全文获取类型
收费全文 | 1166篇 |
免费 | 82篇 |
出版年
2023年 | 6篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 22篇 |
2017年 | 22篇 |
2016年 | 26篇 |
2015年 | 35篇 |
2014年 | 28篇 |
2013年 | 85篇 |
2012年 | 91篇 |
2011年 | 95篇 |
2010年 | 57篇 |
2009年 | 59篇 |
2008年 | 61篇 |
2007年 | 57篇 |
2006年 | 53篇 |
2005年 | 56篇 |
2004年 | 70篇 |
2003年 | 49篇 |
2002年 | 44篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1976年 | 4篇 |
1971年 | 6篇 |
1955年 | 8篇 |
1954年 | 27篇 |
1953年 | 8篇 |
1952年 | 9篇 |
1951年 | 9篇 |
1950年 | 7篇 |
1949年 | 7篇 |
排序方式: 共有1248条查询结果,搜索用时 15 毫秒
191.
Influence of body composition on the metabolic rate of nestling European shags (Phalacrocorax aristotelis) 总被引:2,自引:0,他引:2
C. Bech J. E. Østnes 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):263-270
During the early development of avian nestlings, their mass-specific resting metabolic rate (RMR) changes in a biphasic pattern
with the peak value often being much higher than that expected for an adult bird of similar body mass. In the present study
we examined the possible influence of variations in the size of internal organs in “setting” the high RMR and peak metabolic
rate (PMR) during development in a large altricial species, the European shag (Phalacrocorax aristotelis). Thermoneutral RMR and cold-exposure induced PMR were measured in nestlings 15 days old, the age at which the highest RMR
occurred during development. Body mass averaged 414 g. Mean values of RMR and PMR were 5.75 W and 9.08 W, respectively; the
RMR value corresponds to approximately 250% of the expected value for an adult non-passerine bird of similar body mass. The
masses of all the organs measured (breast and leg muscles, heart, liver, intestine, and kidney) varied isometrically with
total body mass. However, large chicks had a significantly lower fractional water content than small chicks, suggesting that
the former had achieved a higher level of functional maturity. In contrast to what has been suggested for adult birds in general,
the heart and kidney masses of shag nestlings were not significantly correlated with the metabolic rates. The intestine length,
in contrast, was highly and positively correlated with both the RMR and the PMR, i.e. intestine length was a better predictor
of RMR and PMR than was total body mass. In addition, liver mass was positively correlated with RMR. The results of the present
study suggest that the liver in particular may play a key role in establishing the high, mass-specific RMR which is attained
during development in bird chicks. Our results also support previous suggestions that early in their development, altricial
chicks mainly allocate energy to the growth of `energy-processing' organs (such as the intestine and liver) rather than to
`energy-consuming' organs.
Accepted: 3 March 1999 相似文献
192.
E. Fuglei N. A. Øritsland 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(6):361-369
Post-absorptive resting metabolic rates (RMRs), body mass and ad libitum food intake were recorded on an annual cycle in
captive arctic foxes (Alopex lagopus) at Svalbard. During the light season in May and in the dark period in November, RMR during starvation and subsequent re-feeding
were also measured. In contrast to earlier findings, the present study indicated a seasonal trend in post-absorptive RMR (in
W · kg−1 and W · kg−0.75). The values in the light summer were 15% and 11% higher than the values in the dark winter, suggesting a physiological adaptation
aiding energy conservation during winter in arctic foxes. Body mass and ad libitum food intake varied inversely through the
year. A significant reduction in RMR (in W and W · kg−0.75) with starvation (metabolic depression) was recorded both in May and November, indicating an adaptation to starvation in
arctic foxes. The lack of metabolic depression during a period of starvation that was concomitant with extremely cold ambient
temperatures in November 1994 indicates that metabolic responses to starvation may be masked by thermoregulatory needs. At
very low ambient temperatures, arctic foxes may require increased heat production which cannot be achieved via below-average
rates of metabolism.
Accepted: 7 June 1999 相似文献
193.
Gunnar Srensen Mattias Rickhag Damiana Leo Matthew D. Lycas Pernille Herrstedt Ridderstrm Pia Weikop Jamila H. Lilja Pedro Rifes Freja Herborg David Woldbye Gitta Wrtwein Raul R. Gainetdinov Anders Fink-Jensen Ulrik Gether 《The Journal of biological chemistry》2021,297(6)
The dopamine (DA) transporter (DAT) is part of a presynaptic multiprotein network involving interactions with scaffold proteins via its C-terminal PDZ domain–binding sequence. Using a mouse model expressing DAT with mutated PDZ-binding sequence (DAT-AAA), we previously demonstrated the importance of this binding sequence for striatal expression of DAT. Here, we show by application of direct stochastic reconstruction microscopy not only that the striatal level of transporter is reduced in DAT-AAA mice but also that the nanoscale distribution of this transporter is altered with a higher propensity of DAT-AAA to localize to irregular nanodomains in dopaminergic terminals. In parallel, we observe mesostriatal DA adaptations and changes in DA-related behaviors distinct from those seen in other genetic DAT mouse models. DA levels in the striatum are reduced to ∼45% of that of WT, accompanied by elevated DA turnover. Nonetheless, fast-scan cyclic voltammetry recordings on striatal slices reveal a larger amplitude and prolonged clearance rate of evoked DA release in DAT-AAA mice compared with WT mice. Autoradiography and radioligand binding show reduced DA D2 receptor levels, whereas immunohistochemistry and autoradiography show unchanged DA D1 receptor levels. In behavioral experiments, we observe enhanced self-administration of liquid food under both a fixed ratio of one and progressive ratio schedule of reinforcement but a reduction compared with WT when using cocaine as reinforcer. In summary, our data demonstrate how disruption of PDZ domain interactions causes changes in DAT expression and its nanoscopic distribution that in turn alter DA clearance dynamics and related behaviors. 相似文献
194.
Late Pleistocene origin of the entire circumarctic range of the arctic‐alpine plant Kalmia procumbens 下载免费PDF全文
Hajime Ikeda Pernille Bronken Eidesen Valentin Yakubov Vyacheslav Barkalov Christian Brochmann Hiroaki Setoguchi 《Molecular ecology》2017,26(20):5773-5783
The circumarctic ranges of arctic‐alpine plants are thought to have been established in the late Pliocene/early Pleistocene, when the modern arctic tundra was formed in response to climate cooling. Previous findings of range‐wide genetic structure in arctic‐alpine plants have been thought to support this hypothesis, but few studies have explicitly addressed the temporal framework of the genetic structure. Here, we estimated the demographic history of the genetic structure in the circumarctic Kalmia procumbens using sequences of multiple nuclear loci and examined whether its genetic structure reflects prolonged isolation throughout the Pleistocene. Both Bayesian clustering and phylogenetic analyses revealed genetic distinction between alpine and arctic regions, whereas detailed groupings were somewhat discordant between the analyses. By assuming a population grouping based on the phylogenetic analyses, which likely reflects a deeper intraspecific divergence, we conducted model‐based analyses and demonstrated that the intraspecific genetic divergence in K. procumbens likely originated during the last glacial period. Thus, there is no need to postulate range separation throughout the Pleistocene to explain the current genetic structure in this species. This study demonstrates that range‐wide genetic structure in arctic‐alpine plants does not necessarily result from the late Pliocene/early Pleistocene origin of their circumarctic ranges and emphasizes the importance of a temporal framework of the current genetic structure for understanding the biogeographic history of the arctic flora. 相似文献
195.
Biological nitrogen (N2) fixation performed by diazotrophs (N2 fixing bacteria) is thought to be one of the main sources of plant available N in pristine ecosystems like arctic tundra. However, direct evidence of a transfer of fixed N2 to non-diazotroph associated plants is lacking to date. Here, we present results from an in situ 15N–N2 labelling study in the High Arctic. Three dominant vegetation types (organic crust composed of free-living cyanobacteria, mosses, cotton grass) were subjected to acetylene reduction assays (ARA) performed regularly throughout the growing season, as well as 15N–N2 incubations. The 15N-label was followed into the dominant N2 fixer associations, soil, soil microbial biomass and non-diazotroph associated plants three days and three weeks after labelling. Mosses contributed most to habitat N2 fixation throughout the measuring campaigns, and N2 fixation activity was highest at the beginning of the growing season in all plots. Fixed 15N–N2 became quickly (within 3 days) available to non-diazotroph associated plants in all investigated vegetation types, proving that N2 fixation is an actual source of available N in pristine ecosystems. 相似文献
196.
Maria B. Olsen Gunn A. Hildrestrand Katja Scheffler Leif Erik Vinge Katrine Alfsnes Vuk Palibrk Junbai Wang Christine G. Neurauter Luisa Luna Jostein Johansen Jonas D.S. Øgaard Ingrid K. Ohm Geir Slupphaug Anna Kuśnierczyk Arnt E. Fiane Sverre-Henning Brorson Lili Zhang Lars Gullestad Alexandra V. Finsen 《Cell reports》2017,18(1):82-92
197.
Døhn UM Ejbjerg BJ Hasselquist M Narvestad E Møller J Thomsen HS Østergaard M 《Arthritis research & therapy》2008,10(1):R25-8
Background
The objectives of the present study were, with multidetector computed tomography (CT) as the reference method, to determine the performance of magnetic resonance imaging (MRI) and radiography for the detection of bone erosions in rheumatoid arthritis wrist bones, and to test whether measuring volumes of erosions on CT and MRI is reproducible and correlated to semiquantitative assessments (scores) of erosions on CT, MRI and radiography.Methods
Seventeen patients with rheumatoid arthritis and four healthy control individuals underwent CT, MRI and radiography of one wrist, performed on the same day. CT was performed on a Philips Mx8000IDT unit (voxel size 0.4 mm × 0.4 mm × 1 mm) and MRI was performed on a Philips Panorama 0.6T unit (voxel size 0.4 mm × 0.4 mm × 0.4 mm). Images were evaluated separately for erosions in all wrist bones and were scored according to the principles of the Outcome Measures in Rheumatology Rheumatoid Arthritis MRI Scoring System (CT and MRI) and the Sharp/van der Heijde (radiographs) scoring methods. Measurements of erosion volumes of all erosions were performed twice with a 1-week interval.Results
With CT as the reference method, the overall sensitivity, specificity and accuracy (concordance) of MRI for detecting erosions were 61%, 93% and 77%, respectively, while the respective values were 24%, 99% and 63% for radiography. The intramodality agreements when measuring erosion volumes were high for both CT and MRI (Spearman correlation coefficients 0.92 and 0.90 (both P < 0.01), respectively). Correlations between volumes and scores of individual erosions were 0.96 for CT and 0.99 for MRI, while they were 0.83 (CT) and 0.80 (MRI) for persons' total erosion volume and total score (all P < 0.01).Conclusion
With CT as the reference method, MRI showed moderate sensitivity and good specificity and accuracy for detection of erosions in rheumatoid arthritis and healthy wrist bones, while radiography showed very low sensitivity. The tested volumetric method was highly reproducible and correlated to scores of erosions. 相似文献198.
199.
Karen Helene Ørstavik 《Human genetics》2009,126(3):363-373
200.