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1.
Summary Measurements have been made of the sea-level size spectrum of cosmic-ray showers at a number of zenith angles and the relationship
between shower size and atmospheric depth has been derived for a number of integral cosmic-ray fluxes. These measurements
extend the available data to ∼ 1400 g·cm−2 and emphasize the discrepancy between measurements made on Mt. Chacaltaya and those made at other observatories.
Riassunto Sono state fatte misurazioni dello spettro delle dimensioni a livello del mare di sciami di raggi cosmici ad un certo numero di angoli zenitali ed è stata dedotta la relazione tra la grandezza dello sciame e la profondità atmosferica per un certo numero di flussi integrali di raggi cosmici. Queste misurazioni estendono i dati disponibili a∼1400 g·cm−2 ed evidenziano la discrepanza tra le misurazioni fatte sul Monte Chalcaltaya e quelle di altri osservatori.
Резюме Проводятся измерения спектра размеров ливней космических лучей на уровне моря при различных зенитных углах и соотношения между размером ливня и толщиной атмосферы для ряда интегральных потоков космических лучей. Эти измерения уточняют имеющиеся данные до толщии∼1400 г·см−2. Отмечается расхождение между измерениями, проведенными на горе Чакалтайа, и измерениями в других обсерваториях.相似文献
2.
3.
Treatment of pyridine borane (Py.BH3) with iodine, bromine, or strong acids affords activated Py.BH2X complexes that are capable of hydroborating alkenes at room temperature. Evidence is presented for an unusual hydroboration mechanism involving leaving group displacement. In contrast to THF.BH3, hydroboration with Py.BH2I selectively affords the monoadducts. The crude hydroboration products are converted into synthetically useful potassium alkyltrifluoroborate salts upon treatment with methanolic KHF2. 相似文献
4.
Analysis of the ratio of transverse and longitudinal relaxation rates (R2/R1) is an approach commonly used for estimation of overall correlation time and identification of chemical exchange in biological macromolecules. However, this analysis fails to distinguish between chemical exchange and motional anisotropy. We describe a simple method for identifying chemical exchange and motional anisotropy using the product, R1R2. In the slow tumbling regime, the R1R2 product results in a constant value that is independent of overall correlation time and motional anisotropy. This analysis provides a simple method for rapidly estimating and dissociating the effects of motional anisotropy and chemical exchange in NMR heteronuclear spin relaxation data. We demonstrate the utility of the method with 15N relaxation data collected on the proteins E. coli ribonuclease H and the trimeric E. coli membrane associated lipoprotein lpp. 相似文献
5.
Smith AB Doughty VA Sfouggatakis C Bennett CS Koyanagi J Takeuchi M 《Organic letters》2002,4(5):783-786
[reaction: see text] A short, efficient, and stereocontrolled synthesis of (-)-4, an advanced ABCD subunit of the spongistatins, has been achieved. Central to the synthetic strategy is the multicomponent linchpin union of silyl dithianes with epoxides to access both the AB and CD fragments. Fragment coupling was then achieved via an efficient stereoselective aldol reaction. The linear sequence required 22 steps and proceeded in 4.0% overall yield. 相似文献
6.
NEW PHTHALOCYANINE PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY 总被引:2,自引:1,他引:2
Nancy L. Oleinick Antonio R. Antunez Marian E. Clay Boris D. Rihter Malcolm E. Kenney 《Photochemistry and photobiology》1993,57(2):242-247
Six new aluminum and silicon phthalocyanines have been synthesized and their photocytotoxicity toward V79 cells has been studied. The compounds that have been prepared are: AIPcOSi(CH3)2(CH2),N(CH3)2, I; AIPcOSi(CH3)2(CH2)3N(CH3)3+I?, II; CH3SiPcOSi(CH3)2(CH2)3N(CH3)2, III; HOSiPcOSi(CH3)2(CH2)3N(CH3)2, IV; HOSiPcOSi(CH3)2(CH2)3)3(CH3)3+I?, V; and SiPc[OSi(CH3)2(CH2)3N(CH3)3+I?]2, VI. Relative growth delay values for compounds I-VI and relative cytotoxicity values for compounds I, II, IV, V and VI have been determined. Compounds I and II have been shown to be comparable in photocytotoxicity to what is presumed to be AIPcOH.xH2O, and compound IV has been shown to have greater activity. The classes of compounds to which these six compounds belong appear to have potential for photodynamic therapy. 相似文献
7.
Narayani Ramakrishnan Nancy L. Oleinick Marian E. Clay Min-Fen Horng Antonio R. Antunez Helen H. Evans 《Photochemistry and photobiology》1989,50(3):373-378
Two closely related strains of mouse lymphoma L5178Y cells, LY-R and LY-S, have been found to differ in their sensitivity to the cytotoxic effects of photodynamic treatment (PDT) with chloroaluminum phthalocyanine (CAPC) and red light. Strain LY-R is more sensitive to photodynamic cell killing than strain LY-S. Differences in uptake of CAPC could not account for the differences in cytotoxic effects. There was no marked difference between the two strains in the induction of single-strand breaks (which includes frank single-strand breaks and alkali-labile lesions), but substantially more DNA-protein cross-links were formed in strain LY-R by CAPC and light. Repair of single-strand breaks proceeded with similar kinetics in both strains for the first 30 min post-irradiation, suggesting that these lesions are not responsible for the differential sensitivity of the two strains to the lethal effects of photodynamic treatment. Thereafter, alkaline elution revealed the presence of increasing DNA strand breakage in strain LY-R. DNA degradation, as measured by the conversion of prelabeled [14C] DNA to acid-soluble radioactivity, was more rapid and extensive in strain LY-R. 相似文献
8.
Marcus RK Davis WC Knippel BC LaMotte L Hill TA Perahia D Jenkins JD 《Journal of chromatography. A》2003,986(1):17-31
A method utilizing capillary-channeled polymer (C-CP) fibers as stationary phases in high-performance liquid chromatographic separations has been investigated. Polymeric fibers of differing backbones (polypropylene and polyester) having nominal diameters of approximately 50 and approximately 35 microm and a channeled structure on their periphery were packed into stainless steel tubing (305 x 4.6 mm I.D.) for use in reversed-phase separations of various mixtures. The fibers have eight channels running continuously along the axis which exhibit very high surface activity. As such, solvent transport is affected through the channels through wicking action. Bundles of 1000-3000 fibers are loaded co-linearly into the tubing, providing flow channels extending the entire length of the columns. As a result, backing pressures are significantly lowered (approximately 50% reduction) in comparison to packed-sphere columns. In addition, the capital costs of the fiber material (< US$0.25 per column) are very attractive. Flow-rates of up to 5 ml/min can be used to achieve near baseline separation of related compounds in reasonable run times, indicating very fast mobile phase mass transfer (C-terms). The polymer stationary phases demonstrate high selectivity for a wide variety of analytes with gradient elution employed successfully in many instances. Specifically, separations of three polyaromatic hydrocarbons (benzo[a]pyrene, chrysene, pyrene), mixtures of both organic and inorganic lead compounds [chlorotriethyllead, chlorotriphenyllead, lead nitrate, lead(II) phthalocyanine], and a lipid standard of triglycerides were accomplished on the polymeric stationary phases. Other species of biological interest, including groups of aliphatic and aromatic amino acids have also been effectively separated. The reversed-phase nature of the fiber surfaces is supported through atomic force microscopy measurements using hydrophilic and hydrophobic functionalized polystyrene beads as the probe tips. Separations of the various analytes demonstrate the feasibility of utilizing C-CP fibers as stationary phases in reversed-phase LC. It is envisioned that columns of this nature would be particularly useful in prep-scale separations as well as for immobilization matrices for organic constituents in aqueous environments. 相似文献
9.
Narayani Ramakrishnan Marian E. Clay Liang-YAN Xue Helen H. Evans Antonio Rodriguez-Antunez Nancy L. Oleinick 《Photochemistry and photobiology》1988,48(3):297-303
Abstract— Chloroaluminum phthalocyanine (CAPC) is an efficient photosensitizer for the inactivation of Chinese hamster V79 cells. In order to investigate possible molecular mechanisms in the photo-dynamic action of CAPC and visible light, the induction and repair rate of two classes of DNA lesions have been determined, i.e. DNA single-strand breaks and DNA-protein cross-links. In cells pretreated with 1 μ.M CAPC, a fluence of 12 kJ/m2 of red light (>600 nm) kills approximately 50% of the cells and induces 3 to 3.5 Gy-equivalents of single-strand breaks. The repair of these breaks was slower than the repair of single-strand breaks induced by -irradiation. The photodynamic action of CAPC also induces a large number of DNA-protein cross-links which, in contrast to -radiation-induced DNA-protein cross-links, do not appear to be repaired during 4 h of post-treatment incubation in fresh medium. These studies suggest that DNA may be an important target for the cytotoxicity of CAPC + red light. 相似文献
10.
Clay A. Henry Mel Judy Barbara Dyer Martin Wagner James L. Matthews 《Photochemistry and photobiology》1995,61(4):410-413
Abstract— The phototoxicity of argon laser irradiation was studied in aqueous suspensions of Porphyromonas endodontalis (American Type Culture Collection [ATCC] 35406), Porphyromonas gingivalis (ATCC 33277), Prevotella denticola (ATCC 33184) and two strains of Prevotella intermedia (ATCC 15033 and 49046), all "black-pigmented bacteria," BPB, that accumulate cellular porphyrins. Several of these species have been implicated in the etiology of Periodontol disease. Non-black-pigmented bacteria were also studied to test the specificity of irradiation as a potential photodynamic treatment for Periodontol infections. Cell suspensions were irradiated with an argon laser at fluences of 20–200 J/cm2 . When cultured in hemin-supplemented media, ATCC 15033 was the most sensitive to irradiation. However, a second strain of the same species (ATCC 49046) was resistant. The photosensitivity of other species ranked ATCC 33277 > 35406 = 33184 = 35496. When hemin was replaced in media by hemoglobin, ATCC 33277 became resistant to irradiation. Protoporphyrin IX content in BPB cells was shown not to be a major factor determining photosensitivity. Oxygen was required during irradiation for BPB species to be affected. Non-black-pigmented bacteria were much less sensitive to irradiation than BPB. 相似文献