全文获取类型
收费全文 | 986篇 |
免费 | 47篇 |
出版年
2023年 | 13篇 |
2022年 | 17篇 |
2021年 | 31篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 32篇 |
2015年 | 50篇 |
2014年 | 46篇 |
2013年 | 72篇 |
2012年 | 74篇 |
2011年 | 71篇 |
2010年 | 41篇 |
2009年 | 33篇 |
2008年 | 50篇 |
2007年 | 43篇 |
2006年 | 35篇 |
2005年 | 35篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 16篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1966年 | 3篇 |
排序方式: 共有1033条查询结果,搜索用时 31 毫秒
991.
Santha Devi 《Review of Palaeobotany and Palynology》1977,23(2):139-144
Five species of Polystichum are studied under the scanning electron microscope and a comparison made with the light microscope studies of the same species published earlier. The SEM studies present a clear picture of the surface topography, supplying additional information. 相似文献
992.
993.
994.
995.
A novel bioactive Schiff base (HL) named 3-methyl-1-phenyl-5-((5-nitrosalicylidene)amino)pyrazole was prepared by condensing 5-amino-3-methyl-1-phenylpyrazole with 5-nitrosalicyldehyde in methanol on a heating mantle in refluxing condition for 1 h. Some transition metal complexes of the ligand in (1 : 1) and (1 : 2) have also been prepared by condensing the metal acetate salt with the synthesized Schiff base. The Schiff base and metal complexes were characterized by different physiochemical techniques, i. e., 1H-NMR, InfraRed, mass spectroscopy, elemental analysis, Ultraviolet-Visible, Cyclic voltammetry, electronic spectra and Electron spin resonance. The presence of water molecules in the complexes have been calculated with the help of thermogravimetric analysis. Kinetic parameters such that entropy change, enthalpy change and activation energy have been calculated with the help of Coats-Redfern equations. Fluorescence spectra showed enhancement in the fluorescence signal of the metal complexes. Square planar geometry for the copper complexes and octahedral geometry for the other metal complexes have been proposed with help of various methods. Biological activities of all the compounds have been carried out and the results disclosed that the metal complexes have high biological activity than the Schiff base having MIC value in the range 25–3.12 μg/mL and mycelial growth inhibition 60.82–96.98 %. 相似文献
996.
Lu-Yi Wang Amanda M. Franklin Andrew F. Hugall Iliana Medina Devi Stuart-Fox 《Global Ecology and Biogeography》2023,32(3):408-420
Aim
To predict future colour–climate relationships, it is important to distinguish thermal drivers of reflectance from other evolutionary drivers. We aimed to achieve this by comparing relationships between climate and coloration in ultraviolet–visible (UV–Vis) and near-infrared (NIR) light, separately.Location
Samples were distributed primarily across Australia and North America, with some from Africa and Asia.Major taxa studied
Coleoptera: Buprestidae.Methods
We used jewel beetles as models to identify climatic drivers of reflectance, because jewel beetles have highly diverse coloration and a wide distribution and are often active in hot conditions. Specifically, we tested the association between climate, body size and reflectance using a phylogenetic comparative analysis for three wavebands (UV–Vis, NIR and total).Results
Reflectance of jewel beetles was more strongly predicted by body size than by climate. NIR reflectance and total reflectance were not associated with climate, but larger beetles had higher NIR reflectance. For UV–Vis reflectance, small beetles were darker in warmer and more humid environments, whereas there was no association with climate for large beetles.Main conclusions
Our study suggests that variation in reflectance of jewel beetles is not driven by thermal requirements and highlights the importance of considering NIR reflectance when evaluating explanations of the effects of colour on thermoregulation. 相似文献997.
Neelam Sharma S. Vimala Devi Ruchira Pandey 《Journal of plant biochemistry and biotechnology.》2007,16(1):63-65
Shoot multiplication of Curculigo orchioides Gaertn (Kali Musali), a threatened medicinal herb, was achieved using shoot bud explants. Single explants cultured on MS + 0.2 mg l?1 BA + 2.5 mg l?1 spermidine produced multiple shoots with an average of 7 shoots per explant that readily rooted on the same medium. Plantlets were acclimatized before successful transfer to soil. The developed protocol demonstrates the use of spermidine for mass propagation that can help in conservation of germplasm of Curculigo orchioides. 相似文献
998.
999.
Sleep and Biological Rhythms - Up to date, it is found that the presence of obstructive sleep apnea (OSA) contributes to the development of structural, ultra-structural, functional, and proteomics... 相似文献
1000.
Zoe E. Squires Bob B.M. Wong Mark D. Norman Devi Stuart‐Fox 《Biological journal of the Linnean Society. Linnean Society of London》2015,116(2):277-287
Differential sperm usage from consecutive matings, or sperm precedence, is vital in determining male reproductive success and the outcome of sperm competition for many organisms. Sperm precedence also has significant consequences for mating system dynamics, including both male and female adaptations for increasing reproductive success and avoiding the costs of mating. Despite sexual selection being a strong driver of reproductive behaviour and morphology in cephalopods, surprisingly few studies have investigated sperm dynamics in this group. To redress this gap, we experimentally quantified sperm precedence patterns in the dumpling squid, Euprymna tasmanica, controlling for recent male mating history (first vs. second mating), mating position, and mating frequency. We found that the last male to mate gains an advantage in this system, with the second mating male siring up to 75% of offspring at the beginning of the laying period. The proportion of offspring attributable to the second mating male decreases to 54% by the end of the laying period, potentially as a result of changes in the velocity or number of sperm released from spermatangia over time. There is also significant variation among females in patterns of sperm precedence. This variation was not associated with whether it was the male's first or second mating, male mass, the duration of copulation or the number of pumps (sperm removal behaviour) by the second male. If widespread in cephalopods, last male sperm precedence could help to explain the evolution of mate guarding (or long copulation duration) and sperm removal behaviour in this group. 相似文献