全文获取类型
收费全文 | 74篇 |
免费 | 0篇 |
专业分类
化学 | 37篇 |
数学 | 6篇 |
物理学 | 31篇 |
出版年
2013年 | 6篇 |
2012年 | 2篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1966年 | 2篇 |
1929年 | 1篇 |
排序方式: 共有74条查询结果,搜索用时 15 毫秒
1.
Overman LE Larrow JF Stearns BA Vance JM 《Angewandte Chemie (International ed. in English)》2000,39(1):213-215
All three stereoisomers of the hexacyclic 3a,3a'-bispyrrolidino[2,3-b]indoline moiety found in complex indole alkaloids can be prepared, as illustrated by total syntheses of meso-chimonanthine (1) and (+)-chimonanthine (2). A rare example of high diastereoselectivity arising from the combination of a prostereogenic enolate with a chiral electrophile containing a sp(3) carbon atom is the key feature of the asymmetric synthesis of the C(2) stereoisomer. 相似文献
2.
Samuel K Yin W Stearns RA Tang YS Chaudhary AG Jewell JP Lanza T Lin LS Hagmann WK Evans DC Kumar S 《Journal of mass spectrometry : JMS》2003,38(2):211-221
Metabolic activation of drug candidates to electrophilic reactive metabolites that can covalently modify cellular macromolecules may result in acute and/or idiosyncratic immune system-mediated toxicities in humans. This presents a significant potential liability for the future development of these compounds as safe therapeutic agents. We present here an example of an approach where sites of metabolic activation within a new drug candidate series were rapidly identified using online liquid chromatography/multi-stage mass spectrometry on an ion trap mass spectrometer. This was accomplished by trapping the reactive intermediates formed upon incubation of compounds with rat and human liver microsomes as their corresponding glutathione conjugates and mass spectral characterization of these thiol adducts. Based on the structures of the GSH adducts identified, potential sites and mechanisms of bioactivation within the chemical structure were proposed. These metabolism studies were interfaced with iterative structural modifications of the chemical series in order to block these bioactivation sites within the molecule. This strategy led to a significant reduction in the propensity of the compounds to undergo metabolic activation as evidenced by reductions in the irreversible binding of radioactivity to liver microsomal material upon incubation of tritium-labeled compounds with this in vitro system. With the efficiency and throughput achievable with such an approach, it appears feasible to identify and address the metabolic activation potential of new drug leads during routine metabolite identification studies in an early drug discovery setting. 相似文献
3.
4.
5.
Phospholipids (1–5 mg) are mixed with methyl heptadecanoate as an internal standard. One part of the sample is reduced with Vitride in tetrahydrofuran in a sealed tube at 50 2C for 1 hr. The reaction products are acetylated in the same tube by treatment with acetic acid-acetic anhydride at 140 °C. After 1 hr total O-acyl and after 16 additional hours glycerol are determined as the fully acetylated compounds by gas-liquid chromatography.Another part of the sample is subjected to acidic hydrolysis and total O-acyl and N-acyl groups are determined by GLC as fatty-acid methyl esters. The aqueous phase is heated to 100 °C with 6 N HCl for 72 hr and phosphorus is measured colorimetrically. 相似文献
6.
CLAUDIA L. PARKER OSCAR N. VENTURA STAN K. BURT RAÚL E. CACHAU 《Molecular physics》2013,111(17):2659-2668
We present a general purpose QM-MM-MD engine (DYNGA) designed to test alternative hybrid Hamiltonians geared towards the treatment of problems of interest in structural biology including the use of experimental data constraints. In this first presentation we use DYNGA to explore the behaviour of a traditional QM-MM approach in the treatment of the water—water interaction. We find the potential energy hypersurface for the water dimer computed with the HF 4–31G*/TIP3P hybrid Hamiltonian tends to be too flat. We also explore the effect of using traditional QM-MM techniques on proton wires and conclude there is a need for improvement, possibly addressed by using polarizable force fields. 相似文献
7.
M.B. Stearns 《Physics letters. A》1974,47(5):397-398
The measured hyperfine field at a μ+ stopped in Fe is interpreted as being due to the 4s conduction electron polarization (CEP) in Fe and is used to extend the CEP curve to closer distances than nearest neighbors. 相似文献
8.
Klaus H. Berkner David Leung Robert V. Pyle Alfred S. Schlachter J.Warren Stearns 《Physics letters. A》1977,64(2):217-218
Equilibrium charge-state fractions of 2.7–31 keV deuterium in strontium vapor are reported. The energy dependence of the D- equilibrium yield is discussed. The results are compared with the D- yield in cesium and magnesium vapors. 相似文献
9.
Wavelength modulation spectra of SrTiO3 were measured at several temperatures above and below the cubic to tetragonal phase transition. Our results definitely confirm that the fundamental edge is an indirect gap which is only slightly affected by the phase transition. Analysis leads us to favor the conclusion that the conduction band minimum is at X rather than at Λ. 相似文献
10.
Abstract We analyze the efficiency of the international management of the Bay of Biscay anchovy. While a sharing agreement between France and Spain has been in place since 1992, the fish stock collapsed in 2005 and the fishery closed from 2005 to spring 2010. We consider differences in production technologies between both countries and calibrate our model using data from 1987 to 2009. Our results suggest two sources of rent dissipation under the existing sharing agreement: inefficient quota allocation and production inefficiencies due to inflexible national regulations. We discuss several alternatives to improve management. 相似文献