全文获取类型
收费全文 | 479篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 195篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 133篇 |
物理学 | 145篇 |
出版年
2022年 | 10篇 |
2021年 | 4篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 25篇 |
2008年 | 19篇 |
2007年 | 17篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 17篇 |
2003年 | 5篇 |
2001年 | 13篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 10篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 16篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1971年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有489条查询结果,搜索用时 0 毫秒
151.
Meenakshi Goyal V. K. Rattan Diksha Aggarwal R. C. Bansal 《Colloids and surfaces. A, Physicochemical and engineering aspects》2001,190(3):334-238
The adsorption isotherms of Cu(II) ions from aqueous solutions in the concentration range 40–1000 mg l−1 on two samples of granulated and two samples of activated carbon fibres containing varying amounts of associated oxygen have been reported. The adsorption isotherms are type I of BET classification showing initially a rapid adsorption tending to be asymptotic at higher concentrations. The amounts of oxygen associated with the carbon surface has been enhanced by oxidation with nitric acid and ammonium persulphate in the solution phase and with oxygen gas at 350°C and decreased by degassing of the oxidized carbon samples at 400, 650 and 950°C. The adsorption of Cu(II) ions increases on oxidation and decreases on degassing. The increase in adsorption on oxidation depends on the nature of the oxidative treatment while the decrease in adsorption on degassing depends on the temperature of degassing. This has been attributed to the increase in the carbon–oxygen acidic surface groups on oxidation and their decrease on degassing. Suitable mechanisms consistent with the results have been proposed. 相似文献
152.
Propagation algorithm for computer simulation of stationary paraxial self-focusing laser beam in a medium with saturating
nonlinearity is given in Lie-optic form. Accordingly, a very natural piece-wise continuous Lie transformation that reduces
to a restricted Lorentz group of the beam results. It gives rise to a matrix method for self-focusing beam propagation that
is constructed and implemented. Although the results use plasma nonlinearities of saturable type, and a gaussian initial beam,
these results are applicable for other media like linear optical fibers and to more general situations. 相似文献
153.
The oxidation of α-benzoyl-o-hydroxyacetophenones (3a-d) using iodobenzene diacetate in methanolic potassium hydroxide provides a new direct method for the synthesis of 2-benzoylcoumaran-3-ones (4a-c) in good yields. The formation of 4a-d is explained by neighb uring group participation. 相似文献
154.
Sunita Bishnoi Ashutosh Sharma Rahul Singhal Pankaj Gupta Rajendra N. Goyal 《Electroanalysis》2023,35(2):e202200238
In view of the increase in breast cancer cases at the global level, electrochemical sensing of the carcinogenic pesticide, chlorpyrifos (CPF) in breast milk is proposed. The determination is based on the nucleophilic substitution reaction of pralidoxime (PAM) with CPF. The proposed method offers a linear concentration range of 0.002 to 0.08 μmol/L. The limit of detection and limit of quantification was found to be 0.05×10−9 and 0.167×10−9M, respectively. The offered “unmodified edge plane pyrolytic graphite sensor” proved to be a better substrate than the earlier reported modified sensors. The limit of detection for the proposed method was found to be nearly fifty times lower than reported at modified electrodes. The interference study proved the adequate selectivity of the offered sensor. The sensor has good stability and reproducibility along with high sensitivity. The offered sensor is very useful for cancer hospitals, pesticide industries, and the study of environmental toxicity-related issues. 相似文献
155.
Goertz MP Goyal N Montano GA Bunker BC 《Langmuir : the ACS journal of surfaces and colloids》2011,27(9):5481-5491
Supported lipid bilayers containing phosphatidylcholine headgroups are observed to undergo reorganization from a 2D fluid, lipid bilayer assembly into an array of complex 3D structures upon exposure to extreme pH environments. These conditions induce a combination of molecular packing and electrostatic interactions that can create dynamic morphologies of highly curved lipid membrane structures. This work demonstrates that fluid, single-component lipid bilayer assemblies can create complex morphologies, a phenomenon typically only associated with lipid bilayers of mixed composition. 相似文献
156.
Novel high performance aluminum nitride (AlN)/poly(ether-ether-ketone) (PEEK) composites containing 0-50 wt.% fractions of AlN were prepared by solution blending method followed by hot pressing to evaluate their density, melting temperature, crystallization, thermal stability, morphological behavior and Vickers hardness by using different characterization techniques. Differential scanning calorimetry results indicated that the AlN particles are very effective nucleating agent, which results in increase in melting point, hot crystallization temperature and crystallinity of composites as the AlN content increases. Thermogravimetric analysis showed enhanced thermal stability of the composites with respect to PEEK. Density and X-ray diffraction techniques showed that crystallinity of the composites increases as the wt.% of AlN content increases in polymer matrix. Scanning electron microscopy revealed that AlN particles were well dispersed with no porosity in composites. Vickers hardness of the samples increased from 24 kg/mm2 for the pure PEEK to 35 kg/mm2 for AlN/PEEK composites. 相似文献
157.
Precise density and viscosity data at 15, 25 and 35°C for solutions of glycine, DL-alanine, L-threonine, -alanine, -aminobutyric acid and -aminocaproic acid in water and in (1m, 3m, 5m) aqueous potassium thiocyanate were measured and the limiting apparent molar volumes V
o
and the B-coefficients calculated. The V
o
and B values were split into the contributions from the NH
3
+
,COO– and CH2 groups. These data are rationalized on the basis of hydrophillic and hydrophobic interactions between the various groups present in these solutions.Abstracted from the Ph.D Thesis of R. K. Goyal, University of Delhi, 1990. 相似文献
158.
Arivozhi Mohan S. Shanmugavel Ajay Goyal B. R. Venkataraman D. Saravanan 《Chromatographia》2009,12(3)
Five impurities were observed when candesartan cilexetil tablets were subjected to stability and forced degradation studies.
These impurities were successfully isolated and characterized as desethyl candesartan cilexetil, 1N-ethyl candesartan cilexetil, 2N-ethyl candesartan cilexetil, 1N-ethyl oxo candesartan cilexetil, and 2N-ethyl oxo candesartan cilexetil. A gradient reverse phase liquid chromatography (LC) and an isocratic preparative LC method
were used to detect and isolate all five degradation products impurities simultaneously. Mass spectrometry, 1H/13C, DEPT and 2D NMR experiments were extensively utilized to characterize these impurities. Even though desethyl candesartan
cilexetil, 1N-ethyl candesartan cilexetil were 2N-ethyl candesartan cilexetil were documented in the literature as known impurities, the regioisomers 1N-ethyl oxo candesartan cilexetil and 2N-ethyl oxo candesartan cilexetil were never noticed. Single-crystal diffraction data has been used to confirm their structure
unambiguously and synthetic preparations of all known and unknown impurities were also presented. 相似文献
159.
Summary A spectrophotometric determination of hydrogen cyanide in air is described. Hydrogen cyanide from air is collected in dilute sodium hydroxide and then reacted with pyridine forming glutaconic aldehyde. The glutaconic aldehyde thus formed is subsequently coupled with aqueous phloroglucinol solution to form a polymethine red-violet dye having absorbance maxima at 540 nm. The colour system obeys Beer's law in the range of 0.45 to 3.6 mg/m3 of hydrogen cyanide (0.4 to 3.2 g/g). Collection efficiency of absorbing solution, molar absorptivity and Sandell's sensitivity have been evaluated. All other important analytical parameters have been studied and applied for the determination/detection of hydrogen cyanide in air samples and cigarette smoke. 相似文献
160.
S. N. Biswas S. R. Choudhury Ashok Goyal J. N. Passi 《Physics letters. [Part B]》1979,80(4-5):393-395
We argue that the presence of second-class neutral currents can be tested from the observations of
and electron polarisation in η→π0e+e-. Consequences of this model in η→π±eνe,τ±→ηπ±ντ and τ±→ωπ±ντ decays which would establish second-class charged currents are also discussed. 相似文献