全文获取类型
收费全文 | 15442篇 |
免费 | 1176篇 |
国内免费 | 2篇 |
出版年
2023年 | 156篇 |
2022年 | 251篇 |
2021年 | 451篇 |
2020年 | 280篇 |
2019年 | 386篇 |
2018年 | 439篇 |
2017年 | 409篇 |
2016年 | 577篇 |
2015年 | 846篇 |
2014年 | 891篇 |
2013年 | 1156篇 |
2012年 | 1275篇 |
2011年 | 1273篇 |
2010年 | 783篇 |
2009年 | 729篇 |
2008年 | 907篇 |
2007年 | 820篇 |
2006年 | 756篇 |
2005年 | 701篇 |
2004年 | 641篇 |
2003年 | 578篇 |
2002年 | 539篇 |
2001年 | 167篇 |
2000年 | 108篇 |
1999年 | 133篇 |
1998年 | 139篇 |
1997年 | 127篇 |
1996年 | 100篇 |
1995年 | 84篇 |
1994年 | 61篇 |
1993年 | 76篇 |
1992年 | 66篇 |
1991年 | 49篇 |
1990年 | 48篇 |
1989年 | 40篇 |
1988年 | 45篇 |
1987年 | 40篇 |
1986年 | 20篇 |
1985年 | 37篇 |
1984年 | 47篇 |
1983年 | 41篇 |
1982年 | 35篇 |
1981年 | 40篇 |
1980年 | 28篇 |
1979年 | 15篇 |
1978年 | 21篇 |
1977年 | 35篇 |
1976年 | 24篇 |
1975年 | 21篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Laura Miralles Santiago Lens Antonio Rodríguez-Folgar Manuel Carrillo Vidal Martín Bjarni Mikkelsen Eva Garcia-Vazquez 《PloS one》2013,8(8)
Visual species identification of cetacean strandings is difficult, especially when dead specimens are degraded and/or species are morphologically similar. The two recognised pilot whale species (Globicephala melas and Globicephala macrorhynchus) are sympatric in the North Atlantic Ocean. These species are very similar in external appearance and their morphometric characteristics partially overlap; thus visual identification is not always reliable. Genetic species identification ensures correct identification of specimens. Here we have employed one mitochondrial (D-Loop region) and eight nuclear loci (microsatellites) as genetic markers to identify six stranded pilot whales found in Galicia (Northwest Spain), one of them of ambiguous phenotype. DNA analyses yielded positive amplification of all loci and enabled species identification. Nuclear microsatellite DNA genotypes revealed mixed ancestry for one individual, identified as a post-F1 interspecific hybrid employing two different Bayesian methods. From the mitochondrial sequence the maternal species was Globicephala melas. This is the first hybrid documented between Globicephala melas and G. macrorhynchus, and the first post-F1 hybrid genetically identified between cetaceans, revealing interspecific genetic introgression in marine mammals. We propose to add nuclear loci to genetic databases for cetacean species identification in order to detect hybrid individuals. 相似文献
32.
Eva Decru Nathan Vranken Pedro H. N. Bragança Jos Snoeks Maarten Van Steenberge 《Journal of fish biology》2020,96(5):1186-1201
Based on literature, museum collections and three recent expeditions, an annotated species list of the Lake Edward, East Africa, drainage system is presented, excluding the endemic haplochromines. A total of 34 non-Haplochromis species belonging to 10 families and 21 genera are recorded from the system. Three of these are endemic and two others have been introduced in the region. Six species are new records for the Lake Edward system. A species accumulation curve indicates that we probably covered most of the non-Haplochromis species in the area sampled during the recent expeditions, but undetected species might still be present in the Congolese part of the system, which is poorly sampled. A comparison of the species list with those of neighbouring basins confirmed the placement of the Lake Edward system within the east-coast ichthyofaunal province. 相似文献
33.
34.
35.
The pelagic larval duration ( D PL ) for 10 temperate cryptobenthic species belonging to three families: Gobiidae, Gobiesocidae and Blenniidae was investigated. Overall, the Gobiesocidae presented short D PL s varying between 11 and 18 days, the Gobiidae's D PL ranged between 14 and 39 days, and Parablennius pilicornis (Blenniidae) had an average of 33 days (range 31–37 days). Two subtypes of settlement marks were found among individuals of the same species. 相似文献
36.
Manuel M. Dayrit Ofelia T. Monzon Virginia Basaca-Sevilla Curtis G. Hayes 《The Western journal of medicine》1987,147(6):723
A total of 50 carriers of the human immunodeficiency virus (HIV), 46 of them female prostitutes, have been detected through seroprevalence surveys by the Department of Health, Manila. Infection rates are highest in two small cities near foreign military bases and in the tourist district of MetroManila. Nine patients with the acquired immunodeficiency syndrome (AIDS) who contracted the disease outside the country have been reported, with opportunistic infections being the major clinical feature. Public information measures heavily utilize the mass media, and there is anecdotal evidence that awareness of the disease among the urban population is increasing. The National AIDS Committee foresees that a large proportion of the cases seen in the Philippines over the next few years will be returning nationals who were infected abroad. 相似文献
37.
Published data on, and hypotheses regarding the effect of NO− 3 on functioning of legume root nodules are reviewed. It is concluded that a short-term reversible effect of NO− 3 may act via an increased resistance to O2 diffusion in nodules; this is coupled to decreased bacteroid respiration. For longer exposures to NO− 3 nodule activity is irreversibly lost, but how this relates to carbohydrate deprivation or NO-2 accumulation is unclear. Complicating factors include denitrification reactions and the interaction of NO− 2 with leghaemoglobin. 相似文献
38.
Pedro Acevedo-Rodríguez 《Brittonia》1987,39(3):348-352
Two new Brazilian species,Serjania fluminensis andS. unidentata, are described, illustrated, and discussed. 相似文献
39.
40.
Ciliary ganglion neurons and nonneurons can be separated from each other, based on the greater adhesivity of the nonneurons to untreated tissue culture plastic in the presence of serum. When the separation was carried out in the presence of Serum Plus (a commercially available supplemented serum), two populations of neurons were distinguished. Neurons in the first class (50–60% of total) adhered to plastic within 15 min, tended to aggregate into clumps, and were not well supported in long term culture by brain extracts. Neuronal adhesion to plastic was inhibited by heparin but not by chondroitin sulfate. Neurons in the second class did not attach to plastic for up to 90 min (and could thus be purified), were not as prone to aggregation, and were quantitatively supported for long periods (>2 weeks) by the neurotrophic factor(s) present in extracts of injured brain. Although no direct evidence is provided, these populations may correspond to the well characterized ciliary and choroid neurons.Special Issue dedicated to Dr. E. M. Shooter and Dr. S. Varon. 相似文献