全文获取类型
收费全文 | 889篇 |
免费 | 42篇 |
专业分类
931篇 |
出版年
2023年 | 7篇 |
2022年 | 4篇 |
2021年 | 19篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 26篇 |
2017年 | 34篇 |
2016年 | 25篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 61篇 |
2012年 | 43篇 |
2011年 | 53篇 |
2010年 | 49篇 |
2009年 | 21篇 |
2008年 | 38篇 |
2007年 | 24篇 |
2006年 | 24篇 |
2005年 | 13篇 |
2004年 | 21篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1971年 | 2篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1955年 | 29篇 |
1954年 | 77篇 |
1953年 | 42篇 |
1952年 | 27篇 |
1951年 | 22篇 |
1950年 | 59篇 |
1949年 | 12篇 |
1948年 | 5篇 |
1947年 | 3篇 |
1937年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有931条查询结果,搜索用时 0 毫秒
121.
JarosŁaw Ruczyński Brygida Lewandowska Piotr Mucha Piotr Rekowski 《Journal of peptide science》2008,14(3):335-341
The sequence-dependent, acid- or base-catalysed aspartimide formation is one of the most serious side reactions in solid-phase synthesis of peptides containing aspartic acid. In the present work, we investigated the susceptibility of 4-(N-[1-(4,4-dimethyl-2,6-dioxocyclohexylidene)-3-methylbutyl]amino)benzyl (Dmab), an aspartic acid beta-carboxy side-chain protecting group, for aspartimide formation. As a model, 15-amino acid-residue galanin fragment analogue containing the Asp-Ala motif was used during Fmoc-based solid-phase synthesis. Our study showed a strong tendency of Dmab-protected peptide to form aspartimide with unusual high efficiency. Furthermore, to investigate the susceptibility of Asp-Ala motif for aspartimide formation during the synthesis using Asp(ODmab), a 5-amino acid-residue galanin fragment LGPDA, different types of resin linkers, variety of Fmoc-deprotection conditions and coupling methods were applied. 相似文献
122.
Biodegradation of diesel fuel by a microbial consortium in the presence of 1-alkoxymethyl-2-methyl-5-hydroxypyridinium chloride homologues 总被引:1,自引:0,他引:1
Łukasz Chrzanowski Monika Stasiewicz Mikołaj Owsianiak Alicja Szulc Agnieszka Piotrowska-Cyplik Agnieszka K. Olejnik-Schmidt Bogdan Wyrwas 《Biodegradation》2009,20(5):661-671
Fast development of ionic liquids as gaining more and more attention valuable chemicals will undoubtedly lead to environmental
pollution. New formulations and application of ionic liquids may result in contamination in the presence of hydrophobic compounds,
such as petroleum mixtures. We hypothesize that in the presence of diesel fuel low-water-soluble ionic liquids may become
more toxic to hydrocarbon-degrading microorganisms. In this study the influence of 1-alkoxymethyl-2-methyl-5-hydroxypyridinium
chloride homologues (side-chain length from C3 to C18) on biodegradation of diesel fuel by a bacterial consortium was investigated. Whereas test performed for the consortium cultivated
on disodium succinate showed that toxicity of the investigated ionic liquids decreased with increase in side-chain length,
only higher homologues (C8–C18) caused a decrease in diesel fuel biodegradation. As a result of exposure to toxic compounds also modification in cell surface
hydrophobicity was observed (MATH). Disulphine blue active substances method was employed to determine partitioning index
of ionic liquids between water and diesel fuel phase, which varied from 1.1 to 51% for C3 and C18 homologues, respectively. We conclude that in the presence of hydrocarbons acting as a solvent, the increased bioavailability
of hydrophobic homologues is responsible for the decrease in biodegradation efficiency of diesel fuel. 相似文献
123.
M. Parczewski M. Leszczyszyn-Pynka M. Kaczmarczyk G. Adler A. Bińczak-Kuleta B. Łoniewska A. Boroń-Kaczmarska A. Ciechanowicz 《Journal of applied genetics》2009,50(2):159-166
Genetic susceptibility to HIV infection was previously proven to be influenced by some chemokine receptor polymorphisms clustering
on chromosome 3p21. Here the influence of 5 genetic variants was studied: Δ32CCR5, G(-2459)ACCR5, G190ACCR2, G744ACX3CR1 and C838TCX3CR1. They were screened in a cohort of 168 HIV-1 positive adults [HIV(+) group] and 151 newborns [control group] from northwestern
Poland. PCR-RFLP was performed to screen for the variants (except for A32CCR5 polymorphism, where PCR fragment size was sufficient to identify the alleles) and then electrophoresed on agarose gel to
determine fragment size. Distribution of genotypes and alleles was not significantly different between the groups except for
theCCR5 polymorphisms, with the A32 allele and the (-2459)ACCR5 allele more frequent among neonates than in the HIV(+) group. No Δ32/Δ32 homozygotes were found in the HIV(+) group, but
16.1% were Δ32/wt heterozygotes. In the control group, 1.3% were Δ32/Δ32 homozygotes and 26.0% were Δ32/wt heterozygotes.
Linkage between the chemokine polymorphisms was calculated using the most informative loci for haplotype reconstruction. Haplotypes
containing Δ32 CCR5,190GCCR2 and 744ACX3CR1 were found to be significantly more common in the control group. This suggests an association between these haplotypes and
resistance to HIV-1 infection. 相似文献
124.
125.
Olga Wesołowska Andrzej B. Hendrich Barbara Łania-Pietrzak Jerzy Wiśniewski Joseph Molnar Imre Ocsovszki Krystyna Michalak 《Cellular & molecular biology letters》2009,14(2):199-221
The expression of transmembrane transporter multidrug resistance-associated protein 1 (MRP1) confers the multidrug-resistant
phenotype (MDR) on cancer cells. Since the activity of the other MDR transporter, P-glycoprotein, is sensitive to membrane
perturbation, we aimed to check whether the changes in lipid bilayer properties induced by flavones (apigenin, acacetin) and
flavonols (morin, myricetin) were related to their MRP1 inhibitory activity. All the flavonoids inhibited the efflux of MRP1
fluorescent substrate from human erythrocytes and breast cancer cells. Morin was also found to stimulate the ATPase activity
of erythrocyte ghosts. All flavonoids intercalated into phosphatidylcholine bilayers as judged by differential scanning calorimetry
and fluorescence spectroscopy with the use of two carbocyanine dyes. The model of an intramembrane localization for flavones
and flavonols was proposed. No clear relationship was found between the membrane-perturbing activity of flavonoids and their
potency to inhibit MRP1. We concluded that mechanisms other than perturbation of the lipid phase of membranes were responsible
for inhibition of MRP1 by the flavonoids. 相似文献
126.
Łysek R Schütz C Favre S O'Sullivan AC Pillonel C Krülle T Jung PM Clotet-Codina I Esté JA Vogel P 《Bioorganic & medicinal chemistry》2006,14(18):6255-6282
A solid-phase synthesis of new N-substituted valienamines has been developed and new synthesis of (+/-)-conduramine F-1, (-)-conduramine F-1, and (+)-ent-conduramine F-1 is presented, together with the preparation of N-benzylated conduramines F-1. N-Benzylation of both valienamine and (+)-ent-conduramine F-1 improves their inhibitory activity toward alpha-glucosidases significantly. The additional hydroxymethyl group makes valienamine derivatives more active than their (+)-ent-conduramine F-1 analogues. 相似文献
127.
Pex11 is a key player in peroxisome proliferation, but the molecular mechanisms of its function are still unknown. Here, we show that Pex11 contains a conserved sequence at the N-terminus that can adopt the structure of an amphipathic helix. Using Penicillium chrysogenum Pex11, we show that this amphipathic helix, termed Pex11-Amph, associates with liposomes in vitro. This interaction is especially evident when negatively charged liposomes are used with a phospholipid content resembling that of peroxisomal membranes. Binding of Pex11-Amph to negatively charged membrane vesicles resulted in strong tubulation. This tubulation of vesicles was also observed when the entire soluble N-terminal domain of Pex11 was used. Using mutant peptides, we demonstrate that maintaining the amphipathic properties of Pex11-Amph in conjunction with retaining its α-helical structure are crucial for its function. We show that the membrane remodelling capacity of the amphipathic helix in Pex11 is conserved from yeast to man. Finally, we demonstrate that mutations abolishing the membrane remodelling activity of the Pex11-Amph domain also hamper the function of full-length Pex11 in peroxisome fission in vivo. 相似文献
128.
PAWEŁ FILIPIAK MICHAŁ ZATOŃ 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2011,44(4):397-409
Filipiak, P. & Zatoń, M. 2010: Plant and animal cuticle remains from the Lower Devonian of southern Poland and their palaeoenvironmental significance. Lethaia, Vol. 44, pp. 397–409. Assemblages of plant and arthropod remains are reported from the Lower Devonian clastic deposits of the Upper Silesian and Ma?opolska blocks in southern Poland. Most of the plant and animal remains are palynologically dated as Pragian–Emsian/Eifelian. The plant material comprises higher plant cuticles with stomata classified as Drephanophycus and Sawdonia, and more enigmatic remains (nematophytes) classified as Nematothallus, Cosmochlaina and tubular banded tubes. They are associated with abundant and diverse miospores. Animal remains consist of eurypterid respiratory organs, the morphology of which may presumably point to their advance physiological properties, and cuticular remains of eurypterid and probably scorpion origin, as well as some remains of unknown affinity. The presence of such mixed assemblages in the Lower Devonian of Poland indicate marginal‐marine and/or alluvial environments spreading in the southern margin of the Old Red Continent. The dominance of land‐derived plant remains and simultaneous scarcity of marine acritarchs indicate that the environment was very weakly influenced by marine conditions. If nematophytes were really related to extant liverworts, as suggested by some workers, they, together with the other associated spore‐producing plants, may strongly indicate moist environmental conditions, which may have offered suitable habitats for temporary eurypterid migrations onto land. □Cuticles, eurypterids, Lower Devonian, nematophytes, Poland, spores. 相似文献
129.
Paweł Łaniewski Maciej Kuczkowski Klaudia Chrząstek Anna Woźniak Agnieszka Wyszyńska Alina Wieliczko Elżbieta Katarzyna Jagusztyn-Krynicka 《World journal of microbiology & biotechnology》2014,30(1):281-292
Campylobacter spp. are regarded as the most common bacterial cause of gastroenteritis worldwide, and consumption of chicken meat contaminated by Campylobacter is considered to be one of the most frequent sources of human infection in developed countries. Here we evaluated the immunogenicity and protective efficacy of Salmonella Typhimurium χ9718 producing the Campylobacter jejuni CjaA protein as a chicken anti-Campylobacter vaccine. In this study chickens were orally immunized with a new generation S. Typhimurium strain χ9718 with regulated delayed attenuation in vivo and displaying delayed antigen expression. The immunization with the S. Typhimurium χ9718 strain producing C. jejuni CjaA antigen induced strong immune responses against CjaA in both serum IgY and intestinal IgA, however, it did not result in the significant reduction of intestinal colonization by Campylobacter strain. The low level of protection might arise due to a lack of T cell response. Our results demonstrated that a Salmonella strain with regulated delayed attenuation and displaying regulated delayed antigen expression might be an efficient vector to induce immune response against Campylobacter. It seems that an efficient anti-Campylobacter subunit vaccine should be multicomponent. Since S. Typhimurium χ9718 contains two compatible balanced-lethal plasmids, it can provide the opportunity of cloning several Campylobacter genes encoding immunodominant proteins. It may also be used as a delivery vector of eukaryotic genes encoding immunostimulatory molecules to enhance or modulate functioning of chicken immune system. 相似文献
130.