全文获取类型
收费全文 | 10703篇 |
免费 | 969篇 |
国内免费 | 1165篇 |
出版年
2024年 | 25篇 |
2023年 | 121篇 |
2022年 | 313篇 |
2021年 | 470篇 |
2020年 | 377篇 |
2019年 | 455篇 |
2018年 | 406篇 |
2017年 | 330篇 |
2016年 | 447篇 |
2015年 | 622篇 |
2014年 | 814篇 |
2013年 | 803篇 |
2012年 | 972篇 |
2011年 | 881篇 |
2010年 | 569篇 |
2009年 | 544篇 |
2008年 | 658篇 |
2007年 | 547篇 |
2006年 | 510篇 |
2005年 | 424篇 |
2004年 | 394篇 |
2003年 | 368篇 |
2002年 | 341篇 |
2001年 | 161篇 |
2000年 | 160篇 |
1999年 | 150篇 |
1998年 | 130篇 |
1997年 | 118篇 |
1996年 | 85篇 |
1995年 | 77篇 |
1994年 | 70篇 |
1993年 | 48篇 |
1992年 | 74篇 |
1991年 | 52篇 |
1990年 | 43篇 |
1989年 | 43篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 14篇 |
1985年 | 25篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1970年 | 7篇 |
1968年 | 11篇 |
1967年 | 6篇 |
1966年 | 7篇 |
1965年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Plant and Soil - To investigate the effects of polystyrene microplastics (PS-beads) on the soil properties, photosynthesis of Flowering Chinese cabbage, the rhizosphere microbial community and... 相似文献
3.
Jianhua Zhang Mei Liu Hongjian Jin Liandong Deng Jinfeng Xing Anjie Dong 《AAPS PharmSciTech》2010,11(2):894-903
Lactate esters are widely used as food additives, perfume materials, medicine additives, and personal care products. The objective
of this work was to investigate the effect of a series of lactate esters as penetration enhancers on the in vitro skin permeation of four drugs with different physicochemical properties, including ibuprofen, salicylic acid, dexamethasone
and 5-fluorouracil. The saturated donor solutions of the evaluated drugs in propylene glycol were used in order to keep a
constant driving force with maximum thermodynamic activity. The permeability coefficient (K
p), skin concentration of drugs (SC), and lag time (T), as well as the enhancement ratios for K
p and SC were recorded. All results indicated that lactate esters can exert a significant influence on the transdermal delivery
of the model drugs and there is a structure-activity relationship between the tested lactate esters and their enhancement
effects. The results also suggested that the lactate esters with the chain length of fatty alcohol moieties of 10–12 are more
effective enhancers. Furthermore, the enhancement effect of lactate esters increases with a decrease of the drug lipophilicity,
which suggests that they may be more efficient at enhancing the penetration of hydrophilic drugs than lipophilic drugs. The
influence of the concentration of lactate esters was evaluated and the optimal concentration is in the range of 5∼10 wt.%.
In sum, lactate esters as a penetration enhancer for some drugs are of interest for transdermal administration when the safety
of penetration enhancers is a prime consideration. 相似文献
4.
An ecosystem service is a benefit derived by humanity that can be traced back to an ecological process. Although ecosystem services related to surface water have been thoroughly described, the relationship between atmospheric water and ecosystem services has been mostly neglected, and perhaps misunderstood. Recent advances in land-atmosphere modeling have revealed the importance of terrestrial ecosystems for moisture recycling. In this paper, we analyze the extent to which vegetation sustains the supply of atmospheric moisture and precipitation for downwind beneficiaries, globally. We simulate land-surface evaporation with a global hydrology model and track changes to moisture recycling using an atmospheric moisture budget model, and we define vegetation-regulated moisture recycling as the difference in moisture recycling between current vegetation and a hypothetical desert world. Our results show that nearly a fifth of annual average precipitation falling on land is from vegetation-regulated moisture recycling, but the global variability is large, with many places receiving nearly half their precipitation from this ecosystem service. The largest potential impacts for changes to this ecosystem service are land-use changes across temperate regions in North America and Russia. Likewise, in semi-arid regions reliant on rainfed agricultural production, land-use change that even modestly reduces evaporation and subsequent precipitation, could significantly affect human well-being. We also present a regional case study in the Mato Grosso region of Brazil, where we identify the specific moisture recycling ecosystem services associated with the vegetation in Mato Grosso. We find that Mato Grosso vegetation regulates some internal precipitation, with a diffuse region of benefit downwind, primarily to the south and east, including the La Plata River basin and the megacities of Sao Paulo and Rio de Janeiro. We synthesize our global and regional results into a generalized framework for describing moisture recycling as an ecosystem service. We conclude that future work ought to disentangle whether and how this vegetation-regulated moisture recycling interacts with other ecosystem services, so that trade-offs can be assessed in a comprehensive and sustainable manner. 相似文献
5.
6.
Dominique Grizeau Lan Anh Bui Catherine Dupré Jack Legrand 《Critical reviews in biotechnology》2016,36(4):607-618
Over the last decades, production of microalgae and cyanobacteria has been developed for several applications, including novel foods, cosmetic ingredients and more recently biofuel. The sustainability of these promising developments can be hindered by some constraints, such as water and nutrient footprints. This review surveys data on N2-fixing cyanobacteria for biomass production and ways to induce and improve the excretion of ammonium within cultures under aerobic conditions. The nitrogenase complex is oxygen sensitive. Nevertheless, nitrogen fixation occurs under oxic conditions due to cyanobacteria-specific characteristics. For instance, in some cyanobacteria, the vegetative cell differentiation in heterocyts provides a well-adapted anaerobic microenvironment for nitrogenase protection. Therefore, cell cultures of oxygenic cyanobacteria have been grown in laboratory and pilot photobioreactors (Dasgupta et al., 2010; Fontes et al., 1987; Moreno et al., 2003; Nayak & Das, 2013). Biomass production under diazotrophic conditions has been shown to be controlled by environmental factors such as light intensity, temperature, aeration rate, and inorganic carbon concentration, also, more specifically, by the concentration of dissolved oxygen in the culture medium. Currently, there is little information regarding the production of extracellular ammonium by heterocytous cyanobacteria. This review compares the available data on maximum ammonium concentrations and analyses the specific rate production in cultures grown as free or immobilized filamentous cyanobacteria. Extracellular production of ammonium could be coupled, as suggested by recent research on non-diazotrophic cyanobacteria, to that of other high value metabolites. There is little information available regarding the possibility for using diazotrophic cyanobacteria as cellular factories may be in regard of the constraints due to nitrogen fixation. 相似文献
7.
8.
9.
10.