全文获取类型
收费全文 | 17354篇 |
免费 | 1264篇 |
国内免费 | 6篇 |
出版年
2023年 | 143篇 |
2022年 | 300篇 |
2021年 | 491篇 |
2020年 | 323篇 |
2019年 | 489篇 |
2018年 | 536篇 |
2017年 | 492篇 |
2016年 | 719篇 |
2015年 | 1017篇 |
2014年 | 1083篇 |
2013年 | 1364篇 |
2012年 | 1479篇 |
2011年 | 1378篇 |
2010年 | 923篇 |
2009年 | 821篇 |
2008年 | 1008篇 |
2007年 | 985篇 |
2006年 | 830篇 |
2005年 | 744篇 |
2004年 | 676篇 |
2003年 | 572篇 |
2002年 | 532篇 |
2001年 | 154篇 |
2000年 | 116篇 |
1999年 | 149篇 |
1998年 | 129篇 |
1997年 | 94篇 |
1996年 | 81篇 |
1995年 | 90篇 |
1994年 | 75篇 |
1993年 | 57篇 |
1992年 | 79篇 |
1991年 | 58篇 |
1990年 | 40篇 |
1989年 | 64篇 |
1988年 | 42篇 |
1987年 | 37篇 |
1986年 | 41篇 |
1985年 | 41篇 |
1984年 | 28篇 |
1983年 | 39篇 |
1982年 | 20篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 32篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1974年 | 20篇 |
1973年 | 18篇 |
1972年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
Valéria Marques Gabriel Riaño Miguel A. Carretero Iolanda Silva-Rocha Catarina Rato 《Acta zoologica》2023,104(3):419-433
Under temperature sex determination (TSD), sex is determined by temperature during embryonic development. Depending on ecological and physiological traits and plasticity, TSD species may face demographic collapse due to climate change. In this context, asymmetry in bilateral organisms can be used as a proxy for developmental instability and, therefore, deviations from optimal incubation conditions. Using Tarentola mauritanica gecko as a model, this study aimed first to confirm TSD, its pattern and pivotal temperature, and second to assess the local adaptation of TSD and variation of asymmetry patterns across four populations under different thermal regimes. Eggs were incubated at different temperatures, and hatchlings were sexed and measured. The number of lamellae was counted in adults and hatchlings. Results were compatible with a TSD pattern with males generated at low and females at high incubation temperatures. Estimated pivotal temperature coincided with the temperature producing lower embryonic mortality, evidencing selection towards balanced sex ratios. The temperature of oviposition was conservatively selected by gravid females. Asymmetry patterns found were likely related to nest temperature fluctuations. Overall, the rigidity of TSD may compromise reproductive success, and demographic stability in this species in case thermal nest choice becomes constrained by climate change. 相似文献
113.
114.
Tamara Schmey Corinn Small Severin Einspanier Lina Muñoz Hoyoz Tahir Ali Soledad Gamboa Betty Mamani German C. Sepulveda Marco Thines Remco Stam 《Environmental microbiology》2023,25(10):1830-1846
The wild relatives of modern tomato crops are native to South America. These plants occur in habitats as different as the Andes and the Atacama Desert and are, to some degree, all susceptible to fungal pathogens of the genus Alternaria. Alternaria is a large genus. On tomatoes, several species cause early blight, leaf spots and other diseases. We collected Alternaria-like infection lesions from the leaves of eight wild tomato species from Chile and Peru. Using molecular barcoding markers, we characterized the pathogens. The infection lesions were caused predominantly by small-spored species of Alternaria of the section Alternaria, like A. alternata, but also by Stemphylium spp., Alternaria spp. from the section Ulocladioides and other related species. Morphological observations and an infection assay confirmed this. Comparative genetic diversity analyses show a larger diversity in this wild system than in studies of cultivated Solanum species. As A. alternata has been reported to be an increasing problem in cultivated tomatoes, investigating the evolutionary potential of this pathogen is not only interesting to scientists studying wild plant pathosystems. It could also inform crop protection and breeding programs to be aware of potential epidemics caused by species still confined to South America. 相似文献
115.
Neuza Domingues André R. A. Marques Rita Diogo Almeida Calado Inês S. Ferreira Cristiano Ramos José Ramalho Maria I. L. Soares Telmo Pereira Luís Oliveira José R. Vicente Louise H. Wong Inês C. M. Simões Teresa M. V. D. Pinho e Melo Andrew Peden Cláudia Guimas Almeida Clare E. Futter Rosa Puertollano Winchil L. C. Vaz Otília V. Vieira 《Traffic (Copenhagen, Denmark)》2023,24(7):284-307
116.
We studied the effect of heparin on proliferation and signalling in normal NIH/3T3 fibroblasts, and in cells transformed by different oncogenes. Heparin inhibited the proliferation of normal as well as of v-sis and v-erbB transformed fibroblasts in the presence of serum, but failed to inhibit v-erbB-driven proliferation in serum-starved cultures; under these conditions, heparin inhibited by approximately 50% the proliferation of normal and v-sis- transformed cells. Heparin also inhibited PDGF-induced cell proliferation and inositol lipid turnover in v-sis transformants, but it did not affect PDGF mitogenic signalling in NIH/3T3 fibroblasts. 相似文献
117.
Laetitia Mathon Virginie Marques Stéphanie Manel Camille Albouy Marco Andrello Emilie Boulanger Julie Deter Régis Hocdé Fabien Leprieur Tom B. Letessier Nicolas Loiseau Eva Maire Alice Valentini Laurent Vigliola Florian Baletaud Sandra Bessudo Tony Dejean Nadia Faure Pierre-Edouard Guerin Meret Jucker Jean-Baptiste Juhel Kadarusman Andrea Polanco F. Laurent Pouyaud Dario Schwörer Kirsten F. Thompson Marc Troussellier Hagi Yulia Sugeha Laure Velez Xiaowei Zhang Wenjun Zhong Loïc Pellissier David Mouillot 《Global Ecology and Biogeography》2023,32(8):1336-1352
Aim
Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.Location
Tropical, temperate and polar coastal areas.Time period
Present day.Major taxa studied
Marine fishes.Methods
We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.Results
We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.Main conclusions
Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions. 相似文献118.
119.
OBJECTIVES--To determine general practitioners'' responses to and explanations for variation in rates of referral to hospital and how feedback of data on rates of referral could be used to facilitate practices in auditing their own referral behaviour. DESIGN--Visits by audit facilitators to general practices after feedback of details of rates of referral to hospital derived from annual reports in general practice. SETTING--92 general practices in East Anglia. RESULTS--General practitioners judged that access to specialist care, the individual skill of general practitioners, patient demand, and fear of litigation were major determinants of referral behaviour. Because there was widespread scepticism about the accuracy of the data on which the feedback was based and because there is no clear relation between rates of referral and quality of care, it was extremely difficult to encourage doctors to use the feedback as a basis for auditing their own hospital referrals. CONCLUSION--If general practitioners are to contribute meaningfully to monitoring future changes in referral patterns it will be essential to develop reliable information systems in which doctors have confidence. Furthermore, audits need to be based on analysis of clinical cases rather than on rates of referral. 相似文献
120.
PHYLOGENETIC INTERRELATIONSHIPS AND REDUCTIVE EVOLUTION IN NEOTROPICAL CHARACIDIIN FISHES (CHARACIFORMES, OSTARIOPHYSI) 总被引:1,自引:0,他引:1
Paulo Andreas Buckup 《Cladistics : the international journal of the Willi Hennig Society》1993,9(3):305-341
Abstract— Miniaturization, which results in the presence of numerous apparently paedomorphic characters associated with reduced size, is a common phenomenon among neotropical fishes, with over 85 miniature species distributed among the five major ordinal groups. Eleven species are recognized as miniatures within the Characidiinae, a monophyletic subunit of Characiformes. A reconstruction of characidiin phylogeny is used to analyze the history of miniaturization events. Former hypotheses of origin of miniaturization among characidiins are rejected, underscoring the need for phylogenetic frameworks in the study of ontogenetic changes associated with the phenomenon of miniaturization. The 11 instances of miniature species can be most parsimoniously attributed to three independent miniaturization events within the Characidiinae.
Reductive characters comprise a large proportion of phylogenetically informative characters within the Characidiinae. In the largest group of miniatures, reductive characters represent more than half of the character state transformations affecting supraspecific relationships among Elachocharax, Klausewitzia, Odontocharacidium and Microcharacidium . An analysis of patterns of character state distributions fails to reject the null hypothesis of character independence. A distinction is made between the concepts of character independence, defined as the origination of character states from different (non-simultaneous) evolutionary events, and character correlation, defined as the association of character states in terminal taxa. Character correlation is not a sufficient criterion to reject Hennig's auxiliary principle, according to which the "presence of apomorphous characters in different species is always reason for suspecting kinship, and their origin by convergence should not be assumed a priori". High values of character correlation are the expected result of congruent patterns of character distribution. 相似文献
Reductive characters comprise a large proportion of phylogenetically informative characters within the Characidiinae. In the largest group of miniatures, reductive characters represent more than half of the character state transformations affecting supraspecific relationships among Elachocharax, Klausewitzia, Odontocharacidium and Microcharacidium . An analysis of patterns of character state distributions fails to reject the null hypothesis of character independence. A distinction is made between the concepts of character independence, defined as the origination of character states from different (non-simultaneous) evolutionary events, and character correlation, defined as the association of character states in terminal taxa. Character correlation is not a sufficient criterion to reject Hennig's auxiliary principle, according to which the "presence of apomorphous characters in different species is always reason for suspecting kinship, and their origin by convergence should not be assumed a priori". High values of character correlation are the expected result of congruent patterns of character distribution. 相似文献