全文获取类型
收费全文 | 360篇 |
免费 | 17篇 |
专业分类
化学 | 233篇 |
晶体学 | 3篇 |
力学 | 10篇 |
数学 | 57篇 |
物理学 | 74篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 21篇 |
2012年 | 23篇 |
2011年 | 22篇 |
2010年 | 9篇 |
2009年 | 11篇 |
2008年 | 16篇 |
2007年 | 23篇 |
2006年 | 14篇 |
2005年 | 20篇 |
2004年 | 11篇 |
2003年 | 20篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 5篇 |
1967年 | 2篇 |
排序方式: 共有377条查询结果,搜索用时 15 毫秒
81.
The effects of thermal modulation on the tunneling dynamics of a particle moving in a bistable potential with a fluctuating barrier in the presence of bichromatic electromagnetic field are examined. This study brings to light various interesting features. While rate constant increases steadily with increasing fluctuation strength, a stochastic resonance‐like behavior is exhibited when tunneling rate is plotted as a function of barrier fluctuation frequency. The tunneling rate constant decreases with the increase in the differences of the strength of the two electric fields; on the other hand, it displays a maxima when plotted as a function of the ratio of the frequencies of the two fields. When the rate constant is plotted as a function of temperature, it increases and eventually settles down to a saturation value. We have also studied the effect of the phase difference between the two electric fields on the tunneling behavior in the presence of thermal modulation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
82.
Ghosh Kamal Kumar Ray Dipankar Chanda Pranab 《International Journal of Theoretical Physics》1989,28(1):111-117
We present the complete set of solutions of the coupled differential equations of the form ()2=(), 2
=(). Equations of this form appear in several physical situations. 相似文献
83.
Ruthenium is extracted by benzyl alcohol from 5M LiCl containing ethyl-alpha-isonitrosoacetoacetate at pH 4-6. The extraction is quantitative if the solution is heated to boiling for 15 min. The benzyl alcohol extract shows maximum absorbance at 470 nm and at this wavelength Beer's law is obeyed over the ruthenium concentration range 0.1-1.8 mug ml . The error is 4% for 0.5 mug ml . 相似文献
84.
Pranab Haldar 《Tetrahedron》2007,63(14):3049-3056
A simple methodology for the conversion of substituted N-aryl-γ-lactam 2/3-carboxylic acids to substituted N-aryl-2/3-formyl-pyrroles has been developed. Several N-aryl-γ-lactam 2/3-carboxylic acids were reduced to substituted (N-aryl-pyrroliden-2/3-yl)-methanols in good yields by using the NaBH4-I2 system. Aromatisation and in situ oxidation of these alcohols using DDQ produced N-aryl-2/3-formyl-pyrroles, which act as key starting material and intermediates in the synthesis of several bioactive compounds. 相似文献
85.
Mervyn J. Silvapulle Pranab K. Sen 《Annals of the Institute of Statistical Mathematics》1993,45(1):159-171
Consider the linear modelY=X+E in the usual matrix notation where the errors are independent and identically distributed. We develop robust tests for a large class of one- and two-sided hypotheses about when the data are obtained and tests are carried out according to a group sequential design. To illustrate the nature of the main results, let
and
be anM- and the least squares estimator of respectively which are asymptotically normal about with covariance matrices 2(X
t
X)–1 and 2(X
t
X)–1 respectively. Let the Wald-type statistics based on
and
be denoted byRW andW respectively. It is shown thatRW andW have the same asymptotic null distributions; here the limit is taken with the number of groups fixed but the numbers of observations in the groups increase proportionately. Our main result is that the asymptotic Pitman efficiency ofRW relative toW is (2/2). Thus, the asymptotic efficiency-robustness properties of
relative to
translate to asymptotic power-robustness ofRW relative toW. Clearly, this is an attractive result since we already have a large literature which shows that
is efficiency-robust compared to
. The results of a simulation study show that with realistic sample sizes,RW is likely to have almost as much power asW for normal errors, and substantially more power if the errors have long tails. The simulation results also illustrate the advantages of group sequential designs compared to a fixed sample design, in terms of sample size requirements to achieve a specified power. 相似文献
86.
Bittu Saha Bijeta Mitra Dhiraj Brahmin Biswajit Sinha Pranab Ghosh 《Tetrahedron letters》2018,59(41):3657-3663
This is the first reported, unconventional, efficient strategy for the synthesis of quinoxaline from 2 to iodo benzoic acid and sodium azide in presence of organo Cu (II) catalyst. Herein, a very simple, versatile one pot multi-component protocol for the synthesis of biologically active compound, quinoxaline has been described via Schmidt reaction and the nucleophilic substitution reaction. The isolated compounds were characterized by 1H NMR, 13C NMR. Our reported organo catalyst was characterized by single crystal XRD, SEM. 相似文献
87.
Cyclodehydration-condensation of hippuric acid and arylaldehydes have been carried out using a 1:1 mixture of Al2O3-H3BO3 in the presence of stoichiometric quantity of acetic anhydride to give the target compound in good yield. This procedure can be used to synthesize the 4-alkylidene analogs also. 相似文献
88.
Sayan Biswas Amit Kar Joydeb Chanda Nanaocha Sharma Pardeep Kumar Bharadwaj Pallab Kanti Haldar Pulok Kumar Mukherjee 《Biomedical chromatography : BMC》2022,36(5):e5328
A rapid validated ultra-fast liquid chromatography–photodiode array detector (UFLC-PDA) method was developed to identify and quantify ayapanin (AY) and umbelliferone (UM) simultaneously in Ayapana triplinervis Vahl methanolic extract. The method was validated for linearity, limit of detection (LOD; 3:1σ/S), limit of quantification (LOQ; 10:1σ/S), precision, accuracy, specificity and robustness. The response was linear with a good correlation between concentration and mean peak area through a correlation coefficient of 0.9996, y = 7025.7x – 2269.8 and 0.9997, y = y = 16,262x – 946 with LOD of 6.256 ± 0.52 and 3.325 ± 0.36, and LOQ of 18.838 ± 0.18 and 8.870 ± 0.85 for AY (0.67% w/w) and UM (0.18% w/w), respectively. The relative standard deviation (%) of precision and recovery of AY and UM was <2.0%. The proposed method was simple, accurate, specific, precise and reproducible. 相似文献
89.
90.
Bromate exchange resin has been prepared by a simple elution technique and used for the oxidation of aromatic aldehydes to the carboxylic acids. Oxidation is carried out under biphasic condition. Work up is simple. Resin immobilized bromate ions have been used for the first time as an oxidizing agent in organic synthesis. 相似文献