全文获取类型
收费全文 | 3465篇 |
免费 | 214篇 |
国内免费 | 2篇 |
专业分类
3681篇 |
出版年
2023年 | 18篇 |
2022年 | 58篇 |
2021年 | 98篇 |
2020年 | 63篇 |
2019年 | 77篇 |
2018年 | 108篇 |
2017年 | 89篇 |
2016年 | 120篇 |
2015年 | 207篇 |
2014年 | 209篇 |
2013年 | 266篇 |
2012年 | 300篇 |
2011年 | 323篇 |
2010年 | 164篇 |
2009年 | 156篇 |
2008年 | 190篇 |
2007年 | 193篇 |
2006年 | 173篇 |
2005年 | 180篇 |
2004年 | 155篇 |
2003年 | 145篇 |
2002年 | 135篇 |
2001年 | 30篇 |
2000年 | 19篇 |
1999年 | 22篇 |
1998年 | 24篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1978年 | 6篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1958年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有3681条查询结果,搜索用时 9 毫秒
51.
Graziano Di Giuseppe Michele Barbieri Adriana Vallesi Pierangelo Luporini Fernando Dini 《Molecular ecology》2013,22(15):4029-4037
Nuclear (18S and ITS) and mitochondrial (16S) ribosomal RNA gene sequences were determined from genetically distinct wild‐type strains of Antarctic (nine strains), Fuegian (four strains), Greenland (nine strains) and Svalbard (three strains) populations of the marine ciliate, Euplotes nobilii, and analysed for their nucleotide polymorphisms. A close genetic homogeneity was found within and between the Antarctic and Fuegian populations, while more significant levels of genetic differentiation were detected within and between the two Arctic populations, as well as between these populations and the Antarctic/Fuegian ones. The phylogeographical pattern that was derived from these data indicates that gene flow is not limited among Arctic populations; it equally connects the Arctic and Antarctic populations either directly, or through the Fuegian population. This indication reinforces previous evidence from laboratory assays of mating interactions between some of the strains analysed in this work that Southern and Northern polar populations of E. nobilii belong to a unique, panmictic population that substantially share the same gene pool. 相似文献
52.
Morphology and molecular phylogeny constitute the structural elements of diatom taxonomy. These approaches do not, however, give information on the functioning of taxa. Additional methods to serve a more integrated and wide-ranging taxonomy have therefore been called for. Metabolic fingerprinting is one approach used within the field of metabolomics, often applied in classification of samples. Here we apply metabolic fingerprinting in a taxonomic study of a cryptic diatom species. Strains of the cosmopolitan diatom Chaetoceros socialis from two geographical areas; the north-east Atlantic and Arctic and the Gulf of Naples, were cultivated at three different temperatures; 2.5, 8 and 13°C. The strains from the two different geographical areas exhibited different growth rates as well as different photosynthetic efficiencies. Algal extracts, collected at the end of the growth experiments, were analysed by Ultra-Performance Liquid Chromatography High Resolution Mass Spectrometry. The two groups of strains were separated by principal component analysis of their metabolic fingerprints. Analysis of the data revealed both qualitative and quantitative differences in metabolite markers. These phenotypic differences reinforce differences also found for morphology, phylogenetic markers and growth rates, and point at different adaptive characteristics in organisms living under different temperature regimes. 相似文献
53.
Adriana Fonseca Marques Daniel Esser Philip J. Rosenthal Matthias U. Kassack Luis Mauricio T.R. Lima 《Bioorganic & medicinal chemistry》2013,21(13):3667-3673
Falcipain-2 is a cysteine protease of the malaria parasite Plasmodium falciparum that plays a key role in the hydrolysis of hemoglobin, a process that is required by intraerythrocytic parasites to obtain amino acids. In this work we show that the polysulfonated napthylurea suramin is capable of binding to falcipain-2, inhibiting its catalytic activity at nanomolar concentrations against both synthetic substrates and the natural substrate hemoglobin. Kinetic measurements suggest that the inhibition occurs through an noncompetitive allosteric mechanism, eliciting substrate inhibition. Smaller suramin analogues and those with substituted methyl groups also showed inhibition within the nanomolar range. Our results identify the suramin family as a potential starting point for the design of falcipain-2 inhibitor antimalarials that act through a novel inhibition mechanism. 相似文献
54.
María Teresa Aguirrezabala-Cámpano Reyna Ivonne Torres-Acosta Alejandro Blanco-Labra Ma. Elizabeth Mediola-Olaya Sugey Ramona Sinagawa-García Adriana Gutiérrez-Díez Jorge Ariel Torres-Castillo 《Journal of plant biochemistry and biotechnology.》2013,22(3):261-268
Seed proteins recovered after heating a seed extract from Opuntia joconostle Weber (xoconostle, an acid cactus pear) were screened for different biochemical activities, detecting only trypsin-like inhibitory activity. Two trypsin-like inhibitor forms from seeds were separated by RP-HPLC and partially sequenced and characterized as an enriched mixture. They were evaluated for inhibition on several serine proteinases, but only trypsin-like inhibition was detected by the inhibitor extract. The two isolated forms, OjTI 1 and OjTI 2 showed low molecular weights of 4.26 and 4.17 kDa as determined by mass spectrometry. An enriched inhibitory fraction showed a high thermal stability by retaining the activity after heating the sample for 1 h at 90 °C, as well as after heating for at 120 °C under 1 kg/cm2 for 15 min at different pH values. Partial sequence of the two forms was determined by mass spectrometry indicating that they were similar and after alignments analysis they showed the highest similarity with the trypsin inhibitor from O. streptacantha and to a lesser extent to other trypsin inhibitors of the MEROPS database families. The inhibitory spectrum was evaluated against several digestive enzymes from pests and beneficial insects from several taxonomic orders. 相似文献
55.
Giselle X. Perazzo Rafael B. Noleto Marcelo R. Vicari Adriana Gava Marta M. Cestari 《Zoology (Jena, Germany)》2013,116(5):286-292
Chromosomal rearrangements such as inversions can facilitate speciation even in the presence of gene flow. The present study aims to analyze the karyotypic variation in six populations of Geophagus brasiliensis from southern Brazil. All specimens showed 2n = 48 chromosomes, but three karyotypes were found to have one, two or three pairs of submetacentric chromosomes. Although G. brasiliensis did not exhibit variation in the diploid number, it presented a wide interpopulational variation mainly regarding the karyotype formula and specific chromosomal markers. Differences in the location of the major and minor rDNA loci were observed among the populations. Moreover, different patterns were observed in the distribution of the constitutive heterochromatin, presenting intra- and interpopulational variation. This supports the hypothesis that this taxon represents a complex species or that cryptic species are included in this group, indicating a possibleprocess of sympatric speciation. By potentially restricting gene flow between heterokaryotypes, the segregating chromosome rearrangements we describe for G. brasiliensis may play a role in diversification in this species complex. 相似文献
56.
57.
Adriana Pacheco Ileana Hernández‐Mireles Cecilia García‐Martínez Mario M. Álvarez 《Biotechnology progress》2013,29(3):638-644
High‐throughput platforms for microalgae screening are not yet commercially available. In this study, the feasibility of 96‐well microplates was analyzed for microalgae research. Equivalence among wells, as culture microreactors, was investigated in controlled high CO2 conditions. Specific growth rates of two microalgae species, Scenedesmus sp. UTEX1589 and an environmental isolate, were significantly higher in border wells than in internal positions. Furthermore, growth rate gradients analyzed as contours throughout the platform were observed for Scenedesmus sp. However, the output variable exhibited high precision associated with a low coefficient of variation (CV), between 6.8 and 7.8%. In a demonstrative experiment to determine the effect of culture media dilution on six microalgae species, treatments were randomized in the central subset of a microplate. Results were consistent and statistically sound (CV 9.4–12.9%), and showed that microalgae species could grow with no detrimental effect in 50% (v/v) dilution of the culture medium. Provided border wells exclusion and a randomized design, 96‐well microplates are a practical and statistical robust platform for microalgae research. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:638–644, 2013 相似文献
58.
Mercedes Ferrando Xinhai Wan Roberto Meiss Jun Yang Adriana De Siervi Nora Navone Elba Vazquez 《PloS one》2013,8(11)
Prostate cancer (PCa) is a leading cause of death among males. It is currently estimated that inflammatory responses are linked to 15-20% of all deaths from cancer worldwide. PCa is dominated by complications arising from metastasis to the bone where the tumor cells interact with the bone microenvironment impairing the balance between bone formation and degradation. However, the molecular nature of this interaction is not completely understood. Heme oxygenase-1 (HO-1) counteracts oxidative damage and inflammation. Previous studies from our laboratory showed that HO-1 is implicated in PCa, demonstrating that endogenous HO-1 inhibits bone derived-prostate cancer cells proliferation, invasion and migration and decreases tumor growth and angiogenesis in vivo. The aim of this work was to analyze the impact of HO-1 modulated PCa cells on osteoblasts proliferation in vitro and on bone remodeling in vivo. Using a co-culture system of PC3 cells with primary mice osteoblasts (PMOs), we demonstrated that HO-1 pharmacological induction (hemin treatment) abrogated the diminution of PMOs proliferation induced by PCa cells and decreased the expression of osteoclast-modulating factors in osteoblasts. No changes were detected in the expression of genes involved in osteoblasts differentiation. However, co-culture of hemin pre-treated PC3 cells (PC3 Hem) with PMOs provoked an oxidative status and activated FoxO signaling in osteoblasts. The percentage of active osteoblasts positive for HO-1 increased in calvarias explants co-cultured with PC3 Hem cells. Nuclear HO-1 expression was detected in tumors generated by in vivo bone injection of HO-1 stable transfected PC3 (PC3HO-1) cells in the femur of SCID mice. These results suggest that HO-1 has the potential to modify the bone microenvironment impacting on PCa bone metastasis. 相似文献
59.
Esteban Benjamin Sir Eric Kuhnert Christopher Lambert Adriana I. Hladki Andrea I. Romero Marc Stadler 《Mycological Progress》2016,15(4):42
A preliminary account of Hypoxylon species (Xylariaceae) from the hitherto widely unexplored “Yungas” mountain forests of Northwest Argentina is presented. Two new species are described based on extensive morphological, molecular (ITS region of rDNA, partial β-tubulin gene) and chemotaxonomic data. Hypoxylon spegazzinianum is close to H. erythrostroma, but differs by larger ascospores and a virgariella-like asexual morph. Hypoxylon calileguense resembles H. subgilvum when growing on wood, but can be distinguished by larger ascospores and a fawn to brick stromatal surface colour. Stromata found on bark have affinities to H. pelliculosum, but differ in their stromatal surface colour and conspicuous amyloid apical apparatus. In addition, nine taxa of Hypoxylon are reported for Argentina for the first time, and some details on their asexual state and stromatal secondary metabolites are reported. An updated dichotomous key for Hypoxylon species from Argentina is provided. 相似文献