全文获取类型
收费全文 | 71475篇 |
免费 | 11053篇 |
国内免费 | 17527篇 |
专业分类
化学 | 53126篇 |
晶体学 | 2030篇 |
力学 | 4363篇 |
综合类 | 1728篇 |
数学 | 10523篇 |
物理学 | 28285篇 |
出版年
2024年 | 179篇 |
2023年 | 848篇 |
2022年 | 2437篇 |
2021年 | 2458篇 |
2020年 | 2403篇 |
2019年 | 2533篇 |
2018年 | 2171篇 |
2017年 | 2710篇 |
2016年 | 2832篇 |
2015年 | 3496篇 |
2014年 | 3996篇 |
2013年 | 5635篇 |
2012年 | 5882篇 |
2011年 | 6198篇 |
2010年 | 5325篇 |
2009年 | 5513篇 |
2008年 | 6036篇 |
2007年 | 5415篇 |
2006年 | 5132篇 |
2005年 | 4511篇 |
2004年 | 3946篇 |
2003年 | 2889篇 |
2002年 | 3003篇 |
2001年 | 2606篇 |
2000年 | 2576篇 |
1999年 | 1565篇 |
1998年 | 925篇 |
1997年 | 763篇 |
1996年 | 710篇 |
1995年 | 622篇 |
1994年 | 526篇 |
1993年 | 538篇 |
1992年 | 477篇 |
1991年 | 396篇 |
1990年 | 368篇 |
1989年 | 298篇 |
1988年 | 286篇 |
1987年 | 242篇 |
1986年 | 211篇 |
1985年 | 202篇 |
1984年 | 208篇 |
1983年 | 166篇 |
1982年 | 115篇 |
1981年 | 110篇 |
1980年 | 100篇 |
1979年 | 82篇 |
1978年 | 46篇 |
1977年 | 45篇 |
1976年 | 33篇 |
1975年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
It is shown that the presence of mixed-culture growth in batch fermentation processes can be very accurately inferred from total biomass data by means of the wavelet analysis for singularity detection. This is accomplished by considering simple phenomenological models for the mixed growth and the more complicated case of mixed growth on a mixture of substrates. The main quantity provided by the wavelet analysis is the Hölder exponent of the singularity that we determine for our illustrative examples. The numerical results point to the possibility that Hölder exponents can be used to characterize the nature of the mixed-culture growth in batch fermentation processes with potential industrial applications. Moreover, the analysis of the same data affected by the common additive Gaussian noise still lead to the wavelet detection of the singularities although the Hölder exponent is no longer a useful parameter. 相似文献
102.
103.
The compound binomial risk model with time-correlated claims 总被引:1,自引:0,他引:1
Yuntao Xiao 《Insurance: Mathematics and Economics》2007,41(1):124-133
In this paper, we consider the compound binomial risk model with the time-correlated claims. It is assumed that every main claim will produce a by-claim but the occurrence of the by-claim may be delayed. We obtain the recursive formula of the joint distribution of the surplus immediately prior to ruin and deficit at ruin. Furthermore, the ruin probability is given by means of ruin probability and the deficit at ruin of the classical compound binomial risk model. Finally, we derive an upper bound for the ruin probability. 相似文献
104.
We continue the studies on the so–called genuine Bernstein–Durrmeyer operators U
n
by establishing a recurrence formula for the moments and by investigating the semigroup T(t) approximated by U
n
. Moreover, for sufficiently smooth functions the degree of this convergence is estimated. We also determine the eigenstructure
of U
n
, compute the moments of T(t) and establish asymptotic formulas.
Received: January 26, 2007. 相似文献
105.
刘国志 《数学的实践与认识》2006,36(12):1-5
提出一个新的具有积压定单的关于模糊订购量的模糊存储模型.在模糊函数原理下,给出了模糊总存储成本.为了寻找最优解,把最优模糊存储模型转化为双目标最优化模型,利用L ingo8.0求解不等式约束问题,我们发现最优解都是确定的实数.此外,当模糊订购量和模糊总需求都是三角形(或权重均为1/2梯形)模糊数时,我们提出模型的最优解与经典的具有积压定单存储模型具有相同的结果. 相似文献
106.
107.
Hong Ming ZHANG Xian Hong WANG Xiao Jiang ZHAO Ji LI Fo Song WANG 《中国化学快报》2006,17(4):437-440
A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity. 相似文献
108.
109.
M.A. Domínguez-Crespo L. Díaz-García A.M. Torres-Huerta 《Applied Surface Science》2006,253(3):1205-1214
Four NiMo catalyst supported on Al2O3 with different textural properties have been studied in the hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) of a Mexican straight run gasoil (SRGO). All reactions were carried out at three different temperatures 613, 633, and 653 K. Alumina supports were analysed by pyridine FTIR-TPD and nitrogen physisorption in order to determine their surface acidity and textural properties, respectively. TPR studies of the NiMo catalysts were analysed to correlate their hydrogenating properties. Metallic particles were characterized (after sulfidation) using transmission electron microscopy (TEM). Catalytic activities are discussed in relation to the physicochemical properties of NiMo catalysts. The importance of textural properties on coke deposition has been emphasized. The results of catalytic activity of these materials varied depending on dispersed MoS particles and pore distribution in final catalysts. The optimum pore diameter was found around 80 Å for HDS and HDN. 相似文献
110.