全文获取类型
收费全文 | 4523篇 |
免费 | 328篇 |
专业分类
4851篇 |
出版年
2023年 | 26篇 |
2022年 | 67篇 |
2021年 | 128篇 |
2020年 | 79篇 |
2019年 | 96篇 |
2018年 | 132篇 |
2017年 | 107篇 |
2016年 | 175篇 |
2015年 | 253篇 |
2014年 | 265篇 |
2013年 | 368篇 |
2012年 | 407篇 |
2011年 | 389篇 |
2010年 | 236篇 |
2009年 | 234篇 |
2008年 | 301篇 |
2007年 | 252篇 |
2006年 | 216篇 |
2005年 | 224篇 |
2004年 | 200篇 |
2003年 | 183篇 |
2002年 | 145篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 24篇 |
1998年 | 23篇 |
1997年 | 28篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有4851条查询结果,搜索用时 15 毫秒
961.
Rossi Graziano Parolo Gilberto Ferrarini Alessandro 《Biodiversity and Conservation》2009,18(5):1375-1388
“Habitats” Directive 92/43/EEC is the pivotal European law for building a continental network of sites of community importance
(SCIs) for nature conservation. Article 6 of such directive underlines the importance of biodiversity conservation through
the realization of proper management plans. As a result, such plans are increasingly common. A management plan based on intensive
field studies and monitoring activities requires time and financial resources, which are generally limited. The aim of this
paper is to offer a rapid, cost-effective and scientifically based decision tool aimed to achieve GIS-based conservation strategies
for habitats of EU interest within SCIs and, in general, within protected areas. As a case study, we considered species-rich
Nardus grasslands (threatened by natural reconversion and intensive cattle grazing), and transition mires (threatened by pasturing
and human disturbance) in a SCI in the Alps. Through a multi-criteria evaluation, we selected indicators and weights based
upon our knowledge of the study area. As a result, we were able to: (a) quantify the level of existing threats, (b) suggest
urgent conservation strategies, and (c) suggest future monitoring activities. Since the study area is representative of many
protected areas in the Alps and the conservation topics under evaluation are frequent threats impacting habitats of EU interest,
our decision model might be transferable to further areas given proper adaptation of weights to the intensity and the frequency
of current threats. 相似文献
962.
1. The histone complement of oligodendrocyte chromatin at different stages of brain development was studied after acid extraction of nuclei. 2. HCl-soluble proteins were analyzed by different electrophoretic techniques. 3. Our results show an increase in the concentration of histone H1(0) with differentiation. 4. The increase in H1(0) is accompanied by a concomitant decrease in the total amount of the ubiquitinated form of histone H2A (A24). 相似文献
963.
Using an evolutionary game, we show that patients and physicians can interact with predator-prey relationships. Litigious patients who seek compensation are the ‘predators’ and physicians are their ‘prey’. Physicians can adapt to the risk of being sued by performing defensive medicine. We find that improvements in clinical safety can increase the share of litigious patients and leave unchanged the share of physicians who perform defensive medicine. This paradoxical result is consistent with increasing trends in malpractice claims in spite of safety improvements, observed for example in empirical studies on anesthesiologists. Perfect cooperation with neither defensive nor litigious behaviors can be the Pareto-optimal solution when it is not a Nash equilibrium, so maximizing social welfare may require government intervention. 相似文献
964.
Archana Krishnamoorthy Jessica Jackson Taha Mohamed Madison Adolph Alessandro Vindigni David Cortez 《Molecular cell》2021,81(14):3007-3017.e5
- Download : Download high-res image (121KB)
- Download : Download full-size image
965.
The aim of this study was to isolate and identify marine-derived bacteria which exhibited high tolerance to, and an ability to biodegrade, 1-alkyl-3-methylimidazolium chloride ionic liquids. The salinity and hydrocarbon load of some marine environments may induce selective pressures which enhance the ability of microbes to grow in the presence of these liquid salts. The isolates obtained in this study generally showed a greater ability to grow in the presence of the selected ionic liquids compared to microorganisms described previously, with two marine-derived bacteria, Rhodococcus erythropolis and Brevibacterium sanguinis growing in concentrations exceeding 1 M 1-ethyl-3-methylimidazolium chloride. The ability of these bacteria to degrade the selected ionic liquids was assessed using High Performance Liquid Chromatography (HPLC), and three were shown to degrade the selected ionic liquids by up to 59% over a 63-day test period. These bacterial isolates represent excellent candidates for further potential applications in the bioremediation of ionic liquid-containing waste or following accidental environmental exposure. 相似文献
966.
Giovanni Luca Ciampaglia Prashant Shiralkar Luis M. Rocha Johan Bollen Filippo Menczer Alessandro Flammini 《PloS one》2015,10(6)
Traditional fact checking by expert journalists cannot keep up with the enormous volume of information that is now generated online. Computational fact checking may significantly enhance our ability to evaluate the veracity of dubious information. Here we show that the complexities of human fact checking can be approximated quite well by finding the shortest path between concept nodes under properly defined semantic proximity metrics on knowledge graphs. Framed as a network problem this approach is feasible with efficient computational techniques. We evaluate this approach by examining tens of thousands of claims related to history, entertainment, geography, and biographical information using a public knowledge graph extracted from Wikipedia. Statements independently known to be true consistently receive higher support via our method than do false ones. These findings represent a significant step toward scalable computational fact-checking methods that may one day mitigate the spread of harmful misinformation. 相似文献
967.
Celestino Sardu Michelangela Barbieri Maria Luisa Balestrieri Mario Siniscalchi Pasquale Paolisso Paolo Calabrò Fabio Minicucci Giuseppe Signoriello Michele Portoghese Pasquale Mone Davide D’Andrea Felice Gragnano Alessandro Bellis Ciro Mauro Giuseppe Paolisso Maria Rosaria Rizzo Raffaele Marfella 《Cardiovascular diabetology》2018,17(1):159
968.
Rupert A. Collins Alessandro G. Bifi Renildo R. de Oliveira Emanuell D. Ribeiro Nathan K. Lujan Lúcia H. Rapp Py-Daniel 《分类学与生物多样性》2018,16(6):538-550
The rapids-dwelling suckermouth catfish genus Pseudolithoxus was previously only known from the Guiana-Shield-draining Orinoco and Casiquiare river systems of Colombia and Venezuela, but new records have expanded this range considerably further into the Amazon basin of Brazil, and include occurrences from rivers draining the northern Brazilian Shield. These highly disjunct records are now placed in an evolutionary and phylogeographic context using a dated species tree constructed from mitochondrial (Cytb) and nuclear (RAG1) gene sequence data. Due to mito-nuclear discordance, we also delimit the putative species using statistical coalescent models and a range of additional metrics. We infer that at least two species of Pseudolithoxus are present in the Amazon basin: P. nicoi, previously only recorded from the río Casiquiare, but now also reported from the upper rio Negro, and a new species, which we describe herein from south-draining Guiana Shield and north-draining Brazilian Shield. Our data reject a simple model of Miocene vicariance in the group following uplift of the Uaupés Arch separating the Orinoco and Amazon systems, and instead suggest more complex dispersal scenarios through palaeo-connections in the Pliocene and also via the contemporary rio Negro and rio Madeira in the late Pleistocene.
www.zoobank.org/urn:lsid:zoobank.org:pub:46A6BEC1-1A1B-4244-80-A6-FD9CF8DA0384. 相似文献
969.
Alessandro Fisogni Marino Quaranta Francesca-Vittoria Grillenzoni Francesca Corvucci Natasha de Manincor Gherardo Bogo Laura Bortolotti Marta Galloni 《Arthropod-Plant Interactions》2018,12(2):191-200
Bees collect pollen as an important resource for offspring development while acting as pollen vectors for the plants visited. Foraging preferences of pollinators together with plant species availability shape the web of interactions at the local scale. In this study, we focused on the bee pollinator community of a population of the rare protected perennial herb Dictamnus albus, with the aim to characterise the pollen preferences and the foraging niche overlap among species through time. Bees were sampled during four consecutive years in a natural population of D. albus, throughout the blooming period of the plant species. We performed an analysis of insect pollen loads to investigate the interactions with the study species and the co-flowering plants in the area, and to evaluate the degree of foraging overlap among pollinators. Over the study years, all bee species showed a high fidelity to D. albus (60–80%), even if some taxa preferentially collected pollen from other flowering species. The foraging niche overlap in the pollinator community decreased together with an increased diversity of co-flowering plant species. The results obtained indicate that bees preferentially forage on D. albus in the studied area, but that co-flowering species contribute to complement their diet and likely reduce competition for foraging resources. It appears therefore important to maintain a high diversity of co-flowering plants to preserve the diversity in the studied pollinator community of D. albus. 相似文献
970.
Quantitative mass spectrometry enables to monitor the abundance of thousands of proteins across biological conditions. Currently, most data analysis approaches rely on the assumption that the majority of the observed proteins remain unchanged across compared samples. Thus, gross morphological differences between cell states, deriving from, e.g., differences in size or number of organelles, are often not taken into account. Here, we analyzed multiple published datasets and frequently observed that proteins associated with a particular cellular compartment collectively increase or decrease in their abundance between conditions tested. We show that such effects, arising from underlying morphological differences, can skew the outcome of differential expression analysis. We propose a method to detect and normalize morphological effects underlying proteomics data. We demonstrate the applicability of our method to different datasets and biological questions including the analysis of sub‐cellular proteomes in the context of Caenorhabditis elegans aging. Our method provides a complementary perspective to classical differential expression analysis and enables to uncouple overall abundance changes from stoichiometric variations within defined group of proteins. 相似文献