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排序方式: 共有426条查询结果,搜索用时 31 毫秒
71.
A multiresolution analysis is adopted to improve an image reconstruction with a phase-diversity technique. The phase distribution at low resolution is first estimated and then is used as an initial estimate for phase reconstruction at a higher resolution level. Computer simulations are conducted to confirm the proposed method. The method is applied for image reconstruction of solar granulation. 相似文献
72.
以浙江天台山特有种华顶杜鹃为研究对象,分析了它所在群落的结构、物种组成及数量特征.在该群落中,华顶杜鹃不占优势,优势种群为阔叶箬竹、黄山松、山和金钱松等,它们的年龄结构都属于稳定型或增长型.群落垂直结构完整,可分为乔木层、灌木层、草本层,亦有一定数量的层间植物.乔木层的物种多样性偏低,灌木层和草本层的物种多样性较高.各样地间的植物种类相似性较高.华顶杜鹃处于濒危状态,必须采取措施加以保护. 相似文献
73.
基于线路调查和样方调查的基础上,研究了江西九连山国家级自然保护区内常绿阔叶林的主要植被群落的α多样性和β多样性,α多样性测度指标主要采用Patrick丰富度指数、Shannon-wiener多样性指数、Simpson优势度指数、Pielou均匀度指数和Margalef丰富度指数等5个指标,β多样性采 相似文献
74.
George Bashiardes Imad Safir Francis Barbot Joelle Laduranty 《Tetrahedron letters》2004,45(7):1567-1570
A general and rapid synthesis of new families of pyrrolizines and indolizines in good overall yields via an intramolecular [3+2] cycloaddition reaction is described. Diversity of substitutions can be achieved by the appropriate choice of readily available starting materials. The experimental procedures are straightforward and are performed under neutral conditions. New syntheses are also described for the preparation of N-propargylic 2-amino-benzaldehydes and S-propargylic 2-thiobenzaldehydes. 相似文献
75.
There is a natural way to associate to any tree T with leaf set X, and with edges weighted by elements from an abelian group G, a map from the power set of X into G—simply add the elements on the edges that connect the leaves in that subset. This map has been well-studied in the case where
G has no elements of order 2 (particularly when G is the additive group of real numbers) and, for this setting, subsets of leaves of size two play a crucial role. However, the existence and uniqueness results in that setting do not extend to arbitrary abelian groups.
We study this more general problem here, and by working instead with both, pairs and triples of leaves, we obtain analogous existence and uniqueness results. Some particular results for elementary abelian 2-groups
are also described.
Received July 13, 2005 相似文献
76.
Aaron Luntala Nsakanda Wilson L. Price Moustapha Diaby Marc Gravel 《European Journal of Operational Research》2007
The entropy-based measure has been used in previous works to compute the population diversity in solving the cell formation problem with the genetic algorithm. Population diversity is crucial to the genetic algorithm’s ability to continue fruitful exploration as it may be used in choosing an initial population, in defining a stopping criterion, in evaluating the population convergence, and in making the search more efficient throughout the selection of crossover operators or the adjustment of various control parameters (e.g., crossover or mutation rate, population size). We show in this note that, when a non-ordinal chromosome representation corresponding to the allocation of machines to cells is used, the current way of measuring the population diversity is inaccurate. Consequently, it leads to wrong conclusions when, at various iterations, carrying out fruitful exploration or an efficient search of the solution space is guided by the perceived population diversity degree. An alternative approach based on computing the distance and the similarity between chromosomes is discussed. 相似文献
77.
Affinity genetic algorithm 总被引:1,自引:0,他引:1
Based on some phenomena from human society and nature, we propose a binary affinity genetic algorithm (aGA) by adopting the
following strategies: the population is adaptively updated to avoid stagnation; the newly generated individuals will be ensured
to survive for some generations in order for them to have time to show their good genes; new individuals and the old ones
are balanced to have the advantages of both. In order to quantitatively analyze the selective pressure, the concept of selection degree and a simple linear control equation are introduced. We can maintain the diversity of the evolutionary population by controlling
the value of the selection degree. Performance of aGA is further enhanced by incorporating local search strategies.
Partially supported by a National Key Basic Research Project of China and by a USA NSF grant CCR-0201253. 相似文献
78.
针对蚁群算法在寻优过程中容易出现停滞现象,同意在该算法中引入免疫机制,将待求解问题看成抗原,而问题的解看成抗体,通过基于浓度的选择机制和多样性保持策略来提高蚁群算法的全局搜索能力和避免停滞现象.对TSP问题的仿真实验结果表明,该算法极大地提高了搜索能力和避免了停滞现象. 相似文献
79.
Jain AN 《Journal of computer-aided molecular design》2000,14(2):199-213
Recognition of small molecules by proteins depends on three-dimensional molecular surface complementarity. However, the dominant techniques for analyzing the similarity of small molecules are based on two-dimensional chemical structure, with such techniques often outperforming three-dimensional techniques in side-by-side comparisons of correlation to biological activity. This paper introduces a new molecular similarity method, termed morphological similarity (MS), that addresses the apparent paradox. Two sets of molecule pairs are identified from a set of ligands whose protein-bound states are known crystallographically. Pairs that bind the same protein sites form the first set, and pairs that bind different sites form the second. MS is shown to separate the two sets significantly better than a benchmark 2D similarity technique. Further, MS agrees with crystallographic observation of bound ligand states, independent of information about bound states. MS is efficient to compute and can be practically applied to large libraries of compounds. 相似文献
80.
Tze Jing Sum Tze Han Sum Warren R.J.D. Galloway David G. Twigg Joe J. Ciardiello David R. Spring 《Tetrahedron》2018,74(38):5089-5101
Synthetic biflavonoids are associated with interesting biological activities, yet they remain poorly explored within drug discovery. Recent years have witnessed a growing interest in synthetic approaches that can provide access to structurally novel biflavonoids so that the biological usefulness of this compound class can be more fully investigated. Herein, we report upon the exploration of strategies based around Suzuki-Miyaura cross-coupling and alcohol methylenation for the synthesis of two classes of biflavonoids: (i) rare ‘hybrid’ derivatives containing flavonoid monomers belonging to different subclasses, and (ii) homodimeric compounds in which the two flavonoid monomers are linked by a methylenedioxy group. Application of these strategies enabled the preparation of a structurally diverse collection of novel biflavonoids from readily-available starting materials, thereby facilitating the probing of uncharted regions of biologically interesting chemical space. 相似文献