全文获取类型
收费全文 | 1969篇 |
免费 | 79篇 |
国内免费 | 11篇 |
专业分类
化学 | 1043篇 |
晶体学 | 9篇 |
力学 | 57篇 |
数学 | 115篇 |
物理学 | 484篇 |
无线电 | 351篇 |
出版年
2024年 | 7篇 |
2023年 | 27篇 |
2022年 | 37篇 |
2021年 | 67篇 |
2020年 | 63篇 |
2019年 | 45篇 |
2018年 | 39篇 |
2017年 | 34篇 |
2016年 | 67篇 |
2015年 | 39篇 |
2014年 | 88篇 |
2013年 | 113篇 |
2012年 | 106篇 |
2011年 | 135篇 |
2010年 | 99篇 |
2009年 | 89篇 |
2008年 | 126篇 |
2007年 | 75篇 |
2006年 | 81篇 |
2005年 | 86篇 |
2004年 | 55篇 |
2003年 | 47篇 |
2002年 | 40篇 |
2001年 | 29篇 |
2000年 | 32篇 |
1999年 | 33篇 |
1998年 | 21篇 |
1997年 | 18篇 |
1996年 | 18篇 |
1995年 | 18篇 |
1994年 | 20篇 |
1993年 | 22篇 |
1992年 | 16篇 |
1991年 | 24篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 16篇 |
1974年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有2059条查询结果,搜索用时 15 毫秒
81.
82.
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
83.
84.
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
85.
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
86.
An L-shaped array for estimating 2-D directions of wave arrival 总被引:15,自引:0,他引:15
A simple structured 2-D array, the L-shaped array, is presented. The L-shaped array consists of two uniform linear arrays (ULA) connected orthogonally at one end of each ULA. It is shown that the Cramer-Rao bounds (CRB) of the estimated wave directions based on the L-shaped array are about 37% smaller than those for the cross array. The CRB indicates the accuracy potential because it is the (reachable) lower bound on the variance of any unbiased estimate. An efficient maximum likelihood algorithm is developed utilizing the ULA structure inherent in the L-shaped array 相似文献
87.
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
88.
The design of any radio communication system requires a suitable prediction technique for calculating the received signal levels. The optimum prediction method helps to reduce the interference problems, and improves reliability of links. In the present study the path loss values deduced from various prediction techniques are compared against observed path loss values over two troposcatter links situated in northern India. The results show that April and May are the worst months and the present space and frequency diversity configuration is not able to effectively overcome the link outages. A comparison of different path loss prediction techniques showed that Yeh’s prediction method and itu-r’s method I comes close to the observed values. The predicted path loss values for worst month using itu-r’s method deviated considerably from the observed values. The present study provides valuable inputs to the itu-r study group from the tropical countries by evaluating the itu-r prediction methods against the experimental data. 相似文献
89.
90.
Recurrence techniques are described for the generation of Bessel functions of the first and second kinds where both the argument and order may be complex. The method is shown to be accurate for several well known forms of functions, including Kelvin and spherical Bessel functions. The accuracy of the general case of complex order and argument is determined by computing the Wronskians and by verifying some addition theorems of the Bessel functions over wide ranges of order and argument. Procedures for the accurate generation of complex-argument gamma functions are also described. 相似文献