全文获取类型
收费全文 | 1778篇 |
免费 | 128篇 |
国内免费 | 1篇 |
出版年
2023年 | 18篇 |
2022年 | 33篇 |
2021年 | 86篇 |
2020年 | 34篇 |
2019年 | 57篇 |
2018年 | 49篇 |
2017年 | 54篇 |
2016年 | 68篇 |
2015年 | 108篇 |
2014年 | 105篇 |
2013年 | 130篇 |
2012年 | 159篇 |
2011年 | 148篇 |
2010年 | 94篇 |
2009年 | 96篇 |
2008年 | 113篇 |
2007年 | 98篇 |
2006年 | 84篇 |
2005年 | 73篇 |
2004年 | 54篇 |
2003年 | 56篇 |
2002年 | 39篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1985年 | 4篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1972年 | 12篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 7篇 |
1968年 | 3篇 |
1967年 | 8篇 |
1966年 | 3篇 |
1965年 | 5篇 |
排序方式: 共有1907条查询结果,搜索用时 578 毫秒
991.
Essential oil constituents of Valeriana italica and Valeriana tuberosa. Stereochemical and conformational study of 15-acetoxyvaleranone 总被引:1,自引:0,他引:1
Fokialakis N Magiatis P Mitaku S 《Zeitschrift für Naturforschung. C, Journal of biosciences》2002,57(9-10):791-796
The chemical composition of the essential oils obtained by hydrodistillation of roots, stems with leaves and inflorescences of Valeriana italica Lam. and Valeriana tuberosa L. were studied by GC/MS. Seventy-three and forty-one constituents were identified from each plant, respectively. The major constituent of the oil obtained from the roots of V. italica was isolated and identified as 15-acetoxyvaleranone. Its stereochemistry and conformation has been studied using NMR spectroscopy and molecular modelling. The oils obtained from V. tuberosa completely lacked the characteristic valerane or kessane sesquiterpenes. 相似文献
992.
Sulindac is a sulfoxide prodrug that, in vivo, is converted to the metabolites sulindac sulfide and sulindac sulfone. It is therapeutically used as an anti-inflammatory and analgesic in the symptomatic treatment of acute and chronic rheumatoid arthritis, osteoarthritis, and ankylosing spondylitis. In addition to its anti-inflammatory properties, sulindac and its metabolites have been shown to have an important role in the prevention of colonic carcinogenesis. Although the inhibition of prostaglandin synthesis constitutes the primary mechanism of action of sulindac, it is well known that reactive oxygen species (ROS) and reactive nitrogen species (RNS) are implicated in the pathophysiology of inflammation and cancer. Thus, the aim of this study was to evaluate the scavenging activity of sulindac and its sulfone and sulfide metabolites for an array of ROS (HO*, O2(*-), and HOCl) and RNS (*NO and ONOO-) using in vitro systems. The results we obtained demonstrate that the metabolism of sulindac increases its scavenging activity for all RNS and ROS studied, notably with regard to the scavenging of HOCl. These effects may strongly contribute to the anti-inflammatory and anticarcinogenic efficacy that has been shown for sulindac. 相似文献
993.
994.
Sequence comparisons and a revised classification of the Euglenophyceae were based on 92 new SSU rDNA sequences obtained from strains of Euglena, Astasia, Phacus, Trachelomonas, Colacium, Cryptoglena, Lepocinclis, Eutreptia, Eutreptiella and Tetreutreptia. Sequence data also provided molecular signatures for taxa from genus to class level in the SSU rRNA secondary structure, revealed by a novel approach (search for non-homoplasious synapomorphies) and used for taxonomic diagnoses. Photosynthetic euglenoids and secondary heterotrophs formed a clade, designated as Euglenophyceae (emend.) with two orders: Euglenales and Eutreptiales. The mostly marine Eutreptiales (Eutreptia, Eutreptiella; not Distigma) comprised taxa with two or four emergent flagella (the quadriflagellate Tetreutreptia was integrated within Eutreptiella). The Euglenales (freshwater genera with < or = one emergent flagellum) formed nine clades and two individual branches (single strains); however, only two clades were congruent with traditional genera: Trachelomonas (incl. Strombomonas) and Colacium. Euglena was polyphyletic and diverged into four independent clades (intermixed with Astasia, Khawkinea and Lepocinclis) and two individual branches (e.g. E. polymorpha). Phacus was also subdivided into Phacus s. str. and two combined lineages (mixed with Lepocinclis spp. or Cryptoglena). In consequence, Euglena (s. str.), Phacus and other genera were emended and one lineage (mixed Phacus/Lepocinclis-clade) was recognized as the previously neglected genus Monomorphina Mereschkowsky (1877). The sister clade of Phacus s. str. (mixed Euglena/Lepocinclis-clade) was identified as Lepocinclis Perty (emended). 相似文献
995.
van Vollenhoven RF Ernestam S Harju A Bratt J Klareskog L 《Arthritis research & therapy》2003,5(6):R347-R351
Etanercept can be used both as monotherapy and in combination with methotrexate (MTX), but direct comparisons of these two
options have not yet been reported. In order to compare the results seen in actual practice between these two options, clinical
data on 97 patients followed in the Stockholm TNFα Follow-Up Registry were analysed. In 57 of these patients etanercept was
added to previously started MTX while the others were treated with etanercept alone. The two groups had similar levels of
disease activity at baseline. After 3 months, a significantly lower mean disease activity score (28-joint count-based disease
activity score) was attained by the patients on etanercept plus MTX. In this group, the number of patients achieving European
League Against Rheumatism-defined remission was also significantly greater. Other disease outcomes showed non-significant
trends in the same direction. These data suggest that the combination of etanercept plus MTX is clinically more efficacious
than etanercept alone. 相似文献
996.
997.
Black CL Ocaña S Riner D Costales JA Lascano MS Davila S Arcos-Teran L Seed JR Grijalva MJ 《The Journal of parasitology》2007,93(1):12-16
Few studies on the relationship between environmental factors and Trypanosoma cruzi transmission have been conducted in Ecuador. We conducted a cross-sectional study of household risk factors for T. cruzi seropositivity in 2 distinct geographical regions of Ecuador. Exposure information was collected via household surveys, and subjects were tested for serological evidence of T. cruzi infection. In total, 3,286 subjects from 997 households were included. In the coastal region, factors associated with seropositivity were living in a house with a palm roof (odds ratio [OR] = 2.63, 95% confidence interval, [1.61. 4.27]), wood walls (OR = 5.75 [2.04, 16.18]), or cane walls (OR = 2.81 11.31, 6.04]), and the presence of firewood in the peridomicile (OR = 2.48 [1.54, 4.01]). Accumulation of trash outside the home was associated with a reduced risk of seropositivity (OR = 0.25 [0.12, 0.51]). In the Andean region, living in a house with adobe walls was the only factor predictive of T. cruzi seropositivity. In conclusion, risk factors for T. cruzi transmission in Ecuador varied by geographic region, probably because of differing behavior of the triatomine vector species in each region. An understanding of the transmission dynamics of T. cruzi in a particular area is necessary for the development of effective Chagas disease control strategies in those areas. 相似文献
998.
999.
Sofia R. Pauleta Américo G. Duarte Marta S. Carepo Alice S. Pereira Pedro Tavares Isabel Moura José J. G. Moura 《Biomolecular NMR assignments》2007,1(1):81-83
We report the 98% assignment of the apo-form of an orange protein, containing a novel Mo–Cu cluster isolated from Desulfovibrio gigas. This protein presents a region where backbone amide protons exchange fast with bulk solvent becoming undetectable. These
residues were assigned using 13C-detection experiments. 相似文献
1000.