全文获取类型
收费全文 | 1731篇 |
免费 | 104篇 |
国内免费 | 1篇 |
出版年
2023年 | 4篇 |
2022年 | 26篇 |
2021年 | 43篇 |
2020年 | 32篇 |
2019年 | 34篇 |
2018年 | 62篇 |
2017年 | 39篇 |
2016年 | 62篇 |
2015年 | 79篇 |
2014年 | 98篇 |
2013年 | 124篇 |
2012年 | 140篇 |
2011年 | 138篇 |
2010年 | 80篇 |
2009年 | 65篇 |
2008年 | 105篇 |
2007年 | 101篇 |
2006年 | 93篇 |
2005年 | 75篇 |
2004年 | 78篇 |
2003年 | 63篇 |
2002年 | 67篇 |
2001年 | 21篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 24篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1969年 | 2篇 |
1961年 | 2篇 |
1960年 | 3篇 |
1959年 | 4篇 |
1958年 | 2篇 |
1957年 | 7篇 |
排序方式: 共有1836条查询结果,搜索用时 15 毫秒
21.
Arun P. Sharma Merilyn Blair Abraham P. Ollapally 《Nucleosides, nucleotides & nucleic acids》2013,32(5):713-720
Abstract Synthesis of the title compound, an unsaturated ketohexo-pyranosyl nucleoside of 5-fluorouracil is reported. It was prepared by oxidation of the corresponding dibenzoylhexopyranosyl nucleoside with pyridinium dichromate/molecular sieves system. 相似文献
22.
23.
Arun K. Bose Arthur Gessler Andreas Bolte Alessandra Bottero Allan Buras Maxime Cailleret J. Julio Camarero Matthias Haeni Ana‐Maria Here Andrea Hevia Mathieu Lvesque Juan C. Linares Jordi Martinez‐Vilalta Luis Matías Annette Menzel Raúl Snchez‐Salguero Matthias Saurer Michel Vennetier Daniel Ziche Andreas Rigling 《Global Change Biology》2020,26(8):4521-4537
Global climate change is expected to further raise the frequency and severity of extreme events, such as droughts. The effects of extreme droughts on trees are difficult to disentangle given the inherent complexity of drought events (frequency, severity, duration, and timing during the growing season). Besides, drought effects might be modulated by trees’ phenotypic variability, which is, in turn, affected by long‐term local selective pressures and management legacies. Here we investigated the magnitude and the temporal changes of tree‐level resilience (i.e., resistance, recovery, and resilience) to extreme droughts. Moreover, we assessed the tree‐, site‐, and drought‐related factors and their interactions driving the tree‐level resilience to extreme droughts. We used a tree‐ring network of the widely distributed Scots pine (Pinus sylvestris) along a 2,800 km latitudinal gradient from southern Spain to northern Germany. We found that the resilience to extreme drought decreased in mid‐elevation and low productivity sites from 1980–1999 to 2000–2011 likely due to more frequent and severe droughts in the later period. Our study showed that the impact of drought on tree‐level resilience was not dependent on its latitudinal location, but rather on the type of sites trees were growing at and on their growth performances (i.e., magnitude and variability of growth) during the predrought period. We found significant interactive effects between drought duration and tree growth prior to drought, suggesting that Scots pine trees with higher magnitude and variability of growth in the long term are more vulnerable to long and severe droughts. Moreover, our results indicate that Scots pine trees that experienced more frequent droughts over the long‐term were less resistant to extreme droughts. We, therefore, conclude that the physiological resilience to extreme droughts might be constrained by their growth prior to drought, and that more frequent and longer drought periods may overstrain their potential for acclimation. 相似文献
24.
Nripendra Vikram Singh Shilpa Parashuram Jyotsana Sharma Roopa Sowjanya Potlannagari Dhinesh Babu Karuppannan Ram Krishna Pal Prakash Patil Dhananjay M. Mundewadikar Vipul R. Sangnure P.V. Parvati Sai Arun Naresh V.R. Mutha Bipin Kumar Abhishek Tripathi Sathish Kumar Peddamma Harish Kothandaraman Sailu Yellaboina Dushyant Singh Baghel Umesh K. Reddy 《Saudi Journal of Biological Sciences》2020,27(12):3514-3528
25.
Venkatasamy Vignesh Durairaj Rajesh Karuppaiah Parthiban Sridhar Arun Kamaraj Sathish Kumar Ramasamy Thirumurugan 《International journal of peptide research and therapeutics》2021,27(3):1709-1718
International Journal of Peptide Research and Therapeutics - Subtilosin A, a cyclic peptide from Bacillus subtilis is known for its antimicrobial activity against a diverse range of bacteria.... 相似文献
26.
This article addresses the issue of effect of fermentation parameters for conversion of glycerol (in both pure and crude form) into three value-added products, namely, ethanol, butanol, and 1,3-propanediol (1,3-PDO), by immobilized Clostridium pasteurianum and thereby addresses the statistical optimization of this process. The analysis of effect of different process parameters such as agitation rate, fermentation temperature, medium pH, and initial glycerol concentration indicated that medium pH was the most critical factor for total alcohols production in case of pure glycerol as fermentation substrate. On the other hand, initial glycerol concentration was the most significant factor for fermentation with crude glycerol. An interesting observation was that the optimized set of fermentation parameters was found to be independent of the type of glycerol (either pure or crude) used. At optimum conditions of agitation rate (200 rpm), initial glycerol concentration (25 g/L), fermentation temperature (30°C), and medium pH (7.0), the total alcohols production was almost equal in anaerobic shake flasks and 2-L bioreactor. This essentially means that at optimum process parameters, the scale of operation does not affect the output of the process. The immobilized cells could be reused for multiple cycles for both pure and crude glycerol fermentation. 相似文献
27.
Arun Goyal D. P. Tyagi Sarvagya S. Katiyar 《Journal of enzyme inhibition and medicinal chemistry》2013,28(1):111-113
Amino acid analysis of purified dextransucrase (sucrose: 1,6-α-D-glucan 6-α-D-glucosyltransferase EC 2.4.1.5) from Leuconostoc mesenteroides NRRL B-512F was carried out. The enzyme is virtually devoid of cysteine residue there being only one cysteine residue in the whole enzyme molecule comprising over 1500 amino acid residues. The enzyme is rich in acidic amino acid residues. The number of amino acid residues was calculated based on the molecular weight of 188,000 (Goyal and Katiyar 1994). Amino sugars were not found, implying that the enzyme is not a glycoprotein. It has been shown earlier that the cysteine residue in dextransucrase is not essential for enzyme activity (Goyal and Katiyar 1998). The presence of only one cysteine residue per enzyme molecule illustrates that its tertiary structure is solely dependent on other types of non-covalent interactions such as hydrogen bonding, ionic and nonpolar hydrophobic interactions. 相似文献
28.
Arun M. Khurad Ravindra S. Bahekar Min-Juan Zhang Ashish D. Tiple Jae Man Lee Chuan-Xi Zhang Takahiro Kusakabe 《Journal of Asia》2013,16(1):17-22
A Bombyx mori continuous cell line, designated DZNU-Bm-17, was established from larval ovaries. The cells were initially grown in MGM-448 insect cell culture medium supplemented with 10% fetal bovine serum and 3% heat inactivated B. mori hemolymph at 25 ± 1 °C and later adapted gradually to TNM-FH medium. Partially adhered refractive cells were the predominant cell type in the culture. The cells took about 1055 days to complete 100 passages in TNM-FH medium. The population doubling time of the cell line was about 30–34 h at 25 ± 1 °C. The cell population was largely diploid, but a few triploids and tetraploids were also observed. DNA profiles using simple sequence repeat loci established the differences between the DZNU-Bm-1, Bm-5, DZNU-Bm-12, DZNU-Bm-17, and BmN cell lines. The cell line was susceptible to budded virus of B. mori nucleopolyhedrovirus (BmNPV), and 85–92% of the cells harbored BmNPV with an average of 15 occlusion bodies/infected cell. The cells expressed the luciferase and green fluorescent proteins using the BmNPV bacmid vector. We suggest the usefulness of the DZNU-Bm-17 cell line for BmNPV-based baculoviral expression studies. 相似文献
29.
Minakshi Mazumdar Arghya Adhikary Samik Chakraborty Shravanti Mukherjee Argha Manna Shilpi Saha Suchismita Mohanty Amrita Dutta Pushpak Bhattacharjee Pallab Ray Sreya Chattopadhyay Shuvomoy Banerjee Juni Chakraborty Arun K. Ray Gaurisankar Sa Tanya Das 《Apoptosis : an international journal on programmed cell death》2013,18(5):589-604
Mutations in REarranged during Transfection (RET) receptor tyrosine, followed by the oncogenic activation of RET kinase is responsible for the development of medullary thyroid carcinoma (MTC) that responds poorly to conventional chemotherapy. Targeting RET, therefore, might be useful in tailoring surveillance of MTC patients. Here we showed that theaflavins, the bioactive components of black tea, successfully induced apoptosis in human MTC cell line, TT, by inversely modulating two molecular pathways: (i) stalling PI3K/Akt/Bad pathway that resulted in mitochondrial transmembrane potential (MTP) loss, cytochrome-c release and activation of the executioner caspases-9 and -3, and (ii) upholding p38MAPK/caspase-8/caspase-3 pathway via inhibition of Ras/Raf/ERK. Over-expression of either constitutively active myristoylated-Akt-cDNA (Myr-Akt-cDNA) or dominant-negative-caspase-8-cDNA (Dn-caspase-8-cDNA) partially blocked theaflavin-induced apoptosis, while co-transfection of Myr-Akt-cDNA and Dn-caspase-8-cDNA completely eradicated the effect of theaflavins thereby negating the possibility of existence of other pathways. A search for the upstream signaling revealed that theaflavin-induced disruption of lipid raft caused interference in anchorage of RET in lipid raft that in turn stalled phosphorylation of Ras and PI3Kinase. In such anti-survival cellular micro-environment, pro-apoptotic signals were triggered to culminate into programmed death of MTC cell. These findings not only unveil a hitherto unexplained mechanism underlying theaflavin-induced MTC death, but also validate RET as a promising and potential target for MTC therapy. 相似文献
30.
Hui Chen Bing Zhou Matthew Brecher Nilesh Banavali Susan A. Jones Zhong Li Jing Zhang Dilip Nag Laura D. Kramer Arun K. Ghosh Hongmin Li 《PloS one》2013,8(10)
The methyltransferase enzyme (MTase), which catalyzes the transfer of a methyl group from S-adenosyl-methionine (AdoMet) to viral RNA, and generates S-adenosyl-homocysteine (AdoHcy) as a by-product, is essential for the life cycle of many significant human pathogen flaviviruses. Here we investigated inhibition of the flavivirus MTase by several AdoHcy-derivatives. Unexpectedly we found that AdoHcy itself barely inhibits the flavivirus MTase activities, even at high concentrations. AdoHcy was also shown to not inhibit virus growth in cell-culture. Binding studies confirmed that AdoHcy has a much lower binding affinity for the MTase than either the AdoMet co-factor, or the natural AdoMet analog inhibitor sinefungin (SIN). While AdoMet is a positively charged molecule, SIN is similar to AdoHcy in being uncharged, and only has an additional amine group that can make extra electrostatic contacts with the MTase. Molecular Mechanics Poisson-Boltzmann Sovation Area analysis on AdoHcy and SIN binding to the MTase suggests that the stronger binding of SIN may not be directly due to interactions of this amine group, but due to distributed differences in SIN binding resulting from its presence. The results suggest that better MTase inhibitors could be designed by using SIN as a scaffold rather than AdoHcy. 相似文献