全文获取类型
收费全文 | 1169篇 |
免费 | 83篇 |
国内免费 | 167篇 |
专业分类
化学 | 572篇 |
晶体学 | 1篇 |
力学 | 86篇 |
综合类 | 1篇 |
数学 | 87篇 |
物理学 | 339篇 |
综合类 | 333篇 |
出版年
2024年 | 12篇 |
2023年 | 48篇 |
2022年 | 38篇 |
2021年 | 52篇 |
2020年 | 35篇 |
2019年 | 28篇 |
2018年 | 22篇 |
2017年 | 45篇 |
2016年 | 37篇 |
2015年 | 34篇 |
2014年 | 61篇 |
2013年 | 80篇 |
2012年 | 44篇 |
2011年 | 71篇 |
2010年 | 59篇 |
2009年 | 65篇 |
2008年 | 71篇 |
2007年 | 60篇 |
2006年 | 54篇 |
2005年 | 59篇 |
2004年 | 41篇 |
2003年 | 41篇 |
2002年 | 41篇 |
2001年 | 26篇 |
2000年 | 31篇 |
1999年 | 27篇 |
1998年 | 30篇 |
1997年 | 26篇 |
1996年 | 42篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 21篇 |
1990年 | 10篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有1419条查询结果,搜索用时 16 毫秒
951.
张晓京 《南京邮电大学学报(自然科学版)》1987,(2)
本文从把一个有源网络表示成电流图和电压图的观点出发,推导出双口网络的网络函数的拓扑计算公式,并对求电流图和电压图的公共树的算法作了改进。 相似文献
952.
953.
本文根据对3种二阶节有源RC滤波器理论分析的结果作了机助分析和实验,比较三种滤波器国ω_O的偏差和Q的灵敏度及偏差可见,CAB滤波器性能最佳。 相似文献
954.
用K2S2O8代替不稳定而易分解的(NH4)2S2O8,或用氨水中和已分解显酸性的(NH4)2S2O8,而使实验结果满意。并将试剂用量减到原试剂用量的1/2和1/4仍能得到非常好的效果,从而达到对该实验的进一步改进。 相似文献
955.
We investigate the effect of community structure on the evolution of cooperation in the prisoner’s dilemma and the snowdrift game with dynamical linking. We show both analytically and numerically that cooperators are generally more favorable on community networks than on networks without community structure, and in particular, there exists an optimal intermediate value of the model parameter leading to the easiest fixation of cooperators. We show that our results are robust with respect to the initial number of cooperators and are valid for a wide range of the ratio of time scales associated with linking and strategy dynamics. Since community structure is ubiquitous in real social networks, our results may provide new insights into the evolution of cooperation in real world. 相似文献
956.
药物共晶是改善药物活性成分(API)的物理化学特性的新技术和新思维,具有很大的应用潜力。本实验采用研磨法制备了双苯氟嗪盐酸盐(DF-HCl)和苯甲酸的共晶,应用红外光谱(IR)、拉曼光谱(Raman)、差示扫描量热分析(DSC)、X射线衍射(XRD)和太赫兹光谱(THz)对共晶进行了表征。结果表明:双苯氟嗪盐酸盐与苯甲酸之间形成共晶分子,太赫兹谱的研究进一步表明两种分子之间有氢键形成。 相似文献
957.
Synchronization of a chaotic finance system 总被引:1,自引:0,他引:1
Synchronization strategies of a three-dimensional chaotic finance system are investigated in this paper. Based on Lyapunov stability theory and Routh-Hurwitz criteria, some effective controllers are designed for the global asymptotic synchronization on different conditions. When the system parameters are known, the hybrid feedback control and a method based on special matrix structure are adopted respectively, to realize the synchronization of the chaotic finance system. When the parameters are unknown, the active control is extended and introduced to realize the synchronization. Numerical simulations show the validity and feasibility of the synchronization schemes. 相似文献
958.
Ethyl Lauroyl Arginate (LAE) is a cationic tensoactive compound, soluble in water, with a wide activity spectrum against moulds and bacteria. LAE has been incorporated as antimicrobial agent into packaging materials for food contact and these materials require to comply with the specific migration criteria. In this paper, one analytical procedure has been developed and optimized for the analysis of LAE in food simulants after the migrations tests. It consists of the formation of an ionic pair between LAE and the inorganic complex Co(SCN)42− in aqueous solution, followed by a liquid–liquid extraction in a suitable organic solvent and further UV–Vis absorbance measurement. In order to evaluate possible interferences, the ionic pair has been also analyzed by high performance liquid chromatography with UV–Vis detection. Both procedures provided similar analytical characteristics, with linear ranges from 1.10 to 25.00 mg kg−1, linearity higher than 0.9886, limits of detection and quantification of 0.33 and 1.10 mg kg−1, respectively, accuracy better than 1% as relative error and precision better than 3.6% expressed as RSD. Optimization of analytical techniques, thermal and chemical stability of LAE, as well as migration kinetics of LAE from experimental active packaging are reported and discussed. 相似文献
959.
《Analytical letters》2012,45(15):2811-2825
Abstract Simple and rapid chemiluminescence (CL) assays for H2O2, ?OH, ?O2 ? and 1O2 using 5-amino-2,3-dihydro-1,4-phthalazinedione (luminol) or 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-α]pyrazin-3-one (CLA) as CL reagents were developed. The means of the intra-assay relative standard deviations of ten replicate measurements of H2O2 (25-120 μM), ?OH generated from Fe(II) ion (2.5-10 μM) in the presence of 980 μM H2O2, ?O2 ? generated from hypoxanthine (HX) (7-50 μM) in the presence of 9 × 10?3 units xanthine oxidase (XO) and 1O2 generated from NaOCl (3-12 mM) in the presence of 97.6 μM H2O2 were found to be 4.0%, 2.8%, 2.4% and 8.7%, respectively. To validate the proposed methods, the scavenging abilities of three standard antioxidative compounds, such as L-ascorbic acid, (±)-α-tocopherol and superoxide dismutase (SOD) were examined for four active oxygen species and compared with those by anelectron spin resonance (ESR) spin-trapping method. In addition, the CL methods were also applied to establish the relationships between the decrease of CL intensity and the structures as well as redox characters of syringic acid, 3-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid. From the obtained results, the scavenging effects to H2O2, ?OH, ?O2 ? and 1O2 of other dihydroxybenzoic acids were also evaluated. 相似文献
960.
对谐波进行准确、快速检测是有源滤波器发挥良好效果的基础,针对快速、准确检测的需求,提出一种abc坐标直接投影谐波检测法。对广义的IP-IQ检测法进行简单介绍;并在此基础上提出abc直接投影谐波检测法,该检测法直接对旋转坐标进行投影,相对于IP-IQ法省去了坐标变换的中间环节,具有易于编程、计算量相对较小的特点。同时指出该方法存在低通滤波器延时的缺陷;并针对此缺陷进行改进,应用滑动均值算法来替代原检测法中的低通滤波器,缩短了算法延时且省去了复杂的低通滤波器设计环节,将计算量分散开,且编程较为简易。通过搭建MATLAB/Simulink仿真平台对改进的谐波检测算法进行仿真,结果显示,该算法具有准确性高、延时量小的特点,可以满足有源滤波器的谐波检测需要。 相似文献