全文获取类型
收费全文 | 682篇 |
免费 | 15篇 |
国内免费 | 29篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 41篇 |
2012年 | 18篇 |
2011年 | 25篇 |
2010年 | 19篇 |
2009年 | 50篇 |
2008年 | 42篇 |
2007年 | 25篇 |
2006年 | 23篇 |
2005年 | 32篇 |
2004年 | 28篇 |
2003年 | 15篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 14篇 |
1994年 | 7篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 20篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1971年 | 2篇 |
排序方式: 共有726条查询结果,搜索用时 250 毫秒
691.
Distinct tissues and organs of plants exhibit dissimilar responses to light exposure – cotyledon growth is promoted by light, whereas hypocotyl growth is inhibited by light. Light can have different impacts on root development, including impacting root elongation, morphology, lateral root proliferation and root tropisms. In many cases, light inhibits root elongation. There has been much attention given to whether roots themselves are the sites of photoperception for light that impacts light-dependent growth and development of roots. A number of approaches including photoreceptor localization in planta, localized irradiation and exposure of dissected roots to light have been used to explore the site(s) of light perception for the photoregulation of root development. Such approaches have led to the observation that photoreceptors are localized to roots in many plant species, and that roots are capable of light absorption that can alter morphology and/or gene expression. Our recent results show that localized depletion of phytochrome photoreceptors in Arabidopsis thaliana disrupts root development and root responsiveness to the plant hormone jasmonic acid. Thus, root-localized light perception appears central to organ-specific, photoregulation of growth and development in roots. 相似文献
692.
Tadashi Kumagai 《Physiologia plantarum》1983,59(4):590-594
Coniditation the fungus, Alternaria cichorii Nattras (IMI 225641), was repeatedly induced and inhibited by alternating doses of near ultraviolet and blue radiation. The final response largely depended on the last kind of radiation administered. When the final radiation was near ultraviolet, conidiophore formation was induced, and conidia were then produced in the subsequent dark period; when it was blue, the induction of conidiation was suppressed. The inductive effect of near ultraviolet was promoted by anaerobiosis, but the reversing effect by blue radiation was not influenced by molecular oxygen. Thus, the "mycochrome" system apprears to control induction of conidiation in Alternaria cichorii , and oxidation-reduction processes may be involved in its function. 相似文献
693.
Maite Mascaro Luis E. Hidalgo Xavier Chiappa-Carrara Nuno Simoes 《Marine and Freshwater Behaviour and Physiology》2013,45(3):143-159
Size-selective predation by small (30-50 mm carapace width) and large (90-110 mm) Callinectes sapidus when feeding on three different size classes of Litopenaeus setiferus was investigated. Laboratory experiments using no-choice and multiple-choice designs were carried out. Active and passive components of predation were evaluated by comparing the probability of attacking (active) and capturing (passive) shrimp. Small C. sapidus consumed shrimp of all size classes in similar frequencies during multiple and no-choice experiments, and the probability of attacking and capturing shrimp of all size classes was similar. Large crabs consumed large shrimp with a significantly higher frequency during multiple than during no-choice experiments, and the probability of capturing large shrimp was significantly higher than medium and small ones. Results in the present study suggest that size-specific consumption rates of C. sapidus are mainly the result of a passive mechanism associated with the salience of shrimp to predation. However, an active component of foraging behaviour related to the decision to attack an alternative prey whilst consuming one that has already been captured, helps to explain the differences in shrimp consumption between multiple and no-choice experiments. The complex interaction between active, passive components and satiation is discussed. 相似文献
694.
Two forms of glutamine synthetase (EC 6.3.1.2) can be separated in crude extracts of Chlorella kessleri on the basis of their different surface charges. The two enzyme forms (GS1 and GS2) respond differently upon transferring the cells from darkness to autotrophic growth in white light: the activity of GS2 increases, that of GS1 remains unchanged. The increase in GS2 activity is only brought about by blue light; in red light GS2 activity appears to be uninfluenced, while that of GS1 increases. There are no indications of wavelength-dependent oligomerization processes as a cause for the observed activity alterations. There is however, a strong influence of inhibitors of protein biosynthesis. Cycloheximide and lincomycin both affect the blue light-dependent increase in activity of GS2, cycloheximide preventing that of GS1 in red lgiht completely. Since literature data point to localization of GS2 in the chloroplast, and GS1 in the cytosol, the data are discussed in view of two different photoreceptors involved in the regulation of the amounts of GS1 and GS2 in different compartments of the Chlorella cell. 相似文献
695.
The action spectrum of phototaxis was determined and the photoreceptive mechanism was studied in Ectocarpus gametes (Ectocarpales, Phaeophyceae) using a computerized cell-tracking system. The fine structures of the stigma and the flagellar swelling were analyzed, and the reflective function of the stigma was demonstrated for the first time. Under monochromatic light stimulation, Ectocarpus gametes show mainly positive phototaxis between 370 nm and 520 nm. The action spectrum has a minor peak near 380 nm, and two major peaks at 430 nm and 450 nm or 460 nm and a shoulder at 470 nm adjoining a remarkable depression near 440 nm. Under unilateral stroboscopic illumination with more than four pulses per second, the gametes show clear phototaxis. However, the response is disturbed at lower frequencies. Addition of methyl cellulose, which increases the viscosity of the medium and slows down gamete rotation, decreases the threshold frequency. These results indicate that rotation of the gamete plays an essential role in the photoreceptive mechanism. Under equal intensities of bilateral illumination at an angle of 90°, most of the gametes swim on the resultant between the two light beams. This response is disturbed when the angle of the two light beams is as large as 120°. Observations by transmission electron microscopy show that the flagellar swelling fits precisely into a concave depression of the chloroplast at the central region of the stigma. Electron-dense material is present in that sector of the flagellar swelling which faces away from the stigma. Epifluorescence microscopy without a barrier filter and epipolarization microscopy reveal that stigmata reflect blue light. A hypothesis is formulated which discusses the possibility that the reflected light is focused onto the flagellar swelling.We are grateful to Jochen Schäfer and Elke Reinecke for their technical assistance and Dr. G. Konerman for access to epipolarization microscopy. We are also grateful to the Alexander von Humboldt Foundation for a Research Fellowship to H.K. and the Deutsche Forschungsgemeinschaft (University of Freiburg, Freiburg, FRG) for financial aid to D.-P.H.To whom correspondence should be addressed. 相似文献
696.
Solomon H. Katz 《Human nature (Hawthorne, N.Y.)》1990,1(3):233-259
The evolution of human diet is the product of both biological and cultural adaptations to various plants and animals in the
environment. This paper develops a new theory for the evolution of cuisine practices which attempts to account for how food
processing provided a critical link in enhancing the nutrient balance of major domesticated plants.
Dr. Katz is a Professor of Anthropology and Director of the W. M. Krogman Center for Research in Child Growth and Development
at the University of Pennsylvania. He first became interested in food and cuisine research as a result of his work with minerals
in the diets of Inuit (Eskimo) peoples of the Alaskan Arctic and then with maize in the diets of the Lacandon Maya Indians
in the early 1970s. Since then he has published numerous books and papers on developing the theory of cuisine presented in
this paper. 相似文献
697.
698.
In young Acetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva) the formation of the lateral hair whorls can be induced by a short pulse of blue light after continuous red preillumination. In this paper we describe the experimental conditions for optimum response and the properties of the action spectrum. The probit of the cells which eventually form hair whorls is linearly correlated to the logarithm of the incident quanta of blue light. Parallel fluence-response curves for all wavelengths indicate the involvement of only one photoreceptor pigment. The action spectrum shows no effectiveness of wavelengths above 520 nm, a high action peak at 470 nm and two lower ones at 425 and 370 nm, and is in accordance with those of cryptochrome-like photoreceptors. 相似文献
699.
Photoorientation of chloroplasts mediated by phytochrome and blue light-absorbing pigment in protonemal cells of the fernAdiantum was studied by use of inhibitors of the cytoskeleton and was analyzed with a video-tracking system. The photoorientation
responses were inhibited by cytochalasin B and by N-ethylmaleimide (NEM) but not by colchicine, suggesting that the photomovement
depends on the actomyosin system. In the dark, chloroplasts moved randomly, being independent of one another. After induction
of photoorientation by polarized red light, most chloroplasts that had been located at the margin of cells moved almost perpendicularly
to the cell axis toward the site of photoorientation. This type of movement was hardly ever observed in the dark. Under polarized
blue light, such specific movements were less evident but were still observed in the case of a few chloroplasts. After photoorientation
was complete, chloroplasts still moved in random directions but their mobility was lower than that in the dark, indicating
the presence of some anchoring mechanism.
When EGTA was applied, photoorientation was inhibited but this inhibition was overcome by the addition of CaCl2. Video-tracking of chloroplasts in the dark revealed that the mobility of chloroplasts was higher in medium with EGTA than
in medium with EGTA plus CaCl2 and that many of the chloroplasts moved jerkily in the medium with EGTA. This change in the nature of movements was also
seen under polarized light, resulting in the disturbance of photoorientation. These results indicate that the inhibition of
photoorientation at low concentrations of Ca2+ ions may be due to change in the nature of chloroplast movement. 相似文献
700.
Contrasting seasonal patterns of fine root production for blue oaks (Quercus douglasii) and annual grasses in California oak woodland 总被引:1,自引:0,他引:1
In a blue oak woodland in NE California, we used root ingrowth cores to study seasonal patterns of fine root (< 2 mm diameter) production (FRP) for annual grasses and blue oaks (Quercus douglasiiHook and Arn.). At each of three sites (River, Upland and Hilltop) there were three studies: a short-term seasonal study, a long-term cumulative study and a core nutrient enrichment study. In the short-term study, ingrowth cores were installed and harvested in 3-month intervals. Grass and oak FRP dominated in different seasons. Grass FRP was greater in fall (Oct–Dec, 26.0 g m–2 month–1(gmm)) and winter (Jan–Mar, 18.1 gmm), lower in spring (Apr–Jun, 2.9 gmm) and negligible in summer (July–Sep). In contrast, oak FRP was greater in spring (6.1 gmm) with lower, but significant summer growth (2.9 gmm). Grass FRP declined steadily with soil depth (0–40 cm) in all seasons. Oak FRP changed little with soil depth, except in the summer, when production was greatest at lower soil depths. In the long-term study, ingrowth cores were installed and harvested after 3, 6, 9 and 12 months. Oak annual FRP was greater in the long-term study than in the short-term study at the River and Upland sites. Thus production in the short-term study may be an underestimate, due to disturbance effects. Nutrient enrichment of cores with N-P-K increased grass FRP, but surprisingly, decreased oak FRP, suggesting that annual grasses may have competitive advantages in nutrient enriched soil. 相似文献