter Pásztor I. Klebovich Romána Zelkó 《Journal of Thermal Analysis and Calorimetry》2007,87(2):469-473
The present study aimed to apply fragility
index (m) of polymers in the determination
of the optimal amount of plasticizer in polymer films. The fragility index
of different Eudragit polymers (RS, RL, EPO) was assessed by differential
scanning calorimerty (DSC), applying the Arrhenius connection (logq–1/T
g).
The fragility of Eudragit EPO films proved to be the highest, while in the
case of RS and RL, the increase of the alkyl-chain length caused the increase
of fragility. Studying the effect of plasticizer (triethyl citrate, TEC) on
the m value of Eudragit RL and RS films,
a near linear reduction of the fragility index could be observed between 5–30%
TEC concentration, but above 30%, this value leveled out to constant. 相似文献
999.
J Mráz 《Journal of chromatography. A》1988,431(2):361-368
A simple method has been developed for the determination of N-acetyl-S-(N-methylcarbamoyl)cysteine in human urine. Treatment of a urine sample (1 ml) with ethanol (2 ml) and potassium carbonate (1.5 g) produces ethyl N-methylcarbamate, which is extracted into ethanol and measured by packed column gas chromatography with nitrogen-sensitive detection. The limit of quantitation in human urine is 1 microgram/ml and the between-sample coefficient of variation is 5-11%. Simultaneously, N,N-dimethylformamide, N-methylformamide and formamide can also be determined. 相似文献
1000.
The complexes (RN=CH-CH=NR)Co(NO)(CO) with R = isopropyl, 2,6-diisopropylphenyl, or p-tolyl are chemically and electrochemically reducible to radical anions at potentials which strongly depend on R. The DFT calculated structure for the neutral compound with R = iPr agrees with the experiment, and the computed structure of the anion radical reveals changes according to a reduction of the R-DAB ligand. EPR results confirm an (R-DAB)-based singly occupied molecular orbital in [(RNCHCHNR)Co(NO)(CO)](.-), with minor but detectable contributions from NO as supported by IR spectroelectrochemistry and as quantified by DFT spin density calculations. The calculations indicate increasingly stabilized CO, NO, and RNCHCHNR pi* acceptor orbitals, in that order. On the basis of TD-DFT (time-dependent density functional theory) calculations, the lowest-lying excited states are assigned to metal-to-(R-DAB) charge transfer transitions while bands due to the metal-to-nitrosyl charge transfer occur at higher energies but still in the visible region. Resonance Raman studies were used to probe these assignments. 相似文献