全文获取类型
收费全文 | 5988篇 |
免费 | 662篇 |
国内免费 | 1篇 |
出版年
2023年 | 39篇 |
2022年 | 90篇 |
2021年 | 182篇 |
2020年 | 93篇 |
2019年 | 124篇 |
2018年 | 127篇 |
2017年 | 94篇 |
2016年 | 175篇 |
2015年 | 222篇 |
2014年 | 290篇 |
2013年 | 328篇 |
2012年 | 374篇 |
2011年 | 382篇 |
2010年 | 215篇 |
2009年 | 174篇 |
2008年 | 265篇 |
2007年 | 241篇 |
2006年 | 214篇 |
2005年 | 223篇 |
2004年 | 229篇 |
2003年 | 205篇 |
2002年 | 163篇 |
2001年 | 115篇 |
2000年 | 134篇 |
1999年 | 123篇 |
1998年 | 61篇 |
1997年 | 61篇 |
1996年 | 68篇 |
1995年 | 52篇 |
1994年 | 53篇 |
1993年 | 43篇 |
1992年 | 93篇 |
1991年 | 105篇 |
1990年 | 85篇 |
1989年 | 84篇 |
1988年 | 89篇 |
1987年 | 82篇 |
1986年 | 69篇 |
1985年 | 75篇 |
1984年 | 60篇 |
1983年 | 53篇 |
1982年 | 33篇 |
1979年 | 43篇 |
1978年 | 33篇 |
1976年 | 31篇 |
1975年 | 36篇 |
1974年 | 54篇 |
1973年 | 45篇 |
1972年 | 39篇 |
1968年 | 36篇 |
排序方式: 共有6651条查询结果,搜索用时 15 毫秒
1.
2.
3.
The dose of intravenous diazepam required for sedation was estimated in a series of 78 patients aged 17-85 years given the drug for dental and endoscopic procedures. Multiple regression analysis showed a significant correlation (r = 0.71; p less than 0.001) between dose and age, body weight, the taking of regular sedation, and the taking of more than 40 g alcohol daily, but there were no differences in the doses required between men and women, smokers and non-smokers, inpatients and outpatients, or dental and endoscopy patients. Patients aged 80 required an average dose of 10 mg and patients aged 20 an average dose of 30 mg, and the dose required was much higher in those receiving regular sedation or having a high alcohol intake. Plasma total and free diazepam concentrations were measured in the second half of the series of patients (n = 37). Plasma concentrations required for sedation fell twofold to threefold between the ages of 20 and 80 and were significantly higher in those taking regular sedation or alcohol. Differences in the acute response to diazepam appeared to be due to differences in the sensitivity of the central nervous system (pharmacodynamic tolerance) rather than to differences in pharmacokinetic factors. 相似文献
4.
5.
Philippe Fernandez‐Fournier Samantha Straus Ruth Sharpe Leticia Avils 《Ecological Entomology》2019,44(2):157-162
1. Manipulation of host behaviour by parasitoids has long captured the imagination of ecologists. Parasitoid wasps in the Polysphincta group of genera develop as external parasitoids of spiders. 2. In the present study, the previously undescribed interaction between a Zatypota sp. wasp (Ichneumonidae) and a social spider Anelosimus eximius (Theridiidae) is described. The larva of this Zatypota wasp is found to induce its host to disperse from their communal web and build an entirely enclosed web consisting of densely spun silk. 3. The wasp is observed to target primarily immature A. eximius individuals, with 37.5–44% of nests in a given area being parasitised. Of those nests, approximately 1.3–2.0% of individuals are hosts to the parasitoid larvae. Larger spider colonies had a significantly higher probability of harbouring parasitoids. 4. This interaction results in unusual behaviours for A. eximius induced by the parasitoid: (i) leaving the protection of the social nest and (ii) building a unique, altered web that it would not otherwise build. It is suggested that the wasp may be tapping into ancestral dispersal behaviours in its host and that a social species provides this wasp an evolutionary advantage by allowing a stable host source. 相似文献
6.
Elizabeth M. A. Valleley Christine J. Harrison Yvonne Cook Mark W. J. Ferguson Paul T. Sharpe 《Chromosoma》1994,103(7):502-507
Comparative mapping studies of X-linked genes in mammals have provided insights into the evolution of the X chromosome. Many reptiles including the American alligator, Alligator mississippiensis, do not appear to possess heteromorphic sex chromosomes, and sex is determined by the incubation temperature of the egg during embryonic development. Mapping of homologues of mammalian X-linked genes in reptiles could lead to a greater understanding of the evolution of vertebrate sex chromosomes. One of the genes used in the mammalian mapping studies was ZFX, an X-linked copy of the human ZFY gene which was originally isolated as a candidate for the mammalian testis-determining factor (TDF). ZFX is X-linked in eutherians, but maps to two autosomal locations in marsupials and monotremes, close to other genes associated with the eutherian X. The alligator homologue of the ZFY/ZFX genes, Zfc, has been isolated and described previously. A detailed karyotype of A. mississippiensis is presented, together with chromosomal in situ hybridisation data localising the Zfc gene to chromosome 3. Further chromosomal mapping studies using eutherian X-linked genes may reveal conserved chromosomal regions in the alligator that have become part of the eutherian X chromosome during evolution. 相似文献
7.
8.
9.
Stephen C. Votier Anthony Bicknell Samantha L. Cox Kylie L. Scales Samantha C. Patrick 《PloS one》2013,8(3)
Commercial capture fisheries produce huge quantities of offal, as well as undersized and unwanted catch in the form of discards. Declines in global catches and legislation to ban discarding will significantly reduce discards, but this subsidy supports a large scavenger community. Understanding the potential impact of declining discards for scavengers should feature in an eco-system based approach to fisheries management, but requires greater knowledge of scavenger/fishery interactions. Here we use bird-borne cameras, in tandem with GPS loggers, to provide a unique view of seabird/fishery interactions. 20,643 digital images (one min−1) from ten bird-borne cameras deployed on central place northern gannets Morus bassanus revealed that all birds photographed fishing vessels. These were large (>15 m) boats, with no small-scale vessels. Virtually all vessels were trawlers, and gannets were almost always accompanied by other scavenging birds. All individuals exhibited an Area-Restricted Search (ARS) during foraging, but only 42% of ARS were associated with fishing vessels, indicating much ‘natural’ foraging. The proportion of ARS behaviours associated with fishing boats were higher for males (81%) than females (30%), although the reasons for this are currently unclear. Our study illustrates that fisheries form a very important component of the prey-landscape for foraging gannets and that a discard ban, such as that proposed under reforms of the EU Common Fisheries Policy, may have a significant impact on gannet behaviour, particularly males. However, a continued reliance on ‘natural’ foraging suggests the ability to switch away from scavenging, but only if there is sufficient food to meet their needs in the absence of a discard subsidy. 相似文献
10.