全文获取类型
收费全文 | 9736篇 |
免费 | 1328篇 |
国内免费 | 476篇 |
专业分类
化学 | 2382篇 |
晶体学 | 36篇 |
力学 | 609篇 |
综合类 | 285篇 |
数学 | 4695篇 |
物理学 | 3533篇 |
出版年
2024年 | 26篇 |
2023年 | 136篇 |
2022年 | 305篇 |
2021年 | 444篇 |
2020年 | 282篇 |
2019年 | 204篇 |
2018年 | 162篇 |
2017年 | 322篇 |
2016年 | 392篇 |
2015年 | 302篇 |
2014年 | 571篇 |
2013年 | 722篇 |
2012年 | 621篇 |
2011年 | 597篇 |
2010年 | 531篇 |
2009年 | 673篇 |
2008年 | 598篇 |
2007年 | 645篇 |
2006年 | 533篇 |
2005年 | 402篇 |
2004年 | 323篇 |
2003年 | 333篇 |
2002年 | 310篇 |
2001年 | 296篇 |
2000年 | 269篇 |
1999年 | 222篇 |
1998年 | 196篇 |
1997年 | 182篇 |
1996年 | 164篇 |
1995年 | 100篇 |
1994年 | 80篇 |
1993年 | 85篇 |
1992年 | 47篇 |
1991年 | 43篇 |
1990年 | 43篇 |
1989年 | 27篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 27篇 |
1985年 | 65篇 |
1984年 | 61篇 |
1983年 | 20篇 |
1982年 | 43篇 |
1981年 | 40篇 |
1980年 | 25篇 |
1979年 | 19篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1967年 | 1篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
51.
ZHANG Lin-bo LIU Xiao-hua JIANG Yuan GUO Ping SHA Li-jin LI Yu 《高等学校化学研究》2006,22(2):139-144
After establishing hemi-Parkinsonian rat models, the relationships between neuron death and the expression of several proteins, such as c-Fos, GFAP, GDNF, NF-κB and some cytokines were determined. Therapeutics experiments with notoginsenoside-Rg1 were carried out. The research results show that the expressions of GFAP, NF-Kκ and c-Fos will obviously increase in the lesion side of the striatum and the expression of GDNF will decrease, which implies that the signal transduction pathway may participate in the apoptosis in neurons. The levels of some cytokines such as TNF-α, IL-1β in the striatum of PD rat models increased compared to those of normal rats. The results of the therapeutics experiments show that notoginsenoside-Rg1 may repress the immune inflammation response and regulate the immune function through the neuro-immune molecular network. Therefore, notoginsenoside-Rg1 can be used as an effective drug for anti-oxidation and anti-inflammation, and can be used in the therapy of Parkinson's disease(PD). 相似文献
52.
Temperature effects on deposition rate of silicon nitride films were characterized by building a neural network prediction model. The silicon nitride films were deposited by using a plasma enhanced chemical vapor deposition system and process parameter effects were systematically characterized by 26−1 fractional factorial experiment. The process parameters involved include a radio frequency power, pressure, temperature, SiH4, N2, and NH3 flow rates. The prediction performance of generalized regression neural network was drastically improved by optimizing multi-valued training factors using a genetic algorithm. Several 3D plots were generated to investigate parameter effects at various temperatures. Predicted variations were experimentally validated. The temperature effect on the deposition rate was a complex function of parameters but N2 flow rate. Larger decreases in the deposition rate with the temperature were only noticed at lower SiH4 (or higher NH3) flow rates. Typical effects of SiH4 or NH3 flow rate were only observed at higher or lower temperatures. A comparison with the refractive index model facilitated a selective choice of either SiH4 or NH3 for process optimization. 相似文献
53.
运用Lyapunov函数方法,讨论了一维细胞神经网络模型的完全稳定性问题,给出了四组使模型具有完全稳定的充分条件. 相似文献
54.
现代优化计算方法在蛋白质结构预测中的应用 总被引:2,自引:1,他引:1
现代优化计算方法在蛋白质结构预测中占有重要地位.简要地介绍了模拟退火算法,遗传算法,人工神经网络和图论算法在蛋白质结构预测中的应用.对国内外近年来应用这些算法,特别是在蛋白质构象搜索问题中,解决蛋白质结构预测的研究作了回顾,并分析、比较了这几种算法的效果和特点. 相似文献
55.
Huseyin Ince 《Computational Management Science》2006,3(2):161-174
The nature of the financial time series is complex, continuous interchange of stochastic and deterministic regimes. Therefore,
it is difficult to forecast with parametric techniques. Instead of parametric models, we propose three techniques and compare
with each other. Neural networks and support vector regression (SVR) are two universally approximators. They are data-driven
non parametric models. ARCH/GARCH models are also investigated. Our assumption is that the future value of Istanbul Stock
Exchange 100 index daily return depends on the financial indicators although there is no known parametric model to explain
this relationship. This relationship comes from the technical analysis. Comparison shows that the multi layer perceptron networks
overperform the SVR and time series model (GARCH). 相似文献
56.
基于SPA的双枝模糊决策分析 总被引:3,自引:0,他引:3
将集对理论(SPA)与双枝模糊决策理论相结合,用集对分析的方法研究进行双枝模糊决策的方法,分别对双枝模糊决策因素域和双枝模糊决策的上枝、下枝和双枝进行了集对分析,给出了用SPA进行双枝模糊决策的性质,同时讨论了双枝模糊决策的动态分析方法,以及双枝模糊决策度强弱态势预测的方法,从而为双枝模糊决策理论的研究提供了新的视角和方法,为双枝模糊决策的应用提供了更方便的工具和更强的理论支持。 相似文献
57.
58.
59.
A new type of optoelectronic cellular neural network has been developed by providing the capability of coefficients adjusment of cellular neural network (CNN) using Widrow based perceptron learning algorithm. The new supervised cellular neural network is called Widrow-CNN. Despite the unsupervised CNN, the proposed learning algorithm allows to use the Widrow-CNN for various image processing applications easily. Also, the capability of CNN for image processing and feature extraction has been improved using basic joint transform correlation architecture. This hardware application presents high speed processing capability compared to digital applications. The optoelectronic Widrow-CNN has been tested for classic CNN feature extraction problems. It yields the best results even in case of hard feature extraction problems such as diagonal line detection and vertical line determination. 相似文献
60.
Pre—Separation Axioms in Fuzzifying Topology 总被引:1,自引:0,他引:1
K.M.AbdEl-Hakeim F.M.Zeyada 《模糊系统与数学》2003,17(1):28-36
1 IntroductionYing[5,6 ] introduced and elementally developed so called fuzzifying topology with the semanticmethod of continuous valued L ogic.Shen[7] introduced and studied T0 -,T1-,T2 (Hausdorff) -,T3(regularity) -,T4 (normality) -separation axioms in fuzzifying topology.In [3 ]the concepts of thefamily of fuzzifying pre-open sets,fuzzifying pre-neighbourhood structure of a point and fuzzifyingpre-closure are introduced and studied.It is worth to mention that pre-separation axioms are … 相似文献