全文获取类型
收费全文 | 1647篇 |
免费 | 148篇 |
专业分类
1795篇 |
出版年
2023年 | 22篇 |
2022年 | 31篇 |
2021年 | 59篇 |
2020年 | 44篇 |
2019年 | 55篇 |
2018年 | 64篇 |
2017年 | 59篇 |
2016年 | 74篇 |
2015年 | 96篇 |
2014年 | 99篇 |
2013年 | 151篇 |
2012年 | 115篇 |
2011年 | 111篇 |
2010年 | 100篇 |
2009年 | 78篇 |
2008年 | 82篇 |
2007年 | 89篇 |
2006年 | 70篇 |
2005年 | 66篇 |
2004年 | 65篇 |
2003年 | 46篇 |
2002年 | 32篇 |
2001年 | 21篇 |
2000年 | 16篇 |
1999年 | 23篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 12篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有1795条查询结果,搜索用时 0 毫秒
41.
Fiuza SM Gomes C Teixeira LJ Girão da Cruz MT Cordeiro MN Milhazes N Borges F Marques MP 《Bioorganic & medicinal chemistry》2004,12(13):3581-3589
The antiproliferative and cytotoxic properties of polyphenolic acid derivatives, structurally related with the natural models caffeic and gallic acids, have been tested in human cervix adenocarcinoma cells (HeLa). Simultaneous structural information was obtained for these compounds through theoretical ab initio methods. This study was conducted for the following esters: methyl caffeate (MC, 1), propyl caffeate (PC, 2), octyl caffeate (OC, 3), methyl gallate (MG, 4), propyl gallate (PG, 5) and octyl gallate (OG, 6). A significant growth-inhibition effect was assessed for some of these compounds, clearly dependent on their structural characteristics. Marked structure-activity relationships (SARs)--namely the number of hydroxyl ring substituents--were found to rule the biological effect of such systems. 相似文献
42.
Marcelo Telascrea Carla C. de Araújo Márcia O.M. Marques Roselaine Facanali Pedro L.R. de Moraes Alberto J. Cavalheiro 《Biochemical Systematics and Ecology》2007
The composition of the essential oil from leaves of Cryptocarya mandioccana has been determined by chromatographic fractionation and GC–FID, GC–MS and 13C NMR analyses, yielding the identification of 64 compounds with predominance of isomeric sesquiterpenes with molecular weights of 204. The main components of the oil obtained by hydrodistillation were β-caryophyllene, spathulenol, caryophyllene oxide, δ-cadinene, germacrene D, benzaldehyde and bicyclogermacrene. However, the oil obtained by steam distillation contained higher levels of sesquiterpene hydrocarbons, with predominance of β-caryophyllene (C), germacrene D (G) and bicyclogermacrene (B), and was considered to be more representative of the composition of the oil in its natural state. The intraspecific chemical variability of the essential oil obtained by steam distillation was evaluated within populations of trees growing at three separate locations in the state of São Paulo, Brazil. Three distinct chemical groups could be characterised due to differences in the relative percentages of the three main sesquiterpenes from essential oil: CGB [relative contents of C (14–34%), G (5–28%), B (8–15%)], BCG [B (17–34%), C (9–24%), G (12–25%)] and GCB [G (22–42%), C (4–17%), B (7–15%)]. Individuals from groups CGB and BCG were found to be more frequent at south locations while group GCB is predominant in north location. 相似文献
43.
44.
Yasmin Silva Rizk Alice Fischer Marillin de Castro Cunha Patrik Oening Rodrigues Maria Carolina Silva Marques Maria de Fátima Cepa Matos M?nica Cristina Toffoli Kadri Carlos Alexandre Carollo Carla Cardozo Pinto de Arruda 《Memórias do Instituto Oswaldo Cruz》2014,109(8):1050-1056
This study is the first phytochemical investigation of Selaginella sellowii
and demonstrates the antileishmanial activity of the hydroethanolic extract
from this plant (SSHE), as well as of the biflavonoids amentoflavone and
robustaflavone, isolated from this species. The effects of these substances were
evaluated on intracellular amastigotes of Leishmania (Leishmania)
amazonensis, an aetiological agent of American cutaneous leishmaniasis.
SSHE was highly active against intracellular amastigotes [the half maximum inhibitory
concentration (IC50) = 20.2 µg/mL]. Fractionation of the extract led to the isolation
of the two bioflavonoids with the highest activity: amentoflavone, which was about
200 times more active (IC50 = 0.1 μg/mL) and less cytotoxic than SSHE (IC50 = 2.2 and
3 μg/mL, respectively on NIH/3T3 and J774.A1 cells), with a high selectivity index
(SI) (22 and 30), robustaflavone, which was also active against L.
amazonensis (IC50 = 2.8 µg/mL), but more cytotoxic, with IC50 = 25.5
µg/mL (SI = 9.1) on NIH/3T3 cells and IC50 = 3.1 µg/mL (SI = 1.1) on J774.A1 cells.
The production of nitric oxide (NO) was lower in cells treated with amentoflavone
(suggesting that NO does not contribute to the leishmanicidal mechanism in this
case), while NO release was higher after treatment with robustaflavone. S.
sellowii may be a potential source of biflavonoids that could provide
promising compounds for the treatment of cutaneous leishmaniasis. 相似文献
45.
Zooplankton and ichthyoplankton communities in a temperate estuary: spatial and temporal patterns 总被引:7,自引:0,他引:7
Marques Sonia Cotrim; Azeiteiro Ulisses Miranda; Marques Joao Carlos; Neto Joao Miguel; Pardal Miguel Angelo 《Journal of plankton research》2006,28(3):297-312
Zooplankton and ichthyoplankton assemblages were studied fromJanuary 2003 to June 2004 in a temperate shallow estuary (Mondegoestuary, Portugal). Monthly sampling was performed at five stationsat high and low tides, with subsurface tows with 335 and 500µm mesh Bongo nets. Analysis of variance (ANOVA) showeda significant effect (P < 0.05) of the mesh size of the neton the abundance of main zooplankton groups. On average, theabundance of the 500 µm taxocenosis was 67 and 102 timeslower than the 335 µm taxocenosis at high and low tidesrespectively, especially in the south arm. More than 80 specieswere identified in the zooplankton samples. The upper reachesof northern arm are dominated by freshwater crustacean mesozooplanktonlike Acanthocyclops robustus and Diaptomus spp. and the cladoceransDaphnia, Ceriodaphnia and Bosmina, often being codominant. Inthe southern arm, the resident estuarine copepod Acartia tonsawas dominant, eventually being the most abundant taxon. Marinereaches of estuary are usually dominated by the marine calanoidcopepods Acartia clausi and Temora longicornis and the siphonophoresMuggiaea atlantica. Concerning the ichthyoplankton, this wasdominated by the larvae of estuarine resident species, mainlyPomatoschistus sp., and eggs of Engraulis encrasicolus. Theabundance of Pomatoschistus sp. larvae was positively correlatedwith water temperature. Statistical analysis (canonical correspondenceanalysis) used to determine the spatiotemporal structure ofthe zooplankton assemblages and its correlation with environmentalvariables showed that salinity and temperature were the mainfactors influencing the distribution of zooplankton. The resultsobtained also showed that abundance was strongly influencedby the hydrological circulation pattern and direct or indirecthuman impacts that occur in each arm of the estuary.
This article was presented at Plankton Symposium III, held atFiguera da Foz, portugal, between 17 and 20 March 2005, underthe auspices of the University of Coimbra and the Universityof Aveiro, and coordinated by Mário Jorge Pereira andUlisses M. Azeiteiro. 相似文献
46.
47.
48.
Pia Gruber Filipe Carvalho Marco P. C. Marques Brian O'Sullivan Fabiana Subrizi Dragana Dobrijevic John Ward Helen C. Hailes Pedro Fernandes Roland Wohlgemuth Frank Baganz Nicolas Szita 《Biotechnology and bioengineering》2018,115(3):586-596
49.
Daniel Ruivo Marques Paula Castilho Ana Allen Gomes Anabela Pereira 《Chronobiology international》2019,36(4):541-547
It is well established in the literature that morning-type individuals present better health indicators than evening-types. Mindfulness is considered an adaptive self-regulation skill associated with well-being and physical and mental health. However, there is scarce studies that relate chronotype and mindfulness. Thus, in this research, our aim was to study the relationship between chronotype and mindfulness-related variables. For this purpose, a sample composed of 483 participants from the community was recruited through an online survey and invited to fill out the Five Facet Mindfulness Questionnaire, the Self-Compassion Scale, and the Composite Morningness Scale. Regarding mindfulness measure, the results indicated that morning-types presented higher levels of “acting with awareness” than intermediate and evening-types. Additionally, as to self-compassion measure, morning-types presented higher levels of “mindfulness” and “overall self-compassion” than intermediate and evening-types. The remaining associations examined were not statistically significant. In sum, the morning-types showed higher scores in some of the mindfulness and self-compassion scales which seem to suggest that this morningness tendency may function as protective factor concerning eventual disorders´ development. Nonetheless, more systematic studies are needed to better understand this association and subsequently foster changes for psychological intervention. 相似文献
50.