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排序方式: 共有131条查询结果,搜索用时 31 毫秒
31.
ICP-MS measurements of lead isotopic ratios in soils heavily contaminated by lead smelting: tracing the sources of pollution 总被引:6,自引:0,他引:6
The Pb isotopic composition (206Pb/207Pb and 208Pb/206Pb) in smelter-impacted soils was measured using a quadrupole-based ICP-MS. Four forest/tilled soil profiles were sampled according to the distance from the lead smelter in Píbram (Czech Republic), prevailing wind direction, geological background and soil type. The results were compared with the Pb isotopic composition of bedrocks and waste materials from Pb metallurgy (smelting slags, air-pollution-control residues). The isotopic composition of soils confirms the predominant role of metallurgy on the general pollution in the area. The highly contaminated soils from the vicinity of the smelter contain up to 35,300 mg Pb kg–1 and exhibit an isotopic composition close to that of car battery processing (206Pb/207Pb up to 1.177). A coupled concentration/isotopic study of soil profiles showed that the smelter-induced pollution had penetrated even to the mineral soil horizons, indicating an important vertical mobility of Pb contaminant within the soil profile. The calculated downward penetration rate of Pb in soils ranges from 0.3 to 0.36 cm year–1. 相似文献
32.
Julien Verron 《Tetrahedron letters》2007,48(3):377-380
In the course of establishing a flexible synthesis of 2,4,6-substituted pyrimidines, we discovered that 2-hexyl-isothiourea hydrobromide reacts at ambient temperature and in a mildly exothermic fashion with 5,5-diethoxy-pent-3-yn-2-one upon treatment with 2 equiv of triethylamine in tetrahydrofuran to afford 4-diethoxymethyl-2-hexylsulfanyl-6-methyl-pyrimidine in 80% isolated yield. The methodology was developed in the search for an improved synthesis of the GABAB enhancer 4-(2-hexylsulfanyl-6-methyl-pyrimidin-4-ylmethyl)-morpholine. 相似文献
33.
Anionic surfactant penetration into the skin and their subsequent interactions with stratum corneum lipids and proteins has historically been linked with irritation and dryness from the use of soaps, body washes, facial cleansers, shampoos, and other rinse-off personal care products. Mechanisms of surfactant penetration into the skin surface has been a topic of debate for decades. In this review, we discuss relevant theories of surfactant penetration into skin as well as interactions of surfactants with skin components. We present evidence that thermodynamic analyses of surfactant solution equilibria can be useful in modeling these behaviors. A theory of surfactant monomer penetration into stratum corneum is proposed. 相似文献
34.
Biophysical and structural studies of cationic amphipathic antimicrobial peptides have revealed new mechanistic details concerning their membrane interactions. In interfacial environments the peptides adopt amphipathic conformations and the resulting distribution of polar, charged and hydrophobic residues allows them to partition into the bilayer interface. For several helical peptides it was found that their long axis is oriented parallel to the membrane surface, an arrangement which results in considerable perturbations in the packing of the lipid bilayer. Within the molecular shape concept the peptides act as wedge-like structures which impose positive curvature strain on the membrane. As a consequence a wide variety of morphologies are observed of peptide–lipid mixtures which strongly depend on the detailed peptide sequence, the membrane lipid composition, buffer, temperature and other environmental parameters. Therefore, the peptide–lipid systems are best described by phase diagrams, similar to the ones of detergent–lipid mixtures, encompassing on the one extreme regions where the peptide stabilizes the bilayer and on the other extreme regions where membrane lysis occurs. The effects of peptide sequence, membrane penetration depth, lipid composition and membrane surface charge density on membrane-association, -morphology and the resulting phase boundaries are discussed. 相似文献
35.
36.
Khalid R. Temsamani Taoufik Fahmi Dounia Bouchta Angel E. Kaifer 《Journal of Solid State Electrochemistry》1997,1(2):143-147
Self-assembled monolayers of alkanethiols on gold have been reported to be highly stable for voltammetry experiments in aqueous
electrolyte. In this work a gold electrode has been modified by first depositing one layer of an alkylthiol (S-C18) and then coating by phospholipid multilayers. Voltammetric oxidation of the antipsychotic chlorpromazine at this two-step
modified electrode was followed by means of cyclic voltammetry measurements. The results give important information concerning
the behaviour of the pharmacological agent at the lipid-water interface. Measurements made using the pre-concentration method
allow good sensitivity improvement after 5 min accumulation time. The ability of chlorpromazine to penetrate inside the phospholipid
multilayers has also been investigated under different conditions such as the nature of the phospholipid and the pH of the
medium. The accumulation process seems to be closely related to the charge carried by the phospholipid and by the molecule,
while the incorporation process seems to be independent of the charge carried by the phospholipid and dependent of the degree
of fluidity of their hydrocarbon chains. We found through this work that the acid-base equilibrium of chlorpromazine together
with its amphiphilic properties (as compared with the results of similar studies on phenothiazine) could be responsible for
governing the principal aspects of the drug's behaviour toward biological membranes.
Received: 6 January 1997 / Accepted: 27 February 1997 相似文献
37.
气溶胶粒子通过填充柱的保留时间分布测定 总被引:1,自引:0,他引:1
采用亚微米单分散聚苯乙烯球形硬气溶胶粒子和脉冲进样技术,测定了气溶胶粒子通过无规则石英砂填充柱的保留时间分布,从保留时间分布曲线得到了气溶胶粒子在填充柱中的平均保留时间和穿透率.研究了平均保留时间和穿透率与流体流速、填充柱的长度、填料粒度和气溶胶粒子大小之间的关系.研究发现,流速越大,保留时间分布曲线越尖锐,流速越小,保留时间分布曲线越平坦;气溶胶粒子的穿透率随着柱长的增加而降低,随流速、气溶胶粒子粒径和石英砂颗粒大小的减小而减小;平均保留时间随柱长增加而增大,随流速增大而减小,随气溶胶粒子粒径减小而减小,而与石英砂颗粒大小几乎无关. 相似文献
38.
39.
有关荧光素的溴和碘取代物的低温磷光性质与取代度关系的研究表明,随着取代度的增大,磷光量子产率与荧光量子产率之比呈现先增大继而减小的趋势,即溴和碘的充分取代物的磷光反而减弱,故用eosin-ITC作标记物的报道很少.化学结构和环境等因素对磷光发射有重要影响;某些已被重原子(Br或/和I)高度取代的试剂, 相似文献
40.
Various substances have been tested in the laboratory for their suitability as flow enhancers in aqueous solutions. The following maximum drag reductions (%) were obtained with pipes of 14 mm diameter and a Reynolds number of 105: Na-carboxy methylcellulose (32), hydroxyethyl cellulose (42), cetyltrimethylammonium chloride/-naphthol (74; Re=104), polyethylene oxide (76), K-polyphosphate/Na-pyrophosphate (77), polyacrylamide (80). The tested, partially hydrolysed polyacrylamide which was produced by a special process was found to be not only extremely effective and highly resistant to shear degradation but also unaffected by the salt content, the temperature and the water spoilage. Experiments were therefore made with this material on an industrial scale, that is to say with pipes up to 750 mm in diameter and 3200m in length. Whilst in the laboratory (pipes up to 14 mm in diameter) drag reductions were measured according to the Virk asymptote, the results obtained with large pipe diameters were lower. At diameters ranging from 300 to 750 mm a maximum drag reduction of 65% (at a concentration of 30 ppm PAAM and a constant wall shear stress of 50 Pa) has been obtained independently of the diameter.Symbols
c
concentration
-
d
diameter
-
FE
(as index) flow enhancer
-
k
roughness
-
l
length
-
n
degree of polymerization
-
p
pressure drop
-
r
radius
-
Re
Reynolds number
-
T
temperature
-
v
velocity
-
w
(as index) water
-
drag reduction
-
friction factor
-
kinematic viscosity
-
density
-
wall shear stress
Dedicated to Prof. Dr. R. Bonart on the occasion of his 60th birthday 相似文献