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91.
Petr Vlček Vladimír Raus Miroslav Janata Jaroslav Kříž Antonín Sikora 《Journal of polymer science. Part A, Polymer chemistry》2011,49(1):164-173
Here, we present the first example of application of single‐electron transfer living radical polymerization (SET‐LRP) process to a controlled grafting of cellulose esters, cellulose diacetate (CDA), and cellulose acetate butyrate (CAB). The cellulose ester macroinitiators with various functionality densities have been prepared by acylation of the backbones with 2‐bromoisobutyryl (BrIB) and dichloroacetyl (DCA) groups, respectively. Methacrylate monomers were polymerized using DCA‐functionalized macroinitiators in the presence of pentamethyldiethylene triamine as a ligand. At 30 °C, the reaction is rather slow, reaching about 10% conversion after 3 to 6 h of polymerization, whereas the higher temperature (60 °C) perceptibly speeds up the polymerization so that methyl methacrylate (MMA) conversion is ~30% after 5 h. Graft copolymers with random‐type and diblock‐type grafts having amphiphilic character were also synthesized. For acrylate grafting (BuA and t‐BuA), BrIB‐functionalized macroinitiators are more convenient in a combination with a low concentration of Cu(0) and Me6TREN as a ligand and polymerization is detectably faster even at the lower temperature than that of MMA. Kinetic studies show “living” character of both the graftings. Important advantages of SET‐LRP, compared with classic ATRP, are (i) higher polymerization rate, (ii) lower extent of recombination of the growing grafts and (iii) negligible coloration of the products with catalytic residua, so that the prepared polymers do not require additional careful purification. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
92.
93.
Bicyclic graphs for which the least eigenvalue is minimum 总被引:3,自引:0,他引:3
The spread of a graph is defined to be the difference between the greatest eigenvalue and the least eigenvalue of the adjacency matrix of the graph. In this paper we determine the unique graph with minimum least eigenvalue among all connected bicyclic graphs of order n. Also, we determine the unique graph with maximum spread in this class for each n?28. 相似文献
94.
Karel indel JiÍ Holubek Emil Svtek Olue Matouov Jiina Metyov Miroslav Protiva 《Journal of heterocyclic chemistry》1989,26(5):1325-1330
Reactions of dibenzo[b,e]thiepin-11(6H)-one (4) with 2-, 3- and 4-(dimethylaminomethyl)phenylmagnesium bromide afforded the tertiary alcohols 5a,b,c. The aldehydes 7 and 8 gave similarly the secondary alcohols 9a,b,c and 10c . Numerous attempts to prepare the corresponding ketones, especially by oxidation of 9a,b,c and 10c were unsuccessful. Only the oxidation of 9c with tetrabutylammonium chromate in chloroform afforded the desired ketone 16 . Its formation was accompanied by an important side reaction consisting in a cleavage of the “retro-ene-reaction” type leading to compound 11 and the aldehyde 13c which reacted with the chloroform present to give the alcohol 17 . Compounds 5a,b,c, 9a,b,c and 16 were tested as potential antidepressants but with the exception of some effects in the test of potentiation of yohimbine toxicity in mice, they proved inactive in this line. 相似文献
95.
Miroslav Hušek 《Topology and its Applications》2008,155(14):1493-1501
Three approaches to a direct construction of Urysohn universal space are compared, namely those of Urysohn, Hausdorff and Katětov. More details are devoted to the unpublished Hausdorff's approach that is shown to work in a more general situation, too. 相似文献
96.
97.
In this article we present results of rough surface scattering calculations using a graphical processing unit implementation of the Finite Difference in Time Domain algorithm. Numerical results are compared to real measurements and computational performance is compared to computer processor implementation of the same algorithm. As a basis for computations, atomic force microscope measurements of surface morphology are used. It is shown that the graphical processing unit capabilities can be used to speedup presented computationally demanding algorithms without loss of precision. 相似文献
98.
Petr Vlček Miroslav Janata Petra Látalová Jiří Dybal Milena Špírková Luděk Toman 《Journal of polymer science. Part A, Polymer chemistry》2008,46(2):564-573
Graft copolymers with cellulose diacetate (CDA) backbone and both the poly(ε‐caprolactone) and polystyrene, or poly(butyl acrylate) or PMMA grafts were prepared by two‐step process. First, ε‐caprolactone (CL) was polymerized by ring‐opening polymerization (ROP) initiated with CDA, partly funcionalized with 2‐bromo‐isobutyryl groups (degree of functionalization was 0.5). The p(CDA‐g‐CL) copolymers were used in the second step as polyfunctional macroinitiators of ATRP of the vinyl monomer, giving densely grafted copolymers with polyester and PSt, or PBuA, or PMMA grafts. The prepared copolymers were characterized by SEC, some of them also by FTIR spectroscopy and atomic force microscopy (AFM). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 564–573, 2008 相似文献
99.
The main result of the present note states that it is consistent with the ZFC axioms of set theory (relying on Martin's Maximum MM axiom), that every Asplund space of density character ω1 has a renorming with the Mazur intersection property. Combined with the previous result of Jiménez and Moreno (based upon the work of Kunen under the continuum hypothesis) we obtain that the MIP renormability of Asplund spaces of density ω1 is undecidable in ZFC. 相似文献
100.
Approximate expressions of sorptivity have been tested against the Philip's numerical solution for porous materials with a wide range of parameters used in an exponential function of the water diffusivityD versus water content. The Philip-Knight approximation offers the best result when the flux ratio is approximated by the function derived for a constant value ofD. 相似文献