全文获取类型
收费全文 | 1654篇 |
免费 | 30篇 |
国内免费 | 3篇 |
专业分类
化学 | 792篇 |
晶体学 | 10篇 |
力学 | 34篇 |
数学 | 164篇 |
物理学 | 687篇 |
出版年
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 27篇 |
2015年 | 21篇 |
2014年 | 26篇 |
2013年 | 68篇 |
2012年 | 67篇 |
2011年 | 63篇 |
2010年 | 47篇 |
2009年 | 35篇 |
2008年 | 64篇 |
2007年 | 71篇 |
2006年 | 69篇 |
2005年 | 66篇 |
2004年 | 51篇 |
2003年 | 24篇 |
2002年 | 53篇 |
2001年 | 36篇 |
2000年 | 38篇 |
1999年 | 18篇 |
1998年 | 21篇 |
1997年 | 27篇 |
1996年 | 46篇 |
1995年 | 47篇 |
1994年 | 37篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 23篇 |
1990年 | 38篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 25篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 13篇 |
1973年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有1687条查询结果,搜索用时 15 毫秒
91.
R. Witte E. E. B. Campbell C. Richter H. Schmidt I. V. Hertel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,5(2):101-111
A collisional alignment and orientation study with planar symmetry is described, determining the complete density matrix for resonant charge transfer from laser excited atoms. Results are reported for the Na++Na*(3p) system over the collision energy rangeE c.m.=50?100 eV. We communicate the optimal alignment angle γ and linear polarisationP l + of the charge cloud as well as its relative height ρ00 and the angular momentumL ⊥ + transferred in the collision as a function of the scattering angle. For preparation of the sodium 3p orbital in the scattering plane (positive reflection symmetry) we observe that at small reduced scattering angles (<20 eV°) the preparation of apσ at large internuclear distances contributes most to the scattering intensity whereas at larger reduced scattering angles (>60 eV°) apπ+ preparation is more important. In contrast, preparation of thepπ? orbital (perpendicular to the scattering plane) is large at small and vanishes at larger scattering angles. We conclude that orbital following cannot be assumed in this resonant charge transfer process. The angular momentum transfer is observed to be small, indicating only little coherence in the process, but shows nevertheless an interesting behaviour as a function of scattering angle. 相似文献
92.
The metabolism of (+/-)fenfluramine, 1-(m-trifluoromethylphenyl)-2-N-ethylpropane, an anoretic agent, was investigated in humans. The analysis method was based on the use of ion-exchange resin extraction, solid-phase purification on the Bond Elut1M C8 cartridge, gradient elution high-performance liquid chromatography, enzymic hydrolysis of conjugates, further purification by Bond Elut C8 cartridge, derivatisation and capillary column gas chromatography-mass spectrometry (GC-MS). After administration of a 1 mg kg-1 oral dose, four metabolites plus unchanged fenfluramine were recovered in the 0-24 h urine from human volunteers and characterised by GC-MS. In the conjugated form, fenfluramine, norfenfluramine and m-trifluoromethylhippuric acid were detected by GC-MS. In the aglycone form, the major metabolite, 1-(m-trifluoromethylphenyl)-1,2-propane diol (fenfluramine diol), was monitored using GC-MS. The mass spectral characteristics of the m-trifluoromethylhippuric acid methyl ester, 1-(m-trifluoromethylphenyl)-1,2-propane ditrifluoracetate derivatives and the norfenfluramine and fenfluramine free base obtained under electron-impact ionization are presented. The metabolism of fenfluramine is discussed including a metabolic pathway in man accounting for the formation of its biotransformation products. 相似文献
93.
Campbell Keri Judge Elizabeth J. Dirmyer Matthew R. Kelly Dan Czerwinski Ken 《Journal of Radioanalytical and Nuclear Chemistry》2017,313(1):197-206
Journal of Radioanalytical and Nuclear Chemistry - We report a study of a fast radiochemical method to determine the activity of 131I via the radiochemical recovery obtained with a 129I tracer.... 相似文献
94.
Jack B. Campbell Edward R. Lavagnino Jonathan W. Paschal 《Journal of heterocyclic chemistry》1986,23(3):767-768
The spectral similarities of 10 and 11 substituted 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-ones hinder the identification of the individual isomers. Preparation of the 13-methyl p-toluenesulfonate salts of these compounds has allowed the assignment by the use of NOE techniques. Saturation of the N-methyl caused an NOE at H-12. The coupling pattern of H-12 then provides identification of the compound. 相似文献
95.
J. B. Campbell J. M. Greene E. R. Lavagnino D. N. Gardner A. J. Pike J. Snoddy E. C. Taylor 《Journal of heterocyclic chemistry》1986,23(3):669-672
New methods of preparing 2,3-diaminopyridine ( 13 ) from 2-chloro-3-nitropyridine ( 11 ) and 3,4-diaminopy-ridine ( 8 ) from 4-ethoxy-3-nitropyridine hydrochloride ( 5 ) have been explored and evaluated. 相似文献
96.
K. E. Grant G. M. Mong R. B. Lucke J. A. Campbell 《Journal of Radioanalytical and Nuclear Chemistry》1996,211(2):383-402
Considerable attention has been focused on chelators such as ethylenediaminetetraacetic acid (EDTA) and N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), which form water-soluble complexes with most heavy metals. Most radionuclides are included in this class of constituents. As a result, chelator complexes have become very important environmentally because of their tendency to enhance the mobility of heavy metals through the soil and potentially contaminate groundwater. In addition, there is a correlation between chelator concentration and crust formation/gas release. The chelators are a class of compounds whose low volatility and high polarity preclude analysis by gas chromatography/mass spectrometry (GC/MS) without prior derivatization. Waste samples from a double-shell storage tank at Hanford were derivatized with BF3/methanol and analyzed using GC/MS. Results indicate the presence of EDTA, HEDTA, nitrilotriacetic (NTA), and citric acid. Nitrosoiminodiacetic acid was identified and determined to be an artifact of the derivatization procedure; it is assumed to arise from nitrosation of iminodiacetic acid in the waste sample. 相似文献
97.
98.
99.
John T. Gupton Alex Shimozono Evan Crawford Joe Ortolani Evan Clark Matt Mahoney Campbell Heese Jeffrey Noble Carlos Perez Mandry Rene Kanters Raymond N. Dominey Emma W. Goldman James A. Sikorski Daniel C. Fisher 《Tetrahedron》2018,74(21):2650-2663
Highly functionalized pyrroles with appropriate regiochemical functionality represent an important class of marine natural products and potential drug candidates. We describe herein a detailed study of the reaction of α-aminoacid esters with vinylogous amides and also β-halovinylaldehydes for the regiospecific synthesis of 2,3,4-trisubstituted and 1,2,3,4-tetrasubstituted pyrroles. Since the vinylogous amides and β-halovinylaldehydes are readily available precursors, rapid access to a wide variety of unsymmetrically substituted pyrroles is accomplished via this methodology. 相似文献
100.
J Kucera B Smodis K Burns P De Regge M Campbell V Havránek M Makarewicz A Toervenyi E Zeiller 《Fresenius' Journal of Analytical Chemistry》2001,370(2-3):229-233
Several sets of reference air filters were prepared as part of an IAEA evaluation of the performance of laboratories involved in air-pollution studies. Each set comprised three polycarbonate membrane filters, two of which were loaded with urban air particulate matter (APM) obtained in Vienna or Prague, and one unloaded filter. The filters were loaded by filtration of a suspension of the APM materials in water. The homogeneity both of bulk APM materials and of the loaded filters was evaluated and found suitable by determining several elements by instrumental neutron-activation analysis (INAA), proton-induced X-ray emission (PIXE), and micro-X-ray energy-dispersive fluorescence analysis (micro-EDXRF). After evaluation of the homogeneity, INAA, PIXE, EDXRF, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), and ICP mass spectrometry (ICP-MS) were used to characterize the filter materials and establish "target values" and their associated standard deviations for 15 elements. Problems encountered during the preparation of these unique, simulated air filters and the criteria for setting both the target values and standard deviations are presented. 相似文献