全文获取类型
收费全文 | 1360篇 |
免费 | 49篇 |
国内免费 | 15篇 |
专业分类
1424篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 14篇 |
2021年 | 26篇 |
2020年 | 46篇 |
2019年 | 39篇 |
2018年 | 38篇 |
2017年 | 36篇 |
2016年 | 33篇 |
2015年 | 65篇 |
2014年 | 60篇 |
2013年 | 134篇 |
2012年 | 53篇 |
2011年 | 49篇 |
2010年 | 47篇 |
2009年 | 38篇 |
2008年 | 74篇 |
2007年 | 51篇 |
2006年 | 65篇 |
2005年 | 73篇 |
2004年 | 53篇 |
2003年 | 46篇 |
2002年 | 39篇 |
2001年 | 41篇 |
2000年 | 40篇 |
1999年 | 29篇 |
1998年 | 14篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 24篇 |
1992年 | 28篇 |
1991年 | 19篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1972年 | 4篇 |
1971年 | 1篇 |
排序方式: 共有1424条查询结果,搜索用时 15 毫秒
21.
The aim of this work was to study the role of H3O+ and transition-metal (TM) ions in keto-enol and amino-imino tautomeric transitions in DNA base pairs and depurination. In this regard, we discuss the thermodynamic model of ion-DNA interactions and UV display of double-proton transfer (DPT) in GC. The probabilities and energies of rare tautomeric forms of GC pairs in DNA induced by H3O+ and TMwere determined being in the range from0.02 (forMg2+) to 1 ( forCu2+), and from 0 kcal/m (for Cu2+) to 2.3 kcal/m (for Mg2+), respectively. It was shown that 3'ACC5'/5'TGG3' site of DNA double helix, which corresponds to the only triplet 5'UGG3' of RNA that codes the most valuable amino acid tryptophan, is a good target for TM ions to attack. It was also shown that the only way to obtain the tryptophan-coding 5'UGG3' triplet in RNA via transition-type G --> A point mutation caused by TM ions is their interaction with the site of a DNA double helix, which corresponds to 5'CGG3' triplet of RNA that codes arginine. 相似文献
22.
黑犀(奇蹄目,犀科)化石在中国的首次发现 总被引:1,自引:1,他引:1
黑犀(Diceros属)的惟一现生代表D.bicornis生活在非洲。该属在新近纪时期曾广泛分布于希腊、土耳其和伊朗等地区,但从未在东亚地区发现过。新种甘肃黑犀(Diceros gan- suensis sp.nov.)是该属在中国和东亚的首次发现。化石采自甘肃临夏盆地晚中新世柳树组中部。新种以尺寸较小、头型短、枕顶高耸、枕面窄而高、枕嵴无中沟、副枕突短小、下颌上升支距m3较近、前臼齿较小、DP1无后脊、P2原脊孤立、P2和P3后脊细窄而区别于东地中海地区的Diceros neumayri。D.neumayri的分类位置一直是一个争论的焦点,曾在黑犀(Diceros属)和白犀(Ceratotherium属)之间反复变更。研究显示,甘肃黑犀和D.neumayri的一系列共同的原始特征表明它们与更进步的白犀有明显的区别,应该归入黑犀属。 相似文献
23.
24.
Vanessa Julie Roden Imelda M. Hausmann Alexander Nützel Barbara Seuss Mike Reich Max Urlichs Hans Hagdorn Wolfgang Kiessling 《Palaeontology》2020,63(1):85-102
With 1429 animal species, the Triassic Cassian Formation in the Dolomites, Southern Alps (Italy), yields the highest species richness reported from any spatially constrained pre-Quaternary formation known to science. The high preserved diversity is partly attributable to a high primary diversity governed by the tropical setting, increasing alpha diversity, and the breadth of habitats spurring beta diversity. More important is the excellent preservation of fossils and the ease with which they can be extracted from the poorly lithified sediments. We propose the term ‘liberation Lagerstätten’ to capture this preservational window. In contrast to conservation Lagerstätten, liberation Lagerstätten like the Cassian Formation originate from normal marine conditions but low-grade diagenesis. Molluscs contribute substantially to species richness, comprising 67% of all invertebrate species in the Cassian Formation. The gastropod dominance (39% of all species) is nearly as great as in Recent tropical settings, contradicting the concept of a substantial Cenozoic rise. 相似文献
25.
The publication of the scientific name Monjurosuchus splendens in 1940 documented the first tetrapod fossil of the later world-renowned Jehol Biota. For more than half a century since this discovery, however, Monjurosuchus has remained as a monotypic genus of the family Monjurosuchidae, and the relationships of the family with choristoderes have not been correctly recognized until quite recently. In this paper, a new monjurosuchid is named and described based on a nearly complete skull and postcranial skeleton from the Early Cretaceous Chiufotang Formation exposed near Chaoyang, western Liaoning Province, China. This new material documents the first occurrence of monjurosuchid choristoderes outside the type Lingyuan area, and extends the geological range of the family from the Yixian Formation to the younger Chiufotang Formation. Cladistic analyses were conducted with inclusion of monjurosuchids, and the results support the placement of the family Monjurosuchidae as a primitive clade outside the Neochoristodera. A new classification scheme is proposed for choristoderes on the basis of the recovered phylogenetic framework of the group. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 145 , 427–444. 相似文献
26.
27.
Chen Guanfang Institute of Vertebrate Palaeontology Paleoanthropology Academia Sinica 《古脊椎动物学报》1991,(3)
<正> In the present paper a new caprine, Sinocapra minor gen. et sp. nov. is erected on the basis of several horn cores. The type specimen was collected by the Sino-American Palaeontology Expedition from the Upper Pliocene, Mazegou Formation, of Yunzhu Subbasin, Yushe Basin, Shansi province in 1988. All the other ones referred to the new genus were described and identified by Teilhard de Chardin and Trassaert (1938, p. 53, fig. 46) as Antilope gen. et sp. indet. They also came from Zhaozhuang, Yunzhu Subbasin and it is likely that they might be gathered from the same Formation as the type specimen judging by the yellow sandy clay filling into the horn cores. Magnetostratigraphic studies by Prof. N. Opdyke of the Yunzhu Subbasin indicates that this stratigraphic interval only includes the Gauss one, approximately 3.4 to 2.47 Ma. Accounts of the biostratigraphy and dating of Yunzhu Subbasin are giyen by Dr. R. H. Tedford and Dr. Z. Qiu in another paper. 相似文献
28.
系统描述湖北宜昌和秭归新滩晚奥陶世庙坡组三叶虫动物群中的3科6属6种。根据化石保存状态,挤压变形以及个体发育特征,对前人所报道的产于同一层位的有并三叶虫的研究成果作了重新厘定。 相似文献
29.
通过对新疆克拉玛依地区吐孜阿克内沟剖面三工河组孢粉组合的研究,共鉴定孢粉23属32种,藻类化石2属4种,命名为Disacciatrileti-Monocolpates-Cyathidites组合(简称DMC组合)。描述了5种花粉Abietineaepollenites dunrobinensis Couper,Pseudopicea monstruosa Bolch.,Podocarpidites 相似文献
30.
Eviostachya hoegii Stockmans在中国五通组的首次发现 总被引:2,自引:0,他引:2
首次描述了Eviostachya hoegii Stockmans的营养部分,通过大量标本的观察,修订了前人有关其生殖部分和解剖部分的描述,并对其生殖部分进行了复原.同意Emberger(1968)的观点,将其归于Eviostachyrales中. 相似文献