全文获取类型
收费全文 | 355篇 |
免费 | 12篇 |
专业分类
化学 | 294篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 10篇 |
物理学 | 59篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 11篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 46篇 |
2012年 | 18篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 12篇 |
2008年 | 13篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 14篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有367条查询结果,搜索用时 78 毫秒
1.
2.
Vikas V. Vaidya Santosh M. Yetal Shikha M. N. Roy Noel A. Gomes Santosh S. Joshi 《Chromatographia》2007,66(11-12):925-928
A rapid, sensitive and specific method to quantify pregabalin in human plasma using metaxalone as the internal standard is described. Sample preparation involved simple protein precipitation by using acetronitrile as solvent. The extract was analyzed by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (LC-MS–MS). Chromatography was performed isocratically on Thermo Hypurity C18 5 μm analytical column, (50 mm × 4.6 mm i.d.). The assay of pegabalin was linear calibration curve over the range 10.000–10000.000 ng mL?1. The lower limit of quantification was 10.000 ng mL?1 in plasma. The method was successfully applied to the bioequivalence study of pregabalin capsules (150.0 mg) administered as a single oral dose. 相似文献
3.
Krishna Raman Surendra S. Parmar Shiva P. Singh 《Journal of heterocyclic chemistry》1980,17(5):1137-1139
A series of 1-(5-phenyl-2H-tetrazol-2-ylacetyl)-4-substituted thiosemicarbazids were prepared as possible antiinflammatory agents. Their antiproteolytic activity was reported. 相似文献
4.
Perchloric acid supported on silica gel acts as an excellent reagent system in converting glucals into 2,3-unsaturated-O-glucosides in good to excellent yields in short reaction time with good alpha selectivity. Primary, secondary, and allylic alcohols, phenols, and thiols react with 3,4,6-tri-O-acetyl glucal with equal ease. In addition to this, a chiral furan diol is obtained from unprotected D-glucal or D-galactal in good yields. 相似文献
5.
S. P. Singh S. S. Parmar V. I. Stenberg S. A. Farnum 《Journal of heterocyclic chemistry》1978,15(1):13-16
The 13C nmr chemical shifts of phenylbutazone, oxyphenbutazone, indomethacin and indole-3-acetic acid are reported. The assignments of various carbon resonances are made on the basis of the substitution effects on benzene shifts, multiplicities generated in SFORD spectra, nuclear overhauser enhancement for protonated carbons, and the comparison with analogous compounds. 相似文献
6.
The most widely used algorithm for Monte Carlo sampling of electronic transitions in trajectory surface hopping (TSH) calculations is the so-called anteater algorithm, which is inefficient for sampling low-probability nonadiabatic events. We present a new sampling scheme (called the army ants algorithm) for carrying out TSH calculations that is applicable to systems with any strength of coupling. The army ants algorithm is a form of rare event sampling whose efficiency is controlled by an input parameter. By choosing a suitable value of the input parameter the army ants algorithm can be reduced to the anteater algorithm (which is efficient for strongly coupled cases), and by optimizing the parameter the army ants algorithm may be efficiently applied to systems with low-probability events. To demonstrate the efficiency of the army ants algorithm, we performed atom-diatom scattering calculations on a model system involving weakly coupled electronic states. Fully converged quantum mechanical calculations were performed, and the probabilities for nonadiabatic reaction and nonreactive deexcitation (quenching) were found to be on the order of 10(-8). For such low-probability events the anteater sampling scheme requires a large number of trajectories ( approximately 10(10)) to obtain good statistics and converged semiclassical results. In contrast by using the new army ants algorithm converged results were obtained by running 10(5) trajectories. Furthermore, the results were found to be in excellent agreement with the quantum mechanical results. Sampling errors were estimated using the bootstrap method, which is validated for use with the army ants algorithm. 相似文献
7.
8.
Sarjit S. Sandhu Miss Sukhvinder Baweja Swarn S. Parmar 《Transition Metal Chemistry》1980,5(1):299-302
Summary Ten complexes of nickel(II) and cobalt(II) witho-phenylenebis(diphenylarsine), (pdpa) ando-phenylenebis(di-p-tolylarsine), (pdta) have been synthesised. The stoichiometry of complexes is markedly dependent upon the reaction temperature, thus reaction atca. 0° gives the M(A-A)2X2 chelates, [M = Ni, X = Br, (A-A) = pdpa; M = Ni, X = I, (A-A) = pdpa, pdta; M = Co, X = CNS, (A-A) = pdpa] whereas at higher temperatures the M(A-A)X2 chelates [M = Ni, X = Br, I, (A-A) = pdpa, pdta; M = Co, X = CNS, (A-A) = pdpa or pdta] are obtained. The Ni(A-A)2I2 compounds can be converted into Ni(A-A)I2 by boiling under reflux in n-BuOH; the conversion can be reversed by cooling a CH2Cl2 solution of the latter at or below 0°. Stereochemical assignments of all the new complexes have been made on the basis of room temperature eff values, molar conductance, i.r. and u.v. data. 相似文献
9.
Sidra Khan Shikha Chauhan Achu Chandran Michał Czerwiński Jakub Herman Ashok M. Biradar 《Liquid crystals》2020,47(2):263-272
ABSTRACT Here, we present the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal (FLC) mixture, namely W302. The FLC mixture, comprising of pyrimidine compounds, was characterised through dielectric spectroscopy, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and other electro-optical methods. The material parameters such as spontaneous polarisation, rotational viscosity, response time and tilt angle of W302 were found to be 14 nC/cm2, 240 mPa.s, 150 µs and 28?, respectively. The phase transition temperatures of W302 were observed through DSC and further confirmed by the dependence of dielectric loss factor in homogeneously aligned FLC sample with temperature. We also demonstrate the observance of a low-frequency dielectric relaxation mode due to the unwinding of the helix, called as partially unwound helical mode (p-UHM) along with Goldstone mode. The behaviour of p-UHM has been systematically studied with temperature and applied bias field. Further, dispersion of nCuO into host W302 has shown a significant increase in dielectric permittivity. Also, the p-UHM relaxation peak in the dielectric regime has disappeared with the incorporation of nCuO. These studies would be useful to fabricate better electro-optical devices for display, switching and beam steering applications. The formulation and characterization of a ferroelectric liquid crystal (FLC) mixture W302 composed of pyrimidine compounds is presented. Then, we observed the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared and characterized FLC mixture. 相似文献
10.
Bhagwan R. Pandey Sushil Kumar Shiva P. Singh Surendra S. Parmar 《Journal of heterocyclic chemistry》1980,17(5):1119-1120
Several 4-(arylaminothiocarbonyl)-1-(1-o-methoxyphenylcarbamido)-ethylpiperazines were synthesized and evaluated for their anticonvulsant activity against pentylenetetrazol-induced seizures in mice. The ability of substituted piperazines to inhibit in vitro respiratory activity of rat brain homogenates was also determined to study their structure-activity relationship. 相似文献