全文获取类型
收费全文 | 3649篇 |
免费 | 79篇 |
国内免费 | 3篇 |
出版年
2017年 | 19篇 |
2015年 | 22篇 |
2014年 | 20篇 |
2013年 | 85篇 |
2012年 | 102篇 |
2011年 | 115篇 |
2010年 | 191篇 |
2009年 | 191篇 |
2008年 | 169篇 |
2007年 | 239篇 |
2006年 | 118篇 |
2005年 | 134篇 |
2004年 | 69篇 |
2003年 | 46篇 |
2002年 | 29篇 |
2001年 | 32篇 |
2000年 | 38篇 |
1999年 | 47篇 |
1998年 | 63篇 |
1997年 | 100篇 |
1996年 | 117篇 |
1995年 | 63篇 |
1994年 | 61篇 |
1993年 | 74篇 |
1992年 | 69篇 |
1991年 | 77篇 |
1990年 | 79篇 |
1989年 | 83篇 |
1988年 | 64篇 |
1987年 | 70篇 |
1986年 | 37篇 |
1985年 | 61篇 |
1984年 | 62篇 |
1983年 | 42篇 |
1982年 | 51篇 |
1981年 | 43篇 |
1980年 | 43篇 |
1979年 | 59篇 |
1978年 | 57篇 |
1977年 | 43篇 |
1976年 | 39篇 |
1975年 | 57篇 |
1974年 | 43篇 |
1973年 | 38篇 |
1972年 | 68篇 |
1971年 | 70篇 |
1969年 | 20篇 |
1968年 | 22篇 |
1957年 | 32篇 |
1956年 | 19篇 |
排序方式: 共有3731条查询结果,搜索用时 15 毫秒
21.
This article reports on a study of schooling in southwest Nova Scotia. Using Bourdieu's concepts of cultural capital and habitus, I analyze rural men's relationships involving identity, work, place, and schooling to explain continuing high male dropout rates and local traditions of ambivalence and resistance to schooling. I conclude that the tension between formal schooling and place is endemic in many rural communities and that qualitative migration analysis can reveal the complexity of relationships between learning and leaving. 相似文献
22.
SIMON M. TTERNEY MICHAEL P. SCHWARZ TANIA NEVILLE PATRICIA M. SCHWARZ 《Biological journal of the Linnean Society. Linnean Society of London》2002,76(2):211-224
Recent phylogenetic studies based on DNA sequence data indicate that the tropical African bee genus Macrogalea is the sister group to the remaining extant allodapine fauna, whereas previously it was thought to be a distal group. This leads to some fundamental changes in our understanding of social evolution in the allodapines. Earlier studies suggested that Macrogalea showed only weak forms of social behaviour and these were not well characterized. However, large samples of Macrogalea zanzibarica presented here show that this species exhibits marked social behaviour. Nearly half of nests collected contained two or more adult females, with up to 10 females per nest. Brood are reared progressively and brood ages within colonies are staggered, giving rise to colonies with very mixed age structures and therefore frequent opportunities for alloparental care. Ovarian dissections indicate non‐simple forms of reproductive partitioning within colonies and most multi‐female colonies show evidence that more than one female has contributed to egg production, though reproductive episodes among colony members are frequently asynchronous. Some females show signs of much higher wing wear than their nestmates, but always show signs of previous reproduction. Reproductive division of labour appears to be temporally marked, ovarian differentiation among nestmates is linked to relative body size, but permanent worker‐like or queen‐like castes appear to be absent. This is similar to the communal, continuously brooded and multivoltine behaviour of some tropical halictine species and may be due to the aseasonal nature of brood development in tropical regions. Patterns of per capita brood production indicate large benefits to multi‐female nest occupancy, and sex allocation is strongly female biased. These findings strongly suggest that the capacity for complex social interactions and alloparental care is an ancestral trait for all of the extant allodapine lineages. Therefore comparisons among extant allodapines are unlikely to throw light on the initial origin of social behaviour, though they may uncover origins of true caste behaviour and reversals to solitary nesting. Sex ratios in Macrogalea and most other allodapine genera, spanning a broad phylogenetic and ecological range, suggest that one or more allodapine traits have provided persistent selection for female‐biased sex allocation. 相似文献
23.
MICHAEL M. J. FISCHER 《American anthropologist》2006,108(2):440-441
Commons + Borderlands: Working Papers on Interdisciplinarity, Accountability and the Flow of Knowledge . Marilyn Strathern. Wantage, Oxfordshire: Sean Kingston Publishing, 2004. 102 pp. 相似文献
24.
25.
KURT C. VERCAUTEREN MICHAEL J. LAVELLE NATHAN W. SEWARD JUSTIN W. FISCHER GREGORY E. PHILLIPS 《The Journal of wildlife management》2007,71(5):1594-1602
Abstract: Direct and indirect contact between wild and farmed cervids along perimeter fences may play a role in transmission of diseases like chronic wasting disease (CWD), but no studies have quantified such interactions. At 9 high-fenced commercial elk (Cervus elaphus) farms in Colorado, USA, during October 2003 to January 2005, we used animal-activated video to estimate rates of fence-line use by wild cervids, rates of direct contact between farmed and wild cervids, and probability of direct contact when wild cervids were present. We recorded 8-fold-more wild elk per unit time than mule deer (Odocoileus hemionus) at fence lines. Depending on site, we recorded 0.66 to 46.90 wild elk per 1,000 hours of camera monitoring. We documented 77 interactions between wild and farmed elk involving naso-oral contact and no contact between wild mule deer and farmed elk. Rate of direct contact ranged from 0.00 to 1.92 direct contacts per 1,000 hours of camera monitoring among sites. Given recorded presence of wild elk, estimated probability of observing direct contact during a 2-minute video recording ranged from 0.00 to 0.11 among sites. Risk of direct contact was about 3.5 times greater for single woven-wire fence compared with offset electric fence attached to a single woven-wire fence. We observed no direct contact through double woven-wire fences. Because little is currently known about infection rates associated with infection mechanisms, we cannot infer a level of CWD infection risk from our results, but some form of double fencing should reduce potential for direct and indirect transmission of disease into or out of elk farms. 相似文献
26.
The Ordovician-Silurian boundary stratotype: consequences of its approval by the IUGS 总被引:4,自引:0,他引:4
PIERRE J. Lespérance CHRISTOPHER R. Barnes WILLIAM B. N. Berry ARTHUR J. Boucot MU Enzhi 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1987,20(3):217-222
Lespérance, Pierre J., Barnes, Christopher R., Berry, William B. N., Boucot, Arthur J. & Mu En-zhi 1987 07 15: The Ordovician-Silurian boundary stratotype: consequences of its approval by the IUGS.
The Ordovician-Silurian stratotype at Dob's Linn, Scotland is the second systemic boundary approved by the International Union of Geological Sciences (IUGS). A review of the internationally accepted criteria required of a stratotype shows that few of these are possessed by the Dob's Linn section. The strongest attribute of the section is the presence of zonal graptolites, although the boundary is recognized primarily on a single biological event (base of acuminatus Zone) for which the evolutionary relationships of the taxa are not established. In approving this boundary proposal in 1985, which received only simple majority support within the Ordovician-Silurian Boundary Working Group (OSBWG) and which fails to meet most of the accepted prerequisites for a stratotype, the International Commission on Stratigraphy (ICS) and the IUGS have established an unfortunate precedent. It follows that future systemic boundaries need not meet the accepted standards. It raises serious questions on the assessment and voting procedures of the International Commission on Stratigraphy and on the credence accorded the recommendations developed by the International Subcommission on Stratigraphic Classification of IUGS. 相似文献
The Ordovician-Silurian stratotype at Dob's Linn, Scotland is the second systemic boundary approved by the International Union of Geological Sciences (IUGS). A review of the internationally accepted criteria required of a stratotype shows that few of these are possessed by the Dob's Linn section. The strongest attribute of the section is the presence of zonal graptolites, although the boundary is recognized primarily on a single biological event (base of acuminatus Zone) for which the evolutionary relationships of the taxa are not established. In approving this boundary proposal in 1985, which received only simple majority support within the Ordovician-Silurian Boundary Working Group (OSBWG) and which fails to meet most of the accepted prerequisites for a stratotype, the International Commission on Stratigraphy (ICS) and the IUGS have established an unfortunate precedent. It follows that future systemic boundaries need not meet the accepted standards. It raises serious questions on the assessment and voting procedures of the International Commission on Stratigraphy and on the credence accorded the recommendations developed by the International Subcommission on Stratigraphic Classification of IUGS. 相似文献
27.
KNEE MICHAEL; HATFIELD STEPHEN G. S.; BRAMLAGE WILLIAM J. 《Journal of experimental botany》1987,38(6):972-979
Knee, M., Hatfield, S. G. S. and Bramlage, W. B. 1987. Responseof developing fruits to ethylene treatment.J. exp. Bot.38: 972979. Fruits of apple (Malus domestica Borkh. cv. Cox's Orange Pippin)were treated with various concentrations of ethylene usuallyfor 48 h to determine their response in relation to stage ofdevelopment. The main response recorded was the reduction byethylene of the delay in onset of rapid ethylene production(DEP) in individual fruits. Early in development low concentrationsof ethylene had little effect but DEP was progressively reducedby concentrations up to 107 mm3 m3. As the fruit approachedthe natural onset of rapid ethylene synthesis concentrationsof 102 and 103 mm3 m3 became increasingly effective.Increasing the duration of treatments with a fixed concentrationreduced DEP proportionately. Delay after harvest in applyinga 48 h treatment had little effect on the relation between DEPand concentration of ethylene applied. Although resistance todiffusion of gas in fruits increased during fruit developmentthis resistance was never large enough to affect the relationof concentration and response. Key words: ethylene, fruit ripening, Malus domestica 相似文献
28.
29.
A note on a semiparametric estimator of mortality 总被引:1,自引:0,他引:1
30.
ALEC E. AITKEN MICHAEL J. RISK 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1988,21(4):339-350
The presence of organisms whose bodies have low preservation potential may be deduced by searching for the traces produced by them. The addition of predatory gastropods and soft-bodied epizoans to Quaternary marine faunas dominated by bivalves was facilitated by an examination of borings in bivalve shells. Borings attributed to predatory gastropods (ichnogenus Oichnus ) were observed in shells of Astarte spp., Hiatella arctica and Macoma calcarea. Astarte, Hiatella and Macoma were preyed upon in preference to other members of a diverse suspension-feeding bivalve community. Borings attributed to epizoans (ichnogenus Cautostrepsis ) were observed in bivalve shells (Astarte spp. Hiatella arctica ), calcareous algae and limestone clasts. Biotic interactions revealed by trace fossils are employed, for the first time, to reconstruct the trophic structure of arctic Quaternary marine benthic faunas. ▭ Arctic molluscs, palaeoecology, Oichnus, Caulostrepsis. 相似文献