全文获取类型
收费全文 | 758篇 |
免费 | 5篇 |
国内免费 | 35篇 |
出版年
2021年 | 1篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 12篇 |
2014年 | 25篇 |
2013年 | 47篇 |
2012年 | 55篇 |
2011年 | 70篇 |
2010年 | 28篇 |
2009年 | 67篇 |
2008年 | 43篇 |
2007年 | 42篇 |
2006年 | 31篇 |
2005年 | 17篇 |
2004年 | 27篇 |
2003年 | 20篇 |
2002年 | 23篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 21篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 3篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 1篇 |
排序方式: 共有798条查询结果,搜索用时 922 毫秒
81.
Hai Vu-Manh Frank Wendler Hale Bahar Öztürk Thomas Bechtold 《Carbohydrate polymers》2012,87(1):195-201
Dynamic rheology, UV/VIS spectrometry with temperature programming cuvette and reaction calorimetry were conducted on cellulose pulp/FeTNa (NaOH solution containing ferric tartaric acid complex) solutions to investigate their thermostability and spinnability. Color of cellulose/FeTNa solutions changed above 90 °C due to the decomposition of the complex. Thermal activity of cellulose/FeTNa solution started above 130 °C induced by water vapor evolution and complex decomposition. Regeneration of cellulose/FeTNa solutions in a non-solvent (acetic acid and Na-gluconate mixture) resulted in transition from cellulose I into cellulose II structure as revealed by WAXS measurements. Wet-spinning attempts of cellulose/FeTNa solutions yielded fiber-like shaped bodies with a brittle structure. 相似文献
82.
Cellulose acetate (CA) nanofibers webs deserve a special attention because of their very good water retention properties. CA nanofibers based biosensor in certain application come into contact with various liquids and requires high degree of wicking rate to transport liquid to its destination. Cellulose acetate (CA)/polyvinyl alcohol (PVA) blended nanofibers were prepared via co-electrospinning using double nozzle for jetting cellulose acetate and polyvinyl alcohol independently. The CA/PVA blend nanofibers webs were deacetylated in aqueous alkaline solution to convert CA in to regenerated cellulose and to remove PVA nanofibers from the raw web. The resultant nanofibers webs were characterized by wicking rate, water contact angle, SEM and FTIR analysis. The results revealed that by varying concentration of PVA solution enhances the wicking rate. Such a nanofibers web may be used in biosensor strip and other medical applications where the high wicking rates are desired. 相似文献
83.
The powder and tableting properties of cellulose II powders (MCCII) and (SDCII) were evaluated and compared with common direct compression binders. The cellulose II polymorphs offered more benefits in terms of functionality as compared with cellulose I (Avicel® PH-102) spray dried lactose and starch. Spray dried cellulose II (SDCII) had a better disintegrant ability, but a lower compactibility than microcrystalline cellulose I (Avicel® PH-102). However, when mixed and compressed with acetaminophen, SDCII was as compactable as cellulose I. Further, unprocessed cellulose II has a comparable compressibility to that of cellulose I. SDCII was found to be less friable, less sensitive to magnesium stearate, and possessed better acetaminophen loading capacity than unprocessed cellulose II and comparable to that of cellulose I. The cellulose II materials showed potential for use as a direct compression excipient. 相似文献
84.
Bulk cellulose plastic materials with a continuous morphology were successfully processed from cellulose powder through back pressure-equal channel angular pressing (BP-ECAP) at 150 °C without using any additives. The strong shear deformation during the process caused an efficient deformation of cellulose granular and crystalline structures, resulting in effective chain penetration and strong intermolecular interactions throughout the whole material. The mechanical behaviour of the cellulose plastics was comparable to those of polymer/cellulose composites. Ball milling the cellulose powder prior to processing disrupted the crystalline structures thus resulting in more significant modifications of the molecular motions of the cellulose. The outcome of this research provides a potential methodology for manufacturing renewable and biodegradable bulk materials from cellulose-based agricultural waste. 相似文献
85.
Anne Christine Steenkjær Hastrup Caitlin Howell Flemming Hofmann Larsen Noppadon Sathitsuksanoh Barry Goodell Jody Jellison 《Fungal biology》2012,116(10):1052-1063
Wood-decaying basidiomycetes are some of the most effective bioconverters of lignocellulose in nature, however the way they alter wood crystalline cellulose on a molecular level is still not well understood. To address this, we examined and compared changes in wood undergoing decay by two species of brown rot fungi, Gloeophyllum trabeum and Meruliporia incrassata, and two species of white rot fungi, Irpex lacteus and Pycnoporus sanguineus, using X-ray diffraction (XRD) and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. The overall percent crystallinity in wood undergoing decay by M. incrassata, G. trabeum, and I. lacteus appeared to decrease according to the stage of decay, while in wood decayed by P. sanguineus the crystallinity was found to increase during some stages of degradation. This result is suggested to be potentially due to the different decay strategies employed by these fungi. The average spacing between the 200 cellulose crystal planes was significantly decreased in wood degraded by brown rot, whereas changes observed in wood degraded by the two white rot fungi examined varied according to the selectivity for lignin. The conclusions were supported by a quantitative analysis of the structural components in the wood before and during decay confirming the distinct differences observed for brown and white rot fungi. The results from this study were consistent with differences in degradation methods previously reported among fungal species, specifically more non-enzymatic degradation in brown rot versus more enzymatic degradation in white rot. 相似文献
86.
Graber DJ Snyder-Keller A Lawrence DA Turner JN 《Journal of biochemical and molecular toxicology》2012,26(2):45-53
Microglia have been implicated in the pathogenesis of several neurodegenerative diseases, but their precise role remains elusive. Although neuron loss in the presence of lipopolysaccharide-stimulated microglia has been well documented, a novel coculture paradigm was developed as a new approach to assess the diffusible, soluble mediators of neurodegeneration. Isolated microglia were plated on membrane inserts that were coated with a layer of cellulose acetate. The cellulose acetate-coated membranes have nanofiltration properties, in that only molecules with masses less than 350 Da can pass through. Products released from activated microglia that were separated from primary ventral mesencephalon cells beneath the nanofiltering membrane were able to kill the dopamine neurons. Microglial cytokines cannot diffuse through this separating membrane. Addition of a nitric oxide synthase inhibitor prevented the loss of the dopamine neurons. These data describe a novel coculture system for studying diffusible factors and further support nitric oxide production as an important mediator in microglia-induced neuron death. 相似文献
87.
88.
Radical graft functional modification of cellulose with allyl monomers: Chemistry and structure characterization 总被引:1,自引:0,他引:1
Cotton cellulose was successfully functionalized via a free radical graft polymerization process. Potassium persulfate served as an effective water soluble radical initiator to generate cellulosic radicals. The polymeric radicals could react with allyl monomers such as allyl-dimethylhydantion (ADMH) to form surface grafted cellulose. The reaction sites generated by potassium persulfate were probably at carbon 3 and 4 in glucose ring via oxidative hydrogen abstraction. The cellulosic radicals can initiate grafting polymerization of ADMH with a maximum polymerization degree of about 12 based on LC–MS results. The radical graft polymerization mechanisms were proposed based on LC–ESI/MS analysis. The ideal covalent bonding between cellulose and poly (allyl-dimethylhydantion) (PADMH) ensured permanent graft of the monomers on cotton and durability of the expected functions on the treated cotton. 相似文献
89.
To determine the effect of tryptophan and pH on sporulation of Coniothyrium minitans, the fungus was cultivated using a two-stage, agar plate method in which addition of tryptophan and pH were controlled at
the sporulation stage. The spore yield was enhanced by 4 times with 0.1 g tryptophan/l addition after 72 h. The optimal pH
values were 4 for mycelia growth and 5.8–6 for sporulation. Mycelia grown at pH 6 had a higher productivity of spore production
than did those grown at pH 4. 相似文献
90.
Pushpa Singh Archna Suman Priyanka Tiwari Namita Arya Asha Gaur A. K. Shrivastava 《World journal of microbiology & biotechnology》2008,24(5):667-673
Pretreatment of lignocellulosic biomasses, the first step in their conversion to utilizable molecules requires very high energy
(steam and electricity), corrosion resistant high-pressure reactors and high temperatures. These severe conditions not only
add to the cost component of the entire process but also lead to the loss of sugars to the side reactions. Microbial pretreatments
have been reported to be associated with reducing the cost factors as well as the severities of the reactions. Eight bioagents,
including fungi and bacteria, were screened for their pretreatment effects on sugarcane trash. They narrowed down the C:N
ratio of trash from 108:1 to a varying range of approximately 42:1 to 60:1.The maximum drop in C:N ratio of 61% was observed
using Aspergillus terreus followed by Cellulomonas uda (52%) and Trichoderma reesei and Zymomonas mobilis (49%). The bioagents helped in degradation of sugarcane trash by production of cellulases, the maximum being produced by
A. terreus, (12 fold) followed by C. uda (10 fold), Cellulomonas cartae (9 fold) and Bacillus macerans (8 fold). The microbial pretreatment of trash rendered the easy accessibility of sugars for enzymatic hydrolysis, which can be directed
for production of alcohol. 相似文献