全文获取类型
收费全文 | 1662篇 |
免费 | 79篇 |
国内免费 | 3篇 |
专业分类
化学 | 1064篇 |
晶体学 | 9篇 |
力学 | 57篇 |
数学 | 113篇 |
物理学 | 501篇 |
出版年
2023年 | 20篇 |
2022年 | 27篇 |
2021年 | 56篇 |
2020年 | 54篇 |
2019年 | 41篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 66篇 |
2015年 | 37篇 |
2014年 | 79篇 |
2013年 | 101篇 |
2012年 | 103篇 |
2011年 | 136篇 |
2010年 | 94篇 |
2009年 | 83篇 |
2008年 | 111篇 |
2007年 | 65篇 |
2006年 | 66篇 |
2005年 | 76篇 |
2004年 | 42篇 |
2003年 | 38篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 24篇 |
1998年 | 8篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 5篇 |
1974年 | 7篇 |
排序方式: 共有1744条查询结果,搜索用时 234 毫秒
71.
P. Mali S. K. Sarkar A. B. Bhattacharya 《International Journal of Infrared and Millimeter Waves》2001,22(1):153-171
Radio wave operating in millimetrewave and microwave frequency bands are adversely affected due to rain. Particularly the attenuation is of immense significance for sensitive remote measurements by satellites using frequencies greater than 10 GHz. Maintenance of an uninterrupted communication link requires a precise knowledge of the attenuation effect due to rain for commissioning right kind of transmitting sources for various purposes required in present day situation. Precise measurement of attenuation at various frequencies will enable us to choose the right frequency, polarization, incident angle and power of the source for different purposes. In this paper we have compared the results of earlier works using aRb Olsen et al, (1) and the formulation by Moupfouma, (2) on the basis of theoretical analysis for explaining the observed results. Effect of temperature, considered in detail in this communication, has contributed the necessary correction factor of the rain attenuation for explaining the observed results. Theoretical analyses to measure the attenuation of the propagating wave due to temperature variation in the rain path have been presented. Correction factor due to temperature profile (temperature from the ground to the rain height within which the radio wave traces its path) has been incorporated in two models by using the concept of dipole energy changes. The effect of this temperature is noted to be quite significant and incorporates an error to the extent of 7–8%. 相似文献
72.
73.
Oxidation of Ru(III)‐Bound Thiocyanate with Peroxomonosulfate: Kinetic and Mechanistic Studies
下载免费PDF全文
![点击此处可从《国际化学动力学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The reaction of [RuIII(edta)(SCN)]2? (edta4? = ethylenediaminetetraacetate; SCN? = thiocyanate ion) with the peroxomonosulfate ion (HSO5?) has been studied by using stopped‐flow and rapid scan spectrophotometry as a function of [RuIII(edta)], [HSO5?], and temperature (15–30ºC) at constant pH 6.2 (phosphate buffer). Spectral analyses and kinetic data are suggestive of a pathway in which HSO5? effects the oxidation of the coordinated SCN? by its direct attack at the S‐atom (of SCN?) coordinated to the RuIII(edta). The high negative value of entropy of activation (ΔS≠ = ?90 ± 6 J mol?1 deg?1) is consistent with the values reported for the oxygen atom transfer process involving heterolytic cleavage of the O‐O bond in HSO5?. Formation of SO42?, SO32?, and OCN? was identified as oxidation products in ESI‐MS experiments. A detailed mechanism in agreement with the spectral and kinetic data is presented. 相似文献
74.
75.
Priyanka Sarkar 《Journal of luminescence》2009,129(7):704-202
Solution-phase synthesis of nanometer-sized silver particles is reported by sodium borohydride reduction of AgNO3. Two isomeric dicarboxylates (sodium maleate and sodium fumarate) have been used as stabilizing agents. The dicarboxylate-stabilized silver nanoparticles are characterized by UV-vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and fourier transform infrared (FT-IR) spectroscopy. A qualitative comparison is made between the UV-vis spectral characteristic of the SPR band and the simulated curve obtained from modified Mie's theory. Silver nanoparticles prepared using these two isomeric dicarboxylates show intense fluorescence in the visible region. DFT with hybrid functional (B3LYP)-based frequency (IR) calculation of both the dicarboxylates and the respective nanoparticles are in good agreement with the experimental IR frequency. On the basis of this calculation a model has been proposed for the stabilization of silver nanoparticles by these two isomeric dicarboxylate anions. 相似文献
76.
New phenylethanoid glycosides from Bacopa monniera 总被引:1,自引:0,他引:1
Chakravarty AK Sarkar T Nakane T Kawahara N Masuda K 《Chemical & pharmaceutical bulletin》2002,50(12):1616-1618
Three new phenylethanoid glycosides, viz. monnierasides I-III (1-3) along with the known analogue plantainoside B were isolated from the glycosidic fraction of Bacopa monniera. Their structures were elucidated mainly on the basis of two dimensional (2D) NMR spectral analyses. 相似文献
77.
In the present study we consider a mathematical model of a non-interactive type autotroph-herbivore system in which the amount of autotroph biomass consumed by the herbivore is assumed to follow a Holling type II functional response. We have also incorporated discrete time delays in the numerical response term to represent a delay due to gestation, and in the recycling term which represents the time required for bacterial decomposition. We have derived conditions for global asymptotic stability of the model in the absence of delays. Conditions for delay-induced asymptotic stability of the steady state are also derived. The length of the delay preserving stability has been estimated and interpreted ecologically. 相似文献
78.
79.
80.