全文获取类型
收费全文 | 1934篇 |
免费 | 145篇 |
国内免费 | 149篇 |
出版年
2023年 | 70篇 |
2022年 | 45篇 |
2021年 | 113篇 |
2020年 | 88篇 |
2019年 | 123篇 |
2018年 | 89篇 |
2017年 | 93篇 |
2016年 | 67篇 |
2015年 | 70篇 |
2014年 | 94篇 |
2013年 | 146篇 |
2012年 | 63篇 |
2011年 | 99篇 |
2010年 | 51篇 |
2009年 | 90篇 |
2008年 | 81篇 |
2007年 | 122篇 |
2006年 | 92篇 |
2005年 | 86篇 |
2004年 | 61篇 |
2003年 | 63篇 |
2002年 | 51篇 |
2001年 | 25篇 |
2000年 | 26篇 |
1999年 | 42篇 |
1998年 | 21篇 |
1997年 | 26篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 7篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有2228条查询结果,搜索用时 31 毫秒
101.
Deborah M. Ramsey Md. Amirul Islam Lynne Turnbull Rohan A. Davis Cynthia B. Whitchurch Shelli R. McAlpine 《Bioorganic & medicinal chemistry letters》2013,23(17):4862-4866
Described is the antibiotic activity of a marine natural product. Psammaplysin F (1) inhibited the growth of four Gram-positive strains by >80% at 50 μM, and the amine at position C-20 is responsible for the observed antibacterial activity. When tested against two strains of methicillin resistant Staphylococcus aureus (MRSA), the minimum inhibitory concentrations (MICs) for psammaplysin F (40–80 μM) were similar to the structurally-related alkaloid psammaplysin H (2). Psammaplysin F (1) increased membrane permeability by two to four-fold compared to psammaplysin H (2) or control-treated bacteria, respectively. Unlike psammaplysin H (2), we show that psammaplysin F (1) inhibits equal partitioning of DNA into each daughter cell, suggesting that this natural product is a unique prokaryotic cell division inhibitor. 相似文献
102.
Cyanobacteria are effective producers of bioactive metabolites, including both acute toxins and potential pharmaceuticals. In the current work, the biological activity of 27 strains of Baltic cyanobacteria representing different taxonomic groups and chemotypes were tested in a wide variety of assays. The cyanobacteria showed strain-specific differences in the induced effects. The extracts from Nodularia spumigena CCNP1401 were active in the highest number of tests, including protease and phosphatase inhibition assays. Four strains from Nostocales and four from Oscillatoriales increased proliferation of mitogen-stimulated human T cells. In antimicrobial assays, Phormidium sp. CCNP1317 (Oscillatoriales) strongly inhibited the growth of six fouling Gammaproteobacteria. The growth of monocotyl Sorghum saccharatum was inhibited by both toxin-producing and ‘non-toxic’ strains. The Baltic cyanobacteria were also found to be a rich source of commercially important enzymes. Among the 19 enzymatic activities tested, alkaline phosphatase, acid phosphatase, esterase (C4 and C8), and naphthol-AS-BI-phosphohydrolase were particularly common. In the cyanobacterial extracts, different peptides which may have been responsible for the observed effects were identified using LC-MS/MS. Their structures were classified to microcystins, nodularins, anabaenopeptins, cyanopeptolins, aeruginosins, spumigins and nostocyclopeptides. 相似文献
103.
Kevin Lewellyn Dobroslawa Bialonska Melissa J. Loria Stephen W. White Kenneth J. Sufka Jordan K. Zjawiony 《Bioorganic & medicinal chemistry》2013,21(22):7083-7090
Aplysinopsins are tryptophan-derived natural products that have been isolated from a variety of marine organisms and have been shown to possess a range of biological activities. In vitro receptor binding assays showed that of the 12 serotonin receptor subtypes, analogues showed a high affinity for the 5-HT2B and 5-HT2C receptor subtypes, with selectivity for 5-HT2B over 5-HT2C. While no conclusions could be drawn about the number and position of N-methylations, bromination at C-4 and C-5 of the indole ring resulted in greater binding affinities, with Ki’s as low as 35 nM. This data, combined with previous knowledge of the CNS activity of aplysinopsin analogs, suggested that these compounds may have potential as leads for antidepressant drugs. Compounds 3c, 3u, and 3x were evaluated in the chick anxiety–depression model to assess their in vivo efficacy. Compound 3c showed a modest antidepressant effect at a dose of 30 nM/kg in the animal model. 相似文献
104.
常军 《天然产物研究与开发》2013,25(8):1085-1088
本文建立了一个快速高效的HPLC方法同时检测苦杏仁苷及其4个体外酶解产物,色谱分析系统为安捷伦液相色谱系统,自动进样器,迪马ODS C18色谱柱(250 mm×4.6 mm,5μm),柱温25℃,流动相30%甲醇,检测波长210 nm,进样量10μL。结果表明,苦杏仁苷、phenyl-(3,4,5-trihydroxy-6-methyl-tetrahydro-pyran-2-yloxy)-acetonitrile、野樱花苷、苯甲醛和杏仁腈的保留时间分别为5.087、13.836、16.357、22.775和3.307 min。该HPLC方法的重现性好,精确度和准确度高,当柱温低于30℃、pH值介于6.0~7.0时该方法结果稳定、重现性好。 相似文献
105.
106.
107.
108.
《Bioscience, biotechnology, and biochemistry》2013,77(4):930-932
Glyceraldehyde (200 mM) and Nα-acetyllysine (100 mM) were incubated in 0.2 M sodium phosphate buffer (pH 7.4) at 37°C for a week. A major compound, glyceraldehyde-related Maillard reaction product, was purified from the reaction mixture using reverse phase (ODS)-HPLC. It was identified as 1-(5-acetylamino-5-carboxypentyl)-3-hydroxy-5-hydroxymethyl-pyridinium, named as GLAP (Glyceraldehyde derived Pyridinium compound), using NMR and MS analyses. It was suggested that GLAP as a novel advanced glycation end product (AGE) is one of the key compounds in the glyceraldehyde-related Maillard reaction. 相似文献
109.
本研究从食品微生物指标人手,对我国肉类食品的微生物指标检测情况及其产品质量进行分析,在相关政府部门的有力的监管下,肉类产品质量与安全有了较大幅度提高.最后分析了我国肉类食品行业的现存问题,并提出改进的建议,最后对其发展进行展望. 相似文献
110.
《Journal of Plant Interactions》2013,8(2):69-81
Abstract Allelopathy is defined as the suppression of any aspect of growth and/or development of one plant by another through the release of chemical compounds. Although allelopathic interference has been demonstrated many times using in vitro experiments, few studies have clearly demonstrated allelopathy in natural settings. This difficulty reflects the complexity in examining and demonstrating allelopathic interactions under field conditions. In this paper we address a number of issues related to the complexity of allelopathic interference in higher plants: These are: (i) is a demonstrated pattern or zone of inhibition important in documenting allelopathy? (ii) is it ecologically relevant to explain the allelopathic potential of a species based on a single bioactive chemical? (iii) what is the significance of the various modes of allelochemical release from the plant into the environment? (iv) do soil characteristics clearly influence allelopathic activity? (v) is it necessary to exclude other plant interference mechanisms?, and (vi) how can new achievements in allelopathy research aid in solving problems related to relevant ecological issues encountered in research conducted upon natural systems and agroecosystems? A greater knowledge of plant interactions in ecologically relevant environments, as well as the study of biochemical pathways, will enhance our understanding of the role of allelopathy in agricultural and natural settings. In addition, novel findings related to the relevant enzymes and genes involved in production of putative allelochemicals, allelochemical persistence in the rhizosphere, the molecular target sites of allelochemicals in sensitive plant species and the influence of allelochemicals upon other organisms will likely lead to enhanced utilization of natural products for pest management or as pharmaceuticals and nutraceuticals. This review will address these recent findings, as well as the major challenges which continue to influence the outcomes of allelopathy research. 相似文献