全文获取类型
收费全文 | 1628篇 |
免费 | 597篇 |
国内免费 | 116篇 |
专业分类
化学 | 384篇 |
晶体学 | 5篇 |
力学 | 126篇 |
综合类 | 30篇 |
数学 | 139篇 |
物理学 | 1657篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 58篇 |
2021年 | 56篇 |
2020年 | 69篇 |
2019年 | 54篇 |
2018年 | 51篇 |
2017年 | 83篇 |
2016年 | 81篇 |
2015年 | 102篇 |
2014年 | 145篇 |
2013年 | 128篇 |
2012年 | 129篇 |
2011年 | 129篇 |
2010年 | 99篇 |
2009年 | 111篇 |
2008年 | 120篇 |
2007年 | 126篇 |
2006年 | 100篇 |
2005年 | 94篇 |
2004年 | 74篇 |
2003年 | 65篇 |
2002年 | 58篇 |
2001年 | 59篇 |
2000年 | 54篇 |
1999年 | 53篇 |
1998年 | 49篇 |
1997年 | 37篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2341条查询结果,搜索用时 31 毫秒
111.
In CRM (Customer Relationship Management), the importance of a segmentation method for identifying good customers has been increasing. For evaluation of different segmentation methods, Accuracy often plays a key role. This indicator, however, cannot distinguish two types of errors. The purpose of this paper is to overcome this pitfall by introducing two different indicators: Recall and Precision. Assuming that a promotion is addressed exclusively to the selected target customers, the financial effectiveness of the underlying segmentation method is expressed as a function of Recall and Precision. An optimization problem is then formulated so as to maximize the financial measure by finding the optimal threshold level in terms of the severeness for estimating the target set. By introducing a functional form which represents correctness and mistakes about the target set, the unique optimal solution is derived explicitly. The proposed approach is validated by using real customer purchase data. 相似文献
112.
A laser-plasma EUV source is described, which is going to be utilized for characterization of EUV optical components and sensoric devices in the wavelength region from 11 to 13 nm. EUV radiation is generated by focusing a Nd:YAG laser into a double stream gas puff target. By the use of different target gases, broadband as well as narrow-band EUV radiation can be obtained. The emission characteristics of the radiation is monitored by the help of different diagnostic tools including a pinhole camera, an EUV spectrometer, and various EUV photodiodes, either directly or after reflection from multilayer mirrors. Theoretical calculations of collision-induced energy transfer are given in order to explain the observed high degree of electronic excitation in the utilized target gases. 相似文献
113.
一种可用于生产效率评价的灰靶评估算法 总被引:1,自引:0,他引:1
本文在分析和比较了DEA和灰靶评估两种方法之后,给出一种可用于生产效率评价的灰靶评估算法。该算法由于运用了DEA方法中的“生产效率”概念,弥补了灰靶评估算法不能对不同的被评价单元进行效率评价的不足,从而拓宽了灰靶评估算法的应用背景。文章最后给出实例分析。 相似文献
114.
唐雪平 《数学的实践与认识》2008,38(22)
讨论了一般二维井眼轨道设计问题.建立了二维轨道设计一般数学模型,根据轨道设计约束方程,可任意选择两个设计参数作为未知数进行求解,得到了全部解析计算公式.这种方法设计计算简单、精确、快速、灵活,具有普遍适用性.可广泛用于二维定向井、水平井和多目标井的设计,为井眼轨道设计提供了理论依据. 相似文献
115.
Summary The method of iterative target transformation factor analysis (ITTFA) used in conjunction with second derivative peak finding
has shown to be a practical method for the peak deconvolution and reconstruction of HPLC chromatograms and spectra. The second
derivative method of peak finding is acceptable for resolutions above 0.5 for peaks of similar heights. Above 0.5 resolution
the labelling gives correct results where the spectra are substantially different and also when reasonably similar. Below
this value the peak labelling was still accurate where the spectra were different. Solvent effects on the spectra of the compounds
studied are small and do not hinder the peak labelling process. Thus small “local” libraries are feasible.
Presented at the 17th International Symposium on Chromatography, September 25–30, 1988. Vienna, Austria. 相似文献
116.
Payam Mehdipour Kaldiani 《理论物理通讯》2021,73(7):75303
The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model. The total potential energy of the fissioning systems at the scission point is presented in approximate relations as functions of mass numbers,deformation parameters and the temperature of complementary fission fragments. The collective temperature, Tcoll, and the temperature of fission fragments, Ti, are separated and the effect of collective temperature on mass yields results is investigated. The fragment temperature has been calculated with the generalized superfluid model. The sum of deformation parameters of complementary fission fragments has been obtained by fitting the calculated results with the experimental data. To investigate the transitions between symmetric and asymmetric modes mass yields for pre-actinide and heavy actinides are calculated with this model. The transition from asymmetric to symmetric fission is well reproduced using this systematic statistical scission point model. The calculated results are in good agreement with the experimental data with Tcoll= 2 Me V at intermediate excitation energy and with T_(coll)= 1MeV for spontaneous fission.Despite the Langevin model, in the scission point model, a constraint on the deformation parameters of fission fragments has little effect on the results of the mass yield. 相似文献
117.
低温冷冻靶是实现惯性约束聚变(inertial confinement fusion,ICF)的关键部件之一.低温靶靶丸内杂质气体的去除程度和效率对低温靶燃料冰层的在线制备具有重要意义.依据低温靶物理对冰层杂质含量的设计要求,在计算靶丸内杂质气体最大允许分压的基础上,建立了靶丸内气体在微米级充气管内流动的抽空流洗模型.模拟研究了不同微管尺度及结构、温度对靶丸内杂质气体抽空流洗效率的影响规律,获得了靶丸充气微管的最佳管型设计方案.基于最佳管型设计,优化得到了具有最高抽空流洗效率的抽空时间与流洗次数组合策略. 相似文献
118.
为了加快激光等离子体微推进技术(μLPP)在航天领域的应用,介绍了该项技术近10年的发展状况。讨论了激光等离子体微推进技术发展过程中衍生出的各种工作模式,并简略分析了不同工作模式的优缺点。着重介绍了靶特性对激光微推进性能的影响,包括靶材的选择、靶的结构、靶材掺杂,以及靶物相特性等。针对该项技术的最终发展目标是研制微小卫星姿轨控的激光等离子体微推力器(μLPT),介绍并分析了美国Phipps小组开展的激光微推力器的研制工作。最后,指出了激光等离子体微推进技术目前存在的一些问题,并展望了它的发展前景。 相似文献
119.
120.