全文获取类型
收费全文 | 3160篇 |
免费 | 363篇 |
国内免费 | 7篇 |
出版年
2021年 | 30篇 |
2019年 | 34篇 |
2018年 | 40篇 |
2017年 | 41篇 |
2016年 | 54篇 |
2015年 | 75篇 |
2014年 | 97篇 |
2013年 | 108篇 |
2012年 | 131篇 |
2011年 | 137篇 |
2010年 | 102篇 |
2009年 | 84篇 |
2008年 | 134篇 |
2007年 | 137篇 |
2006年 | 113篇 |
2005年 | 147篇 |
2004年 | 102篇 |
2003年 | 102篇 |
2002年 | 118篇 |
2001年 | 93篇 |
2000年 | 110篇 |
1999年 | 73篇 |
1998年 | 34篇 |
1997年 | 41篇 |
1996年 | 35篇 |
1995年 | 33篇 |
1994年 | 36篇 |
1993年 | 39篇 |
1992年 | 49篇 |
1991年 | 58篇 |
1990年 | 51篇 |
1989年 | 50篇 |
1988年 | 48篇 |
1987年 | 48篇 |
1986年 | 47篇 |
1985年 | 37篇 |
1984年 | 53篇 |
1983年 | 42篇 |
1982年 | 40篇 |
1981年 | 38篇 |
1980年 | 33篇 |
1979年 | 36篇 |
1978年 | 29篇 |
1976年 | 35篇 |
1975年 | 44篇 |
1974年 | 31篇 |
1973年 | 46篇 |
1972年 | 35篇 |
1971年 | 31篇 |
1968年 | 29篇 |
排序方式: 共有3530条查询结果,搜索用时 15 毫秒
1.
2.
Interactions among species with contrasting dispersal modes explain distributions for epiphytic lichens 下载免费PDF全文
Understanding how the biodiversity response to climate change will be modified at ecological scales, e.g. by species interactions, is a major challenge. Lichen epiphytes – the close interdependent relationship between a heterotrophic fungus and photosynthetic partner (photobiont) – are used here to explore how interaction regimes (between lichen species, and between lichens and their photobionts) explain distribution patterns along spatial climatic gradients. To do this we tested field evidence for the ‘core‐fringe hypothesis’, which proposes a facilitative interaction; sexually‐reproducing and spore‐dispersed lichens with a requirement for resynthesis with a compatible photobiont (Nostoc) are facilitated by the prior establishment of asexual lichens which disperse both the fungus and photobiont together. We used two closely related Nephroma species which differ in their reproductive mode – N. laevigatum (sexual spore‐dispersed) and N. parile (asexual) – and compared their occurrence along a bioclimatic gradient to local habitat factors, including the co‐occurrence of asexual lichens which have shared specificity for compatible Nostoc genotypes. The results showed that: 1) N. laevigatum is significantly more likely to occur on trees that have already been colonised by asexual lichens with shared specificity for Nostoc, supporting the core‐fringe hypothesis, while 2) N. parile is independent of this association (strengthening the core‐fringe hypothesis), with its response to a precipitation gradient modified by microhabitat factors. This positive test for the core‐fringe hypothesis demonstrates how interaction regimes can fundamentally alter expectations under climate change. There is an assumption that spore‐dispersed lichen species could more easily track their suitable bioclimatic space through fragmented habitat, compared to asexual species with larger and heavier propagules. However, the establishment of spore‐dispersed lichen epiphytes into new habitat may be limited by the dispersal rates of asexual species, which act as key facilitators. 相似文献
3.
Eric S. Goetzman John F. Alcorn Sivakama S. Bharathi Radha Uppala Kevin J. McHugh Beata Kosmider Rimei Chen Yi Y. Zuo Megan E. Beck Richard W. McKinney Helen Skilling Kristen R. Suhrie Anuradha Karunanidhi Renita Yeasted Chikara Otsubo Bryon Ellis Yulia Y. Tyurina Valerian E. Kagan Rama K. Mallampalli Jerry Vockley 《The Journal of biological chemistry》2014,289(15):10668-10679
Long-chain acyl-CoA dehydrogenase (LCAD) is a mitochondrial fatty acid oxidation enzyme whose expression in humans is low or absent in organs known to utilize fatty acids for energy such as heart, muscle, and liver. This study demonstrates localization of LCAD to human alveolar type II pneumocytes, which synthesize and secrete pulmonary surfactant. The physiological role of LCAD and the fatty acid oxidation pathway in lung was subsequently studied using LCAD knock-out mice. Lung fatty acid oxidation was reduced in LCAD−/− mice. LCAD−/− mice demonstrated reduced pulmonary compliance, but histological examination of lung tissue revealed no obvious signs of inflammation or pathology. The changes in lung mechanics were found to be due to pulmonary surfactant dysfunction. Large aggregate surfactant isolated from LCAD−/− mouse lavage fluid had significantly reduced phospholipid content as well as alterations in the acyl chain composition of phosphatidylcholine and phosphatidylglycerol. LCAD−/− surfactant demonstrated functional abnormalities when subjected to dynamic compression-expansion cycling on a constrained drop surfactometer. Serum albumin, which has been shown to degrade and inactivate pulmonary surfactant, was significantly increased in LCAD−/− lavage fluid, suggesting increased epithelial permeability. Finally, we identified two cases of sudden unexplained infant death where no lung LCAD antigen was detectable. Both infants were homozygous for an amino acid changing polymorphism (K333Q). These findings for the first time identify the fatty acid oxidation pathway and LCAD in particular as factors contributing to the pathophysiology of pulmonary disease. 相似文献
4.
5.
Plants of four isolines of soyabean [Glycine max(L.) Merrill]Clark, vizL71-920 (maturity genecomplemente1e2e3 ), L80-5914 (E1e2e3), Clark(e1E2E3), and L65-3366 (E1E2E3), were grown inshort (12.25 h d - 1natural light) and long days (12.25 h d- 1natural light supplemented with 2.75 h d - 1low-irradianceartificial light) from first flowering to maturity in a polythenetunnel maintained at 30/24°C (day/night). Whereas therewere few differences among the isolines grown in short days,in long days the dominant alleles increased crop duration, biomassand seed yield substantially. Increases in biological and economicyield were not solely a consequence of longer crop duration:the dominant alleles also increased crop growth rate and radiationuse efficiency in long days (from 1.3 g MJ - 1total radiationine1e2e3 to 2.8 g MJ - 1inE1E2E3 ). Greater radiation use efficiencyresulted from a relatively longer leaf area duration, betterdistribution and orientation of a larger mass of leaves withinthe canopy, and smaller partitioning of assimilates to reproductivestructures. The work reveals the substantial effects of thethree lociE1 / e1, E2/ e2and E3/e3 on the response of plantgrowth, as well as development, to environment. Their relevanceto crop adaptation is discussed. Copyright 2000 Annals of BotanyCompany Glycine max(L.) Merrill, soyabean, maturity genes, flowering, phenology, growth, yield 相似文献
6.
7.
Ellis R. Kerley 《American journal of physical anthropology》1978,49(3):395-396
8.
9.
10.
phi6 bacteriophage from Pseudomonas phaseolicola has a pleomorphic shape due to an outer layer of lipid. This layer was removed with organic solvents or sodium dodecyl sulfate revealing a 50-nm cubic particle. The virus was found only in the central portion of the cell and not near the cell wall. 相似文献