全文获取类型
收费全文 | 1721篇 |
免费 | 408篇 |
国内免费 | 611篇 |
出版年
2024年 | 32篇 |
2023年 | 121篇 |
2022年 | 117篇 |
2021年 | 126篇 |
2020年 | 105篇 |
2019年 | 128篇 |
2018年 | 98篇 |
2017年 | 100篇 |
2016年 | 103篇 |
2015年 | 93篇 |
2014年 | 132篇 |
2013年 | 136篇 |
2012年 | 97篇 |
2011年 | 118篇 |
2010年 | 107篇 |
2009年 | 119篇 |
2008年 | 114篇 |
2007年 | 102篇 |
2006年 | 95篇 |
2005年 | 79篇 |
2004年 | 72篇 |
2003年 | 64篇 |
2002年 | 61篇 |
2001年 | 45篇 |
2000年 | 43篇 |
1999年 | 39篇 |
1998年 | 23篇 |
1997年 | 25篇 |
1996年 | 23篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 24篇 |
1992年 | 9篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有2740条查询结果,搜索用时 375 毫秒
151.
In human females cyclic shifts in preference have been documented for odour and physical and behavioral male traits. Women prefer the smell of dominant males, more masculine male faces and men behaving more dominantly when at peak fertility than at other times in their menstrual cycle. Here we examine variation in preferences for body sexual dimorphism. Across two studies, both between- and within-participant, we show that women prefer greater masculinity in male bodies at times when their fertility is likely highest, in the follicular phase of their cycle. Shifts were seen when rating for a short-term but not when rating for a long-term relationship. In line with studies showing similar effects for facial sexual dimorphism, we also show that women prefer greater masculinity when they think themselves attractive than when they think themselves less attractive. These results indicate that women's preferences for sexual dimorphism in male bodies follow a similar pattern as found for sexual dimorphism and dominance in other domains and such differences in preference may serve a similar function. Cyclic preferences could influence women to select partners when most likely to become pregnant that possess traits that may be most likely to maximize their offspring's quality via attraction to masculinity or serve to help acquire investment via attraction to femininity. 相似文献
152.
人类活动对广西合浦海草床服务功能价值的影响 总被引:3,自引:0,他引:3
近年来,中国海草生态系统受到严重破坏。本文以广西合浦海草床生态系统为例,采用1980—2005年当地统计资料,综合运用生态经济学的基本理论,以海草床的食物生产、调节大气、生态系统营养循环、净化水质、维持生物多样性和科学研究功能作为指标体系,对人类活动造成合浦海草床生态系统的价值损失进行了初步估算。结果表明,从1980—2005年,合浦海草床由于人类活动造成的价值损失为34657.95万元,损失率为71.97%。直接利用价值增加了4452.88万元,而间接利用价值损失为39110.83万元,损失率高达81.82%。说明人类对合浦海草床的开发利用强度增大趋势明显。 相似文献
153.
Developments in insect transgenesis using transposons combined with available mass rearing technology for insects such as
the Medfly, Ceratitis capitata, provide opportunity for the production of protein for industrial, agricultural and healthcare purposes on a very large scale.
In this study, we report the germ-line transformation and expression of a cDNA encoding human growth hormone (hGH) in transgenic
Drosophila using the Minos transposon. Production and secretion of a bioactive hGH into the haemolymph of transgenic larvae was demonstrated by immunoblot
analysis, ELISA and a proliferation bioassay. Stable expression of hGH was observed over 50 generations. The results indicate
that mass reared transgenic diptera with a rapid period of larval growth could provide cost effective production systems for
the manufacture of therapeutic and other high value proteins. 相似文献
154.
Talita Lopes Honorato Maria Cristiane Rabelo Luciana Rocha Barros Gonçalves Gustavo Adolfo Saavedra Pinto Sueli Rodrigues 《World journal of microbiology & biotechnology》2007,23(10):1409-1415
The use of agriculture substrates in industrial biotechnological processes has been increasing because of its low cost. Cashew
apples are considered an agriculture low cost product in the Brazilian Northeast because the cashew cultivation is done mainly
to produce cashew nuts. About 90% of the cashew apples production is lost in the field after removing the nut. In this work,
the use of clarified cashew apple juice as substrate for microbial cultivation was investigated. The results showed that cashew
apple juice is a good source of reducing sugars and can be used to grow Leuconostoc mesenteroides to produce high added value products such as dextran, lactic acid, mannitol and oligosaccharides. 相似文献
155.
苦瓜的营养价值、化学成分以及药理作用研究进展 总被引:1,自引:0,他引:1
本文总结了半个多世纪来国内外学者对苦瓜的研究,为苦瓜进一步开发提供了借鉴。 相似文献
156.
《Current biology : CB》2022,32(24):5364-5373.e4
157.
Edward K. Mengich Daniel K. Too Joseph M. Macharia Ralph Mitloehner 《African Journal of Ecology》2015,53(1):3-15
This study assessed the composition and natural distribution of indigenous trees and shrubs as possible criteria for selecting suitable species for rehabilitation of degraded sites in semi‐arid rangelands. Study sites were identified at Nthangu, Kathonzweni and Kibwezi forests of Makueni County, Kenya using existing vegetation, agro‐climatic maps and Landsat imageries. The sites had mean annual rainfalls of 974 mm, 700 mm and 616 mm, respectively, and moisture indices of 49%, 35% and 32%. Data were collected by establishing sample plots and assessing species counts and diameters at breast height (DBH). Basal area, relative dominance, relative abundance, relative frequency and important value indices (IVIs) were computed for individual families and species at each site. The number of families, genera and species declined from Nthangu (33, 60, 77) through Kibwezi (30, 48, 70) to Kathonzweni (28, 42, 69). Corresponding mean basal areas were 16.7 m2 ha?1, 76.8 m2 ha?1 and 19.3 m2 ha?1. The families Combretaceae, Burseraceae and Mimosaceae were the most important and widely distributed. Based on ecological importance values, candidate species for rehabilitation of degraded sites at Nthangu, Kathonzweni and Kibwezi were Combretum molle and Acacia hockii; Combretum collinum, Commiphora campestris and Acacia tortilis; and Commiphora africana and A. tortilis, respectively. 相似文献
158.
本研究在不同p H和温度条件下以离体方式对野生棘胸蛙(Quasipaa spinosa)不同消化器官的蛋白酶活力进行了分析。结果表明,食道、胃、胰的蛋白酶活力受到酶体系p H的显著影响(P0.05),且随p H升高呈现典型的单峰型活力曲线。食道和胃的蛋白酶活力在p H为1.5时达到峰值,胰的酶活力在p H为9.6时达到峰值,而肠道酶活力在p H为7.4时达到峰值。各消化器官蛋白酶活力具有明显的温度依赖性(P0.05),酶活力随温度升高也均呈典型的单峰型活力曲线,不同消化器官的最大酶活力温度分别为,食道50℃、胃50℃、胰45℃、前肠45℃、后肠45℃、直肠45℃。在最大酶活力的p H和30℃条件下,各消化器官蛋白酶活力由高到低依次为胰、食道、胃、直肠、前肠、后肠。由此可见,蛋白酶在棘胸蛙消化系统的分布具有明确的规律性,且不同来源的蛋白酶需要在特定p H和温度下才能表现出最大的反应活性。 相似文献
159.
160.
Ergul Belge Kurutas Yakup Gumusalan Ali Cetinkaya Ekrem Dogan 《Biological procedures online》2015,17(1)