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571.
Pace A Pibiri I Piccionello AP Buscemi S Vivona N Barone G 《The Journal of organic chemistry》2007,72(20):7656-7666
The experimental investigation of the base-catalyzed rearrangements of 3-acylamino-1,2,4-oxadiazoles evidenced a new reaction pathway which competes with the well-known ring-degenerate Boulton-Katritzky rearrangement (BKR). The new reaction consists of a one-atom side-chain rearrangement that is base-activated, occurs at a higher temperature than the BKR, and irreversibly leads to the corresponding 2-acylamino-1,3,4-oxadiazoles. An extensive DFT study is reported to elucidate the proposed reaction mechanism and to compare the three possible inherent routes: (i) the reversible three-atom side-chain ring-degenerate BKR, (ii) the ring contraction-ring expansion route (RCRE), and (iii) the one-atom side-chain rearrangement. The results of the computational investigation point out that the latter route is kinetically preferred over the RCRE and can be considered as the ground-state analogue of a previously proposed C(3)-N(2) migration-nucleophilic attack-cyclization (MNAC) photochemically activated pathway. The MNAC consists of the formation of a diazirine intermediate, involving the exocyclic nitrogen, that eventually evolves into a carbodiimide intermediate (migration); the latter undergoes a single intramolecular nucleophilic attack-cyclization step leading to the final 2-acylamino-1,3,4-oxadiazole. 相似文献
572.
In high-throughput proteomics, the bottom-up approach has become a widely used method for the identification of proteins that is based on tryptic peptide MS/MS analysis. Separation methodologies that use IEF of tryptic peptides have recently been introduced and provide an extra dimension of peptide separation. In addition to its great fractionation capability, tryptic peptide prefractionation by IEF can also increase the protein identification success. The pI information of the peptide gained can be successfully used in a post-database search filtering step. We introduce a filtering algorithm that is based on the comparison of the experimental and theoretical pI's to validate peptide identifications by MS/MS data search engines. 相似文献
573.
Ragno G Risoli A De Luca M Ioele G Oliverio F 《Analytical and bioanalytical chemistry》2007,389(3):923-929
A novel analytical technique able to determine the anti-ischemic drug trapidil in human serum and urine is proposed. In order
to achieve satisfactory sensitivity and selectivity, an extraction procedure was required to isolate the drug from complex
matrixes such as serum and urine. A solid-phase extraction procedure was investigated to both increase the analyte concentration
and eliminate the interfering molecules present in large amounts in both matrixes. Optimization of the extraction step was
realized by selecting a new polymeric sorbent based on a surface-modified styrene–divinylbenzene polymer which provided fast
and efficient drug extraction. Drug quantification was performed by using the third-order derivative spectra of the SPE eluates.
Absorbance specific signals at 3D335,316 and 3D316 nm for urine and serum, respectively, were demonstrated to be directly proportional to drug concentration and barely affected
by residual matrix interferences. Under the optimized experimental conditions the calibration plots were linear over the concentration
range 0.2–50 μg mL−1. The method was validated by analysis of a series of spiked samples. Accuracy (recovery of 95 and 94% for serum and urine,
respectively) and precision (RSD below 4%) were good.
Figure Assay of Trapidil in biological fluids by SPE and derivative spectrophotometry 相似文献
574.
Boatto G Nieddu M Pirisi MA Dessì G 《Rapid communications in mass spectrometry : RCM》2007,21(22):3716-3720
A simple method for the simultaneous identification and quantification of four 2,5-methylenedioxy derivatives of 4-thioamphetamine (ALEPH series) in plasma samples was developed. The method consists of solid-phase extraction (SPE) using a Bond Elut C(18) cartridge and capillary electrophoresis coupled with electrospray ionisation mass spectrometry (CE/ESI-MS). The SPE method used required only simple steps and provided a clean extract from which identification of each drug was feasible, even at low concentrations. The method was validated according to international guidelines. The calibration curves were linear over the concentration range of 50 to 1000 ng/mL for all drugs with correlation coefficients that exceeded 0.998. The lower limits of detection of the drugs were 23-43 ng/mL. The absolute recoveries for the drugs were 64-92% and 75-96% at concentrations of 100 and 500 ng/mL, respectively. The validation data (precision, accuracy, and recovery) show the reproducibility and selectivity of the method. This clean and simple method allows the routine detection of designer drugs such as thioamphetamines which may become a serious problem in the control of illegal drugs. 相似文献
575.
A single-laboratory validation was completed for a method to determine total terpene lactones in Ginkgo biloba products. The method determines terpene lactones on the basis of the main terpene lactones (Bilobalide, Ginkgolide A, Ginkgolide B, Ginkgolide C, and Ginkgolide J) by high-performance liquid chromatography with evaporative light-scattering detection after extraction. Nine matrixes were chosen for study, including crude leaf material, standardized dry powder extract, single- and multiple-entity finished products, and alcohol and glycerin tinctures. The sample purification with prepacked columns allows selective extraction of the terpene lactones with no interferences from any matrix under study. A Youden ruggedness trial testing 7 instrumental and preparation factors with the potential to affect quantitative results showed that 2 factors (volume of the column elution solvent and pH of the diluent) were the most important parameters to control during sample preparation. The method performed well in terms of precision; 4 matrixes tested in triplicate over a 3-day period showed an overall repeatability relative standard deviation (RSD) of about 3%. HorRat values were within the limits for performance acceptability, ranging from 0.5 to 1.0. Analysis of variance testing at a = 0.05 showed no significant differences among the within-or between-group sources of variation, although comparison of within-day, between-day, and total precision showed that most of the RSD came from within-day determinations except those for the Ginkgo dry extract (Gb-SLV-2). Accuracy testing at 4 concentration levels of terpene lactones obtained by spiking a negative control matrix at approximately 300, 750, 1500, and 2250 microg/mL gave recoveries of about 91% for the 300 microg/mL level, about 98% for the 750 microg/mL level, about 99% for the 1500 microg/mL level, and 97% for the 2250 microg/mL level with an overall recovery of 96% and an RSD of 3.2%. 相似文献
576.
577.
578.
We consider a nonlinear Neumann problem driven by the p-Laplacian differential operator with a nonsmooth potential (hemivariational
inequality). By combining variational with degree theoretic techniques, we prove a multiplicity theorem. In the process, we
also prove a result of independent interest relating and local minimizers, of a nonsmooth locally Lipschitz functional.
相似文献
579.
Effective monoallylation of anilines catalyzed by supported KF 总被引:1,自引:0,他引:1
A mild and straightforward monoallylation procedure for different anilines is described using the efficient, inexpensive, noncorrosive, and environmentally friendly reagent KF-Celite. By using only a 1/1.2 stoichiometric ratio of electrophilic reagent to aniline, in very short reaction times, the monoallylated products are obtained in high isolated yields via this procedure, which works very effectively regardless of the electronic nature of the substituent on the ring, although electron withdrawing groups make the reactions go even faster. 相似文献
580.
Fang J Wallikewitz BH Gao F Tu G Müller C Pace G Friend RH Huck WT 《Journal of the American Chemical Society》2011,133(4):683-685
A new zwitterionic conjugated polyelectrolyte without free counterions has been used as an electron injection material in polymer light-emitting diodes. Both the efficiency and maximum brightness were considerably improved in comparison with standard Ca cathode devices. The devices showed very fast response times, indicating that the improved performance is, in addition to hole blocking, due to dipoles at the cathode interface, which facilitate electron injection. 相似文献