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981.
Many aspects of the behavior of surfactants have not been well understood due to the coupling of many different mechanisms.
Computer simulation is, therefore, attractive in the sense that it can explore the effect of different mechanisms separately.
In this paper, the shapes, structures and sizes of sodium dodecylbenzenesulfonate (SDBS) micelles under different concentrations
in an oil/water mixture were studied via molecular dynamics (MD) simulations using a simplified atomistic model which basically
maintains the hydrophile and lipophile properties of the surfactant molecules. Above the critical micellar concentration (cmc),
surfactant molecules aggregate spontaneously to form a wide variety of assemblies, from spherical to rodlike, wormlike and
bilayer micelles. Changes in their ratios of the principle moments of inertia (g1/g3, g2/g3) indicated the transition of micelle shapes at different concentrations. The aggregation number of micelle is found to have
a power-law dependence on surfactant concentration. 相似文献
982.
Zinc(II) and mercury(II) complexes were prepared by reacting isatin-3-thiosemicarbazone (ISTSCH) with zinc(II) acetate or mercury(II) bromide. The complexes were characterized by IR, Raman, diffuse reflectance, 1H and 13C NMR spectra and elemental analysis. Tetrahedral structures for Zn(ISTSC)2 and Hg(ISTSCH)Br2 are suggested. 相似文献
983.
Rakesh?Kumar?MahajanEmail author Jyoti?Chawla Mandeep?Singh?BakshiEmail author 《Colloid and polymer science》2004,282(10):1165-1168
Cloud point (CP) measurements of Tween 20 and Tween 80 were carried out in the presence of various glycol oligomers and triblock polymers (TBP). The cloud points of both Tween 20 and 80 decrease in the presence of both types of additives. Among the glycol oligomeric additives, ethylene glycol monobutyl ether was found to reduce the CP maximum. An increase in the repeating units of polymeric glycol additives leads to a decrease in CP. Reduction in the CP in the presence of TBP depends upon the increase in hydrophobic/hydrophilic ratio among the polypropylene to polyethylene units. 相似文献
984.
When a benzene ring bears two 2-methyl-1-naphthyl moieties in the para, meta or ortho positions as in 1,4-bis(2-methyl-1-naphthyl)benzene, 1, 1,3-bis(2-methyl-1-naphthyl)benzene, 2 and 1,2-bis(2-methyl-1-naphthyl)benzene 3, two rotational isomers (atropisomers) are generated, with the two naphthyl substituents in a syn or anti relationship. In the case of the para and meta derivatives (1 and 2, respectively) these atropisomers could not be separated but were detected by NMR spectroscopy, that also allowed the determination of their syn-anti interconversion barriers in solution (19.5 and 20.4 kcal mol−1, respectively) and, in the case of 2, also in the solid state (26.7 kcal mol−1). In the more hindered ortho derivative 3, the syn (meso) and anti (racemic) atropisomers interconvert in solution with a barrier (31.2 kcal mol−1) sufficiently high to allow their physical separation. The racemic form could also be separated (by enantioselective HPLC) into the PP and MM enantiomers. Analysis of the corresponding CD spectra allowed the assignment of the absolute configuration. When three such naphthyl substituents are bonded to the phenyl in a meta relationship, two atropisomers in statistical proportions were observed: the anti (Cs symmetry) and the syn (C3v symmetry) display a 3:1 ratio at the equilibrium in solution. This ratio is different in the solid state, as is the interconversion barrier (22.1 and 32.1 kcal mol−1 in solution and in the solid, respectively). 相似文献
985.
Paints and coatings are frequently encountered as types of materials that are submitted to forensic science laboratories as a result of trace evidence transfers. The aim of this study was to develop a method to complement the commonly used techniques in a forensic laboratory in order to better characterize these samples for forensic purposes. A laser ablation method has been used to simultaneously sample several layers directly prior to introduction into an inductively coupled plasma-mass spectrometer for the detection and quantification of the trace metals present in the layer(s). Time-resolved analysis plots displaying the elemental response and quantification of selected metals are compared to associate/discriminate paint samples. Matrix-matched standards were successfully incorporated into the analysis scheme for quantification of lead in the solid paint samples. Preparation of new matrix-matched standards for quantification of additional elements developed for this study are also presented. A sample set of eighteen (18) survey automotive paint samples have been analyzed with the developed method in order to determine the utility of LA-ICP-MS for trace element analysis of paints. 相似文献
986.
Barrett B Borek-Dohalský V Fejt P Vaingátová S Huclová J Nemec B Jelínek I 《Analytical and bioanalytical chemistry》2005,383(2):210-217
A validated, highly sensitive, and selective HPLC method with MS–MS detection has been developed for quantitative determination
of azithromycin (AZI) in human Na2EDTA plasma. Roxithromycin (ROX) was used as internal standard. Human plasma containing AZI and internal standard was ultrafiltered
through Centrifree Micropartition devices and the concentration of AZI was determined by isocratic HPLC–MS–MS. Multiple reaction
monitoring mode (MRM) was used for MS–MS detection. The calibration plot was linear in the concentration range 2.55–551.43 ng mL−1. Inter-day and Intra-day precision and accuracy of the proposed method were characterized by R.S.D and percentage deviation,
respectively; both were less than 8%. Limit of quantification was 2.55 ng mL−1. The proposed method was used to determine the pharmacokinetic profile of AZI (250-mg tablets). 相似文献
987.
A quantitative analysis method for penicillins including ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO) is proposed that makes use of the totally internally reflected resonance light scattering (TIR-RLS) signal from the penicillin at the H2O/CCl4 interface in the presence of cetyltrimethylammonium bromide (CTMAB), and enables the pharmacokinetics of penicillin taken orally and excreted through urine to be monitored. Penicillin is coadsorbed with CTMAB at the H2O/CCl4 interface in neutral solution, resulting in the formation of ion associates that display greatly enhanced TIR-RLS signals (maximum at 368–372 nm). This enhanced TIR-RLS intensity was found to be proportional to the penicillin concentration over the range 0.2×10–6 to 2.2×10–6 mol L–1, with limits of determination (3) of 5.0×10–8 to 7.0×10–8 mol L–1. Pharmacokinetics studies performed using the present method show that the excretion of orally-taken ampicillin through urine has a half-time of 1.05 h and an excremental quantum over 8 h of 49.3%, respectively. 相似文献
988.
Klaus Burger Gabor Radics Lothar Hennig Christoph B?ttcher Jan Spengler Fernando Albericio 《Monatshefte für Chemie / Chemical Monthly》2005,5(3):763-776
Starting from L-malic, L-citramalic, and rac. thiomalic acids routes to L-homoisoserine, 2-methyl-L-homoisoserine and rac. homoisocysteine have been developed. The new orthogonally protected and carboxy-activated building blocks are GABA as well as -hydroxy and -mercapto acid derivatives, suitable for the construction of peptide and depsipeptide surrogates. 相似文献
989.
Summary A simple method has been developed to determine the concentration of organic chlorine in waste oil. The determination is based on the conversion of organic chlorine to inorganic chloride by reaction with sodium biphenyl followed by extraction with nitric acid and a mixture of nitric acid and water. The concentration of chloride is determined by direct potentiometry with an ion-selective electrode. The limit of determination amounts to 3·10–5 mol·l–1 chloride ions with a standard deviation of 3.5%. Different samples of waste oil have been analyzed and the results have been compared to those obtained by combustion in a H2/O2 flame followed by potentiometric titration with silver nitrate. 相似文献
990.
Miloš Milovanovi? 《Polymer Degradation and Stability》2006,91(12):3221-3229
The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studied by thermogravimetry, as well as by analysis of the thermolysis volatiles and polymer residue. The characteristic mass loss temperatures were determined, as were the overall thermal degradation activation energies of three PDEF samples of varying molar mass. Ethylene and ethanol were present in the thermolysis volatiles at degradation temperatures below 300 °C, while diethyl fumarate was also evidenced at higher degradation temperatures. The amount of monomer increased with increasing degradation temperature. The dependence of the molar mass of the residual polymer on the degradation time and temperature was established and the number of main-chain scissions per monomer unit, s/P0, calculated. A thermal degradation mechanism including de-esterification and random main-chain scission is proposed. The thermal degradation of PDEF was compared to the thermolysis of poly(ethyl methacrylate) (PEMA), poly(diethyl itaconate) (PDEI) and poly(ethyl acrylate) (PEA). 相似文献