全文获取类型
收费全文 | 727篇 |
免费 | 52篇 |
国内免费 | 7篇 |
专业分类
786篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 25篇 |
2017年 | 29篇 |
2016年 | 26篇 |
2015年 | 22篇 |
2014年 | 43篇 |
2013年 | 82篇 |
2012年 | 24篇 |
2011年 | 40篇 |
2010年 | 38篇 |
2009年 | 45篇 |
2008年 | 27篇 |
2007年 | 41篇 |
2006年 | 17篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 19篇 |
2002年 | 13篇 |
2001年 | 25篇 |
2000年 | 21篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有786条查询结果,搜索用时 0 毫秒
31.
Lindsay R. Mehrkam Nicolle T. Verdi Clive D. L. Wynne 《Journal of applied animal welfare science : JAAWS》2014,17(1):43-58
Private nonhuman animal sanctuaries are often financially limited in their ability to implement traditional environmental enrichment strategies. One possible solution may be to provide socialized animals with human interaction sessions. However, the merit of human interaction as enrichment has received little empirical attention to date. The present study aimed to evaluate whether human interaction could be enriching for socialized, pair-housed wolves and wolf–dog crosses at a private sanctuary. Observations of each subject were conducted in a reversal design to measure species-typical affiliation, activity levels, and aberrant behaviors when caretakers were both present and absent. The results demonstrate significantly higher levels of conspecific-directed affiliation and activity levels and reduced aberrant behavior when human interaction was available. Social play also increased when caregivers were present, supporting the hypothesis that play among conspecifics may be maintained by positive changes in an animal's environment. The potential for human interaction to be established as a scientifically validated, cost-effective enrichment strategy is supported by these findings. 相似文献
32.
33.
The genus Dysoxylum is a large genus comprising of about a dozen species, distributed in India. This is the genus which is rich in compounds like terpenoids and alkaloids. The isolated compounds from the genus were reported to have interesting biological activities. This review contains the chemical structures, along with their biological activities reported in the literature. 相似文献
34.
Nitric oxide synthase (NOS) activity was studied in the gray and white matter regions of the spinal cord 2 and 5 days after multiple cauda equina constrictions of the central processes of L7-Co5 dorsal root ganglia neurons. The results show considerable differences in enzyme activity in the thoracic, upper lumbar, lower lumbar, and sacral segments. Increased NOS activity was observed at 2 days after multiple cauda equina constrictions in the dorsal, lateral, and ventral columns of the lower lumbar segments and in the ventral column of the upper lumbar segments. The values returned to control levels within 5 postconstriction days. In the lateral columns of thoracic segments taken 2 and 5 days after surgery, NOS activity was enhanced by 54% and 55% and in the upper lumbar segments by 130% and 163%, respectively. Multiple cauda equina constrictions performed surgically for 2 and 5 days caused a significant increase in NOS activity predominantly in the gray matter regions of thoracic segments. A quite different response was found 5 days postconstriction in the upper lumbar segments, where the enzyme activity was significantly decreased in the dorsal horn, intermediate zone, and ventral horn. No such extreme differences could be seen in the lower lumbar segments, where NOS activity was significantly enhanced only in the ventral horn. The data correspond with a higher number of NOS immunoreactive somata, quantitatively evaluated in the ventral horn of the lower lumbar segments at 5 days after multiple cauda equina constrictions. While the great region-dependent heterogeneity in NOS activity seen 2 and 5 days after multiple cauda equina constrictions is quite apparent and suggestive of an active role played by nitric oxide in neuroprotective or neurotoxic processes occurring in the gray and white matter of the spinal cord, the extent of damage or the degree of neuroprotection caused by nitric oxide in compartmentalized gray and white matter in this experimental paradigm would be possible only using longer postconstriction periods. 相似文献
35.
Øyvind M. Andersen Monica Jordheim Angella Mbabazi Irene Skaar 《Phytochemistry》2010,71(13):1558-1563
Four anthocyanins, cyanidin 3-O-(2″-(5?-(E-p-coumaroyl)-β-apiofuranosyl)-β-xylopyranoside)-5-O-β-glucopyranoside, cyanidin 3-O-(2″-(5?-(E-p-coumaroyl)-β-apiofuranosyl)-β-xylopyranoside), cyanidin 3-O-(2″-(5?-(E-caffeoyl)-β-apiofuranosyl)-β-xylopyranoside) and cyanidin 3-O-(2″-(5?-(E-feroyl)-β-apiofuranosyl)-β-xylopyranoside) were isolated from leaves of African milk bush, (Synadeniumgrantii Hook, Euphorbiaceae) together with the known cyanidin 3-O-β-xylopyranoside-5-O-β-glucopyranoside and cyanidin 3-O-β-xyloside. The four former pigments are the first reported anthocyanins containing the monosaccharide apiose, and the three 5?-cinnamoyl derivative-2″-(β-apiosyl)-β-xyloside subunits have previously not been reported for any compound. 相似文献
36.
Rebecca D. Bryan Michael B. Wunder 《Ethology : formerly Zeitschrift fur Tierpsychologie》2014,120(2):180-188
Animals sharing a common habitat can indirectly receive information about their environment by observing information exchanges between other animals, a process known as eavesdropping. Animals that use an auditory alarm calling system are an important indirect information source for eavesdropping individuals in their environments. We investigated whether Western burrowing owls (Athene cunicularia hypugaea) nesting on black‐tailed prairie dog (Cynomys ludovicianus) colonies responded to broadcasts of prairie dog alarm calls. Western burrowing owls are closely associated with black‐tailed prairie dogs in Colorado and neighboring states on the Great Plains of the United States. Prairie dog burrows in active colonies can serve as nesting sites for Western burrowing owls, and prairie dogs may act as an alternative prey source for predators, potentially decreasing the burrowing owls' risk of predation through the dilution effect. Burrowing owls nesting on prairie dog colonies may also eavesdrop on prairie dog alarm calls, enhancing their survival and nesting success on prairie dog colonies. We performed broadcast experiments with three different sounds: a prairie dog alarm call, a biological control (cattle mooing), and a non‐biological control (an airplane engine), and characterized burrowing owl responses as either alert or relaxed. For each sound stimulus, we recorded the time to first alert response to broadcast sounds (latency) and also how frequently the target burrowing owl exhibited an alert response within the first ten seconds of the broadcast (intensity). Burrowing owls reacted more quickly to the prairie dog alarm than to the biological control. They significantly increased the intensity of alert behaviors in response to broadcasts of the alarm, but did not show an increased reaction to either the biological or the non‐biological control. Our results suggest that burrowing owls nesting on prairie dog colonies eavesdrop on, and increase their alert behaviors in response to, prairie dog alarm calls. 相似文献
37.
Sara C. Owczarczak-Garstecka Francine Watkins Rob Christley Huadong Yang Carri Westgarth 《Anthrozo?s》2018,31(5):537-549
Dog bites are a human public health and dog welfare problem. This qualitative study is the first to use YouTube? to examine how viewers perceive risk of, and attribute blame for, dog bites. Comments underneath 10 videos, chosen to represent a diversity of dog-bite scenarios, were analyzed inductively using thematic analysis. Six themes emerged: 1) Commentators thought that dogs are inherently good-natured but wild animals and emphasized how dogs try to avoid biting people; 2) all recognized breeds of dogs were stereotyped and breed stereotypes were used to shift the blame away from the dog and onto a bite victim, unless the dog identified in a video was a pit bull type. The dog was often blamed in such case; 3) It was argued that a breed limits the extent to which a dog can be trained and controlled; 4) Owners/handlers were often blamed for bites due to their inability to control the dog, and commentators identified the need for appropriate training and socialization in order to control dogs and reduce bite risk; 5) Bite victims were also blamed for the bites when their behavior was perceived as provoking a dog. Although children's behavior was identified as causing a risk, parents of children bitten in the videos were blamed for bites instead due to their approach to child supervision; 6) Bites in a range of contexts, such as play or when viewers thought that the victim's behavior provoked a dog, were seen as well-de-served and normal. It was concluded that although comments on publicly available videos need to be interpreted with caution due to a self-selection bias, their analysis can help to identify attitudes and perceptions towards risk around dogs that could aid bite prevention interventions and policies. 相似文献
38.
Exocrine pancreatic secretion in response to a new CCK-analog, CCK33 and caerulein in dogs 总被引:2,自引:0,他引:2
We studied the relative molar potencies of a newly synthetized cholecystokinin nonapeptide [Thr28,Nle31]CCK[25-33], natural porcine CCK33 and synthetic caerulein in conscious dogs with chronic gastric and pancreatic fistulas. Peptides were dissolved in albumin-containing solutions to prevent loss from solution. The three peptides were found to be equipotent on a molar basis in stimulating exocrine pancreatic secretion. As [Thr28,Nle31]CCK9 is a peptide less susceptible to oxidation than other forms of CCK, it is an interesting analog with many uses for medical and biological research. 相似文献
39.
A breeding programme to eradicate copper toxicosis in Danish Bedlington terriers has been established based on a DNA marker test. Genotyping of both parents is compulsory and after 1 January 2000, only homozygous non-carriers are used for breeding. In this study, two groups of Bedlington terriers were genotyped at 18 microsatellite loci. One group represented the original population of Bedlington terriers before introducing the breeding programme (n = 23); the other represented a group of homozygous non-carriers (n = 24) available for breeding after year 2000. Allele numbers, allele frequencies, observed heterozygosities (Ho), expected heterozygosities (He), locus-specific coefficients of inbreeding (Fl) and Nei's genetic distance (D) was calculated. Individual coefficients of inbreeding (Fi) were calculated from the pedigrees and an assignment test was performed. Four rare alleles were lost in the group of homozygous non-carriers. No significant differences were observed between the mean values of allele numbers, Ho, He, Fl and Fi of the two populations of dogs. Nei's genetic distance between the two populations was 0.06 and 88% of the homozygous non-carriers were assigned correctly in the assignment test. The overall diversity of the breed was low (Ho = 0.41) and the breeders were advised to include the heterozygous carriers again. 相似文献
40.
Dr. Katharina Spanel-Borowski 《Cell and tissue research》1981,214(1):155-168
Summary Morphologically, canine ovaries show two types of regression pattern in secondary follicles. In type A necrotic changes of the oocytes and the zona pellucida dominate, whereas in type B degeneration, necrobiosis and necrosis of the granulosa prevail. The atretic course of type B regression results in a pseudoantrum and leads, by pseudogrowth, to a structure imitating tertiary follicles. In both type A and type B regression, four consecutive stages of atresia are distinguished by light- and electron microscopy.True tertiary follicles display only one regression pattern which resembles type B of secondary follicles. Early, advanced, late, and terminal stages of atresia are again described. 相似文献