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971.
Vladimir Mityushev 《Proceedings of the American Mathematical Society》1998,126(8):2399-2406
The Poincaré -series for a multiply connected circular region can be either convergent or divergent absolutely. In this paper we prove a uniform convergence result for such a region.
972.
Thek-partitioning problem 总被引:1,自引:0,他引:1
Luitpold Babel Hans Kellerer Vladimir Kotov 《Mathematical Methods of Operations Research》1998,47(1):59-82
Thek-partitioning problem is defined as follows: Given a set of items {I
1,I
2,...,I
n} where itemIj is of weightwj 0, find a partitionS
1,S
2,...,S
m
of this set with ¦S
i
¦ =k such that the maximum weight of all subsetsS
i
is minimal,k-partitioning is strongly related to the classical multiprocessor scheduling problem of minimizing the makespan on identical machines. This paper provides suitable tools for the construction of algorithms which solve exactly the problem. Several approximation algorithms are presented for this NP-hard problem. The worst-case behavior of the algorithms is analyzed. The best of these algorithms achieves a performance bound of 4/3. 相似文献
973.
By generalizing some well-known results, we first obtain an inequality involving the volume and product of s-contents of s-faces of an n-simplex. Using this we generalize two inequalities maximizing the volume of one or two simplices in terms of their edge lengths. 相似文献
974.
Probing alkali coordination environments in alkali borate glasses by multinuclear magnetic resonance
Vladimir K. Michaelis 《Journal of Non》2007,353(26):2582-2590
Five series of binary alkali borate glasses were prepared to compare the alkali dependence of network and modifier short-range order. 11B magic-angle spinning (MAS) NMR reveals that the fraction of four-coordinate boron depends strongly upon alkali type at high-alkali concentrations: heavier alkalis favour the formation of non-bridging oxygens, whereas lithium borates contain a much higher concentration of tetrahedral boron units. The alkali modifiers were observed directly by MAS NMR to measure the change in chemical shift with composition. All alkali peaks shift to higher frequency with increasing loading, indicative of decreasing average coordination numbers. Relative to their known chemical shift ranges, the heavier alkalis exhibit the greatest shifts, whereas the lithium shifts are subtle. This is interpreted in terms of the availability of charged and partially charged coordinating oxygens in the network. Moreover, the 133Cs chemical shifts plateau at 40 mol%, implying that the Cs+ coordination number reaches a lower limit at this composition. This work demonstrates that NMR instrumentation and methodology have reached a level where even challenging nuclei like 39K and 87Rb can be probed to yield structural information in glasses. 相似文献
975.
Merritt?C.?Helvenston Vladimir?N.?NesterovEmail author Horace?J.?Jenkins 《Journal of chemical crystallography》2005,35(2):113-118
Synthesis and X-ray structural investigations have been carried out for the two title compounds C14H10N2O (3a) and C22H26N2O (3b). Compound 3a crystallizes in the monoclinic space group P21/c, with a = 3.843(1) Å, b = 24.618(5) Å, c = 11.318(2) Å, = 92.61(3), V = 1069.7(4) Å,3 and Z = 4. Compound 3b crystallizes in the triclinic space group P-1, with a = 9.004(2) Å, b = 9.447(2) Å, c = 11.713(2) Å, = 76.70(3), = 83.12(3), = 82.16(3), V = 956.5(3) Å,3 and Z = 2. Both stilbazole derivatives have Z-geometry about the ethylene bridge which links the heterocyclic and aromatic rings. The molecular skeleton of 3a is slightly non-planar: the dihedral angles between the acrylonitrile linkage and the pyridine ring, and between this linkage and the p-hydroxyphenyl ring are 7.2(2) and 4.1(2), respectively. The molecular skeleton of 3b is less planar: the values of similar dihedral angles are 17.0(2) and 20.8(2), respectively. In the crystal of 3a, the molecules are packed in stacks along the a axis with head-to-head orientation. Intermolecular hydrogen bonds O=H s N and C=H s N link molecules into sheets parallel to (100) plane. In the crystals of 3b, the molecules have a head-to-tail orientation and intermolecular hydrogen bonds O=H s N link the molecules into infinite chains along [01-1] direction. 相似文献
976.
Janusz Lipkowski Marina S. Fonari Victor Ch. Kravtsov Yurii A. Simonov Edward V. Ganin Vladimir O. Gelmboldt 《Journal of chemical crystallography》1996,26(12):823-833
Four crystalline molecular complexes between antimony(III) fluoride and 18-membered crown ethers have been obtained and their structures investigated by single crystal X-ray diffraction techniques: [18-crown-6·SbF3], C12H24F3O6Sb,P212121,a=8.328(4),b=11.573(4),c=18.094(4),V=1744(1)3,Z=4; [benzo-18-crown-6·SbF3], C16H24F3O6Sb,P21/n,a=10.490(2),b=13.714(1),c=13.442(2), =101.94(1)°,V=1892(1)3,Z=4; [cis-syn-cis-dicyclohexano-18-crown-6·SbF3·CH3OH], C21H40F3O7Sb,P21/n,a=8.270(4),b=23.386(3),c=12.772(1), =96.31(2)°,V=2455(1)3,Z=4; [cis-anti-cis-dicyclohexano-18-crown-6·SbF3], C20H36F3O6Sb,Pna21,a=21.091(8),b=12.829(5),c=8.437(3),V=2283(2)3,Z=4. All species are the perching-type complexes with the antimony fluoride above the cavity and the metal lone pair pointed toward the center of the crown ring. The antimony atom interacts with all six crown oxygen atoms with Sb–O distances of 2.837(2)–3.344(2) . The antimony atom is displaced from the least square plane of the crown oxygen atoms at the distances of 1.288–1.383 . 相似文献
977.
Organocopper reagents smoothly react with heterocyclic propargyl mesylates at low temperature to produce N-fused heterocycles. The copper reagent plays a "double duty" in this novel cascade transformation, which proceeds via an SN2' substitution followed by a subsequent cycloisomerization step. 相似文献
978.
The interactions of non-ionic surfactant Triton X-100 and the coat protein of tobacco mosaic virus, which is an established model for both ordered and non-ordered protein aggregation, were studied using turbidimetry, differential scanning calorimetry, isothermal titration calorimetry, and dynamic light scattering. It was found that at the critical aggregation concentration (equal to critical micelle concentration) of 138 x 10(-6) M, Triton X-100 induces partial denaturation of tobacco mosaic virus coat protein molecules followed by protein amorphous aggregation. Protein aggregation has profound ionic strength dependence and proceeds due to hydrophobic sticking of surfactant-protein complexes (start aggregates) with initial radii of 46 nm. It has been suggested that the anionic surfactant sodium dodecyl sulfate forms mixed micelles with Triton X-100 and therefore reverses protein amorphous aggregation with release of protein molecules from the amorphous aggregates. A stoichiometric ratio of 5 was found for Triton X-100-sodium dodecyl sulfate interactions. 相似文献
979.
980.