全文获取类型
收费全文 | 2198篇 |
免费 | 125篇 |
国内免费 | 39篇 |
专业分类
2362篇 |
出版年
2023年 | 16篇 |
2022年 | 36篇 |
2021年 | 44篇 |
2020年 | 57篇 |
2019年 | 44篇 |
2018年 | 44篇 |
2017年 | 71篇 |
2016年 | 66篇 |
2015年 | 53篇 |
2014年 | 124篇 |
2013年 | 153篇 |
2012年 | 69篇 |
2011年 | 104篇 |
2010年 | 63篇 |
2009年 | 112篇 |
2008年 | 124篇 |
2007年 | 127篇 |
2006年 | 91篇 |
2005年 | 94篇 |
2004年 | 70篇 |
2003年 | 67篇 |
2002年 | 53篇 |
2001年 | 29篇 |
2000年 | 35篇 |
1999年 | 55篇 |
1998年 | 48篇 |
1997年 | 34篇 |
1996年 | 33篇 |
1995年 | 35篇 |
1994年 | 40篇 |
1993年 | 33篇 |
1992年 | 35篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 25篇 |
1987年 | 23篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 27篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 4篇 |
1973年 | 5篇 |
排序方式: 共有2362条查询结果,搜索用时 15 毫秒
1.
2.
3.
The cost of mutualism in a fly-fungus interaction 总被引:2,自引:0,他引:2
The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study,
I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous
stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions
to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure
and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s
ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure
on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management.
Received: 14 July 1999 / Accepted: 23 March 2000 相似文献
4.
Akihisa Hattori 《Journal of Ethology》2006,24(1):51-57
The distribution patterns of the leathery sea anemone, Heteractis crispa, which contains an algal endosymbiont (zooxanthellae) and anemonefish, were investigated in relation to size distribution on a shallow fringing reef (3.2 ha, 0–4 m depth) in Okinawa, Japan. Individual growth and movements were also examined. Large individuals (>1,000 cm2) inhabited reef edges up to a depth of 4 m, while small anemone (<500 cm2) inhabited shallow reefs including inner reef flats. Individuals rarely moved, and their sizes were significantly correlated with their water depths. Growth of small anemones was negatively correlated with their distance from the reef edge, suggesting that reef edges provide more prey and lower levels of physiological stress. This study suggested that deep reef edges are suitable habitats for H. crispa. Large anemones were inhabited by large Amphiprion perideraion or large Amphiprion clarkii, both of which are effective defenders against anemone predators. Anemones that settle in deep reef edges may enjoy a higher survival rate and attain a large size because of their symbiotic relationship with anemonefish. However, early settlers do not harbor anemonefish. Their mortality rate would be higher in the deep edges than in shallow edges, the complicated topography of which provides refuge. 相似文献
5.
E. Golomer P. Dupui H. Monod 《European journal of applied physiology and occupational physiology》1997,76(2):140-144
We investigated the effects of maturation on the dynamic body sways of healthy girls. Prepubertal and postpubertal girls
practising professional physical activities requiring a good ability to maintain equilibrium (acrobats and dancers) were asked
to stand on a free seesaw platform and the results compared to those for untrained age-matched girls. This platform (stabilometer)
allows self-induced body sways. Stabilograms were obtained by a double integration of the angular acceleration from the recordings
of the platform sways made with an accelerometer. Fast Fourier transform processing of stabilograms allowed spectral frequency
analysis. The total spectrum energy and the energies of three frequency bands (0–0.5 Hz, 0.5–2 Hz, 2–20 Hz) were determined.
ANOVA showed that, for all groups of different equilibrium activity and independent of visual input, prepubertal girls had
higher energy values than postpubertal girls in the 0- to 0.5-Hz band whereas the opposite was true for 0.5- to 2-Hz band.
Ballet dancers were more dependent than acrobats on visual inputs for the regulation of their postural control but were less
dependent than untrained girls at both ages. Maturation seemed to shift body sways towards higher frequencies and the utilization
of the cues of postural control was different according to the type of equilibrium activity practised by the subjects.
Accepted: 7 February 1997 相似文献
6.
This article is part of a Special Issue “Energy Balance”. 相似文献
7.
Abstract. The influences of hatchling character and rearing density on body colour at the last-nymphal stadium are investigated for the desert locust, Schistocerca gregaria . Hatchlings are divided into five groups based on the darkness of the body colour and reared either under isolated or crowded conditions. Two types of body colour variation at the last-nymphal stadium are separately analysed (i.e. the background colour and black patterns). Under isolated conditions, the background body colour is either greenish or brownish. Most individuals are greenish and the highest percentage of brownish insects is obtained from hatchlings with the darkest body colour. Under crowded conditions, the background colour is yellow or orange and the percentage of yellowish nymphs tends to decrease when they are darker at hatching. The intensity of black patterns differs depending on the body colour at hatching and subsequent rearing density. Most isolated-reared nymphs exhibit few or no black patterns but nymphs with some black patterns also appear, particularly among those that had been dark at hatching. Under crowded conditions, the black patterns become more intense when they are darker at hatching. Therefore, last-stadium nymphs with typical solitarious or gregarious body colouration appear when they have the phase-specific body colouration at hatching as well. The present results demonstrate that both body colour at hatching and rearing density during nymphal development influence body colouration at the last-nymphal stadium. 相似文献
8.
9.
THE COMBINED EFFECTS OF LOW TEMPERATURE AND SO2 +NO2 POLLUTION ON THE NEW SEASON'S GROWTH AND WATER RELATIONS OF PICEA SITCHENSIS 总被引:6,自引:5,他引:1
Picea sitchensis (Bong.) Carr. seedlings were exposed to SO2 , NO2 and SO2 + NO2 during dormancy in controlled environments, and were taken to night temperatures of 4, 0, −5, −10 and −15 °C in a freezer. Conditions in the freezer were carefully monitored during the low–temperature treatments. In two experiments, different photoenvironments and temperature regimes were imposed prior to the cold treatments, and different effects were observed. In the first, only limited frost hardiness was achieved and night temperatures of −15 °C were lethal. Temperatures of −5 and − 10 °C led to poor survival of lateral buds, particularly in plants exposed to 45 ppb SO2 . The poor bud break in plants exposed to SO2 and to − 5 °C resulted in a loss of the effectiveness of this temperature as a chill requirement. Pressure-volume analysis showed that the shoots of plants exposed to NO2 had greater elasticity (lower elastic moduli, e), so that loss of turgor occurred at lower relative water contents. In contrast, a hardening period (2 weeks in night/day temperatures of 3/10 °C and 8 h days at 50 μmol m−2 s−1 PAR) gave decreased elasticity and lower solute potentials of spruce shoots. In the second experiment, exposure to 30 ppb SO2 and SO2 + NO2 led to slight, but consistent, increases in frost injury to the needles of plants frozen to − 5 and − 10 °C. The results suggest that the main interaction of low temperatures and winter pollutants may be on bud survival rather than on needle damage, but that effects are subtle, only occurring with certain combinations of pollutant dose and cold treatment. 相似文献
10.
Summary The maximum density achievable by aquatic organisms is an inverse linear function of their body size. As a consequence, the maximum achievable biomass is independent of body size, and is 2 orders of magnitude higher than the biomass in natural populations. The minimum interorganismic terorganismic distance, calculated from the maximum density to allow comparison between aquatic and terrestrial organisms, scales as the 1/3 power of body size in both habitats. The similarities in the interorganismic distance of terrestrial and aquatic plant and animal communities suggest a fundamental regularity in the way organisms use the space. 相似文献