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11.
Brain magnetic resonance imaging (MRI) lesion volume measurement is an advantageous tool for assessing disease burden in multiple sclerosis (MS). We have evaluated two computer-assisted techniques: MSA multispectral automatic technique that is based on bayesian classification of brain tissue and NIH image analysis technique that is based on local (lesion by lesion) thresholding, to establish reliability and repeatability values for each technique. Brain MRIs were obtained for 30 clinically definite relapsing-remitting MS patients using a 2.0 Tesla MR scanner with contiguous, 3 mm thick axial, T1, T2 and PD weighted modalities. Digital (Dicom 3) images were analyzed independently by three observers; each analyzed the images twice, using the two different techniques (Total 360 analyses). Accuracy of lesion load measurements using phantom images of known volumes showed significantly better results for the MSA multispectral technique (p < 0.001). The mean intra-and inter-observer variances were, respectively, 0.04 ± 0.4 (range 0.04–0.13), and 0.09 ± 0.6 (range 0.01–0.26) for the multispectral MSA analysis technique, 0.24 ± 2.27 (range 0.23–0.72) and 0.33 ± 3.8 (range 0.47–1.36) for the NIH threshold technique. These data show that the MSA multispectral technique is significantly more accurate in lesion volume measurements, with better results of within and between observers’ assessments, and the lesion load measurements are not influenced by increased disease burden. Measurements by the MSA multispectral technique were also faster and decreased analysis time by 43%. The MSA multispectral technique is a promising tool for evaluating MS patients. Non-biased recognition and delineation algorithms enable high accuracy, low intra-and inter-observer variances and fast assessment of MS related lesion load. 相似文献
12.
In its simplest form the Tiebout hypothesis suggests that redistribution by local government is not sustainable because individuals, when confronted by negative net fiscal benefits, will vote with their feet, changing their residential locations to jurisdictions which offer a more favorable fiscal balance. It is usually thought, moreover, that they will move (e.g. from central city to suburbs) in descending order of income.Recognition of extended preference modifies this simple characterization of the tiebout process, in which the process of relocation is like ‘peeling an onion’. Any relocation sequence is possible, with either sympathy or antipathy. Even for sympathetic individuals with identical tastes, restrictive and unrealistic assumptions are required to predict, with certainty, that individuals with higher incomes would be the first to move. In particular the marginal tax rate must exceed unity. With antipathy, individuals with lower incomes may move before those with higher incomes, even if net fiscal benefits decrease with income, if they become more willing to begrudge transfers to others as their incomes increase. 相似文献
13.
Shmuel Gal 《Israel Journal of Mathematics》1972,12(1):32-45
The minimax solution is found for a game in which player I chooses a real number and player II seeks it by choosing a trajectory
represented by a positive function.
This work was supported by the Israel Council for Research and Development. 相似文献
14.
PHOTOACOUSTIC SPECTROSCOPY AND RADIANT ENERGY CONVERSION: THEORY OF THE EFFECT WITH SPECIAL EMPHASIS ON PHOTOSYNTHESIS 总被引:3,自引:0,他引:3
Abstract—The use of photoacoustic spectroscopy in the study of photoactive samples (photochemical, luminescent, photovoltaic) is considered. After a short explanation of the parameters important in this technique and ways of measuring them, photochemical processes are considered in detail. Relations are derived for the determination of the energy stored in photochemical products and the quantum yield for the photochemical processes.
One- and two-step photochemical processes are treated in detail and the dependence of the photo-acoustically detected products on modulation frequency is considered, showing the possibility of separating reaction steps according to their rate constants. Particular attention is given to the photosynthetic process and the potential of this method for determination of energy conversion efficiencies of the different stages of photosynthesis is demonstrated. Also the use of the technique in the study of photovoltaic processes is outlined. 相似文献
One- and two-step photochemical processes are treated in detail and the dependence of the photo-acoustically detected products on modulation frequency is considered, showing the possibility of separating reaction steps according to their rate constants. Particular attention is given to the photosynthetic process and the potential of this method for determination of energy conversion efficiencies of the different stages of photosynthesis is demonstrated. Also the use of the technique in the study of photovoltaic processes is outlined. 相似文献
15.
The quantum resonances occurring with delta-kicked particles are studied with the help of a fictitious classical limit, establishing a direct correspondence between the nearly resonant quantum motion and the classical resonances of a related system. A scaling law which characterizes the structure of the resonant peaks is derived and numerically demonstrated. 相似文献
16.
In this Letter we provide what is believed to be the first experimental evidence of suppression of the number of filaments for high-intensity laser pulses propagating in air by beam astigmatism. We also show that the number, pattern, and spatial stability of the filaments can be controlled by varying the angle that a focusing lens makes with the axial direction of propagation. This new methodology can be useful for applications involving atmospheric propagation, such as remote sensing. 相似文献
17.
The vector partition problem concerns the partitioning of a set A of n vectors in d-space into p parts so as to maximize an objective function c which is convex on the sum of vectors in each part. Here all parameters d, p, n are considered variables. In this paper, we study the adjacency of vertices in the associated partition polytopes. Using our adjacency characterization for these polytopes, we are able to develop an adaptive algorithm for the vector partition problem that runs in time O(q(L)v) and in space O(L), where q is a polynomial function, L is the input size and v is the number of vertices of the associated partition polytope. It is based on an output-sensitive algorithm for enumerating all vertices of the partition polytope. Our adjacency characterization also implies a polynomial upper bound on the combinatorial diameter of partition polytopes. We also establish a partition polytope analogue of the lower bound theorem, indicating that the output-sensitive enumeration algorithm can be far superior to previously known algorithms that run in time polynomial in the size of the worst-case output. 相似文献
18.
A uniform random vector over a simplex is generated. An explicit expression for the first moment of its largest spacing is
derived. The result is used in a proposed diagnostic tool which examines the validity of random number generators. It is then
shown that the first moment of the largest uniform spacing is related to the dependence measure of random vectors following
any extreme value distribution. The main result is proved by a geometric proof as well as by a probabilistic one. 相似文献
19.
Calcination of sepiolite and of two sepiolite/CsCl mixtures, unground and air-ground was investigated by thermo-XRD-analysis.
At 200 °C sepiolite, neat, mixed or air-ground with CsCl lost interparticle and zeolitic water. The framework of sepiolite
persisted during the dehydration but became defected, mainly in the air-ground mixture, less in the unground mixture and little
in the neat clay. At 500 °C, with the loss of bound water, the neat clay was folded and transformed into sepiolite anhydride.
In sepiolite/CsCl mixtures the dehydrated variety persisted but the degree of crystal-imperfection increased in the air-ground
mixture more than in the unground mixture. At 700 °C the neat clay remained crystallized, but the CsCl mixtures became amorphous.
Some crystalline dehydrated sepiolite or sepiolite anhydride persisted in the unground and air-ground CsCl mixtures, respectively.
At 850 °C, the neat clay crystallized into protoenstatite with some enstatite and clinoenstatite. The amorphous fraction of
sepiolite in the unground sepiolite/CsCl mixtures crystallized into pollucite and forsterite and the crystalline fraction
was transformed into enstatite, protoenstatite, and clinoenstatite. In the air-ground mixture, the amorphous phase was transformed
into pollucite with some forsterite and the crystalline fraction into enstatite. 相似文献
20.
Shmuel Weinberger 《纯数学与应用数学通讯》1987,40(5):609-610