全文获取类型
收费全文 | 7137篇 |
免费 | 495篇 |
国内免费 | 1篇 |
出版年
2023年 | 38篇 |
2022年 | 114篇 |
2021年 | 225篇 |
2020年 | 167篇 |
2019年 | 205篇 |
2018年 | 276篇 |
2017年 | 220篇 |
2016年 | 312篇 |
2015年 | 400篇 |
2014年 | 466篇 |
2013年 | 513篇 |
2012年 | 653篇 |
2011年 | 578篇 |
2010年 | 356篇 |
2009年 | 283篇 |
2008年 | 384篇 |
2007年 | 384篇 |
2006年 | 309篇 |
2005年 | 265篇 |
2004年 | 258篇 |
2003年 | 201篇 |
2002年 | 198篇 |
2001年 | 110篇 |
2000年 | 85篇 |
1999年 | 84篇 |
1998年 | 46篇 |
1997年 | 40篇 |
1996年 | 26篇 |
1995年 | 25篇 |
1994年 | 18篇 |
1993年 | 21篇 |
1992年 | 37篇 |
1991年 | 35篇 |
1990年 | 26篇 |
1989年 | 23篇 |
1988年 | 25篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1974年 | 9篇 |
1972年 | 7篇 |
排序方式: 共有7633条查询结果,搜索用时 484 毫秒
991.
992.
993.
Assessment of the environmental factors that control species richness (S) is a central issue in ecology. In this study, aquatic macrophyte S was estimated in 235 sampling sites distributed in 8 arms of a large (1350 km2) subtropical reservoir (Itaipu Reservoir, Brazil). Morphometric variables (area, shoreline development and length of shoreline, all measured for each arm; n= 8) and environmental variables measured at each sampling site (extinction coefficient of light (k), electrical conductivity, fetch, distance from the main reservoir body; n = 235) were used to predict aquatic macrophyte S at two spatial scales. At arm scale, linear regression analysis indicated that length of shoreline was a better predictor of S than area. At sampling site scale, multiple regression analysis indicated that S was significantly predicted by electrical conductivity, fetch and distance from the main body. However, other relationships with predictive interest was demonstrated by using non-traditional regression approaches. This analysis started by the visual inspection of scatter plots. The bivariate relationship between S and fetch, for example, showed an envelope or a `left triangle' pattern. The relationship between the number of submerged species and k showed an asymmetrical left triangle pattern. Using randomization procedures, it was demonstrated that these patterns were not generated by chance alone. Beta diversity (estimated within the arms) was significantly and positively correlated with spatial environmental variability. Overall, these results indicate that the prediction of aquatic macrophytes assemblage variables in large waterbodies, specially S, is more complex than previous studies have suggested. 相似文献
994.
Johara Boldrini-França Renata Santos Rodrigues Ludier Kesser Santos-Silva Dayane Lorena Naves de Souza Mário Sérgio Rocha Gomes Camila Takeno Cologna Edwin de Pauw Loïc Quinton Flávio Henrique-Silva Veridiana de Melo Rodrigues Eliane Candiani Arantes 《Applied microbiology and biotechnology》2015,99(23):9971-9986
995.
996.
Joana Darc Souza Chaves Jaqueline Lopes Damasceno Marcela Cristina Ferreira Paula Pollyanna Francielli de Oliveira Gustavo Chevitarese Azevedo Renato Camargo Matos Maria Cristina S. Lourenço Denise Crispim Tavares Heveline Silva Ana Paula Soares Fontes Mauro Vieira de Almeida 《Biometals》2015,28(5):845-860
997.
Raimundo Wagner Souza Aguiar Suetonio Fernandes dos Santos Fabricio da Silva Morgado Sergio Donizeti Ascencio Magnólia de Mendon?a Lopes Kelvinson Fernandes Viana Julcemar Didonet Bergmann Morais Ribeiro 《PloS one》2015,10(2)
This study investigated the toxic effects of essential oils isolated from Siparuna guianensis against Aedes aegypti, Culex quinquefasciatus (eggs, larvae, pupae, and adult) and Aedes albopictus (C6/36) cells. The oviposition-deterring activity, egg viability, and repellence activity in the presence of different essential oils concentrations were determined. The essential oils showed high toxicity to all developmental stages of A. aegypti and C. quinquefasciatus. Furthermore, the oils also showed high repellent activity towards the adult stage of mosquitoes (0.025 to 0.550 μg/cm2 skin conferred 100% repellence up to 120 min) and in contact with cultured insect cells (C6/36) induced death possibly by necrosis. The results presented in this work show the potential of S. guianensis essential oils for the development of an alternative and effective method for the natural control of mosquitoes in homes and urban areas. 相似文献
998.
Pachycondyla marginata (P.m.), a migratory and termitophageous ant, hunting only the termite species Neocapritermes opacus, migrates significantly oriented 13 degrees with respect to the magnetic North-South axis. Results of hysteresis curves at room temperature of four Pachycondyla marginata heads, thorax, pairs of antennae and abdomens, oriented parallel to the magnetic field, indicate that the antennae give the strongest saturation magnetization, suggesting this sensory organ as being also a magnetic sensory organ. The total saturation magnetization in a whole P.m. is composed by 42 +/- 3%, 24 +/- 3%, 19 +/- 3% and 15 +/- 3% of antennae, head, thorax and abdomen contributions, respectively. The abdomen hysteresis curve presents a wasp-waisted loop with Hcr/Hc of 4.75, characteristic of mixed magnetic systems. 相似文献
999.
Mitracarpus longicalyx is here described and illustrated from sandy areas of the caatingas of northeastern Brazil. The new species is similar toM. hirtus andM. megapotamicus. 相似文献
1000.
D D Paskulin J S L Cunha-Filho C A B Souza M C Bortolini P Hainaut P Ashton-Prolla 《Cell death & disease》2012,3(9):e392
p53 has a crucial role in human fertility by regulating the expression of leukemia inhibitory factor (LIF), a secreted cytokine critical for blastocyst implantation. To examine whether TP53 polymorphisms may be involved with in vitro fertilization (IVF) failure and endometriosis (END), we have assessed the associations between TP53 polymorphism in intron 2 (PIN2; G/C, intron 2), PIN3 (one (N, non-duplicated) or two (D, duplicated) repeats of a 16-bp motif, intron 3) and polymorphism in exon 4 (PEX4; C/G, p.P72R, exon 4) in 98 women with END and 115 women with post-IVF failure. In addition, 134 fertile women and 300 women unselected with respect to fertility-related features were assessed. TP53 polymorphisms and haplotypes were identified by amplification refractory mutation system polymerase chain reaction. TP53 PIN3 and PEX4 were associated with both END (P=0.042 and P=0.007, respectively) and IVF (P=0.004 and P=0.009, respectively) when compared with women both selected and unselected for fertility-related features. Haplotypes D-C and N-C were related to higher risk for END (P=0.002, P=0.001, respectively) and failure of IVF (P=0.018 and P=0.002, respectively) when compared with the Fertile group. These results support that specific TP53 haplotypes are associated with an increased risk of END-associated infertility and with post-IVF failure. 相似文献