全文获取类型
收费全文 | 6359篇 |
免费 | 475篇 |
国内免费 | 434篇 |
专业分类
7268篇 |
出版年
2024年 | 32篇 |
2023年 | 99篇 |
2022年 | 156篇 |
2021年 | 236篇 |
2020年 | 232篇 |
2019年 | 250篇 |
2018年 | 207篇 |
2017年 | 193篇 |
2016年 | 219篇 |
2015年 | 213篇 |
2014年 | 234篇 |
2013年 | 345篇 |
2012年 | 221篇 |
2011年 | 237篇 |
2010年 | 207篇 |
2009年 | 290篇 |
2008年 | 322篇 |
2007年 | 358篇 |
2006年 | 288篇 |
2005年 | 271篇 |
2004年 | 213篇 |
2003年 | 213篇 |
2002年 | 217篇 |
2001年 | 152篇 |
2000年 | 142篇 |
1999年 | 134篇 |
1998年 | 142篇 |
1997年 | 143篇 |
1996年 | 145篇 |
1995年 | 113篇 |
1994年 | 118篇 |
1993年 | 97篇 |
1992年 | 98篇 |
1991年 | 113篇 |
1990年 | 73篇 |
1989年 | 88篇 |
1988年 | 53篇 |
1987年 | 52篇 |
1986年 | 59篇 |
1985年 | 56篇 |
1984年 | 44篇 |
1983年 | 42篇 |
1982年 | 46篇 |
1981年 | 26篇 |
1980年 | 29篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有7268条查询结果,搜索用时 15 毫秒
991.
Malcolm G. Keeping 《Journal of Insect Behavior》1997,10(2):265-278
Colonies ofBelonogaster petiolata in Gauteng (South Africa) produced reproductive offspring (gynes and males) in late January and early February of each nesting
season; their appearance was associated with a decline in worker and brood numbers. Brood decline could commence in the presence
of a dominant, reproductively active queen, and loss or removal of the queen was not followed directly by cessation of nest
growth and brood care. An older worker usually took over the α-position in queenless colonies. Several factors appear to contribute
to brood decline and, ultimately, termination of the colony cycle in this species. These include (1) cessation of the supply
of solid food to colonies (and particularly their larvae) during the reproductive phase, (2) a decrease in the worker/larva
ratio during the latter phase due to the progressive loss of workers, (3) increasing number of gynes and males, and (4) an
adult priority over food reception from foragers. 相似文献
992.
Whether female crickets choose among males based on characteristics of the courtship song is uncertain, but in many species,
males not producing courtship song do not mate. In the house cricket,Acheta domesticus, we examined whether a female chose or rejected a male based on his size, latency to chirp, latency to produce courtship
song, or rate of the high-frequency pulse of courtship song (“court rate”). We confirmed that females mated only with males
that produced courtship song, but we found no evidence that the other factors we measured affected a female’s decision to
mate. In addition, we investigated whether the outcome of male agonistic encounters affected the subsequent production of
courtship song. In one experiment, we observed courtship and mating behavior when a single female was placed with a pair of
males following a 10-min interaction period between the two males. Winners of male agonistic encounters had higher mating
success. However, winners and losers of agonistic encounters were not different in their likelihood or latency to produce
courtship song or in the number of times they were disrupted by the other male in the pair. In a second experiment, we allowed
two males to interact for a 10-min period, but following this interaction period, we placed a female with each male separately
and observed courtship and mating behavior. The mating success of winners and losers was not different under these circumstances,
and we found no differences between winners and losers in any subsequent courtship or mating behavior examined. We conclude
that winning agonistic encounters influences a male’s mating success in ways other than his production of courtship song and
this effect is lost when winning and losing males are separated and each is given an opportunity to mate. 相似文献
993.
The flight behavior of Anopheles gambiae s.s. Giles and An. stephensi Patton exposed to different odor cues was studied in
a wind tunnel. Odors consisted of CO2, CO2 + acetone (at two concentrations), and CO2
+ 1-octen-3-ol. Mosquitoes were released singly and their behavior was recorded on video. Parameters studied included flight
velocity, percentage of time spent flying, percentage of time spent in plume, and number of turns toward the plume. Large
differences in behavior toward the odors tested were observed. An. gambiaedid not respond well to CO
2,whereas An. stephansiwas positively affected by this compound. In contrast, An. gambiaeresponded significantly to CO
2
+ acetone (at a low concentration), but the behavior of An. stephensiwas completely suppressed by this combination of odor stimuli. CO
2
+ a high concentration of acetone or CO
2
+ 1-octen-3-ol did not cause significant effects in An. gambiaecompared to no odor, while these treatments elicited strong behavioral responses in An. stephensi.The latter species responded particularly well to CO
2
+ 1-octen-3-ol. The results suggest that the observed differences may be inherent to the known differences in host preferences,
where An. gambiaeis highly anthropophilic and An. stephensimore zoophilic. This would explain why the latter species responds well to CO
2
and even better to CO
2
+ 1-octen-3-ol, a compound readily emitted by bovine ruminants. 相似文献
994.
We examined alternative hypotheses for the benefits of footdrummingin the presence of snakes by the banner-tailed kangaroo rat,Dipodomys spectabitis, by testing whether the target of thesignal includes conspecifics, the predator or both. Footdrummingrecorded in the field revealed that rats altered their footdrummingsignatures when drumming at snakes. In playback tests, however,neighbors failed to show any measurable change in behavior tobroadcasts of the snake drumming pattern, but mothers footdrummedsignificantly more than nonmothen in the presence of a tetheredsnake. Gopher snakes, Pituophis melanolsucus affinis, respondedto footdrumming vibrations created by a mechanical thumper.Nonhungry snakes avoided footdrumming, while hungry snakes approachedthe seismic footdrumming. Snakes decreased stalking rates asfootdrumming increased, but they spent more time stalking drummingthan nondnimming rats. We conclude that D. spectabilis footdrumsin individual defense and in parental care, rather than to warnadult conspecfics. Footdrumming deters pursuit by informingthe snake that the rat is alert and the chances of predationare low. We find little evidence that footdrumming startles,confuses, or harasses the snake. Hungry gopher snakes, however,may locate prey by eavesdropping on territorial footdrumming 相似文献
995.
The phenology and pollination ecology of three native fig species were studied in southeastern Brazil. Populations displayed continual syconia production, with one species showing intra-tree flowering asynchrony. Pollination of the fig flowers was necessary for the development of the syconia; lack of pollination induced abortion of syconia. All three species follow the general pattern of pollination known for figs, but the behavior of the pollinator wasps, Pegoscapus spp., differed in some aspects from those of other neotropical and paleotropical fig wasps, mainly with respect to pollen loading and unloading during pollination. The longevity of Pegoscapus wasps outside the syconium was about two days. 相似文献
996.
捕食风险与动物行为及其决策的关系 总被引:8,自引:0,他引:8
捕食风险与动物行为及其决策的关系边疆晖樊乃昌(中国科学院西北高原生物研究所,西宁810001)(浙江师范大学,金华310000)TheEfectofPredationRiskonAnimals’BehaviorandTheirDecision.Bia... 相似文献
997.
Kazunori Matsumoto Kohji Mabuchi Masanori Kohda Tetsuji Nakabo 《Ichthyological Research》1997,44(4):379-384
The reproductive behavior of two wrasses,Pseudolabrus eoethinus (Richardson, 1846) andP. sieboldi Mabuchi & Nakabo, 1997, was studied on a rocky coast in Shikoku, Japan, where the two species occur sympatrically. In the
study area, individual males of each species established mating territories within which pair spawnings occurred. Pair spawnings
were observed only between conspecifics, indicating that the two coexisting species were reproductively isolated. Both species
usually spawned during the afternoon in early winter and had similar reproductive behavior. Although habitat, temporal and
behavioral isolation mechanisms were not apparent, reproductive isolation seemed to occur via premating isolation through
visual recognition of conspecific mates because the two species differed in body size and coloration. On one occasion a maleP. sieboldi was observed to perform streaking behavior to join a spawning pair ofP. eoethinus. Thus, postmating isolation between the two species is also discussed. 相似文献
998.
Western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae), is the most important insect pest for greenhouse flower crops, but chemical control is often difficult because of the thrips' location in flowers and buds. Thripinema nicklewoodi (Tylenchida: Allantonematidae) is an entomoparasitic nematode that attacks and sterilizes WFT, but its biology and impact on WFT are poorly understood. Methods to propagate and study T. nicklewoodi with a microscope slide arena for observation and a rolled bean leaf arena for rearing were developed. On average, 21.4 nematodes were excreted per day by a parasitized female WFT. The sex ratio of the excreted nematodes was 6.0/1.0 (female/male). After dissection of adult WFT, a maximum of 11 ovoid-shaped first-generation nematodes in a female thrips and 6 in a male thrips were found. There were more second-generation nematodes in the adult female WFT (192.6) than in the adult male WFT (93.7). When 50 healthy first instar WFT were exposed to 4 parasitized female WFT in a rolled bean leaf, a 75.3% mean parasitization rate in the adult stage of the thrips was obtained. In contrast to previous reports, male WFT can be parasitized as readily as females. Parasitism reduced the longevity of both adult female and adult male WFT, and the degree of reduction was higher in adult male WFT. T. nicklewoodi, when presented with various WFT life stages (first instar, second instar, prepupa, pupa, adult female, and adult male), achieved the highest attack rate in first and second instars and prepupa. The free-living nematodes excreted by the hosts actively migrated to a trichome on leaf disks in the observation arena and moved up this structure. Then, the nematode actively waved the anterior part of its body while attaching itself to the trichome with the posterior part of its body. After a nematode contacted the leg of a thrips, the nematode immediately moved up along the leg toward the abdomen of the host. Increased understanding of the biology of T. nicklewoodi is important to better assess its potential for biological control of WFT. 相似文献
999.
Three commercial and six experimental plant growth bioregulators were surveyed for their effect on aphid reproduction when applied to sorghum. Only CCC and PIX had a significant effect on the greenbug, Schizaphis graminum. Application of the commercial bioregulators CCC and PIXR caused about a 50% decrease in aphid reproduction rate when applied to greenbug susceptible sorghum but had little effect when applied to a greenbug resistant sorghum line. Electronic monitoring of aphid probing behavior on CCC treated, greenbug-susceptible sorghum showed a response pattern which was indistinguishable from that normally observed on greenbug resistant lines and was different from that associated with aphid probing behavior on untreated susceptible lines. The isolated pectin content of the CCC treated susceptible sorghum was twice that of the controls and had twice the methoxy content. These results support the argument that pectin is a barrier to aphid-stylet penetration for phloem feeding aphids which probe intercellularly and that manipulation of pectin content and/or structure can be a major factor in host-plant resistance to sap-sucking insects. 相似文献
1000.
"Flipper rubbing" behavior was quantitatively analyzed in wild Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) around Mikura Island, Tokyo, Japan. We observed two types of flipper rubbing: (1) F-B rubbing; one dolphin (Rubber) rubbed its flipper over various parts of a partner's (Rubbee) body, and (2) F-F rubbing; both dolphins rubbed each other's anterior flipper edge in alternating shifts. F-B rubbings tended to be initiated by the Rubbee and were terminated by the Rubber. The Rubbee often moved actively its body part that was in contact with the Rubber's flipper, and assumed side-up, upside-down, or other postures while the Rubber remained horizontal in most cases. These facts suggest that the Rubbee engaged in F-B rubbing more actively than the Rubber, and might receive some benefit from the frictional contact during F-B rubbing. Dolphins often switched their roles as Rubber and Rubbee between episodes of flipper rubbing bout. Adults and sub-adults exchanged F-B rubbing and F-F rubbing most often with individuals of the same sex in the same age class. F-B rubbing was frequent in mother-and-calf dyads. Our results suggest that flipper rubbing is an affiliative behavior which could be a quantitative measure of social relationships among individuals of this species in future studies. 相似文献