全文获取类型
收费全文 | 248篇 |
免费 | 10篇 |
专业分类
化学 | 162篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 25篇 |
物理学 | 63篇 |
出版年
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 6篇 |
2013年 | 17篇 |
2012年 | 8篇 |
2011年 | 13篇 |
2010年 | 19篇 |
2009年 | 13篇 |
2008年 | 8篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 13篇 |
2004年 | 7篇 |
2003年 | 14篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有258条查询结果,搜索用时 490 毫秒
1.
A. A. Mak E. A. Viktorov O. A. Orlov V. I. Ustyugov 《Radiophysics and Quantum Electronics》2004,47(10-11):743-746
We present the results of experiments with a CW single-mode Nd:YAG laser, tunable in the vicinity of 1064 nm, with an intracavity narrow-band Cs 2 vapor saturable absorber. It is shown that the laser dynamics is determined by both the pump level and detuning of the laser frequency from the absorption-line center. 相似文献
2.
3.
Lyudmila V. Chernykh Jitka Eysseltova Mikhail Y. Skripkin 《Monatshefte für Chemie / Chemical Monthly》2003,134(5):751-761
Summary. Solubility isotherms in the CuBr2−MBr−H2O (M
+ = Li+, Na+, Cs+) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide
systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated
solutions was performed.
Corresponding author. E-mail: jitka@prfdec.natur.cuni.cz
Received August 6, 2002; accepted (revised) November 29, 2002
Published online April 3, 2003 相似文献
4.
In this contribution, the on-line coupling of solid phase extraction (SPE), based on a restricted-access material (RAM), with sequential injection technique (SIA) for the analysis of biological samples, is described. The SIA-RAM system was tested with a new potential antileucotrienic drug (VUFB-19363 (Quinlukast)) for serum analysis. The method is based on SPE with the novel internal-surface reversed-phase column packing material-alkyl-diol silica (ADS). The supports tolerate direct and repetitive injection of proteinaceous fluids (plasma, serum) and allow reversed-phase partitioning at the internal surface. A column packed with a 25 microm C18 alkyl-diol support was used for direct serum injection. Using a 6-port selection valve and the system of three mobile phases, the polar matrix compounds and metabolites are removed by sequentially aspirated mobile phases with lower content of the organic part (methanol-water (2:98) and following acetonitrile-water (20:80)) to the waste, and then, the analyte enriched on the column is eluted by a strong mobile phase (acetonitrile-methanol-water (40:20:40)) to the UV detector without transfer loss. With the fully automated SIA system, a total analysis time of less than 10 min was achieved. The only off-line sample pre-treatment step required to remove particulate matter was centrifugation. The studies showed a range of linearity (2-40 microg ml(-1)) and a high recovery (93.6-96.8%) of drug from the biological matrix with coefficients of variation (RSD) less than 5.0% (n = 6). This paper introduces a new, simple and robust analytical technique suitable for screening determination and direct analysis of drugs in biological materials. 相似文献
5.
Baldacci A Theurillat R Caslavska J Pardubská H Brenneisen R Thormann W 《Journal of chromatography. A》2003,990(1-2):99-110
γ-Hydroxybutyric acid (GHB), a minor metabolite or precursor of γ-aminobutyric acid (GABA), acts as a neurotransmitter/neuromodulator via binding to GABA receptors and to specific presynaptic GHB receptors. Based upon the stimulatory effects, GHB is widely abused. Thus, there is great interest in monitoring GHB in body fluids and tissues. We have developed an assay for urinary GHB that is based upon liquid–liquid extraction and capillary zone electrophoresis (CZE) with indirect UV absorption detection. The background electrolyte is composed of 4 mM nicotinic acid (compound for indirect detection), 3 mM spermine (reversal of electroosmosis) and histidine (added to reach a pH of 6.2). Having a 50 μm I.D. capillary of 40 cm effective length, 1-octanesulfonic acid as internal standard, solute detection at 214 nm and a diluted urine with a conductivity of 2.4 mS/cm, GHB concentrations ≥2 μg/ml can be detected. Limit of detection (LOD) and limit of quantitation (LOQ) were determined to be dependent on urine concentration and varied between 2–24 and 5–60 μg/ml, respectively. Data obtained suggest that LOD and LOQ (both in μg/ml) can be estimated with the relationships 0.83 κ and 2.1 κ, respectively, where κ is the conductivity of the urine in mS/cm. The assay was successfully applied to urines collected after administration of 25 mg sodium GHB/kg body mass. Negative electrospray ionization ion-trap tandem mass spectrometry was used to confirm the presence of GHB in the urinary extract via selected reaction monitoring of the m/z 103.1→m/z 85.1 precursor–product ion transition. Independent of urine concentration, this approach meets the urinary cut-off level of 10 μg/ml that is required for recognition of the presence of exogenous GHB. Furthermore, data obtained with injection of plain or diluted urine indicate that CZE could be used to rapidly recognize GHB amounts (in μg/ml) that are ≥ 4 κ. 相似文献
6.
Lyudmila V. Chernykh Jitka Eysseltova Mikhail Y. Skripkin 《Monatshefte für Chemie / Chemical Monthly》2003,124(1):751-761
Solubility isotherms in the CuBr2−MBr−H2O (M
+ = Li+, Na+, Cs+) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide
systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated
solutions was performed. 相似文献
7.
V. N. Torocheshnikov N. M. Sergeyev N. A. Viktorov G. S. Goldin V. G. Poddubny A. N. Koltsova 《Journal of organometallic chemistry》1974,70(3)
The 1H and 13C NMR spectra of the following six compounds have been examined over a wide range of temperatures: four derivatives of 3,5-dimethylpyrazole substituted at the nitrogen atom by organometallic groups such as Si(CH3)3 (I), Si(C2H5)3 (II), Si(OC2H5)3 (III), Ge(CH3)3 (IV), 3,5-dimethyl-1-trimethylsilyl-1,2,4-triazole (V) and 1-trimethylsilylimidazole (VI). Activation energies of the metal migration have been found for the compounds (I–V) by the total NMR line-shape analysis. Proton and carbon spectra of the compound (VI) show equivalence of the positions 4 and 5 in the imidazole ring. No temperature-dependent changes in the spectra were observed at –80 to +80°. These facts may be interpreted by assuming that the organometallic group undergoes an intermolecular exchange. 相似文献
8.
Summary The properties of stannic oxide as a combustion aid in elemental analysis for carbon, hydrogen and nitrogen, and its modification with silver for the retention of halogens and oxides of sulphur are described. The optimum combustion temperature with stannic oxide is 1000±50° C. It is suitable as a combustion tube packing for automated methods. A universal packing for analysis of various types of compounds is shown.
Zinn(IV)oxid als Oxydationsmittel für die Elementaranalyse von C, H und N
Zusammenfassung Die Eigenschaften des Zinnoxids als Katalysator für die Bestimmung von C, H und N und seine Modifikation mit Silber für die Retention der Halogene und der Schwefeloxide wurden beschrieben. Die Optimaltemperatur für die Verbrennung mit Zinnoxid ist 1000±50° C. Es eignet sich als Rohrfüllung für automatisierte Methoden. Eine Universalfüllung für Analysen verschiedener Verbindungstypen wurde angegeben.相似文献
9.
A two-step supercritical fluid extraction of polycyclic aromatic hydrocarbons from roadside soil samples 总被引:1,自引:0,他引:1
A two-step procedure for the supercritical fluid extraction (SFE) of polycyclic aromatic hydrocarbons from soil samples was developed. The procedure consists of a static supercritical fluid treatment in a closed extraction cell at a high temperature (T=250 or 340degreesC for 20 min) and an SFE with a solvent trapping. During the static phase, the sample is exposed to a supercritical organic solvent (methanol, toluene, dichloromethane, ACN, acetone, and hexane). The solvent penetrates particles of the matrix to substitute strongly bonded molecules and dissolves the analytes in the supercritical phase. At ambient temperature, supercritical fluids became liquid and lost their solvation abilities. Most of the analytes condense on the surface of the particles or on the extraction cell walls without forming strong bonds or penetrating deep into the matrix. Thus, the pretreatment liberates the analytes and they behave similar to those in freshly spiked samples. The common SFE with toluene-modified CO2 as an extraction fluid follows the static phase. With the use of the most suitable extraction phases (toluene, ACN), the extraction efficiency of the combined procedure is much higher (approximately100%). The results of the combined procedure are compared to the SFE procedure of the same untreated sample (difference less than 5%) and to the Soxhlet extraction. The extracts were analyzed using a GC with the flame ionization detection. 相似文献
10.
Richard Paout Jaroslav Maixner Jitka Holakovsk Michal Duek Petr Ka
er 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(12):m340-m343
Another new substance from the family of Pt‐based coordination complexes with potential use in cancer chemotherapy has been synthesized, crystallized and structurally characterized. In this compound {systematic name cis‐dibromido[(1R,2R)‐cyclohexane‐1,2‐diamine‐κ2N,N′]platinum(II)}, cis‐[PtBr2(C6H14N2)], there are two molecules with very similar conformations in the asymmetric unit. The component species interact by way of N—H...Br and C—H...Br hydrogen bonds to give two‐dimensional networks which lie parallel to the (100) plane. 相似文献