全文获取类型
收费全文 | 4188篇 |
免费 | 419篇 |
国内免费 | 3篇 |
专业分类
4610篇 |
出版年
2022年 | 34篇 |
2021年 | 71篇 |
2020年 | 29篇 |
2019年 | 52篇 |
2018年 | 59篇 |
2017年 | 51篇 |
2016年 | 104篇 |
2015年 | 151篇 |
2014年 | 164篇 |
2013年 | 203篇 |
2012年 | 269篇 |
2011年 | 281篇 |
2010年 | 180篇 |
2009年 | 148篇 |
2008年 | 193篇 |
2007年 | 207篇 |
2006年 | 208篇 |
2005年 | 183篇 |
2004年 | 152篇 |
2003年 | 158篇 |
2002年 | 168篇 |
2001年 | 99篇 |
2000年 | 89篇 |
1999年 | 84篇 |
1998年 | 51篇 |
1997年 | 52篇 |
1996年 | 33篇 |
1995年 | 22篇 |
1994年 | 37篇 |
1993年 | 26篇 |
1992年 | 59篇 |
1991年 | 38篇 |
1990年 | 61篇 |
1989年 | 48篇 |
1988年 | 42篇 |
1987年 | 49篇 |
1986年 | 56篇 |
1985年 | 44篇 |
1984年 | 59篇 |
1983年 | 35篇 |
1982年 | 40篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 38篇 |
1978年 | 35篇 |
1977年 | 46篇 |
1976年 | 29篇 |
1975年 | 28篇 |
1974年 | 38篇 |
1972年 | 35篇 |
排序方式: 共有4610条查询结果,搜索用时 15 毫秒
141.
142.
Isolated pea chloroplasts undergo both cyclic and non-cyclic electron flow. Both processes are coupled to photophosphorylation. During non-cyclic flow the rate of oxygen production showed ADP-governed ;photosynthetic control' analogous to respiratory control of isolated mitochondria. Measurements of ADP/O and photosynthetic control ratios yielded values of 1-1.3 and 2-5.7 respectively. ;Photosynthetic control' was shown to be dependent on the intactness of the chloroplasts. 相似文献
143.
In a prospective study of 52 consecutive women who required acceleration of labour intravenous prostaglandin E2 (PGE2) was used as the oxytocic agent. These mothers were matched for age, parity, height, gestational age, initial cervical dilatation, and station and position of the fetal head with 52 women whose labours were accelerated with oxytocin; both drugs were equally effective. Acceleration to delivery intervals, second-stage durations, the number of assisted deliveries, and Apgar scores were similar regardless of the oxytocic used. Although PGE2 compares well with oxytocin, it offers no further advantages and is more expensive and less well tried than oxytocin. 相似文献
144.
145.
Chad Husby 《The Botanical review》2013,79(2):147-177
Horsetails are unique survivors of a very ancient group of vascular plants, the Sphenophyta, which has a history reaching back to the Upper Devonian. Despite the striking conservatism of Equisetum architecture and anatomy and the small number of species (15) in the modern flora, their ability to thrive under a wide range of conditions is remarkable. This is due to a diverse suite of adaptations that allow tolerance of disturbance, soil anoxia, high metals, and salinity, along with efficient nutrient uptake and nitrogen fixation. The giant horsetails represent the largest living Sphenophyta and provide insights into how their larger ancestors lived and how this ancient lineage has managed to survive in tropical regions. 相似文献
146.
Kevin M. King Jonathan S. West Patrick C. Brunner Paul S. Dyer Bruce D. L. Fitt 《PloS one》2013,8(10)
The fungal genus Rhynchosporium (causative agent of leaf blotch) contains several host-specialised species, including R. commune (colonising barley and brome-grass), R. agropyri (couch-grass), R. secalis (rye and triticale) and the more distantly related R. orthosporum (cocksfoot). This study used molecular fingerprinting, multilocus DNA sequence data, conidial morphology, host range tests and scanning electron microscopy to investigate the relationship between Rhynchosporium species on ryegrasses, both economically important forage grasses and common wild grasses in many cereal growing areas, and other plant species. Two different types of Rhynchosporium were found on ryegrasses in the UK. Firstly, there were isolates of R. commune that were pathogenic to both barley and Italian ryegrass. Secondly, there were isolates of a new species, here named R. lolii, that were pathogenic only to ryegrass species. R. lolii was most closely related to R. orthosporum, but exhibited clear molecular, morphological and host range differences. The species was estimated to have diverged from R. orthosporum ca. 5735 years before the present. The colonisation strategy of all of the different Rhynchosporium species involved extensive hyphal growth in the sub-cuticular regions of the leaves. Finally, new species-specific PCR diagnostic tests were developed that could distinguish between these five closely related Rhynchosporium species. 相似文献
147.
148.
149.
Taylor Lotem Curson David Verutes Gregory M. Wilsey Chad 《Wetlands Ecology and Management》2020,28(3):527-541
Wetlands Ecology and Management - Salt marshes are at risk globally if they cannot keep pace with sea level rise. Along the United States Mid-Atlantic coast, high marsh has already declined, and is... 相似文献
150.
Vegetation History and Archaeobotany - Laguna Santa Elena (8.9290° N, 82.9257° W, 1055 m a.s.l.) is a small lake in the Diquís archaeological sub-region of southern Pacific... 相似文献