全文获取类型
收费全文 | 601篇 |
免费 | 39篇 |
国内免费 | 1篇 |
专业分类
641篇 |
出版年
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 23篇 |
2015年 | 22篇 |
2014年 | 33篇 |
2013年 | 34篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 27篇 |
2006年 | 23篇 |
2005年 | 28篇 |
2004年 | 27篇 |
2003年 | 33篇 |
2002年 | 41篇 |
2001年 | 8篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1966年 | 3篇 |
1905年 | 2篇 |
1902年 | 2篇 |
排序方式: 共有641条查询结果,搜索用时 0 毫秒
101.
Krizanauskiene A Hellgren O Kosarev V Sokolov L Bensch S Valkiunas G 《The Journal of parasitology》2006,92(6):1319-1324
A parasite's shift to a new host may have serious evolutionary consequences, since host switching usually is associated with a change in virulence and may lead to the evolution of emerging diseases. This phenomenon remains insufficiently studied in wildlife. Here, we combine microscopic examination of blood films and PCR-based methods to investigate the natural host specificity of Haemoproteus and Plasmodium spp. in birds of 4 families of the Passeriformes within a small geographic area. The material was collected on the Curonian Spit in the Baltic Sea between May and July in 2003-2004. A nested-PCR protocol was used for amplifying and sequencing a fragment of 480 nucleotides of the cytochrome b gene of the mtDNA of these parasites. Blood samples from 282 birds, which were positive both by microscopic examination of blood films and mtDNA amplification, were used in this study. We found that Haemoproteus majoris (lineages hPARUS1, hCCF5, hWW2, and hPHSIB1), Haemoproteus sp. (hWW1), Plasmodium (Haemamoeba) sp. (pSGS1), and Plasmodium (Haemamoeba) sp. (pGRW11) are capable of infecting birds belonging to different families of passeriform birds. Some species of Haemoproteus are less specific than have been traditionally believed. Haemoproteus majoris appears to have a genetic predisposition to have a broad host range. The level of host specificity varies markedly among different species of hemosporidian parasites of birds. The natural host range is thus not a reliable taxonomic character in the systematics of these parasites in the form in which it is still accepted in some recent taxonomic studies. 相似文献
102.
103.
104.
105.
When host species colonize new areas, the parasite assemblage infecting the hosts might change, with some parasite species being lost and others newly acquired. These changes would likely lead to novel selective forces on both host and its parasites. We investigated the avian blood parasites in the passerine bird community on the mid-Atlantic island of S?o Miguel, Azores, a bird community originating from continental Europe. The presence of haemosporidian blood parasites belonging to the genera Haemoproteus, Plasmodium, and Leucocytozoon was assessed using polymerase chain reaction. We found two Plasmodium lineages and two Leucocytozoon lineages in 11 bird species (84% of all breeding passerine species) on the island. These lineages were unevenly distributed across bird species. The Eurasian Blackbird (Turdus merula) was the key-host species (total parasite prevalence of 57%), harboring the main proportion of parasite infections. Except for Eurasian Blackbirds, all bird species had significantly lower prevalence and parasite diversity compared to their continental populations. We propose that in evolutionary novel bird communities, single species may act as key hosts by harboring the main part of the parasite fauna from which parasites "leak" into the other species. This would create very different host-parasite associations in areas recently colonized by hosts as compared to in their source populations. 相似文献
106.
Jedel E Labrie F Odén A Holm G Nilsson L Janson PO Lind AK Ohlsson C Stener-Victorin E 《American journal of physiology. Endocrinology and metabolism》2011,300(1):E37-E45
Polycystic ovary syndrome (PCOS), the most common endocrine disorder in women of reproductive age, is characterized by hyperandrogenism, oligo/amenorrhea, and polycystic ovaries. We aimed to determine whether low-frequency electro-acupuncture (EA) would decrease hyperandrogenism and improve oligo/amenorrhea more effectively than physical exercise or no intervention. We randomized 84 women with PCOS, aged 18-37 yr, to 16 wk of low-frequency EA, physical exercise, or no intervention. The primary outcome measure changes in the concentration of total testosterone (T) at week 16 determined by gas and liquid chromatography-mass spectrometry was analyzed by intention to treat. Secondary outcome measures were changes in menstrual frequency; concentrations of androgens, estrogens, androgen precursors, and glucuronidated androgen metabolites; and acne and hirsutism. Outcomes were assessed at baseline, after 16 wk of intervention, and after a 16-wk follow-up. After 16 wk of intervention, circulating T decreased by -25%, androsterone glucuronide by -30%, and androstane-3α,17β-diol-3-glucuronide by -28% in the EA group (P = 0.038, 0.030, and 0.047, respectively vs. exercise); menstrual frequency increased to 0.69/month from 0.28 at baseline in the EA group (P = 0.018 vs. exercise). After the 16-wk follow-up, the acne score decreased by -32% in the EA group (P = 0.006 vs. exercise). Both EA and exercise improved menstrual frequency and decreased the levels of several sex steroids at week 16 and at the 16-wk follow-up compared with no intervention. Low-frequency EA and physical exercise improved hyperandrogenism and menstrual frequency more effectively than no intervention in women with PCOS. Low-frequency EA was superior to physical exercise and may be useful for treating hyperandrogenism and oligo/amenorrhea. 相似文献
107.
Thomas Ranius Petter Bohman Olof Hedgren Lars‐Ove Wikars Alexandro Caruso 《Ecography》2014,37(8):797-804
Despite increasing awareness of the theoretical importance of habitat dynamics on metapopulations, only a few empirical studies have been conducted. We aimed to increase our understanding of how patch size, dynamics and connectivity affect colonization–extinction dynamics and the occurrence patterns of a beetle (Stephanopachys linearis), which breeds only in burned trees, existing as dynamic habitat patches that have become rare in managed forest landscapes. We assessed species’ presence/absence twice in all known habitat patches (i.e. > 1 ha sites where forest fires had occurred during the previous 2–15 yr) in a 200 × 150 km region of central Sweden, dominated by managed boreal forest. Evaluated over six years, the colonization rate was 47% and the local extinction risk was 65%. Probability of colonization increased with patch size (number of suitable trees in a site) and connectivity to occupied patches within 30 km, and decreased with increasing time since fire. Local extinction risk decreased with habitat patch size but increased, unexpectedly, with connectivity. Occurrence increased with patch size and decreased with increasing time since fire. At a regional scale, S. linearis tracks the fire dynamics by colonising sites with burned trees and by becoming extinct at rates which make the species rare at sites where burnt trees are more than eight years old. In managed boreal forest landscapes, a large proportion of sites may be created by prescribed burning (in our study area: 82%), and consequently human decisions strongly affect the future amount of habitat for fire‐dependent species and its spatial distribution. Stephanopachys linearis uses burned sites more often if more trees are retained and, to some extent, if sites are concentrated in those parts of a region that already support high population densities of the species. 相似文献
108.
Mika Bendiksby Yasaman Salmaki Christian Bräuchler Olof Ryding 《Plant Systematics and Evolution》2014,300(5):961-971
We have investigated the phylogenetic position of Stachys tibetica by use of both plastid (rps16 intron, trnL-F region and matK) and nuclear ribosomal (ITS) DNA sequence data and both parsimony and Bayesian phylogenetic methods. All data corroborate that S. tibetica is extraneous in Stachys (tribe Stachydeae) and suggest a phylogenetic affiliation in a different lamioid tribe, Lamieae. The molecular data suggest that the species is most closely related to the genus Stachyopsis, while most of the morphological data suggest an intermediate position between Stachyopsis and Eriophyton. Due to difficulties in distinguishing Stachyopsis and Eriophyton, and the possible embedding of the former in the latter genus, we prefer to amalgamate the two closely related genera and refer S. tibetica to the expanded Eriophyton. As a consequence, five new combinations are made: Eriophyton lamiflorum (Rupr.) Bräuchler, Eriophyton maleolens (Rech.f.) Salmaki, Eriophyton marrubioides (Regel) Ryding, Eriophyton oblongatum (Schrenk) Bendiksby and Eriophyton tibeticum (Vatke) Ryding. 相似文献
109.
110.
Michael B. Cook Douglas A. Corley Liam J. Murray Linda M. Liao Farin Kamangar Weimin Ye Marilie D. Gammon Harvey A. Risch Alan G. Casson Neal D. Freedman Wong-Ho Chow Anna H. Wu Leslie Bernstein Olof Nyrén Nirmala Pandeya David C. Whiteman Thomas L. Vaughan 《PloS one》2014,9(7)