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211.
Silvana Halac Ernesto García-Mendoza Anastazia T. Banaszak 《Photochemistry and photobiology》2009,85(3):807-815
This study demonstrates that UV radiation (UVR) reduces the photoprotective capacity of the diatom Phaeodactylum tricornutum by affecting xanthophyll cycle (XC) activity. The short‐term reduction of photosystem II (PSII) maximum efficiency of charge separation (Fv/Fm) in cells exposed to UVR could be explained mainly by a reduced photoprotective capacity under this condition. Phaeodactylum tricornutum cells acclimated to two different photosynthetically active radiation (PAR) intensities, high light (HL, 200 μmol quanta m?2 s?1) and low light (LL, 50 μmol quanta m?2 s?1), were exposed to saturating irradiance (1100 μmol quanta m?2 s?1) in the presence (PAR + UVR) and absence of UVR (PAR). HL cells exhibited a greater reduction in Fv/Fm in PAR + UVR when compared with the PAR treatment that was related to a reduction in the de‐epoxidation of XC pigments. In contrast, in LL cells, UVR did not considerably affect XC de‐epoxidation even though the reduction in Fv/Fm was greater than in HL cells. The negative effect of UVR on photoprotection was more pronounced in HL cells because they synthesized more XC pigments than LL cells. This was confirmed when XC activity was blocked with dithiothreitol and when PSII repair was inhibited with chloramphenicol (CAP). The differential reduction of Fv/Fm between PAR + UVR and PAR treatments disappeared when XC was blocked in HL cells. A higher reduction and an incomplete recovery of Fv/Fm were observed in cells incubated with CAP in the presence of UVR. Such responses confirm that UVR had a negative effect on photoprotective mechanisms causing an enhancement of damage by PAR, especially in HL‐acclimated cells in which heat dissipation is important for PSII regulation. 相似文献
212.
Lisia M.G. dos Santos Rennan G.O. Araujo Silvana do C. Jacob Helmut Becker-Ross 《Talanta》2009,78(2):577-583
Cadmium and iron are antagonistic elements in the sense that they produce different effects in the human body. Both elements have to be determined routinely in grain products, cadmium because of its toxicity, and iron because all grain products, according to Brazilian law, have to contain a minimum of 42 mg kg−1 Fe to combat anemia. A routine screening method has been developed for the quasi simultaneous determination of cadmium and iron using high-resolution continuum source electrothermal atomic absorption spectrometry and direct solid sampling. The primary absorption line at 228.802 nm has been used for Cd, and an adjacent secondary line at 228.726 nm for the determination of Fe. Various chemical modifiers have been investigated, and a mixture of tungsten and iridium, applied as a permanent modifier, showed the best performance; it stabilized Cd up to a pyrolysis temperature of 700 °C and did not over-stabilize Fe. Two atomization temperatures were used sequentially, 1700 °C for Cd and 2600 °C for Fe, because of their significantly different volatilities. The characteristic masses obtained were 0.9 pg for Cd and 1.2 ng for Fe. The limits of detection (3σ, n = 10) were 0.6 μg kg−1 for Cd and 0.5 mg kg−1 for Fe. The relative standard deviation ranged from 3 to 7% for Cd and from 4 to 13% for Fe, which is satisfactory for the purpose. The accuracy of the method was confirmed by the analysis of three certified reference materials; the results were in agreement with the certified values at a 95% confidence interval. The Cd content in the investigated grain products was between 0.9 and 10.5 μg kg−1, but most of them did not contain the required minimum amount of iron. 相似文献
213.
Tandem mass spectrometry has been applied to differentiate three sets of o-, m- and p-methyl, -methoxy and -nitro-substituted-6-phenyl-dibenzo(d,f)(1,3)dioxepines. Collision-induced dissociation (CID) experiments have been carried out on 2-phenylbenzo[b]furan fragment ions, which originate from the decomposition of the molecular ions after their EI-induced isomerization to spirocyclic structures. With the exception of m- and p-methylphenylbenzo[b]furan isomers, which display identical CID mass spectra, the three isomeric methoxy- and nitrophenylbenzo[b]furan fragment ions display very characteristic CID behavior which allows unequivocal differentiation of the 6-phenyl-dibenzo(d,f)(1,3)dioxepine isomers. 6-(o-nitrophenyl)-dibenzo(d,f)(1,3)dioxepine isomer, does not form a 2-(o-nitrophenyl)benzo[b]furan ion and, therefore, it can be differentiated from the m- and p- isomers based on the mere EI mass spectra. Furthermore, it shows a characteristic ion most likely due to an ortho effect between the nitro group and the dioxepine ring. Multiple stage mass spectrometric techniques (MSn), labeled derivatives and reference compounds were used in order to gain additional information on the structures of product ion from the CID fragmentation. 相似文献
214.
In the present Letter we discuss the role of different boundary conditions on the Casimir effect between parallel lines in a planar (2+1) system, specifically in the context of a Maxwell theory with a Chern-Simons mass term. We consider parallel lines of a different nature, namely a perfectly conducting line and an infinitely permeable one. We also discuss the case of two infinitely permeable lines. We compare our results with those found in the literature for the case of two perfectly conducting lines. 相似文献
215.
Cordeiro RS Scarano WR Campos SG Santos FC Vilamaior PS Góes RM Taboga SR 《Micron (Oxford, England : 1993)》2008,39(8):1312-1324
The normal growth, differentiation and maintenance of the morphofunctional integrity of the prostate gland are dependent on the interaction of constant levels of androgens with their receptors. The need to study the responses to hormones under several conditions and the effect of their blockage is due to the fact that the human prostate is the site of a great number of age-related diseases, and the ones with a major medical importance are prostate cancer (CaP) and benign prostatic hyperplasia (BPH), which can both be treated with androgen suppression. Seventy-five male gerbils were divided, randomly, into 3 groups of 25 animals each, where each group corresponded to one phase of postnatal development. In each phase, it was possible to morphologically and stereologically analyze the compartments of prostatic ventral lobe, as well as to immunohistochemically analyze the degree of expression of androgen receptors (ARs) after the androgen blockage therapies. In addition, it was possible to establish the hormonal dosage of serum testosterone levels given the comparative approach of the expression of androgen receptors. There is a pattern of AR distribution in the prostatic ventral lobe throughout postnatal development, in which the younger the animal is the higher, the interaction of circulating androgens that stimulate the AR expression in both the epithelial and stromal compartments. The androgen blockage therapies decreased AR expression in the prostatic compartments, but the androgen reposition after these blockages was not sufficient to recover the glandular structure or stimulate the AR expression up to normal physiological conditions. Both the regulation and distribution of androgen receptors along the gerbil prostatic tissues are complex mechanisms that are likely to be genetically regulated by androgens prenatally or by other factors that are still unknown. This rodent species seems to be a valuable model in the attempt to improve the understanding of the morphophysiological and pathological behavior of this important gland in humans throughout aging and to stimulate new therapeutic ideas to fight prostate cancer. 相似文献
216.
Mario Cetina Ante Nagl Svjetlana Prekupec Silvana Rai‐Mali Mladen Mintas 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(3):o158-o160
In the title compound, C10H14N2O3, a pyrimidine ring is fused with a piperidine ring. The pyrimidine ring is planar, whereas the piperidine ring adopts a half‐chair conformation. The molecules of the title compound are connected via O—H⋯O intermolecular hydrogen bonds into infinite zigzag chains. The pyrimidine ring is involved in three C—H⋯π interactions, which link the hydrogen‐bonded chains into a three‐dimensional framework. 相似文献
217.
Caputo R De Nisco M Festa P Guaragna A Palumbo G Pedatella S 《The Journal of organic chemistry》2004,69(21):7033-7037
4-Deoxy-l-hexoses were synthesized starting from our previously reported reagent 1 and (R)-benzyl glycidyl ether, which led in few steps to a substituted dihydropyran 6. The stereocontrolled hydroxylation of the latter afforded the corresponding 4-deoxy-l-hexoses 7a, 9, and 11. The same procedure, starting from (S)-benzyl glycidyl ether, enabled the preparation of their d-series enantiomers. 相似文献
218.
The author recently proved that 1-cotilting modules are pure-injective;however, the problem of determining whether n-cotilting modulesare pure-injective remained open. In this paper, necessary andsufficient conditions are given for the pure-injectivity ofn-cotilting modules. 2000 Mathematics Subject Classification16D90 (primary), 16D30 (secondary). 相似文献
219.
Silvana Bernasconi Giancarlo Jommi Roberto Pagliarin Paolo Tavecchia 《Journal of heterocyclic chemistry》1988,25(3):725-729
Eight compounds containing N- or N′-alkylated imidazole rings have been synthesized and their structures have been chemically and spectroscopically demonstrated. These molecules, submitted to biological tests in order to evaluate their activity as juvenile hormones, provoke morphological changes in the pupae of Tenebrio Molitor. 相似文献
220.
Riassunto In questo lavoro sono studiati gli isomorfismi tra reticoli di sottogruppi normali di gruppi nilpotenti senza torsione. Si
prova che ogni gruppo iperciclico con la struttura normale di gruppo nilpotente senza torsione è un gruppo nilpotente sanza
torsione.
Summary Lattice isomorphisms between the normal structures of torsion-free nilpotent groups are studied in this paper. We prove that every hypercyclic group with the normal structure of a torsion-free nilpotent group is a torsion-free nilpotent group.相似文献