全文获取类型
收费全文 | 1279篇 |
免费 | 107篇 |
国内免费 | 37篇 |
专业分类
化学 | 344篇 |
晶体学 | 4篇 |
力学 | 104篇 |
综合类 | 78篇 |
数学 | 269篇 |
物理学 | 624篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 29篇 |
2021年 | 29篇 |
2020年 | 40篇 |
2019年 | 28篇 |
2018年 | 35篇 |
2017年 | 73篇 |
2016年 | 73篇 |
2015年 | 54篇 |
2014年 | 70篇 |
2013年 | 93篇 |
2012年 | 57篇 |
2011年 | 67篇 |
2010年 | 45篇 |
2009年 | 57篇 |
2008年 | 54篇 |
2007年 | 82篇 |
2006年 | 50篇 |
2005年 | 61篇 |
2004年 | 79篇 |
2003年 | 55篇 |
2002年 | 53篇 |
2001年 | 41篇 |
2000年 | 27篇 |
1999年 | 33篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 20篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1423条查询结果,搜索用时 265 毫秒
171.
为了实现对股票价格变化的短期预测,提出了一种基于小波神经网络(WNN)与自回归积分滑动平均模型(ARIMA)的组合预测模型.将股票的收盘价序列数据划分为线性以及非线性(误差项)两个部分,分别利用统计学中ARIMA模型和小波神经网络分别对两部分数据进行预测并得到结果,将两部分结果组合相加合成为整个股票价格的预测结果.实验结果表明该组合模型在预测精度方面有提高,是一种比较有效的预测模型. 相似文献
172.
Ilana Lavy 《The Journal of Mathematical Behavior》2010,29(1):11-24
In the present study we explore changes in perceptions of our class of prospective mathematics teachers (PTs) regarding their mathematical knowledge. The PTs engaged in problem posing activities in geometry, using the “What If Not?” (WIN) strategy, as part of their work on computerized inquiry-based activities. Data received from the PTs’ portfolios reveals that they believe that engaging in the inquiry-based activity enhanced both their mathematical and meta-mathematical knowledge. As to the mathematical knowledge, they deepened their knowledge regarding the geometrical concepts and shapes involved, and during the process of creating the problem and checking its validity and its solution, they deepened their understanding of the interconnections among the concepts and shapes involved. As to meta-mathematical knowledge, the PTs refer to aspects such as the meaning of the givens and their relations, validity of an argument, the importance and usefulness of the definitions of concepts and objects, and the importance of providing a formal proof. 相似文献
173.
软件可靠性模型和估计 总被引:1,自引:1,他引:0
本文根据何国伟提出的软件可靠性模型,特别是输入空间和输入分布的概念,分析软件测试数据特征,给出软件可靠性的点估计和置信下界的计算公式。 相似文献
174.
175.
176.
Manuel A.P. Segurado Margarida F.B. Silva Rita Castro 《International Journal of Mathematical Education in Science & Technology》2013,44(5):664-679
The mathematical language and its tools are complementary to the formalism in chemistry, in particular at an advanced level. It is thus crucial, for its understanding, that students acquire a solid knowledge in Calculus and that they know how to apply it. The frequent occurrence of indeterminate forms in multiple areas, particularly in Physical Chemistry, justifies the need to properly understand the limiting process in such cases. This article emphasizes the importance of the L’Hôpital's rule as a practical tool, although often neglected, to obtain the more common indeterminate limits, through the use of some specific examples as the radioactive decay, spectrophotometric error, Planck's radiation law, second-order kinetics, or consecutive reactions. 相似文献
177.
Leonie Tickle Tim Kyng Leigh N. Wood 《International Journal of Mathematical Education in Science & Technology》2013,44(2):200-213
The role of universities in preparing students to use spreadsheet and other technical software in the financial services workplace has been investigated through surveys of university graduates, university academics, and employers. It is found that graduates are less skilled users of software than employers would like, due at least in part to a lack of structured formal training opportunities in the workplace, and a lack of targeted, coherent learning opportunities at university. The widespread and heavy use of software in the workplace means that there is significant potential for productivity gains if universities and employers address these issues. 相似文献
178.
应用因子分析模型针对不同的污染区逐一分析其污染源,应用spss软件确定主要影响因子,给各污染源确定名称.结果表明,低污染区受人类活动影响较小,在中污染区和高污染区以混合污染源为主,其中主干道路区和工业区属于较重污染,交通污染和冶炼厂、化工厂工业废气影响较为突出,建议采取有效措施减少其对土壤重金属污染. 相似文献
179.
An investigation by high-resolution transmission electron microscopy of the precipitation process during ageing a Cu–1.2?wt%Be–0.1?wt%Co alloy at 320°C has revealed that the transition phases follow a γ″→ γ″?+?γ′?→?γ sequence. The γ′ phase heterogeneously precipitates on the γ″ phase. The effects of an external stress on the nucleation and growth of disc-shaped γ″ and plate-shaped γ′ precipitates have been examined for the alloy aged at 320°C. A compressive stress applied in the [001] direction during ageing preferentially accelerates the nucleation and growth of the γ″ variant normal to the [001] axis among three crystallographically equivalent variants and the specific four γ′ variants formed on the γ″ variant normal to the [001] axis. A tensile stress does not significantly affect those of γ″ and γ′ precipitates. The critical diameter of the disc-shaped γ″ nucleus is estimated as about 1?nm from evaluation of the interaction energy between the applied stress and the misfit strains of γ″ precipitates. It is proposed that applied external stress does not affect the diffusion rate but the interphase boundary velocity. 相似文献
180.
Q.-M. Nie W. Zhou Q.-H. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):485-489
The non-equilibrium phase transitions of the fullyfrustrated (f = 1/2) square lattice Coulomb gas (CG) modeldriven by external
electrical fields are studied in the frameworkof the short-time dynamic scaling approach. The criticaltemperature Tc, the static and dynamic critical exponents2β/ν, ν, and z are obtained for several smalldriving fields. The results show that
Tc decreases with theincrease of electric field, and 2β/ν and z arestrongly dependent on the external electric field. Interestingly,contrary
to the equilibrium case, in the presence of smallelectric field, the calculated exponent ν is close to that inpure 2D Ising
model, which provides numerical evidence thatexternal electric field may change the universality class of thef = 1/2 CG system. 相似文献