全文获取类型
收费全文 | 7675篇 |
免费 | 573篇 |
国内免费 | 3篇 |
出版年
2023年 | 24篇 |
2022年 | 74篇 |
2021年 | 137篇 |
2020年 | 81篇 |
2019年 | 105篇 |
2018年 | 179篇 |
2017年 | 123篇 |
2016年 | 219篇 |
2015年 | 314篇 |
2014年 | 353篇 |
2013年 | 506篇 |
2012年 | 602篇 |
2011年 | 561篇 |
2010年 | 362篇 |
2009年 | 314篇 |
2008年 | 461篇 |
2007年 | 436篇 |
2006年 | 396篇 |
2005年 | 385篇 |
2004年 | 327篇 |
2003年 | 312篇 |
2002年 | 273篇 |
2001年 | 154篇 |
2000年 | 111篇 |
1999年 | 123篇 |
1998年 | 77篇 |
1997年 | 66篇 |
1996年 | 50篇 |
1995年 | 64篇 |
1994年 | 47篇 |
1993年 | 38篇 |
1992年 | 72篇 |
1991年 | 88篇 |
1990年 | 72篇 |
1989年 | 57篇 |
1988年 | 46篇 |
1987年 | 51篇 |
1986年 | 47篇 |
1985年 | 31篇 |
1984年 | 40篇 |
1983年 | 43篇 |
1982年 | 32篇 |
1981年 | 31篇 |
1979年 | 28篇 |
1978年 | 26篇 |
1977年 | 39篇 |
1976年 | 26篇 |
1975年 | 27篇 |
1974年 | 23篇 |
1973年 | 26篇 |
排序方式: 共有8251条查询结果,搜索用时 19 毫秒
11.
Francisco Del Pino Claudia Jara Luis Pino María Cristina Medina-Mu?oz Eduardo Alvarez Raúl Godoy-Herrera 《PloS one》2015,10(8)
We investigated the role of Drosophila larva olfactory system in identification of congeners and aliens. We discuss the importance of these activities in larva navigation across substrates, and the implications for allocation of space and food among species of similar ecologies. Wild type larvae of cosmopolitan D. melanogaster and endemic D. pavani, which cohabit the same breeding sites, used species-specific volatiles to identify conspecifics and aliens moving toward larvae of their species. D. gaucha larvae, a sibling species of D. pavani that is ecologically isolated from D. melanogaster, did not respond to melanogaster odor cues. Similar to D. pavani larvae, the navigation of pavani female x gaucha male hybrids was influenced by conspecific and alien odors, whereas gaucha female x pavani male hybrid larvae exhibited behavior similar to the D. gaucha parent. The two sibling species exhibited substantial evolutionary divergence in processing the odor inputs necessary to identify conspecifics. Orco (Or83b) mutant larvae of D. melanogaster, which exhibit a loss of sense of smell, did not distinguish conspecific from alien larvae, instead moving across the substrate. Syn
97CS and rut larvae of D. melanogaster, which are unable to learn but can smell, moved across the substrate as well. The Orco (Or83b), Syn
97CS and rut loci are necessary to orient navigation by D. melanogaster larvae. Individuals of the Trana strain of D. melanogaster did not respond to conspecific and alien larval volatiles and therefore navigated randomly across the substrate. By contrast, larvae of the Til-Til strain used larval volatiles to orient their movement. Natural populations of D. melanogaster may exhibit differences in identification of conspecific and alien larvae. Larval locomotion was not affected by the volatiles. 相似文献
12.
13.
14.
L Morbiato F Tombola S Campello G Del Giudice R Rappuoli M Zoratti E Papini 《FEBS letters》2001,508(3):479-483
The protein vacuolating toxin A (VacA) of Helicobacter pylori converts late endosomes into large vacuoles in the presence of permeant bases. Here it is shown that this phenomenon corresponds to an accumulation of permeant bases and Cl(-) in HeLa cells and requires the presence of extracellular Cl(-). The net influx of Cl(-) is due to electroneutral, Na(+), K(+), 2Cl(-) cotransporter-mediated transport. Cell vacuolation leads to cell volume increase, consistent with water flux into the cell, while hyper-osmotic media decreased vacuole formation. These data represent the first evidence that VacA-treated cells undergo an osmotic unbalance, reinforcing the hypothesis that the VacA chloride channel is responsible for cell vacuolation. 相似文献
15.
16.
G Del Boccio C Di Ilio E Casalone A Pennelli A Aceto P Sacchetta G Federici 《The Italian journal of biochemistry》1987,36(1):8-17
An anionic (pI 4.6) isoenzyme of glutathione transferase was purified to homogeneity from human thyroid by affinity chromatography followed by isoelectric focusing. The content of enzyme was calculated to constitute about 0.2% of soluble proteins. The enzyme is formed by two identical subunits of 23,000 daltons approximately. The thyroid transferase did not catalyze the reduction of peroxides. Physical, catalytic and immunological analyses demonstrated extensive similarities between the thyroid transferase and the transferase from placenta, erythrocytes and breast. On the other hand, the thyroid transferase appears catalytically different from transferase 7-7, even if both cross-react with the antibodies raised against human placenta transferase. 相似文献
17.
G Del Bino R Silvestrini A Costa G Mazzini P Giordano 《Basic and applied histochemistry》1987,31(2):183-190
A flow cytometric study of DNA and protein contents was performed on cell suspensions obtained from 73 adult patients with non-Hodgkin lymphoma. Bivariate analysis identified a second subpopulation, not revealed by DNA determination, in 25% of the tumors. Protein heterogeneity was more frequently observed in diffuse than in nodular histology according the Rappaport classification and in high-grade than in low-grade malignancy tumors by the Kiel classification and the Working Formulation, but it was not related to ploidy or cell proliferative rate. The presence of an additional subpopulation, detected by protein analysis, defined as monoclonal by DNA analysis, could adversely affect clinical outcome in terms of response to treatment and overall survival. 相似文献
18.
Abstract. This study was designed to define some biological aspects of cell suspensions, obtained by mechanical or enzymatic disaggregations, and to verify whether single cell suspensions are representative of original solid tumours. The study was performed on a series of 25 human solid tumours including breast carcinoma, ovarian carcinoma and malignant melanoma. A higher cell viability and a loss of aneuploid subpopulations, or a lower fraction of aneuploid cells, were observed in enzymatically-released samples than in samples obtained by the mechanical procedure. Moreover, the proliferative activity, which was generally similar for the cell suspensions obtained by the two disaggregation procedures, was always markedly lower in the cell suspensions than in solid samples from the same tumour. In conclusion, the results from this study indicate that many changes, such as selective release of cell populations from the tumour matrix, damage and destruction of aneuploid and proliferating cells can be induced to various extents by different disaggregation procedures. 相似文献
19.
20.
M Fidanza M Dentini V Crescenzi P Del Vecchio 《International journal of biological macromolecules》1989,11(6):372-376
Viscosity, optical activity, and differential scanning calorimetry data clearly point out that partial and/or total removal of charged substituent groups, i.e. succinate and pyruvyl residues, from succinoglycan lead to water soluble derivatives exhibiting a higher stability order → disorder conformational changes with respect to the native polysaccharide. The new succinoglycan derivatives also exhibit very little, if any, hysteresis upon ‘renaturation’ (cooling) as opposed to the case of the parent polymer. The absence of ionized groups is thus beneficial, thermodynamically and kinetically, to the attainment in dilute aqueous solution of an ordered conformation by the uncharged succinoglycan backbone, as allowed by the regular enchainment of its constituent sugar residues. 相似文献