全文获取类型
收费全文 | 44209篇 |
免费 | 6034篇 |
国内免费 | 4505篇 |
学科分类
工业技术 | 54748篇 |
出版年
2024年 | 168篇 |
2023年 | 712篇 |
2022年 | 1176篇 |
2021年 | 1379篇 |
2020年 | 1398篇 |
2019年 | 1269篇 |
2018年 | 1229篇 |
2017年 | 1471篇 |
2016年 | 1589篇 |
2015年 | 1756篇 |
2014年 | 2510篇 |
2013年 | 2748篇 |
2012年 | 3232篇 |
2011年 | 3401篇 |
2010年 | 2714篇 |
2009年 | 2917篇 |
2008年 | 2963篇 |
2007年 | 3380篇 |
2006年 | 2975篇 |
2005年 | 2624篇 |
2004年 | 2147篇 |
2003年 | 1792篇 |
2002年 | 1448篇 |
2001年 | 1222篇 |
2000年 | 1090篇 |
1999年 | 913篇 |
1998年 | 727篇 |
1997年 | 625篇 |
1996年 | 570篇 |
1995年 | 496篇 |
1994年 | 432篇 |
1993年 | 303篇 |
1992年 | 283篇 |
1991年 | 231篇 |
1990年 | 210篇 |
1989年 | 185篇 |
1988年 | 121篇 |
1987年 | 72篇 |
1986年 | 39篇 |
1985年 | 41篇 |
1984年 | 30篇 |
1983年 | 37篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 365 毫秒
101.
郭广海 《青岛科技大学学报(自然科学版)》2008,29(3)
采用多项式函数代替乌龟坐标的方法,给出静态球对称时空中黑洞事件视界和宇宙视界区域内标量场方程的解,并对事件视界附近势垒的性质进行了讨论。发现对带电量不同的时空,标量场辐射的形式亦有所不同;势垒随宇宙学常数的减小而变窄、变高。 相似文献
102.
Gabriel Nivasch 《Information Processing Letters》2004,90(3):135-140
We present an algorithm for detecting periodicity in sequences produced by repeated application of a given function. Our algorithm uses logarithmic memory with high probability, runs in linear time, and is guaranteed to stop within the second loop through the cycle. We also present a partitioning technique that offers a time/memory tradeoff. Our algorithm is especially well suited for sequences where the cycle length is typically small compared to the length of the acyclic prefix. 相似文献
103.
The transit time of the coolant, and thus its velocity, has been measured using the temperature fluctuation at the outlet of a reactor core. An impulse response function estimation is introduced, which substitutes the widely used cross-correlation measurement technique. It is shown in theory and practice that the time delay estimation is improved when using the impulse response function instead of the cross-correlation function in parameter estimation. Extremely low velocities (down to 2 cm/sec) have been measured in a natural circulation regime in a research reactor. 相似文献
104.
对大化肥气化装置的安全系统的作用、硬件组成、信号的处理以及顺序控制和安全联锁进行了介绍,并详细描述了气化炉的开、停车及吹扫顺序的过程以及安全联锁的功能。 相似文献
105.
106.
Boiling: Size Distribution of Bubbles as Demanded by the Principle of Maximum Information 总被引:1,自引:0,他引:1
The principle of maximum informational entropy is used to find the probability density function for the departure radius of a bubble in boiling on a solid surface. A general relation is derived, which leads to particular expressions. 相似文献
107.
108.
Chouping Luo Marek Klisinski 《International journal for numerical methods in engineering》2004,61(2):159-188
The present study is a continuation of our previous work with the aim to reduce problems caused by standard higher order elements in contact problems. The difficulties can be attributed to the inherent property of the Galerkin method which gives uneven distributions of nodal forces resulting in oscillating contact pressures. The proposed remedy is use of piece‐wise linear weight functions. The methods to establish stiffness and/or mass matrix for 8‐node quadrilateral element in 2D are presented, i.e. the condensing and direct procedures. The energy and nodal displacement error norms are also checked to establish the convergence ratio. Interpretation of calculated contact pressures is discussed. Two new 2D 8‐node quadrilateral elements, QUAD8C and QUAD8D, are derived and tested in many examples, which show their good performance in contact problems. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
109.
110.
Differential pressure fluctuation time series were obtained at different locations in a two-dimensional spout-fluid bed with a cross section of 300 × 30 mm and height 2000 mm. Shannon entropy analysis of differential pressure fluctuations was developed to characterize the dynamic behavior. Effects of two important operating parameters (spouting gas velocity and fluidizing gas flow rate) on the Shannon entropy were examined. It was demonstrated that a spout-fluid bed at a high spouting gas velocity or fluidizing gas flow rate was a deterministic chaos system since the Shannon entropies at all bed locations increased sharply and asymmetric unstable flows occurred. Shannon entropies were found to be significantly different at various bed locations. Shannon entropies of different flow regimes were distinct, so they were used to identify the flow regimes. The results show that the Shannon entropy helps to grasp the complex characteristics of dynamic behavior in spout-fluid beds. 相似文献