全文获取类型
收费全文 | 1028篇 |
免费 | 70篇 |
出版年
2023年 | 14篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 34篇 |
2017年 | 18篇 |
2016年 | 39篇 |
2015年 | 40篇 |
2014年 | 41篇 |
2013年 | 72篇 |
2012年 | 87篇 |
2011年 | 84篇 |
2010年 | 50篇 |
2009年 | 37篇 |
2008年 | 56篇 |
2007年 | 70篇 |
2006年 | 63篇 |
2005年 | 62篇 |
2004年 | 58篇 |
2003年 | 43篇 |
2002年 | 42篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1961年 | 1篇 |
1960年 | 2篇 |
1914年 | 1篇 |
排序方式: 共有1098条查询结果,搜索用时 15 毫秒
101.
Adaptive radiations in butterflies: evolutionary history of the genus Erebia (Nymphalidae: Satyrinae)
下载免费PDF全文
![点击此处可从《Biological journal of the Linnean Society. Linnean Society of London》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Carlos Peña Heike Witthauer Irena Klečková Zdeněk Fric Niklas Wahlberg 《Biological journal of the Linnean Society. Linnean Society of London》2015,116(2):449-467
We studied the speciose butterfly genus Erebia by reconstructing its phylogenetic relationships using parsimony and Bayesian approaches. We estimated times and rates of diversification for its lineages and employed a biogeographical analysis in order to reconstruct its evolutionary history. DNA sequence data from one mitochondrial gene and three nuclear genes were analyzed for a total of 74 species in Erebia. The estimated dates of origin and diversification for clades, in combination with a biogeographical analysis, suggest that the genus originated in Asian Russia and started its diversification process around 23 Myr. An important event was the dispersal of a lineage from Asia to Western Europe between 23 and 17 Myr, which allowed the radiation of most of species in the genus. The diversification pattern is consistent with a model of diversity limited by clade richness, which implies an early rapid diversification followed by deceleration due to a decrease in speciation. We argue that these characteristics of the evolutionary history of Erebia are consistent with a density‐dependent scenario, with species radiation limited by filling of niche space and reduced resources. We found that the Boeberia parmenio appears strongly supported in the genus Erebia and therefore we place Boeberia Prout, 1901 as a junior synonym of Erebia Dalman, 1816 ( syn. nov. ). 相似文献
102.
103.
Erebia aethiops is an aberrant lowland representative of a predominately arctic and alpine butterfly genus. We used behavioral records obtained
during a mark-recapture study (MR) to extract information about its adult diurnal and within-season activity, and to compare its activity with previously studied mountain Erebia species. Similarly to them, maintenance activities (nectaring, basking) increased with season. Contrary to mountain relatives,
E. aethiops nectars in morning hours and spends the hottest parts of the day in the shade. Therefore, high rather than low temperatures
seem to be limiting E. aethiops activity. We also compared microhabitat preferences of sexes, finding that females preferred grassy patches, whereas males
often entered scrub and sparse canopy forest. The study illustrates the utility of auxiliary MR data to analyze butterfly
activity, and points to the necessity of finely structured habitat mosaics for E. aethiops, an open woodland species that retracted to abandoned grasslands and has become vulnerable in Central Europe. 相似文献
104.
The aim of this study was to investigate the influence of experimental conditions on levothyroxine sodium release from two
immediate-release tablet formulations which narrowly passed the standard requirements for bioequivalence studies. The in vivo study was conducted as randomised, single-dose, two-way cross-over pharmacokinetic study in 24 healthy subjects. The in vitro study was performed using various dissolution media, and obtained dissolution profiles were compared using the similarity
factor value. Drug solubility in different media was also determined. The in vivo results showed narrowly passing bioequivalence. Considering that levothyroxine sodium is classified as Class III drug according
to the Biopharmaceutics Classification System, drug bioavailability will be less sensitive to the variation in its dissolution
characteristics and it can be assumed that the differences observed in vitro in some of investigated media probably do not have significant influence on the absorption process, as long as rapid and
complete dissolution exists. The study results indicate that the current regulatory criteria for the value of similarity factor
in comparative dissolution testing, as well as request for very rapid dissolution (more than 85% of drug dissolved in 15 min),
are very restricted for immediate-release dosage forms containing highly soluble drug substance and need further investigation.
The obtained results also add to the existing debate on the appropriateness of the current bioequivalence standards for levothyroxine
sodium products. 相似文献
105.
Wnt-signalling is involved in a number of biological processes in the course of embryonic development, cell fate determination, proliferation, stem cell maintenance and oncogenesis. Wnt ligands are secreted glycoproteins and the number of Wnt isoforms varies between five in nematodes and 27 in fish. The highly conserved group of Wnt7 genes has been found to signal via at least three Wnt-signalling pathways dependent on the developmental context. These ligands have been identified as important regulators in a number of processes ranging from formation of bones, lungs, kidneys, reproductive organs and placenta to vasculogenesis and synaptogenesis in the brain. The importance of Wnt7 function is underscored by their implication in disease syndromes in man. Unlike the single Wnt7a and Wnt7b mammalian genes we find that the zebrafish genome contains two paralogues genes for each Wnt7 ligand. Here, we compare these four Wnt7 genes evolutionarily and analyse their expression during the first two days of embryonic development. We find Wnt7 genes mainly expressed in a number of CNS structures at developmental stages at which patterning and neural specification takes place. The timely and spatially overlapping as well as complementary gene expression suggests diverse as well as redundant involvements during brain development. 相似文献
106.
Baranowska I Magiera S Baranowski J 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2011,879(9-10):615-626
A rapid-resolution ultra high-performance liquid chromatography separation method (UHPLC) for the simultaneous determination of the following β-blockers: milrinone, sotalol, metoprolol, propranolol and carvedilol, and their metabolites: 5′-hydroxylphenyl-carvedilol, O-desmethylcarvedilol, 4-hydroxypropranolol, α-hydroxy-metoprolol, O-desmethyl-metoprolol; the following isoflavones: genistein, daidzein, glycitin, glycitein, puerarin and biochanin A; as well as their metabolites: dihydrogenistein, desmethylglycitein, 8-hydroxygenistein, daidzein-7,4′-diglucoside, 8-hydroxydaidzein, dihydrobiochanin A in human urine was optimized. The analysed compounds were extracted from human urine by means of solid phase extraction (SPE). The effective UHPLC separation of the examined compounds was applied on a Hypersil GOLD? (50 mm × 2.1 mm, 1.9 μm) column with a gradient mobile phase system and a UV detector. The complete separation of all analytes was achieved within 8.0 min. The method was validated for the determination of the aforementioned substances in human urine. The linear ranges, limits of detection (LOD) and limits of quantification (LOQ) for β-blockers, isoflavones and their metabolites were determined. The intra- and inter-day precision (%C.V.) was less than 4.48%, and the intra-day and inter-day accuracy was less than 4.74%. The tested SPE sorbent proved that appropriate absolute recoveries can be obtained for Oasis HLB (Waters). The mean recovery of the analytes, using the new SPE procedure, amounted from 70.14% to 99.85%. The present paper reports, for the first time, the method for the determination of β-blockers, isoflavones and their metabolites in human urine samples. The newly developed method was suitably validated and successfully applied for the analysis of the certain of the aforementioned analytes in human urine samples obtained from the patients suffering cardiovascular disease. 相似文献
107.
Drac H Kabzińska D Moszyńska I Strugalska-Cynowska H Hausmanowa-Petrusewicz I Kochański A 《Journal of applied genetics》2011,52(2):177-183
Mutations in the myelin protein zero (MPZ) gene are the third most frequent cause of hereditary motor and sensory neuropathies (HMSN), also called Charcot–Marie–Tooth
disorders (CMT). Only in case of recurrent mutations occurring in the MPZ gene is it possible to draw phenotype–genotype correlations essential for establishing the prognosis and outcomes of CMT1.
We have surveyed a cohort of 67 Polish patients from CMT families with demyelinating neuropathy for mutations in the MPZ gene. In this study, we report two CMT families in which the Ile135Thr and Pro132Leu mutations have been identified for the
MPZ gene. These MPZ gene mutations had not been identified hitherto in the Polish population. The Pro132Leu mutation segregates with a severe
early-onset dysmyelinating–hypomyelinating neuropathy, whereas the Ile135Thr substitution is associated with the classical
phenotype of CMT1. To the best of our knowledge, we present here, for the first time, morphological data obtained in two sural
nerve biopsies pointing to a hypomyelination–dysmyelination process in a family harboring the Pro132Leu mutation in the MPZ gene. 相似文献
108.
Jan Pergl Jana Müllerová Irena Perglová Tomáš Herben Petr Pyšek 《Diversity & distributions》2011,17(4):725-738
Aim Long‐distance dispersal is important for plant population dynamics at larger spatial scales, but our understanding of this phenomenon is mostly based on computer modelling rather than field data. This paper, by combining field data and a simulation model, quantifies the fraction of the seed of the alien species Heracleum mantegazzianum that needs to disperse over a long distance for successful invasion. Location Central Europe, Czech Republic. Methods To assess the role of random dispersal in long‐term population dynamics of the studied species, we combined longitudinal data covering 50 years of the invasion of this plant from its very start, inferred from a series of aerial photographs of 60‐ha plots, with data on population dynamics at a fine scale of 10‐m2 plots. Results A simulation model based on field data indicates that the fraction of seed that is dispersed from source plants not described by the short‐distance dispersal kernel ranges from 0.1 to 7.5% of the total seed set. The fraction of long‐distance dispersed seed that provides the best prediction of the observed spread was significantly negatively correlated with the percentage of habitats suitable for invasion. Main conclusions Our results indicate that the fraction of seeds that needed to be dispersed over long distances to account for the observed invasion dynamics decreased with increasing proportion of invasible habitats, indicating that the spatial pattern of propagule pressure differs in landscapes prone to invasion. Long‐distance dispersal is an important component of the population dynamics of an invasive species even at relatively small scales. 相似文献
109.
110.