全文获取类型
收费全文 | 50426篇 |
免费 | 7011篇 |
国内免费 | 5187篇 |
专业分类
化学 | 26130篇 |
晶体学 | 455篇 |
力学 | 2486篇 |
综合类 | 374篇 |
数学 | 4040篇 |
物理学 | 14086篇 |
无线电 | 15053篇 |
出版年
2024年 | 195篇 |
2023年 | 1123篇 |
2022年 | 1366篇 |
2021年 | 1805篇 |
2020年 | 1841篇 |
2019年 | 1687篇 |
2018年 | 1504篇 |
2017年 | 1502篇 |
2016年 | 2031篇 |
2015年 | 2208篇 |
2014年 | 2732篇 |
2013年 | 3494篇 |
2012年 | 4076篇 |
2011年 | 4156篇 |
2010年 | 2986篇 |
2009年 | 2985篇 |
2008年 | 3202篇 |
2007年 | 3017篇 |
2006年 | 2807篇 |
2005年 | 2401篇 |
2004年 | 1730篇 |
2003年 | 1504篇 |
2002年 | 1363篇 |
2001年 | 1117篇 |
2000年 | 1090篇 |
1999年 | 1106篇 |
1998年 | 951篇 |
1997年 | 875篇 |
1996年 | 965篇 |
1995年 | 757篇 |
1994年 | 682篇 |
1993年 | 586篇 |
1992年 | 537篇 |
1991年 | 437篇 |
1990年 | 349篇 |
1989年 | 255篇 |
1988年 | 195篇 |
1987年 | 172篇 |
1986年 | 165篇 |
1985年 | 143篇 |
1984年 | 103篇 |
1983年 | 70篇 |
1982年 | 48篇 |
1981年 | 38篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1975年 | 34篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
提出了一种新的器件结构——非对称Halo L DD低功耗器件,该器件可以很好地抑制短沟效应,尤其可以很好地改善DIBL效应、热载流子效应以及降低功耗等,是低功耗高集成度电路的优选结构之一.分析了非对称HaloL DD器件的主要特性,并将其与常规结构、非对称L DD结构、非对称Halo结构的器件进行了比较并进行了参数优化分析. 相似文献
122.
Yeqin Huang Narayanan R.M. Kadambi G.R. 《Antennas and Propagation, IEEE Transactions on》2003,51(11):3064-3071
Electromagnetic coupling effects on the antenna in a conducting cavity are studied theoretically and experimentally. It is observed in experiments that at the resonant frequencies of the cavity, the input resistance of the antenna attains values two or three orders of magnitude higher than that at frequencies away from resonance. It is shown via theoretical analysis that the input resistance of the antenna measured at the resonant frequencies of the cavity is not merely the loss resistance desired in computing the antenna efficiency, but is actually the sum of the loss resistance of the antenna and the coupling resistance between the antenna and cavity. This coupling effect is demonstrated quantitatively by numerical computations for dipole and monopole antennas. The computational results for the input resistance are in agreement with the measured data. A method is proposed to avoid the cavity-antenna antiresonance in the measurement. 相似文献
123.
LaNiO3导电金属氧化物薄膜在现代应用科学研究中作为电极和过渡阻挡层倍受青睐,它具有很好的导电特性和稳定性。该文采用射频溅射法制备了具有(100)择优取向的赝立方结构LaNiO3-x薄膜,并进行了原位热处理。实验结果表明,在265℃的处理条件下,LaNiO3薄膜表现出不稳定性,晶格中的氧在2h内失去了2.7%。氧的损失对品格结构没有明显影响,但薄膜的导电性能明显下降,折射率和消光系数也具有相同幅度的下降。对薄膜的应用具有一定的影响。该文从LaNiO3薄膜的导电机理方面对实验现象给出了分析和解释。 相似文献
124.
125.
126.
四种多变量校准方法在FTIR多组分分析中的性能比较 总被引:1,自引:0,他引:1
本文对四种多变量校准方法--经典最小二乘法(CLS),偏最小二乘法(PLS),卡尔曼滤波法(KFM)以及人工神经网络法(ANN)--在多组分浓度分析方面的性能进行了比较。选择五种红外谱图严重混叠的大气有机毒物--1,3-丁二烯,苯,邻二甲苯,氯苯和丙烯醛--作为分析对象。分别计算各种方法对该5组分体系的平均预测误差MPE和平均相对误差MRE进行比较。结果表明,偏最小二乘法在处理这类问题中是最稳健的方法。 相似文献
127.
Dashan Huang Yoshitaka Kai Frank J. Fabozzi Masao Fukushima 《European Journal of Operational Research》2007
This paper presents a model for optimally designing a collateralized mortgage obligation (CMO) with a planned amortization class (PAC)-companion structure using dynamic cash reserve. In this structure, the mortgage pool’s cash flow is allocated by rule to the two bond classes such that PAC bondholders receive substantial prepayment protection, that protection being provided by the companion bondholders. The structure we propose provides greater protection to the PAC bondholders than current structures during periods of rising interest rates when this class of bondholders faces greater extension risk. We do so by allowing a portion of the cash flow from the collateral to be reserved to meet the PAC’s scheduled cash flow in subsequent periods. The greater protection is provided by the companion bondholders exposure to interest loss. To tackle this problem, we transform the problem of designing the optimal PAC-companion structure into a standard stochastic linear programming problem which can be solved efficiently. Moreover, we present an extended model by considering the quality of the companion bond and by relaxing the PAC bondholder shortfall constraint. Based on numerical experiments through Monte Carlo simulation, we show the utility of the proposed model. 相似文献
128.
To satisfy the volatile nature of today’s markets, businesses require a significant reduction in product development lead times. Consequently, the ability to develop precise product sales forecasts is of fundamental importance to decision-makers. Over the years, many forecasting techniques of varying capabilities have been introduced. The precise extent of their influences, and the interactions between them, has never been fully clarified, although various forecasting factors have been explored in previous studies. Accordingly, this study adopts the Taguchi method to calibrate the controllable factors of a forecasting model. An L9(34) inner orthogonal array is constructed for the controllable factors of data period, horizon length, and number of observations required. An experimental design is then performed to establish the appropriate levels for each factor. At the same time, an L4(23) outer orthogonal array is used to consider the inherited parameters of forecasting method as the noise factors of Taguchi method simultaneously. An illustrated example, employing data from a power company, serves to demonstrate the thesis. The results show that the proposed model permits the construction of a highly efficient forecasting model through the suggested data collection method. 相似文献
129.
130.