全文获取类型
收费全文 | 32303篇 |
免费 | 6636篇 |
国内免费 | 2559篇 |
专业分类
化学 | 7490篇 |
晶体学 | 611篇 |
力学 | 2915篇 |
综合类 | 633篇 |
数学 | 9829篇 |
物理学 | 20020篇 |
出版年
2024年 | 46篇 |
2023年 | 286篇 |
2022年 | 525篇 |
2021年 | 763篇 |
2020年 | 784篇 |
2019年 | 678篇 |
2018年 | 729篇 |
2017年 | 1140篇 |
2016年 | 1287篇 |
2015年 | 1096篇 |
2014年 | 1790篇 |
2013年 | 2523篇 |
2012年 | 1965篇 |
2011年 | 2122篇 |
2010年 | 1754篇 |
2009年 | 2051篇 |
2008年 | 2419篇 |
2007年 | 2366篇 |
2006年 | 2062篇 |
2005年 | 1871篇 |
2004年 | 1722篇 |
2003年 | 1477篇 |
2002年 | 1405篇 |
2001年 | 1211篇 |
2000年 | 1085篇 |
1999年 | 991篇 |
1998年 | 843篇 |
1997年 | 760篇 |
1996年 | 603篇 |
1995年 | 632篇 |
1994年 | 456篇 |
1993年 | 376篇 |
1992年 | 290篇 |
1991年 | 282篇 |
1990年 | 186篇 |
1989年 | 137篇 |
1988年 | 153篇 |
1987年 | 114篇 |
1986年 | 86篇 |
1985年 | 92篇 |
1984年 | 69篇 |
1983年 | 38篇 |
1982年 | 49篇 |
1981年 | 44篇 |
1980年 | 33篇 |
1979年 | 31篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
31.
In circuit-switched networks call streams are characterized by their mean and peakedness (two-moment method). The GI/M/C/0 system is used to model a single link, where the GI-stream is determined by fitting moments appropriately. For the moments of the overflow traffic of a GI/M/C/0 system there are efficient numerical algorithms available. However, for the moments of the freed carried traffic, defined as the moments of a virtual link of infinite capacity to which the process of calls accepted by the link (carried arrival process) is virtually directed and where the virtual calls get fresh exponential i.i.d. holding times, only complex numerical algorithms are available. This is the reason why the concept of the freed carried traffic is not used. The main result of this paper is a numerically stable and efficient algorithm for computing the moments of freed carried traffic, in particular an explicit formula for its peakedness. This result offers a unified handling of both overflow and carried traffics in networks. Furthermore, some refined characteristics for the overflow and freed carried streams are derived. 相似文献
32.
Using the continuous shape space formalism, we develop an immune system model involving both B lymphocytes and antibody molecules. The binding and cross-linking of receptors on B cells stimulates the cells to divide and, with a lag, to secrete antibody. Using the method of multiple scales, we show how to correctly formulate long-time-scale equations for the population dynamics of B cells, the total antibody concentration, and rate of antibody secretion. We compare our model with previous phenomenological formulations. 相似文献
33.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems. 相似文献
34.
卫星振动对星间光码分多址系统性能的影响 总被引:2,自引:2,他引:0
卫星振动是影响星间光CDMA通信系统性能的一个重要因素.考虑多用户干扰、背景光噪音、热噪音、接收机噪音和卫星振动,给出了基于PPM信号格式的星间二维光CDMA通信系统的系统模型.采用数值分析的方法,详细分析了卫星振动对该系统误码率性能的影响.结果表明,码速率、通信波长和卫星振动都会影响星间二维光CDMA通信系统的误码率性能.当卫星振动标准偏差σ≤4×10-7时,卫星振动对系统误码率性能的影响较小;当卫星振动标准偏差σ≥1.2×10-6,卫星振动对系统误码率性能的影响很大,得到的误码率难以满足系统的通信要求,需要采用卫星振动抑制或补偿等技术提高星间二维光CDMA通信系统的误码率性能. 相似文献
35.
瞄准线高精度稳定是机载光电稳瞄系统的主要指标和关键技术。根据四框架稳瞄系统的工作原理,以手动跟踪模式为主要研究对象,建立了稳瞄伺服控制系统模型。考虑到直升机扰动特点,对线扰动、角速率扰动、摩擦力矩、弹性力矩等各种扰动因素也建立相应的数学模型,同时在各种扰动因素作用下利用Matlab对机载高精度稳瞄系统的手动跟踪控制模式进行了仿真设计分析和理论研究,设计出适合的控制器。此模型在实际系统中获得验证,对稳瞄伺服控制系统的设计具有参考意义。 相似文献
36.
The relation between the total variation of classical field theory and the multisymplectic structure is shown. Then the multisymplectic structure and the corresponding multisymplectic conservation of the coupled nonlinear Schrodinger system are obtained directly from the variational principle. 相似文献
37.
Stability of chirped bright and dark soliton-like solutions of the cubic complex Ginzburg-Landau equation with variable coefficients 总被引:1,自引:0,他引:1
Fang Fang 《Optics Communications》2006,268(2):305-310
We consider an inhomogeneous optical fiber system described by the generalized cubic complex Ginzburg-Landau (CGL) equation with varying dispersion, nonlinearity, gain (loss), nonlinear gain (absorption) and the effect of spectral limitation. Exact chirped bright and dark soliton-like solutions of the CGL equation were found by using a suitable ansatz. Furthermore, we analyze the features of the solitons and consider the problem of stability of these soliton-like solutions under finite initial perturbations. It is shown by extensive numerical simulations that both bright and dark soliton-like solutions are stable in an inhomogeneous fiber system. Finally, the interaction between two chirped bright and dark soliton-like pulses is investigated numerically. 相似文献
38.
Abstract
In this note, we consider a Frémond model of shape memory alloys. Let us imagine a piece of a shape memory alloy which is
fixed on one part of its boundary, and assume that forcing terms, e.g., heat sources and external stress on the remaining
part of its boundary, converge to some time-independent functions, in appropriate senses, as time goes to infinity. Under
the above assumption, we shall discuss the asymptotic stability for the dynamical system from the viewpoint of the global
attractor. More precisely, we generalize the paper [12] dealing with the one-dimensional case. First, we show the existence
of the global attractor for the limiting autonomous dynamical system; then we characterize the asymptotic stability for the
non-autonomous case by the limiting global attractor.
* Project supported by the MIUR-COFIN 2004 research program on “Mathematical Modelling and Analysis of Free Boundary Problems”. 相似文献
39.
WANG Libin 《数学年刊B辑(英文版)》2002,23(4):439-454
The author gets a blow-up result of C1 solution to the Cauchy problem for a first order quasilinear non-strictly hyperbolic system in one space dimension. 相似文献
40.