全文获取类型
收费全文 | 1346篇 |
免费 | 151篇 |
出版年
2023年 | 7篇 |
2022年 | 12篇 |
2021年 | 43篇 |
2020年 | 14篇 |
2019年 | 31篇 |
2018年 | 44篇 |
2017年 | 37篇 |
2016年 | 50篇 |
2015年 | 70篇 |
2014年 | 57篇 |
2013年 | 75篇 |
2012年 | 67篇 |
2011年 | 86篇 |
2010年 | 50篇 |
2009年 | 63篇 |
2008年 | 74篇 |
2007年 | 76篇 |
2006年 | 51篇 |
2005年 | 54篇 |
2004年 | 50篇 |
2003年 | 60篇 |
2002年 | 46篇 |
2001年 | 39篇 |
2000年 | 40篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 12篇 |
1996年 | 17篇 |
1995年 | 19篇 |
1994年 | 10篇 |
1993年 | 16篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1972年 | 5篇 |
1971年 | 4篇 |
1967年 | 6篇 |
排序方式: 共有1497条查询结果,搜索用时 718 毫秒
911.
Njoud Gallala Dalila Zaghbib-Turki Ignacio Arenillas Jos Antonio Arz Eustoquio Molina 《Marine Micropaleontology》2009,72(3-4):196-209
A high-resolution biostratigraphic analysis of planktic foraminifers confirms that the Bidart section at the eastern margin of the Atlantic Ocean exhibits a continuous and complete Cretaceous/Paleogene (K/Pg) transition interval. The biozones and subzones recorded in this section are less expanded than their equivalent in Tunisian sections: El Kef (Global Stratotype Section and Point: GSSP for the K/Pg boundary) and Ellès (auxiliary section), but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the K/Pg transition.Throughout the uppermost 4 m Maastrichtian, the planktic foraminiferal assemblages are highly diversified, containing up to 72 species. These Maastrichtian assemblages are rich in cosmopolitan taxa (70%), dominated by small biserial morphotypes which belong mainly to the genus Heterohelix which coexist with less abundant but highly diverse tropical and subtropical species.The extinction pattern at the Bidart section suggests a sudden catastrophic mass extinction at the K/Pg boundary which affected at least 53 out of 72 species. The species becoming extinct include globotruncanids (e.g. Contusotruncana spp., Globotruncana spp., Globotruncanita spp.) and complex heterohelicids (e.g. Racemiguembelina spp., Pseudotextularia spp., Gublerina spp.). At the Bidart section, only Archaeoglobigerina cretacea disappears 2 m below the K/Pg boundary event. Specimens of 18 small and even tiny Maastrichtian species, are found at the lowermost Danian. Only a few of these species belonging to the genera of Guembelitria, Hedbergella and Heterohelix are considered to be real “Cretaceous survivor species”, whereas the specimens belonging to the rest, are most probably reworked, because they differ in their preservation.Throughout lowermost Danian, the planktic foraminiferal assemblages are dominated by “opportunistic” species of the genus Guembelitria. These opportunists are associated to small and poorly diversified pioneer globigerinids (Palaeoglobigerina spp. and Parvularugoglobigerina spp.). These assemblages became progressively more diversified across the early Danian containing species with cancellate walls (Eoglobigerina spp., Parasubbotina spp., Subbotina triloculinoides and Praemurica spp.) and new taxa of biserial heterohelicids (Woodringina spp. and Chiloguembelina spp.) suggesting a paleoenvironmental recovery. 相似文献
912.
Lucas M. Molina Macarena S. Valiñas Paula D. Pratolongo Rodolfo Elias Gerardo M. E. Perillo 《Biological invasions》2009,11(2):409-416
We report the occurrence of the orange-striped green anemone Diadumene lineata (Verrill 1871) (=Haliplanella lineata) in salt marshes at the Bahía Blanca Estuary for the first time in August 2005. We also found this species attached to roots
and stems of Spartina alterniflora, an association that has never been registered before. After their determination, sampling was performed during a year to
evaluate seasonal abundance of this sea anemone. Results showed that D. lineata was present through the whole year, indicating the existence of a stable population. All individuals sampled were found attached
to roots or stems of S. alterniflora, with the higher abundances detected in summer. Further studies are necessary to precise the potential effects of this exotic
sea anemone on salt marsh communities. 相似文献
913.
The order Anguilliformes comprises 15 families, 141 genera and 791 fish species. Eight families had at least one karyotyped species, with a prevalence of 2n = 38 chromosomes and high fundamental numbers (FN). The only exception to this pattern is the family Muraenidae, in which the eight species analyzed presented 2n = 42 chromosomes. Despite of the large number of Anguilliformes species, karyotypic reports are available for only a few representatives. In the present work, a species of Ophichthidae, Myrichthys ocellatus (2n = 38; 8m+14sm+10st+6a; FN = 70) and four species of Muraenidae, Enchelycore nigricans (2n = 42; 6m+8sm+12st+16a; FN = 68), Gymnothorax miliaris (2n = 42; 14m+18sm+10st; FN = 84), G. vicinus (2n = 42; 8m+6sm+28a; FN = 56) and Muraena pavonina (2n = 42; 6m+4sm+32a; FN = 52), collected along the Northeastern coast of Brazil and around the St Peter and St Paul Archipelago were analyzed. Typical large metacentric chromosomes were observed in all species. Conspicuous polymorphic heterochromatic regions were observed at the centromeres of most chromosomes and at single ribosomal sites. The data obtained for Ophichthidae corroborate the hypothesis of a karyotypic diversification mainly due to pericentric inversions and Robertsonian rearrangements, while the identification of constant chromosome numbers in Muraenidae (2n = 42) suggests a karyotype diversification through pericentric inversions and heterochromatin processes. 相似文献
914.
915.
916.
C. Pinto-Cruz J. A. Molina M. Barbour V. Silva M. D. Espírito-Santo 《Hydrobiologia》2009,634(1):11-24
Temporary ponds are seasonal wetlands annually subjected to extreme and unstable ecological conditions, neither truly aquatic
nor truly terrestrial. This habitat and its flora have been poorly studied and documented because of the ephemeral character
of the flora, the changeable annual weather that has a great effect on the small, herbaceous taxa and the declining abundance
of temporary ponds. The objectives of this study are: (a) to define plant community diversity in terms of floristic composition
of ephemeral wetlands in SW Portugal, (b) to identify temporary pond types according to their vegetation composition and (c)
to identify those ponds that configure the European community priority habitat (3170* – Mediterranean temporary ponds).
Vegetation sampling was conducted in 29 ponds, identifying 168 species grouped among 15 plant communities. Soil texture, pH,
organic C and N content were measured, but only N and percent of clay appear to be related with the distribution of each community
type. The results showed that ephemeral wetlands could be classified into four type: vernal pools, marshlands, deep ponds
and disturbed wetlands. Vernal pools correspond to the Mediterranean temporary ponds (3170*), protected as priority habitat
under the EU Habitats Directive. Submersed Isoetes species (Isoetes setaceum and Isoetes velatum) represents, together with Eryngium corniculatum, the indicator species for vernal pools. We identify also indicator plant communities of this priority habitat, namely I. setaceum and E. corniculatum–Baldellia ranunculoides plant communities. In this region, the conservation of temporary ponds has so far been compatible with traditional agricultural
activities, but today these ponds are endangered by the intensification of agriculture and the loss of traditional land use
practices and by the development of tourism.
Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle
Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16
May 2008 相似文献
917.
918.
Liu B Molina H Kalume D Pandey A Griffith JD Englund PT 《Molecular and cellular biology》2006,26(14):5382-5393
Trypanosomes have an unusual mitochondrial genome, called kinetoplast DNA, that is a giant network containing thousands of interlocked minicircles. During kinetoplast DNA synthesis, minicircles are released from the network for replication as theta-structures, and then the free minicircle progeny reattach to the network. We report that a mitochondrial protein, which we term p38, functions in kinetoplast DNA replication. RNA interference (RNAi) of p38 resulted in loss of kinetoplast DNA and accumulation of a novel free minicircle species named fraction S. Fraction S minicircles are so underwound that on isolation they become highly negatively supertwisted and develop a region of Z-DNA. p38 binds to minicircle sequences within the replication origin. We conclude that cells with RNAi-induced loss of p38 cannot initiate minicircle replication, although they can extensively unwind free minicircles. 相似文献
919.
Rothman JM Dierenfeld ES Molina DO Shaw AV Hintz HF Pell AN 《American journal of primatology》2006,68(7):675-691
Foods eaten by gorillas (Gorilla beringei) in Bwindi Impenetrable National Park (BINP), Uganda, were analyzed for their nutrient content. The goal of the study was to assess the amounts of fiber, protein, and sugars in the foods eaten by the Bwindi gorillas, and to determine whether condensed tannins and cyanide are present in these foods. A total of 127 food plant parts representing 84 plant species eaten by two groups of Bwindi gorillas were collected, processed, and analyzed for their chemical contents. The Bwindi gorilla ate foods that contain 2-28% crude protein (CP), 21-88% neutral detergent fiber (NDF), 14-60% acid detergent fiber (ADF), 2-42% acid detergent lignin (ADL), and =1-50% water-soluble carbohydrates (WSC) on a dry matter (DM) basis. Moisture in these foods ranged from 7% to 96%. Approximately 35% of the foods analyzed contained condensed tannins, and two foods contained cyanogenic glycosides. This is the first detailed report regarding the nutritional chemistry of gorilla foods in Bwindi, many of which are also eaten by other primates. This unique data set adds to our knowledge about the nutritional composition of foods eaten by gorillas across habitats, is useful for understanding aspects of feeding behavior, and provides valuable comparative data for optimizing the diets of gorillas ex situ. 相似文献
920.
Discontinuous epitope prediction based on mimotope analysis 总被引:2,自引:0,他引:2
Moreau V Granier C Villard S Laune D Molina F 《Bioinformatics (Oxford, England)》2006,22(9):1088-1095
MOTIVATION: Phage display is a widespread technique used to obtain peptide mimotopes selected by binding to a given monoclonal antibody in a similar way as the native epitope. However, the localization of the interaction site mimicked by the mimotopes on the surface of the antigen is not always a straightforward task. MIMOP is a computational tool developed with the aim of helping experimentalists to analyze a set of mimotope sequences and guide them in the identification of the mimicked region. RESULTS: To predict potential epitopic regions, MIMOP integrates two different approaches combining two- and three-dimensional analyses: MimAlign starts from degenerated alignment analyses, and MimCons is based on consensus identification. The relevance and usefulness of the tool are illustrated by four use cases corresponding to real-life situations. 相似文献