全文获取类型
收费全文 | 14482篇 |
免费 | 2322篇 |
国内免费 | 1130篇 |
专业分类
化学 | 5637篇 |
晶体学 | 94篇 |
力学 | 1102篇 |
综合类 | 275篇 |
数学 | 2876篇 |
物理学 | 7950篇 |
出版年
2024年 | 30篇 |
2023年 | 197篇 |
2022年 | 463篇 |
2021年 | 556篇 |
2020年 | 445篇 |
2019年 | 411篇 |
2018年 | 358篇 |
2017年 | 516篇 |
2016年 | 638篇 |
2015年 | 541篇 |
2014年 | 908篇 |
2013年 | 1222篇 |
2012年 | 950篇 |
2011年 | 1047篇 |
2010年 | 834篇 |
2009年 | 986篇 |
2008年 | 930篇 |
2007年 | 1003篇 |
2006年 | 806篇 |
2005年 | 639篇 |
2004年 | 541篇 |
2003年 | 517篇 |
2002年 | 508篇 |
2001年 | 379篇 |
2000年 | 388篇 |
1999年 | 295篇 |
1998年 | 264篇 |
1997年 | 216篇 |
1996年 | 195篇 |
1995年 | 162篇 |
1994年 | 148篇 |
1993年 | 170篇 |
1992年 | 100篇 |
1991年 | 91篇 |
1990年 | 79篇 |
1989年 | 50篇 |
1988年 | 50篇 |
1987年 | 38篇 |
1986年 | 44篇 |
1985年 | 52篇 |
1984年 | 43篇 |
1983年 | 15篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
71.
Electron paramagnetic resonance (EPR) investigations has been carried out on the new family of molybdenum doped vanadium sesquioxides (V1−xMox)2−δO3. The oxidation effects were monitored from the rate of paramagnetic V4+ created when the sample is exposed to the air. The effects of the oxidation time, sample temperature, and annealing at 1000 °C under a diluted hydrogen atmosphere on the EPR signal features are analyzed. The V4+ concentration in the oxidized samples is determined and the relaxation effects driven by the conduction electrons are pointed out from the thermal behaviour of the EPR line features. EPR spectra of all the oxidized samples also reveal a small ferromagnetic contribution strongly correlated with the V4+ content. 相似文献
72.
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
73.
Infrared and nuclear magnetic resonance (NMR) spectroscopies have been applied for quantitative comparison on unsaturated bonds in tetrafluoroethylene (TFE)-propylene (P)-vinylidene fluoride (VdF) terpolymers. These spectroscopies have led to consistent results while they are based on completely different principles. It is shown that the absolute concentration can be evaluated from NMR measurements. The behavior of unsaturation has been discussed in terms of after-treatment such as wet and dry treatments. The result obtained here can give the important information to improve the performance of fluoroelastomer based on TFE-P-VdF terpolymers. 相似文献
75.
76.
77.
78.
An effect of Berry’s phase on the NQR spectrum of the rotating powder sample is described and applied for the determination of the electric field gradient asymmetry. The proposed method involves the analysis of the frequency singularities in the NQR powder patterns of the rotating samples. The Berry’s phases for the eigenstates, associated with an adiabatically changing quadrupole hamiltonian, are calculated for nuclei with a spin I = 3/2 and I = 1 as a function of the asymmetry parameter. 相似文献
79.
从大型复杂武器装备系统的具体特点出发,运用基于神经网络的评价方法,构建了大型复杂武器装备质量综合评价模型。实证分析的结果表明该方法得出的结果与实际情况相符。 相似文献
80.
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