全文获取类型
收费全文 | 609篇 |
免费 | 12篇 |
国内免费 | 12篇 |
专业分类
化学 | 331篇 |
力学 | 4篇 |
数学 | 212篇 |
物理学 | 86篇 |
出版年
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 16篇 |
2014年 | 18篇 |
2013年 | 22篇 |
2012年 | 17篇 |
2011年 | 35篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 26篇 |
2007年 | 23篇 |
2006年 | 23篇 |
2005年 | 16篇 |
2004年 | 20篇 |
2003年 | 25篇 |
2002年 | 28篇 |
2001年 | 9篇 |
2000年 | 13篇 |
1999年 | 19篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1971年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有633条查询结果,搜索用时 31 毫秒
71.
Gottfried Glöckner Manfred Stickler Winfried Wunderlich 《Fresenius' Journal of Analytical Chemistry》1987,328(1-2):76-81
Summary Copolymers of styrene and ethyl methacrylate have been separated according to composition by gradient HPLC on silica columns or CN bonded phase columns. This mode of separation according to composition was applied to fractions obtained by size exclusion chromatography (SEC). From viscosity and molecular mass data of copolymers with a styrene content ranging from 7.5 to 95.3 mass-% it can be concluded that SEC separates mainly by molecular mass even in this copolymer system. Thus, chromatographic cross-fractionation is possible by prefractionation by SEC and subsequent separation according to composition by gradient HPLC.
Untersuchung von Copolymeren von Styrol und Ethylmethacrylat durch Ausschluß-Chromatographie und Gradienten-HPLC相似文献
72.
Baron A Herrero C Quaranta A Charlot MF Leibl W Vauzeilles B Aukauloo A 《Chemical communications (Cambridge, England)》2011,47(39):11011-11013
Spectroscopic, electrochemical and theoretical characterisations of photoactive systems readily assembled via click-chemistry show an efficient bi-directional charge shift through the triazole link. 相似文献
73.
We discuss some properties of exponents of q-product expansions of specific generalized modular functions on the congruence subgroup Γ0(N). 相似文献
74.
Winfried K. Grassmann 《Methodology and Computing in Applied Probability》2011,13(4):873-886
In 1953, Smith (Proc Camb Philos Soc 49:449–461, 1953), and, following him, Syski (1960) suggested a method to find the waiting time distribution for one server queues with Erlang-n arrivals and Erlang-m service times by using characteristic roots. Syski shows that these roots can be determined from a very simple equation,
but an equation of degree n + m. Syski also shows that almost all of the characteristic roots are complex. In this paper, we derive a set of equations, one
for each complex root, which can be solved by Newton’s method using real arithmetic. This method simplifies the programming
logic because it avoids deflation and the subsequent polishing of the roots. Using the waiting time distribution, Syski then
derived the distribution of the number in the system after a departure. E
n
/E
m
/1 queues can also formulated as quasi birth-death (QBD) processes, and in this case, the characteristic roots discussed by
Syski are closely related to the eigenvalues of the QBD process. The QBD process provides information about the number in
system at random times, but they are much more difficult to formulate and solve. 相似文献
75.
We describe some of the determinantal ideals attached to symmetric, exterior and tensor powers of a matrix. The methods employed use elements of Zariski's theory of complete ideals and of representation theory. 相似文献
76.
77.
B. Fankhänel Eberhard Müller Torsten Fankhänel Winfried Siegel 《Analytical and bioanalytical chemistry》1998,361(6-7):574-576
Electrical and mechanical properties of ceramic composites are investigated to develop “smart materials” and establish a fracture prediction technique. The “smart materials” are based on silicon carbide fibre-reinforced composites. The SiC-fibres were checked to determine the changes in mechanical and electrical properties during the composites’ production. Samples were produced for the determination of the mechanical strength with in situ detection of the degree of damage by recording the electrical resistance. 相似文献
78.
Antje Schüle Winfried Rasemann Cordula Preue 《Particle & Particle Systems Characterization》1997,14(1):21-29
There are many applications of particle technology in which solid mixtures consisting of particles having the same chemical, mineralogical and physical properties are used. The particles are then distinguishable only by shape. The particle shape significantly influences the technological behaviour of the mixture and the properties of the materials produced. Therefore, mathematical procedures are necessary in order to determine the composition of such a mixture according to the proportions of certain particle shape classes. These classes are the respective components of the mixture. In this work, various statistical methods were tested to classify the particles by shape analysis. A two-component mixture of quartz and muscovite was used as a reference material. The results obtained by different theoretical methods were compared with each other. Alternative methods such as histogram fit and the EM algorithm provided better results than the conventional method of discriminant analysis, as expected. Because the statistical behaviour of the components can be estimated only using reference samples, a statistical error of about 5–10% depending on the respective sample size was met. However, this is a satisfactory result. It turned out that it is possible to conclude exclusively on the basis of the particle shape distribution about the composition of a mixture. The methodical knowledge obtained can be used in industrial applications such as the ceramic industry, the production of paints and the bulk solids technology. 相似文献
79.
CHANGES IN TRANSMISSION CHARACTERISTICS OF POLYMETHYLMETHACRYLATE AND CELLULOSE (III) ACETATE DURING EXPOSURE TO ULTRAVIOLET LIGHT 总被引:2,自引:0,他引:2
Steef F. Steeneken Anita G. J. Buma Winfried W. C. Gieskes 《Photochemistry and photobiology》1995,61(3):276-280
Abstract— Ultraviolet-transparent polymethylmethacrylate (PMMA) and cellulose (III) acetate (CA) (often used as a cut-off filter in UVB [280–320 nm] biological effect studies) were exposed to a 20 W Philips TL 12 lamp to examine changes in transmission characteristics due to UVB exposure. Transmission of UVB and biologically weighted UVB (UVBE(DNA) ) through PMMA were similar, 88.3 and 83.5%, respectively. The absorption characteristics of PMMA did not change with time at any of the UV irradiance levels applied. However, transmission of UVB and UVBBE(DNA) ) through new CA differed considerably: 59% versus only 11%, respectively. Also, spectral absorption characteristics changed with time due to degradation of CA, at a rate that was dependent on the incident UVB irradiance. The decrease in transmission through CA of both UVB and UVBE(DNA) can be described by exponential functions. The CA that was wrapped around the UV lamp showed dramatic changes in UV absorption over the first few hours of use. However, when CA was placed at a longer distance from the light source initial degradation was less. It is concluded that PMMA can be applied in UV effect studies as a reasonable alternative for quartz. The CA should, however, be used with care, because the large transmission decreases that were observed strongly hamper an accurate calculation of (biologically weighted) UVB dose rates. 相似文献
80.
Helmut Kacholdt Peer Berges Günter Klar Winfried Hinrichs 《Transition Metal Chemistry》1987,12(6):515-520
Summary The chalcogenanthrenes Vn2EE; 2, 3, 7, 8-tetramethoxythianthrene (E=E=S), 2, 3, 7, 8-tetramethoxydibenzothiaselenin (E=S, E=Se), and 2, 3, 7, 8-tetramethoxyselenanthrene (E=E=Se), react with [{ReBr(CO)3(THF)}2] and [{PtXMe3}4] (X=Cl or Br) to give the dinuclear complexes [(fac-L3M)2(-X)2 (-Vn2EE)] (M=Re, L=CO, X=Br; M=Pt, L=Me, X=Cl or Br) in which the chalcogenanthrenes reveal a hitherto unknown co-ordination mode as bridging ligands. Telluranthrene (Pn2 Te2), however, forms mononuclear complexes of compositionfac-[L3MX(Pn2Te2)] (M=Re, L=CO, X=Br; M=Pt, L=Me, X=Br) with a chelating chalcogenanthrene ligand. Whereas the rhenium compounds are not stable enough in solution to be studied by i.r. spectroscopy, the platinum compounds can be well characterised by their1H n.m.r. spectra. Furthermore, the results of a single-crystal structure determination of [Pt2Cl2Me6(Vn2Se2)] are reported. The Pt–Se distance of 259 pm indicates a relatively weak interaction between the chalcogenanthrene and the remaining dinuclear fragment of the molecule. 相似文献