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991.
The first examples of rotaxanes based on calixarenes threaded by dialkylammonium ions, which also represent the first examples of calixarene-based molecular shuttles, are reported. The base/acid treatment demonstrated that these systems act as molecular shuttles, which move between three sites on the axle. When small OMe groups are appended at the calix[6]arene lower rim an unprecedented inversion of its shuttling direction is observed, which occurs through a cone-to-cone inversion of the macrocycle. 相似文献
992.
Correia VG Bonifácio VD Raje VP Casimiro T Moutinho G da Silva CL Pinho MG Aguiar-Ricardo A 《Macromolecular bioscience》2011,11(8):1128-1137
A method using supercritical CO(2) to obtain biocompatible 2-oxazoline-based oligomers quaternized with different amines is described. The synthesized oligo(2-oxazoline)s display partial carbamic-acid insertion at one end. The syntheses of quaternary oligo(2-bisoxazoline)s and linear oligoethylenimine hydrochlorides are reported. Oligo(2-methyl-2-oxazoline) and oligo(2-bisoxazoline) quaternized with N,N-dimethyldodecylamine are the most efficient biocidal agents showing fast killing rates against Staphylococcus aureus and Escherichia coli. Linear oligoethylenimine hydrochloride shows the lowest MIC values but higher killing times against both bacteria. Based on the antimicrobial activity studies, a cooperative action of carbamic acid with the ammonium end group is proposed. 相似文献
993.
Doménech-Carbó MT Silva MF Aura-Castro E Fuster-López L Kröner S Martínez-Bazán ML Más-Barberá X Mecklenburg MF Osete-Cortina L Doménech A Gimeno-Adelantado JV Yusá-Marco DJ 《Analytical and bioanalytical chemistry》2011,399(9):2921-2937
This work proposes a multi-method approach that combines advanced microscopy (SEM/EDX, AFM) and spectroscopy (UV-vis and FTIR) techniques. This approach not only characterises the behaviour of the additives of two commercial poly(vinyl acetate) (PVAc) and acrylic emulsion paints but also simultaneously characterises the changes in chemical composition and morphology observed in the paint films as a result of ageing due to the paints being exposed to an intense source of simulated daylight. In parallel, a series of mechanical tests were performed that correlate the chemical changes in composition and the changes observed in the films' mechanical properties. This work was a comparative study between both types of acrylic and PVAc paints. The results obtained are of great interest for the modern paint conservation field as they provide valuable information on the mid- and long-term behaviours of these synthetic paints. 相似文献
994.
Dariusz Wyrzykowski Michał Wera Artur Sikorski Dagmara Jacewicz Lech Chmurzyński 《Central European Journal of Chemistry》2011,9(6):1096-1101
The crystal structure of 2-methylpyridinium tetrachloroferrate(III) was determined. The iron cation is tetracoordinated by
chloride anions, and it adopts a slightly distorted tetrahedral coordination with three angles smaller, two almost equal and
one larger than the tetrahedral. The compound is isostructural with its 3-, and 4-methylpyridinium analogues. The thermal
properties of 2-, 3- and 4-methylpyridinium tetrachloroferrates(III) have been studied using TG and DSC techniques. The compounds
exhibit a high stability in the melt.
相似文献
995.
Clara S. B. Gomes Cludia A. Figueira Patrícia S. Lopes D. Suresh Pedro T. Gomes M. Teresa Duarte 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(8):o315-o318
The crystal structures of two p‐substituted phenylformiminopyrrole derivatives, namely 2‐[(4‐fluorophenyl)iminomethyl]pyrrole, C11H9FN2, (1), and 2‐[(1H‐pyrrol‐2‐ylmethylidene)amino]benzonitrile, C12H9N3, (2), bear F and C[triple‐bond]N electron‐withdrawing groups, respectively. Both structures feature two independent molecules in the asymmetric unit forming dimers via N—H...N hydrogen bonds. In the case of (1), each dimer interacts with two other dimers via C—H...F contacts, thus forming one‐dimensional chains in the b direction, whereas in the case of (2), a weak C—H...N interaction connects the dimers in one‐dimensional chains in the (110) direction. 相似文献
996.
Ana María Atria Gino Corsini Natalia Herrera Maria Teresa Garland Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(5):m169-m172
The two isomorphous title compounds, [M(C5H7N6)2(C9H6O4)2(H2O)2]·4H2O or M2+(Hdap+)2(hpt2−)2(H2O)2·4H2O {where dap is 2,6‐diaminopurine, H2hpt is homophthalic acid [2‐(2‐carboxyphenyl)acetic acid] and M is NiII or CoII}, consist of neutral M2+(Hdap+)2(hpt2−)2(H2O)2 monomers, where the MII cation lies on an inversion centre and its MN2O4 octahedral environment is defined by one N atom (from Hdap+), two O atoms (from one hpt2− dianion and one water molecule) and their inversion images. The structures are unusual in that the Hdap+ cation occurs in an uncommon protonated state (as 2,6‐diamino‐7H‐purin‐1‐ium) and both ligands bind in an unprecedented monodentate fashion. The existence of a large number of donors and acceptors for hydrogen bonding, together with π–π interactions, leads to a rather complex three‐dimensional structure. 相似文献
997.
For a family of differential equations with infinite delay, we give sufficient conditions for the global asymptotic, and global exponential stability of an equilibrium point. This family includes most of the delayed models of neural networks of Cohen-Grossberg type, with both bounded and unbounded distributed delay, for which general asymptotic and exponential stability criteria are derived. As illustrations, the results are applied to several concrete models studied in the literature, and a comparison of results is given. 相似文献
998.
Aqueous sulfuric acid can be used as the mobile phase in cation ion chromatography to separate the three biogenic amines, putrescine, cadaverine, and histamine, from fish. Various concentrations of aqueous sulfuric acid were investigated to optimize the separation of these three biogenic amines. Aqueous sulfuric acid (5.0 mM) was found to be optimum for the separation and was used to determine the three biogenic amines in fish. The LOQ, defined as the lowest level of the standard calibration curve, was 0.055 ppm (equivalent to 0.55 microg/g sample) for putrescine, 0.05 ppm (equivalent to 0.5 microg/g sample) for cadaverine, and 1.0 ppm (equivalent to 10 microg/g sample) for histamine. From statistical analysis of the LOQ, the method detection limit was 0.003 ppm for putrescine, 0.009 ppm for cadaverine, and 0.16 ppm for histamine. For sample preparation, the fish was composited, homogenized in methanol-water (75 + 25, v/v), incubated for 15 min at 60 degrees C, and centrifuged. The sample solution was micron-filtered before injection. The mobile phase flow rate was 0.8 mL/min under isocratic conditions at room temperature (15-25 degrees C). The three biogenic amines were separated in the order of increasing retention time, i.e., putrescine, cadaverine, and histamine, within 30 min. The chromatograms showed complete peak separation of the three amines regardless of the difference in fish matrixes. 相似文献
999.
Sajewicz M Staszek D Natic M Waksmundzka-Hajnos M Kowalska T 《Journal of chromatographic science》2011,49(7):560-567
In the previous paper from this series, we proposed mass spectrometric fingerprinting of complex botanical samples upon the examples of the pharmacologically important phenolic acids and flavonoids selectively extracted from Salvia lavandulifolia. In this study, we explore fingerprinting efficiency with a novel two-dimensional analytical system composed of the reversed-phase thin-layer chromatography and the reversed-phase high performance liquid chromatography with mass spectrometric detection (2D RP-TLC-RP-LC-MS). We also compare its efficiency with that of the one-dimensional analytical system (the reversed-phase thin-layer chromatography with mass spectrometric detection; 1D RP-TLC-MS). As our present study is basically focused on the method development, we considered it as justified to carry out our comparison with the phenolic acid extracts selectively derived from the Salvia lavandulifolia species, similar as it was done in Part II from this series. Upon the results obtained, it was established that the 1D RP-TLC-MS mode and the 2D RP-TLC-RP-LC-MS mode can be applied to fingerprinting of herbal extracts, and that the 2D RP-TLC-RP-LC mode can provide a more abundant information than that originating from the 1D RP-TLC mode. 相似文献
1000.
A focused ultrasonic solid-liquid extraction (FUSLE) and high performance liquid chromatography (HPLC) with a diode array detector (DAD) is proposed for the determination of ten fat-soluble UV filters in packaging. FUSLE technique is relatively new and has been used for the extraction of a few analytes; such as polycyclic aromatic hydrocarbons and other organic pollutants. In this work, it has been demonstrated that FUSLE is a useful, fast and simple extraction methodology for UV filters because the complete extraction was carried out with just 6ml of tetrahydrofuran and in only one cycle of 30s. The developed method has been validated and applied to the analysis of polyethylene-based multilayer packaging samples. The FUSLE-based method allows the sensitive detection of most of the UV-filters in polyethylene, with limits of detection between 0.4 and 8.5ngmg(-1) (except for BDM). Intra and inter-day relative standard deviation values were below 5 and 14%, respectively, except for MBP. In addition, the proposed method was more efficient than tetrahydrofuran extraction under reflux for 2.5h for all the analytes except for EMT and BDM. Therefore, the developed method can be used to establish the absorption capability of different types of packaging and this information will be very useful in packaging selection. 相似文献