全文获取类型
收费全文 | 530944篇 |
免费 | 59229篇 |
国内免费 | 320篇 |
出版年
2018年 | 5223篇 |
2017年 | 5097篇 |
2016年 | 6943篇 |
2015年 | 8774篇 |
2014年 | 10497篇 |
2013年 | 15263篇 |
2012年 | 16971篇 |
2011年 | 17357篇 |
2010年 | 11719篇 |
2009年 | 10748篇 |
2008年 | 15159篇 |
2007年 | 15713篇 |
2006年 | 14680篇 |
2005年 | 14070篇 |
2004年 | 13928篇 |
2003年 | 13283篇 |
2002年 | 12803篇 |
2001年 | 28346篇 |
2000年 | 28195篇 |
1999年 | 21871篇 |
1998年 | 6548篇 |
1997年 | 7138篇 |
1996年 | 6537篇 |
1995年 | 6212篇 |
1994年 | 5985篇 |
1993年 | 5959篇 |
1992年 | 17040篇 |
1991年 | 16291篇 |
1990年 | 15704篇 |
1989年 | 15215篇 |
1988年 | 13923篇 |
1987年 | 12942篇 |
1986年 | 12041篇 |
1985年 | 11818篇 |
1984年 | 9664篇 |
1983年 | 8080篇 |
1982年 | 5998篇 |
1981年 | 5373篇 |
1980年 | 5094篇 |
1979年 | 8944篇 |
1978年 | 6813篇 |
1977年 | 6270篇 |
1976年 | 5646篇 |
1975年 | 6235篇 |
1974年 | 6764篇 |
1973年 | 6535篇 |
1972年 | 5974篇 |
1971年 | 5432篇 |
1970年 | 4679篇 |
1969年 | 4401篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Characteristics of morphology and number of melanomacrophage centers (MMCs) in the liver and spleen of the roach Rutilus rutilus and the amount of pigments in MMCs during the Haff disease outbreak and the death of fish in Lake Kotokel in relation to these parameters in the roach from Lake Baikal are described. Pathological changes in the microvasculature and parenchyma in the liver of the roach from Lake Kotokel were found. The area of melanomacrophage centers in the liver of the roach from this lake was significantly smaller, whereas the number and size of these centers in the spleen was significantly larger than in the roaches from Lake Baikal. Among the pigments studied, the strongest response to the content of this toxin in the water body was shown by hemosiderin. An increase in its amount in the spleen MMCs testifies to an enhanced degradation of erythrocytes and iron release, which may be caused by the damage of cells of the erythrocyte lineage by the toxin. 相似文献
2.
3.
Cortney C. Winkle Leslie M. McClain Juli G. Valtschanoff Charles S. Park Christopher Maglione Stephanie L. Gupton 《The Journal of cell biology》2014,205(2):217-232
Developmental axon branching dramatically increases synaptic capacity and neuronal surface area. Netrin-1 promotes branching and synaptogenesis, but the mechanism by which Netrin-1 stimulates plasma membrane expansion is unknown. We demonstrate that SNARE-mediated exocytosis is a prerequisite for axon branching and identify the E3 ubiquitin ligase TRIM9 as a critical catalytic link between Netrin-1 and exocytic SNARE machinery in murine cortical neurons. TRIM9 ligase activity promotes SNARE-mediated vesicle fusion and axon branching in a Netrin-dependent manner. We identified a direct interaction between TRIM9 and the Netrin-1 receptor DCC as well as a Netrin-1–sensitive interaction between TRIM9 and the SNARE component SNAP25. The interaction with SNAP25 negatively regulates SNARE-mediated exocytosis and axon branching in the absence of Netrin-1. Deletion of TRIM9 elevated exocytosis in vitro and increased axon branching in vitro and in vivo. Our data provide a novel model for the spatial regulation of axon branching by Netrin-1, in which localized plasma membrane expansion occurs via TRIM9-dependent regulation of SNARE-mediated vesicle fusion. 相似文献
4.
5.
6.
Lucília S. Miranda Jimena García-Rodríguez Allen G. Collins André C. Morandini Antonio C. Marques 《Organisms Diversity & Evolution》2017,17(4):753-766
The claustrum in Cnidaria is a tissue in the gastrovascular cavity delimited by a central layer of mesoglea surrounded by gastrodermis (i.e., gastrodermis-mesoglea-gastrodermis), without communication with epidermis. By dividing the gastrovascular cavity, the four claustra provide an additional level of complexity. The presence of claustra in Cubozoa and Staurozoa has been used as evidence supporting a close relationship between these two cnidarian classes. However, the detailed anatomy of the claustrum has never been comparatively analyzed, rendering the evolution of this character among Cnidaria and its homology in Staurozoa and Cubozoa uncertain. This study provides a comparative investigation of the internal anatomy of the claustrum in Staurozoa and Cubozoa, addressing its evolutionary history based on recent phylogenetic hypotheses for Cnidaria. We conclude that the claustrum is a character exclusive to some species of Staurozoa, with a homoplastic evolution in the class, and that the structure called the “claustrum” in Cubozoa corresponds to the valve of gastric ostium, a structure at the base of the manubrium, which is also present in Staurozoa with and without claustrum. Thus, the claustrum cannot be a synapomorphy of a hypothetical clade uniting Staurozoa and Cubozoa, nor can its hypothetical presence in enigmatic fossils be used to support cubozoan affinities. 相似文献
7.
8.
Calling at the highway: The spatiotemporal constraint of road noise on Pacific chorus frog communication 下载免费PDF全文
Danielle V. Nelson Holger Klinck Alexander Carbaugh‐Rutland Codey L. Mathis Anita T. Morzillo Tiffany S. Garcia 《Ecology and evolution》2017,7(1):429-440
Loss of acoustic habitat due to anthropogenic noise is a key environmental stressor for vocal amphibian species, a taxonomic group that is experiencing global population declines. The Pacific chorus frog (Pseudacris regilla) is the most common vocal species of the Pacific Northwest and can occupy human‐dominated habitat types, including agricultural and urban wetlands. This species is exposed to anthropogenic noise, which can interfere with vocalizations during the breeding season. We hypothesized that Pacific chorus frogs would alter the spatial and temporal structure of their breeding vocalizations in response to road noise, a widespread anthropogenic stressor. We compared Pacific chorus frog call structure and ambient road noise levels along a gradient of road noise exposures in the Willamette Valley, Oregon, USA. We used both passive acoustic monitoring and directional recordings to determine source level (i.e., amplitude or volume), dominant frequency (i.e., pitch), call duration, and call rate of individual frogs and to quantify ambient road noise levels. Pacific chorus frogs were unable to change their vocalizations to compensate for road noise. A model of the active space and time (“spatiotemporal communication”) over which a Pacific chorus frog vocalization could be heard revealed that in high‐noise habitats, spatiotemporal communication was drastically reduced for an individual. This may have implications for the reproductive success of this species, which relies on specific call repertoires to portray relative fitness and attract mates. Using the acoustic call parameters defined by this study (frequency, source level, call rate, and call duration), we developed a simplified model of acoustic communication space–time for this species. This model can be used in combination with models that determine the insertion loss for various acoustic barriers to define the impact of anthropogenic noise on the radius of communication in threatened species. Additionally, this model can be applied to other vocal taxonomic groups provided the necessary acoustic parameters are determined, including the frequency parameters and perception thresholds. Reduction in acoustic habitat by anthropogenic noise may emerge as a compounding environmental stressor for an already sensitive taxonomic group. 相似文献
9.
Nonalcoholic fatty liver disease and measures of early brain health in middle‐aged adults: The CARDIA study 下载免费PDF全文
10.