全文获取类型
收费全文 | 29104篇 |
免费 | 2327篇 |
国内免费 | 4篇 |
出版年
2023年 | 192篇 |
2022年 | 132篇 |
2021年 | 288篇 |
2020年 | 331篇 |
2019年 | 313篇 |
2018年 | 538篇 |
2017年 | 476篇 |
2016年 | 1000篇 |
2015年 | 1628篇 |
2014年 | 1600篇 |
2013年 | 2170篇 |
2012年 | 2729篇 |
2011年 | 2251篇 |
2010年 | 1258篇 |
2009年 | 1001篇 |
2008年 | 1851篇 |
2007年 | 1732篇 |
2006年 | 1848篇 |
2005年 | 1567篇 |
2004年 | 1553篇 |
2003年 | 1437篇 |
2002年 | 1363篇 |
2001年 | 634篇 |
2000年 | 763篇 |
1999年 | 394篇 |
1998年 | 208篇 |
1997年 | 115篇 |
1996年 | 137篇 |
1995年 | 154篇 |
1994年 | 121篇 |
1993年 | 117篇 |
1992年 | 133篇 |
1991年 | 113篇 |
1990年 | 104篇 |
1989年 | 90篇 |
1988年 | 62篇 |
1987年 | 48篇 |
1986年 | 54篇 |
1985年 | 77篇 |
1984年 | 95篇 |
1983年 | 57篇 |
1982年 | 73篇 |
1981年 | 47篇 |
1980年 | 56篇 |
1979年 | 47篇 |
1978年 | 42篇 |
1977年 | 39篇 |
1976年 | 58篇 |
1975年 | 44篇 |
1974年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Structure‐based classification of FAD binding sites: A comparative study of structural alignment tools 下载免费PDF全文
A total of six different structural alignment tools (TM‐Align, TriangleMatch, CLICK, ProBis, SiteEngine and GA‐SI) were assessed for their ability to perform two particular tasks: (i) discriminating FAD (flavin adenine dinucleotide) from non‐FAD binding sites, and (ii) performing an all‐to‐all comparison on a set of 883 FAD binding sites for the purpose of classifying them. For the first task, the consistency of each alignment method was evaluated, showing that every method is able to distinguish FAD and non‐FAD binding sites with a high Matthews correlation coefficient. Additionally, GA‐SI was found to provide alignments different from those of the other approaches. The results obtained for the second task revealed more significant differences among alignment methods, as reflected in the poor correlation of their results and highlighted clearly by the independent evaluation of the structural superimpositions generated by each method. The classification itself was performed using the combined results of all methods, using the best result found for each comparison of binding sites. A number of different clustering methods (Single‐linkage, UPGMA, Complete‐linkage, SPICKER and k‐Means clustering) were also used. The groups of similar binding sites (proteins) or clusters generated by the best performing method were further analyzed in terms of local sequence identity, local structural similarity and conservation of analogous contacts with the FAD ligands. Each of the clusters was characterized by a unique set of structural features or patterns, demonstrating that the groups generated truly reflect the structural diversity of FAD binding sites. Proteins 2016; 84:1728–1747. © 2016 Wiley Periodicals, Inc. 相似文献
932.
933.
934.
935.
936.
937.
Marcos Vinicius Meiado Mariana Rojas‐Aréchiga José Alves de Siqueira‐Filho Inara Roberta Leal 《Plant Species Biology》2016,31(2):87-97
Environmental factors are used by plants as spatio‐temporal indicators of favorable conditions for seed germination. Thus, the objective of this study was to determine the effect of light and temperature on seed germination of 30 taxa of Cactaceae occurring in northeastern Brazil and to evaluate whether fluctuations in temperature are capable of altering light sensitivity. The seeds were tested for germination under two light conditions (12 h photoperiod and continuous darkness) and 10 temperature treatments: eight constant temperatures (10, 15, 20, 25, 30, 35, 40 and 45°C) and two alternating temperatures (30/20°C and 35/25°C). The species studied showed two photoblastic responses. All cacti from the Cactoideae subfamily (22 taxa) were classified as positive photoblastic (i.e., no germination in darkness), regardless of the temperature treatment used. Likewise, temperature fluctuation did not alter the seed sensitivity to light. On the other hand, the species of the Opuntioideae (five taxa) and Pereskioideae (three taxa) subfamilies are indifferent to light (i.e., germinated both in the presence and absence of light). The cacti from the areas of Caatinga and Cerrado showed an optimal germination temperature of 30°C, while the species from Atlantic Forest and Restinga areas showed an optimal germination temperature of 25°C. 相似文献
938.
Here we aimed to investigate the association between poor quality of sleep, sleep debt during weekdays and the performance on an interval timing task, using the method of production of time and consisting on five sessions a day for nine days. The sleep of our volunteers was particularly restricted on weekdays. Moreover, later chronotype was associated with the need for compensation on weekends. Regarding the production of time, produced durations were consistently over-produced and there was an evident increase in the mean coefficient of variation (CV) from the wake-up morning to afternoon sessions, followed by a sharp decrease in the evening sessions. Importantly, CV was mainly determined by the interaction between MSFdiff, sleep duration on weekdays and age. In conclusion, our results indicate that when university students are under the effects of social jet lag and reduced sleep duration during weekdays, their performance in interval timing tasks may be compromised. 相似文献
939.
José Angel Herrera‐Vásquez Deibis Ortega Ana Belkis Romero Salvatore Davino Luis Carlos Mejía Stefano Panno Mario Davino 《Journal of Phytopathology》2016,164(2):102-113
The key regions in Panama involved in open field‐ and greenhouse‐grown commercial tomato production, including the Chiriquí, Veraguas, Herrera, Los Santos, Coclé and Panama Oeste provinces, were surveyed for the incidence and distribution of begomoviruses in the growing seasons of 2011 and 2012. The surveys took place in 14 of the 51 districts of the above‐mentioned provinces and comprised all relevant tomato production areas of the provinces. A total of 28 tomato plots were surveyed. The exact location of each plot was geo‐referenced using a hand‐held Global Positioning System unit. In total, 319 individual tomato plants (181 in 2011 and 138 in 2012) were sampled. Plants displayed diverse combinations of virus‐like symptoms of different severity, including necrosis, yellowing, mosaic, mottling, rolling, curling, distortion and puckering of leaves, reduced leaf size, and stunted growth. DNA was extracted from each plant for a subsequent polymerase chain reaction (PCR) analysis, using two sets of degenerate primers able to detect members of the genus Begomovirus. The samples displaying a positive reaction were subsequently analysed with specific primer pairs to identify the affecting begomoviruses. A total of 42.3% of all collected samples showed a positive signal to PCRs. Three begomovirus species were detected with the species‐specific set of primers; in particular, in the samples obtained in 2011, Potato yellow mosaic Panama virus (PYMPV), Tomato leaf curl Sinaloa virus (ToLCSiV) and Tomato yellow mottle virus (TYMoV) were detected, while in the 2012 samples, only PYMPV and ToLCSiV were found. To our knowledge, this is the first reported incidence of ToLCSiV and TYMoV in Panamanian tomato crops. 相似文献
940.
Leonor Mendoza-Vargas Pilar Ortega Beatriz Fuentes-Pardo José A. Viccon-Pale 《Biological Rhythm Research》2016,47(1):93-101
Crayfish Procambarus acanthophorus is a burrower that spends long periods building deep tunnels to reach the water table during the dry season; thus, its survival entertains a close ecological relationship with the sediment. The aim of this work was to determine whether the properties of the circadian rhythm of locomotor activity could be modified by the sediment availability. Experiments were conducted in both aquaria filled with sediment or filled with water, under cycles of Bright and Dim Illumination (BI:DI, 12:12 h) or under continuous DI:DI. The rhythm of locomotor activity was entrained with the photoperiod in aquaria with sediment or water; however, statistical differences between conditions were obtained comparing the period and the level of activity under free-running. These data suggest that the substrate’s sensorial perception could be encoded as a significant ecological parameter that exerts influence in the physiological mechanisms that control the temporal order in P. acanthophorus. 相似文献