全文获取类型
收费全文 | 360篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
化学 | 202篇 |
晶体学 | 10篇 |
力学 | 8篇 |
数学 | 36篇 |
物理学 | 114篇 |
出版年
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 14篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 24篇 |
2012年 | 18篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 8篇 |
2008年 | 22篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 5篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1990年 | 5篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1966年 | 3篇 |
1960年 | 2篇 |
1926年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 15 毫秒
1.
Development of a 100 MeV CW proton LINAC has been planned at CAT. This LINAC will be needing CW rf power in the frequency
ranges of 350 MHz and 700 MHz for its RFQ and DTL/CCDTL/SFDTL structures respectively. The power to the accelerating structures
will be produced by either 1 MW CW or 250 kW CW klystrons/inductive output tubes (HOM IOTs). The power needed by respective
feed points in the structure is max. 250 kW which will be powered by splitting the power from 1 MW klystron/klystrode into
four channels by using a wave-guide system. In case of using 250 kW tubes the power to the structures will be provided directly
from each tube. Two types of wave-guide transmission system have been considered, viz, WR 2300 for 350 MHz rf needs and WR
1500 for 700 MHz rf needs. The typical wave-guide system has been designed using the 1 MW CW klystron followed by wave-guide
filter, dual directional coupler, high-power circulator, three 3 dB magic TEE power dividers to split the main channel into
four equal channels of 250 kW each. Each individual channel has dual directional couplers, flexible wave-guide sections and
high power ceramic vacuum window. The circulator and each power divider is terminated into the isolated ports by high power
CW loads. Out of the four channels three channels have phase shifters. Present paper describes the technological aspects and
design specifications-considerations for these stringent requirements. 相似文献
2.
A finite element solution of the Navier-Stokes equations for steady flow under the magnetic effect through a double-branched two-dimensional section of a three-dimensional model of the canine aorta is discussed. The numerical scheme involves transforming the physical co-ordinates to a curvilinear boundary-fitted co-ordinate system. The shear stress at the wall is calculated for a Reynolds number of 1000 with the branch-to-main aortic flow rate ratio as a parameter. The results are compared with earlier works involving experimental data and found to be in reasonable qualitative agreement. The steady flow, shear stress and branch flow under the effect of a magnetic field have been discussed in detail. 相似文献
3.
From flash photolysis data of benzil and 2,2′-dichlorobenzil, the role of conformeric triplets in the formation of hydrogen
adduct radicals has been discussed. The planar relaxed triplet absorbing at 470 nm is less efficient in forming a hydrogen
adduct radical as compared to its puckered conformeric partner. Among the hydrogen donors, triethyl amine and isopropanol,
the former is more efficient in converting puckered triplets and less efficient in the case of planar conformers. Absorptions
of radicals and radical anions of 2,2′-dichlorobenzil appear at 355 nm and 460 nm respectively. These are blue-shifted as
compared to those of the parent compound benzil appearing at 370 nm and 540 nm, respectively. This blue-shift has been discussed
in terms of steric hindrance due to ortho-substitution. 相似文献
4.
K. Suvardhan K. Suresh Kumar D. Rekha K. Kiran B. Jaya Raj P. Chiranjeevi 《Journal of Analytical Chemistry》2007,62(4):336-341
Newly synthesized 2-propylpiperidine-1-carbodithioate (2-PPC) was used for the extraction of Cr(III), Ni(II), and Zn(II) from
various water samples. In the present investigation, the use of a syringe loaded with sorbent for the separation and enrichment
of Cr(III), Ni(II), and Zn(II) prior to their determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES)
was proposed to substitute the batch and column techniques. The described method was compared with the column technique with
respect to fastness, simplicity, recovery, and risk of contamination. The syringe was loaded with 1.0 g of sorbent in order
to retain the analyte elements. Next, 7.0 mL of sample solution (pH 5.0 ± 0.2) was drawn into the syringe in 15 s and discharged
over 15 s. Then, an eluent (3.0 M HCl) was drawn into the syringe and ejected back to desorb the analyte elements. At the
optimum conditions, the percentage recoveries of Cr(III), Ni(II), and Zn(II) were in the range of 94.50 to 99.62% with a standard
deviation (S.D.) of 0.03%. The elements could be concentrated by drawing and discharging several portions of sample successively
and eluting only one time. The detailed study of various interferences proved the method to be highly selective. The risk
of contamination is less than that with the column technique. The method was successfully applied to the determination of
Cr(III), Ni(II), and Zn(II) in spiked and natural water samples. The results obtained are in good agreement with those obtained
by the reported methods at the 95% confidence level.
The text was submitted by the authors in English. 相似文献
5.
A. Karnik S. Kailas A. Chatterjee P. Singh A. Navin D. C. Biswas D. M. Nadkarni A. Shrivastava S. S. Kapoor 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(2):195-198
The fission fragment angular distributions for the system12C +232Th have been measured in the energy range 0.97<>c.m./VB<1.22. the=" measured=" anisotropies=" have=" been=" compared=" with=" the=" predictions=" of=" the=" standard=" saddle=" point=" statistical=" model,=" using=" the=" second=" moment=" of=" the=" compound=" nucleus=" spin=" distribution=">1.22.>l2 deduced from a Wong model fit to the fission excitation function. While the measured anisotropies agree with the standard saddle point statistical model for Ec.m./VB>1.05, they are abnormally large at lower energies. This is also true for the existing measurements of16O and19F +232Th systems. Since for this system pre-equilibrium fission contributions are not expected, this anomaly indicates strong channel coupling effects leading to an increase in l2 at sub-barrier energies.The authors thank Drs. R.K. Choudhury and A. Saxena for useful discussions, Dr. R.J. Singh for making the thorium target and the Pellectron operation staff for excellent operation of the machine. 相似文献
6.
Underpotential deposition studies of copper on glassy carbon 总被引:1,自引:0,他引:1
Studies on the deposition and dissolution of copper from 0·5 M sulphuric acid solutions onto glassy carbon (GC) using potential
sweep techniques indicated that an additional peak occurs at higher positive potentials than the bulk stripping peak. This
peak is identified as due to the stripping of underpotential deposited (UPD) copper. Results of investigations on the effect
of sweep rate, deposition potential and time of deposition on the peak characteristics of UPD and bulk deposited copper are
also reported. 相似文献
7.
Development of new reactions requires finding and understanding of novel reaction pathways. In challenging reactions such as C–H activations, these pathways often involve highly reactive intermediates which are the key to our understanding, but difficult to study. Mass spectrometry has a unique sensitivity for detecting low abundant charged species; therefore it is increasingly used for detection of such intermediates in metal catalysed- and organometallic reactions. This perspective shows recent developments in the field of mass spectrometric research of reaction mechanisms with a special focus on going beyond mass-detection. Chapters discuss the advantages of collision-induced dissociation, ion mobility and ion spectroscopy for characterization of structures of the detected intermediates. In addition, we discuss the relationship between the condensed phase chemistry and mass spectrometric detection of species from solution.Modern approaches of mass spectrometry can identify reaction intermediates and provide a unique insight into their structure, properties and kinetics. 相似文献
8.
9.
10.
JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatographic (HPTLC) method has been established for quantitative analysis of andrographolide, the... 相似文献