全文获取类型
收费全文 | 4035篇 |
免费 | 401篇 |
国内免费 | 82篇 |
出版年
2024年 | 12篇 |
2023年 | 88篇 |
2022年 | 68篇 |
2021年 | 139篇 |
2020年 | 177篇 |
2019年 | 198篇 |
2018年 | 168篇 |
2017年 | 177篇 |
2016年 | 227篇 |
2015年 | 288篇 |
2014年 | 274篇 |
2013年 | 326篇 |
2012年 | 158篇 |
2011年 | 219篇 |
2010年 | 180篇 |
2009年 | 216篇 |
2008年 | 228篇 |
2007年 | 194篇 |
2006年 | 112篇 |
2005年 | 103篇 |
2004年 | 102篇 |
2003年 | 95篇 |
2002年 | 94篇 |
2001年 | 63篇 |
2000年 | 51篇 |
1999年 | 62篇 |
1998年 | 48篇 |
1997年 | 51篇 |
1996年 | 57篇 |
1995年 | 31篇 |
1994年 | 43篇 |
1993年 | 37篇 |
1992年 | 26篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有4518条查询结果,搜索用时 156 毫秒
51.
Melinda A. Novak Amy Musante Heather Munroe Peggy L. O'Neill Cristofer Price Stephen J. Suomi 《Zoo biology》1993,12(3):285-298
Recent research has indicated that old, individually housed monkeys show little interest in novel objects. Yet unanswered is whether this effect is caused primarily by age or housing condition. The purpose of this study was to assess the role of social living in promoting responsiveness to objects. We measured the rates of object manipulation in older animals, assessed responsiveness over time to particular objects as a measure of habituation, and examined social influences on object use. Several social groups of rhesus monkeys that contained older adults were studied. These groups were housed in indoor pens or in an outdoor enclosure, and all monkeys had continuous access to a variety of objects in their home environment. In contrast to previous studies of individually housed monkeys, our group-housed monkeys showed sustained interest in objects. Old monkeys manipulated objects extensively, and this response was all the more significant, given that the objects were not novel. Monkeys housed in an outdoor enclosure showed object manipulation patterns that were not different from monkeys housed in indoor pens. However, females exhibited much higher object-related responses than males. Social facilitation played a role in the reactions of some monkeys to objects. Patterns of social facilitation as well as avoidance were present in two of the three indoor groups that were observed. Failure to manipulate objects in rhesus macaques appears to be more a function of individual housing than of old age. Factors such as environmental complexity, social needs, and early experience should be considered in order to understand why individually housed rhesus monkeys are unresponsive to objects. © 1993 Wiley-Liss, Inc. 相似文献
52.
The density of a Japanese serow (Capricornis crispus) population, which has been in stable habitat conditions and free from hunting and predation, was investigated by direct
observation of serows at Kusoudomari (336 ha), Wakinosawa village, Aomori Prefecture, Japan, during 1977–89. The vegetation,
composed of mature mixed forest ofThujopsis with deciduous trees (43.2%), secondary forest of deciduous trees (23.4%) and a plantation of coniferous trees (30.0%) showed
little change during the study period. The serows were counted 17 times each winter for 14 consecutive years. The serow population
maintained a stable density with a mean of 12.5 individuals km−2 (SD=1.4) ranging from 8.6 to 14.6 km−2. The ratio of the proportion of kids (<1 year old) to serows more than 1 year old decreased, but density did not decrease
during the study period. Though extremely severe winters with heavy snowfall in 1984–86 caused a decline in serow density,
the density recovered within a few years. It was considered that the stability of the serow density resulted mainly from the
stable food supply and the lack of human disturbance, such as forest cutting in the habitat. Stable population density for
a long period is probably related to the social organization of the serow. 相似文献
53.
Ten sampling sites were selected to represent six distinct habitat types used by capybaras (clean lagoons, dirty lagoons, cutwaters, fens and marshes, gallery forests, and erosion ditches). The sites were sampled during winter (July and August); densities were expressed as number of capybaras per linear km of shoreline (C/LKS). The sites were classified as protected from poachers (P), under light hunting pressure (LHP), and under heavy hunting pressure (HHP). Clean protected (P) lagoons had three times as many capybaras as LHP ones (30.7 and 10.9 C/LKS, respectively), and thirty times those under HHP (1.0 C/LKS). Protected marshes and dirty lagoons had even higher capybara densities (52.5 and 50.0 C/LKS, respectively). Gallery forests under LHP had low densities (6.3 C/LKS), and protected cutwaters intermediate densities (27.5 C/LKS). Erosion ditches had exceptionally high densities (900 C/LKS), probably because cattle were fenced out, reducing forage competition. These densities, when converted to the standard unit area measurement (individuals/ha), were similar to those obtained by other researchers in the Brazilian Pantanal, and somewhat smaller than those in the Venezuelan Llanos. Mean number of capybaras per group remained relatively constant in all habitats (averages ranged between 9.2 and 11.8 individuals/group) but its coefficient of variation was much higher in LHP sites, probably because social structure was altered severely by hunting. The overall ratio of young to adults and juveniles was 1:7.4. In one of the sites, 13 of 34 groups (38.2%) were with young (average of 17 capybaras per group, 4.7 of which were young), confirming that this species can reproduce all year long.Requests for reprints should be sent to: Dr. J. Rabinovich. 相似文献
54.
55.
Substance use disorders (SUDs) are highly prevalent and exact a large toll on individuals’ health, well-being, and social functioning. Long-lasting changes in brain networks involved in reward, executive function, stress reactivity, mood, and self-awareness underlie the intense drive to consume substances and the inability to control this urge in a person who suffers from addiction (moderate or severe SUD). Biological (including genetics and developmental life stages) and social (including adverse childhood experiences) determinants of health are recognized factors that contribute to vulnerability for or resilience against developing a SUD. Consequently, prevention strategies that target social risk factors can improve outcomes and, when deployed in childhood and adolescence, can decrease the risk for these disorders. SUDs are treatable, and evidence of clinically significant benefit exists for medications (in opioid, nicotine and alcohol use disorders), behavioral therapies (in all SUDs), and neuromodulation (in nicotine use disorder). Treatment of SUDs should be considered within the context of a Chronic Care Model, with the intensity of intervention adjusted to the severity of the disorder and with the concomitant treatment of comorbid psychiatric and physical conditions. Involvement of health care providers in detection and management of SUDs, including referral of severe cases to specialized care, offers sustainable models of care that can be further expanded with the use of telehealth. Despite advances in our understanding and management of SUDs, individuals with these conditions continue to be stigmatized and, in some countries, incarcerated, highlighting the need to dismantle policies that perpetuate their criminalization and instead develop policies to ensure support and access to prevention and treatment. 相似文献
56.
Ermias Admasu Simon J. Thirgood Afework Bekele M. Karen Laurenson 《African Journal of Ecology》2004,42(2):144-152
The spatial ecology of golden jackal Canis aureus was studied on farmland adjacent to the Bale Mountains National Park in southern Ethiopia during 1998–2000. Three adult and four subadult jackals were captured in leg‐hold traps and radiotagged. The range size of the adult jackals varied from 7.9 to 48.2 km2 and the subadults from 24.2 to 64.8 km2 . These ranges are the largest recorded for this species. Range overlap of the tagged jackals averaged 54%, which, in conjunction with observations of associations between individuals, suggested that all the tagged jackals belonged to one social group. Tagged jackals were observed alone on 87% of occasions despite the extensive overlap in individual ranges. Pairs consisting of a male and female were the most commonly observed group and larger groups were seen on only five occasions. Jackals in this population appeared less gregarious than observed elsewhere. The jackals used all the habitats available to them, particularly at night when they foraged in Artemesia and Hypericum bush and farmland. During the day they were more frequently found in Hagenia and Juniper woodland and their diurnal resting sites were characterized by thick cover. This is the first detailed study of golden jackals in a human‐modified landscape in Africa and further demonstrates the flexibility in behaviour and ecology exhibited by this species throughout its range. 相似文献
57.
Summary The genusPlebeia has a special significance for the study of social evolution of stingless bees: morphologically primitive, its species display a wealth of behavioural evolution, especially with respect to the oviposition process. We comparePlebeia remota with the few other members of the genus studied so far.Related to its subtropical geographical range, brood production is seasonal (there is no brood in the colony in colder months), and adult workers occur as summer and winter bees. The nest is in tree cavities, and the involucrum is absent or restricted to the winter period. Brood cells are arranged in horizontal combs, and new cells are built completely synchronously. Each series consists of up to 50 cells, their number being mainly dependent on colony size. Construction speed is remarkably constant, allowing 4–6 batches per 24 hours. Cell building and provisioning are activities of a small group of specialized workers.The oviposition cycle follows the classical subdivisions for stingless bees. During the patrolling phase a worker may offer a trophic egg in a most remarkable way: while retreating backward from the queen she bends the abdomen under thorax and head, and lays an egg on the comb. This egg is eaten by the queen or a worker.The provisioning, oviposition and operculation of all cells occur simultaneously, each cell is provisioned by 4–9 workers. Localization of a cell by the queen may be facilitated by its characteristic guard, which defends the cell against the approaching queen. The degree of synchronization within a batch is very high: the duration per cell lasts 420–950 sec, the batch of up till 50 cells needs only 557–1160 sec. Operculation is done by a worker that was not involved in the previous steps.Males are generally produced by the queen. Several male producing cycles per year occur. In orphan colonies laying workers give rise to males, and in queenright colonies workers may occasionally reproduce as well.Division of labour follows the general pattern for stingless bees; however, cell building and provisioning are activities of a specialized group of workers. 相似文献
58.
Summary Colonies and nests ofApoica pallens in the llanos region of Venezuela range from small foundress nests to large mature colonies. Nests are sited on small diameter, near-horizontal branches in a variety of shrub and tree species. During the day, adult wasps cluster on the face of the nest in an array that seems to be determined by orientation to gravity; defense of the colony against parasitoids and ants by the resting wasps may be more a passive than an active behavior. Wasps fan their wings to cool the colony during the day, but no foraging for water accompanies the fanning behavior. Nightly foraging activity begins with the explosive departure from the nest of hundreds of wasps, most of which rapidly return. Moderate foraging levels early at night give way to very low foraging levels in pre-dawn hours. The period of moderate foraging may be extended for longer hours during increased moonlight. Foraging wasps collect arthropod provisions for larvae. Larvae produce a trophallactic saliva; adults engage in inter-adult trophallaxis; brood are cannibalized. During cluster formation prior to swarm emigration, adult wasps do not appear to scent-mark substrates such as leaves. Instead,A. pallens exhibits a calling behavior, unique among polistine wasps studied to date, in which the gaster is held rigidly away from the thorax and metasomal sternal glands are exposed. Swarms can emigrate during the day.A. pallens may incorporate absconding and colony relocation as features of its colony cycle in the highly seasonal llanos. 相似文献
59.
Today, the search for new energy sources continues unabated throughout the North. At the same time, scientists are increasingly concerned over the degradation of the Arctic and sub-Arctic environment stemming from fossil fuel and other large-scale energy projects already underway. Similar apprehensions are expressed by indigenous peoples who have often suffered from the impact of such development. While the most dramatic evidence of environmental devastation and social disruption is found in the Russian North, serious problems are by no means confined to that area alone. Nor are these negative effects necessarily limited to the borders of the country in which they originated. Indeed, the deleterious environmental impact of our global industrial economy has become sufficiently profound that social analysts are beginning to ask whether development strategies that cause such harm to the Arctic and sub-Arctic region should continue; and if not, what should replace them. This article addresses these issues as they relate to questions of sustainability, equity, political empowerment, and human rights in northwest Siberia and northern North America. 相似文献
60.
QUANTITATIVE BEHAVIORAL STUDY OF BOTTLENOSE DOLPHINS IN SWIM-WITH-DOLPHIN PROGRAMS IN THE UNITED STATES 总被引:1,自引:0,他引:1
The behavior of dolphins in four Swim-With-Dolphin programs was compared by type of Swim encounter, defined by the presence ("Controlled") or absence ("Not-Controlled") of explicit trainer regulation of interactions between dolphins and human swimmers. Dolphin-swimmer interactions involving aggressive, submissive, or sexual behavior were designated as "high-risk" in the Swim context; sexual behavior was included as high-risk based on analyses that demonstrated co-occurrence of sexual and agonistic behaviors. High-risk activity comprised a substantial proportion of dolphin-swimmer social activity during Not-Controlled Swims. In contrast, high-risk activity rarely occurred during Controlled Swims, even though agonistic and sexual behaviors were normal components of the same dolphins' free-time social repertoire. These results indicated that direct trainer control of dolphin-swimmer interactions virtually eliminated high-risk activity from the Swim context, and thereby diminished the potential for dolphin distress, swimmer injury, and rejection of dolphins from Swim programs due to swimmer injury. This study illustrates effective use of quantitative behavioral sampling techniques for evaluation of captive management concerns and promotes broader use of these techniques for a better understanding of cetacean behavior. 相似文献