全文获取类型
收费全文 | 1729篇 |
免费 | 115篇 |
国内免费 | 1篇 |
专业分类
1845篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 31篇 |
2021年 | 54篇 |
2020年 | 27篇 |
2019年 | 26篇 |
2018年 | 45篇 |
2017年 | 53篇 |
2016年 | 51篇 |
2015年 | 73篇 |
2014年 | 88篇 |
2013年 | 160篇 |
2012年 | 211篇 |
2011年 | 240篇 |
2010年 | 208篇 |
2009年 | 114篇 |
2008年 | 103篇 |
2007年 | 45篇 |
2006年 | 39篇 |
2005年 | 27篇 |
2004年 | 33篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1991年 | 4篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 8篇 |
1969年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有1845条查询结果,搜索用时 15 毫秒
1.
A crocodilian skeleton from the «série du gypse d'Aix (basal Aquitanian) at Venelles (Bouches-du-Rhône) is described and referred to Diplocynodon cf. rateli. The specimen seems to have been mutilated by scavengers before burial. The occurrence of the freshwater crocodilian Diplocynodon in the «série du gypse d'Aix is in agreement with recent reconstructions of the depositional environment, which suggest a basin with a fluctuating, but usually low, salinity. 相似文献
2.
JOSÉ L. CARBALLIDO OLIVER W. M. RAUHUT DIEGO POL LEONARDO SALGADO 《Zoological Journal of the Linnean Society》2011,163(2):605-662
The diversification and early evolution of neosauropod dinosaurs is mainly recorded from the Upper Jurassic of North America, Europe, and Africa. Our understanding of this evolutionary stage is far from complete, especially in the Southern Hemisphere. A partial skeleton of a large sauropod from the Upper Jurassic Cañadón Calcáreo Formation of Patagonia was originally described as a ‘cetiosaurid’ under the name Tehuelchesaurus benitezii. The specimen is here redescribed in detail and the evidence presented indicates that this taxon is indeed a neosauropod, thus representing one of the oldest records of this clade in South America. A complete preparation of the type specimen and detailed analysis of its osteology revealed a great number of features of phylogenetic significance, such as fully opisthocoelous dorsal vertebrae, the persistence of true pleurocoels up to the first sacral vertebra, associated with large camerae in the centrum and supraneural camerae, and an elaborate neural arch lamination, including two apomorphic laminae in the infradiapophyseal fossa. The phylogenetic relationships of this taxon are tested through an extensive cladistic analysis that recovers Tehuelchesaurus as a non‐titanosauriform camarasauromorph, deeply nested within Neosauropoda. Camarasauromorph sauropods were widely distributed in the Late Jurassic, indicating a rapid evolution and diversification of the group. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 605–662. 相似文献
3.
4.
5.
JAVIER GUTIÉRREZ ILLÁN DAVID GUTIÉRREZ SONIA B. DÍEZ ROBERT J. WILSON 《Ecological Entomology》2012,37(2):134-144
1. Impacts of global change on the distribution, abundance, and phenology of species have been widely documented. In particular, recent climate change has led to widespread changes in animal and plant seasonality, leading to debate about its potential to cause phenological mismatches among interacting taxa. 2. In mountainous regions, populations of many species show pronounced phenological gradients over short geographic distances, presenting the opportunity to test for effects of climate on phenology, independent of variation in confounding factors such as photoperiod. 3. Here we show for 32 butterfly species sampled for five years over a 1700 m gradient (560–2260 m) in a Mediterranean mountain range that, on average, annual flight period is delayed with elevation by 15–22 days per kilometre. Species mainly occurring at low elevations in the region, and to some extent those flying earlier in the year, showed phenological delays of 23–36 days per kilometre, whereas the flight periods of species that occupy high elevations, or fly in late summer, were consistently more synchronised over the elevation gradient. 4. Elevational patterns in phenology appear to reflect a narrowing phenological window of opportunity for larval and adult butterfly activity of high elevation and late‐flying species. 5. Here, we speculate as to the causes of these patterns, and the consequences for our ability to predict species responses to climate change. Our results raise questions about the use of space–time substitutions in predicting phenological responses to climate change, since traits relating to flight period and environmental associations may influence the capacity of species to adapt to changing climates. 相似文献
6.
The orientation to and landing on a source of human odour by female Culex quinquefasciatus Say (Diptera: Culicidae) is observed in a wind tunnel without an airflow or with a laminar airflow of 0.2 m s?1. Odours from human feet are collected by ‘wearing’ clean glass beads inside a stocking and presenting beads in a Petri dish in a wind tunnel. Mosquitoes are activated by brief exposure to a 1 L min?1 jet of 4% CO2 positioned 10 cm from the release cage. In moving air at 0.2 m s?1, a mean ± SE of 3.45 ± 0.49 landings are observed in 10‐min trials (five mosquitoes per trial), whereas 6.50 ± 0.96 landings are recorded in still air. Furthermore, 1.45 ± 0.31 mosquitoes are recorded on beads at any one time in moving air (a measure of individuals landing versus one landing multiple times) compared with 3.10 ± 0.31 in still air. Upwind flight to beads in moving air is demonstrated by angular headings of flight immediately before landing, whereas approaches to beads in still air are oriented randomly. The mean ± SE latency until first landing is 226.7 ± 17.98 s in moving air compared with 122.5 ± 24.18 in still air. Strategies used to locate a prospective host at close range in still air are considered. 相似文献
7.
8.
D. K. Kambarova V. V. Belyaev A. V. Volkova S. G. Oganesyan V. Z. El Salim G. A. Oganesyan 《Journal of Evolutionary Biochemistry and Physiology》2010,46(5):501-510
A possibility is discussed of use of methods of nonlinear dynamics for analysis of spontaneous EEG and of the EEG caused by
low acoustic stimuli in healthy people and in patients with epilepsy. The use of methods of nonlinear dynamics—the fractal
dimension of EEG—in clinical and scientific practice is described. 相似文献
9.
Ricardo Fagundes da Rocha Marcos Roberto de Oliveira Matheus Augusto de Bittencourt Pasquali Michael Éverton Andrades Max William Soares Oliveira Guilherme Antônio Behr José Cláudio Fonseca Moreira 《Cell biochemistry and function》2010,28(3):190-196
Exercise training has been used for treatment/prevention of many cardiovascular diseases, but the mechanisms need to be clarified. Thus, our aim was to compare oxidative stress parameters between rats submitted to a swimming training and sedentary rats (control). Twelve male rats were divided into two groups: control and exercise training. The exercise training had daily 1 h swimming sessions for 8 weeks and a load (5% of its body mass) was placed in rat's tail. Thereafter the animals were killed, aorta and heart were surgically removed and blood was collected. Body mass gain, thiobarbituric acid reactive species (TBARS), carbonyl content, total reactive antioxidant potential (TRAP), total antioxidant reactivity (TAR), superoxide dismutase (SOD) activity and catalase (CAT) activity were evaluted. The trained rats showed a lower body mass gain and no modifications on heart. An increased SOD activity was observed on aorta after the training, but no changes were seen for CAT activity, which led to an increased SOD/CAT ratio. The arterial TBARS was also increased for trained rats. The decrease in TRAP in exercise training was the single modification on plasma. Our findings suggest that the increased SOD activity could play a role in vascular adaptations to exercise training. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.