全文获取类型
收费全文 | 1917篇 |
免费 | 104篇 |
国内免费 | 34篇 |
出版年
2023年 | 14篇 |
2022年 | 33篇 |
2021年 | 41篇 |
2020年 | 43篇 |
2019年 | 37篇 |
2018年 | 34篇 |
2017年 | 62篇 |
2016年 | 58篇 |
2015年 | 47篇 |
2014年 | 112篇 |
2013年 | 139篇 |
2012年 | 60篇 |
2011年 | 96篇 |
2010年 | 56篇 |
2009年 | 99篇 |
2008年 | 110篇 |
2007年 | 121篇 |
2006年 | 84篇 |
2005年 | 85篇 |
2004年 | 63篇 |
2003年 | 53篇 |
2002年 | 43篇 |
2001年 | 23篇 |
2000年 | 29篇 |
1999年 | 52篇 |
1998年 | 39篇 |
1997年 | 27篇 |
1996年 | 28篇 |
1995年 | 33篇 |
1994年 | 35篇 |
1993年 | 30篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1973年 | 5篇 |
1972年 | 3篇 |
排序方式: 共有2055条查询结果,搜索用时 15 毫秒
1.
2.
Electron-microscopic and immunocytochemical analyses of Weibel-Palade bodies in the human umbilical vein during pregnancy 总被引:3,自引:0,他引:3
Summary The present study was done to elucidate the biological significance of the Weibel-Palade body of human umbilical vein endothelial cells. Quantitative determinations of these endothelial-specific granules throughout pregnancy revealed that their numbers and size per cell profile were maintained at low levels from 12 to 19 weeks of gestation; then both rapidly increased from 33 weeks to full term. This increase coincided with the development of the rough endoplasmic reticulum and an increase in the number of endothelial cell pinocytotic vesicles. Light-microscopic peroxidase anti-peroxidase and electron-microscopic protein A-gold techniques provided evidence that factor VIII-related antigen was localized in the Weibel-Palade bodies. Furthermore, in vitro treatment of incubated umbilical vein tissue with compound 48/80, a histamine releaser, induced degranulation of Weibel-Palade bodies from the endothelium. The present study indicates that Weibel-Palade bodies are storage sites of both histamine and factor VIII-related antigen and have an important role in the obliteration of this vessel. 相似文献
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.
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
10.
Invertebrate predator-prey body size relationships: an explanation for upper triangular food webs and patterns in food web structure? 总被引:1,自引:0,他引:1
Summary It has been suggested by Cohen and Newman (1985) that many of the patterns in published food webs can be derived from a stochastic model in which the species are arranged in a trophic hierarchy (the cascade model). We suggest that, if predators are larger than their prey, a trophic hierarchy can be generated on the basis of body size Empirical evidence from the literature shows that there is a positive relationship between predator and prey size for a range of invertebrates and that predators are usually larger than their prey. Using experimental data on an aquatic food web we show that body size can lead to the type of trophic hierarchy used in the cascade model, suggesting that many food web patterns may be a product of body size. This conclusion is discussed with respect to the limitations of the food web data and the relationship between static and dynamic models of web structure. 相似文献