全文获取类型
收费全文 | 1261篇 |
免费 | 101篇 |
国内免费 | 1篇 |
出版年
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 42篇 |
2020年 | 27篇 |
2019年 | 42篇 |
2018年 | 55篇 |
2017年 | 27篇 |
2016年 | 49篇 |
2015年 | 66篇 |
2014年 | 84篇 |
2013年 | 78篇 |
2012年 | 105篇 |
2011年 | 104篇 |
2010年 | 63篇 |
2009年 | 35篇 |
2008年 | 63篇 |
2007年 | 43篇 |
2006年 | 47篇 |
2005年 | 49篇 |
2004年 | 39篇 |
2003年 | 29篇 |
2002年 | 13篇 |
2001年 | 21篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1997年 | 6篇 |
1995年 | 11篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1970年 | 5篇 |
1969年 | 4篇 |
1968年 | 7篇 |
1967年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有1363条查询结果,搜索用时 15 毫秒
91.
MicroRNA-451 Regulates LKB1/AMPK Signaling and Allows Adaptation to Metabolic Stress in Glioma Cells
92.
Jakub Těšitel Pavel Říha Šárka Svobodová Tamara Malinová Milan Štech 《Folia Geobotanica》2010,45(4):347-367
Rhinanthoid Orobanchaceae form a monophyletic lineage that include the hemiparasitic genera Euphrasia, Melampyrum, Tozzia, Bartsia, Nothobartsia, Odontites (s.l.), Rhinanthus, Rhynchocorys, Parentucellia, Hedbergia and holoparasitic Lathraea. In this study, we aimed to reconstruct the phylogeny, evolution of life-history traits (life cycle and seed size) and explain the extant biogeographical patterns in this group. For phylogenetic reconstruction, we used molecular data obtained by sequencing the nuclear ITS region and the chloroplast trnT-trnL intergenic spacer and matK?+?trnK regions. The genus Melampyrum was found to occupy the sister position to the rest of the group. The other genera were assembled in the sister Rhinanthus-Rhynchocorys-Lathraea and Bartsia-Euphrasia-Odontites subclades. The reconstruction of life-cycle evolution yielded ambiguous results suggesting nonetheless a substantially higher likelihood of perenniality compared to annuality in most ancestor lineages. Seed size varied across two orders of magnitude (average weight per seed: 0.02–7.22 mg) and tended to decrease in the Bartsia-Euphrasia-Odontites subclade compared to the rest of the group. Seed-size evolution was correlated with life-history evolution in the group if the generally small-seeded Bartsia-Euphrasia-Odontites subclade is excluded. We formulated hypotheses relating the extant biogeographical affinities of individual genera to the geological history of the Euro-Caucasian diversity center of the group. Notable dispersal events in Euphrasia and Bartsia were hypothesized to be allowed or at least facilitated by a specific combination of the life-history traits. 相似文献
93.
Jakub Kreisinger Pavel Munclinger Veronika Javůrková Tomáš Albrecht 《Journal of avian biology》2010,41(5):551-557
A method that was based on non‐invasive sampling of genetic material was used to determine the rates of extra‐pair paternity (EPP) and conspecific brood parasitism (CBP) in mallards. Maternal and offspring DNA were extracted from feathers in nest material and hatched eggshell membranes. Using 8 microsatelite loci, extra‐pair offspring were detected in 48% of nests and accounted for 9.3% of all offspring. In addition, 10.1% of the offspring were confirmed to result from CBP, and 24% of all nests contained at least 1 offspring from CBP. Rates of conspecific nest parasitism were higher than those of related species, which might have been due to higher breeding densities at our study site. The incidence of EPP was distributed randomly (i.e. did not deviate from bionomial distribution) throughout the population, indicating that variations in pre‐copulatory (e.g. female choice, mate guarding) or post‐copulatory processes (e.g. sperm competition, cryptic female choice) do not affect the distribution of EPP among breeding pairs markedly. Yet, our data provide evidence of variation in the risk of being parasitized among breeding females. The occurrence of CBP and EPP was unaffected by the timing of the breeding attempt or breeding synchrony. 相似文献
94.
Lenka Monincová Miloš Buděšínský Jiřina Slaninová Oldřich Hovorka Josef Cvačka Zdeněk Voburka Vladimír Fučík Lenka Borovičková Lucie Bednárová Jakub Straka Václav Čeřovský 《Amino acids》2010,39(3):763-775
Two novel antimicrobial peptides, named halictines, were isolated from the venom of the eusocial bee Halictus sexcinctus. Their primary sequences were established by ESI-QTOF mass spectrometry, Edman degradation and enzymatic digestion as Gly-Met-Trp-Ser-Lys-Ile-Leu-Gly-His-Leu-Ile-Arg-NH2 (HAL-1), and Gly-Lys-Trp-Met-Ser-Leu-Leu-Lys–His-Ile-Leu-Lys-NH2 (HAL-2). Both peptides exhibited potent antimicrobial activity against Gram-positive and Gram-negative bacteria but also noticeable hemolytic activity. The CD spectra of HAL-1 and HAL-2 measured in the presence of trifluoroethanol or SDS showed ability to form an amphipathic α-helical secondary structure in an anisotropic environment such as bacterial cell membrane. NMR spectra of HAL-1 and HAL-2 measured in trifluoroethanol/water confirmed formation of helical conformation in both peptides with a slightly higher helical propensity in HAL-1. Altogether, we prepared 51 of HAL-1 and HAL-2 analogs to study the effect of such structural parameters as cationicity, hydrophobicity, α-helicity, amphipathicity, and truncation on antimicrobial and hemolytic activities. The potentially most promising analogs in both series are those with increased net positive charge, in which the suitable amino acid residues were replaced by Lys. This improvement basically relates to the increase of antimicrobial activity against pathogenic Pseudomonas aeruginosa and to the mitigation of hemolytic activity. 相似文献
95.
Molecular sensors based on intramolecular Förster resonance energy transfer (FRET) have become versatile tools to monitor regulatory molecules in living tissue. However, their use is often compromised by low signal strength and excessive noise. We analyzed signal/noise (SNR) aspects of spectral FRET analysis methods, with the following conclusions: The most commonly used method (measurement of the emission ratio after a single short wavelength excitation) is optimal in terms of signal/noise, if only relative changes of this uncalibrated ratio are of interest. In the case that quantitative data on FRET efficiencies are required, these can be calculated from the emission ratio and some calibration parameters, but at reduced SNR. Lux-FRET, a recently described method for spectral analysis of FRET data, allows one to do so in three different ways, each based on a ratio of two out of three measured fluorescence signals (the donor and acceptor signal during a short-wavelength excitation and the acceptor signal during long wavelength excitation). Lux-FRET also allows for calculation of the total abundance of donor and acceptor fluorophores. The SNR for all these quantities is lower than that of the plain emission ratio due to unfavorable error propagation. However, if ligand concentration is calculated either from lux-FRET values or else, after its calibration, from the emission ratio, SNR for both analysis modes is very similar. Likewise, SNR values are similar, if the noise of these quantities is related to the expected dynamic range. We demonstrate these relationships based on data from an Epac-based cAMP sensor and discuss how the SNR changes with the FRET efficiency and the number of photons collected. 相似文献
96.
Michal Dabrowski Norbert Dojer Malgorzata Zawadzka Jakub Mieczkowski Bozena Kaminska 《BMC systems biology》2010,4(1):86
Background
It is often desirable to separate effects of different regulators on gene expression, or to identify effects of the same regulator across several systems. Here, we focus on the rat brain following stroke or seizures, and demonstrate how the two tasks can be approached simultaneously. 相似文献97.
Ji?í Svoboda 《Phytochemistry》2010,71(13):1445-1449
Our understanding of plant defensive mechanisms against herbivore and pathogen attack has significantly increased over the past decade. The complex cascade of defensive events is initiated and controlled by a network of interacting plant hormones. Especially, the conjugate of jasmonate and isoleucine is a major regulator which controls gene expression and production of secondary metabolites after (a)biotic challenges. This review offers a survey of both natural and synthetic mimetics of the natural hormone which can be used for a selective manipulation and the study of the plant’s secondary metabolism. 相似文献
98.
Background
Transposable elements (TEs) are considered to be an important source of genome size variation and genetic and phenotypic plasticity in eukaryotes. Most of our knowledge about TEs comes from large genomic projects and studies focused on model organisms. However, TE dynamics among related taxa from natural populations and the role of TEs at the species or supra-species level, where genome size and karyotype evolution are modulated in concert with polyploidy and chromosomal rearrangements, remain poorly understood. We focused on the holokinetic genus Eleocharis (Cyperaceae), which displays large variation in genome size and the occurrence of polyploidy and agmatoploidy/symploidy. We analyzed and quantified the long terminal repeat (LTR) retrotransposons Ty1-copia and Ty3-gypsy in relation to changes in both genome size and karyotype in Eleocharis. We also examined how this relationship is reflected in the phylogeny of Eleocharis. 相似文献99.
After injection into male and female fifth-instar larvae of Manduca sexta, [14C]cholesterol was converted to C21 steroids, [14C]pregn-5-ene-3 beta,20-diols. These metabolites were isolated from 8-day-old pupae and were identified by TLC, HPLC, and GC-MS as the C-20 isomers of pregnene-3 beta,20-diol. They also were isolated from male and female meconium fluid (of 16-day-old pupae) following injection of [14C]cholesterol into 14-day-old pupae. 相似文献
100.
Gabriela Ludwig Lucas M. Aguiar João M. D. Miranda Gustavo M. Teixeira Walfrido K. Svoboda Luciano S. Malanski Marcos M. Shiozawa Carmen L. S. Hilst Italmar T. Navarro Fernando C. Passos 《International journal of primatology》2007,28(1):39-46
Researchers consider predation rates by terrestrial animals to be lower in the case of arboreal primates, particularly among
large-bodied species. We recorded the consumption of black-and-gold howlers (Alouatta caraya) by cougars (Puma concolor) as evidence of predation on an island of the upper Paraná River. We collected and processed fecal samples of the felid in
2004 and 2005. We identified items in the laboratory by comparison with museum specimens. We considered each species in a
fecal sample as a single occurrence. Based on analysis of the cuticle scale pattern, we identified the felid as cougar. Howlers
occurred in 4 out of the 8 fecal samples (40% of the occurrences). In addition to howlers, we also recorded 5 occurrences
of agouti (Dasyprocta azarae; 50%) and a small unidentified sigmodontine rodent (10%). The abundance of howlers and the low forest canopy in a successional
vegetation might have facilitated the predation of the large primates by a primarily terrestrial predator. The versatility
of cougars is corroborated by the consumption of prey species that were abundant in the region and that were available in
different forest strata, such as howlers and agoutis. 相似文献