全文获取类型
收费全文 | 6195篇 |
免费 | 441篇 |
国内免费 | 2篇 |
出版年
2023年 | 33篇 |
2022年 | 86篇 |
2021年 | 157篇 |
2020年 | 82篇 |
2019年 | 115篇 |
2018年 | 140篇 |
2017年 | 115篇 |
2016年 | 199篇 |
2015年 | 327篇 |
2014年 | 357篇 |
2013年 | 410篇 |
2012年 | 583篇 |
2011年 | 543篇 |
2010年 | 327篇 |
2009年 | 302篇 |
2008年 | 367篇 |
2007年 | 338篇 |
2006年 | 288篇 |
2005年 | 292篇 |
2004年 | 287篇 |
2003年 | 246篇 |
2002年 | 223篇 |
2001年 | 60篇 |
2000年 | 34篇 |
1999年 | 47篇 |
1998年 | 61篇 |
1997年 | 41篇 |
1996年 | 51篇 |
1995年 | 30篇 |
1994年 | 45篇 |
1993年 | 30篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 35篇 |
1988年 | 17篇 |
1987年 | 25篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 27篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有6638条查询结果,搜索用时 0 毫秒
991.
Collusion-resistant fingerprinting paradigm seems to be a practical solution to the piracy problem as it allows media owners to detect any unauthorized copy and trace it back to the dishonest users. Despite the billionaire losses in the music industry, most of the collusion-resistant fingerprinting systems are devoted to digital images and very few to audio signals. In this paper, state-of-the-art collusion-resistant fingerprinting ideas are extended to audio signals and the corresponding parameters and operation conditions are proposed. Moreover, in order to carry out fingerprint detection using just a fraction of the pirate audio clip, block-based embedding and its corresponding detector is proposed. Extensive simulations show the robustness of the proposed system against average collusion attack. Moreover, by using an efficient Fast Fourier Transform core and standard computer machines it is shown that the proposed system is suitable for real-world scenarios. 相似文献
992.
993.
Nian Zhou Wayne Zeller Jun Zhang Emmanuel Onua Alex S. Kiselyov Jose Ramirez Guðrún Palsdottir Guðrún Halldorsdottir Þorkell Andrésson Mark E. Gurney Jasbir Singh 《Bioorganic & medicinal chemistry letters》2009,19(5):1528-1531
A series of potent and selective EP3 receptor antagonists are described. Utilizing a pharmacophore model developed for the EP3 receptor, a series of 3,4-disubstituted indoles were found to be efficient ligands for this target. These compounds showed high selectivity over IP, FP and other EP receptors. An optimized molecule 7c featured a sound profile and potency in the functional rat and human platelet aggregation assays. 相似文献
994.
995.
Claudia Götz Andreas Gratz Uwe Kucklaender Joachim Jose 《Biochimica et Biophysica Acta (BBA)/General Subjects》2012,1820(7):970-977
BackgroundAbnormally high activity of protein kinase CK2 is linked to various diseases including cancer. Therefore, the inhibition of CK2 is a promising therapeutic strategy to fight this disease.MethodsWe screened a library of synthetic molecules concerning their capacity to inhibit CK2. The activity of CK2 and their IC50 and Ki values were determined by a capillary electrophoresis assay. The effects of the inhibitor in a cell culture model were analyzed by cell counting, a viability assay, cytofluorimetry and Western blot.ResultsThe best CK2 inhibitor found in this screen was 6,7-dichloro-1,4-dihydro-8-hydroxy-4-[(4-methylphenylamino)methylen]dibenzo [b,d]furan-3(2H)-one, which we refer to as “TF”. TF showed tight binding to CK2 with low IC50 (29 nM) and Ki (15 nM) values. TF inhibited only seven out of 61 human kinases tested (> 70% inhibition). Incubation of LNCaP cells with 50 μM TF for 48 h decreased the intracellular CK2 activity by 50%, confirming that the inhibitor is membrane permeable. The decrease in activity was correlated with a severe reduction in cell viability. The reduction in cell viability is at least partly due to the induction of apoptosis.General significanceIn many cancers the protein kinase CK2 is significantly up-regulated and supports the neoplastic phenotype. New therapeutic strategies should be based on diverse reliable inhibitors to reverse the abnormal high levels to normal settings. 相似文献
996.
Vanessa Joglar Xosé Antón Álvarez-Salgado Ana Gago-Martinez Jose M. Leao Clara Pérez-Martínez Benjamin Pontiller Daniel Lundin Jarone Pinhassi Emilio Fernández Eva Teira 《Environmental microbiology》2021,23(3):1559-1583
Cobalamin (B12) is an essential cofactor that is exclusively synthesized by some prokaryotes while many prokaryotes and eukaryotes require an external supply of B12. The spatial and temporal availability of B12 is poorly understood in marine ecosystems. Field measurements of B12 along with a large set of ancillary biotic and abiotic factors were obtained during three oceanographic cruises in the NW Iberian Peninsula, covering different spatial and temporal scales. B12 concentrations were remarkably low (<1.5 pM) in all samples, being significantly higher at the subsurface Eastern North Atlantic Central Water than at shallower depths, suggesting that B12 supply in this water mass is greater than demand. Multiple regression models excluded B12 concentration as predictive variable for phytoplankton biomass or production, regardless of the presence of B12-requiring algae. Prokaryote production was the best predictor for primary production, and eukaryote community composition was better correlated with prokaryote community composition than with nutritional resources, suggesting that biotic interactions play a significant role in regulating microbial communities. Interestingly, co-occurrence network analyses based on 16S and 18S rRNA sequences allowed the identification of significant associations between potential B12 producers and consumers (e.g. Thaumarchaeota and Dynophyceae, or Amylibacter and Ostreococcus respectively), which can now be investigated using model systems in the laboratory. 相似文献
997.
Jaime Pascual Jose Castresana Matti Saraste 《BioEssays : news and reviews in molecular, cellular and developmental biology》1997,19(9):811-817
We now know that the evolution of multidomain proteins has frequently involved genetic duplication events. These, however, are sometimes difficult to trace because of low sequence similarity between duplicated segments. Spectrin, the major component of the membrane skeleton that provides elasticity to the cell, contains tandemly repeated sequences of 106 amino acid residues. The same repeats are also present in α-actinin, dystrophin and utrophin. Sequence alignments and phylogenetic trees of these domains allow us to interpret the evolutionary relationship between these proteins, concluding that spectrin evolved from α-actinin by an elongation process that included two duplications of a block of seven repeats. This analysis shows how a modular protein unit can be used in the evolution of large cytoskeletal structures. 相似文献
998.
Carlos E. Plancha Maria Carmo-Fonseca Jose F. David-Ferreira 《Differentiation; research in biological diversity》1991,48(2):67-74
In vivo obtained golden hamster embryos were used to study, by immunofluorescence and immunoelectron microscopy, the main cytokeratin pattern rearrangements during completion of meiosis and the first cleavage division. Our results point to three major re-organization steps: (1) diffuse immunofluorescent cytokeratin spots characteristic of recently ovulated oocytes rearrange into large cortical patches interconnected by fibrils in one-cell embryos; (2) during mitosis a homogeneous cytokeratin spotty pattern reappears; (3) in two-cell embryos cortical and perinuclear cytokeratin fibrillar networks become prominent. Parthenogenotic oocytes were able to mimic the major cytokeratin patterns observed until the first embryonic mitosis, supporting the concept of a maternally established common response to activation. Despite the lack of fibrillar immunofluorescent reactivity during mitosis, electron microscopy demonstrates persistence of 10 nm filament meshworks. These cytokeratin meshworks often associate with clusters of interchromatinlike granules, which persist in the cytoplasm for a short period after nuclear envelope reassembly. 相似文献
999.
Abstract The nucleotide sequence of a gene coding for a 37 kDa subunit of a cytosolic malate dehydrogenase of Trichomonas vaginalis was established. The sequences of a gDNA clone and a cDNA clone, which lacked seven amino-terminal codons, were identical, indicating an absence of introns from the gene. Cell fractionation combined with sequencing of peptide fragments of the purified enzyme showed that the gene codes for an expressed cytosolic enzyme. The derived amino acid sequence was closely related to cytosolic malate dehydrogenases from animals and plants and from the eubacteria Thermus aquaticus and Mycobacterium leprae and was more distant from the enzyme of mitochondria and from Escherichia coli and certain other eubacteria. In phylogenetic reconstructions this enzyme shared a most recent common ancestor with other cytosolic enzymes. 相似文献
1000.
Jose A. G. Ferreira John C. Penner Richard B. Moss Janus A. J. Haagensen Karl V. Clemons Alfred M. Spormann Hasan Nazik Kevin Cohen Niaz Banaei Elisabete Carolino David A. Stevens 《PloS one》2015,10(8)
Aspergillus fumigatus (Af) and Pseudomonas aeruginosa (Pa) are leading fungal and bacterial pathogens, respectively, in many clinical situations. Relevant to this, their interface and co-existence has been studied. In some experiments in vitro, Pa products have been defined that are inhibitory to Af. In some clinical situations, both can be biofilm producers, and biofilm could alter their physiology and affect their interaction. That may be most relevant to airways in cystic fibrosis (CF), where both are often prominent residents.We have studied clinical Pa isolates from several sources for their effects on Af, including testing involving their biofilms. We show that the described inhibition of Af is related to the source and phenotype of the Pa isolate. Pa cells inhibited the growth and formation of Af biofilm from conidia, with CF isolates more inhibitory than non-CF isolates, and non-mucoid CF isolates most inhibitory. Inhibition did not require live Pa contact, as culture filtrates were also inhibitory, and again non-mucoid>mucoid CF>non-CF. Preformed Af biofilm was more resistant to Pa, and inhibition that occurred could be reproduced with filtrates. Inhibition of Af biofilm appears also dependent on bacterial growth conditions; filtrates from Pa grown as biofilm were more inhibitory than from Pa grown planktonically. The differences in Pa shown from these different sources are consistent with the extensive evolutionary Pa changes that have been described in association with chronic residence in CF airways, and may reflect adaptive changes to life in a polymicrobial environment. 相似文献