全文获取类型
收费全文 | 5532篇 |
免费 | 215篇 |
国内免费 | 1篇 |
出版年
2023年 | 18篇 |
2022年 | 24篇 |
2021年 | 54篇 |
2020年 | 24篇 |
2019年 | 50篇 |
2018年 | 100篇 |
2017年 | 89篇 |
2016年 | 125篇 |
2015年 | 109篇 |
2014年 | 140篇 |
2013年 | 237篇 |
2012年 | 485篇 |
2011年 | 680篇 |
2010年 | 301篇 |
2009年 | 94篇 |
2008年 | 461篇 |
2007年 | 426篇 |
2006年 | 379篇 |
2005年 | 333篇 |
2004年 | 257篇 |
2003年 | 254篇 |
2002年 | 192篇 |
2001年 | 72篇 |
2000年 | 149篇 |
1999年 | 83篇 |
1998年 | 51篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1987年 | 20篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1982年 | 18篇 |
1980年 | 19篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1974年 | 18篇 |
1973年 | 12篇 |
1971年 | 10篇 |
1970年 | 12篇 |
1967年 | 9篇 |
排序方式: 共有5748条查询结果,搜索用时 15 毫秒
61.
62.
Alena J. Raymond James R. Tipton Alissa Kendall Jason T. DeJong 《Journal of Industrial Ecology》2020,24(3):485-499
Life cycle assessment (LCA) has only had limited application in the geotechnical engineering discipline, though it has been widely applied to civil engineering systems such as pavements and roadways. A review of previous geotechnical LCAs showed that most studies have tracked a small set of impact categories, such as energy and global warming potential. Accordingly, currently reported environmental indicators may not effectively or fully capture important environmental impacts and tradeoffs associated with geotechnical systems, including those associated with land and soil resources. This research reviewed previous studies, methods, and models for assessment of land use and soil‐related impacts to understand their applicability to geotechnical LCA. The results of this review show that critical gaps remain in current knowledge and practice. In particular, further development or refinement of environmental indicators, impact categories, and cause–effect pathways is needed as they pertain to geotechnical applications—specifically those related to soil quality, soil functions, and the ecosystem services soils provide. In addition, many existing methods emerge from research on land use and land use change related to other disciplines (e.g., agriculture). For applicability to geotechnical projects, the resolution of many of these methods and resulting indicators need to be downscaled from the landscape/macro scale to the project scale. In the near term, practitioners of geotechnical LCA should begin tracking changes to soil properties and report impacts to land and soil resources qualitatively. 相似文献
63.
Nešić Andrijana Čavić Milena Popović Milica Gavrović-Jankulović Marija 《Molecular biology reports》2021,48(5):4065-4072
Molecular Biology Reports - Actinidin (Act d 1), a highly abundant cysteine protease from kiwifruit, is one of the major contributors to the development of kiwifruit allergy. Many studies have... 相似文献
64.
Alena Bartukov Arinawa Liz Filartiga Tom Herben Jianqiang Qian Jitka Klimeov 《Annals of botany》2021,127(7):931
Background and AimsRoot sprouting (RS), i.e. the ability to form adventitious buds on roots, is an important form of clonal growth in a number of species, and serves as both a survival strategy and a means of spatial expansion, particularly in plants growing in severely and recurrently disturbed habitats. Occurrence and/or success of plants in severely and recurrently disturbed habitats are determined by two components, namely the ability to produce adventitious buds on roots and the vigour of their production. As mechanisms behind different magnitudes of RS remain unclear, our study investigates: (1) whether the presence or absence of specific tissues in roots can promote or limit RS; and (2) whether there is some relationship between RS ability, RS vigour and species niche.MethodsWe studied RS ability together with RS vigour in 182 Central European herbaceous species under controlled experimental conditions. We used phylogenetic logistic regressions to model the presence of RS, RS vigour, the relationship between RS and anatomical traits and the relationship between RS and parameters of species niches.Key ResultsA quarter of herbs examined were able to produce adventitious buds on roots. They were characterized by their preference for open dry habitats, the presence of secondary root thickening and the occurrence of sclerified cortical cells in roots. Root sprouting vigour was not associated with any specific anatomical pattern, but was correlated with the environmental niches of different species, indicating that preferred disturbed and dry habitats might represent a selection pressure for more vigorous root sprouters than undisturbed and wet habitats.ConclusionsOur study shows that sprouting from roots is quite common in temperate dicotyledonous herbs. Two components of RS – ability and vigour – should be considered separately in future studies. We would also like to focus more attention on RS in herbs from other regions as well as on external forces and internal mechanisms regulating evolution and the functions of RS in both disturbed and undisturbed habitats. 相似文献
65.
Matić Ivana Z. Ergün Sercan Đorđić Crnogorac Marija Misir Sema Aliyazicioğlu Yüksel Damjanović Ana Džudžević-Čančar Hurija Stanojković Tatjana Konanç Kalbiye Petrović Nina 《Cytotechnology》2021,73(3):373-389
Cytotechnology - Six extracts were obtained from plant species Hypericum perforatum L., collected at Samsun in Turkey. The aim of this study was to examine the mechanisms of the anticancer activity... 相似文献
66.
Alexandru Paraschiv Thibaut J. Lagny Christian Vanhille Campos Evelyne Coudrier Patricia Bassereau Anđela Šarić 《Biophysical journal》2021,120(4):598-606
The cell membrane is an inhomogeneous system composed of phospholipids, sterols, carbohydrates, and proteins that can be directly attached to underlying cytoskeleton. The protein linkers between the membrane and the cytoskeleton are believed to have a profound effect on the mechanical properties of the cell membrane and its ability to reshape. Here, we investigate the role of membrane-cortex linkers on the extrusion of membrane tubes using computer simulations and experiments. In simulations, we find that the force for tube extrusion has a nonlinear dependence on the density of membrane-cortex attachments: at a range of low and intermediate linker densities, the force is not significantly influenced by the presence of the membrane-cortex attachments and resembles that of the bare membrane. For large concentrations of linkers, however, the force substantially increases compared with the bare membrane. In both cases, the linkers provided membrane tubes with increased stability against coalescence. We then pulled tubes from HEK cells using optical tweezers for varying expression levels of the membrane-cortex attachment protein Ezrin. In line with simulations, we observed that overexpression of Ezrin led to an increased extrusion force, while Ezrin depletion had a negligible effect on the force. Our results shed light on the importance of local protein rearrangements for membrane reshaping at nanoscopic scales. 相似文献
67.
Senka Vidović Alena Tomšik Jelena Vladić Stela Jokić Krunoslav Aladić Kristian Pastor Igor Jerković 《化学与生物多样性》2021,18(4):e2100058
The aim of this study was to extract Allium ursinum L. for the first time by supercritical carbon dioxide (SC−CO2) as green sustainable method. The impact of temperature in the range from 40 to 60 °C and pressure between 150 and 400 bar on the quality of the obtained extracts and efficiency of the extraction was investigated. The highest extraction yield (3.43 %) was achieved by applying the extraction conditions of 400 bar and 60 °C. The analysis of the extracts was performed by gas chromatography and mass spectrometry (GC/MS). The most dominant sulfur-containing constituent of the extracts was allyl methyl trisulfide with the highest abundance at 350 bar and 50 °C. In addition, the presence of other pharmacologically potent sulfur compounds was recorded including S-methyl methanethiosulfinate, diallyl trisulfide, S-methyl methylthiosulfonate, and dimethyl trisulfide. Multivariate data analysis tool was utilized to investigate distributions of the identified compounds among the extracts obtained under various extraction conditions and yields. It was determined that the SC−CO2 extraction can by efficiently used for A. ursinum. 相似文献
68.
Abstract The present study examined a sub-Mediterranean pastoral system in the central Apennines (Italy) with a long history of grazing, where winter cold stress is alternated with summer drought stress. The research goals were to ascertain whether different floristic structures correspond to different stress conditions (xeric and semimesic), and whether peculiar functional plant traits (such as avoidance and tolerance mechanisms) respond to stress/disturbance intensities, and understand how vegetation reacts to changeable livestock pressure (through floristic and plant trait variations). Cluster analysis indicated that separate communities develop under different stress intensities. Other analyses highlighted how avoidance strategies predominate within the pastoral system. Observations of grazed and ungrazed patches conducted in 10-m transects revealed spiny cushion formation in semimesic grassland, where a brief period of overgrazing occurs in late summer, causing variations in plant community structure. All these results confirm the importance of historical grazing and current land use, showing how small disturbances and stress variations cause ecosystem responses. Best practices for management were identified. In xeric conditions, it is advisable that the intensity of disturbance be lessened, while in semimesic grassland overgrazing should be forbidden during the dry period, because it could facilitate the development of spiny patches, and subsequent spread of Brachypodium rupestre. 相似文献
69.
Abstract In the present study, an additional combination of end‐points was applied on the natural populations of the common plantain, previously estimated using morphometric assays. Here, besides measuring developmental instability (DI), by determining the level of fluctuating asymmetry (FA) and the total amount of phenotypic variability (PV), we tried to distinguish the three natural populations under contrasting environmental conditions using the morphological data. Results obtained using both FA indices were the same; higher asymmetry levels in the reference than in the polluted environments were detected for leaf width, vein distances within a leaf and lobe length. The one‐way analysis of variance results revealed that there were significant differences in PV values among populations analysed for each character. When all leaf traits were considered together, the PV median value was significantly higher in Crni Lug leaves compared with leaves from other sites. The multivariate analysis of variance results revealed the significant effect of environment on both FA4 and PV values. The component scores of first factor (PC1) were significantly different between the Karaburma and Crni Lug populations. Besides, component scores of both PC1 and PC2 were significantly different between the Zemun and Crni Lug samples. The stepwise discriminant functional analysis results allowed us to identify a set of four variables, with a sufficient discriminating ability (75%). 相似文献
70.
The study is based on four leaf parameters: leaf width (LW), lobe length (LL), leaf size (LS) and leaf shape which is calculated as LW to leaf length (LW/LL) ratio. Under different environmental conditions, LL is an isometric character, LW shows positive allometry, whereas LW/LL shows negative allometry. Regression analysis results indicated that there is no significant difference either in slopes or in regression coefficients between investigated sites. Thus, in this study, we found that allometric relationships between leaf parameters and LS are character specific and that they tended not to differ significantly between Tilia cordata Mill. outer leaves exposed to different environmental conditions. Also, there are no significant interpopulation differences for both principal component PC1 and PC2 scores. The stepwise discriminant functional analysis results allowed us to identify a set of two leaf parameters (LS and LL) with a moderate discriminating ability (59.8%). T. cordata outer leaves are significantly larger and broader in the reference area (R-leaves) than leaves from polluted (P-leaves) site. The data also indicated that there is a relatively larger petiole size in R-leaves than in P-leaves. We found that in P-leaves, LW increased faster with increasing LS than in R-leaves. 相似文献