全文获取类型
收费全文 | 4395篇 |
免费 | 478篇 |
国内免费 | 494篇 |
专业分类
化学 | 619篇 |
晶体学 | 13篇 |
力学 | 427篇 |
综合类 | 143篇 |
数学 | 2224篇 |
物理学 | 1941篇 |
出版年
2024年 | 5篇 |
2023年 | 22篇 |
2022年 | 72篇 |
2021年 | 93篇 |
2020年 | 92篇 |
2019年 | 68篇 |
2018年 | 84篇 |
2017年 | 109篇 |
2016年 | 116篇 |
2015年 | 95篇 |
2014年 | 195篇 |
2013年 | 305篇 |
2012年 | 196篇 |
2011年 | 257篇 |
2010年 | 224篇 |
2009年 | 273篇 |
2008年 | 286篇 |
2007年 | 305篇 |
2006年 | 264篇 |
2005年 | 227篇 |
2004年 | 237篇 |
2003年 | 227篇 |
2002年 | 208篇 |
2001年 | 178篇 |
2000年 | 155篇 |
1999年 | 152篇 |
1998年 | 127篇 |
1997年 | 150篇 |
1996年 | 94篇 |
1995年 | 86篇 |
1994年 | 71篇 |
1993年 | 51篇 |
1992年 | 51篇 |
1991年 | 32篇 |
1990年 | 48篇 |
1989年 | 36篇 |
1988年 | 43篇 |
1987年 | 35篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有5367条查询结果,搜索用时 796 毫秒
211.
汽配件颜色喷涂顺序问题通常以生产线上相邻汽配件颜色切换次数少为最优目标,以进一步降低生产成本.该类问题具有所有汽配件都必须喷涂一次且只喷涂一次的特点,为此提出了TSP转化与建模的方法.将待喷涂汽配件定义为TSP顶点,任意两个待喷涂汽配件的颜色切换定义为顶点的距离,仿照TSP问题构建0-1规划模型;类似于顶点距离,将某些... 相似文献
212.
In an Internet auction, the expected payoff acts as a benchmark of the reasonableness of the price that is paid for the purchased
item. Since the number of potential bidders is not observable, the expected payoff is difficult to estimate accurately. We
approach this problem by considering the bids as a record and 2-record sequence of the potential bidder’s valuation and using
the Extreme Value Theory models to model the tail distribution of the bidder’s valuation and study the expected payoff. Along
the discussions for three different cases regarding the extreme value index γ, we show that the observed payoff does not act as an accurate estimation of the expected payoff in all the cases except a
subclass of the case γ = 0. Within this subclass and under a second order condition, the observed payoff consistently converges to the expected
payoff and the corresponding asymptotic normality holds.
相似文献
213.
We introduce the inverted prefix tries (a variation of suffix tries) as a convenient formalism for stating and proving properties of the Ehrenfeucht–Mycielski sequence [A. Ehrenfeucht, J. Mycielski, A pseudorandom sequence—how random is it? American Mathematical Monthly 99 (1992) 373-375]. We also prove an upper bound on the position in the sequence by which all strings of a given length will have appeared; our bound is given by the Ackermann function, which, in light of experimental data, may be a gross over-estimate. Still, it is the best explicitly known upper bound at the moment. Finally, we show how to compute the next bit in the sequence in a constant number of operations. 相似文献
214.
Full field laser Doppler imaging (LDI) and single exposure laser speckle contrast imaging (LSCI) are directly compared using a novel instrument which can concurrently image blood flow using both LDI and LSCI signal processing. Incorporating a commercial CMOS camera chip and a field programmable gate array (FPGA) the flow images of LDI and the contrast maps of LSCI are simultaneously processed by utilizing the same detected optical signals. The comparison was carried out by imaging a rotating diffuser. LDI has a linear response to the velocity. In contrast, LSCI is exposure time dependent and does not provide a linear response in the presence of static speckle. It is also demonstrated that the relationship between LDI and LSCI can be related through a power law which depends on the exposure time of LSCI. 相似文献
215.
216.
Let M
n
denote the partial maximum of a strictly stationary sequence (X
n
). Suppose that some of the random variables of (X
n
) can be observed and let [(M)\tilde]n\tilde M_n
stand for the maximum of observed random variables from the set {X
1, ..., X
n
}. In this paper, the almost sure limit theorems related to random vector ([(M)\tilde]n\tilde M_n
, M
n
) are considered in terms of i.i.d. case. The related results are also extended to weakly dependent stationary Gaussian sequence as its covariance function satisfies
some regular conditions. 相似文献
217.
PARK Kyewon Koh 《中国科学 数学(英文版)》2011,(3):531-538
We introduce the notion of entropy generating sequence for infinite words and define its dimension when it exists. We construct an entropy generating sequence for each symbolic example constructed by Cassaigne such that the dimension of the sequence is the same as its topological entropy dimension. Hence the complexity can be measured via the dimension of an entropy generating sequence. Moreover, we construct a weakly mixing example with subexponential growth rate. 相似文献
218.
219.
Atom interferometry is a rapidly advancing field and this Letter proposes an experiment based on existing technology that can search for new short distance forces. With current technology it is possible to improve the sensitivity by up to a factor of 102 and near-future advances may be able to rewrite the limits for forces with ranges from 1 mm to 100 m. 相似文献
220.
Lucas P. Tendela Alejandro FedericoGuillermo H. Kaufmann 《Optics and Lasers in Engineering》2011,49(2):281-284
This paper presents an interferometric measurement of the out-of-plane deflections produced by a piezoelectric transducer, manufactured by thick-film deposition of a ceramic paste over an alumina substrate, when is subjected to a DC electric voltage. It is shown that a digital speckle pattern interferometer with an incorporated phase-shifting facility allows the measurement of nanometer displacements generated by the piezoelectric device. These measurements are used to evaluate the effective piezoelectric charge constant along the polarization direction (d33)eff that characterizes the thick-film transducer. 相似文献