全文获取类型
收费全文 | 6024篇 |
免费 | 162篇 |
国内免费 | 1篇 |
专业分类
化学 | 3852篇 |
晶体学 | 27篇 |
力学 | 199篇 |
数学 | 777篇 |
物理学 | 1332篇 |
出版年
2023年 | 29篇 |
2022年 | 34篇 |
2021年 | 49篇 |
2020年 | 69篇 |
2019年 | 75篇 |
2018年 | 100篇 |
2017年 | 70篇 |
2016年 | 138篇 |
2015年 | 177篇 |
2014年 | 150篇 |
2013年 | 332篇 |
2012年 | 382篇 |
2011年 | 373篇 |
2010年 | 251篇 |
2009年 | 151篇 |
2008年 | 376篇 |
2007年 | 336篇 |
2006年 | 315篇 |
2005年 | 303篇 |
2004年 | 262篇 |
2003年 | 248篇 |
2002年 | 205篇 |
2001年 | 124篇 |
2000年 | 136篇 |
1999年 | 65篇 |
1998年 | 85篇 |
1997年 | 57篇 |
1996年 | 82篇 |
1995年 | 45篇 |
1994年 | 50篇 |
1993年 | 49篇 |
1992年 | 54篇 |
1991年 | 32篇 |
1990年 | 37篇 |
1989年 | 32篇 |
1988年 | 45篇 |
1986年 | 34篇 |
1985年 | 48篇 |
1984年 | 59篇 |
1983年 | 31篇 |
1982年 | 41篇 |
1981年 | 54篇 |
1980年 | 41篇 |
1979年 | 36篇 |
1978年 | 47篇 |
1977年 | 45篇 |
1976年 | 55篇 |
1975年 | 37篇 |
1974年 | 28篇 |
1973年 | 29篇 |
排序方式: 共有6187条查询结果,搜索用时 0 毫秒
61.
C. F. Gonzàlez-Fernandez M. Espinosa-Jimènez F. Gonzàlez-Caballero 《Colloid and polymer science》1983,261(8):688-693
An experimental investigation on streaming potentials of porous plugs of cellulose in both the linear and the non-linear range is described. The variation of the electrokinetic coefficients as a function of fibre concentration in the porous pad has been studied, using solutions of different concentration of Congo Red dye as a permeant. The trend observed for changes of both linear electrokinetic coefficientL 21 and non-linear coefficientL 211 as packing density,c F, increases, is somewhat analogous, the similarity suggesting some proportionality between both coefficients. The electroviscous effect accounts for the decrease ofL 211 with the increase ofc F. The coefficientL 221 was found to be always negative and, in absolute value, to decrease with increasingc F. Second-order coefficients have been interpreted in terms of modifications of “generalized conductivities” produced by the changes of thermodynamic forces. 相似文献
62.
The formalism developed in the first two papers of this series is applied to the investigation of a new weak-field model. This crystal-field model lies on the use of a symmetry-adapted weak-field basis and an effective Hamiltonian involving in a symmetrical way both spin- and orbit-dependent contributions. Some general properties of this Hamiltonian are studied and complete calculation of its matrix elements is conducted in a symmetry-adapted weak-field basis in the case of an arbitrary configuration nlN in any symmetry. The case of a configuration ndN in octahedral symmetry is fully explored. In this case, the proposed weak-field model is restricted to a 12-parameter model which accounts for isotropic and anisotropic Coulomb interactions, isotropic and anisotropic spin-orbit interactions, and crystal-field interactions. A comparison between this 12-parameter weak-field model and the 14-parameter strong-field model is established. Equivalence between the latter two models requires two constraint relations to be satisfied for some strong-field parameters. These two relations are examined with various viewpoints. 相似文献
63.
Paul De Bièvre 《Accreditation and quality assurance》2000,5(10-11):423-428
Talking about "traceability" means talking about a "property of the result of a measurement", about "the value of a standard", about "stated references" and about an "unbroken chain of comparisons". It describes by which comparison, and to which other value, the result of a measurement has been obtained, i.e. is "traceable to". It is about the underlying structure of the measurement process of the result of a measurement and therefore about the authority of the result. Since values carried by (certified) reference materials have also been obtained by measurement, the definition of traceability equally applies. Traceability in the context of reference materials is also about the authority of the values carried by the (certified) reference materials and is, therefore, of key importance for the authority of the reference materials themselves. Hence, values of results of measurements constitute part of the traceability chain and their uncertainties are an intrinsic accompanying phenomenon. Uncertainties need a traceability chain against which they can be evaluated, and a traceability chain is an a priori requirement for evaluating the uncertainty budget of a measurement result. An attempt has been made to exemplify "traceability" chains in some types of chemical measurement and to identify the degree of international agreement on the key elements of "traceability". It is concluded that there is less than universal agreement on this issue. The debate should continue in order to arrive at the international understanding and agreement needed, as "traceability" is now being incorporated in the International Organization for Standardization (ISO), the International Laboratory Accreditation Co-operation (ILAC) and in other "guiding" or regulatory documents. It is also the reason why the Institute for Reference Materials and Measurements (IRMM) has taken up the study of the concept in its core programme on Metrology in Chemistry, and why it sponsored the Workshop in Bratislava. 相似文献
64.
Thérèse Dupuis 《Mikrochimica acta》1967,55(3):461-464
Résumé Dans le spectre d'absorption infrarouge de l'iodatochromate de potassium K[(CrO3)(IO3)], on peut identifier la présence de bandes de vibration de valence de ponts Cr-0-I à 508 et680 cm–1.
Summary The infrared absorption spectrum of potassium iodatochromate K(CrO3)(IO3) contains vibration bands of the valence bridges Cr-O-I at 508 and 680 cm–1.
Zusammenfassung Im Infrarot-Absorptionsspektrum des Kaliumjodatochromats lassen sich Banden der Valenzschwingungen der Atomgruppe Or-O-J bei 508 und 680 cm–1 nachweisen.相似文献
65.
M. C. Bergère C. de Calan A. P. C. Malbouisson 《Communications in Mathematical Physics》1978,62(2):137-158
For any Feynman amplitude, where any subset of invariants and/or squared masses is scaled by a real parameter going to zero or infinity, the existence of an expansion in powers of and ln is proved, and a method is given for determining such an expansion. This is shown quite generally in euclidean metric, whatever the external momenta (exceptional or not) and the internal masses (vanishing or not) may be, and for some simple cases in minkowskian metric, assuming only finiteness of the — eventually renormalized — amplitude before scaling. The method uses what is called Multiple Mellin representation, the validity of which is related to a generalized power-counting theorem.On leave of absence from University of Bahia (Brazil). Fellow of CAPES, Brazil 相似文献
66.
M. Nève de Mévergnies 《Applied Physics A: Materials Science & Processing》1981,25(3):275-282
The multiphoton dissociation of CF3Cl induced by TEA-CO2 laser pulses has been studied in a focused beam geometry. TheR(10) [00°1–02°0] (
) laser line was used, so as to dissociate preferentially the minor isotopic component13CF3Cl. The isotopic selectivityS and the dissociation probability per pulse ω were measured in the pressure range between 0.25 and 8 Torr. With short laser
pulses (90 ns FWHM),S is found to increase slightly with gas pressure up to 2 Torr, and ω, to increase almost linearly over the whole pressure
range studied. A schematic model is proposed which satisfactorily explains these results if the transition rates across the
energy level spectrum of the CF3Cl molecules are assumed to increase with gas pressure. 相似文献
67.
This paper discusses heuristic branch and bound methods for solving mixed integer linear programming problems. The research presented on here is the follow on to that recorded in [3].After a resumé of the concept of pseudo-costs and estimations, new heuristic rules for generating a tree which make use of pseudo-costs and estimations are presented. Experiments have shown that models having a low percentage of integer variables behave in a radically different way from models with a high percentage of integer variables. The new heuristic rules seem to apply generally to the first type of model.Later, other heuristic rules are presented that are used with models having a high percentage of integer variables and with models having a special structure (models including special ordered sets.)The rules introduced here have been implemented in the IBM Mathematical Programming System Extended/370. They are used to solve large mixed integer linear programming models.Numerical results that permit comparisons to be made among the different rules are provided and discussed. 相似文献
68.
Brunetto R Gutiérrez L Delgado Y Gallignani M Burguera JL Burguera M 《Analytical and bioanalytical chemistry》2003,375(4):534-538
A column-switching high-performance liquid chromatographic method with UV detection for the determination of cocaine (COC) and benzoylecgonine (BZE) in human blood plasma samples is described. The method uses an alkyl-diol-silica ADS-C18 extraction precolumn. A 50- micro L plasma sample was introduced to the ADS precolumn in order to separate the analytes from proteins and endogenous compounds. The fraction containing COC and BZE was back-flushed and transferred to an Alltech mixed-mode C(18)/cation-exchange analytical column for final separation. The validation of the method revealed quantitative recoveries from 95.0 to 99.0% for COC at three different concentrations (0.5, 1.0 and 2.0 micro g mL(-1)), and from 96.0 to 99.0% for BZE at the same concentration levels with coefficients of variation <4.00% (n=5). The detection limit (signal to noise ratio (S/N)>3) was 0.03 micro g mL(-1) for all the compounds with an injection volume of 50 micro L. However, it was possible to enhance the sensitivity further by injecting larger plasma volumes, up to 200 micro L, at the same optimal conditions. The overlap of sample preparation, analysis and reconditioning of the extraction column, increase the overall sample throughput to 5 samples h(-1). The developed method has been applied to human blood plasma samples from subjects suspected of cocaine abuse. 相似文献
69.
The [Ru(bipy)(2)(1)](PF(6))(2) (bipy refers to 2,2'-bipyridine) complex, comprising a ruthenium(II) tris(2,2'-bipyridine) luminophore covalently linked to a di[(o-triethyleneglycoxy)phenyl]amine crown ether 1, has been synthesized and fully characterized. The photophysical properties of this metal complex have been examined in solution at ambient temperature. Luminescence from the metal complex is enhanced significantly in the presence of various adventitious cations, including protons. In particular, Li(+) cations bind to the crown ether, as evidenced by (1)H NMR and luminescence spectroscopy. Cation binding serves to decrease the rate of reductive quenching of the triplet state of the metal complex, thereby increasing the extent of luminescence. The solution-phase conformation of [Ru(bipy)(2)(1)](PF(6))(2), with and without encapsulated Li(+), has been examined by 2-D NMR and by molecular dynamics simulations. 相似文献
70.
The need for accurate (< 0.06%) isotopic blends of 6Liand 7Li is explained and their preparation is discussed. It is shown that lithium must be determined at an accuracy level better than 0.035%. Four methods — acid-base titration with hydrochloric acid or benzoic acid, and weighing as sulphate or carbonate — were tested and improved for the precise and accurate analysis of lithium hydroxide solutions. The results of these four methods for a 0.1 M solution agreed within ± 0.02%. The preparation of pure isotopically enriched lithium hydroxide solutions, with specially purified cation- and anion-exchangers, is described. The prepared products contain as little as 100 μg of other alkali metals and 50 μg of alkaline-earth metals per gram of lithium, and are sufficiently free of anions to permit accurate chemical assay of lithium. No changes in the isotopic compositions of 99% 6Li or 99.99% 7Li were detected during the treatment. 相似文献