首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   633篇
  免费   57篇
  2021年   6篇
  2019年   5篇
  2018年   6篇
  2017年   9篇
  2016年   7篇
  2015年   16篇
  2014年   17篇
  2013年   24篇
  2012年   31篇
  2011年   34篇
  2010年   15篇
  2009年   18篇
  2008年   32篇
  2007年   26篇
  2006年   24篇
  2005年   28篇
  2004年   20篇
  2003年   28篇
  2002年   32篇
  2001年   30篇
  2000年   20篇
  1999年   13篇
  1998年   10篇
  1997年   6篇
  1995年   4篇
  1994年   7篇
  1993年   6篇
  1992年   16篇
  1991年   12篇
  1990年   13篇
  1989年   9篇
  1988年   9篇
  1987年   7篇
  1986年   6篇
  1985年   9篇
  1984年   4篇
  1983年   5篇
  1982年   7篇
  1981年   4篇
  1980年   10篇
  1979年   6篇
  1978年   11篇
  1977年   6篇
  1976年   4篇
  1975年   9篇
  1973年   7篇
  1972年   7篇
  1970年   4篇
  1966年   3篇
  1964年   3篇
排序方式: 共有690条查询结果,搜索用时 15 毫秒
1.
2.
The distribution in the human uterus of the enzyme cyclooxygenase, involved in prostaglandin synthesis, was studied using the peroxidase-antiperoxidase immunohistochemical technique. Specific staining was observed only during the luteal phase of the menstrual cycle. It was found that cyclooxygenase was localised in the surface and glandular epithelium of the endometrium but could not be demonstrated in the endometrial stroma, myometrium or blood vessels. The location of specific staining for cyclooxygenase and its variation during the menstrual cycle was the same regardless of the amount of menstrual blood loss. Tissue samples obtained from early pregnant and post-menopausal patients failed to exhibit any specific staining.  相似文献   
3.
CPS'71     
J. C. Turnbull 《CMAJ》1971,104(2):164
  相似文献   
4.
Current issues in fish welfare   总被引:11,自引:0,他引:11  
Human beings may affect the welfare of fish through fisheries, aquaculture and a number of other activities. There is no agreement on just how to weigh the concern for welfare of fish against the human interests involved, but ethical frameworks exist that suggest how this might be approached. Different definitions of animal welfare focus on an animal's condition, on its subjective experience of that condition and/or on whether it can lead a natural life. These provide different, legitimate, perspectives, but the approach taken in this paper is to focus on welfare as the absence of suffering. An unresolved and controversial issue in discussions about animal welfare is whether non‐human animals exposed to adverse experiences such as physical injury or confinement experience what humans would call suffering. The neocortex, which in humans is an important part of the neural mechanism that generates the subjective experience of suffering, is lacking in fish and non‐mammalian animals, and it has been argued that its absence in fish indicates that fish cannot suffer. A strong alternative view, however, is that complex animals with sophisticated behaviour, such as fish, probably have the capacity for suffering, though this may be different in degree and kind from the human experience of this state. Recent empirical studies support this view and show that painful stimuli are, at least, strongly aversive to fish. Consequently, injury or experience of other harmful conditions is a cause for concern in terms of welfare of individual fish. There is also growing evidence that fish can experience fear‐like states and that they avoid situations in which they have experienced adverse conditions. Human activities that potentially compromise fish welfare include anthropogenic changes to the environment, commercial fisheries, recreational angling, aquaculture, ornamental fish keeping and scientific research. The resulting harm to fish welfare is a cost that must be minimized and weighed against the benefits of the activity concerned. Wild fish naturally experience a variety of adverse conditions, from attack by predators or conspecifics to starvation or exposure to poor environmental conditions. This does not make it acceptable for humans to impose such conditions on fish, but it does suggest that fish will have mechanisms to cope with these conditions and reminds us that pain responses are in some cases adaptive (for example, suppressing feeding when injured). In common with all vertebrates, fish respond to environmental challenges with a series of adaptive neuro‐endocrine adjustments that are collectively termed the stress response. These in turn induce reversible metabolic and behavioural changes that make the fish better able to overcome or avoid the challenge and are undoubtedly beneficial, in the short‐term at least. In contrast, prolonged activation of the stress response is damaging and leads to immuno‐suppression, reduced growth and reproductive dysfunction. Indicators associated with the response to chronic stress (physiological endpoints, disease status and behaviour) provide a potential source of information on the welfare status of a fish. The most reliable assessment of well‐being will be obtained by examining a range of informative measures and statistical techniques are available that enable several such measures to be combined objectively. A growing body of evidence tells us that many human activities can harm fish welfare, but that the effects depend on the species and life‐history stage concerned and are also context‐dependent. For example, in aquaculture, adverse effects related to stocking density may be eliminated if good water quality is maintained. At low densities, bad water quality may be less likely to arise whereas social interactions may cause greater welfare problems. A number of key differences between fish and birds and mammals have important implications for their welfare. Fish do not need to fuel a high body temperature, so the effects of food deprivation on welfare are not so marked. For species that live naturally in large shoals, low rather than high densities may be harmful. On the other hand, fish are in intimate contact with their environment through the huge surface area of their gills, so they are vulnerable to poor water quality and water borne pollutants. Extrapolation between taxa is dangerous and general frameworks for ensuring welfare in other vertebrate animals need to be modified before they can be usefully applied to fish. The scientific study of fish welfare is at an early stage compared with work on other vertebrates and a great deal of what we need to know is yet to be discovered. It is clearly the case that fish, though different from birds and mammals, however, are sophisticated animals, far removed from unfeeling creatures with a 15 s memory of popular misconception. A heightened appreciation of these points in those who exploit fish and in those who seek to protect them would go a long way towards improving fish welfare.  相似文献   
5.
6.
A series of 140 previously untreated patients with tonic-clonic or partial seizures were randomised to receive either phenytoin or sodium valproate. There was no difference between the treatment groups in pretreatment variables that might influence outcome. Sodium valproate and phenytoin in the treatment of tonic-clonic or partial seizures showed no difference in efficacy as regards time to two year remission or time to first seizure. When the possible prognostic factors were studied, including history and results of clinical examination and investigations before treatment; the only factor which influenced the proportion of patients achieving two year remission was type of seizure. Patients with a clinical history of partial seizures did significantly less well than those with a history of tonic-clonic seizures only. This study showed no major difference in efficacy between sodium valproate and phenytoin in adults with recent onset of epilepsy, irrespective of the type of seizures that the patient suffered.  相似文献   
7.
A novel series of tetrahydrobenzodioxinopyrroles has been identified as potent and selective α2-adrenoceptor antagonists. Convergent syntheses have been developed that allowed the preparation of analogues and their enantiomers. A compound of particular interest is the 5-fluoro substituted analogue (fluparoxan).  相似文献   
8.
The IgG anti-protective antigen subclass antibody response of individuals who had been infected with anthrax was compared with that of healthy individuals immunized with the UK licensed anthrax vaccine. The predominant subclass in both groups was IgG1. In addition, IgG3 was seen in convalescent serum while vaccinees produced IgG2, IgG3 and IgG4 subclass. The significance of these results is discussed. Further work is required to determine the role of antibodies in mediating protective immunity in man.  相似文献   
9.
10.
Abstract Sequences based on the conserved 20 bp inverted repeat of IS 231 variants were used as polymerase chain reaction-based fingerprinting primers of the member species of the Bacillus cereus group ( B. anthracis, B. cereus, B. thuringiensis and B. mycoides ), because of their close association with transposons, principally Tn 4430 in B. thuringiensis . Fingerprints of B. anthracis were simple, and specifically allowed its identification and sub-differentiation from other members of the group. Fingerprints for B. cereus were strain-specific; those for B. thuringensis gave a 1650 bp product, characteristic of 1S 231 variants A-F. The same reaction conditions gave one or two bands for both B. anthracis and B. cereus that differed by restriction endonuclease mapping from the B. thuringiensis PCR product and established IS 231 restriction maps; this does not preclude some kind of relationship between these products and IS 231 .  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号