全文获取类型
收费全文 | 6686篇 |
免费 | 379篇 |
国内免费 | 21篇 |
专业分类
7086篇 |
出版年
2024年 | 11篇 |
2023年 | 94篇 |
2022年 | 248篇 |
2021年 | 354篇 |
2020年 | 331篇 |
2019年 | 477篇 |
2018年 | 367篇 |
2017年 | 258篇 |
2016年 | 345篇 |
2015年 | 370篇 |
2014年 | 455篇 |
2013年 | 580篇 |
2012年 | 539篇 |
2011年 | 538篇 |
2010年 | 284篇 |
2009年 | 245篇 |
2008年 | 267篇 |
2007年 | 273篇 |
2006年 | 238篇 |
2005年 | 196篇 |
2004年 | 146篇 |
2003年 | 106篇 |
2002年 | 97篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 19篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 14篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1976年 | 3篇 |
1974年 | 7篇 |
1973年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有7086条查询结果,搜索用时 14 毫秒
31.
Azam Sadat Hosseini Alhashemi Abdolreza R. Karbassi Bahram Hassanzadeh Kiabi Seyed Masoud Monavari Seyed Mohammad Bagher Nabavi Mohammad Sadegh Sekhavatjou 《Biological trace element research》2011,142(3):500-516
Present study investigates relationships between total and bioaccessibility of trace elements (Cd, Co, Cr, Cu, Mn, NI, Pb,
V, and Zn) concentrations in sediment and their bioaccumulation in species in Shadegan wetland in southwest of Iran. Bioavailability
factor (BAF) and translocation factor (TF) were calculated in plants and trophic transfer factor (TTF) was determined in bird
species. For this purpose, sampling of sediments, aquatic plants including Phragmites australis, Typha australis, Scripus maritimus and two bird species encircling Porphyrio porphyrio and globally threatened Marmaronetta angustirostris were carried out during winter 2009. Result of chemical analysis show that bioaccessibility concentrations of Mn (8.31 mg/kg),
V (1.33 mg/kg), and Pb (1.03 mg/kg) are higher than other metals. The uptake trend of trace elements in plant decreases as
root > stem > leaf. Accumulation levels of trace elements in different tissues of P. porphyrio and M. angustirostris are almost identical and considerable. Accumulation and toxicity of Cd in birds is more than plants. In addition, BAF of
V, Pb, and Cr indicates high accumulation by plants and great pollution rate in the area of study. In S. maritimus TF for Mn, Cu, Pb, and V are high whereas in T. australis, Cu and Pb posses the highest TF. Also Cr, Co, Mn, Ni, and Zn have higher TF from stem to leaf than root to stem in P. australis. Finally, TTFs were compared in various bird species. 相似文献
32.
Ethanol production from glucose and dilute-acid hydrolyzates by encapsulated S. cerevisiae 总被引:1,自引:0,他引:1
The performance of encapsulated Saccharomyces cerevisiae CBS 8066 in anaerobic cultivation of glucose, in the presence and absence of furfural as well as in dilute-acid hydrolyzates, was investigated. The cultivation of encapsulated cells in 10 sequential batches in synthetic media resulted in linear increase of biomass up to 106 g/L of capsule volume, while the ethanol productivity remained constant at 5.15 (+/-0.17) g/L x h (for batches 6-10). The cells had average ethanol and glycerol yields of 0.464 and 0.056 g/g in these 10 batches. Addition of 5 g/L furfural decreased the ethanol productivity to a value of 1.31 (+/-0.10) g/L x h with the encapsulated cells, but it was stable in this range for five consecutive batches. On the other hand, the furfural decreased the ethanol yield to 0.41-0.42 g/g and increased the yield of acetic acid drastically up to 0.068 g/g. No significant lag phase was observed in any of these experiments. The encapsulated cells were also used to cultivate two different types of dilute-acid hydrolyzates. While the free cells were not able to ferment the hydrolyzates within at least 24 h, the encapsulated yeast successfully converted glucose and mannose in both of the hydrolyzates in less than 10 h with no significant lag phase. However, since the hydrolyzates were too toxic, the encapsulated cells lost their activity gradually in sequential batches. 相似文献
33.
34.
Mahboudi Somayeh Moosavi-Nasab Marzieh Kazemi Bahram Rahimpour Azam Eskandari Mohammad Hadi Mohammadian Omid Shams Forough 《Molecular biology reports》2021,48(5):4405-4412
Molecular Biology Reports - Monoclonal antibodies (mAbs) are widely employed as invaluable therapeutics for a vast number of human disorders. Several approaches have been introduced for the... 相似文献
35.
Mehdi Khoshneviszadeh Mohammad H. Ghahremani Alireza Foroumadi Ramin Miri Omidreza Firuzi Armin Madadkar-Sobhani Najmeh Edraki Maliheh Parsa Abbas Shafiee 《Bioorganic & medicinal chemistry》2013,21(21):6708-6717
A series of 16 novel 1,2,4-triazine derivatives bearing hydrazone moiety (7a–7p) have been designed, synthesized and evaluated for their activity to inhibit IL-1β and TNF-α production. All compounds are reported for the first time. The chemical structures of all compounds were confirmed by spectroscopic methods and elemental analyzes. Most of the synthesized compounds were proved to have potent anti-cytokine activity and low toxicity on PBMC and MCF-7 cell lines. Compounds 7f, 7k, 7l and 7j presented simultaneously good levels of inhibition of both cytokines. Moreover, compound 7l exhibited good anti-inflammatory effect in carrageenan-induced rat paw edema. The results of Western blotting demonstrated that the anti-cytokine potential of compound 7l is mainly mediated through the inhibition of p38 MAPK signaling pathway. Molecular docking was performed to position compound 7l into p38α binding site in order to explore the potential target. The information of this work might be helpful for the design and synthesis of novel scaffold toward the development of new therapeutic agent to fight against inflammatory diseases. 相似文献
36.
Ghias Uddin Abdul Latif Mohammad Arfan Mumtaz Ali Syed Hamid Hussain Thomas J. Simpson Russel J. Cox Muhammad Iqbal Choudhary 《Phytochemistry letters》2013,6(1):84-89
Three new phenolic compounds, sorlanin (4-(3-(hydroxymethyl)-5-methoxy-7-phenyl-2,3-dihydrobenzo[b][1,4]dioxin-2-yl)-2-methoxyphenol, 1), sorbanin (2-((3,5-dimethoxy-[1,1′-biphenyl]-4-yl)oxy)-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol, 2) and sorbalanin (4-(3-(hydroxymethyl)-5,6-dimethoxy-2,3-dihydrobenzo[b][1,4]dioxino[2,3-g]benzofuran-2-yl)-2-methoxyphenol, 3), together with eight known compounds, polystachyol (4), isolariciresinol (5), dihydrodehydrodiconiferyl alcohol (6), tuberculatin (7), ovafolinin E (8), aucuparin (9), 2′-methoxyaucuparin (10), and tetracosyl-3-(3,4-dihydroxyphenyl)acrylate (11), were isolated from Sorbus lanata. The structures of these phytoconstituents were elucidated through extensive spectroscopic techniques, including UV, IR, 1D and 2D NMR, ESI-MS and HRESI-MS experiments. All the compounds except 9 and 10 were isolated for the first time from the genus Sorbus. The isolated compounds were also tested in DPPH radical scavenging reaction where compounds 6, 7, 10 and 11 showed significant activities with IC50 values of 9.2, 11.7, 23.0 and 33.7 μM, respectively. 相似文献
37.
Mohammad Nasif Sarowar Albert Hendrik van den Berg Debbie McLaggan Mark R. Young Pieter van West 《Fungal biology》2014,118(7):579-590
Saprolegnia species are destructive pathogens to many aquatic organisms and are found in most parts of the world. Reports based on phylogenetic analysis suggest that Saprolegnia strains isolated from aquatic animals such as crustaceans and frogs are close to Saprolegnia strains isolated from infected fish or fish eggs and vice versa. However, it has often been assumed that host specificity occurs for each individual isolate or strain. Here we demonstrate that Saprolegnia spp. can have multiple hosts and are thus capable of infecting different aquatic organisms. Saprolegnia delica, Saprolegnia hypogyna, and 2 strains of Saprolegnia diclina were isolated from aquatic insects and amphipods while S. delica, Saprolegnia ferax, Pythium pachycaule, and a Pythium sp. were isolated from the water of a medium to fast flowing river. The ITS region of the rRNA gene was sequenced for all isolates. In challenge experiments, all four isolates from insects were found to be highly pathogenic to eggs of Atlantic salmon (Salmo salar) and embryos of the African clawed frog (Xenopus laevis). We found that Saprolegnia spp. isolated from salmon eggs were also able to successfully establish infection in nymphs of stonefly (Perla bipunctata) and embryos of X. laevis). These results suggest that Saprolegnia spp. are capable of infecting multiple hosts, which may give them an advantage during seasonal variation in their natural environments. 相似文献
38.
39.
Md Sultan Ahamad Sahabjada Siddiqui Asif Jafri Sheeba Ahmad Mohammad Afzal Md Arshad 《PloS one》2014,9(10)
A natural predominant flavanone naringenin, especially abundant in citrus fruits, has a wide range of pharmacological activities. The search for antiproliferative agents that reduce skin carcinoma is a task of great importance. The objective of this study was to analyze the anti-proliferative and apoptotic mechanism of naringenin using MTT assay, DNA fragmentation, nuclear condensation, change in mitochondrial membrane potential, cell cycle kinetics and caspase-3 as biomarkers and to investigate the ability to induce reactive oxygen species (ROS) initiating apoptotic cascade in human epidermoid carcinoma A431 cells. Results showed that naringenin exposure significantly reduced the cell viability of A431 cells (p<0.01) with a concomitant increase in nuclear condensation and DNA fragmentation in a dose dependent manner. The intracellular ROS generation assay showed statistically significant (p<0.001) dose-related increment in ROS production for naringenin. It also caused naringenin-mediated epidermoid carcinoma apoptosis by inducing mitochondrial depolarization. Cell cycle study showed that naringenin induced cell cycle arrest in G0/G1 phase of cell cycle and caspase-3 analysis revealed a dose dependent increment in caspase-3 activity which led to cell apoptosis. This study confirms the efficacy of naringenin that lead to cell death in epidermoid carcinoma cells via inducing ROS generation, mitochondrial depolarization, nuclear condensation, DNA fragmentation, cell cycle arrest in G0/G1 phase and caspase-3 activation. 相似文献
40.