全文获取类型
收费全文 | 29397篇 |
免费 | 1857篇 |
国内免费 | 1069篇 |
专业分类
化学 | 3751篇 |
晶体学 | 75篇 |
力学 | 6806篇 |
综合类 | 108篇 |
数学 | 6125篇 |
物理学 | 4406篇 |
综合类 | 11052篇 |
出版年
2024年 | 71篇 |
2023年 | 281篇 |
2022年 | 501篇 |
2021年 | 529篇 |
2020年 | 629篇 |
2019年 | 656篇 |
2018年 | 731篇 |
2017年 | 631篇 |
2016年 | 645篇 |
2015年 | 894篇 |
2014年 | 1261篇 |
2013年 | 1661篇 |
2012年 | 1467篇 |
2011年 | 1882篇 |
2010年 | 1371篇 |
2009年 | 1701篇 |
2008年 | 1620篇 |
2007年 | 1902篇 |
2006年 | 1614篇 |
2005年 | 1315篇 |
2004年 | 1241篇 |
2003年 | 1170篇 |
2002年 | 941篇 |
2001年 | 747篇 |
2000年 | 801篇 |
1999年 | 686篇 |
1998年 | 639篇 |
1997年 | 627篇 |
1996年 | 563篇 |
1995年 | 500篇 |
1994年 | 459篇 |
1993年 | 392篇 |
1992年 | 400篇 |
1991年 | 334篇 |
1990年 | 284篇 |
1989年 | 264篇 |
1988年 | 213篇 |
1987年 | 167篇 |
1986年 | 127篇 |
1985年 | 110篇 |
1984年 | 81篇 |
1983年 | 42篇 |
1982年 | 79篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1976年 | 6篇 |
1971年 | 6篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
C. Foias A. E. Frazho I. Gohberg M. A. Kaashoek 《Integral Equations and Operator Theory》1997,29(4):455-490
The family of all solutions of the three chains completion problem with a prescribed tolerance is described explicitly. It is shown that this family can be parameterized by a natural set of contractive upper triangular operators. As an application all solutions to a suboptimal nonstationary Nehari problem are described. 相似文献
132.
感应加热钢包炉是国外新发展的一种二次精炼及加热设备,具有高效、低能耗、无污染的特点,本文在感应加热钢包炉电磁与结构分析工作的基础上,用电磁场数值模拟方法对感应加热钢包炉的电磁设计和包壳结构进行优化。 相似文献
133.
134.
本文对某一型号的一类轴流通风机的出口紊流流场进行了测量,得出了风机出口流场紊流度的变化特性和紊流流场的波形图,根据实验结果的分析,指出了该类通风机的空气动力噪声源。 相似文献
135.
Heat transfer in lattice BGK modeled fluid 总被引:1,自引:0,他引:1
The thermal lattice BGK model is a recently suggested numerical tool aiming at solving problems of thermohydrodynamics. The quality of the lattice BGK simulation is checked in this paper by calculating temperature profiles in the Couette flow under different Eckert and Mach numbers. A revised lower order model is proposed to improve the accuracy and the higher order model is proved to be advantageous in this respect, especially in the flow regime with a higher Mach number. 相似文献
136.
On the departure process of a leaky bucket system with long-range dependent input traffic 总被引:2,自引:0,他引:2
Due to the strong experimental evidence that the traffic to be offered to future broadband networks will display long-range
dependence, it is important to study the possible implications that such traffic may have for the design and performance of
these networks. In particular, an important question is whether the offered traffic preserves its long-range dependent nature
after passing through a policing mechanism at the interface of the network. One of the proposed solutions for flow control
in the context of the emerging ATM standard is the so-called leaky bucket scheme. In this paper we consider a leaky bucket
system with long-range dependent input traffic. We adopt the following popular model for long-range dependent traffic: Time
is discrete. At each unit time a random number of sessions is initiated, having the distribution of a Poisson random variable
with mean λ. Each of these sessions has a random duration τ, where the integer random variable τ has finite mean, infinite
variance, and a regularly varying tail, i.e., P(τ >К) ~ К-Lα
L(К), where 1 < α < 2 L(·) is a slowly varying function. Once a session is initiated, it generates one cell at each unit of time until its termination.
We examine the departure process of the leaky bucket policing mechanism driven by such an arrival process, and show that it
too is long-range dependent for any token buffer size and any - finite or infinite - cell buffer size. Moreover, upper and
lower bounds for the covariance sequence of the output process are established. The above results demonstrate that long-range
dependence cannot be removed by the kinds of flow control schemes that are currently being envisioned for broadband networks.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
137.
138.
科技论文摘要的写作 总被引:1,自引:0,他引:1
孙晓玲 《西北师范大学学报(自然科学版)》1994,30(4):81-86
科技论文摘要作为二次文献,具有举要性、示导性、贮存性、传扬性及商品性等功能,具有客观性、说明性、简练性等特征;摘要的写作要求是以精练的文字高度概括地反映论文的主题、结论及有关实质性信息。在内容在述与文字长短允许的情况下,尽可能运用报道性或报道-指示性文体;要保证摘要的独立性、自含性和完整性。 相似文献
139.
The Stokes motions of three-dimensional screw-sensed slender particles in a homogeneous shear field are investigated, including the effects of buoyancy. Conclusions are drawn about the possibility of achieving a separation of mixtures of right- and left-handed particles. The linearity of the Stokes equations allows complex flows to be solved by adding the effects of the several terms which describe the flow in which the particle is immersed. The homogeneous shear flow considered here consists of three such terms; solutions for a series of 12 unit motions are sufficient to determine the hydrodynamic resistance tensors. The forces and torques experienced by screw-sensed particles are calculated from these 51 resistance tensors, using slender-filament theory. The results allow an estimate of the range of buoyancy parameters for which gravitational sedimentation can be neglected. The fundamental component of the particle motion is a rotation, at approximately the same angular velocity as that of the fluid. Superimposed on this are variations, of large period, in the particle orientation. A phase plane analysis is used to find the terminal orientations. Very long calculation times are required for the phase portrait. An approximate method based on azimuthally-averaged equations is developed to avoid the requirements for long time integration. 相似文献
140.
从计划角度重点分析了钢铁生产中炼钢、连铸、热轧三者之间联接的较高模式-直接热装轧制计划系统的实现方式,并给出了较为具体的方案。 相似文献