全文获取类型
收费全文 | 2395篇 |
免费 | 217篇 |
国内免费 | 1篇 |
出版年
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 25篇 |
2019年 | 41篇 |
2018年 | 33篇 |
2017年 | 36篇 |
2016年 | 80篇 |
2015年 | 123篇 |
2014年 | 137篇 |
2013年 | 151篇 |
2012年 | 208篇 |
2011年 | 153篇 |
2010年 | 114篇 |
2009年 | 84篇 |
2008年 | 127篇 |
2007年 | 135篇 |
2006年 | 137篇 |
2005年 | 126篇 |
2004年 | 114篇 |
2003年 | 117篇 |
2002年 | 131篇 |
2001年 | 29篇 |
2000年 | 20篇 |
1999年 | 25篇 |
1998年 | 34篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 17篇 |
1975年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有2613条查询结果,搜索用时 15 毫秒
101.
Katriina Alhola Sven‐ Olof Ryding Hanna Salmenper Niels Juul Busch 《Journal of Industrial Ecology》2019,23(1):96-109
The objective of a circular economy (CE) is to maintain the value of products, materials, and resources in the economy by closing material loops and minimizing waste generation. In recent years, the role of public procurement has been recognized as an important, but as yet not fully exploited, opportunity by cities and municipalities in their transition toward circular societies. This study analyzed public procurement opportunities to promote CE. Different approaches and examples of circular public procurement were identified using case studies. In addition, opportunities to promote CE through sustainable and green public procurement policy were identified analyzing predefined sustainable or green public procurement criteria. The study concludes that public procurement can promote CE and related business models by setting criteria and requirements for the extension of product life spans, efficiency and/or intensity of use, and efficient cycling of biological or technical materials, as well as for the securing of clean and nonrisky cycles. Circular procurement can occur through the procurement of better‐quality products in circular terms, the procurement of new circular products, the use of business concepts that support the CE, and investments in circular ecosystems. Several sectors and product groups were identified as having potential for circular procurement, such as construction, waste, and wastewater management, transportation, food, and catering, furniture, and textiles. The study also suggests that the use of certain tools, such as performance‐based procurement, life cycle approach, and life cycle costing, as well as criteria concerning reuse and recycling of materials, could promote circular procurement. Market dialogue and cooperation between procurers and actors in the supply chains are important for the future development of circular procurement. 相似文献
102.
Jonathan Wright Geir H. Bolstad Yimen G. Araya‐Ajoy Niels J. Dingemanse 《Biological reviews of the Cambridge Philosophical Society》2019,94(1):230-247
We present a novel perspective on life‐history evolution that combines recent theoretical advances in fluctuating density‐dependent selection with the notion of pace‐of‐life syndromes (POLSs) in behavioural ecology. These ideas posit phenotypic co‐variation in life‐history, physiological, morphological and behavioural traits as a continuum from the highly fecund, short‐lived, bold, aggressive and highly dispersive ‘fast’ types at one end of the POLS to the less fecund, long‐lived, cautious, shy, plastic and socially responsive ‘slow’ types at the other. We propose that such variation in life histories and the associated individual differences in behaviour can be explained through their eco‐evolutionary dynamics with population density – a single and ubiquitous selective factor that is present in all biological systems. Contrasting regimes of environmental stochasticity are expected to affect population density in time and space and create differing patterns of fluctuating density‐dependent selection, which generates variation in fast versus slow life histories within and among populations. We therefore predict that a major axis of phenotypic co‐variation in life‐history, physiological, morphological and behavioural traits (i.e. the POLS) should align with these stochastic fluctuations in the multivariate fitness landscape created by variation in density‐dependent selection. Phenotypic plasticity and/or genetic (co‐)variation oriented along this major POLS axis are thus expected to facilitate rapid and adaptively integrated changes in various aspects of life histories within and among populations and/or species. The fluctuating density‐dependent selection POLS framework presented here therefore provides a series of clear testable predictions, the investigation of which should further our fundamental understanding of life‐history evolution and thus our ability to predict natural population dynamics. 相似文献
103.
Mycoplasma alkalescens is an arginine-metabolizing mycoplasma, which has been found in association with mastitis and arthritis in cattle. Routine
bacteriological examination of 17 bronchoalveolar lavage samples from calves with pneumonia in a single herd in Denmark, identified
M. alkalescens in eight samples. The organism was found as a sole bacterilogical findings in five of the samples as well as in combination
with Mannheimia haemolytica, Haemophilus somni and Salmonella Dublin. This is the first report of isolation of M. alkalescens in Denmark. 相似文献
104.
105.
In proteomic analysis of complex samples at the peptide level (termed shotgun proteomics), an effective prefractionation is crucial to decrease the complexity of the peptide mixture for further analysis. In this perspective, the high-resolving power of the IEF fractionation step is a determining parameter, in order to obtain well-defined fractions and correct information on peptide isoelectric points, to provide an additional filter for protein identification. Here, we explore the resolving power of OFFGEL IEF as a prefractionation tool to separate peptides. By modeling the peak width evolution versus the peptide charge gradient at pI, we demonstrate that for the three proteomes considered in silico (Deinococcus radiodurans, Saccharomyces cerevisiae, and Homo sapiens), 90% of the peptides should be correctly focused and recovered in two wells at most. This result strongly suggests OFFGEL to be used as a powerful fractionation tool in shotgun proteomics. The influence of the height and shape of the compartments is also investigated, to give the optimal cell dimensions for an enhanced peptide recovery and fast focusing time. 相似文献
106.
Valeria Agamennone Joeri van Straalen Abraham Brouwer Tjalf E. de Boer Paul J. Hensbergen Niels Zaagman Martin Braster Nico M. van Straalen Dick Roelofs Thierry K.S. Janssens 《Entomologia Experimentalis et Applicata》2019,167(3):269-285
Antibiotic resistance necessitates the search for new bioactive compounds with novel mechanisms of action. Natural products derived from bacteria and fungi are widely used in the field of medicine and new environments can be explored as sources of antimicrobials. Bacteria associated with springtails have shown high inhibitory activity against pathogens. Here, we characterized a bacterial strain with high potential for antimicrobial activity, isolated from the gut of the springtail Folsomia candida Willem (Collembola: Isotomidae). The strain was characterized using the ‘analytical profile index’ and the ‘minimal inhibitory concentration’ assay to test for antibiotic resistance. Agar overlay and agar disk diffusion assays were used to test the inhibitory activity of the strain and its extract against a variety of pathogens, and reporter assays were used to investigate the mode of action. High‐performance liquid chromatography was used to analyze and fractionate the extract of bacterial culture, followed by additional assays on the fractions. The genome of the strain was screened for presence of antibiotic resistance genes and secondary metabolite gene clusters. The isolate was identified as Bacillus toyonensis Jiménez et al., but it displayed differences in metabolic profile when compared to the type species. The isolate was highly resistant to penicillin and inhibited the growth of a variety of pathogenic microorganisms. Genome analysis revealed an enrichment of resistance genes for β‐lactam antibiotics compared to the type isolate. Also, secondary metabolite clusters involved in the production of siderophores, bacteriocins, and nonribosomal peptide synthetases were identified. In conclusion, a unique Bacillus strain was isolated from the gut of F. candida, for which we provide evidence of inhibitory activity against an array of pathogens. This, coupled with high resistance to penicillin as substantiated by the presence of resistance genes, points to the potential of B. toyonensis VU‐DES13 to provide a new source of antimicrobial compounds. 相似文献
107.
Jacob C. Douma Jorad de Vries Erik H. Poelman Marcel Dicke Niels P.R. Anten Jochem B. Evers 《Plant, cell & environment》2019,42(3):1065-1077
Plants balance the allocation of resources between growth and defence to optimize fitness in a competitive environment. Perception of neighbour‐detection cues, such as a low ratio of red to far‐red (R:FR) radiation, activates a suite of shade‐avoidance responses that include stem elongation and upward leaf movement, whilst simultaneously downregulating defence. This downregulation is hypothesized to benefit the plant either by mediating the growth‐defence balance in favour of growth in high plant densities or, alternatively, by mediating defence of individual leaves such that those most photosynthetically productive are best protected. To test these hypotheses, we used a 3D functional–structural plant model of Brassica nigra that mechanistically simulates the interactions between plant architecture, herbivory, and the light environment. Our results show that plant‐level defence expression is a strong determinant of plant fitness and that leaf‐level defence mediation by R:FR can provide a fitness benefit in high densities. However, optimal plant‐level defence expression does not decrease monotonically with plant density, indicating that R:FR mediation of defence alone is not enough to optimize defence between densities. Therefore, assessing the ecological significance of R:FR‐mediated defence is paramount to better understand the evolution of this physiological linkage and its implications for crop breeding. 相似文献
108.
Niels W. P. Brev Hendry Vis Bram Houben Andr Breukelaar Marie‐Laure Acolas 《Zeitschrift fur angewandte Ichthyologie》2019,35(1):61-68
Working towards a future Rhine Sturgeon Action Plan the outmigration pathways of stocked juvenile European sturgeon (Acipenser sturio L., 1758) were studied in the River Rhine in 2012 and 2015 using the NEDAP Trail system. A total of 87 sturgeon of 3 to 5 years old (n = 43 in 2012, n = 44 in 2015) were implanted with transponders and released in May and June in the river Rhine at the Dutch‐German border, approximately 160 km from the sea. In total three sturgeons (3%) were found dead on river banks within seven days after the release. Based upon their wounds these sturgeons were likely hit by ship‐propellers. Tracking results were obtained from 57 (66%) of the sturgeons, of which 39 (45%) indicated movement into the Port of Rotterdam. Here the sturgeons remained for an average of two weeks, which suggests they spent time to acclimatize to higher salinities before entering the North Sea. Of the 45 (52%) sturgeons that were confirmed to have entered the North Sea, ten (22%) were recaptured (mainly by shrimpers and gill‐nets) close to the Dutch coastline; nine were alive and were released. From the results we obtained the preferred outmigration pathways, movement speeds and an indication of impacting factors (i.e. ship propellers and bycatch). Bycatches provided also localisations information in the coastal area. A next step to complete this work would be to assess habitat selection in freshwater and downstream migration of young of the year (YOY sturgeons) in the Lower Rhine. 相似文献
109.
Katja Irob Niels Blaum Selina Baldauf Leon Kerger Ben Strohbach Angelina Kanduvarisa Dirk Lohmann Britta Tietjen 《Ecology and evolution》2022,12(3)
Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle‐dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land‐use strategies on a Namibian savanna: grazer‐ versus browser‐dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land‐use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing‐dominated land‐use strategies, land‐use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services. 相似文献
110.
Anne Lrke Spangmose Niels Skipper Sine Knorr Tina Wullum Gundersen Rikke Beck Jensen Peter Damm Erik Lykke Mortensen Anja Pinborg Jannet Svensson Tine Clausen 《PLoS medicine》2022,19(4)
BackgroundConflicting results have been reported concerning possible adverse effects on the cognitive function of offspring of mothers with type 1 diabetes (O-mT1D). Previous studies have included offspring of parents from the background population (O-BP), but not offspring of fathers with type 1 diabetes (O-fT1D) as the unexposed reference group.Methods and findingsThis is a population-based retrospective cohort study from 2010 to 2016. Nationally standardized school test scores (range, 1 to 100) were obtained for public school grades 2, 3, 4, 6, and 8 in O-mT1D and compared with those in O-fT1D and O-BP. Of the 622,073 included children, 2,144 were O-mT1D, and 3,474 were O-fT1D. Multiple linear regression models were used to compare outcomes, including the covariates offspring with type 1 diabetes, parity, number of siblings, offspring sex, smoking during pregnancy, parental age, and socioeconomic factors. Mean test scores were 54.2 (standard deviation, SD 24.8) in O-mT1D, 54.4 (SD 24.8) in O-fT1D, and 56.4 (SD 24.7) in O-BP. In adjusted analyses, the mean differences in test scores were −1.59 (95% CI −2.48 to −0.71, p < 0.001) between O-mT1D and O-BP and −0.78 (95% CI −1.48 to −0.08, p = 0.03) between O-fT1D and O-BP. No significant difference in the adjusted mean test scores was found between O-mT1D and O-fT1D (p = 0.16). The study’s limitation was no access to measures of glycemic control during pregnancy.ConclusionsO-mT1D achieved lower test scores than O-BP but similar test scores compared with O-fT1D. Glycemic control during pregnancy is essential to prevent various adverse pregnancy outcomes in women with type 1 diabetes. However, the present study reduces previous concerns regarding adverse effects of in utero hyperglycemia on offspring cognitive function.Anne Lærke Spangmose and colleagues examine the association between school performance and exposure to maternal or paternal type 1 diabetes in utero in Denmark. 相似文献