全文获取类型
收费全文 | 1221篇 |
免费 | 47篇 |
国内免费 | 83篇 |
专业分类
1351篇 |
出版年
2023年 | 7篇 |
2021年 | 3篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 13篇 |
2016年 | 23篇 |
2015年 | 19篇 |
2014年 | 36篇 |
2013年 | 90篇 |
2012年 | 27篇 |
2011年 | 25篇 |
2010年 | 28篇 |
2009年 | 63篇 |
2008年 | 66篇 |
2007年 | 48篇 |
2006年 | 57篇 |
2005年 | 42篇 |
2004年 | 68篇 |
2003年 | 56篇 |
2002年 | 42篇 |
2001年 | 40篇 |
2000年 | 40篇 |
1999年 | 27篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 29篇 |
1991年 | 29篇 |
1990年 | 31篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 23篇 |
1984年 | 29篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1971年 | 3篇 |
排序方式: 共有1351条查询结果,搜索用时 0 毫秒
81.
B.S.C. Leadbeater 《欧洲藻类学杂志》2013,48(1):57-69
A preliminary study of the fine structure of various stages in the life cycle of von Stosch's solate of ‘Syracosphaera carterae’ has been made by means of sections and whole mounts. Protoplast structure appears to be similar throughout the cycle. However, the Apistonema thallus possesses a cell wall composed of numerous layers of closely adpressed rimless unmineralised scales. Two types of asexual swarmers are shown to be covered with one or two layers of somewhat similar scales. One type of swarmer possesses a short haptonema which is covered with small scales. In addition the coccolith-bearing stages are shown to be identical with Hymenomonas carterae sensu Manton and Peterfi (1969) and this isolate has therefore been transferred to H. carterae. 相似文献
82.
The conspicuous macroscopic stage of the freshwater red alga Thorea ramosissima has been re-discovered in the River Thames after a lapse of almost 140 years. In the 1840s it was reported only from Walton-on-Thames, but is now known from 13 localities along a 133 km stretch between Oxford and Teddington. It is transient, often remaining undetected at known localities in subsequent years. All British records are assessed, especially 19th century collections from the Thames. The ecology and the morphology of the macroscopic stage are discussed. 相似文献
83.
84.
85.
From time to time, small, fragile, previously unknown fossil invertebrates are found in specialized habitats. Occasionally, as in the present case, a fragment of the original habitat that existed millions of years ago is also preserved. The present article describes a previously unknown microinvertebrate in Dominican amber that cannot be placed in any group of extant invertebrates. Placed in a new family, genus, and species, the fossil shares characters with both tardigrades and mites, but clearly belongs to neither group. The several hundred fossil individuals preserved in the amber shared their moist, warm habitat with pseudoscorpions, nematodes, fungi, and protozoa. The large number of fossils provided additional evidence of their biology, including their reproductive behavior, developmental stages, and food. While there is no extant group that can accommodate these fossils, and we have no knowledge of any extant descendants, this discovery shows that unique lineages of minute invertebrates were surviving in the mid‐Tertiary. 相似文献
86.
牛肝菌类一新种——蔚青华牛肝菌 总被引:1,自引:0,他引:1
蔚青华牛肝菌,其盖表有绒毛,柄等粗而细长,具棱纹无网纹,担孢子长短兼存,6–16μm兼之。本种庆祝著名真菌学家蔚青王云章教授,欣逢公百年华诞,其对西南菌学研究和人才培养,屡蒙厚贶,感不胜言,谨以此名,敬寄慕念。 相似文献
87.
Li WJ Jiang Y Kroppenstedt RM Xu LH Jiang CL 《Systematic and applied microbiology》2004,27(3):308-312
A novel actinomycete strain, designated YIM 30243T, was isolated from a soil sample in Yunnan Province, China. Based on the results of phenotypic and genotypic characteristics, strain YIM 30243T should be assigned to a new species of the genus Nocardia, for which the name Nocardia alba sp. nov. is proposed. The type strain is YIM 30243T (= CCTCC AA001030T = DSM 44684T). 相似文献
88.
We investigated the taxonomic significance of nest shape and its putative role in speciation in Trigona (Heterotrigona) carbonaria and T. (H.) hockingsi, two sibling species of stingless bee species from eastern Australia. These species are primarily distinguished by their nest architecture, as in all other respects they are nearly identical. We genotyped 130 colonies from six locations in Queensland at 13 microsatellite loci together with 106 additional colonies from six other Indo-Pacific Trigona species. Whether they were present in allopatry or in sympatry, colonies that displayed the T. carbonaria or the T. hockingsi nest architecture could be unambiguously differentiated at the genetic level. However, T. hockingsi colonies were classifiable into two highly differentiated paraphyletic and geographically separate populations, one in northern and one in southern Queensland. These two populations probably belong to two distinct species, T. hockingsi and T. davenporti nov. sp. Our results suggest that nest architecture characters are relevant but not sufficient criteria to identify species in this group. Consequently, modifications of nest architecture are probably not of prime importance in the speciation process of Australian stingless bees, although nest architecture differences probably result from relatively simple mechanisms. The rare interspecific hybrid colonies detected did not display a nest with an intermediate form between T. hockingsi and T. carbonaria. 相似文献
89.
Effects of estrogen treatment on glutamate uptake in cultured human astrocytes derived from cortex of Alzheimer's disease patients 总被引:4,自引:0,他引:4
Estrogen is thought to play a protective role against neurodegeneration through a variety of mechanisms including the activation of growth factors, the control of synaptic plasticity, and the reduction of response to various insults, such as iron and glutamate. Increasing evidence indicates an increased level of extracellular glutamate and a down-regulation of glutamate transporters in Alzheimer's disease (AD). In this study, we show that glutamate uptake in astrocytes derived from Alzheimer's patients is significantly lower than that from non-demented controls. Estrogen treatment increases glutamate uptake in a dose-dependent pattern. Two glutamate transporters, GLT-1 and GLAST, are expressed in the astrocytes. Up-regulation of the glutamate transporters is induced by estrogen treatment in AD astrocytes only. Our data suggest that the action of estrogen on glutamate uptake by astrocytes might contribute to its potential neuroprotective role in AD. 相似文献
90.
Aurélien HuguetAndré Nel Xavier Martinez-DelclosGunter Bechly Rafael Martins-Neto 《Geobios》2002,35(5):537
The Permian suborder Protanisoptera (Insecta: Odonatoptera) is revised and a new phylogenetic hypothesis proposed after analyses based on wing venation and different outgroups. After our study the families Camptotaxineuridae and Kaltanoneuridae are excluded from the Protanisoptera. After a new phylogenetic analysis, the family Permaeschnidae is redefined and the families Pholidoptilidae, Polytaxineuridae, Callimokaltaniidae and Hemizygopteridae are restored, as already proposed for the latter three families by Bechly (1996). The new genus Proditaxineura is described. The genus Gondvanoptilon RÖSLER et al., 1981 is excluded from the Meganisoptera: Erasipteridae and re-included in the Permaeschnidae, as already proposed by Bechly (1998). Permaeschna proxima MARTYNOV, 1931 is considered as a junior synonym of Permaeschna dolloi MARTYNOV, 1931. Pholidoptilon camense ZALESSKY, 1931 is excluded from Permaeschna MARTYNOV, 1931 and the genus Pholidoptilon
[Zalessky, 1931a] and [Zalessky, 1931b] is restored. Ditaxineurella stigmalisMARTYNOV, 1940 is excluded from the Hemizygopteridae and considered as a Protanisoptera Incertae sedis. 相似文献