全文获取类型
收费全文 | 3003篇 |
免费 | 285篇 |
国内免费 | 1篇 |
专业分类
3289篇 |
出版年
2023年 | 24篇 |
2022年 | 46篇 |
2021年 | 89篇 |
2020年 | 63篇 |
2019年 | 54篇 |
2018年 | 88篇 |
2017年 | 69篇 |
2016年 | 142篇 |
2015年 | 166篇 |
2014年 | 176篇 |
2013年 | 233篇 |
2012年 | 261篇 |
2011年 | 237篇 |
2010年 | 142篇 |
2009年 | 116篇 |
2008年 | 179篇 |
2007年 | 175篇 |
2006年 | 135篇 |
2005年 | 136篇 |
2004年 | 125篇 |
2003年 | 115篇 |
2002年 | 85篇 |
2001年 | 26篇 |
2000年 | 20篇 |
1999年 | 26篇 |
1998年 | 22篇 |
1997年 | 18篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1971年 | 5篇 |
1970年 | 7篇 |
排序方式: 共有3289条查询结果,搜索用时 15 毫秒
981.
Tanmay Dixit Jana M. Riederer Stanley Quek Kate Belford Tadzio Tavares de Wand Roxanne Sicat Chris D. Jiggins 《Ecological Entomology》2020,45(6):1367-1372
1. Mutualisms, including plant-pollinator interactions, are an important component of ecosystems. 2. Plants can avoid the costs of variation in pollinator benefit by maintaining specificity. 3. We hypothesise a novel mechanism to ensure specificity, which takes advantage of the cognitive abilities of specific pollinators to exclude non-specific flower visitors. 4. Inflorescences of the tropical vine genus Psiguria produce flowers at regular intervals, with subsequent flowers smaller than predecessors. 5. The principle pollinators, Heliconius spp., possess an excellent spatial memory. 6. Therefore, decreasing flower size may ensure specific pollination: once Heliconius individuals have learnt the location of an inflorescence they will return, but inconspicuous flowers should reduce visits by non-specific pollinators with poorer spatial memories. 7. We tested the predictions of this hypothesis with field experiments in Panama. We confirmed that flowers on inflorescences are smaller than their predecessors. 8. Paired experiments showed that larger flowers attracted more pollinators and that the presence of an initial large flower increased subsequent visitation by Heliconius spp. to small flowers, indicating learning behaviour. 9. These results suggest that learning behaviour and decreasing flower size maintain visits from specific pollinators while reducing those from non-specific pollinators. We propose this as a novel mechanism for promoting pollinator specificity and discuss its ecological significance. 相似文献
982.
983.
Ashton KS St Jean DJ Poon SF Lee MR Allen JG Zhang S Lofgren JA Zhang X Fotsch C Hungate R 《Bioorganic & medicinal chemistry letters》2011,21(18):5191-5196
Through the analysis of X-ray crystallographic information and previous SAR studies, a novel series of protein kinase B (PKB/AKT) inhibitors was developed. The compounds showed nanomolar inhibition of AKT1 and were selective against cyclin-dependent kinase 2 (CDK2). 相似文献
984.
985.
986.
David D. Gustine Perry S. Barboza James P. Lawler Stephen M. Arthur Brad S. Shults Kate Persons Layne G. Adams 《Oikos》2011,120(10):1546-1556
Identifying links between nutritional condition of individuals and population trajectories greatly enhances our understanding of the ecology, conservation, and management of wildlife. For northern ungulates, the potential impacts of a changing climate to populations are predicted to be nutritionally mediated through an increase in the severity and variance in winter conditions. Foraging conditions and the availability of body protein as a store for reproduction in late winter may constrain productivity in northern ungulates, yet the link between characteristics of wintering habitats and protein status has not been established for a wild ungulate. We used a non‐invasive proxy of protein status derived from isotopes of N in excreta to evaluate the influence of winter habitats on the protein status of muskoxen in three populations in Alaska (2005–2008). Multiple regression and an information‐theoretic approach were used to compare models that evaluated the influence of population, year, and characteristics of foraging sites (components of diet and physiography) on protein status for groups of muskoxen. The observed variance in protein status among groups of muskoxen across populations and years was partially explained (45%) by local foraging conditions that affected forage availability. Protein status improved for groups of muskoxen as the amount of graminoids in the diet increased (?0.430 ± 0.31, β± 95% CI) and elevation of foraging sites decreased (0.824 ± 0.67). Resources available for reproduction in muskoxen are highly dependent upon demographic, environmental, and physiographic constraints that affect forage availability in winter. Due to their very sedentary nature in winter, muskoxen are highly susceptible to localized foraging conditions; therefore, the spatial variance in resource availability may exert a strong effect on productivity. Consequently, there is a clear need to account for climate–topography effects in winter at multiple scales when predicting the potential impacts of climatic shifts on population trajectories of muskoxen. 相似文献
987.
988.
989.
990.
Irina T. Zaharieva Mattia Calissano Mariacristina Scoto Mark Preston Sebahattin Cirak Lucy Feng James Collins Ryszard Kole Michela Guglieri Volker Straub Kate Bushby Alessandra Ferlini Jennifer E. Morgan Francesco Muntoni 《PloS one》2013,8(11)
Duchenne muscular Dystrophy (DMD) is an inherited disease caused by mutations in the dystrophin gene that disrupt the open reading frame, while in frame mutations result in Becker muscular dystrophy (BMD). Ullrich congenital muscular dystrophy (UCMD) is due to mutations affecting collagen VI genes. Specific muscle miRNAs (dystromirs) are potential non-invasive biomarkers for monitoring the outcome of therapeutic interventions and disease progression. We quantified miR-1, miR-133a,b, miR-206 and miR-31 in serum from patients with DMD, BMD, UCMD and healthy controls. MiR-1, miR-133a,b and miR-206 were upregulated in DMD, but unchanged in UCMD compared to controls. Milder DMD patients had higher levels of dystromirs than more severely affected patients. Patients with low forced vital capacity (FVC) values, indicating respiratory muscle weakness, had low levels of serum miR-1 and miR-133b. There was no significant difference in the level of the dystromirs in BMD compared to controls.We also assessed the effect of dystrophin restoration on the expression of the five dystromirs in serum of DMD patients treated systemically for 12 weeks with antisense oligomer eteplirsen that induces skipping of exon 51 in the dystrophin gene. The dystromirs were also analysed in muscle biopsies of DMD patients included in a single dose intramuscular eteplirsen clinical trial. Our analysis detected a trend towards normalization of these miRNA between the pre- and post-treatment samples of the systemic trial, which however failed to reach statistical significance. This could possibly be due to the small number of patients and the short duration of these clinical trials.Although longer term studies are needed to clarify the relationship between dystrophin restoration following therapeutic intervention and the level of circulating miRNAs, our results indicate that miR-1 and miR-133 can be considered as exploratory biomarkers for monitoring the progression of muscle weakness and indirectly the remaining muscle mass in DMD. 相似文献