全文获取类型
收费全文 | 2618篇 |
免费 | 321篇 |
国内免费 | 111篇 |
专业分类
化学 | 477篇 |
晶体学 | 6篇 |
力学 | 409篇 |
综合类 | 92篇 |
数学 | 973篇 |
物理学 | 1093篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 36篇 |
2021年 | 38篇 |
2020年 | 54篇 |
2019年 | 46篇 |
2018年 | 50篇 |
2017年 | 73篇 |
2016年 | 97篇 |
2015年 | 82篇 |
2014年 | 104篇 |
2013年 | 157篇 |
2012年 | 133篇 |
2011年 | 124篇 |
2010年 | 113篇 |
2009年 | 114篇 |
2008年 | 139篇 |
2007年 | 156篇 |
2006年 | 124篇 |
2005年 | 132篇 |
2004年 | 125篇 |
2003年 | 127篇 |
2002年 | 117篇 |
2001年 | 100篇 |
2000年 | 88篇 |
1999年 | 92篇 |
1998年 | 88篇 |
1997年 | 82篇 |
1996年 | 63篇 |
1995年 | 65篇 |
1994年 | 46篇 |
1993年 | 51篇 |
1992年 | 47篇 |
1991年 | 26篇 |
1990年 | 14篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有3050条查询结果,搜索用时 31 毫秒
61.
An efficient hybrid field solution to the general multilayer substrates transmission line problems with full shielded and half open cross-sectional geometry is presented by using the waveguide modes coupling and decoupling procedure in the spectral domain. Modal transverse transmission lines corresponding to the LSE and LSM modes are taken into account so that the Green's elements for the edge conditions can be derived by a simple iterative method. In this paper, we analyze not only the propagation constants and characteristic impedances but also the available transmission power capacity and power distribution of most commonly used structures. Normalized eigenmode power levels characterizing the propagation features are computed. 相似文献
62.
63.
Fast folding and comparison of RNA secondary structures 总被引:40,自引:0,他引:40
I. L. Hofacker W. Fontana P. F. Stadler L. S. Bonhoeffer M. Tacker P. Schuster 《Monatshefte für Chemie / Chemical Monthly》1994,125(2):167-188
Summary Computer codes for computation and comparison of RNA secondary structures, the Vienna RNA package, are presented, that are based on dynamic programming algorithms and aim at predictions of structures with minimum free energies as well as at computations of the equilibrium partition functions and base pairing probabilities.An efficient heuristic for the inverse folding problem of RNA is introduced. In addition we present compact and efficient programs for the comparison of RNA secondary structures based on tree editing and alignment.All computer codes are written in ANSI C. They include implementations of modified algorithms on parallel computers with distributed memory. Performance analysis carried out on an Intel Hypercube shows that parallel computing becomes gradually more and more efficient the longer the sequences are.
Schnelle Faltung und Vergleich von Sekundärstrukturen von RNA
Zusammenfassung Die im Vienna RNA package enthaltenen Computer Programme für die Berechnung und den Vergleich von RNA Sekundärstrukturen werden präsentiert. Ihren Kern bilden Algorithmen zur Vorhersage von Strukturen minimaler Energie sowie zur Berechnung von Zustandssumme und Basenpaarungswahrscheinlichkeiten mittels dynamischer Programmierung.Ein effizienter heuristischer Algorithmus für das inverse Faltungsproblem wird vorgestellt. Darüberhinaus präsentieren wir kompakte und effiziente Programme zum Vergleich von RNA Sekundärstrukturen durch Baum-Editierung und Alignierung.Alle Programme sind in ANSI C geschrieben, darunter auch eine Implementation des Faltungs-algorithmus für Parallelrechner mit verteiltem Speicher. Wie Tests auf einem Intel Hypercube zeigen, wird das Parallelrechnen umso effizienter je länger die Sequenzen sind.相似文献
64.
The reaction of electroreduction of platinum(II) aquachloride complexes on a negatively charged dropping mercury electrode is used to determine specific features of interpretation of experimental data in the case of parallel conversion of several forms of a reactant, connected with the manner of introducing a correction for the concentration polarization. The difference in the charges of species undergoing simultaneous reduction gives rise to ambiguity when analyzing kinetic data on the dependence of current on the supporting-electrolyte concentration at constant electrode charge. A new self-consistent technique for deducing model parameters (ratio between reactant discharge rate constants) is proposed. 相似文献
65.
Using a probabilistic approach, the deterministic and the stochastic parallel dynamics of aQ-Ising neural network are studied at finiteQ and in the limitQ. Exact evolution equations are presented for the first time-step. These formulas constitute recursion relations for the parallel dynamics of the extremely diluted asymmetric versions of these networks. An explicit analysis of the retrieval properties is carried out in terms of the gain parameter, the loading capacity, and the temperature. The results for theQ network are compared with those for theQ=3 andQ=4 models. Possible chaotic microscopic behavior is studied using the time evolution of the distance between two network configurations. For arbitrary finiteQ the retrieval regime is always chaotic. In the limitQ the network exhibits a dynamical transition toward chaos. 相似文献
66.
Prospecting for oil and gas resources poses the problem of determining the geological structure of the earth's crust from indirect measurements. Seismic migration is an acoustic image reconstruction technique based on the inversion of the scalar wave equation. Extensive computation is necessary before reliable information can be extracted from large sets of recorded data. In this paper a collection of industrial migration techniques, each giving rise to a data parallel algorithm, is outlined. Computer simulations on synthetic seismic data illustrate the problem and the approach. 相似文献
67.
Emanuele Galligani 《Numerical Algorithms》1993,5(11):549-555
Givenn pairwise distinct and arbitrarily spaced pointsP
i in a domainD of thex–y plane andn real numbersf
i, consider the problem of computing a bivariate functionf(x, y) of classC
1 inD whose values inP
i are exactlyf
i,i=1,,n, and whose first or second order partial derivatives satisfy appropriate equality and inequality constraints on a given set ofp pointsQ
l inD.In this paper we present a method for solving the above problem, which is designed for extremely large data sets. A step of this method requires the solution of a large scale quadratic programming (QP) problem.The main purpose of this work is to analyse an iterative method for determining the solution of this QP problem: such a method is very efficient and well suited for parallel implementation on a multiprocessor system.Work supported by MURST Project of Computational Mathematics, Italy. 相似文献
68.
The procedure and method for the transfer of two sets of 14 pairs of wheatgrass (Agropyron interrnedium) chromosomes into common wheat to establish two sets of wheat-wheatgrass alien addition lines are reported. Meanwhile, observations and analyses have been made on the phenotypicaI characters of all the 14 alien addition lines established. It is determined that wheatgrass chromosomes in some of the established addition lines carry the rustresistant genes. In addition, questions concerning the location and distribution of certain agriculturally important genes of wheatgrass chromosomes have been discussed. 相似文献
69.
E. C. C. Vasconcellos K. M. Evenson 《International Journal of Infrared and Millimeter Waves》1985,6(11):1157-1167
We have obtained laser action on 34 far infrared lines for the first time in fully deuterated methyl alcohol with the13C isotope (13CD3OD), and we have measured the frequency of 13 lines. The molecule was pumped by a cw CO2 laser. We have measured the wavelength, the relative polarization, the relative intensity of most lines, the frequency, and the CO2 pump frequency offset of the strongest lines. The new lines are distributed in the wavelength region from 75.27 m to 464.7 m.Supported in part by a joint grant with the U.S. National Science Foundation grant # INT 80-19014 and the Brazilian Conselho Nacional de Pesquisas (CNPq). 相似文献
70.
In this paper,large-sized sapphire (230×210 mm,27.5 kg) was grown by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center). Dislocation peculiarity in large sapphire boule (0001) basal plane was investigated by chemical etching,scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6×101~8.0×102 cm-2,in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally,the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method. 相似文献