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831.
Yurii N. Panchenko Charles W. Bock Joseph D. Larkin Alexander V. Abramenkov Frank Kühnemann 《Structural chemistry》2008,19(3):421-428
The ab initio-based, scaled quantum-mechanical molecular force field (SQM-FF) analysis of the vibrational spectra of the s-trans and s-gauche conformers of 2-methylbuta-1,3-diene (isoprene), reported previously at the HF/6-31G//HF/6-31G computational level [Bock,
et al. J Mol Struct 160: 337, 1987], has been updated in this article using a more complete set of experimental data on the
s-gauche conformer along with revised results for the s-trans conformer obtained in the gas phase, in a low-temperature matrix, and in neat crystals. Geometrical parameters and the calculated
wavenumbers derived from the SQM-FF at the MP2(FC)/aug-cc-pVDZ//MP2(FC)/aug-cc-pVDZ level are compared to experiment. The
analyses performed are consistent with the presence of a twisted high-energy s-gauche conformer of isoprene. 相似文献
832.
TheseparationofxyleneisomersusingGCisamuchdifficulttaskforalongtime,ontheotherhandtheyareveryimpoFtantindustrialmaterials,sofindingagoodstationaryphasehasbeenaninterestingwork.Anexcellentseparationofxyleneisomerswasobtainedbyusing2,6-di-O-pentyl-3-O... 相似文献
833.
A high level of ab initio and several density functional theory studies were performed with the target being to elucidate structural, spectroscopic, and energetic properties of triafulvene, cyclobutadiene, and tetrahedrane as three C4H4 isomers. For triafulvene all of the experimental values are available, but for cyclobutadiene only the IR spectra is known, while for tetrahedrane none of these physical values have been estimated experimentally. An excellent agreement between the computed and the experimental values were obtained where data are available, which makes it confident that the computed data should be very accurate. New structural data, IR spectra, and enthalpies of formation for both cyclobutadiene and tetrahedrane are offered. 相似文献
834.
835.
HP-β-环糊精对盐酸舍曲林异构体手性选择包合和色谱保留行为影响的研究 总被引:6,自引:0,他引:6
研究了不同色谱条件下HP-β-环糊精(HP-β-CD)作为反相高效液相色谱(RP-HPLC)手性添加剂对盐酸舍曲林异构体的手性选择性和色谱保留行为的影响。通过保留因子(k)的倒数1/k对[HP-β-CD]的良好线性关系证明HP-β-CD与盐酸舍曲林异构体形成了包合比为1∶1的包合物,并通过1/k对[HP-β-CD]的直线求得其结合常数。同时系统研究了pH值、缓冲液浓度(离子强度)、乙腈溶剂强度及温度对结合常数的影响,对结合常数与它们的关系做出了定量的描述;计算了手性分离过程中的热力学参数,并结合所计算的结 相似文献
836.
837.
838.
Tainara Boareto Capelari Arnaldo César Pereira Leandro Luan Gonçalves de Oliveira 《Analytical letters》2019,52(9):1462-1476
A simple, low-cost and sensitive electroanalytical method was developed for the simultaneous determination of p-nitrophenol and o-nitrophenol isomers in water samples at a glassy carbon electrode (CGE) in the presence of cationic surfactant. The electrochemical behavior of p-nitrophenol and o-nitrophenol was studied by cyclic voltammetry (CV) in 0.1?mol L?1 acetate/acetic acid buffer (pH 3.70) in the presence and absence of cetylpyridinium bromide. The resolution of overlapped cathodic peaks potentials (Epc) of isomers was successfully improved in the presence of 100.0?µmol L?1 cetylpyridinium bromide, thus making this approach ideal for the simultaneous determination of isomers. Under the optimized conditions in 0.05?mol L?1 HEPES buffer at pH 7.0 using differential pulse voltammetry (DPV) at a scan rate of 45?mV s?1, pulse amplitude of 220?mV and modulation time of 10?ms, limits of detection 0.59?µmol L?1 for p-nitrophenol and 1.14?µmol L?1 for o-nitrophenol were obtained with linear ranges from 2.0 to 60.0?µmol L?1 and 3.0 to 60.0?µmol L?1, respectively. The intraday precision was assessed as relative standard deviation (%) for 20.0 and 40.0?µmol L?1 concentrations were 4.30% and 2.41% for p-nitrophenol and 4.87% and 2.20% for o-nitrophenol, respectively. The developed method was applied for the determination of the isomers in lake water samples. The accuracy was attested by comparison with high-performance liquid chromatography with diode array detection (HPLC-DAD) as a reference analytical technique. Recovery values ranging from 90.3% to 111.8% also attested to the accuracy of method for analysis of real samples. 相似文献
839.
该文以Nafion膜为固定相,采用动态涂覆法将其涂覆在毛细管内壁,并研究了其在气相色谱分离烷烃、醇及取代芳香烃等方面的性能。结果表明,通过改变色谱分析条件,不同碳数的直链烷烃、直链醇、蒎烯类异构体、C8芳烃异构体取代芳香位置异构体均在Nafion膜固定相上得到了有效的分离,大部分异构体在该固定相上基本按照沸点从低到高的顺序依次洗脱。此外,还对基于Nafion膜的色谱柱分离蒎烯异构体和芳香位置异构体进行了热力学研究,并发现该柱分离异构体过程为放热过程,蒎烯分离受焓变和熵变共同控制,而芳香异构体分离过程主要受焓变的控制。 相似文献
840.
Takaya Murakami Yoshiaki Iwamuro Reiko Ishimaru Satoshi Chinaka Noriyuki Kato Yuki Sakamoto Natsuhiko Sugimura Hiroshi Hasegawa 《Journal of mass spectrometry : JMS》2019,54(3):205-212
A reliable method for structural analysis is crucial for the forensic investigation of new psychoactive substances (NPSs). Towards this end, mass spectrometry is one of the most efficient and facile methods for the identification of NPSs. However, the differentiation among 2‐, 3‐, and 4‐fluoromethcathinones (o‐, m‐, and p‐FMCs), which are ring‐fluorinated positional isomers part of the major class of NPSs referred to as synthetic cathinones, remains a challenge. This is mostly due to their similar retention properties and nearly identical full scan mass spectra, which hinder their identification. In this study, we describe a novel and practical method for differentiating the fluorine substitution position on the phenyl ring of FMCs, based on energy‐resolved mass spectrometry (ERMS) using an electron ionization‐triple quadrupole mass spectrometer. ERMS measurements showed that the three FMC positional isomers exhibited differences in relative abundances of both the fluorophenyl cation (m/z 95) and the fluorobenzoyl cation (m/z 123). The logarithmic plots of the abundance ratio of these two cations (m/z 95 to m/z 123) as a function of the collision energy (CE) followed the order of o‐FMC < p‐FMC < m‐FMC at each CE, which allowed the three isomers to be unambiguously and reliably differentiated. The theoretical dissociation energy calculations confirmed the relationship obtained by ERMS analyses, and additional ERMS measurements of methylmethcathinone positional isomers showed that the differences in abundance among the FMCs were attributed to the differences in their collision‐induced dissociation reactivities arising from the halogen‐induced resonance effects on the phenyl ring. Moreover, the method for differentiation described herein was successfully applied to the actual samples containing seized drugs. We expect that the described methodology will also contribute significantly to the reliable and accurate structural identification of NPSs in the fields of therapeutic, clinical, and forensic toxicology. 相似文献