全文获取类型
收费全文 | 1262篇 |
免费 | 95篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 19篇 |
2021年 | 53篇 |
2020年 | 25篇 |
2019年 | 32篇 |
2018年 | 38篇 |
2017年 | 26篇 |
2016年 | 39篇 |
2015年 | 76篇 |
2014年 | 67篇 |
2013年 | 92篇 |
2012年 | 109篇 |
2011年 | 120篇 |
2010年 | 64篇 |
2009年 | 74篇 |
2008年 | 91篇 |
2007年 | 75篇 |
2006年 | 71篇 |
2005年 | 57篇 |
2004年 | 48篇 |
2003年 | 43篇 |
2002年 | 35篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有1357条查询结果,搜索用时 15 毫秒
991.
Bacterial communities reside in basal ice, sediment, and meltwater in the supra-, sub-, and proglacial environments of John Evans Glacier, Nunavut, Canada. We examined whether the subglacial bacterial community shares common members with the pro- and supraglacial communities, and by inference, whether it could be derived from communities in either of these environments (e.g., by ice overriding proglacial sediments or by in-wash of surface meltwaters). Terminal restriction fragment length polymorphism analysis of bacterial 16S rRNA genes amplified from these environments revealed that the subglacial water, basal ice, and sediment communities were distinct from those detected in supraglacial meltwater and proglacial sediments, with 60 of 142 unique terminal restriction fragments (T-RFs) detected exclusively in subglacial samples and only 8 T-RFs detected in all three environments. Supraglacial waters shared some T-RFs with subglacial water and ice, likely reflecting the seasonal flow of surface meltwater into the subglacial drainage system, whereas supraglacial and proglacial communities shared the fewest T-RFs. Thus, the subglacial community at John Evans Glacier appears to be predominantly autochthonous rather than allochthonous, and it may be adapted to subglacial conditions. Chemical analysis of water and melted ice also revealed differences between the supraglacial and proglacial environments, particularly regarding electrical conductivity and nitrate, sulfate, and dissolved organic carbon concentrations. Whereas the potential exists for common bacterial types to be broadly distributed throughout the glacial system, we have observed distinct bacterial communities in physically and chemically different glacial environments. 相似文献
992.
Yossi Yovel Maya Geva-Sagiv Nachum Ulanovsky 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(5):515-530
Echolocating bats of the genus Rousettus produce click sonar signals, using their tongue (lingual echolocation). These signals are often considered rudimentary and
are believed to enable only crude performance. However, the main argument supporting this belief, namely the click’s reported
long duration, was recently shown to be an artifact. In fact, the sonar clicks of Rousettus bats are extremely short, ~50–100 μs, similar to dolphin vocalizations. Here, we present a comparison between the sonar systems
of the ‘model species’ of laryngeal echolocation, the big brown bat (Eptesicus fuscus), and that of lingual echolocation, the Egyptian fruit bat (Rousettus aegyptiacus). We show experimentally that in tasks, such as accurate landing or detection of medium-sized objects, click-based echolocation
enables performance similar to laryngeal echolocators. Further, we describe a sophisticated behavioral strategy for biosonar
beam steering in clicking bats. Finally, theoretical analyses of the signal design—focusing on their autocorrelations and
wideband ambiguity functions—predict that in some aspects, such as target ranging and Doppler-tolerance, click-based echolocation
might outperform laryngeal echolocation. Therefore, we suggest that click-based echolocation in bats should be regarded as
a viable echolocation strategy, which is in fact similar to the biosonar used by most echolocating animals, including whales
and dolphins. 相似文献
993.
Maya Fuerstenau-Sharp Martina E. Zimmermann Klaus Stark Nico Jentsch Melanie Klingenstein Marzena Drzymalski Stefan Wagner Lars S. Maier Ute Hehr Andrea Baessler Marcus Fischer Christian Hengstenberg 《PloS one》2015,10(5)
Induced pluripotent stem (iPS) cells have an enormous potential for physiological studies. A novel protocol was developed combining the derivation of iPS from peripheral blood with an optimized directed differentiation to cardiomyocytes and a subsequent metabolic selection. The human iPS cells were retrovirally dedifferentiated from activated T cells. The subsequent optimized directed differentiation protocol yielded 30-45% cardiomyocytes at day 16 of differentiation. The derived cardiomyocytes expressed appropriate structural markers like cardiac troponin T, α-actinin and myosin light chain 2 (MLC2V). In a subsequent metabolic selection with lactate, the cardiomyocytes content could be increased to more than 90%. Loss of cardiomyocytes during metabolic selection were less than 50%, whereas alternative surface antibody-based selection procedures resulted in loss of up to 80% of cardiomyocytes. Electrophysiological characterization confirmed the typical cardiac features and the presence of ventricular, atrial and nodal-like action potentials within the derived cardiomyocyte population. Our combined and optimized protocol is highly robust and applicable for scalable cardiac differentiation. It provides a simple and cost-efficient method without expensive equipment for generating large numbers of highly purified, functional cardiomyocytes. It will further enhance the applicability of iPS cell-derived cardiomyocytes for disease modeling, drug discovery, and regenerative medicine. 相似文献
994.
Humberto L. Perotto-Baldivieso Elvia Meléndez-Ackerman Miguel A. García Peter Leimgruber Susan M. Cooper Alma Martínez Paulina Calle Olga M. Ramos Gonzáles Maya Quiñones Catherine A. Christen Gaspar Pons 《Biodiversity and Conservation》2009,18(4):905-917
The Caribbean region is one of the five leading biodiversity hotspots in the world. Analysis of the spatial structure of critical
habitats and how it affects endemic species in this region is essential baseline information for biodiversity monitoring and
management. We quantified and evaluated the spatial structure and connectivity of depression forests on Mona Island and their
potential impact on Mona Island rock iguana habitat, as a framework to assess spatial distribution, connectivity, and the
issue of scale in small and widely dispersed habitats. Using IKONOS imagery, we mapped and delineated depression forests at
four different scales (minimum mapping units: <100, 100, 500, and 1,000 m), and calculated landscape metrics describing their
spatial structure, and connectivity, for each map resolution. Our approach resulted in a more detailed map than previously
described maps, providing better information on habitat connectivity for iguanas. The comparison of the island landscape mapped
at different scales provided evidence on how changing scales affect the output of spatial metrics and may have a significant
impact when planning decisions and assigning conservation priorities. It also highlighted the importance of adequate ecological
scales when addressing landscape management and conservation priorities. The analysis of landscapes at multiple scales provided
a mechanism to evaluate the role of patch detection and its effect on the interpretation of connectivity and spatial structure
of suitable areas for species with small and widely dispersed habitats. These methodologies can be applied other species,
in different environments, with similar limitations related to connectivity and habitat availability. 相似文献
995.
Two bacteria associated with the marine sponge Ircinia variabilis were isolated using commercial and experimental media. The use of media containing marine derived proteins improved the growth of both isolated bacteria, showing that marine bacteria need of marine derived proteins for a better growth. The composition of free and total fatty acids of both strains cultivated under different carbon source was investigated. Several diketopiperazines were isolated from both bacteria and the hypothesis of their role in the bacterial-spongy interaction is discussed. 相似文献
996.
997.
998.
999.
A thyroxine binding globulin (TBG)-like protein in the sera of developing and adult rats 总被引:1,自引:0,他引:1
L Savu R Vranckx M Maya E A Nunez 《Biochemical and biophysical research communications》1987,148(3):1165-1173
We report evidence based on equilibrium binding, electrophoretic, autoradiographic studies, that the rat possesses a major high affinity thyroid hormone binding protein, with an electrophoretic mobility and binding properties similar to those of the human thyroxine binding globulin (TBG). We show that in the sera of postnatal developing animals, the thyroxine and the triiodothyronine binding activities increase up to 10 times over adult or foetal levels, due to a high transient post-natal surge of the rat TBG. In the adult serum, the TBG persists in decreased amounts: it then yields the predominant role as thyroxine carrier to the thyroid binding prealbumin, but retains the major role as binder of triiodothyronine i.e. of the biologically active thyroid hormone. 相似文献
1000.