全文获取类型
收费全文 | 497809篇 |
免费 | 53668篇 |
国内免费 | 5056篇 |
专业分类
556533篇 |
出版年
2021年 | 6238篇 |
2019年 | 5122篇 |
2018年 | 6521篇 |
2017年 | 5629篇 |
2016年 | 7818篇 |
2015年 | 11233篇 |
2014年 | 13029篇 |
2013年 | 17369篇 |
2012年 | 19759篇 |
2011年 | 19373篇 |
2010年 | 12501篇 |
2009年 | 11494篇 |
2008年 | 15876篇 |
2007年 | 15677篇 |
2006年 | 14689篇 |
2005年 | 13649篇 |
2004年 | 13101篇 |
2003年 | 12488篇 |
2002年 | 12019篇 |
2001年 | 20323篇 |
2000年 | 20484篇 |
1999年 | 16874篇 |
1998年 | 6446篇 |
1997年 | 6590篇 |
1996年 | 6398篇 |
1995年 | 5865篇 |
1994年 | 5909篇 |
1993年 | 5615篇 |
1992年 | 13761篇 |
1991年 | 13027篇 |
1990年 | 12916篇 |
1989年 | 12803篇 |
1988年 | 11621篇 |
1987年 | 11039篇 |
1986年 | 10242篇 |
1985年 | 10275篇 |
1984年 | 8357篇 |
1983年 | 7275篇 |
1982年 | 5589篇 |
1981年 | 4986篇 |
1980年 | 4825篇 |
1979年 | 7911篇 |
1978年 | 6138篇 |
1977年 | 5499篇 |
1976年 | 5327篇 |
1975年 | 5714篇 |
1974年 | 6003篇 |
1973年 | 5910篇 |
1972年 | 5293篇 |
1971年 | 4671篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
The infection of Planorbarius banaticus with sporocysts of Cotylurus cornutus is accompanied by an increase in aldolase activity of molluscs' haemolymph of 1.2 fold. In solutions of nitroammofoska (0.1, 1 and 10 mg/1) the activity of this ferment in infected individuals increases much higher than in non-infected ones. This results in fast carbohydrate expenditures by molluscs, intermediate hosts of trematodes, and their death from exhaustion. 相似文献
152.
We recorded the age of individual wing and tail feathers of Black-browed and Grey-headed Albatrosses Diomedea melanophris and D. chrysostoma of known age and breeding status at Bird Island, South Georgia. Breeders and non-breeders of both species moult their rectrices annually. Non-breeders moult primaries biennially. In the first year of a cycle, the outer three and some inner primaries are moulted descendantly; in the next year the inner primaries are moulted ascendantly, starting from primary seven. There is a general progression to moulting equal numbers of primaries in each half of the cycle by the time breeding starts at about 10 years of age. Grey-headed Albatrosses usually moult fewer primaries than Black-browed Albatrosses, particularly as 3-year-olds, when they undertake substantial plumage change in body moult. Most secondaries in Black-browed Albatrosses have been replaced once by age 4 years. Breeding Black-browed Albatrosses continue the moult pattern established as immatures whether they fail or not, as do failed Grey-headed Albatrosses. Successful Grey-headed Albatrosses, which breed again 16 months later, moult their three innermost primaries after breeding in the remainder of the current year and, after a period when moult is interrupted, renew the remaining primaries the following year. Comparisons between species and between failed and successful birds within species indicate that moult rate is not closely linked to the length of the interval between breeding attempts. Interspecies differences are better explained by breeding latitude, with tropical albatrosses moulting twice as fast as sub-Antarctic species, possibly reflecting food availability outside the breeding season. 相似文献
153.
154.
155.
156.
A Ba?sset J Cotonat P Montastruc 《Comptes rendus des séances de la Société de biologie et de ses filiales》1975,169(2):444-448
The authors have studied in the dog--normal or diabetic insipidus after hypothalamic lesion--submitted to oral ingestion of ethanol the effects of a few antidiuretic drug: chlorpropamid, atromid-S, carbamazepin and carisoprodol. The carisoprodol only can reduce the diuresis and the drinking provoked by ethanol. 相似文献
157.
158.
159.
160.
N. L. Biddington P. A. Brocklehurst A. S. Dearman Jane Dearman 《Physiologia plantarum》1982,55(4):407-410
Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion. 相似文献