全文获取类型
收费全文 | 7126篇 |
免费 | 644篇 |
国内免费 | 1057篇 |
出版年
2024年 | 27篇 |
2023年 | 219篇 |
2022年 | 166篇 |
2021年 | 268篇 |
2020年 | 308篇 |
2019年 | 390篇 |
2018年 | 258篇 |
2017年 | 304篇 |
2016年 | 310篇 |
2015年 | 280篇 |
2014年 | 316篇 |
2013年 | 514篇 |
2012年 | 293篇 |
2011年 | 343篇 |
2010年 | 262篇 |
2009年 | 371篇 |
2008年 | 315篇 |
2007年 | 381篇 |
2006年 | 379篇 |
2005年 | 363篇 |
2004年 | 300篇 |
2003年 | 267篇 |
2002年 | 245篇 |
2001年 | 182篇 |
2000年 | 195篇 |
1999年 | 175篇 |
1998年 | 149篇 |
1997年 | 115篇 |
1996年 | 113篇 |
1995年 | 101篇 |
1994年 | 96篇 |
1993年 | 103篇 |
1992年 | 115篇 |
1991年 | 84篇 |
1990年 | 72篇 |
1989年 | 60篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 31篇 |
1985年 | 40篇 |
1984年 | 41篇 |
1983年 | 20篇 |
1982年 | 34篇 |
1981年 | 34篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1977年 | 11篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有8827条查询结果,搜索用时 171 毫秒
171.
M. J. van Steenis K. A. M. H. El-Khawass 《Entomologia Experimentalis et Applicata》1995,76(2):121-131
Life table data forAphis gossypii Glover (Homoptera: Aphididae), an important pest in glasshouse cucumber crops, were studied at 20, 25 and 30°C on two cucumber
cultivars (Cucumis sativus L.) in controlled climate cabinets. The development time on the cucumber cv. ‘Sporu’ ranged from 4.8 days at 20°C to 3.2
days at 30°C. Immature mortality was approximately 20% and did not differ between temperatures. Most mortality occurred during
the first instar. Reproduction periods did not differ among temperatures, but at 25 and 30°C more nymphs were produced (65.9
and 69.8 nymphs/♀, respectively) than at 20°C (59,9 nymphs/♀) because of a higher daily reproduction. Intrinsic rate of increase
was greatest at 25°C (r
m
=0.556 day−1). At 20 and 30°C the intrinsic rate of increase was 0.426 and 0.510, respectively. On cv. ‘Aramon’, the development time
ofA. gossypii was approximately 20% longer at all temperatures. Immature mortality did not differ between the two cultivars. The intrinsic
rate of increase on cv. ‘Aramon’ was 15% smaller than on cv. ‘Sporu’. The use of cucumber cultivars partially resistant to
aphids is discussed in relation to biological control of cotton aphid in glasshouses. Development time and immature mortality
on leaves of the middle and upper leaf layer of glasshouse grown cucumber plants (cv. ‘Aramon’) were comparable to development
in the controlled climate cabinets. On the lower leaves immature mortality was much higher (approximately 82%) than on leaves
of the middle (24.0%) and upper leaf layer (24.5%). Reproduction was less on the lower leaf layer (45.9, 70.5 and 70.1 nymphs/♀
on leaves of the lower, middle and upper leaf layer, respectively).
Aphids, successfully parasitized byAphidius colemani Viereck (Hymenoptera: Braconidae) only reproduced when they were parasitized after the third instar. Fecundity was 0.1 to
0.9 and 10.5 to 13.3 nymphs/♀ for aphids parasitized in the fourth instar or as adults, respectively. Reproduction of aphids
that were stung but survived the attack was lower than for aphids not stung. Average longevity of these aphids was equal to
the longevity of aphids not stung byA. colemani. 相似文献
172.
We investigated the ability of entomopathogenic nematodes to infect diamondback moth (DBM),Plutella xylostella (L.) (Lepidoptera: Plutellidae) on a leaf surface. In a leaf disk assay, mortality of late stage DBM larvae ranged from <7%
caused bySteinernema kushidai Mamiya to >95% caused byS. carpocapsae (Weiser) All strain. LC50 values forS. carpocapsae, S. riobravis Cabanillas, Poinar & Raulston, andHeterorhabditis bacteriophora Poinar NC1 strain were 14.6, 15.4, and 65.4 nematodes/larva, respectively.S. carpocapsae, S. riobravis, andH. bacteriophora caused 29%, 33%, and 14% mortality of DBM pupae, respectively. DBM mortality caused byS. carpocapsae on radish declined at low (<76%) to moderate (76–90%) RH, because nematode survival and infectivity declined at low (<76%)
to moderate (76–90%) RH. However, DBM mortality caused byS. riobravis did not decline with RH.S. riobravis survival declined with RH, but infectivity did not. Overall, nematode survival and infectivity to DBM larvae were lower forS. riobravis than forS. carpocapsae. In addition, DBM mortality was higher on radish plants (pubescent leaves) than on cabbage plants (glaborous leaves). 相似文献
173.
Timothy A. Heard 《Entomologia Experimentalis et Applicata》1995,76(2):203-209
The oviposition and feeding preferences ofCoelocephalapion aculeatum Fall (Coleoptera: Apionidae), a host specific florivore ofMimosa pigra L. (Mimosaceae), were studied in relation to conspecific damage to its hostplant. Adults ofC. aculeatum cease ovipositing in inflorescences when the egg load reaches a number consistent with the larval carrying capacity of the
inflorescence. The basis for this oviposition deterrence was examined by offering inflorescences damaged by adult feeding
alone, larval feeding alone and a combination of adult feeding and oviposition. Adults preferred to oviposit on inflorescences
which are not damaged by either adult feeding, larval feeding, or oviposition. No evidence for the existence of an oviposition
deterring pheromone (ODP) was found. I suggest that the ability of a single host inflorescence to support the development
of many larvae causes selection for the use of these oviposition deterring cues which can convey more quantitative information
about the level of previous infestation than can ODPs. Adults fed a similar amount on damaged compared to undamaged inflorescences.
These results assisted in the design of host range testing trials and allows predictions to be made about the effectiveness
of this insect as a biological control agent. 相似文献
174.
Ricardo Godoy Nicholas Brokaw David Wilkie 《Human ecology: an interdisciplinary journal》1995,23(1):29-52
We use microeconomic theory to frame hypotheses about the effects of income on the use of non-timber rain forest products. We hypothesize that an increase in income: (a) encourages foraging specialization, resulting in the extraction of fewer goods; (b) increases the share of household income from occupations besides foraging; (c) produces a yearly value from the extraction of nontimber forest goods of about $50 per hectare; and (d) produces depletion of forest goods entering commercial channels and sustainable extraction of goods facing cheaper industrial substitutes. To examine these hypotheses we present worldwide ethnographic information and preliminary findings from field work carried out among the Sumu Indians of Nicaragua. Field work suggests that higher income produces: (a) foraging specialization with animals rather than with plants; (b) a decline in the economic importance of forest goods in household income; (c) and a rise in the value of non-timber goods removed from the forest to about $35/ha/year. We did not have time to test hypothesis d. 相似文献
175.
M. J. Bidochka S. R. A. Walsh M. E. Ramos R. J. St. Leger R. I. Carruthers J. C. Silver & D. W. Roberts 《Molecular ecology》1997,6(4):303-308
Entomophaga grylli is a fungal pathogen of grasshoppers and at least three pathotypes are recognized world-wide. Pathotypes 1 and 2 are endemic to North America while the Australian pathotype 3 had been released into two field sites in North Dakota between 1989 and 1991. Grasshoppers were collected over the summer at the field sites in 1992 and assessed for pathotype infection by cloned DNA probe analysis. The three most predominant grasshopper species that were infected ( Melanoplus sanguinipes, M. bivittatus and Camnula pellucida ) were assessed for pathotype infection with respect to their life stages (nymphal instars and adult males and females). Pathotype 1 predominantly infected grasshoppers in the subfamilies Oedipodinae and Gomphocerinae and pathotype 2 predominantly infected grasshoppers in the subfamily Melanoplinae. Early-instar M. sanguinipes and M. bivittatus had higher pathotype 2 infection frequencies, while late-instar and adult C. pellucida had higher pathotype 1 infection frequencies. Cross-infection by the pathotypes did occur in up to 3% of the individuals, on a per species basis, and primarily in later instar and adult grasshoppers. Pathotype 3 infections occurred in later instar and adults of the three grasshopper species. Infection of grasshoppers by E. grylli pathotypes is discussed with reference to the fungal life cycles. 相似文献
176.
本文对观赏植物异色芋(ColocasiaheterochromaH.LietZ.X.Wei)在昆明栽培环境下的生物学特性进行总结,为商品化栽培异色芋提供了理论依据,为其分类也提供了一定的有益补充。结果表明:一年生植株不开花,根茎也不产生分枝;二年生植株开花率为73.6%,根茎平均分枝3.6条。异色芋3月上旬开始萌动,7月中旬抽花梗,8月上旬开花,11月份地上部分枯萎,因此在昆明异色芋生育期约260d。 相似文献
177.
178.
Compatibility of Soil Amendments with Entomopathogenic Nematodes 总被引:1,自引:0,他引:1
The impact of inorganic and organic fertilizers on the infectivity, reproduction, and population dynamics of entomopathogenic nematodes was investigated. Prolonged (10- to 20-day) laboratory exposure to high inorganic fertilizer concentrations inhibited nematode infectivity and reproduction, whereas short (1-day) exposures increased infectivity. Heterorhabditis bacteriophora was more sensitive to adverse effects than were two species of Steinernema. In field studies, organic manure resulted in increased densities of a native population of Steinernema feltiae, whereas NPK fertilizer suppressed nematode densities regardless of manure applications. Inorganic fertilizers are likely to be compatible with nematodes in tank mixes and should not reduce the effectiveness of nematodes used for short-term control as biological insecticides, but may interfere with attempts to use nematodes as inoculative agents for long-term control. Organic manure used as fertilizer may encourage nematode establishment and recycling. 相似文献
179.
JANINE W. A. M. PIJLS KEES D. HOFKER MARTIN J. VAN STAALDUINEN JACQUES J. M. VAN ALPHEN 《Ecological Entomology》1995,20(4):326-332
Abstract.
- 1 Choice experiments on interspecific host discrimination in A.lopezi and A. diversicornis were carried out on discs of cassava leaf containing four hosts (P.manihoti) that had been parasitized by the other species and four unparasitized hosts.
- 2 A.lopezi accepted both host types equally for oviposition, whereas A.diversicornis accepted fewer hosts that had been parasitized by A.lopezi than unparasitized ones. A.diversicornis is therefore capable of interspecific host discrimination, but such a capability was not demonstrated for A.lopezi.
- 3 Survival probability in singly parasitized hosts was 0.85 for both parasitoid species. When the time interval between ovipositions was 2 h or less, survival in multiparasitized hosts was 0.68 for A.lopezi and 0.17 for A.diversicornis, irrespective of priority. Increasing A.lopezi priority to 24±2h did not increase A.lopezi survival. A.diversicornis survival, however, increased to 0.43 when A.diversicornis was given 24 ± 2 h priority. A.diversicornis eggs took 19 h longer than A.lopezi eggs to hatch. This could explain the difference in competitive abilities in multiparasitized hosts.
- 4 The observed difference in host selection behaviour between A.lopezi and A.diversicornis is in accordance with the different benefits of multiparasitism: A.lopezi gains more than A.diversicornis because of its superior within-host competitive abilities.
- 5 Neither species avoided multiparasitism completely. The low survival probability of A.diversicornis in multiparasitized hosts may partly explain its failure to establish when introduced into Africa as part of a biological control programme of P.manihoti.
180.