全文获取类型
收费全文 | 7669篇 |
免费 | 660篇 |
国内免费 | 3篇 |
出版年
2023年 | 39篇 |
2022年 | 51篇 |
2021年 | 127篇 |
2020年 | 83篇 |
2019年 | 105篇 |
2018年 | 122篇 |
2017年 | 113篇 |
2016年 | 176篇 |
2015年 | 278篇 |
2014年 | 314篇 |
2013年 | 404篇 |
2012年 | 492篇 |
2011年 | 474篇 |
2010年 | 369篇 |
2009年 | 289篇 |
2008年 | 421篇 |
2007年 | 433篇 |
2006年 | 364篇 |
2005年 | 381篇 |
2004年 | 347篇 |
2003年 | 300篇 |
2002年 | 301篇 |
2001年 | 147篇 |
2000年 | 135篇 |
1999年 | 129篇 |
1998年 | 104篇 |
1997年 | 70篇 |
1996年 | 90篇 |
1995年 | 66篇 |
1994年 | 58篇 |
1993年 | 69篇 |
1992年 | 80篇 |
1991年 | 99篇 |
1990年 | 82篇 |
1989年 | 64篇 |
1988年 | 63篇 |
1987年 | 78篇 |
1986年 | 56篇 |
1985年 | 73篇 |
1984年 | 60篇 |
1983年 | 55篇 |
1982年 | 56篇 |
1981年 | 42篇 |
1980年 | 45篇 |
1979年 | 49篇 |
1976年 | 57篇 |
1975年 | 52篇 |
1974年 | 42篇 |
1973年 | 52篇 |
1969年 | 35篇 |
排序方式: 共有8332条查询结果,搜索用时 218 毫秒
1.
2.
3.
The Asian Tree Toad genus Pedostibes, as currently understood, exhibits a conspicuously disjunct distribution, posing several immediate questions relating to the biogeography and taxonomy of this poorly known group. The type species, P. tuberculosus and P. kempi, are known only from India, whereas P. hosii, P. rugosus, and P. everetti are restricted to Southeast Asia. Several studies have shown that these allopatric groups are polyphyletic, with the Indian Pedostibes embedded within a primarily South Asian clade of toads, containing the genera Adenomus, Xanthophryne, and Duttaphrynus. Southeast Asian Pedostibes on the other hand, are nested within a Southeast Asian clade, which is the sister lineage to the Southeast Asian river toad genus Phrynoidis. We demonstrate that Indian and Southeast Asian Pedostibes are not only allopatric and polyphyletic, but also exhibit significant differences in morphology and reproductive mode, indicating that the Southeast Asian species’ are not congeneric with the true Pedostibes of India. As a taxonomic solution, we describe a new genus, Rentapia
gen. nov. to accommodate the Southeast Asian species. 相似文献
4.
The distribution of grooming and touching behaviours was recorded in a group of captive ring-tailed lemurs. Grooming was found
to be performed chiefly by older, higher ranking animals; touching (i.e., “reach out and touch” behaviour) was directed primarily
by younger, low ranking animals to older, high ranking individuals. It is suggested that such touching is a submissive gesture
in this species. 相似文献
5.
The time course of changes in the level of uncoupling protein mRNA when cold-acclimated mice were returned to a thermoneutral environment (33 degrees C) was examined using a cDNA probe. Upon deacclimation, there was a marked loss of uncoupling protein mRNA within 24 h, which precedes the loss of uncoupling protein from mitochondria. This loss of uncoupling protein mRNA was selective, since there was no change in the relative proportion of cytochrome c oxidase subunit IV mRNA or poly(A)+ RNA in total RNA. The results suggest that the decrease in the mitochondrial content of uncoupling protein during deacclimation is likely the result of turnover of existing protein, with very little replacement due to a lower level of its mRNA. 相似文献
6.
Cultured porcine thoracic aorta endothelial cells were covalently labeled with 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance spectrometry revealed two major binding environments representing strongly and weakly immobilized species. The disorder parameter of weak/strong, determined from the respective peak amplitudes, was irreversibly elevated following incubation of endothelial cells with a superoxide-generating system, indicating increased membrane fluidity. The rate of increase in membrane disorder was dependent upon superoxide generation rates. Incorporation of the spin-label at concentrations less than 250 microM had no effect on cell viability. The cellular proteins reacting with the spin-label were predominantly membrane proteins, characterized by immunoblotting using a rabbit anti-4-maleimido-2,2,6,6-tetramethylpiperidinooxyl IgG, following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophorectic transfer to nitrocellulose. 相似文献
7.
Sandra L. Almeyda Zambrano Eben N. Broadbent Sam Shanee Noga Shanee Anneke Deluycker Michael Steinberg Scott A. Ford Alma Hernndez Jaramillo Robin Fernandez‐Hilario Carolina Lagos Castillo Angelica M. Almeyda Zambrano 《American journal of primatology》2019,81(8)
Habitat loss is one of the main threats to wildlife. Therefore, knowledge of habitat use and preference is essential for the design of conservation strategies and identification of priority sites for the protection of endangered species. The yellow‐tailed woolly monkey (Lagothrix flavicauda Humboldt, 1812), categorized as Critically Endangered on the IUCN Red List, is endemic to montane forests in northern Peru where its habitat is greatly threatened. We assessed how habitat use and preference in L. flavicauda are linked to forest structure and composition. The study took place near La Esperanza, in the Amazonas region, Peru. Our objective was to identify characteristics of habitat most utilized by L. flavicauda to provide information that will be useful for the selection of priority sites for conservation measures. Using presence records collected from May 2013 to February 2014 for one group of L. flavicauda, we classified the study site into three different use zones: low‐use, medium‐use, and high‐use. We assessed forest structure and composition for all use zones using 0.1 ha Gentry vegetation transects. Results show high levels of variation in plant species composition across the three use zones. Plants used as food resources had considerably greater density, dominance, and ecological importance in high‐use zones. High‐use zones presented similar structure to medium‐ and low‐use zones; thus it remains difficult to assess the influence of forest structure on habitat preference. We recommend focusing conservation efforts on areas with a similar floristic composition to the high‐use zones recorded in this study and suggest utilizing key alimentation species for reforestation efforts. 相似文献
8.
9.
10.