全文获取类型
收费全文 | 3978篇 |
免费 | 451篇 |
国内免费 | 1743篇 |
出版年
2024年 | 26篇 |
2023年 | 182篇 |
2022年 | 188篇 |
2021年 | 237篇 |
2020年 | 240篇 |
2019年 | 249篇 |
2018年 | 200篇 |
2017年 | 219篇 |
2016年 | 238篇 |
2015年 | 221篇 |
2014年 | 267篇 |
2013年 | 322篇 |
2012年 | 251篇 |
2011年 | 265篇 |
2010年 | 196篇 |
2009年 | 254篇 |
2008年 | 245篇 |
2007年 | 287篇 |
2006年 | 249篇 |
2005年 | 186篇 |
2004年 | 185篇 |
2003年 | 158篇 |
2002年 | 161篇 |
2001年 | 110篇 |
2000年 | 96篇 |
1999年 | 116篇 |
1998年 | 79篇 |
1997年 | 59篇 |
1996年 | 63篇 |
1995年 | 65篇 |
1994年 | 65篇 |
1993年 | 59篇 |
1992年 | 49篇 |
1991年 | 53篇 |
1990年 | 48篇 |
1989年 | 50篇 |
1988年 | 23篇 |
1987年 | 31篇 |
1986年 | 30篇 |
1985年 | 37篇 |
1984年 | 31篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 4篇 |
排序方式: 共有6172条查询结果,搜索用时 31 毫秒
51.
J. P. Michaud 《Journal of Insect Behavior》1996,9(5):683-694
Two-day-old mated females ofAphidius ervi Haliday andMonoctonus paulensis (Ashmead) were each provided with two sequential host patches. Patches were comprised of plastic petri dishes containing either 15 pea aphids,Acyrthosiphum pisum (Harris), or 15 alfalfa aphids,Macrosiphum creelii Davis. Both wasp species parasitized more hosts in patches containing pea aphids than in those containing alfalfa aphids, regardless of sequence. Females ofA. ervi also laid more eggs per aphid in patches containing pea aphids than in patches containing alfalfa aphids. When both patches contained alfalfa aphids,M. paulensis females parsitized more aphids in the second patch than in the first. Fewer alfalfa aphids were parasitized in the second patch when the first patch contained pea aphids, and fewer eggs were laid per alfalfa aphid. Parasitoid females of both species exhibited consistently higher rates of oviposition into their preferred host species and adjusted their reproductive allocation to hosts and host patches as a function of their experience in previous patches. 相似文献
52.
Analysis of the multi-stem clump structure ofLitsea japonica Juss. growing in a coastal dwarf forest
The multi-stem clump structure of a coastal dwarf forest dominated byLitsea japonica Juss. was investigated in order to clarify the sprouting characteristics and self-maintenance of clumps by stem alternation.
The size and age distribution of multi-stem clumps were analyzed using cumulative relative frequency curves.L. japonica had a large number of stems and an even height distribution or young age-biased distribution of stems within a clump. These
results indicated the sequential flushing of sprouts at high frequency. Height distribution within a clump ofL. japonica was relatively even compared to other species. This clump structure suggested the stable self-maintenance of individuals
in all ranges of size and age without disturbances. It originated specific sprouting characteristics as a response to the
severe stress of salty wind.Ardisia sieboldii Miq. had few stems within a clump. Although the stem height distribution of large individuals tended to be even, most clumps
had a large size-biased distribution of stem height which indicated simultaneous sprouting. From this structure, sprouts of
this species were thought to be of less significance in the stable self-maintenance of individuals thanL. Japonica. 相似文献
53.
Stephen B. Heard 《Evolutionary ecology》1994,8(5):493-502
Summary
Wyeomyia smithii mosquitoes distribute their eggs across available oviposition sites (water-holding pitcher plant leaves) of varying quality. I experimentally examined responses to three components of site quality: conspecific larval density, larval density of the pitcher plant midge,Metriocnemus knabi, and pitcher size. Responses to larval treatments were complex and apparently suboptimal. Although mosquito larval performance is better in leaves with fewer conspecific and more midge larvae, females did not lay more eggs in such pitchers. Instead, more eggs were laid in experimental pitchers containing either midge or mosquito larvae, but fewer eggs in pitchers with neither or both. More eggs were laid in larger pitchers, which tend to accumulate more resources and dry out less often. Therefore, although the oviposition decisions made were suboptimal, they were better than random. 相似文献
54.
55.
M. S. J. Simmonds W. M. Blaney R. Mithen A. N. E. Birch J. Lewis 《Entomologia Experimentalis et Applicata》1994,71(1):41-57
This study investigates the behavioural and neural mechanisms involved in the oviposition behaviour of the turnip root fly,Delia floralis (Fallen). Behavioural studies showed that glucosinolates modulated the oviposition behaviour of the flies on artificial leaves
as well as the number of eggs laid in the soil at the base of these leaves. Electrophysiological responses to glucosinolates
were obtained from type A and type D sensilla on the prothoracic and mesothoracic tarsi, as well as from the long contact
sensilla on the labellum. The neural responses from these sensilla were positively correlated with the oviposition behaviour
of the flies and with the number of eggs laid. Of the eleven glucosinolates tested in the behavioural and electrophysiological
tests, the flies were most responsive to glucobrassicanapin, gluconapin and glucobrassicin. The type D tarsal sensilla were
more responsive to the glucosinolates than either the type A tarsal sensilla or the labellar sensilla. The structure-activity
investigations showed that slight modifications to the chemical composition of the glucosinolates resulted in changes in neural
activity. 相似文献
56.
The nest site characteristics of the freshwater three-spined stickleback, Gasterosteus aculeatus (form leiurus ), were quantitatively investigated in springs and the main stream of the Yamayoke and the Tsuya River system, central Japan. Most nests (93·4%) were on a muddy or sandy substratum, at depths of 10–40 cm (84·3%), in water velocities less than 15 cm s−1 (76·2%) and in the temperature range of 14 to 16° C (82·7%), Spring-fed localities provided more of these conditions than the main stream channel and hence contained more potential nesting areas. Thus, they were utilized by male sticklebacks both temporally (prolonged breeding season) and spatially (more nest sites). 相似文献
57.
Ronald J. Prokopy Chris Bergweiler Luis Galarza Jeri Schwerin 《Journal of Insect Behavior》1994,7(5):663-677
Females of the apple maggot fly,Rhagoletis pomonella, were allowed for 3 days to alight upon and oviposit in green or red 18- to 20-mm hawthorn host fruit (Crategus mollis) or green or red 45- to 55-mm apple host fruit (Malus pumila) hung from branches of potted host trees in field enclosures. Subsequently, when females were released individually on potted host trees harboring fruit of one of these types, their ability to find fruit of unfamiliar size proved unaffected by prior experience with fruit but their ability to find fruit of unfamiliar color was significantly affected. Specifically, females exposed to red hawthorns or red apples were less able to find green hawthorns or green apples than were females experienced with either of the latter fruit types. Fruit odor was found to have no effect on female ability to find familiar compared with unfamiliar green fruit. In contrast, a difference in size (or surface chemistry) between familiar and unfamiliar fruit but not a difference in fruit color had a significant negative influence on the propensity of alighting females to bore into unfamiliar fruit. Three bouts of experience with alighting upon and ovipositing into fruit over a period of about 1 h had no detectable effect on female ability to find unfamiliar fruit but did reduce propensity to bore into unfamiliar fruit. Our findings are discussed in relation to insect ability to learn visual and chemical stimuli of resources and insect propensity to form host races. We also discuss the potential impact of our findings on nonpesticidal, behavioral methods of managingR. pomonella in commercial apple orchards. 相似文献
58.
Organisms inhabiting metal-contaminated areas can be stressed by metal exposure and are possibly subject to selection, resulting
in increased metal tolerance and changes in growth and/or reproduction characteristics. In a previous study it was found that
in the terrestrial isopod Porcellio scaber, sampled from the vicinity of a zine smelter, the body size was small and the brood size was large compared to isopods from
a reference area. To assess whether these differences were due to genetic differentiation between strains, isopods collected
from a reference wood, a zinc smelter area and a lead mine were cultured on non-polluted food, while growth, reproduction
and metal concentrations were studied in first and second laboratory generations. The isopods from the three populations differed
in age and weight at first reproduction, although there were hardly any differences in growth. The females of the mine and
the smelter population started to reproduce earlier, at a lower weight, which resulted in fewer young per female. However,
reproductive allocation (=wight of young relative to the weight of the mother) was higher in mine and smelter isopods. We
conclude that the isopods at the metal-contaminated sites have been selected for early reproduction and increased reproductive
allocation. The results indicate that populations inhabiting metal-polluted sites have probably undergone evolutionary changes.
This study showed that growth and reproduction characteristics of different populations under laboratory conditions may provide
information on selection processes in the field. 相似文献
59.
《Journal of Asia》2023,26(2):102057
In this study, we investigated the morphological and biological characteristics of a serious insect pest of conifer cones, the western conifer seed bug (WCSB), Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae), in Korea. WCSB adults shared external morphology with overseas populations, including zig-zag fascia on the coria, dilation of the hind tibiae, and color pattern on the abdominal dorsum. The average body length and width of WCSB adults were 17.20 and 4.85 mm, respectively, in males and 19.05 and 5.55 mm in females. The average body weights were 111.27 and 169.89 mg in adult males and females, respectively. On average, eggs were 2.12 mm long and 1.17 mm wide. The average body lengths of the first- to fifth-instar nymphs were 3.07, 4.76, 8.77, 13.56, and 15.53 mm, respectively. For biological characteristics, developmental durations of the egg and five nymphal instar stages were 8.6, 3.7, 7.6, 5.8, 5.8, and 9.1 days, respectively, in laboratory conditions. Nymphal mortality was 47.5% in total. The average life expectancy of WCSB adults was 58.2 and 63.9 days in males and females, respectively. Oviposition of the adult females started 23.4 days after emergence, and the total number of eggs laid by a single adult female was 68.6 on average. The results of this study offer basic morphological and biological information that can be used to design an effective control strategy to manage the WCSB population in Korea. 相似文献
60.
泉州的常绿阔叶林包括南亚热带雨林和南亚热带山地照叶林。通过对这两种植被类型的区分成分、生活型、叶的性质以及群落的结构与分布的分析,说明海拔450m以下具有较明显的以厚壳桂、红楠等为优势种的南亚热带雨林的特征和景观;海拔450~900m主要以米槠等拷类为优势种的群落,但仍有南亚热带雨林的某些特征;海拔900~1400m以甜槠为主要建群种的群落,属于中亚热带照叶林的群落特征。 相似文献