全文获取类型
收费全文 | 2716篇 |
免费 | 181篇 |
国内免费 | 1篇 |
出版年
2022年 | 14篇 |
2021年 | 34篇 |
2020年 | 27篇 |
2019年 | 26篇 |
2018年 | 32篇 |
2017年 | 25篇 |
2016年 | 62篇 |
2015年 | 90篇 |
2014年 | 108篇 |
2013年 | 132篇 |
2012年 | 153篇 |
2011年 | 149篇 |
2010年 | 99篇 |
2009年 | 90篇 |
2008年 | 154篇 |
2007年 | 148篇 |
2006年 | 128篇 |
2005年 | 132篇 |
2004年 | 105篇 |
2003年 | 127篇 |
2002年 | 123篇 |
2001年 | 64篇 |
2000年 | 53篇 |
1999年 | 49篇 |
1998年 | 45篇 |
1997年 | 36篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 37篇 |
1992年 | 52篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 25篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 32篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 29篇 |
1978年 | 17篇 |
1977年 | 17篇 |
1975年 | 19篇 |
1974年 | 14篇 |
1973年 | 17篇 |
1972年 | 17篇 |
排序方式: 共有2898条查询结果,搜索用时 15 毫秒
101.
102.
103.
Flowering requirements of Scandinavian Festuca pratensis 总被引:1,自引:0,他引:1
O.M. Heide 《Physiologia plantarum》1988,74(3):487-492
Flowering requirements of three Scandinavian cultivars of Festuca pratensis Huds, have been studied in controlled environments. At 3 and 6°C, primary induction was independent of photoperiod, while short days (8 h) were more effective than long days (24 h) at higher temperatures. The critical temperature for induction was about 15°C in short days and about 12°C in long days. Saturation of induction required 18–20 weeks of exposure to optimal conditions. At temperatures below 12°C both induction and initiation of inflorescence primordia took place in long days, while a transition to long days was required for inflorescence initiation after primary induction in short days. A minimum of 8 long-day cycles were required for flowering of plants primary induced in short days and saturation of flowering required more than 16 cycles. The critical photoperiod for secondary induction was about 13 h. High temperature (21°C) had some devernalization effect in primary induced plants, suppressing flowering compared with 15°C. 相似文献
104.
105.
Federico Perozeni Stefano Cazzaniga Thomas Baier Francesca Zanoni Gianni Zoccatelli Kyle J. Lauersen Lutz Wobbe Matteo Ballottari 《Plant biotechnology journal》2020,18(10):2053-2067
The green alga Chlamydomonas reinhardtii does not synthesize high‐value ketocarotenoids like canthaxanthin and astaxanthin; however, a β‐carotene ketolase (CrBKT) can be found in its genome. CrBKT is poorly expressed, contains a long C‐terminal extension not found in homologues and likely represents a pseudogene in this alga. Here, we used synthetic redesign of this gene to enable its constitutive overexpression from the nuclear genome of C. reinhardtii. Overexpression of the optimized CrBKT extended native carotenoid biosynthesis to generate ketocarotenoids in the algal host causing noticeable changes the green algal colour to reddish‐brown. We found that up to 50% of native carotenoids could be converted into astaxanthin and more than 70% into other ketocarotenoids by robust CrBKT overexpression. Modification of the carotenoid metabolism did not impair growth or biomass productivity of C. reinhardtii, even at high light intensities. Under different growth conditions, the best performing CrBKT overexpression strain was found to reach ketocarotenoid productivities up to 4.3 mg/L/day. Astaxanthin productivity in engineered C. reinhardtii shown here might be competitive with that reported for Haematococcus lacustris (formerly pluvialis) which is currently the main organism cultivated for industrial astaxanthin production. In addition, the extractability and bio‐accessibility of these pigments were much higher in cell wall‐deficient C. reinhardtii than the resting cysts of H. lacustris. Engineered C. reinhardtii strains could thus be a promising alternative to natural astaxanthin producing algal strains and may open the possibility of other tailor‐made pigments from this host. 相似文献
106.
107.
Temmink Ralph J. M. Dorenbosch Martijn Lamers Leon P. M. Smolders Alfons J. P. Rip Winnie Lengkeek Wouter Didderen Karin Fivash Gregory S. Bouma Tjeerd J. van der Heide Tjisse 《Hydrobiologia》2021,848(17):3987-3999
Hydrobiologia - Aquatic ecosystems provide vital services, and macrophytes play a critical role in their functioning. Conceptual models indicate that in shallow lakes, plants with different growth... 相似文献
108.
Tjisse van der Heide Christine Angelini Jimmy de Fouw Johan S. Eklf 《Ecology and evolution》2021,11(1):29-44
Ecosystems worldwide depend on habitat‐forming foundation species that often facilitate themselves with increasing density and patch size, while also engaging in facultative mutualisms. Anthropogenic global change (e.g., climate change, eutrophication, overharvest, land‐use change), however, is causing rapid declines of foundation species‐structured ecosystems, often typified by sudden collapse. Although disruption of obligate mutualisms involving foundation species is known to precipitate collapse (e.g., coral bleaching), how facultative mutualisms (i.e., context‐dependent, nonbinding reciprocal interactions) affect ecosystem resilience is uncertain. Here, we synthesize recent advancements and combine these with model analyses supported by real‐world examples, to propose that facultative mutualisms may pose a double‐edged sword for foundation species. We suggest that by amplifying self‐facilitative feedbacks by foundation species, facultative mutualisms can increase foundation species’ resistance to stress from anthropogenic impact. Simultaneously, however, mutualism dependency can generate or exacerbate bistability, implying a potential for sudden collapse when the mutualism's buffering capacity is exceeded, while recovery requires conditions to improve beyond the initial collapse point (hysteresis). Thus, our work emphasizes the importance of acknowledging facultative mutualisms for conservation and restoration of foundation species‐structured ecosystems, but highlights the potential risk of relying on mutualisms in the face of global change. We argue that significant caveats remain regarding the determination of these feedbacks, and suggest empirical manipulation across stress gradients as a way forward to identify related nonlinear responses. 相似文献
109.
110.