全文获取类型
收费全文 | 612篇 |
免费 | 95篇 |
国内免费 | 5篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 12篇 |
2021年 | 26篇 |
2020年 | 30篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 33篇 |
2016年 | 28篇 |
2015年 | 27篇 |
2014年 | 35篇 |
2013年 | 46篇 |
2012年 | 39篇 |
2011年 | 25篇 |
2010年 | 27篇 |
2009年 | 30篇 |
2008年 | 25篇 |
2007年 | 29篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 8篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 11篇 |
2000年 | 4篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有712条查询结果,搜索用时 125 毫秒
91.
HMGB1‐induced inflammatory response promotes bone healing in murine tooth extraction socket 下载免费PDF全文
92.
Flavia Strani Antonio Profico Giorgio Manzi Diana Pushkina Pasquale Raia Raffaele Sardella Daniel DeMiguel 《Ecology and evolution》2018,8(14):7022-7030
Mastication of dietary items with different mechanical properties leaves distinctive microscopic marks on the surface of tooth enamel. The inspection of such marks (dental microwear analysis) is informative about the dietary habitus in fossil as well as in modern species. Dental microwear analysis relies on the morphology, abundance, direction, and distribution of these microscopic marks. We present a new freely available software implementation, MicroWeaR, that, compared to traditional dental microwear tools, allows more rapid, observer error free, and inexpensive quantification and classification of all the microscopic marks (also including for the first time different subtypes of scars). Classification parameters and graphical rendering of the output are fully settable by the user. MicroWeaR includes functions to (a) sample the marks, (b) classify features into categories as pits or scratches and then into their respective subcategories (large pits, coarse scratches, etc.), (c) generate an output table with summary information, and (d) obtain a visual surface‐map where marks are highlighted. We provide a tutorial to reproduce the steps required to perform microwear analysis and to test tool functionalities. Then, we present two case studies to illustrate how MicroWeaR works. The first regards a Miocene great ape obtained from through environmental scanning electron microscope, and other a Pleistocene cervid acquired by a stereomicroscope. 相似文献
93.
Piotr Matyjasiak Paweł Boniecki Maciej Fuszara Mateusz Okołowski Izabela Olejniczak 《Animal cells and systems.》2018,22(2):124-131
Feather holes are small (0.5–1?mm in diameter) deformities that appear on the vanes of flight feathers. Such deformities were found in many bird species, including galliforms and passerines. Holey flight feathers may be more permeable to air, which could have a negative effect on their ability to generate aerodynamic forces. However, to date the effects of feather holes on flight performance in birds remained unclear. In this study we investigated the relationship between the number of feather holes occurring in the wing or tail feathers and short term flight performance traits – aerial manoeuvrability, maximum velocity and maximum acceleration – in barns swallows, which are long distance migrating aerial foragers. We measured short-term flight performance of barn swallows in a standardized manner in flight tunnels. We found that acceleration and velocity were significantly negatively associated with the number of holes in the wing flight feathers, but not with those in the tail feathers. In the case of acceleration the negative relationship was sex specific – while acceleration significantly decreased with the number of feather holes in females, there was no such significant association in males. Manoeuvrability was not significantly associated with the number of feather holes. These results are consistent with the hypothesis that feather holes are costly in terms of impaired flight. We discuss alternative scenarios that could explain the observed relationships. We also suggest directions for future studies that could investigate the exact mechanism behind the negative association between the number of feather holes and flight characteristics. 相似文献
94.
Thomas Martin 《Journal of Mammalian Evolution》1997,4(1):1-18
The discovery of juvenile dentitions of late Jurassic (Kimmeridgian) Dryolestidae (Eupantotheria, Mammalia) from Guimarota, Portugal, yields for the first time information on the mode of tooth replacement in therian mammals prior to the dichotomy of placentals and marsupials. As in extant placentals, tooth replacement occurs at all antemolar positions [incisors (I1–I4), canine (C), premolars (P1–P4)]. P1 and P2 have premolariform milk predecessors, whereas the large premolariform third (P3) and fourth premolars (P4) are preceded by molariform deciduous premolars (dP3, dP4). Tooth replacement takes place in two waves, at least in the lower jaw, with I2, I4, P1, and P3 in the first series and I1, I3, C, P2, and P4 in the second. P4 is the last premolar to erupt, and it is present when the sixth molar (M6) starts to break through. The reduced tooth replacement pattern of marsupials (with only dP3 being replaced postnatally) evolved secondarily from the primitive or plesiomorphic mammalian condition, which was retained in Dryolestidae and Eutheria. 相似文献
95.
The trade-off between tooth strength and tooth penetration: predicting optimal shape of canine teeth
We investigate the shape of canine teeth under the assumption that the tooth's morphology is optimized by the evolutionary trade-off to minimize breakage and maximize ease of the penetration of prey. A series of experiments using artificial teeth to puncture the hides of a deer Odocoileus virginianus and pig Sus scrofa domesticus were conducted to establish the relationships between the tooth shape and the force needed to puncture the hide. The shapes of these teeth were also used in a beam theory analysis to calculate the strength of the teeth. Because the relative costs of puncturing and breakage were not known, a complete prediction of tooth shape was not possible. Instead, we used two independent measures of tooth shape: aspect ratio (total tooth length/tooth width at base) and rate of taper along the shank of the tooth. We quantified rate of taper in several species of felids, and by assuming this was the optimal design, we determined the relative costs of breakage and puncturing that would produce such a taper. Then, we used the relative costs to predict the aspect ratio of the optimum tooth. The average predicted value is about 2.5, very close to the average value in extant species of cats. 相似文献
96.
Several aspects of the life history of reindeer (Rangifer tarandus) are related to the nutritional condition of the animals. Moreover, compensatory growth and fattening in summer decreases
with age. The interaction of tooth wear and the standing crop of lichens on age-related variation in body size and tissue
reserves was examined to evaluate the proximate causes of density-dependent food limitation on life history parameters in
female reindeer. Studies in nine semi-domesticated free-ranging reindeer herds showed that molar height depended on the mean
standing crop of terrestrial lichens in winter habitats. The extent of tooth wear had the strongest effect on body reserves
among the oldest females (11–14 years). This indicates that severe tooth wear limits the animals′ ability to process food
efficiently and, hence, to maintain their body reserves. Both tooth wear and the biomass of lichens influenced body mass in
old females, probably because on heavily exploited winter ranges reindeer had to use higher proportions of lower-ranking coarser
foods, especially dwarf shrubs.
Received: 1 December 1997 / Accepted: 13 July 1998 相似文献
97.
98.
99.
100.