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71.
含主应力轴旋转的土体本构关系研究进展 总被引:6,自引:0,他引:6
主应力轴旋转对岩土工程的影响日益受到人们的重视.本文从纯主应力轴旋转、纯应力洛德角变化、多种因素变化、排水与不排水等方面较全面地描述了含主应力轴旋转情况下土体的基本变形特性.对当前较有影响的含主应力轴旋转的土体本构模型(基于一般应力空间的土体本构模型、运动硬化模型、边界面模型、土体弹塑性应力应变关系的完全应力增量表述等等)进行了较为系统的评述.提出了合主应力轴旋转的实验研究中存在的核心问题与建立合主应力轴旋转的土体本构关系的根本途径. 相似文献
72.
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74.
Abdolrasoul Sakhaei Gharagezlou Mahdi Nangir Amir Poorfaraj Liqvan Azadeh Abedi Jirdehi 《International Journal of Communication Systems》2023,36(1):e5370
There are many challenges in fifth generation (5G) telecommunication systems, due to the increasing demands and applications. The most important of which are need to have higher energy efficiency (EE) and spectral efficiency (SE). They are critical in the practical multiple-input multiple-output (MIMO) telecommunication systems. Non-orthogonal multiple access (NOMA) methods and millimeter-waves can be used in conjunction with MIMO systems to improve their EE and SE performance. In this paper, we investigate the application of NOMA and mm-Wave transmission in the downlink of MIMO systems. Then, we formulate the optimization problem for users in MIMO-NOMA systems to maximize the EE that is subject to minimum data rate to satisfy required quality of service (QoS) and maximum transmission power. To achieve the optimal power allocation for users, we reach a problem for the EE maximization that is non-convex and solution of the optimization problem is not trivial. We exploit a lower bound of the data rate and the Lagrange dual function to convert it to a convex and unconstrained problem, which is easy to solve. In the next step, we derive a relation for determining the optimal power allocation of users. In addition, a numerical algorithm is presented that can be used to solve the problem. According to the simulation results of the proposed algorithm, our method performs better and provides higher EE than both orthogonal multiple access and equal power allocation schemes. 相似文献
75.
V Sasisekharan 《Pramana》1986,26(3):L283-L293
A new geometrical method for generating aperiodic lattices forn-fold non-crystallographic axes is described. The method is based on the self-similarity principle. It makes use of the principles
of gnomons to divide the basic triangle of a regular polygon of 2n sides to appropriate isosceles triangles and to generate a minimum set of rhombi required to fill that polygon. The method
is applicable to anyn-fold noncrystallographic axis.
It is first shown how these regular polygons can be obtained and how these can be used to generate aperiodic structures. In
particular, the application of this method to the cases of five-fold and seven-fold axes is discussed. The present method
indicates that the recursion rule used by others earlier is a restricted one and that several aperiodic lattices with five
fold symmetry could be generated. It is also shown how a limited array of approximately square cells with large dimensions
could be detected in a quasi lattice and these are compared with the unit cell dimensions of MnAl6 suggested by Pauling.
In addition, the recursion rule for sub-dividing the three basic rhombi of seven-fold structure was obtained and the aperiodic
lattice thus generated is also shown.
Based on the lecture by the author “Quasi crystals: Is Linus Pauling right” and delivered on 16 December 1985 and arranged
by the Departments of Physics, Metallurgy, Materials Research Laboratory, and Instrumentation Services Unit, Indian Institute
of Science, Bangalore. 相似文献
76.
In order to solve the problem of maximizing the sum rate under the constraints of transmission power limitation and users’ rates requirements,precoder and receiver were devised by combining multiple-input multiple-output (MIMO) and non-orthogonal multiple access (NOMA) based on imperfect channel state information (CSI).To take advantage of successive interference cancellation (SIC) techniques to eliminate interference from weak user’s signal,each data stream of the strong user needed to decode the corresponding weak user’s signal.Since the problem formed was non-convex,it was converted into the problem with the difference of two convex functions (D.C.) by using semi-positive definite programming and first-order Taylor expansion,and a penalty function was used to solve the constraint of the rank of the precoding covariance matrix.The simulation results show that compared with the orthogonal multiple access technology,the proposed D.C.algorithm can improve system sum rate. 相似文献
77.
Paul D. Ahn Roger Bishop Donald C. Craig Marcia L. Scudder 《Journal of inclusion phenomena and macrocyclic chemistry》1995,23(4):313-327
The 1,5-dichloro-(1) and 1,5-dibromo-(2) naphthalene-2,6-diols form isostructural lattices incorporating ...O–H...O–H...O–H... hydrogen bonding surrounding 21 screw axes. Each phenolic hydroxy group participates in one donor and one acceptor hydrogen bond. When crystallised from dioxane, both compounds form new 1:1 co-crystalline materials whose lattices are closely related but not isostructural. All inter-phenolic hydrogen bonding is now absent with each hydroxy group acting instead as a donor to a dioxane oxygen atom. In consequence, the hydrogen bonded layer structures of pure1 or2 are now replaced by hydrogen bonded chain arrangements. All four crystal structures are analysed and compared in crystal engineering terms through discussion of the various types of other weak intermolecular attractions involved in their lattice constructions.
Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82202 (19 pages). 相似文献
78.
Because of a different imaging mechanism and highly complexity of body tissues and structures. Different modality medical images provide non-overlay complementary information. This has very important significance for multimodal medical image registration. Image registration is the first and key part of problem to be solved in the integrations. When the spatial position of two medical images is same, the registration could be achieved. For two CT and PET images, the principal axis method is adopted to achieve the rough registration. The modified simplex algorithm is employed to implement global search using the mutual information as similarity measure. The initial registration parameters are achieved through principal axis Based on the results of test, improved simplex method can adjust reflecting distance. Stepped-up optimization algorithm on the new experimental points through the methods of “reflection”, “enlargement”, “shrinkage” or “global systolic”. A mutual information registration based on modified simplex optimization method is presented in this paper to improve the speed of medical image registration.Results indicate that the proposed registration method prevents the optimizing process from falling into local extremum and improves the convergence speed while keeping the precision. The accurate registration of multimodal image with different resolutions is achieved. 相似文献
79.
所谓拟主轴标架,是一个单位正交标架,且相对于该标架的剪应变分量很小。作为Hill的主轴法的一种实用推广,我们在拟主轴杯架下建立了应变、转动、旋率、应变率、共轭应力和应力率在拟主轴标架下的近似表示形式。发展拟主轴法的目的,是试图既保留主轴法的主要优点,又可作为某种分析大变形问题的高效数值示析方法的基础。 相似文献
80.