全文获取类型
收费全文 | 5027篇 |
免费 | 344篇 |
国内免费 | 2篇 |
专业分类
5373篇 |
出版年
2023年 | 25篇 |
2022年 | 59篇 |
2021年 | 153篇 |
2020年 | 90篇 |
2019年 | 95篇 |
2018年 | 149篇 |
2017年 | 116篇 |
2016年 | 154篇 |
2015年 | 226篇 |
2014年 | 289篇 |
2013年 | 358篇 |
2012年 | 414篇 |
2011年 | 433篇 |
2010年 | 253篇 |
2009年 | 234篇 |
2008年 | 284篇 |
2007年 | 328篇 |
2006年 | 301篇 |
2005年 | 253篇 |
2004年 | 232篇 |
2003年 | 225篇 |
2002年 | 192篇 |
2001年 | 42篇 |
2000年 | 32篇 |
1999年 | 32篇 |
1998年 | 39篇 |
1997年 | 27篇 |
1996年 | 16篇 |
1995年 | 35篇 |
1994年 | 25篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1972年 | 4篇 |
1970年 | 7篇 |
排序方式: 共有5373条查询结果,搜索用时 0 毫秒
71.
72.
Amin Soltangheisi Paul J. A. Withers Paulo Sergio Pavinato Maurício Roberto Cherubin Raffaella Rossetto Janaina Braga Do Carmo Gustavo Casoni da Rocha Luiz Antonio Martinelli 《Global Change Biology Bioenergy》2019,11(12):1444-1455
Phosphorus (P) use in global food and bioenergy production needs to become more efficient and sustainable to reduce environmental impacts and conserve a finite and critical resource (Carpenter & Bennett, Environmental Research Letters, 2011, 6, 014009; Springmann et al., Nature, 2018, 562, 519). Sugarcane is one crop with a large P footprint because production is centered on P‐fixing soils with low P availability (Roy et al., Nature Plants, 2016, 2, 16043; Withers et al., Scientific Reports, 2018, 8, 2537). As global demand for processed sugar and bioethanol continues to increase, we advocate that improving P efficiency could become a key sustainability goal for the sugarcane industry. Here, we applied the 5R global P stewardship framework (Withers et al., Ambio, 2015, 44, 193) to identify more sustainable options to manage P in Brazilian sugarcane production. We show that current inputs of P fertilizer to the current crop area could be reduced by over 305 Gg, or 63%, over the next three decades by reducing unnecessary P fertilizer use, better utilization of recyclable bioresources and redesigning recommendation systems. Adoption of these 5R options would save the sugarcane industry in Brazil 528 US$ million and help safeguard global food and energy security. 相似文献
73.
Susan C. Fitzer Rona A. R. McGill Sergio Torres Gabarda Brian Hughes Michael Dove Wayne O'Connor Maria Byrne 《Global Change Biology》2019,25(12):4105-4115
Commercial shellfish aquaculture is vulnerable to the impacts of ocean acidification driven by increasing carbon dioxide (CO2) absorption by the ocean as well as to coastal acidification driven by land run off and rising sea level. These drivers of environmental acidification have deleterious effects on biomineralization. We investigated shell biomineralization of selectively bred and wild‐type families of the Sydney rock oyster Saccostrea glomerata in a study of oysters being farmed in estuaries at aquaculture leases differing in environmental acidification. The contrasting estuarine pH regimes enabled us to determine the mechanisms of shell growth and the vulnerability of this species to contemporary environmental acidification. Determination of the source of carbon, the mechanism of carbon uptake and use of carbon in biomineral formation are key to understanding the vulnerability of shellfish aquaculture to contemporary and future environmental acidification. We, therefore, characterized the crystallography and carbon uptake in the shells of S. glomerata, resident in habitats subjected to coastal acidification, using high‐resolution electron backscatter diffraction and carbon isotope analyses (as δ13C). We show that oyster families selectively bred for fast growth and families selected for disease resistance can alter their mechanisms of calcite crystal biomineralization, promoting resilience to acidification. The responses of S. glomerata to acidification in their estuarine habitat provide key insights into mechanisms of mollusc shell growth under future climate change conditions. Importantly, we show that selective breeding in oysters is likely to be an important global mitigation strategy for sustainable shellfish aquaculture to withstand future climate‐driven change to habitat acidification. 相似文献
74.
Vilizzi Lorenzo Copp Gordon H. Adamovich Boris Almeida David Chan Joleen Davison Phil I. Dembski Samuel Ekmekçi F. Güler Ferincz Árpád Forneck Sandra C. Hill Jeffrey E. Kim Jeong-Eun Koutsikos Nicholas Leuven Rob S. E. W. Luna Sergio A. Magalhães Filomena Marr Sean M. Mendoza Roberto Mourão Carlos F. Neal J. Wesley Onikura Norio Perdikaris Costas Piria Marina Poulet Nicolas Puntila Riikka Range Inês L. Simonović Predrag Ribeiro Filipe Tarkan Ali Serhan Troca Débora F. A. Vardakas Leonidas Verreycken Hugo Vintsek Lizaveta Weyl Olaf L. F. Yeo Darren C. J. Zeng Yiwen 《Reviews in Fish Biology and Fisheries》2019,29(3):529-568
Reviews in Fish Biology and Fisheries - The freshwater Fish Invasiveness Screening Kit (FISK) has been applied in 35 risk assessment areas in 45 countries across the six inhabited continents (11... 相似文献
75.
Sara Martinez Maria del Mar Delgado Ruben Martinez Marin Sergio Alvarez 《Journal of Industrial Ecology》2019,23(4):879-892
The implementation of global sustainability has gained worldwide attention in recent years. The Organization Environmental Footprint, which encompasses 14 impact categories, is a multicriteria measure of the environmental performance of goods and services provided by an organization from a life cycle perspective. In this article, the focus is on quantifying the Organization Environmental Footprint of a construction company in Spain. By applying an environmentally extended input‐output approach, its total footprint and impacts along the supply chain from two consecutive years were calculated. The results show that the environmental impacts from the second year of implementation were significantly higher than those from the first year. The impact category climate change was found to have experienced the greatest increase from one year to the other, with a 31% increase. This work provides an overview of 14 environmental impact categories of the company assessed, as well as recommendations for the implementation of this indicator in companies and public procurement. This approach could pave the way to shape organizations’ action plans and meet the European environmental challenges. 相似文献
76.
Enrico Baria Simone Morselli Suresh Anand Riccardo Fantechi Gabriella Nesi Mauro Gacci Marco Carini Sergio Serni Riccardo Cicchi Francesco S. Pavone 《Journal of biophotonics》2019,12(11)
Urothelial carcinoma (UC) is the most common bladder tumour. Proper treatment requires tumour resection for diagnosing its grade (aggressiveness) and stage (invasiveness). White‐light cystoscopy and histopathological examination are the gold standard procedures for clinical and histopathological diagnostics, respectively. However, cystoscopy is limited in terms of specificity, histology requires long tissue processing, both procedures rely on operator's experience. Multimodal optical spectroscopy can provide a powerful tool for detecting, staging and grading bladder tumours in a fast, reliable and label‐free modality. In this study, we collected fluorescence, Raman and reflectance spectra from 50 biopsies obtained from 32 patients undergoing transurethral resection of bladder tumour using a multimodal fibre‐probe. Principal component analysis allowed distinguishing normal from pathological tissues, as well as discriminating tumour stages and grades. Each individual spectroscopic technique provided high specificity and sensitivity in classifying all tissues; however, a multimodal approach resulted in a considerable increase in diagnostic accuracy (≥95%), which is of paramount importance for tumour grading and staging. The presented method offers the potential for being applied in cystoscopy and for providing an automated diagnosis of UC at the clinical level, with an improvement with respect to current state‐of‐the‐art procedures. 相似文献
77.
Carbohydrate-based vinyl selenides of the arabino, ribo and 2-deoxy-ribo configuration have been prepared by Wittig-type reactions of various protected furanoses. Moderate yields were always obtained due to the nature and reactivity of both carbohydrate lactols and selenium-based olefinating reagents under the conditions tested. A detailed study of the olefination reaction and the behaviour of vinyl selenides towards the electrophilic-induced cyclization will be discussed. 相似文献
78.
79.
Sergio Branciamore Sacha Barion Enzo Gallori Massimo Di Giulio 《Annals of microbiology》2007,57(4):645-649
We have conducted a check by substituting, in a previous phylogenetic analysis, an outgroup of sequences from hyperthermophilic archaea with another of mesophilic sequences of archaea. This should remove a possible compositional bias which might be responsible for the deep position of Thermotogales and Aquificales in the Bacteria domain, as observed in previous analyses. This check brought to light a weak compositional bias which does not seem, however, to entirely explain the deep position occupied by hyperthermophilic bacteria. The present analysis also seems to show that Planctomycetes are one of the deepest lines of divergence in the Bacteria domain, although they do not seem to be the very deepest. 相似文献
80.