全文获取类型
收费全文 | 5354篇 |
免费 | 331篇 |
国内免费 | 2篇 |
出版年
2024年 | 3篇 |
2023年 | 46篇 |
2022年 | 78篇 |
2021年 | 157篇 |
2020年 | 125篇 |
2019年 | 132篇 |
2018年 | 144篇 |
2017年 | 144篇 |
2016年 | 258篇 |
2015年 | 289篇 |
2014年 | 310篇 |
2013年 | 405篇 |
2012年 | 474篇 |
2011年 | 450篇 |
2010年 | 297篇 |
2009年 | 232篇 |
2008年 | 314篇 |
2007年 | 324篇 |
2006年 | 276篇 |
2005年 | 242篇 |
2004年 | 195篇 |
2003年 | 188篇 |
2002年 | 162篇 |
2001年 | 60篇 |
2000年 | 61篇 |
1999年 | 47篇 |
1998年 | 46篇 |
1997年 | 29篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1968年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有5687条查询结果,搜索用时 31 毫秒
91.
Micaela Medina Magali Prez Flores Juan Francisco Goya Paula Ines Campanello Martin Alcides Pinazo Luis Javier Ritter Marcelo Fabian Arturi 《Austral ecology》2020,45(2):229-239
Deforestation is a global process that has strongly affected the Atlantic Forest in South America, which has been recognised as a threatened biodiversity hotspot. An important proportion of deforested areas were converted to forest plantations. Araucaria angustifolia is a native tree to the Atlantic Forest, which has been largely exploited for wood production and is currently cultivated in commercial plantations. An important question is to what extent such native tree plantations can be managed to reduce biodiversity loss in a highly diverse and vulnerable forest region . We evaluated the effect of stand age, stand basal area, as a measure of stand density, and time since last logging on the density and richness of native tree regeneration in planted araucaria stands that were successively logged over 60 years, as well as the differences between successional groups in the response of plant density to stand variables. We also compared native tree species richness in planted araucaria stands to neighbouring native forest. Species richness was 71 in the planted stands (27 ha sampled) and 82 in native forest (18 ha sampled) which approximate the range of variation in species richness found in the native forests of the study area. The total abundance and species richness of native trees increased with stand age and time since last logging, but ecological groups differed in their response to such variables. Early secondary trees increased in abundance with stand age 3–8 times faster than climax or late secondary trees. Thus, the change in species composition is expected to continue for a long term. The difference in species richness between native forest and planted stands might be mainly explained by the difference in plant density. Therefore, species richness in plantations can contribute to local native tree diversity if practices that increase native tree density are implemented. 相似文献
92.
Juan F. Espínola‐Novelo M. Teresa Gonzlez Aldo S. Pacheco Jos L. Luque Marcelo E. Oliva 《Ecology letters》2020,23(4):631-641
Parasite communities are similar to free‐living communities; decay of similarity over geographic distance, theory of island biogeography, species–area relationships and nestedness have been documented in both communities. Ecological succession has been studied in free‐living communities but has rarely been examined in parasite communities. We use seriation with replication to test the hypothesis that succession of parasite community structure is deterministic, thus developing throughout consecutive changes along the fish ontogeny, via a seriated pattern. 12 306 marine fishes (95 species) were studied. In 40 species, a seriated pattern was detected; 25 had a tendency towards a seriated pattern, and for 31 species, succession was at random. Age‐classes for each host species explained deterministic successional patterns for whole parasite communities and ectoparasites. Richness and number of age‐classes explained this pattern for endoparasites. Seriated successional pattern was evident for parasite communities of long‐lived marine fish, indicating that parasite communities follow sequential changes over time, like many free‐living communities. 相似文献
93.
Marcelo H. Cassini 《Biological reviews of the Cambridge Philosophical Society》2020,95(5):1467-1478
Herein, I review existing criticisms of the field of invasion biology. Firstly, I identifiy problems of conceptual weaknesses, including disagreements regarding: (i) definitions of invasive, impact, and pristine conditions, and (ii) ecological assumptions such as species equilibrium, niche saturation, and climax communities. Secondly, I discuss methodological problems include the misuse of correlations, biases in impact reviews and risk assessment, and difficulties in predicting the effects of species introductions or eradications. Finally, I analyse the social conflict regarding invasive species management and differences in moral and philosophical foundations. I discuss the recent emergence of alternatives to traditional invasion biology approaches, including the concept of novel ecosystems, conciliation biology, and compassionate conservation. Understanding different value systems will be the first step to reconciling the different perspectives related to this controversial topic. 相似文献
94.
Thdia Evelyn de Araújo Iliana Claudia Balga Milin Guilherme de Souza Rafaela Jos da Silva Alessandra Monteiro Rosini Pmela Mendona Guirelli Priscila Silva Franco Bellisa Freitas Barbosa Eloisa Amlia Vieira Ferro Idessania Nazareth da Costa 《Cell biology international》2020,44(1):36-50
During pregnancy, the placenta regulates the transfer of oxygen, nutrients, and residual products between the maternal and fetal bloodstreams and is a key determinant of fetal exposure to xenobiotics from the mother. To study the disposition of substances through the placenta, various experimental models are used, especially the perfused placenta, placental villi explants, and cell lineage models. In this context, nanotechnology, an area of study that is on the rise, enables the creation of particles on nanometric scales capable of releasing drugs aimed at specific tissues. An important reason for furthering the studies on transplacental transfer is to explore the potential of nanoparticles (NPs), in new delivery strategies for drugs that are specifically aimed at the mother, the placenta, or the fetus and that involve less toxicity. Due to the fact that the placental barrier is essential for the interaction between the maternal and fetal organisms as well as the possibility of NPs being used in the treatment of various pathologies, the aim of this review is to present the main experimental models used in studying the maternal–fetal interaction and the action of NPs in the placental environment. 相似文献
95.
Fernando Sequeira Adam Bessa‐Silva Pedro Tarroso Tiago Sousa‐Neves Marcelo Vallinoto Helena Gonalves Iigo Martínez‐Solano 《Journal of evolutionary biology》2020,33(2):202-216
The study of natural hybrid zones can illuminate aspects of lineage divergence and speciation in morphologically cryptic taxa. We studied a hybrid zone between two highly divergent but morphologically similar lineages (south‐western and south‐eastern) of the Iberian endemic Bosca's newt (Lissotriton boscai) in SW Iberia with a multilocus dataset (microsatellites, nuclear and mitochondrial genes). STRUCTURE and NEWHYBRIDS analyses retrieved few admixed individuals, which classified as backcrosses involving parental individuals of the south‐western lineage. Our results show asymmetric introgression of mtDNA beyond the contact from this lineage into the south‐eastern lineage. Analysis of nongeographic introgression patterns revealed asymmetries in the direction of introgression, but except for mtDNA, we did not find evidence for nonconcordant introgression patterns across nuclear loci. Analysis of a 150‐km transect across the hybrid zone showed broadly coincident cline widths (ca. 3.2–27.9 km), and concordant cline centres across all markers, except for mtDNA that is displaced ca. 60 km northward. Results from ecological niche modelling show that the hybrid zone is in a climatically homogenous area with suitable habitat for the species, suggesting that contact between the two lineages is unlikely to occur further south as their distributions are currently separated by an extensive area of unfavourable habitat. Taken together, our findings suggest the genetic structure of this hybrid zone results from the interplay of historical (biogeographic) and population‐level processes. The narrowness and coincidence of genetic clines can be explained by weak selection against hybrids and reflect a degree of reproductive isolation that is consistent with cryptic speciation. 相似文献
96.
Athanasios Paschalis Simone Fatichi Jakob Zscheischler Philippe Ciais Michael Bahn Lena Boysen Jinfeng Chang Martin De Kauwe Marc Estiarte Daniel Goll Paul J. Hanson Anna B. Harper Enqing Hou Jaime Kigel Alan K. Knapp Klaus S. Larsen Wei Li Sebastian Lienert Yiqi Luo Patrick Meir Julia E. M. S. Nabel Rom Ogaya Anthony J. Parolari Changhui Peng Josep Peuelas Julia Pongratz Serge Rambal Inger K. Schmidt Hao Shi Marcelo Sternberg Hanqin Tian Elisabeth Tschumi Anna Ukkola Sara Vicca Nicolas Viovy Ying‐Ping Wang Zhuonan Wang Karina Williams Donghai Wu Qiuan Zhu 《Global Change Biology》2020,26(6):3336-3355
Changes in rainfall amounts and patterns have been observed and are expected to continue in the near future with potentially significant ecological and societal consequences. Modelling vegetation responses to changes in rainfall is thus crucial to project water and carbon cycles in the future. In this study, we present the results of a new model‐data intercomparison project, where we tested the ability of 10 terrestrial biosphere models to reproduce the observed sensitivity of ecosystem productivity to rainfall changes at 10 sites across the globe, in nine of which, rainfall exclusion and/or irrigation experiments had been performed. The key results are as follows: (a) Inter‐model variation is generally large and model agreement varies with timescales. In severely water‐limited sites, models only agree on the interannual variability of evapotranspiration and to a smaller extent on gross primary productivity. In more mesic sites, model agreement for both water and carbon fluxes is typically higher on fine (daily–monthly) timescales and reduces on longer (seasonal–annual) scales. (b) Models on average overestimate the relationship between ecosystem productivity and mean rainfall amounts across sites (in space) and have a low capacity in reproducing the temporal (interannual) sensitivity of vegetation productivity to annual rainfall at a given site, even though observation uncertainty is comparable to inter‐model variability. (c) Most models reproduced the sign of the observed patterns in productivity changes in rainfall manipulation experiments but had a low capacity in reproducing the observed magnitude of productivity changes. Models better reproduced the observed productivity responses due to rainfall exclusion than addition. (d) All models attribute ecosystem productivity changes to the intensity of vegetation stress and peak leaf area, whereas the impact of the change in growing season length is negligible. The relative contribution of the peak leaf area and vegetation stress intensity was highly variable among models. 相似文献
97.
Mariane P. Zubieta Jaqueline A. Gerhardt Marcelo V. Rubio César R. F. Terrasan Gabriela F. Persinoti Everton P. Antoniel Fabiano J. Contesini Rolf A. Prade André Damasio 《Microbial biotechnology》2020,13(4):1245-1253
Filamentous fungi are important cell factories for large-scale enzyme production. However, production levels are often low, and this limitation has stimulated research focusing on the manipulation of genes with predicted function in the protein secretory pathway. This pathway is the major route for the delivery of proteins to the cell exterior, and a positive relationship between the production of recombinant enzymes and the unfolded protein response (UPR) pathway has been observed. In this study, Aspergillus nidulans was exposed to UPR-inducing chemicals and differentially expressed genes were identified by RNA-seq. Twelve target genes were deleted in A. nidulans recombinant strains producing homologous and heterologous GH10 xylanases. The knockout of pbnA (glycosyltransferase), ydjA (Hsp40 co-chaperone), trxA (thioredoxin) and cypA (cyclophilin) improved the production of the homologous xylanase by 78, 171, 105 and 125% respectively. Interestingly, these deletions decreased the overall protein secretion, suggesting that the production of the homologous xylanase was specifically altered. However, the production of the heterologous xylanase and the secretion of total proteins were not altered by deleting the same genes. Considering the results, this approach demonstrated the possibility of rationally increase the production of a homologous enzyme, indicating that trxA, cypA, ydjA and pbnA are involved in protein production by A. nidulans. 相似文献
98.
99.
Mikovski Andréia Izabel da Silva Nayara Tayane Silva Lázara Aline Simões Machado Mariana de Souza Barbosa Lília Cristina Reis Aryane Campos de Matos Elyabe Monteiro Viccini Lyderson Facio da Silva Souza Claudinei Machado Marcelo Dias Otoni Wagner Campos de Carvalho Ilio Fealho Rocha Diego Ismael da Silva Maurecilne Lemes 《Plant Cell, Tissue and Organ Culture》2021,145(2):239-259
Plant Cell, Tissue and Organ Culture (PCTOC) - Somaclonal variation during in vitro culture is often an undesirable phenomenon but may also be a source of genetic variation useful for breeders. The... 相似文献
100.
da Silva Gessiane Pereira de Melo Josi Teixeira Monteiro Frederico Ozanan Barros Ferreira Ana Karolyna Pereira Carneiro Liliane Almeida Takeshita Rafaela S. C. 《International journal of primatology》2021,42(5):722-736
International Journal of Primatology - The hormone dehydroepiandrosterone (DHEA) and its sulfate ester (DHEAS) are the most abundant circulating steroids in human and some nonhuman primates, and... 相似文献