全文获取类型
收费全文 | 544篇 |
免费 | 14篇 |
国内免费 | 54篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 4篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 25篇 |
2012年 | 31篇 |
2011年 | 23篇 |
2010年 | 31篇 |
2009年 | 35篇 |
2008年 | 32篇 |
2007年 | 19篇 |
2006年 | 21篇 |
2005年 | 22篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 14篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 19篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1959年 | 8篇 |
1958年 | 16篇 |
1957年 | 13篇 |
1956年 | 25篇 |
1955年 | 14篇 |
1954年 | 10篇 |
1953年 | 20篇 |
1952年 | 13篇 |
1951年 | 15篇 |
1950年 | 14篇 |
排序方式: 共有612条查询结果,搜索用时 43 毫秒
151.
泉州湾河口湿地生态系统服务价值的动态评价及驱动力分析 总被引:3,自引:0,他引:3
以泉州湾河口湿地为研究对象,结合服务指标分类和去重复计算,采用市场价值法、替代价值法及机会成本法等,对泉州湾河口湿地1997、2005、2013、2015年的生态系统服务价值进行了动态评价,并采用逐步回归分析法、通径分析方法探讨服务价值变化的主要驱动因子及其作用途径和强度.结果表明: 泉州湾河口湿地的主导服务为调蓄洪水、气候调节及食物供给服务;对泉州湾河口湿地生态系统主导服务价值变化直接影响最大的因子分别为供水量、海水养殖量和地区生产总值,其他驱动因子则通过间接影响作用于服务价值的变化. 相似文献
152.
ZHAO-QIAN TENG LE KANG 《Insect Science》2007,14(3):193-199
This study reports on two parthenogenetic strains of the migratory locust Locusta migratoria. The offspring of thelytokou females had a single fragment per microsatellite loci. All offspring of the parthenogenetic F1 females were genetically identical. These results further confirmed that restitution of the sister products of early cleavage mitoses and cell fusion might be the most likely diploidization mechanisms in the thelytokous locusts. Polymerase chain reaction amplification results demonstrated that thelytoky in the locust was not induced by Wolbachia bacteria. Apart from the low fitness gained in thelytokous females, large populations with migration and losing heterozygosity may be other reasons why regular parthenogenesis has not evolved in the locust. 相似文献
153.
154.
Our understanding of the effects of habitat loss on individual performance is limited due to a lack of experimental studies that take the potential genetic and parental effects producing phenotypic variation into consideration. To assess the relative role of habitat loss on offspring phenotype while controlling for the confounding effects of genetic and parental variation we performed a partial cross‐fostering experiment using the Eurasian Treecreeper Certhia familiaris. The experiment was carried out by swapping half the nestlings in a brood between small and large nesting forest patches to determine the effect of nesting forest patch size on five nestling traits reflecting morphological size, body condition, physiological stress and inflammation status. There was no effect of nesting forest patch size on the offspring traits examined. Instead, we found evidence of genetic and early parental effects on all traits except inflammation status, as well as parental effects after cross‐fostering for all of the measured offspring traits. Our results suggest that genetic and parental effects should be taken into account when making inferences about species’ responses to habitat loss. 相似文献
155.
MATTHEW J. STRUEBIG STEVEN C. LE COMBER STEPHEN J. ROSSITER 《Molecular ecology》2012,21(12):2850-2851
Nazareno & Jump (2012) highlight potential issues with using small sample sizes in population genetic studies. By reanalysing allelic richness data from our recent publication on habitat fragmentation (Struebig et al. 2011), they assert that the observed relationship has been driven by three sites with the lowest number of individuals sampled. While sample size issues have been raised before in the genetic literature, Nazareno & Jump’s (2012) comment serves as a useful reminder to us all. Nevertheless, we disagree that our findings were significantly biased by sampling limitations. Here, we demonstrate by jackknifing that, contrary to the claims of Nazareno & Jump (2012), our correlations of allelic richness and fragment area are not driven solely by sites with low sample sizes. We maintain that small sample sizes can be accounted for in fragmentation studies and that sampling limitations should not detract from undertaking conservation genetic research. 相似文献
156.
本研究探讨猪骨胶原蛋白肽降血脂作用和抑制高脂饮食诱导肝脏抗氧化应激的作用机理。40只小鼠分为5组,分别饲喂6 w正常日粮、高脂日粮、添加1.6%钙的高脂日粮、添加1%胶原蛋白肽的高脂日粮和添加1.6%钙+1%胶原蛋白肽的高脂日粮。研究发现:与正常组相比,高脂日粮小鼠血脂和体重明显升高。1.6%钙处理可抑制体重过度升高,1%胶原蛋白肽和高钙可协同抑制调节血脂,防止体重升高。高脂主要通过影响肝脏生理节律和过氧化物酶体增生物激活受体信号通路引起脂代谢异常,高钙和骨胶原蛋白肽可显著抑制肝脏氧化应激,抑制生理节律紊乱。 相似文献
157.
抗MRP3单链抗体-sTRAIL融合蛋白诱导U251多形性胶质母细胞瘤凋亡 总被引:1,自引:0,他引:1
采用重组PCR技术获得抗多药耐药相关蛋白3(multidrug resistance protein 3, MRP3)的单链抗体(scFv)与人源可溶性肿瘤坏死因子相关凋亡诱导配体(soluble TNF-related apoptosis inducing ligand, sTRAIL)的融合蛋白质的基因编码序列, 利用原核表达载体pMAL-c2,构建含麦芽糖结合蛋白(maltose binding protein, MBP)标签肽的antiMRP3(scFv)-sTRAIL融合蛋白, 经亲和层析柱纯化. 获得纯化的antiMRP3(scFv)-sTRAIL融合蛋白,用MRP3阳性U251多形性胶质母细胞瘤做增殖抑制实验、细胞凋亡诱导实验,结果均显示具有明显的活性, 而MBP无明显作用. 上述结果表明,成功表达了antiMRP3(scFv)-sTRAIL融合蛋白, 该融合蛋白具有诱导U251多形性胶质母细胞瘤细胞凋亡的活性, 为开发靶向性抗肿瘤药物奠定了基础. 相似文献
158.
CHRISTIAN KERBIRIOU FRANÇOISE GOURMELON FREDERIC JIGUET ISABELLE LE VIOL FREDERIC BIORET & ROMAIN JULLIARD 《Ibis》2006,148(2):352-364
As changes in land use have been identified as the main factor explaining the decline in Red-billed Chough Pyrrhocorax pyrrochorax populations across western Europe, a study was carried out in Ouessant (western France) in order to assess the relationship between territory quality and reproductive success. As such an approach could be hindered by the fact that the birds' reproductive performance could be influenced by their breeding experience, we analysed both inter- and intranest-site variation in fledging success. Territory quality was quantified, combining habitat selection, territory size, the amount of feeding area and distance between nest and feeding area. Feeding habitats selected positively by Red-billed Choughs were characterized by a mean sward height of less than 5 cm. Foraging area was on average 21 557 m2 . Feeding areas (i.e. feeding habitat within foraging area) close to the nest were used preferentially. Fledging success appeared to be influenced neither by the total area of feeding sites in a Chough territory, nor by the mean feeding flight distance. However, fledging success adjusted to nest-site and year appeared to be influenced by feeding area close to the nest: one additional fledgling was expected for each additional 10 000 m2 of feeding habitat within 300 m of the nest. These first results allowed us to consider recommending landscape management measures to ensure a favourable conservation status of local Chough populations. 相似文献
159.
RENAUD RIFFLART GEORGES CARREL YANN LE COARER BENEDICTE NGUYEN THE FONTEZ 《Freshwater Biology》2009,54(7):1544-1559
1. The River Durance, the last alpine tributary of the River Rhône, is a large, braided alluvial hydrosystem. Following large-scale regulation, flow downstream of the Serre-Ponçon dam has been maintained at 1/40th of previous annual mean discharge. To assess the effects of historical disturbances, fish assemblages and habitat use were analysed during five summers in a representative reach of the middle Durance.
2. Habitat availability and use were assessed with a multi-scale approach including the variables water depth, current velocity, roughness height of substratum, amount of woody debris and lateral/longitudinal location. Eighteen fish species were sampled by electrofishing in 289 habitat sample units.
3. Partial least square (PLS) regression showed that taxa were mainly distributed according to relationships between their total length and water depth/velocity variables. Fish assemblage composition was also related to roughness height as well as distance from the bank or to the nearest large woody debris. However, PLS regression revealed no significant differences in habitat selection between two periods of varying hydromorphological stability.
4. Fish distribution patterns and density were related to proximity to the bank and cover, indicating that local scale variables need to be considered in conservation and restoration programmes. 相似文献
2. Habitat availability and use were assessed with a multi-scale approach including the variables water depth, current velocity, roughness height of substratum, amount of woody debris and lateral/longitudinal location. Eighteen fish species were sampled by electrofishing in 289 habitat sample units.
3. Partial least square (PLS) regression showed that taxa were mainly distributed according to relationships between their total length and water depth/velocity variables. Fish assemblage composition was also related to roughness height as well as distance from the bank or to the nearest large woody debris. However, PLS regression revealed no significant differences in habitat selection between two periods of varying hydromorphological stability.
4. Fish distribution patterns and density were related to proximity to the bank and cover, indicating that local scale variables need to be considered in conservation and restoration programmes. 相似文献
160.
在扫描电子显微镜下,对豆科土儿属(Ap ios)和旋花豆属(Coch lianthus)7个种植物的花粉进行了观察.结果表明,2个属的花粉均为三孔沟,形状为三角球形或球形.土儿属的花粉可划分为2种类型:肉色土儿(A.carnea)的花粉外壁为典型的网状纹饰,其它种的花粉外壁较光滑,具颗粒状或短条纹状纹饰,研究结果不支持土儿属下亚属的划分;肉色土儿花粉外壁的网状纹饰式样可能反映了其在土儿属中处在较进化的位置.土儿属东亚分布种的花粉类型较为多样,原始和进化2种类型并存,表明东亚可能是土儿属的起源地和演化中心.旋花豆属的花粉特征和肉色土儿相似,说明两者之间的亲缘关系可能较近. 相似文献