全文获取类型
收费全文 | 281篇 |
免费 | 39篇 |
国内免费 | 19篇 |
专业分类
化学 | 51篇 |
力学 | 79篇 |
综合类 | 15篇 |
数学 | 119篇 |
物理学 | 75篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 1篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 29篇 |
2012年 | 15篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 19篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 31 毫秒
331.
Teng Tien‐Hsi 《International Journal of Mathematical Education in Science & Technology》2013,44(1):145-153
It is my firm belief that mathematics is methodology. The briefer is the method, the more effective it is in treating problems. The novel methodized treatment in this article features all the concepts of conics relating to transformation between coordinate systems and standard forms with graphic illustrations. Denote O’ as the centre of an ellipse or a hyperbola or the vertex of a parabola and F as a focus of a conic. Let O'F=cu, u=[cosθ, sinθ], v = [‐sinθ, cosθ] and P(x,y), then the transformation x’ = u.O'P, y‘ = v.O'P which leads to the standard form for each conic relative to x’ — O'—y‘ The theorem on normal projection in this article is very important in analytic geometry and especially useful for problems involving conies when a directrix or an axis is given. 相似文献
332.
尝试运用最新发展的自回归分布滞后模型(ARDL)对福建省1978-2009年能源消费、劳动力和经济增长三者的因果关系进行检验和分析.常规单位根检验认为能源消费、劳动力和经济增长是一阶单整,I(1);而Zivot & Andrews(ZA)内生性结构突变单位根检验发现三个序列为带有结构突变的趋势平稳过程.ARDL边界检验和格兰杰因果检验结果表明能源消费、劳动力和经济增长间存在稳定的长期均衡关系,表现为从经济增长、劳动力到能源消费的长期因果关系;而在短期因果关系上,表现为经济增长到能源消费单向因果关系,以及经济增长与劳动力之间的双向因果关系.研究同时对福建省经济增长和能源保护战略提出了政策建议. 相似文献
333.
Ludwig Stork Xiaohui Liu Boniface P. T. Fokwa Richard Dronskowski Prof. Dr. 《无机化学与普通化学杂志》2007,633(9):1339-1342
Orange‐red single crystals of thallium carbodiimide, Tl2NCN, have been grown from an aqueous solution of cyanamide and thallium carbonate under strongly basic conditions. Tl2NCN crystallizes in space group with a = 5.338(1), b = 6.626(2), c = 9.645(3) Å, α = 98.765(4)°, β = 98.685(4)°, γ = 113.178(4)°, and Z = 3; the structure can be considered a strongly distorted anti‐CdI2 type. One finds two crystallographically different and irregular [NCN]Tl6 octahedra in which the Tl–N distances of the three‐coordinate monovalent thallium ions lie between 2.52 and 2.72Å. The two symmetry‐inequivalent NCN2? units adopt the carbodiimide shape, and the course of its molar volume as a function of the monovalent counter cation is analyzed. 相似文献
334.
Function projective lag synchronization of different structural fractional-order chaotic systems is investigated. It is shown that the slave system can be synchronized with the past states of the driver up to a scaling function matrix. According to the stability theorem of linear fractional-order systems, a nonlinear fractional-order controller is designed for the synchronization of systems with the same and different dimensions. Especially, for two different dimensional systems, the synchronization is achieved in both reduced and increased dimensions. Three kinds of numerical examples are presented to illustrate the effectiveness of the scheme. 相似文献
335.
Susanne Burri Patrick Sturm Thomas Baur Matti Barthel Alexander Knohl Nina Buchmann 《Isotopes in environmental and health studies》2014,50(4):497-513
Pulse labelling experiments provide a common tool to study short-term processes in the plant–soil system and investigate below-ground carbon allocation as well as the coupling of soil CO2 efflux to photosynthesis. During the first hours after pulse labelling, the measured isotopic signal of soil CO2 efflux is a combination of both physical tracer diffusion into and out of the soil as well as biological tracer release via root and microbial respiration. Neglecting physical back-diffusion can lead to misinterpretation regarding time lags between photosynthesis and soil CO2 efflux in grassland or any ecosystem type where the above-ground plant parts cannot be labelled in gas-tight chambers separated from the soil. We studied the effects of physical 13CO2 tracer back-diffusion in pulse labelling experiments in grassland, focusing on the isotopic signature of soil CO2 efflux. Having accounted for back-diffusion, the estimated time lag for first tracer appearance in soil CO2 efflux changed from 0 to 1.81±0.56 h (mean±SD) and the time lag for maximum tracer appearance from 2.67±0.39 to 9.63±3.32 h (mean±SD). Thus, time lags were considerably longer when physical tracer diffusion was considered. Using these time lags after accounting for physical back-diffusion, high nocturnal soil CO2 efflux rates could be related to daytime rates of gross primary productivity (R2=0.84). Moreover, pronounced diurnal patterns in the δ13C of soil CO2 efflux were found during the decline of the tracer over 3 weeks. Possible mechanisms include diurnal changes in the relative contributions of autotrophic and heterotrophic soil respiration as well as their respective δ13C values. Thus, after accounting for physical back-diffusion, we were able to quantify biological time lags in the coupling of photosynthesis and soil CO2 efflux in grassland at the diurnal time scale. 相似文献
336.
Finite‐Time lag synchronization of delayed neural networks via periodically intermittent control 下载免费PDF全文
The problem of finite‐time lag synchronization of delayed neural networks via periodically intermittent control is studied. In two sections, based on the same finite‐time stability theory and using the same sliding mode control, by designing a periodically intermittent feedback controller and adjusting periodically intermittent control strengths with the updated laws, we achieve the finite‐time lag synchronization between two time delayed networks. In addition, we ensure that the trajectory of the error system converges to a chosen sliding surface within finite time and keeps it on forever. Finally, two examples are presented to verify the effectiveness of the analytical results obtained here. © 2015 Wiley Periodicals, Inc. Complexity 21: 211–219, 2016 相似文献
337.
王文胜 《数学物理学报(A辑)》2004,4(5):521-529
该文通过建立关于部分和学生化增量的大偏差不等式, 在稳定律吸引场中证得了学生化的Hanson Russo型增量定理. 相似文献
338.
339.
Jiaqi Teng Shuzhen Ding Xiaoping Shi Huiguo Zhang Xijian Hu 《Entropy (Basel, Switzerland)》2022,24(7)
Medical data are often missing during epidemiological surveys and clinical trials. In this paper, we propose the MCMCINLA estimation method to account for missing data. We introduce a new latent class into the spatial lag model (SLM) and use a conditional autoregressive specification (CAR) spatial model-based approach to impute missing values, making the model fit into the integrated nested Laplace approximation (INLA) framework. Combining the advantages of both the Markov chain Monte Carlo (MCMC) and INLA frameworks, the MCMCINLA algorithm is used to implement imputation of the missing data and fit the model to derive estimates of the parameters from the posterior margins. Finally, the economic data and the hemorrhagic fever with renal syndrome (HFRS) disease data of mainland China from 2016–2018 are used as examples to explore the development of public health in China in the post-epidemic era. The results show that compared with expectation maximization (EM) and full information maximum likelihood estimation (FIML), the predicted values of the missing data obtained using our method are closer to the true values, and the spatial distribution of HFRS in China can be inferred from the imputation results with a southern-heavy and northern-light distribution. It can provide some references for the development of public health in China in the post-epidemic era. 相似文献