全文获取类型
收费全文 | 2101篇 |
免费 | 153篇 |
专业分类
2254篇 |
出版年
2023年 | 15篇 |
2022年 | 29篇 |
2021年 | 50篇 |
2020年 | 25篇 |
2019年 | 39篇 |
2018年 | 47篇 |
2017年 | 38篇 |
2016年 | 54篇 |
2015年 | 88篇 |
2014年 | 105篇 |
2013年 | 121篇 |
2012年 | 132篇 |
2011年 | 139篇 |
2010年 | 81篇 |
2009年 | 92篇 |
2008年 | 112篇 |
2007年 | 112篇 |
2006年 | 96篇 |
2005年 | 76篇 |
2004年 | 83篇 |
2003年 | 72篇 |
2002年 | 68篇 |
2001年 | 33篇 |
2000年 | 32篇 |
1999年 | 36篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 26篇 |
1989年 | 22篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 21篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1970年 | 7篇 |
排序方式: 共有2254条查询结果,搜索用时 15 毫秒
71.
Mireille Rack Sonia Valdivia Guido Sonnemann 《The International Journal of Life Cycle Assessment》2013,18(7):1413-1420
Purpose
The paper provides a late report from the United Nations Environment Program (UNEP)/Society of Environmental Toxicology and Chemistry (SETAC) Life Cycle Initiative workshop “Life Cycle Impact Assessment (LCIA)—where we are, trends, and next steps;” it embeds this report into recent development with regard to the envisaged development of global guidance on environmental life cycle impact assessment indicators and related methodologies.Methods
The document is the output of the UNEP/SETAC Life Cycle Initiative’s workshop on “Life Cycle Impact Assessment—where we are, trends, and next steps.” The presentations and discussions held during the workshop reviewed the first two phases of the Life Cycle Initiative and provided an overview of current LCIA activities being conducted by the Initiative, governments and academia, as well as corporate approaches. The outcomes of the workshop are reflected in light of the implementation of the strategy for Phase 3 of the Life Cycle Initiative.Results
The range of views provided during the workshop indicated different user needs, with regards to, amongst other things, the required complexity of the LCIA methodology, associated costs, and the selection of LCIA categories depending on environmental priorities. The workshop’s results signified a number of potential focus areas for Phase 3 of the Initiative, including capacity building efforts concerning LCIA in developing countries and emerging economies, the preparation of training materials on LCIA, the production of global guidance on LCIA, and the potential development of a broader sustainability indicators framework.Conclusions
These suggestions have been taken into account in the strategy for Phase 3 of the Life Cycle Initiative in two flagship projects, one on global capability development on life cycle approaches and the other on global guidance on environmental life cycle impact assessment indicators. In the context of the latter project, first activities are being organized and planned. Moreover, UNEP has included the recommendations in its Rio + 20 Voluntary Commitments: UNEP and SETAC through the UNEP/SETAC Life Cycle Initiative commit to facilitate improved access to good quality life cycle data and databases as well as expanded use of key environmental indicators that allows the measurement and monitoring of progress towards the environmental sustainability of selected product chains. 相似文献72.
Sonia Valdivia Cassia M. L. Ugaya Jutta Hildenbrand Marzia Traverso Bernard Mazijn Guido Sonnemann 《The International Journal of Life Cycle Assessment》2013,18(9):1673-1685
Purpose
To contribute to the upcoming United Nations Conference on Sustainable Development (Rio+20) in 2012 by introducing a life cycle sustainability assessment (LCSA) and showing how it can play a crucial role in moving towards sustainable consumption and production. The publication, titled Towards a Life Cycle Sustainability Assessment, and published by the UNEP/SETAC Life Cycle Initiative aims to show how three life cycle techniques—(environmental) LCA, S-LCA and LCC—can be combined as part of an over-arching LCSA.Methods
The method was demonstrated by evaluating the characteristics of each phase for each life cycle technique. In defining the goal and scope of an LCSA, for example, different aspects should be taken into account to establish the aim of the study as well as the functional unit, system boundaries, impact category and allocation. Then, the data to be collected for the life cycle sustainability inventory can be either in a unit process or on an organisational level. They can also be quantitative or qualitative. Life cycle sustainability impact assessment should consider the relevance of the impacts as well as the perspective of stakeholders. The interpretation should not add up the results, but rather evaluate them jointly. In order to clarify the approach, a case study is presented to evaluate three types of marble according to the proposed method.Results and discussion
The authors have identified that while LCSA is feasible, following areas need more development: data production and acquisition, methodological development, discussion about LCSA criteria (e.g. cutoff rules), definitions and formats of communication and dissemination of LCSA results and the expansion of research and applications combining (environmental) LCA, LCC and S-LCA. The authors also indicate that it is necessary to develop more examples and cases to improve user capacity to analyse the larger picture and therefore address the three dimensions or pillars of sustainability in a systematic way. Software and database providers are called for in order to facilitate user-friendly and accessible tools to promote LCSAs.Conclusions
The application demonstrated that, although methodological improvements are still needed, important steps towards an overarching sustainability assessment have been accomplished. LCSA is possible and should be pursued; however, more efforts should be made to improve the technique and facilitate the studies in order to contribute to a greener economy. 相似文献73.
Estimates of population size are critical for conservation and management, but accurate estimates are difficult to obtain for many species. Noninvasive genetic methods are increasingly used to estimate population size, particularly in elusive species such as large carnivores, which are difficult to count by most other methods. In most such studies, genotypes are treated simply as unique individual identifiers. Here, we develop a new estimator of population size based on pedigree reconstruction. The estimator accounts for individuals that were directly sampled, individuals that were not sampled but whose genotype could be inferred by pedigree reconstruction, and individuals that were not detected by either of these methods. Monte Carlo simulations show that the population estimate is unbiased and precise if sampling is of sufficient intensity and duration. Simulations also identified sampling conditions that can cause the method to overestimate or underestimate true population size; we present and discuss methods to correct these potential biases. The method detected 2–21% more individuals than were directly sampled across a broad range of simulated sampling schemes. Genotypes are more than unique identifiers, and the information about relationships in a set of genotypes can improve estimates of population size. 相似文献
74.
Parathyroidectomy Improves Survival In Patients with Severe Hyperparathyroidism: A Comparative Study
Patricia Taschner Goldenstein Rosilene Motta Elias Lilian Pires de Freitas do Carmo Fernanda Oliveira Coelho Luciene Pereira Magalh?es Gisele Lins Antunes Melani Ribeiro Custódio Fábio Luiz de Menezes Montenegro Silvia Maria Titan Vanda Jorgetti Rosa Maria Affonso Moysés 《PloS one》2013,8(8)
Background and objectives
Secondary hyperparathyroidism (SHPT) in CKD is associated with an increased risk for mortality, but definitive data showing that parathormone control decreases mortality is still lacking. This study aimed to compare the mortality of patients with severe SHPT submitted to parathyroidectomy(PTX) with those who did not have access to surgery.Methods
This is a retrospective study in a cohort of 251 CKD patients with severe SHPT who were referred to a CKD-MBD Center for PTX from 2005 until 2012.Results
Most of our patients had indication of PTX, but only 49% of them had access to this surgical procedure. After a mean follow-up of 23 months, 72 patients had died. Non-survivors were older; more often had diabetes, lower serum 25 vitamin D and mostly had not been submitted to surgery. The relative risk of death was lower in the PTX patients (0.428; 95% CI, 0.28 to 0.67; p<0.0001). After adjustments, mortality risk was dependent on age (1.04; 95% CI, 1.01 to 1.07; p = 0.002), 25 vitamin D (0.43; 95% CI, 0.24 to 0.81; p = 0.006) and no access to PTX (4.13; 95% CI, 2.16 to 7.88; p<0.0001). Results remained the same in a second model using the PTX date as the study start date for the PTX group.Conclusions
Our data confirms the benefit of PTX on mortality in patients with severe SHPT. The high mortality encountered in our population is significant and urges the need to better treat these patients. 相似文献75.
Kasia Weina Huizi Wu Nathalie Knappe Elias Orouji Daniel Novak Mathias Bernhardt Laura Hüser Lionel Larribère Viktor Umansky Christoffer Gebhardt Jochen Utikal 《Pigment cell & melanoma research》2016,29(4):453-458
The sry‐related high‐mobility box (SOX)‐2 protein has recently been proven to play a significant role in progression, metastasis, and clinical prognosis spanning several cancer types. Research on the role of SOX2 in melanoma is limited and currently little is known about the mechanistic function of this gene in this context. Here, we observed high expression of SOX2 in both human melanoma cell lines and primary melanomas in contrast to melanocytic nevi. This overexpression in melanoma can, in part, be explained by extra gene copy numbers of SOX2 in primary samples. Interestingly, we were able to induce SOX2 expression, mediated by SOX4, via TGF‐β1 stimulation in a time‐dependent manner. Moreover, the knockdown of SOX2 impaired TGF‐β‐induced invasiveness. This phenotype switch can be explained by SOX2‐mediated cross talk between TGF‐β and non‐canonical Wnt signaling. Thus, we propose that SOX2 is involved in the critical TGF‐β signaling pathway, which has been shown to correlate with melanoma aggressiveness and metastasis. In conclusion, we have identified a novel downstream factor of TGF‐β signaling in melanoma, which may have further implications in the clinic. 相似文献
76.
Brigitta Ine Van Tussenbroek Tania Valdivia‐Carrillo Irene Teresa Rodríguez‐Virgen Sylvia Nashieli Marisela Sanabria‐Alcaraz Karina Jiménez‐Durán Kor Jent Van Dijk Guadalupe Judith Marquez‐Guzmán 《Ecology and evolution》2016,6(15):5542-5556
The high prevalence of dioecy in marine angiosperms or seagrasses (>50% of all species) is thought to enforce cross‐fertilization. However, seagrasses are clonal plants, and they may still be subject to sibling‐mating or bi‐parental inbreeding if the genetic neighborhood is smaller than the size of the genets. We tested this by determining the genetic neighborhoods of the dioecious seagrass Thalassia testudinum at two sites (Back‐Reef and Mid‐Lagoon) in Puerto Morelos Reef Lagoon, Mexico, by measuring dispersal of pollen and seeds in situ, and by fine‐scale spatial autocorrelation analysis with eight polymorphic microsatellite DNA markers. Prevalence of inbreeding was verified by estimating pairwise kinship coefficients; and by analysing the genotypes of seedlings grown from seeds in mesocosms. Average dispersal of pollen was 0.3–1.6 m (max. 4.8 m) and of seeds was 0.3–0.4 m (max. 1.8 m), resulting in a neighborhood area of 7.4 m2 (range 3.4–11.4 m2) at Back‐Reef and 1.9 (range 1.87–1.92 m2) at Mid‐Lagoon. Neighborhood area (Na) derived from spatial autocorrelation was 0.1–20.5 m2 at Back‐Reef and 0.1–16.9 m2 at Mid‐Lagoon. Maximal extensions of the genets, in 19 × 30 m plots, were 19.2 m (median 7.5 m) and 10.8 m (median 4.8 m) at Back‐Reef and Mid‐Lagoon. There was no indication of deficit or excess of heterozygotes nor were coefficients of inbreeding (FIS) significant. The seedlings did not show statistically significant deficit of heterozygotes (except for 1 locus at Back‐Reef). Contrary to our expectations, we did not find evidence of bi‐parental inbreeding in this dioecious seagrass with large genets but small genetic neighborhoods. Proposed mechanisms to avoid bi‐parental inbreeding are possible selection against homozygotes during fecundation or ovule development. Additionally, the genets grew highly dispersed (aggregation index Ac was 0.09 and 0.10 for Back‐Reef and Mid‐Lagoon, respectively); such highly dispersed guerrilla‐like clonal growth form likely increases the probability of crossing between different potentially unrelated genets. 相似文献
77.
78.
79.
80.
Manuel J. Steinbauer Richard Field John‐Arvid Grytnes Panayiotis Trigas Claudine Ah‐Peng Fabio Attorre H. John B. Birks Paulo A. V. Borges Pedro Cardoso Chang‐Hung Chou Michele De Sanctis Miguel M. de Sequeira Maria C. Duarte Rui B. Elias José María Fernández‐Palacios Rosalina Gabriel Roy E. Gereau Rosemary G. Gillespie Josef Greimler David E. V. Harter Tsurng‐Juhn Huang Severin D. H. Irl Daniel Jeanmonod Anke Jentsch Alistair S. Jump Christoph Kueffer Sandra Nogué Rüdiger Otto Jonathan Price Maria M. Romeiras Dominique Strasberg Tod Stuessy Jens‐Christian Svenning Ole R. Vetaas Carl Beierkuhnlein 《Global Ecology and Biogeography》2016,25(9):1097-1107