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91.
Rao M Li Q Feng L Xia X Ruan L Sheng X Ge M 《Analytical and bioanalytical chemistry》2011,401(2):699-706
The diversity of microbial metabolites has been of interest and concern for a long time, yet a suitable method for discovering
these is still unavailable. In the work discussed in this report, ultra-performance liquid chromatography coupled with tandem
quadrupole and time of flight high-resolution mass spectrometry (UPLC–Q–TOF-HRMS), with MS data analysis, was set up to study
the metabolites of Streptomyces strain HCCB10043. It was found that besides antibacterial substances (A21978C complex) and two anti-aminopeptidase compounds
(valistatin and bestatin), this strain can produce a new aminopeptidase inhibitor, identified as 3-amino-2-hydroxy-4-phenylbutanoylvalylisoleucine.
This new compound had greater activity than valistatin or bestatin in aminopeptidase N (APN) inhibition assay. The results
proved that combination of UPLC–Q–TOF-MS analysis and classic purification and identification steps as complementary strategies
can provide a method with high reliability for research on microbial secondary metabolites. Furthermore, it has shown that
the study of secondary metabolic profiling might be the key to discovering new drugs. 相似文献
92.
A series of polysubstituted furans and dihydrofurans have been prepared from readily available oxodienes and bromonitromethane in modest to excellent yields. This facile synthetic method is developed on the basis of proprietary properties of nitro group such as strong electron-withdrawing ability and cleavability. The conversion of nitro-substituted dihydrofurans to furans is presumably realized by elimination of HNO2 under the aid of DABCO. 相似文献
93.
94.
Hui Min Wu Li Ping Lin Qin Lan Xu Wen Bo Han Song Zhang Ze Wen Liu Ya Ning Mei Zhu Jun Yao Ren Xiang Tan 《Tetrahedron letters》2017,58(7):663-665
Nodupetide (1), a new cyclodepsipeptide unique in its incorporation of a 3-hydroxy-4-methylhexanoic acid (HMHA) derived motif, was discovered from Nodulisporium sp. IFB-A163, a fungus residing in the insect (Riptortus pedestris) gut. The nodupetide structure was elucidated by its MS/MS and 2D NMR spectra, and its absolute configuration by the X-ray crystallography and modified Marfey’s method. Nodupetide is insecticidal against rice brown planthopper (Nilaparvata lugens) with an LD50 value of 70 ng/larva, and inhibitory towards the drug-resistant human pathogenic bacterium Pseudomonas aeruginosa with its MIC value (5.0 μM) comparable to that (3.2 μM) of ciprofloxacin, a prescribed antibacterial agent co-assayed equally. 相似文献
95.
96.
We propose different types of Łojasiewicz inequality at infinity for polynomials in two real variables. The formulas for the
Łojasiewicz exponents are given. 相似文献
97.
水稻叶片色素含量近红外光谱估测模型研究 总被引:5,自引:0,他引:5
以不同品种类型和不同施氮水平的水稻(Oryza sativa)叶片近红外光谱信息为基础,运用逐步多元回归法(Stepwise multiple linear regression,SMLR)、主成分回归法(Principal component regression,PCR)、偏最小二乘法(Partial least square,PLS)和BP神经网络法(Back-propagation neural network,BPNN),建立了水稻叶片中叶绿素a(Chl a)、叶绿素b(Chl b)、叶绿素a+b (Chl a+b)和类胡萝卜素(Car)的近红外预测模型.结果显示,利用8000~4000 cm-1波段范围的一阶导数(First derivative,FD)建模效果最佳.其中,基于PLS的预测模型效果最好;4类近红外色素模型的内部交叉验证误差分别为0.251,0.063,0.305和0.073;外部交叉验证的误差RMSEP分别为0.335,0.123,0.302和0.072,表明的预测效果较好.因此,可以基于近红外模型对水稻叶片色素含量进行快速测定. 相似文献
98.
设计了一个长度为20个核苷酸的分子信标,建立了有机磷农药和分子信标竞争结合适配体鉴定其活性的方法,对前期筛选的两条适配体进行了活性位点分析和改造.结果表明,分子信标设计合理,性能稳定,其发夹结构在室温下既可成功闭合也可成功打开,最佳的活性鉴定条件为分子信标与适配体添加比例1.25∶1,孵育时间50 min,孵育温度为室温.活性位点分析表明Loop2-4是4种有机磷农药共有的活性位点,Loop2-3及SS4-54适配体5’端和3 '端残余的核苷酸是甲拌磷重要的活性位点,Loop2-2和Loop4-2是丙溴磷和水胺硫磷共有的活性位点,Loop4-3是丙溴磷和氧化乐果共有的活性位点,Loop2-1和Loop4-1是水胺硫磷重要的活性位点.通过基因拼接改造的SS24-PJ-35适配体对丙溴磷和水胺硫磷的结合活性明显提高. 相似文献
99.
100.
A phytotoxic compound, identified as 2-(2-acetyl-3,5-dihydroxyphenyl) acetic acid (curvulinic acid), was isolated from liquid cultures of the phytopathogenic fungus Nimbya alternantherae. The activity of curvulinic acid on seed germination and seedling growth of Capsella bursa-pastoris was evaluated. Percentage seed germination of C. bursa-pastoris was decreased with increasing concentrations of curvulinic acid. The compound had stronger inhibitory effects on root length than shoot length. At a concentration of 600 microg x mL(-1), curvulinic acid caused 73.5% and 66.7% growth inhibition on roots and shoots with IC50 values of 204.7 and 281.1 microg x mL(-1), respectively. The finding of curvulinic acid in N. alternantherae and its herbicidal activity are reported here for the first time. 相似文献