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991.
The velocity imaging photoionisation coincidence (VIPCO) technique is shown to be a powerful tool for studies of ion pair formation. Sequential mechanisms are demonstrated for some three-body ion pair formation reactions. Observation of a new type of reaction producing one negatively and two positively charged ions plus an electron is reported. 相似文献
992.
F. Cataldo Y. Keheyan S. Baccaro 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):443-450
Anthracite coal and oil bitumen were submitted to γ-radiation at a total dose of 1 MGy and the radiation-processed samples
were studied by FT-IR spectroscopy, thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The coal samples
were studied also by TGA coupled with FT-IR spectroscopy of the evolved gases. Thermal analysis has revealed a completely
different behavior of the radiolyzed samples in comparison to the unirradiated samples. Both for coal and bitumen significantly
less volatile fraction was released during the TGA and in both cases a significant increase in the amount of carbon coke produced
at 800-900 °C was observed. The radiation processed bitumen increased significantly its ethyl acetate insolubles content.
These results were interpreted in terms of extensive crosslinking and coalification of the samples under the action of γ-radiation.
The results of this study have been applied to the carbonization process of terrestrial sedimentary organic matter which is
commonly attributed to the action of heat flux from the depth of the Earth but which may be also due to the action of natural
radiation. Other application of the results of the present study is to the complex organic matter present on the surfaces
of comets and meteorites. This complex matter was formed by exposure of simple precursors to a field of high energy radiation
for millions or billions of years and is consequently transformed into coal-like and bitumen-like matter. The same arguments
apply to the carbon grains present in the interstellar and circumstellar medium.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
993.
R. K. Chernova L. M. Kozlova E. M. Spiridonova L. V. Burmistrova 《Journal of Analytical Chemistry》2006,61(8):760-766
The main analytical characteristics of the reaction of hexaoxacycloazochrom with lead were determined. A method for the sorption preconcentration of lead on the Thiopan 14 sorbent was proposed. Procedures were developed for the photometric determination of lead in natural waters, air, and soil at the level of the maximum permissible concentration. A new melange gel technique for preparing silicic acid xerogels modified with hexaoxacycloazochrom was developed for the test determination of lead in environmental samples at the level of the maximum permissible concentration. 相似文献
994.
The low vapor pressure and the versatility of the physico-chemical properties of ionic liquids make them really attractive as an alternative for conventional molecular solvents. The knowledge of their physico-chemical properties (viscosity, conductivity, miscibility with organic solvents and anion-cation interactions) has appeared mandatory for better targeting their applications, although it is generally still lacking or incomplete.This work promotes capillary electrophoresis instrumentation as an integrated apparatus for measurement of viscosity, conductivity and absorbance of pure ionic liquids and ionic liquid-molecular solvent mixtures. Compared to current conventional techniques, the assets of this instrumentation for this purpose are the combined availability of a pressure delivery system, power supply, diode array absorbance detector and thermoregulation device, allowing unattended, automatic and easy operation, involving minimum sample handling. Most importantly, the required sample volume can be reduced to about 50 μL, making this protocol very cost-effective. A protocol was optimized with respect to time, sample consumption and data reliability for the determination of these physico-chemical parameters. Ionic liquids selected for method development and validation differed in the nature of their cation (butyl- and ethyl-methylimidazolium) and anion (trifluoromethanesulfonate and bis(trifluoromethanesulfonyl)imide). Various molecular solvents were mixed with these ionic liquids (acetonitrile, methanol, dimethylformamide and trifluoroethanol) and the same physico-chemical properties were determined by optimized methods. The knowledge of these data should be of great support in various application areas, including the development of new separation media for capillary electrophoresis and chromatographic techniques. 相似文献
995.
P. Quevauviller M. Lachica E. Barahona A. Gomez G. Rauret A. Ure H. Muntau 《Fresenius' Journal of Analytical Chemistry》1998,360(5):505-511
Single extraction tests are commonly used to study the eco-toxicity and mobility of metals in soils, e.g. to assess the bioavailable
metal fraction (and thus to estimate the related phyto-toxic and nutritional deficiency effects) and the environmentally accessible
trace metals upon disposal of e.g. sediment on to a soil (e.g. contamination of ground waters). However, the lack of uniformity
in the different procedures does not allow the results to be compared worldwide nor the procedures to be validated. This paper
describes the interlaboratory testing of EDTA- and DTPA-extraction procedures for soil analysis, followed by the preparation
of a calcareous soil reference material (CRM 600), the homogeneity and stability studies and the analytical work performed
for the certification of the EDTA- and DTPA- extractable contents of some trace metals (following the standardized extraction
procedures).
Received: 21 May 1997 / Revised: 4 July 1997 / Accepted: 9 July 1997 相似文献
996.
S. J. Parry B. A. Bennett R. Benzing A. E. Lally 《Journal of Radioanalytical and Nuclear Chemistry》1997,219(2):191-196
Radiochemical techniques play an important role in nuclear waste management studies at the Centre for Analytical Research in the Environment. Current research includes the measurement of atmospheric emissions from a reprocessing plant, modelling of environmental pathways, and evaluation of reactor materials for the prediction of releases from ultimate disposal sites. A radiochemical separation procedure has been developed for129I, which has been applied to a study of emissions from the Sellafield nuclear reprocessing plant. Atmospheric emissions, rainfall, grass, milk and wild food are analysed to model the ultimate fate of129I. A new procedure has been developed for measuring sub-ppm concentrations of chlorine in archive steel samples as part of programme to produce an inventory of arisings of36Cl from nuclear power stations. The method has been extended to other reactor materials and this paper describes the application of the radiochemical method for Magnox alloys, mild steel and cast iron. 相似文献
997.
L. Ya. Zakharova S. B. Fedorov L. A. Kudryavtseva V. A. Bel'skii A. B. Mirgorodskaya B. E. Ivanov 《Russian Chemical Bulletin》1990,39(8):1555-1559
The hydrolysis of bis(chloromethyl)phosphonic acid p-nitroanilide has been studied in the pH range 6.86–13.0 and the effects of ionic surfactant micelles on this process have also been examined. The nature of the micellar effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) on this reaction lead us to conclude that both the neutral and anionic forms of the substrate are reactive, and that in the range of pH > pKa hydrolysis of the ionic form of the anilide predominates, while at pH < pKa the reaction of the neutral form is predominant. The binding constants for both the neutral and anionic forms of bis(chloromethyl)phosphonic acid p-nitroanilide in micellar CTAB and SDS solutions have been determined using a kinetic method, as well as by measuring the changes in the acid-base properties of the substrate resulting from the influence of micelles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1718–1722, August, 1990. 相似文献
998.
The selectivity of the oxides under consideration to the oxidation of methanol to formaldehyde is shown to increase in the sequence V2O5–Nb2O5–Ta2O5. The same sequence corresponds to the decrease in specific activity. The activation energy of the reaction is 12 kcal/mol for V2O5, 14 kcal/mol for Nb2O5 and 22 kcal/mol for Ta2O5.
, V2O5–Nb2O5–Ta2O5. . : V2O5 12 /, Nb2O5 14 / Ta2O5 22 /.相似文献
999.
Copolymers of acrylic acid, methyl methacrylate and glycidyl methacrylate have been synthesized and converted into cross-linked hydrophilic membranes by successive treatments with heat, alkali solution and acidic solution. The copolymerization was carried out in solution using tetrahydrofuran and p-dioxane as solvents. The polymer was obtained as a clear viscous solution at yields of approximately 95%. The polymerization was stopped before gelation took place. This gelation resulted from the reaction of epoxy and carboxylic groups of the polymeric chain. The polymerization time ranged from 3.5 to 7 hr depending on the content of the glycidyl methacrylate in the feed. The monomer mixture consisted of 25–45 mol% of acrylic acid, 40–70 mol% of methyl methacrylate and 2.5–15 mol% of glycīdyl methacrylate. With increasing content of acrylic acid, the membranes became soft and elastic; with decreasing content, they became brittle and hydrophobic. The swelling of the cured polymeric film increased with increase in the acrylic acid content of the monomer mixture and decreased with increasing glycidyl methacrylate content. Dialysis runs were conducted with sodium chloride, urea and a series of ethylene glycols with molecular weights up to 600. The permeability coefficients through the membranes for the ethylene glycols were similar to those through a commercial cellulose membrane (Cuprophane). The permeability proportional to . The membranes showed very low permeabilities to sodium chloride compared with those of commercial nonionic membranes. This appears to be due to the ionic exclusion mechanisms expected for ion exchange membranes. 相似文献
1000.
A. J. Blotcky E. P. Rack R. R. Recker J. A. Leffler S. Teitelbaum 《Journal of Radioanalytical and Nuclear Chemistry》1978,43(2):381-388
A destructive neutron activation analysis procedure was developed for determining trace aluminum content in bone. It was found
that soil contamination can influence the aluninum bone levels in prehistoric bone specimens. These maximum aluninum content
values for prehistoric bone are larger than those of modern bone and comparable to aluminum levels present in bone from renal
patients. 相似文献