全文获取类型
收费全文 | 666篇 |
免费 | 25篇 |
国内免费 | 11篇 |
专业分类
化学 | 503篇 |
晶体学 | 3篇 |
力学 | 3篇 |
数学 | 140篇 |
物理学 | 53篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 23篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 15篇 |
2014年 | 25篇 |
2013年 | 55篇 |
2012年 | 37篇 |
2011年 | 60篇 |
2010年 | 40篇 |
2009年 | 27篇 |
2008年 | 46篇 |
2007年 | 38篇 |
2006年 | 40篇 |
2005年 | 25篇 |
2004年 | 23篇 |
2003年 | 24篇 |
2002年 | 21篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1937年 | 2篇 |
1931年 | 1篇 |
排序方式: 共有702条查询结果,搜索用时 15 毫秒
11.
Irena Baranowska Katarzyna Barszczweska 《Fresenius' Journal of Analytical Chemistry》1994,350(7-9):568-569
A selective and sensitive method for the determination of europium was developed. Other lanthanides and oxidants do not require separation. The method is based on the redox reaction of Eu(III) with 2,2-biquinoxalyl. It was checked for the range of 0.5 to 10 g/Eu/mL. Sm(III) does not interfere in 1000-fold excess.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday 相似文献
12.
Maleš Željan Plazibat Miško Vundać Vjera Bilušić Žuntar Irena Pilepić Kroata Hazier 《平面色谱法杂志一现代薄层色谱法》2004,17(4):280-285
JPC – Journal of Planar Chromatography – Modern TLC - The flowering tops of Hypericum hirsutum, H. montanum, H. perforatum subsp. angustifolium, H. perforatum subsp. perforatum, and H.... 相似文献
13.
A new, accurate, sensitive and fast reversed-phase high-performance liquid chromatography (RP-HPLC) as an analytical method for the quantitative determination of 11 drugs in human urine was worked out, optimized and validated. The objects of analysis were imipenem (IMP), paracetamol (PAR), dipyrone (DPR), vancomycin (VCM), amikacin (AMK), fluconazole (FZ), cefazolin (CFZ), prednisolone (PRE), dexamethasone (DEX), furosemide (FUR) and ketoprofen (KET) belonging to four different groups (antibiotics, analgesic, demulcent and diuretic). For HPLC analysis, diode array (DAD) and fluorescence (FL) detectors were used. The separation of analyzed compounds was conducted by means of a LiChroCART® Purospher® C18e (125 mm × 3 mm, particle size 5 μm) analytical column with LiChroCART® LiChrospher® C18 (4 mm × 4 mm, particle size 5 μm) pre-column with gradient elution. Analyzed drugs were determined within 20 min. The mobile phase was comprised of various proportions of methanol, acetonitrile and 0.05% trifluoroacetic acid in water. AMK was separated and determined from human urine using ortho-phthaldialdehyde-3-mercaptopropionic acid (OPA-3-MPA) as a fluorescent reagent by RP-HPLC-FL. The following retention times for drugs IMP, PAR, DPR, VCM, AMK, FZ, CFZ, PRE, DEX, FUR and KET in human urine were found: 4.01 min, 4.86 min, 6.71 min, 8.14 min, 9.46 min, 10.01 min, 10.90 min, 13.34 min, 14.06 min, 16.03 min and 18.98 min, respectively. Excellent linearity was obtained for compounds in the range of concentration: 0.35-42 μg ml−1, 0.5-45 μg ml−1, 4.5-38 μg ml−1, 0.25-25 μg ml−1, 0.5-35 μg ml−1, 0.25-22 μg ml−1, 0.03-52 μg ml−1, 0.15-25 μg ml−1, 0.25-28 μg ml−1, 0.05-18 μg ml−1 and 0.15-35 μg ml−1 for IMP, PAR, DPR, VCM, AMK, FZ, CFZ, PRE, DEX, FUR and KET, respectively. The limits of detection (LOD) and limits of quantification (LOQ) for analyzed drugs were calculated in all cases and recovery studies were also performed. Ten human urine samples obtained from patients treated in hospital have been tested. In analyzed samples, one or more drugs from the 11 examined drugs were detected. The concentrations of examined drugs in urine samples ranged between: 1.5-12 μg ml−1 of PAR, 5.2-11.5 μg ml−1 of DPR, 0.13-9.5 μg ml−1 of CFZ and 0.1-8 μg ml−1 of FUR. This method can be successfully applied to routine determination of all these drugs in human urine samples. 相似文献
14.
A combination of "black box" and "calendar-time" methods for the determination of calibration intervals of an analytical
measuring instrument is discussed. Since the methods require information on the distributions of the calibration parameters,
such information is described for an atomic absorption spectrophotometer, as an example. The hypotheses on the normal distribution
of the calibration parameters are tested using the ω2-criterion and accepted at 0.90–0.95 levels of confidence. Corresponding control charts are designed for indication of warning
and action limits of the calibration parameters, and diagnoses of outliers in further calibrations. Control charts indicate
also when the calibration should be done according to the full program of the equipment manufacturer.
Received: 15 April 2000 / Accepted: 24 July 2000 相似文献
15.
Skorić I Basarić N Marinić Z Visnjevac A Kojić-Prodić B Sindler-Kulyk M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(2):543-551
New heteroaryl-substituted o-divinylbenzenes, 2,2'-(1,2-phenylenedivinylene)difuran (9), 2,2'-(1,2-phenylenedivinylene)bisbenzo[b]furan (10), and 2,2'-(1,2-phenylenedivinylene)bisnaphtho[2,1-b]furan (11), were prepared and irradiated at various concentrations; intramolecular photocycloaddition and intermolecular [2+2] twofold photoaddition reactions took place to give bicyclo[3.2.1]octadiene derivatives 12-14 and cyclophane derivatives 15-17, respectively. Compound 11 was the most selective of these o-divinylbenzenes, which, owing to pi-pi intra- or intermolecular complexation, gave only the exo-bicyclo[3.2.1]octadiene derivative 14 at low concentrations, and only the cyclophane derivative 17 at high concentrations. 相似文献
16.
Thermal
and structural properties of model silicate-phosphate glasses containing the
different amounts of the glass network modifiers, i.e. Mg2+
and Ca2+ were studied. To explain the changes of
the parameters characterizing the glass transition effect (Tg, Δcp) and the crystallization
process (Tc, ΔH) depending on the cations modifiers additions,
analysis of the bonds and chemical interactions of atoms in the structure
of glasses was used.
31P
MAS-NMR spectra of SiO2–P2O5–MgO(CaO)–K2O glasses show that the phosphate complexes are mono- and diphosphate. It
has been found that increasing amounts of Mg2+
or Ca2+ cations in the structure of glasses causes
the reduction of the degree of polymerization of the phosphate framework (Q1→Q0).
The influence of increasing of modifiers in the structure of silicate- phosphate
glasses on the number of non-bridging oxygens per SiO4
tetrahedron and density of glasses was presented. 相似文献
17.
Irena Lasiecka 《Numerische Mathematik》1992,63(1):357-390
Summary Approximations schemes for the solutions of the Algebraic Riccati Equations will be considered. We shall concentrate on the case when the input operator is unbounded and the dynamics of the system is described by an analytic semigroup. The main goal of the paper is to establish the optimal rates of convergence of the underlying approximations. By optimal, we mean such approximations which would reconstruct the optimal regularity of the original solutions as well as the best approximation properties of the finite-dimensional subspaces. It turns out that, if one aims to obtain the optimal rates in the case of unbounded input operators, the choice of the approximations to the generator, as well as to the control operator, is very critical. While the convergence results hold with any consistent approximations, the optimal rates require a careful selection of the approximating schemes. Our theoretical results will be illustrated by several examples of boundary/point control problems where the optimal rates of convergence are achieved with the appropriate numerical algorithms.Research partially supported by the NSF Grant DMS-8301668 and by the AFOSR Grant AFOSR 89-0511 相似文献
18.
19.
20.
Szymon Godlewski Jakub S. Prauzner-Bechcicki Janusz Budzioch Lukasz Walczak Irena G. Stará Ivo Starý Petr Sehnal Marek Szymonski 《Surface science》2012,606(21-22):1600-1607
Helicenes are carbon-rich materials with an ordered structure that possess interesting and remarkable electronic, chiroptical, mechanical and magnetic properties either in bulk or as single molecule devices. We report on the first attempt to anchor and organize [11]anthrahelicene ([11]AH) molecules onto a metal oxide surface. Molecular structures obtained on the (110) and (011) faces of rutile titania are characterized using scanning probe microscopy. On the (110) surface, [11]AH molecules form islands that are comprised of small domains of two types that are mirror reflections of each other and have an ordered quasi-hexagonal lattice. In contrast, molecules form unordered clusters on the (011) surface. Single molecules on both faces are imaged with sub-molecular resolution. 相似文献