全文获取类型
收费全文 | 1127篇 |
免费 | 143篇 |
专业分类
1270篇 |
出版年
2021年 | 25篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 41篇 |
2014年 | 52篇 |
2013年 | 45篇 |
2012年 | 45篇 |
2011年 | 66篇 |
2010年 | 46篇 |
2009年 | 45篇 |
2008年 | 44篇 |
2007年 | 53篇 |
2006年 | 52篇 |
2005年 | 44篇 |
2004年 | 40篇 |
2003年 | 38篇 |
2002年 | 24篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 22篇 |
1998年 | 21篇 |
1997年 | 24篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 15篇 |
1972年 | 9篇 |
1969年 | 12篇 |
1967年 | 7篇 |
1932年 | 8篇 |
排序方式: 共有1270条查询结果,搜索用时 15 毫秒
81.
82.
Past and current gene flow in the selfing, wind-dispersed species Mycelis muralis in western Europe 总被引:2,自引:0,他引:2
Chauvet S van der Velde M Imbert E Guillemin ML Mayol M Riba M Smulders MJ Vosman B Ericson L Bijlsma R Giles BE 《Molecular ecology》2004,13(6):1391-1407
The distribution of genetic diversity in Mycelis muralis, or wall lettuce, was investigated at a European scale using 12 microsatellite markers to infer historical and contemporary forces from genetic patterns. Mycelis muralis has the potential for long-distance seed dispersal by wind, is mainly self-pollinated, and has patchily distributed populations, some of which may show metapopulation dynamics. A total of 359 individuals were sampled from 17 populations located in three regions, designated southern Europe (Spain and France), the Netherlands, and Sweden. At this within-region scale, contemporary evolutionary forces (selfing and metapopulation dynamics) are responsible for high differentiation between populations (0.34 < F(ST) < 0.60) but, contrary to expectation, levels of within-population diversity, estimated by Nei's unbiased expected heterozygosity (H(E)) (0.24 < H(E) < 0.68) or analyses of molecular variance (50% of the variation found within-populations), were not low. We suggest that the latter results, which are unusual in selfing species, arise from efficient seed dispersal that counteracts population turnover and thus maintains genetic diversity within populations. At the European scale, northern regions showed lower allelic richness (A = 2.38) than populations from southern Europe (A = 3.34). In light of postglacial colonization hypotheses, these results suggest that rare alleles may have been lost during recolonization northwards. Our results further suggest that mutation has contributed to genetic differentiation between southern and northern Europe, and that Sweden may have been colonized by dispersers originating from at least two different refugia. 相似文献
83.
A fungal metallothionein is required for pathogenicity of Magnaporthe grisea 总被引:1,自引:0,他引:1 下载免费PDF全文
Tucker SL Thornton CR Tasker K Jacob C Giles G Egan M Talbot NJ 《The Plant cell》2004,16(6):1575-1588
The causal agent of rice blast disease, the ascomycete fungus Magnaporthe grisea, infects rice (Oryza sativa) plants by means of specialized infection structures called appressoria, which are formed on the leaf surface and mechanically rupture the cuticle. We have identified a gene, Magnaporthe metallothionein 1 (MMT1), which is highly expressed throughout growth and development by M. grisea and encodes an unusual 22-amino acid metallothionein-like protein containing only six Cys residues. The MMT1-encoded protein shows a very high affinity for zinc and can act as a powerful antioxidant. Targeted gene disruption of MMT1 produced mutants that show accelerated hyphal growth rates and poor sporulation but had no effect on metal tolerance. Mmt1 mutants are incapable of causing plant disease because of an inability to bring about appressorium-mediated cuticle penetration. Mmt1 appears to be distributed in the inner side of the cell wall of the fungus. These findings indicate that Mmt1-like metallothioneins may play a novel role in fungal cell wall biochemistry that is required for fungal virulence. 相似文献
84.
Nygren A Kondo C Clark RB Giles WR 《American journal of physiology. Heart and circulatory physiology》2003,284(3):H892-H902
An imaging system suitable for recordings from Langendorff-perfused rat hearts using the voltage-sensitive dye 4-[beta-[2-(di-n-butylamino)-6-naphthyl]vinyl]pyridinium (di-4-ANEPPS) has been developed. Conduction velocity was measured under hyper- and hypokalemic conditions, as well as at physiological and reduced temperature. Elevation of extracellular [K(+)] to 9 mM from 5.9 mM caused a slowing of conduction velocity from 0.66 +/- 0.08 to 0.43 +/- 0.07 mm/ms (35%), and reduction of the temperature to 32 degrees C from 37 degrees C caused a slowing from 0.64 +/- 0.07 to 0.46 +/- 0.05 mm/ms (28%). Ventricular activation patterns in sinus rhythm showed areas of early activation (breakthrough) in both the right and left ventricle, with breakthrough at a site near the apex of the right ventricle usually occurring first. The effects of mechanically immobilizing the preparation to reduce motion artifact were also characterized. Activation patterns in epicardially paced rhythm were insensitive to this procedure over the range of applied force tested. In sinus rhythm, however, a relatively large immobilizing force caused prolonged PQ intervals as well as altered ventricular activation patterns. The time-dependent effects of the dye on the rat heart were characterized and include 1) a transient vasodilation at the onset of dye perfusion and 2) a long-lasting prolongation of the PQ interval of the electrocardiogram, frequently resulting in brief episodes of atrioventricular block. 相似文献
85.
Lomax AE Kondo CS Giles WR 《American journal of physiology. Heart and circulatory physiology》2003,285(5):H1837-H1848
Consistent differences in K+ currents in left and right atria of adult mouse hearts have been identified by the application of current- and voltage-clamp protocols to isolated single myocytes. Left atrial myocytes had a significantly (P < 0.05) larger peak outward K+ current density than myocytes from the right atrium. Detailed analysis revealed that this difference was due to the rapidly activating sustained K+ current, which is inhibited by 100 muM 4-aminopyridine (4-AP); this current was almost three times larger in the left atrium than in the right atrium. Accordingly, 100 muM 4-AP caused a significantly (P < 0.05) larger increase in action potential duration in left than in right atrial myocytes. Inward rectifier K+ current density was also significantly (P < 0.05) larger in left atrial myocytes. There was no difference in the voltage-dependent L-type Ca2+ current between left and right atria. As expected from this voltage-clamp data, the duration of action potentials recorded from single myocytes was significantly (P < 0.05) shorter in myocytes from left atria, and left atrial tissue was found to have a significantly (P < 0.05) shorter effective refractory period than right atrial tissue. These results reveal similarities between mice and other mammalian species where the left atrium repolarizes more quickly than the right, and provide new insight into cellular electrophysiological mechanisms responsible for this difference. These findings, and previous results, suggest that the atria of adult mice may be a suitable model for detailed studies of atrial electrophysiology and pharmacology under control conditions and in the context of induced atrial rhythm disturbances. 相似文献
86.
87.
Elliott NC Giles KL Royer TA Kindler SD Tao FL Jones DB Cuperus GW 《Journal of economic entomology》2003,96(5):1585-1593
The numbers of greenbugs, Schizaphis graminum (Rondani), and bird cherry-oat aphids, Rhopalosiphum padi L., per wheat tiller (stem) were estimated in 189 production winter wheat (Triticum aestivum L.) fields located throughout Oklahoma. Taylor's power law regressions were calculated from these data and used to construct fixed precision sequential sampling schemes for each species. An evaluation data set was constructed from 240 samples taken during three growing seasons from winter wheat fields at four locations in Oklahoma. Wheat cultivar and growth stage were recorded for each field on the day of sampling. Taylor's power law parameters for evaluation fields differed significantly for both species among growing seasons, locations, and plant growth stages. Median precision achieved using the fixed precision sequential sampling schemes for each species departed <20% from expected precision over the range population intensity in the evaluation data. For the 10% of samples with greatest deviation between observed and expected precision, observed precision was 13.8-81.8% greater than that expected precision depending on aphid species and population intensity. For the greenbug, the distribution of the percentage deviation between observed and expected precision was positively skewed, so that the sampling scheme tended to over-predict precision. For the bird cherry-oat aphid, the distribution was more symmetric. Even though precision observed using the sampling schemes frequently varied from expected precision, because of the inevitable consequence of sampling error and environmental variation, the sampling schemes yielded median observed precision levels close to expected precision levels over a broad range of population intensity. 相似文献
88.
89.
90.
Hippodamia convergens Guérin-Méneville and Coccinella septempunctata L. (Coleoptera: Coccinellidae) larvae were supplied daily with 1, 2, 4, or 16 mg of Acyrthosiphon kondoi Shinji (Homoptera: Aphididae) reared on one of two susceptible ('OK08' or 'CUF-101') or one resistant ('54H55') alfalfa cultivar (IMedicago sativa L.) . Hippodamia convergens survived to the adult stage when supplied with > or = 1 mg of A. kondoi per day from both susceptible and aphid-resistant cultivars, whereas C. septempunctata required > or = 2 mg of A. kondoi per day (from each cultivar) for survival to the adult stage. For both H. convergens and C. septempunctata, no consistent differences in survivorship or developmental times were observed between predator larvae supplied with increasing daily levels of A. kondoi from susceptible (OKO8 orCUF-101) versus resistant (54H55) cultivars. Additionally, alfalfa cultivar had no indirect influence on adult weight of H. convergens or C. septempunctata. Results from our study suggest that the resistant alfalfa cultivar (54H55) would have little to no effect on the nutritional value of A. kondoi for ladybeetle predators. 相似文献