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排序方式: 共有315条查询结果,搜索用时 15 毫秒
81.
S. N. Bhadani Madhu Tewari Archana Agrawal K. Chandra Sekhar 《Fresenius' Journal of Analytical Chemistry》1994,349(6):478-481
A red, water-soluble complex of nickel with PAR can be extracted into chloroform with CTAB at pH 7.0. The system obeys Beer's law upto 0.5 g/ml with a molar absorptivity of 45 200 L·mol–1·cm–1 at 540 nm. Job's method of continuous variations revealed that the composition of the extracting species is 1:2:2 for nickel:PAR:CTAB. Based on this extraction, a highly sensitive and selective spectrophotometric method for the determination of nickel in polymetallic sea-bed nodules and in steels, after prior separation of iron and manganese, was developed. The standard deviation was 0.04–0.127 g for 5–25 g of nickel. 相似文献
82.
Sanjeev Jain Rajani Saktimayi Madhu Dubey Suresh Kumar Nema 《Macromolecular Symposia》1999,148(1):361-371
A novel polyimide-epoxy or PI-EP alloys are prepared by the modification of polyamic acid in the concentration range of 1.54×10−6 to 1.54×10−2 mol/L. The methanol sorption for these alloys at 24 hrs and at equilibrium conditions are determined and the residual solvent in fully cyclized polyimides were calculated. The presence of the residual solvent is visualized in fully imidized polymer and a structure containing partly imidized amic acid moiety is proposed and their concentration (in percentage) is calculated. The water sorption for these alloys at 24 hrs and at equilibrium conditions and the values of the water diffusion coefficient are determined from absorption isotherms. The PI-EP alloys have shown comparatively lower water sorption and higher diffusion coefficient than the unmodified polyimide. The mechanistic aspects of water sorption and diffusion are discussed. 相似文献
83.
84.
A simple method is described for the preparation of 3-aryl-2-thioxo-4(3H)-quinazolinones (4) by the reaction of anthranilic acids and ammonium or triethylammonium N-aryl-dithiocarbamates in ethanol. The method is
also applicable to the preparation of 3-ethyl-2-thioxo-4(3H)-quinazolinone. 相似文献
85.
86.
Bell PW Anand M Fan X Enick RM Roberts CB 《Langmuir : the ACS journal of surfaces and colloids》2005,21(25):11608-11613
Iso-stearic acid, a short, stubby compound with branched, methylated tails has been shown to have high solubility in carbon dioxide. Tail solvation by carbon dioxide makes iso-stearic acid a good choice for use as a ligand to sterically stabilize metallic nanoparticles. Iso-stearic acid coated silver nanoparticles have been stably dispersed in carbon dioxide with hexane cosolvent. Neat carbon dioxide has successfully dispersed iso-stearic acid coated silver nanoparticles that had been deposited on either quartz or polystyrene surfaces. These results are the first reports of sterically stabilized nanoparticles in carbon dioxide without the use of any fluorinated compounds. 相似文献
87.
This paper presents an environmentally friendly, inexpensive, rapid, and efficient process for size-selective fractionation of polydisperse metal nanoparticle dispersions into multiple narrow size populations. The dispersibility of ligand-stabilized silver and gold nanoparticles is controlled by altering the ligand tails-solvent interaction (solvation) by the addition of carbon dioxide (CO2) gas as an antisolvent, thereby tailoring the bulk solvent strength. This is accomplished by adjusting the CO2 pressure over the liquid, resulting in a simple means to tune the nanoparticle precipitation by size. This study also details the influence of various factors on the size-separation process, such as the types of metal, ligand, and solvent, as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. The pressure range required for the precipitation process is the same for both the silver and gold particles capped with dodecanethiol ligands. A change in ligand or solvent length has an effect on the interaction between the solvent and the ligand tails and therefore the pressure range required for precipitation. Stronger interactions between solvent and ligand tails require greater CO2 pressure to precipitate the particles. Temperature is another variable that impacts the dispersibility of the nanoparticles through changes in the density and the mole fraction of CO2 in the gas-expanded liquids. Recursive fractionation for a given system within a particular pressure range (solvent strength) further reduces the polydispersity of the fraction obtained within that pressure range. Specifically, this work utilizes the highly tunable solvent properties of organic/CO2 solvent mixtures to selectively size-separate dispersions of polydisperse nanoparticles (2 to 12 nm) into more monodisperse fractions (+/-2 nm). In addition to providing efficient separation of the particles, this process also allows all of the solvent and antisolvent to be recovered, thereby rendering it a green solvent process. 相似文献
88.
Anuradha Sharma Gurmeet K. Bakshi V. C. Dumir Madhu Raka 《Finite Fields and Their Applications》2004,10(4):133
Let q be an odd prime power and p be an odd prime with gcd(p,q)=1. Let order of q modulo p be f,
and qf=1+pλ. Here expressions for all the primitive idempotents in the ring Rpn=GF(q)[x]/(xpn−1), for any positive integer n, are obtained in terms of cyclotomic numbers, provided p does not divide λ if n2. The dimension, generating polynomials and minimum distances of minimal cyclic codes of length pn over GF(q) are also discussed. 相似文献
89.
Levitt MH Madhu PK Hughes CE 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,155(2):300-306
A new method for constructing phase cycles is described. The new schemes apply to experiments involving several consecutive coherence transfer steps. The radiofrequency phases of two or more irradiation blocks are incremented simultaneously, as opposed to the traditional "nested" scheme, in which the block phases are incremented independently. In many cases, the "cogwheel" phase cycles achieve the same selectivity as traditional phase cycles, using fewer steps. Significant time savings are achievable in a wide range of NMR experiments. 相似文献
90.
Wang J Pumera M Chatrathi MP Escarpa A Konrad R Griebel A Dörner W Löwe H 《Electrophoresis》2002,23(4):596-601
A fully disposable microanalytical device based on combination of poly(methylmethacrylate) (PMMA) capillary electrophoresis microchips and thick-film electrochemical detector strips is described. Variables influencing the separation efficiency and amperometric response, including separation voltage or detection potential are assessed and optimized. The versatility, simplicity and low-cost advantages of the new design are coupled to an attractive analytical performance, with good precision (relative standard deviation RSD = 1.68% for n = 10). Applicability for assays of mixtures of hydrazine, phenolic compounds, and catecholamines is demonstrated. Such coupling of low-cost PMMA-based microchips with thick-film electrochemical detectors holds great promise for mass production of single-use micrototal analytical systems. 相似文献