全文获取类型
收费全文 | 587篇 |
免费 | 45篇 |
国内免费 | 26篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 19篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 35篇 |
2012年 | 19篇 |
2011年 | 12篇 |
2010年 | 16篇 |
2009年 | 23篇 |
2008年 | 32篇 |
2007年 | 29篇 |
2006年 | 20篇 |
2005年 | 21篇 |
2004年 | 16篇 |
2003年 | 34篇 |
2002年 | 24篇 |
2001年 | 24篇 |
2000年 | 11篇 |
1999年 | 20篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有658条查询结果,搜索用时 15 毫秒
111.
How Texas wild rice, Zizania texana, became isolated in the San Marcos River of Central Texas, hundreds of kilometres from other wild rice populations is not known. Zizania seeds are intolerant of short-term desiccation. Seeds desiccated at 14% relative humidity (RH) and 75% RH do not survive after only 5-6 d and 2-3 wk of drying. Water loss is rapid and reaches a maximum at the time of seed death due to drying. And although all Zizania seeds germinate well following a long, cold dormancy period, Z. texana seeds readily germinate in the isothermic water (22°C) of the San Marcos River and Springs without an obligate, cold dormant period. Within 30-60 d of collection, Z. texana seeds germinate in substantial numbers, unlike seeds of Z. palustris, which require a long, cold dormant period. The Texas population of Z. texana may represent a relict population of a once more widely dispersed wild rice population, since the San Marcos springs probably have never gone dry. 相似文献
112.
《Biotechnic & histochemistry》2013,88(4):278-287
AbstractDespite many reports concerning processing of ancient soft tissues, scant attention has been paid to optimizing procedures for processing soft tissues that have been altered by taphonomic processes. To determine the best procedures, we investigated the rehydration solution, time of exposure to the solutions, fixative solution and exposure to heat. Processes were evaluated based on the minimum section thickness, degree of tissue fragmentation, definition of tissue architecture and penetration of stains. We found that in desiccated samples, tissue architecture was optimized by using Ruffer's solution for rehydration and Schaffer's solution as fixative, because these tissues require water restoration within the tissues due to their compacted character. Heating enhanced penetration of dyes in these specimens, which improved diagnosis. Saponified tissues that had suffered extensive decomposition were more labile and required slow water uptake. The best histological sections were obtained using Sandison's solution followed by fixation with formaldehyde and avoiding heat. To obtain the best results with paleohistological specimens, the procedure must be determined by the condition of the sample and by accounting for the nature of its damage. 相似文献
113.
枇杷种子不耐贮藏,属于脱水敏感的种子。在干燥脱水过程中,子叶和胚轴的超氧物歧化酶(SOD) 和过氧化物酶(POD) 活性不断下降,而丙二醛( MDA) 含量及种子浸泡液的电导率不断增加,种子活力逐渐降低。外源0 .05 ~0 .25 mmol/L 的抗坏血酸(ASA) ,0 .05 ~5 .0 mmol/L 的还原性谷胱甘肽(GSH)和0 .05 ~0 .5 mmol/L 的Ca2 + 处理能有效地增强种胚防御过氧化的能力,缓解氧自由基对种胚的伤害,提高脱水劣变的种子活力。 相似文献
114.
The physiological basis of bryophyte production 总被引:6,自引:0,他引:6
M. C. F. PROCTOR 《Botanical journal of the Linnean Society. Linnean Society of London》1990,104(1-3):61-77
In the main features of their carbon metabolism and physiological responses, bryophytes behave as normal C:) plants. However, their small size and frequent poikilohydric habit have important effects on the context in which these characteristics are expressed, and on their environmental physiology. Many are tolerant of drying out to low water contents (c. 5–10%, of dry weight). Photosynthesis declines rapidly with water loss, and resumes with greater or lesser delay on remoistening. The rate and completeness of recovery depend on the intensity and duration of desiccation, and on drought-hardening (perhaps largely related to protection of cell components from oxidative damage) which lakes place as the bryophyte dries. Most bryophytes, including species of well-illuminated habitats, function in effect as shade plants, with low chlorophyll a/b ratios, and become light-saturated at relatively low irradiance. Boundary-layer resistance is critically important in determining water loss from bryophytes in many situations. The time for which a poikilohydric species can photosynthesize after rain is determined by storage capacity and rate of water loss, both strongly influenced by growth-form. In sheltered habitats with extensive bryophyte cover water loss is largely determined by radiation balance, and may be very slow in deeply shaded places. Bryophyte growth-forms must represent an adaptive balance between water economy and needs for light capture and carbon and mineral nutrient acquisition. 相似文献
115.
Protective mechanism of desiccation tolerance in Reaumuria soongorica: Leaf abscission and sucrose accumulation in the stem 总被引:2,自引:0,他引:2
Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive soil drought imposed by the cessation of watering. The results showed that R. soongorica was char-acterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem and leaf abscission under desiccation. The maximum Pn increased at first and then de-clined during drought, but intrinsic WUE increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PSII(ΦPSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dis-sipation of the excitation energy (measured as NPQ) with the increasing intensity of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves. However, when leaf water potential was less than –21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon re-watering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation. 相似文献
116.
Maturation and germination of walnut somatic embryos 总被引:4,自引:0,他引:4
Walnut somatic embryos were multiplied by repetitive embryogenesis on a solid basal DKW medium at 25°C in the dark. When the embryos were isolated at early cotyledonary stage (1–2 mm long) from the primary embryos and cultured on the medium for 3 weeks, they developed into mature embryos showing white, enlarged cotyledons and shoot and root apex. After transfer to light on solid germination medium, however, few mature embryos (0–5%) germinated. Germination percentage increased to about 10% when the mature embryos were pretreated by a storage at 4°C in the dark for 2 months, or by desiccation at 25°C in the dark for 3 or 5 days under an air-humidity conditioned by saturated salt solutions (Mg(NO3)2.6H2O, or ZnSO4.7H2O). Similar results were obtained by the addition of gibberellic acid (GA3) to the germination medium. When mature embryos were desiccated and then placed on medical cotton compresses in liquid germination medium, 45% of the embryos germinated into complete plantlets. These plantlets continued their growth after transplanting to a mixture of peat and vermiculite in pots.Abbreviations GA3
gibberellic acid
- DKW medium
Driver & Kuniyuki Walnut medium 相似文献
117.
脱水导致的胞内溶质变化与植物耐干性的获得 总被引:2,自引:0,他引:2
植物耐干性是指许多植物个体和部分植物种子能在含水量极低的条件下存活,在回水的过程中迅速启动修复机制,细胞经重新水合修复所受损伤的能力。在脱水过程中,植物会合成和积累某些小分子物质、碳水化合物和特殊的蛋白质;在极度脱水状态下,多组分参与的玻璃化的形成和两性物质的重新分配、耐干性植物中特有的抗氧化机制都是植物获得耐干性的重要条件。复苏植物(resurrection plant)和部分被子植物种子是当前研究植物耐干性的模式材料。 相似文献
118.
119.
Anne M Visscher Filip Vandelook Eduardo Fernndez-Pascual Laura Victoria Prez-Martínez Tiziana Ulian Mauricio Diazgranados Efisio Mattana 《Annals of botany》2022,130(6):773
BackgroundPlant seeds have many traits that influence ecological functions, ex situ conservation, restoration success and their sustainable use. Several seed traits are known to vary significantly between tropical and temperate regions. Here we present three additional traits for which existing data indicate differences between geographical zones. We discuss evidence for geographical bias in availability of data for these traits, as well as the negative consequences of this bias.ScopeWe reviewed the literature on seed desiccation sensitivity studies that compare predictive models to experimental data and show how a lack of data on populations and species from tropical regions could reduce the predictive power of global models. In addition, we compiled existing data on relative embryo size and post-dispersal embryo growth and found that relative embryo size was significantly larger, and embryo growth limited, in tropical species. The available data showed strong biases towards non-tropical species and certain families, indicating that these biases need to be corrected to perform truly global analyses. Furthermore, we argue that the low number of seed germination studies on tropical high-mountain species makes it difficult to compare across geographical regions and predict the effects of climate change in these highly specialized tropical ecosystems. In particular, we show that seed traits of geographically restricted páramo species have been studied less than those of more widely distributed species, with most publications unavailable in English or in the peer-reviewed literature.ConclusionsThe low availability of functional seed trait data from populations and species in the tropics can have negative consequences for macroecological studies, predictive models and their application to plant conservation. We propose that global analyses of seed traits with evidence for geographical variation prioritize generation of new data from tropical regions as well as multi-lingual searches of both the grey- and peer-reviewed literature in order to fill geographical and taxonomic gaps. 相似文献