全文获取类型
收费全文 | 2712篇 |
免费 | 143篇 |
出版年
2023年 | 28篇 |
2022年 | 41篇 |
2021年 | 64篇 |
2020年 | 58篇 |
2019年 | 54篇 |
2018年 | 71篇 |
2017年 | 70篇 |
2016年 | 101篇 |
2015年 | 134篇 |
2014年 | 173篇 |
2013年 | 208篇 |
2012年 | 213篇 |
2011年 | 227篇 |
2010年 | 133篇 |
2009年 | 104篇 |
2008年 | 148篇 |
2007年 | 155篇 |
2006年 | 144篇 |
2005年 | 115篇 |
2004年 | 114篇 |
2003年 | 92篇 |
2002年 | 88篇 |
2001年 | 27篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1974年 | 12篇 |
1973年 | 5篇 |
1966年 | 4篇 |
1943年 | 5篇 |
1942年 | 7篇 |
排序方式: 共有2855条查询结果,搜索用时 26 毫秒
91.
Eva Kabaš Snežana Vukojičić Renata Ćušterevska Rossen Tzonev Dmitar Lakušić 《Plant biosystems》2019,153(3):461-477
The heterogeneity of the ultramafic vegetation of the Central Balkans is rather great. Although this vegetation has been continuously investigated, some gaps are still to be filled. For example, the lack of available data on ultramafic vegetation of the Republic of Macedonia is evident. In that light, we have investigated different relic Stipa species-dominated dry grasslands over ultramafic bedrock. Twenty relevés were made and compared to the similar vegetation types (i.e. Potentilla visianii, Centaureo kosaninii-Bromion fibrosi, “Thymion jankae”, Saturejo-Thymion and Alyssion heldreichii) by means of numerical analyses. We distinguished one new association and one informal community, providing them with diagnosis and lists of diagnostic, constant and dominant species. We also determined their syntaxonomic positions and relations to ultramafic syntaxa from the neighboring countries. 相似文献
92.
93.
Jacob Ball Renata A. G. Reis Johnson Agniswamy Irene T. Weber Giovanni Gadda 《Protein science : a publication of the Protein Society》2019,28(1):167-175
The crystal structure of the NADH:quinone oxidoreductase PA1024 has been solved in complex with NAD+ to 2.2 Å resolution. The nicotinamide C4 is 3.6 Å from the FMN N5 atom, with a suitable orientation for facile hydride transfer. NAD+ binds in a folded conformation at the interface of the TIM‐barrel domain and the extended domain of the enzyme. Comparison of the enzyme‐NAD+ structure with that of the ligand‐free enzyme revealed a different conformation of a short loop (75–86) that is part of the NAD+‐binding pocket. P78, P82, and P84 provide internal rigidity to the loop, whereas Q80 serves as an active site latch that secures the NAD+ within the binding pocket. An interrupted helix consisting of two α‐helices connected by a small three‐residue loop binds the pyrophosphate moiety of NAD+. The adenine moiety of NAD+ appears to π–π stack with Y261. Steric constraints between the adenosine ribose of NAD+, P78, and Q80, control the strict specificity of the enzyme for NADH. Charged residues do not play a role in the specificity of PA1024 for the NADH substrate. 相似文献
94.
Francielly Cristina Machado Renata Prandini Adum de Matos Fernando Lucas Primo Antonio Claudio Tedesco Paula Rahal Marília Freitas Calmon 《Bioorganic & medicinal chemistry》2019,27(9):1882-1890
Curcumin, a natural compound has several antineoplastic activities and is a promising natural photosensitizer used in photodynamic therapy. However, its low solubility in physiological medium limit the clinical use of curcumin. This study aimed to analyze the action of curcumin-nanoemulsion, a new and well-designed Drug Delivery System (DDS+) molecule, used as a photosensitizing agent in photodynamic therapy in an in vitro breast cancer model, MCF-7 cells. The empty nanoemulsion fulfils all necessary requirements to be an excellent DDS. Furthermore, the use of curcumin-nanoemulsion in photodynamic therapy resulted in a high phototoxic effect after activation at 440?nm, decreasing to <10% viable tumor cells after two irradiations and increasing the reactive oxygen species (ROS) production. The use of curcumin-nanoemulsion associated with photodynamic therapy resulted in an increase in the levels of caspase 3/7 activity for the studied MCF-7 cell model, indicating that this therapy triggers a cascade of events that lead to cell death, such as cellular apoptosis. In conclusion, curcumin-nanoemulsion proved to be efficient as a photosensitizing agent, had phototoxic effects, significantly decreased the proliferation of MCF-7 cells and stimulating the ROS production in combination with photodynamic therapy, so, this formulation has a great potential for use in treatment of breast cancer. 相似文献
95.
Justyna Sulej Monika Osińska-Jaroszuk Magdalena Jaszek Marcin Grąz Jolanta Kutkowska Anna Pawlik Agata Chudzik Renata Bancerz 《Fungal biology》2019,123(12):875-886
Cellobiose dehydrogenase (CDH, EC 1.1.99.18) is a glycoprotein having many biotechnological applications. In the present study, CDHs isolated from Phlebia lindtneri (PlCDH), Phanerochaete chrysosporium (PchCDH), Cerrena unicolor (CuCDH), and Pycnoporus sanguineus (PsCDH) were studied the first time for their ability to generate antioxidant and antimicrobial agents. The aim of the research was to evaluate the antioxidant and antimicrobial activity of systems composed of four CDHs and lactose or cellobiose as a reaction substrate. The free radical scavenging effect of free and immobilised enzymes was evaluated using the DPPH method. The lowest values of EC50 (10.04 ± 0.75 /ml) was noted for PlCDH/lactose and for PlCDH/cellobiose (12.06 ± 1.35 /ml). The EC50value reached 12.6 ± 1.51 /ml in the case of PsCDH/lactose and 15.96 ± 1.35 for PsCDH. The CDH preparations were also effectively immobilised in alginate (the immobilisation efficiency expressed as a protein yield ranged from 61.6 to 100 %). The operational stability expressed as a scavenging effect showed the possibility of using the alginate beads 4 times. Both the free and immobilised CDHs as well as the CDH/substrate were tested against Gram-negative Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Gram-positive Staphylococcus aureus ATCC 25923 bacteria. All samples, except PlCDH, were potentially effective in suppression of bacterial growth. The highest percentage of inhibition (100 %) was obtained for S. aureus bacteria using PsCDH and PchCDH with lactose as a substrate, whereas a slightly lesser effect was observed for E. coli and P. aeruginosa bacterial cells, i.e. 64.1 % and 86.5 % (PsCDH) and 94.1 % and 41.4 % (PchCDH), respectively. Furthermore, the concentrations of the reaction products (aldonic acids and hydrogen peroxide) were quantified and the surface morphology of the alginate beads was analysed using SEM visualisation. 相似文献
96.
97.
Utilization of ethanol produced from biomass has the potential to offset the use of gasoline and reduce CO(2) emissions. This could reduce the effects of global warming, one of which is the current outbreak of epidemic proportions of the mountain pine beetle (MPB) in British Columbia (BC), Canada. The result of this is increasing volumes of dead lodgepole pine with increasingly limited commercial uses. Bioconversion of lodgepole pine to ethanol using SO(2)-catalyzed steam explosion was investigated. The optimum pretreatment condition for this feedstock was determined to be 200 degrees C, 5 min, and 4% SO(2) (w/w). Simultaneous saccharification and fermentation (SSF) of this material provided an overall ethanol yield of 77% of the theoretical yield from raw material based on starting glucan, mannan, and galactan, which corresponds to 244 g ethanol/kg raw material within 30 h. Three conditions representing low (L), medium (M), and high (H) severity were also applied to healthy lodgepole pine. Although the M severity conditions of 200 degrees C, 5 min, and 4% SO(2) were sufficiently robust to pretreat healthy wood, the substrate produced from beetle-killed (BK) wood provided consistently higher ethanol yields after SSF than the other substrates tested. BK lodgepole pine appears to be an excellent candidate for efficient and productive bioconversion to ethanol. 相似文献
98.
The synthesis of Nalpha-fluorenylmethoxycarbonyl-trans-4-hydroxy-4-O-[(2,3,4,6-tetra-O-acetyl)-alpha-d-mannopyranosyl]-l-proline allyl ester and Nalpha-fluorenylmethoxycarbonyl-trans-4-hydroxy-4-O-[(2,3,4,6-tetra-O-benzoyl)-alpha-d-mannopyranosyl]-l-proline allyl ester is described. Glycosylation using K?nigs-Knorr conditions with a benzoyl protected glycosyl donor provided the optimum method. Removal of the allyl ester gave two mannosylated building blocks suitable for solid phase glycopeptide synthesis. 相似文献
99.
Neves RH Miranda de Barros Alencar AC Costa-Silva M Aguila MB Mandarim-de-Lacerda CA Machado-Silva JR Gomes DC 《Experimental parasitology》2007,115(4):324-332
This study investigated whether long-term feeding a high-fat diet (HFC) has an effect on schistosomiasis mansoni outcome compared to standard chow diet (SC). Swiss Webster female mice (3 wk old) fed each diet over 5 months, and then were infected with 50 Schistosoma mansoni cercariae. Their nutritional status was assessed by monitoring growth rates twice a week and measuring serum levels of lipoproteins. Mice were euthanised 63 days after infection. Parasitological and liver histological analyses were performed. The levels of TC, HDL-C and LDL-C, fecal and tissue schistosome eggs were statistically different (p<0.05) between groups. Livers from HFC mice showed exudative, exudative/exudative-productive, exudative-productive and productive granulomas, some degree of hepatic steatosis and focal necrosis. Mice fed normal-chow did not present productive granulomas and hepatic steatosis. The morphometric evaluation of hepatic granulomas did not reach statistical significance (p>0.05) between diets assayed. The high-fat diet for long-term produces effects on schistosomiasis mansoni outcome. 相似文献
100.
Investigations on the effects of the 5-HT agonists and antagonists on the phase of the circadian locomotor activity rhythm of animals kept in constant light conditions (LL) are rare. Therefore the influence of R-(+)-OH-DPAT (5-HT1A receptors agonist) and metergoline (5-HT1/2/7 receptors antagonist) on the phase shift of the locomotor-activity rhythm alone and when combined with dark pulses in mice kept in LL are examined. The results indicate that 8-OH-DPAT administered independently at 12.00CT (Circadian Time) shifted the phase of the circadian rhythm and reinforced the effect of dark pulses on this parameter. 12.00CT was defined arbitrarily as the onset of locomotor activity in constant conditions. Metergoline diminished the phase shifts after dark pulses compared to 8-OH-DPAT. The influence of the serotonin agonist showed that serotonin can reinforce the phase shifting effect of the locomotor activity rhythm after dark pulses in LL condition. 相似文献