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101.
Scale-free networks are ultrasmall 总被引:1,自引:0,他引:1
We study the diameter, or the mean distance between sites, in a scale-free network, having N sites and degree distribution p(k) proportional, variant k(-lambda), i.e., the probability of having k links outgoing from a site. In contrast to the diameter of regular random networks or small-world networks, which is known to be d approximately ln(N, we show, using analytical arguments, that scale-free networks with 23, d approximately ln(N. We also show that, for any lambda>2, one can construct a deterministic scale-free network with d approximately ln(ln(N, which is the lowest possible diameter. 相似文献
102.
Typical two-dimensional surface pressures prevalent within floating monolayer (Langmuir) films are on the order of a few dozen megapascals. One might expect, therefore, that some chemical reactions should be directly and strongly affected by this surface pressure, along with the well-known effect of pressure on the orientational order and the mere proximity of the molecules within the film. Here, we show that the two-dimensional surface pressure in Langmuir films provides a direct driving force, decreasing the activation energy of a cooperative oriented coalescence of ZnS nanorods into nanowires near room temperature. At low film surface pressure or low temperature, the nanorods do not react, while in solution, they react only above 140 degrees C, even though in all of these cases, the rods are organized in similar super-crystalline clusters. Electron microscopy and measurements of the reaction rates give a detailed picture of the order of the rods, their rearrangement, and their coalescence. 相似文献
103.
A one-dimensional microscopic quantum mechanical model is used to inquire whether it is possible to enhance the desorption rate by employing a laser to induce vibrational excitation of the chemisorptive bond. For model parameters simulating CO/Cu it is found that the required laser intensity is very large, roughly 104 times that of a conventional high power CO2 laser (whose intensity we take to be ). We suggest that surface roughness can be used to enhance substantially the effect of the laser and possibly to enable the observation of laser enhanced desorption. 相似文献
104.
105.
Shlomo Halfin 《Journal of Optimization Theory and Applications》1970,6(5):356-363
Letn linear, time-invariant subsystems with transfer functionsT
1(s),T
2(s),...,T
n
(s) be given. We are required to cascade these subsystems into a system with the transfer functionT(s)=kT
1(s)T
2(s) ...T
n
(s), wherek>0, by determining the order of the subsystems and choosing for each subsystemi an amplification factork
i
such thatk=k
1
k
2 ...k
n
.We do this using the following optimality criterion: Given a setI, minimize the ratio of the maximum and the minimum of all the absolute values of all the intermediate outputs inI, for a flat input. This criterion is applicable in cases where the intermediate outputs should not be overdriven or underdriven. In particular, the method is applicable to the problem of determining an optimal ordering and intermediate amplifications of cascadedRC-active filters.The author is indebted to E. Lueder (Ref. 1) and J. Tow, who presented various criteria for optimal arrangements ofRC-active filters and motivated the formulation of this problem. 相似文献
106.
A detailed study of the possibility that the long standing discrepancies between theory and experiment in the values of Coulomb displacement energies have their origin in the charge asymmetry of the nuclear force is presented. A review of the present status of the theory of Coulomb displacement energies of mirror states is given. We have constructed a phenomenological charge asymmetric potential that can remove the Coulomb energy discrepancies for several mirror nuclei yet having only minimal effect on the 1S0 nucleon-nucleon scattering length. The form of this potential is however not compatible with the contributions due to charge asymmetric meson exchange processes that have been considered in the literature. We assume that these meson exchange effects can be reasonably described, up to strength factors, by a sum of one-pion, one-scalar-meson (σ) and one-vector-meson exchange potentials. The need for some additional type of charge asymmetric effect, e.g. three-body forces, is pointed out. 相似文献
107.
2-Carbomethoxy-1,1-bis(methylsulfide)-1-alkenes, easily made from carboxylic acids, CS(2) and MeI, were treated with BrF(3) producing eventually the desired alpha-trifluoromethyl carboxylate derivatives--RCH(CF(3))COOR'--in good yields. 相似文献
108.
Under the right conditions, bromine trifluoride can be a useful tool for generating new types of reactions and compounds. Thus, tris(methylthio)alkyl derivatives, easily prepared from the corresponding alkyl bromides, were converted to the corresponding RCHBrCF2SMe or RCHBrCF3 compounds. The bromine atom, however, could be easily reduced forming eventually R'CF2SMe or R'CF3. If desired, the bromine atom can serve as an entry for constructing terminal difluoroolefins. 相似文献
109.
Gold electrode was modified with a 4-aminothiophenol layer (4-ATPh) to immobilize DNA. The immobilized DNA served as a template for the alignment of positively charged anilinium ions. The electrochemical oxidation of the anilinium ions resulted in wrapping of the DNA with polyaniline. This polyaniline coated DNA was characterized by cyclic voltammetry (CV), impedance spectroscopy and UV-VIS absorption spectroscopy. 相似文献
110.
Summary. Continuing our previous analysis, we derive the exact number of conjugate gradient iterations needed (to achieve a given
tolerance) for the one-dimensional discrete Poisson equation on a uniform grid, and a particularly smooth solution vector.
Received July 29, 1998 / Published online March 16, 2000 相似文献