全文获取类型
收费全文 | 8398篇 |
免费 | 162篇 |
国内免费 | 3篇 |
专业分类
化学 | 4695篇 |
晶体学 | 189篇 |
力学 | 175篇 |
数学 | 1372篇 |
物理学 | 2132篇 |
出版年
2022年 | 157篇 |
2021年 | 173篇 |
2020年 | 119篇 |
2019年 | 164篇 |
2018年 | 167篇 |
2017年 | 154篇 |
2016年 | 274篇 |
2015年 | 215篇 |
2014年 | 279篇 |
2013年 | 657篇 |
2012年 | 419篇 |
2011年 | 478篇 |
2010年 | 378篇 |
2009年 | 338篇 |
2008年 | 400篇 |
2007年 | 365篇 |
2006年 | 312篇 |
2005年 | 265篇 |
2004年 | 241篇 |
2003年 | 253篇 |
2002年 | 200篇 |
2001年 | 159篇 |
2000年 | 147篇 |
1999年 | 111篇 |
1998年 | 120篇 |
1997年 | 91篇 |
1996年 | 82篇 |
1995年 | 117篇 |
1994年 | 66篇 |
1993年 | 55篇 |
1992年 | 75篇 |
1991年 | 49篇 |
1990年 | 74篇 |
1989年 | 66篇 |
1988年 | 68篇 |
1987年 | 60篇 |
1986年 | 69篇 |
1985年 | 105篇 |
1984年 | 118篇 |
1983年 | 70篇 |
1982年 | 69篇 |
1981年 | 78篇 |
1980年 | 86篇 |
1979年 | 58篇 |
1978年 | 65篇 |
1977年 | 71篇 |
1976年 | 64篇 |
1975年 | 61篇 |
1974年 | 50篇 |
1973年 | 43篇 |
排序方式: 共有8563条查询结果,搜索用时 15 毫秒
131.
The measurement of the isotope-exchange reaction between U/IV/ in the organic phase and U/III/ in the aqueous phase in the extraction systems: 7-8M HCl—5–40% TBP /aromatic diluent or CCL4/ were made. The high rate of exchange with the rate constant >102M–1min–1 was observed. 相似文献
132.
Kazimierz?DarowickiEmail author Waldemar?Felisiak Artur?Zieliński 《Journal of mathematical chemistry》2005,38(4):701-711
Oscillations of species concentration are phenomena accompanying several types of electrochemical and purely chemical processes.
Importance of analyzing of such processes results from both scientific and practical reasons. In the paper the authors deal
with investigation of time dependent spectra of various stages of Belousov-Zhabotinsky type chemical oscillations. As the
analytical tool the discrete wavelet transform is proposed. 相似文献
133.
Miroslaw Truszczyski 《Journal of Graph Theory》1984,8(1):171-176
In this note the second moment of the vertex degree sequence of planar graphs is considered. We prove that
- 1 If G is an outerplanar graph of order n ? 3 then
- 2 If G is a planar graph of order n ? 4 then
134.
Application of the ellipsoid method in an interactive procedure for multicriteria linear programming
Prof. Dr. R. Slowiński Dr. J. Warczyński 《Mathematical Methods of Operations Research》1984,28(3):89-100
The research reported in this paper is concerned with an application of the ellipsoid algorithm in the interactive multicriteria linear programming step method (STEM) byBenayoun et al. [1971]. Due to this application we eliminate some drawbacks of the original version of STEM and, moreover, we avoid extra computations connected with sensitivity analysis in every iteration. Specifically, we use the ellipsoid algorithm to minimize the Euclidean norm in the criterion space instead of the Chebyshev norm, which ensures that every solution submitted to the decision maker is efficient. As follows from a computational experiment, in comparison with the application of the simplex method, the proposed modification of STEM shows a smaller increase of the computational effort when the number of criteria increases. However, the absolute computation time becomes worse for problems of larger size.
Zusammenfassung In dieser Arbeit wird über eine Anwendungsmöglichkeit der Khachiyan-Shor-Algorithmus (Ellipsoid-Algorithmus) im Rahmen des STEM-Verfahrens zur interaktiven Lösung linearer Vektoroptimierungsmodelle berichtet. Auf diese Weise können einige spezifische Nachteile des STEM-Verfahrens in seiner Originalversion vermieden werden. Durch die Verwendung der Euklidischen Norm anstelle der beim STEM-Verfahren üblichen Tschebyscheff-Norm wird garantiert, daß dem Entscheidungsträger nur effiziente Lösungen vorgeschlagen werden. Die numerischen Erfahrungen zeigen, daß der Lösungsaufwand der hier vorgeschlagenen Modifikation des STEM-Verfahrens mit steigender Anzahl von Zielfunktionen weniger stark zunimmt als bei der üblichen Version. Dies gilt jedoch nicht hinsichtlich der allgemeinen Problemgröße.相似文献
135.
Bogusław Zegarliński 《Communications in Mathematical Physics》1984,96(2):195-221
The uniqueness and the global Markov property for the regular Gibbs measure corresponding to the interaction $$U_\Lambda (\varphi ): = \lambda \int\limits_\Lambda {d_2 x\int {d\varrho (\alpha ):e^{\alpha \varphi } :_0 (x)} } $$ [forλ>0,d?(α) a probability measure with support in \(( - 2\sqrt {\pi ,} 2\sqrt \pi )\) ] is proved. 相似文献
136.
The paper presents the results of testing
the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates
with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan
NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified
silica. The test results were obtained with the use of a derivatograph, measurements
of flammability by the method of oxygen index, in air and also with the use
of a cone calorimeter. The effect of the modification on the zeta potential
was also examined.
A considerable reduction in the flammability
of nitrile rubber vulcanizates filled with silica can be obtained by the modification
of filler with bromine or iodine. All the vulcanizates containing modified
silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates
with bromine-modified silica makes it possible to obtain non-flammable polymeric
materials. They neither ignite nor glow under the action of a flame source
for 30 s.
The findings can be a rational basis for the synthesis
of modified silica that can act as active filler and effective flame-retardant
agent at the same time. 相似文献
137.
The synthesised complex cis-[Cr(C2O4)(AaraNH2)(OH2)(OSO2)]− anion with SO
3
2−
as a ligand in the inner coordination sphere, where AaraNH2 denotes methyl 3-amino-2,3-dideoxy-α-d-arabino-hexopyranoside, was hydrolysed in the presence of acid at H+ concentrations from 0.01 to 2.7 m (HClO4). The reaction kinetics was studied with the stopped-flow spectrophotometric (u.v.–vis.) technique at temperatures of 5,
10, 15, 18 and 20 °C. This hydrolysis turned out to be a single-step process. Determined for this reaction were the rate constant
k
1 for the removal of SO2 from the coordination sphere of the cis-[Cr(C2O4)(AaraNH2)(OH2)(OSO2)]− ion and the constant pK
1 of the protonation of this species in the reaction preceding the hydrolysis. The final product of this reaction – a new complex
of CrIII, cis-[Cr(C2O4)(AaraNH2)(OH2)2]+, was obtained. A mechanism for the acid hydrolysis reaction is put forward based on the analysis of the rate constants obtained. 相似文献
138.
J. W. Mietelski P. Gaca P. Zagrodzki M. Jasińska M. Zalewski M. Tomczak N. Vajda E. M. Dutkiewicz 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(2):363-370
Activity concentration of 90 Sr and stable strontium concentration was analysed in 42 samples of animal (deer, roe-deer, elk and boar) bones, which mostly originated from north-eastern Poland. Strontium separation was performed by extraction chromatography. Determination of chemical yield was controlled by means of stable Sr determination using atomic spectrometry at the beginning and at the end of the separation procedure. Equilibrated 90 Sr and 90 Y activity was measured using a liquid scintillator spectrometer. Stable strontium range was from 55.4±1.7 ppm to 91.8±4.5 ppm, the mean was 71.84 ppm with a standard deviation (SD) of 9.31 ppm. The mean recovery of strontium was 26.7% with SD = 16.1%. The maximum activity of 90 Sr, equal to 629±13 Bq/kg (ash) was found for a deer sample from Augustów Primeval Forest. In average, deer show the highest radiostrontium level, followed by roe-deer, elk and the lowest level were observed for boar. Differences between boar and deer or roe-deer are significant in terms of Kruskal-Wallis statistical test. Animal bones from north-eastern Poland showed about twice the mean concentration of 90 Sr, compared to those of south-central Poland, but the difference was found not significant. Activities observed in roe-deer bones suggest the deposition of a concentration of 1.9 to 3.5 kBq/m2 in the average of Chernobyl-origin 90 Sr in 1986 in north-eastern Poland. 相似文献
139.
Zainuddin J. Albinska P. Ulański J. M. Rosiak 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(3):339-344
The effects of g-irradiation on solid poly(ethylene oxide) (PEO) of an initial weight-average molecular weight of 6.3.105 Da were investigated by gel permeation chromatography and viscometry. The parameters studied were changes in number- and weight-average molecular weight, molecular weight distribution and viscosity of PEO in aqueous solution. Irradiation of poly(ethylene oxide) powder in the presence of oxygen leads to the dominance of chain scission reactions. Their high radiation-chemical yield [G(scission) » 2.5.10-6 mol/J] indicates the occurrence of effective chain reactions. Upon irradiation in vacuum, crosslinking and scission occur side-by-side and the changes in molecular weight are less pronounced in the studied dose range (up to 20 kGy). Scission dominates for doses up to ca. 15 kGy, while for higher doses intermolecular crosslinking gains in importance. The competition between these processes seems to depend not only on the applied dose but also to be influenced by the inhomogenity of the material (molecular weight and/or possibly the crystallinity). Parallel occurrence of scission and crosslinking leads to the broadening of the molecular weight distribution. 相似文献
140.
The interaction of oxygen with preadsorbed hydrogen on thermally activated magnesium oxide has been studied by temperature-programmed desorption (TPD) method. It was found that oxygen at 450 K reacts with preadsorbed hydrogen and the resulting hydroxylation suppresses the adsorptive capacity of magnesia with respect to oxygen.
. , 450 K , .相似文献