全文获取类型
收费全文 | 6304篇 |
免费 | 530篇 |
国内免费 | 5篇 |
出版年
2023年 | 25篇 |
2022年 | 41篇 |
2021年 | 101篇 |
2020年 | 73篇 |
2019年 | 83篇 |
2018年 | 104篇 |
2017年 | 126篇 |
2016年 | 162篇 |
2015年 | 283篇 |
2014年 | 388篇 |
2013年 | 428篇 |
2012年 | 547篇 |
2011年 | 483篇 |
2010年 | 323篇 |
2009年 | 281篇 |
2008年 | 333篇 |
2007年 | 367篇 |
2006年 | 345篇 |
2005年 | 325篇 |
2004年 | 300篇 |
2003年 | 292篇 |
2002年 | 273篇 |
2001年 | 64篇 |
2000年 | 52篇 |
1999年 | 60篇 |
1998年 | 75篇 |
1997年 | 56篇 |
1996年 | 57篇 |
1995年 | 45篇 |
1994年 | 58篇 |
1993年 | 48篇 |
1992年 | 68篇 |
1991年 | 40篇 |
1990年 | 46篇 |
1989年 | 41篇 |
1988年 | 28篇 |
1987年 | 33篇 |
1986年 | 20篇 |
1985年 | 27篇 |
1984年 | 39篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 33篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 15篇 |
1976年 | 17篇 |
1975年 | 13篇 |
1974年 | 23篇 |
1972年 | 18篇 |
排序方式: 共有6839条查询结果,搜索用时 234 毫秒
141.
142.
Background and AimsHorizontal gene transfer (HGT) is an important evolutionary mechanism because it transfers genetic material that may code for traits or functions between species or genomes. It is frequent in mitochondrial and nuclear genomes but has not been demonstrated between plastid genomes of different green land plant species.MethodsWe Sanger-sequenced the nuclear internal transcribed spacers (ITS1 and 2) and the plastid rpl16 G2 intron (rpl16). In five individuals with foreign rpl16 we also sequenced atpB-rbcL and trnLUAA-trnFGAA.Key ResultsWe discovered 14 individuals of a moss species with typical nuclear ITSs but foreign plastid rpl16 from a species of a distant lineage. None of the individuals with three plastid markers sequenced contained all foreign markers, demonstrating the transfer of plastid fragments rather than the entire plastid genome, i.e. entire plastids were not transferred. The two lineages diverged 165–185 Myr BP. The extended time interval since lineage divergence suggests that the foreign rpl16 is more likely explained by HGT than by hybridization or incomplete lineage sorting.ConclusionsWe provide the first conclusive evidence of interspecific plastid-to-plastid HGT among land plants. Two aspects are critical: it occurred at several localities during the massive colonization of recently disturbed open habitats that were created by large-scale liming as a freshwater biodiversity conservation measure; and it involved mosses whose unique life cycle includes spores that first develop a filamentous protonema phase. We hypothesize that gene transfer is facilitated when protonema filaments of different species intermix intimately when colonizing disturbed early succession habitats. 相似文献
143.
Tolar Tjaša Galik Alfred Le Bailly Matthieu Dufour Benjamin Caf Nina Toškan Borut Bužan Elena Zver Lars Janžekovič Franc Velušček Anton 《Vegetation History and Archaeobotany》2021,30(1):107-118
Vegetation History and Archaeobotany - Multi-proxy analysis of the coprolites which were found during excavations at two Late Neolithic (fourth millennium bc) pile-dwelling sites (Črnelnik and... 相似文献
144.
Barry J. Grant Lars Skjrven Xin‐Qiu Yao 《Protein science : a publication of the Protein Society》2021,30(1):20-30
Bio3D is a family of R packages for the analysis of biomolecular sequence, structure, and dynamics. Major functionality includes biomolecular database searching and retrieval, sequence and structure conservation analysis, ensemble normal mode analysis, protein structure and correlation network analysis, principal component, and related multivariate analysis methods. Here, we review recent package developments, including a new underlying segregation into separate packages for distinct analysis, and introduce a new method for structure analysis named ensemble difference distance matrix analysis (eDDM). The eDDM approach calculates and compares atomic distance matrices across large sets of homologous atomic structures to help identify the residue wise determinants underlying specific functional processes. An eDDM workflow is detailed along with an example application to a large protein family. As a new member of the Bio3D family, the Bio3D‐eddm package supports both experimental and theoretical simulation‐generated structures, is integrated with other methods for dissecting sequence‐structure–function relationships, and can be used in a highly automated and reproducible manner. Bio3D is distributed as an integrated set of platform independent open source R packages available from: http://thegrantlab.org/bio3d/ . 相似文献
145.
146.
147.
148.
Mathias Weber Alexandra R. Wey-Fabrizius Lars Podsiadlowski Alexander Witek Ralph O. Schill László Sugár Holger Herlyn Thomas Hankeln 《Molecular phylogenetics and evolution》2013,66(1):182-189
The metazoan taxon Syndermata (Monogononta, Bdelloidea, Seisonidea, Acanthocephala) comprises species with vastly different lifestyles. The focus of this study is on the phylogeny within the syndermatan subtaxon Acanthocephala (thorny-headed worms, obligate endoparasites). In order to investigate the controversially discussed phylogenetic relationships of acanthocephalan subtaxa we have sequenced the mitochondrial (mt) genomes of Echinorhynchus truttae (Palaeacanthocephala), Paratenuisentis ambiguus (Eoacanthocephala), Macracanthorhynchus hirudinaceus (Archiacanthocephala), and Philodina citrina (Bdelloidea). In doing so, we present the largest molecular phylogenetic dataset so far for this question comprising all major subgroups of Acanthocephala. Alongside with publicly available mt genome data of four additional syndermatans as well as 18 other lophotrochozoan (spiralian) taxa and one outgroup representative, the derived protein-coding sequences were used for Maximum Likelihood as well as Bayesian phylogenetic analyses. We achieved entirely congruent results, whereupon monophyletic Archiacanthocephala represent the sister taxon of a clade comprising Eoacanthocephala and monophyletic Palaeacanthocephala (Echinorhynchida). This topology suggests the secondary loss of lateral sensory organs (sensory pores) within Palaeacanthocephala and is further in line with the emergence of apical sensory organs in the stem lineage of Archiacanthocephala. 相似文献
149.
150.
Ilan Kurz Lars Oddsson Itshak Melzer 《Journal of electromyography and kinesiology》2013,23(4):814-819
ObjectiveOlder adults who have recently fallen demonstrate increased postural sway compared with non-fallers. However, the differences in postural control between older adults who were seriously injured (SI) as a result of a fall, compared with those who fell but were not injured (NSI) and non-fallers (NFs), has not been investigated. The objective of the present study was to investigate the underlying postural control mechanisms related to injuries resulting from a fall.MethodsBoth traditional postural sway measures of foot center-of-pressure (CoP) displacements and fractal measures, the Stabilogram-Diffusion Analysis (SDA), were used to characterize the postural control. One hundred older adults aged 65–91 years were tested during narrow base upright stance in eyes closed condition; falls were monitored over a 1-year period.ResultsForty-nine older adults fell during the 1-year follow-up, 13 were seriously injured as a result of a fall (SI), 36 were not injured (NSI), and 49 were non-fallers (NFs); two passed away. The SDA showed significantly higher short-term diffusion coefficients and critical displacements in SI in the anterior–posterior direction compared with both NSI and NF. However, in the medio-lateral direction there were no statistically significant differences between groups. For the traditional measures of sway, the average anterior–posterior CoP range was also larger in SI individuals.ConclusionsThis work suggests that older fallers with a deterioration of anterior–posterior postural control may be at higher risk of serious injury following fall events. 相似文献