全文获取类型
收费全文 | 1338篇 |
免费 | 107篇 |
国内免费 | 184篇 |
出版年
2023年 | 37篇 |
2022年 | 42篇 |
2021年 | 37篇 |
2020年 | 41篇 |
2019年 | 54篇 |
2018年 | 42篇 |
2017年 | 34篇 |
2016年 | 43篇 |
2015年 | 34篇 |
2014年 | 67篇 |
2013年 | 103篇 |
2012年 | 45篇 |
2011年 | 73篇 |
2010年 | 56篇 |
2009年 | 68篇 |
2008年 | 70篇 |
2007年 | 78篇 |
2006年 | 81篇 |
2005年 | 68篇 |
2004年 | 50篇 |
2003年 | 45篇 |
2002年 | 41篇 |
2001年 | 21篇 |
2000年 | 25篇 |
1999年 | 24篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 13篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 30篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1977年 | 4篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有1629条查询结果,搜索用时 203 毫秒
991.
The Oriental fruit moth, Cydia molesta (Busck, 1916) (Lepidoptera: Tortricidae), is a key pest of fruit and is widely distributed around the world. There are important connections between its behavior and biology and its management in agriculture, but few studies have investigated the associations between adult behaviors and oviposition. In this study, adult emergence, mating, and reproduction were investigated under laboratory and field conditions. The ratio of females to males at eclosion was approximately 1:1. When one virgin female had access to one virgin male, 66% and 34% of the couples copulated just once and twice, respectively; and the infertility rate of eggs (21.39 ± 1.25%) did not vary daily. Males, given access to one new female daily, could copulate multiple times, whereas females seldom mated more than once, indicating a male-biased operational sex ratio, but mating status of the male parent had no effect on progeny egg reproduction. Also, the number of eggs that hatched by all female partners of a male was inversely proportional to copulation duration for the female laying the eggs for total female reproductive success; and the number of eggs laid by all female partners of a male was proportional to their number of matings for total male reproductive success. However, the total number of eggs that hatched did not significantly differ for eggs laid by a female given new virgin males daily for mating (17.75 ± 4.28) versus eggs laid by virgin females (19.17 ± 7.51) presented daily with a male that re-mated daily with the series of females. Therefore, our results showed that females engaged in mate choice and males engaged in mate competition, affecting egg production, a factor that may be used to enhance mating disruption technology against Cydia molesta. 相似文献
992.
Annabel Tremlett 《Ethnic and racial studies》2013,36(11):1706-1725
AbstractGypsy, Roma or traveller minorities remain a group that is still homogenized as the ‘other’1. The European imagination continues to be entrenched in the spectacle of their difference – images of weddings, musicians, funerals and fights are fascinating and are thus prioritized. But what would happen if the cameras were given to these people themselves? What if they became the image-makers? This article examines how ethnic studies might contribute to breaking the mould of the exoticized Gypsy through self-representations. The study here formed part of an ethnographic project among primary school pupils in Hungary. Using the photo elicitation method, children were given disposable cameras producing 451 photographs that then formed the basis of interviews. The results reveal very few indicators that could be described as significantly or distinctively divided into ‘Gypsy’ or ‘non-Gypsy’ identifications, questioning the status of difference in discourses around such minorities. 相似文献
993.
Endothelial NO, which is synthesized by endothelial nitric oxide synthase (eNOS), has been reported to be related with the occurrence of pre-eclampsia (PE). However, the polymorphisms of eNOS (− 786 T > C, 4b/a and G894T), the level of nitric oxide and the risk of PE remain unclear. Thus we performed this meta-analysis to determine the associations between them in order to predict the risk for PE and interference with PE development in the early period of antenatal care. All studies investigating the associations between PE risk and polymorphisms of eNOS, or PE risk and serum concentration of NO were reviewed. Finally, 29 studies were included, involving 11 for − 786 T > C, 11for 4b/a, and 22 for G894T polymorphisms and PE risk. In the overall analysis, − 786 T > C polymorphism was found to be related with increased PE risk in the dominant model (OR = 1.17, 95% CI = 1.02-1.35). a allele for 4b/a suffers the high risk of PE (OR = 1.46, 95% CI = 1.01–2.10). In the subgroup analysis, significantly increased risk was detected among Europeans for − 786 T > C polymorphism (OR = 1.40, 95%CI = 1.14–1.73).However, no significant association was detected for G894T polymorphism in the overall and subgroup analysis. The comprehensive evaluation of 9 available studies indicated that serum NO level was significantly decreased in case group (SMD = − 0.96 umol/mL, 95%CI = − 1.80, − 0.12 umol/mL).Hence, we concluded that eNOS gene − 786 T > C and 4b/a except for G894T polymorphisms were contributed significantly to PE risk, especially for Europeans, and a low NO concentration in serum increased the risk for PE. 相似文献
994.
在文献分析、开放式问卷调查和专家访谈的基础上编制幼犬(Canis lupus familiaris)个性量表,对德国牧羊犬、拉布拉多犬和英国史宾格犬3个品种的60日龄幼犬进行标准化行为测验,运用探索性因素分析得出,幼犬存在游戏性、社会性和好奇/无畏3个个性特质.分析品种间个性特征差异时发现,拉布拉多犬游戏性特质显著高于德国牧羊犬和史宾格犬(P<0.01),德国牧羊犬社会性特质显著高于拉布拉多犬和史宾格犬(P<0.01),拉布拉多犬好奇/无畏特质显著高于德国牧羊犬和史宾格犬(P<0.01).结果表明,编制的幼犬个性量表具有较高的信度和效度,可用于描述和比较幼犬个体差异.不同品种幼犬个性特征存在差异. 相似文献
995.
Milan Oldřich Urban Miroslav KlímaPavel Vítámvás Jakub VašekAlois Albert Hilgert-Delgado Vratislav Kučera 《Journal of plant physiology》2013
Five winter oilseed rape cultivars (Benefit, Californium, Cortes, Ladoga, Navajo) were subjected to 30 days of cold treatment (4 °C) to examine the effect of cold on acquired frost tolerance (FT), dehydrin (DHN) content, and photosynthesis-related parameters. The main aim of this study was to determine whether there are relationships between FT (expressed as LT50 values) and the other parameters measured in the cultivars. While the cultivar Benefit accumulated two types of DHNs (D45 and D35), the other cultivars accumulated three additional DHNs (D97, D47, and D37). The similar-sized DHNs (D45 and D47) were the most abundant; the others exhibited significantly lower accumulations. The highest correlations were detected between LT50 and DHN accumulation (r = −0.815), intrinsic water use efficiency (WUEi; r = −0.643), net photosynthetic rate (r = −0.628), stomatal conductance (r = 0.511), and intracellular/intercellular CO2 concentration (r = 0.505). Those cultivars that exhibited higher Pn rate in cold (and further a significant increase in WUEi) had higher levels of DHNs and also higher FT. No significant correlation was observed between LT50 and E, PRI, or NDVI. Overall, we have shown the selected physiological parameters to be able to distinguish different FT cultivars of winter oilseed rape. 相似文献
996.
Gender differences in susceptibility to chronic mild stress (CMS) and effects of venlafaxine in rats have been investigated in the current study. Male and female SD rats were exposed to CMS or CMS plus chronic venlafaxine administration (10 mg/kg, 21 days) in order to study depressive behavior in rats. Rats were tested in open field test and sucrose preference test to figure out gender differences in behavior. Then serum corticosterone and the expression of FKBP5 in hippocampus of rats were detected to explore the possible mechanism. The results showed that the CMS impact on behavioral parameters and corticosterone levels and response to venlafaxine were gender dependent. Female rats appeared more vulnerable in the dysregulation of HPA axis to CMS. Venlafaxine treatment normalized depressive-like behavior in both gender. However, venlafaxine treated male rats exhibited better improved explore behavior and anhedonia. FKBP5 might be involved in the explanation of gender differences in CMS and venlafaxine treatment. Male and female rats respond differently to chronic stress and venlafaxine continuous treatment. This results have guiding meaning in design of trials related to stress induced depression. 相似文献
997.
Identifying robust environmental predictors of infection probability is central to forecasting and mitigating the ongoing impacts of climate change on vector‐borne disease threats. We applied phylogenetic hierarchical models to a data set of 2,171 Western Palearctic individual birds from 47 species to determine how climate and landscape variation influence infection probability for three genera of haemosporidian blood parasites (Haemoproteus, Leucocytozoon, and Plasmodium). Our comparative models found compelling evidence that birds in areas with higher vegetation density (captured by the normalized difference vegetation index [NDVI]) had higher likelihoods of carrying parasite infection. Magnitudes of this relationship were remarkably similar across parasite genera considering that these parasites use different arthropod vectors and are widely presumed to be epidemiologically distinct. However, we also uncovered key differences among genera that highlighted complexities in their climate responses. In particular, prevalences of Haemoproteus and Plasmodium showed strong but contrasting relationships with winter temperatures, supporting mounting evidence that winter warming is a key environmental filter impacting the dynamics of host‐parasite interactions. Parasite phylogenetic community diversities demonstrated a clear but contrasting latitudinal gradient, with Haemoproteus diversity increasing towards the equator and Leucocytozoon diversity increasing towards the poles. Haemoproteus diversity also increased in regions with higher vegetation density, supporting our evidence that summer vegetation density is important for structuring the distributions of these parasites. Ongoing variation in winter temperatures and vegetation characteristics will probably have far‐reaching consequences for the transmission and spread of vector‐borne diseases. 相似文献
998.
为了更深入地了解青头潜鸭的越冬行为模式及性别差异,以期为后续青头潜鸭的保护管理提供科学的理论参考,2018年11-12月采用定点观察法、扫描取样法等方法,对河南民权国家湿地公园越冬期青头潜鸭的越冬行为模式及性别差异进行了观察分析。观察期间共记录到青头潜鸭158只,超过全球种群数量1000只的10%。分析结果表明:(1)民权湿地公园,青头潜鸭越冬期行为时间分配以静息、觅食和运动三类行为为主,其次是修整和飞行两类行为;运动行为与觅食、修整、社会等行为之间呈极显著正相关,修整行为与社会行为之间呈极显著正相关,静息行为与修整、运动、社会等行为之间呈极显著负相关,飞行行为与觅食、静息、修整等行为之间呈极显著负相关;(2)静息行为具有全时段高时间分配的特征,不存在峰期和谷期;觅食行为(峰期为10:30-11:30、13:30-14:30,谷期为11:30-12:30、14:30-15:30)和飞行行为(峰期为11:30-12:30、14:30-15:30,谷期为10:30-11:30、13:30-14:30、15:30-16:30)具有明显的错峰式节律;(3)不同性别青头潜鸭越冬行为时间分配存有差异,其中静息、觅食、运动是雄性青头潜鸭主要行为类别(超过70%),雌性青头潜鸭的主要行为为运动、飞行、觅食(接近70%);雌雄青头潜鸭在静息、修整、运动和飞行四类行为时间分配方面存在显著性差异,雄性的静息、修整行为的时间分配极显著高于雌性,而运动、飞行行为的时间分配极显著低于雌性;(4)不同性别青头潜鸭越冬行为活动节律方面,除飞行行为外,其余行为均在行为峰期与谷期节律方面存有差异。进一步分析表明:民权湿地公园青头潜鸭越冬行为模式符合行为投资与收益的能量学理论,越冬行为模式在行为时间分配和行为节律方面存在性别差异。 相似文献
999.
ALAN DE QUEIROZ ROBIN LAWSON 《Biological journal of the Linnean Society. Linnean Society of London》2008,95(2):409-424
The recent shift toward dispersal rather than vicariant explanations of disjunct distributions has been driven by the use of molecular data to estimate divergence dates between lineages. However, other kinds of evidence can also be critical in evaluating such biogeographic hypotheses. In the present study, we used a multifaceted approach employing diverse analyses of mitochondrial DNA sequences to assess explanations for the disjunct distribution of the gartersnake Thamnophis validus. The occurrence of this species in the Cape Region of the Baja California peninsula, isolated from mainland populations that occur along the west coast of Mexico, might be explained by: (1) separation of the peninsula from mainland Mexico through rifting 4–8 Mya (tectonic vicariance); (2) fragmentation of the range of this semi‐aquatic species because of post‐Pleistocene aridification (vicariance by aridification); (3) natural overwater dispersal across the Gulf of California; or (4) human introduction. Divergence dating indicates that peninsular and mainland T. validus separated from each other within the last 0.5 Myr, thus rejecting tectonic vicariance. In addition, the estimated closest mainland relatives of peninsular snakes are found farther north than expected under this hypothesis. Three findings argue against vicariance by aridification: (1) peninsular snakes and their closest mainland relatives are more genetically similar than predicted; (2) the location of closest mainland relatives is farther south than predicted; and (3) the species is absent from areas where one might expect to find relict populations. Taken together, refutation of the vicariance hypotheses and the fact that the estimated closest mainland relatives are found almost directly across the Gulf from the Cape Region supports some form of overwater colonization. Various additional arguments suggest that natural dispersal is more likely than human introduction. The present study emphasizes the need for multiple kinds of evidence, beyond divergence dates, to discriminate among hypotheses and to provide independent sources of corroboration or refutation in historical biogeography. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 409–424. 相似文献
1000.