全文获取类型
收费全文 | 6005篇 |
免费 | 609篇 |
国内免费 | 1647篇 |
专业分类
化学 | 4861篇 |
晶体学 | 27篇 |
力学 | 210篇 |
综合类 | 20篇 |
数学 | 1522篇 |
物理学 | 1621篇 |
出版年
2024年 | 8篇 |
2023年 | 224篇 |
2022年 | 241篇 |
2021年 | 245篇 |
2020年 | 279篇 |
2019年 | 193篇 |
2018年 | 222篇 |
2017年 | 241篇 |
2016年 | 253篇 |
2015年 | 280篇 |
2014年 | 384篇 |
2013年 | 459篇 |
2012年 | 564篇 |
2011年 | 538篇 |
2010年 | 405篇 |
2009年 | 414篇 |
2008年 | 360篇 |
2007年 | 349篇 |
2006年 | 326篇 |
2005年 | 241篇 |
2004年 | 207篇 |
2003年 | 150篇 |
2002年 | 144篇 |
2001年 | 163篇 |
2000年 | 255篇 |
1999年 | 211篇 |
1998年 | 103篇 |
1997年 | 86篇 |
1996年 | 65篇 |
1995年 | 61篇 |
1994年 | 58篇 |
1993年 | 46篇 |
1992年 | 57篇 |
1991年 | 50篇 |
1990年 | 34篇 |
1989年 | 30篇 |
1988年 | 71篇 |
1987年 | 123篇 |
1986年 | 83篇 |
1985年 | 22篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有8261条查询结果,搜索用时 15 毫秒
161.
Xi Chen Changqing YiMeijin Li Xin LuZhen Li Peiwei LiXiaoru Wang 《Analytica chimica acta》2002,466(1):79-86
Electrogenerated chemiluminescences (ECLs) based on tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+) and lupin alkaloids, for instance, sophoridine (SRI), matrine (MT), sophoranol (SR) and sophocarpine (SC) in an aqueous alkaline buffer solution (pH 9.0) are studied. The light emission is mainly caused by an electro-oxidation reaction between tertiary amino group on the alkaloid compounds and Ru(bpy)32+ in a thin layer flow cell equipped with a glassy carbon disc electrode (22.1 mm2) at the potential of +1.50 V (versus Ag/AgCl). The luminescence wavelength of 610 nm confirmed that ECL is caused by Ru(bpy)32+∗ to its ground state. ECL intensities of these lupin alkaloids are affected by the substituent character, three-dimensional conformation of hydrogen on β-carbon atom. Ionization potentials taken from calculation data further confirm the experimental results. In addition, the factors affecting the determination and HPLC separation of the four alkaloids are also investigated. 相似文献
162.
Wenjie Zhang Xiling Ding Zijie Li Xiaolan Chen Yufen Zhao 《Phosphorus, sulfur, and silicon and the related elements》2020,195(5):359-366
AbstractA one-pot synthetic strategy was developed for the synthesis of heterocyclic 1,4,2-oxazaphosphinanes via a three component Kabachnik-Fields reaction of 2-aminophenol, diphenyl H-phosphonate and carbonyl compounds. Through this newly developed method, 12 organophosphorus heterocycles and 2 related chrysin derivatives were synthesized with high yields. The target compounds were characterized by 1H, 31P and 13C NMR and MS. 相似文献
163.
Surface-enhanced Raman scattering in the ultraviolet spectral region: UV-SERS on rhodium and ruthenium electrodes 总被引:3,自引:0,他引:3
Ren B Lin XF Yang ZL Liu GK Aroca RF Mao BW Tian ZQ 《Journal of the American Chemical Society》2003,125(32):9598-9599
We report the first observation of surface-enhanced Raman scattering (SERS) excited with ultraviolet (UV) light from transition metal electrodes. Adsorbed pyridine and SCN- on rough rhodium (Rh) and ruthenium (Ru) electrodes, respectively, have been studied using 325 nm laser excitation. In contrast, the best enhancers in the visible and near infrared, silver and gold, do not produce UV-SERS. The experimental data of UV-SERS are in agreement with our preliminary theoretical calculation based on the electromagnetic enhancement mechanism. The enhancement factor is about 2 orders of magnitude for the Rh and Ru electrodes when they are excited at 325 nm. 相似文献
164.
Rong-Bin Huang Chun-Ru Wang Zhao-Yang Liu Lan-Sun Zheng Fei Qi Liu-Si Sheng Shu-Qin Yu Yun-Wu Zhang 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,33(1):49-52
A series of cluster anions C n X? are produced from laser ablation of appropriate samples, where X is selected as a group-VB element. The recorded mass spectra of these cluster anions display a drastic even/odd alternation on ion intensities: For C n N?, only anions with oddn can be observed; For C n P? and C n As?, cluster anions with evenn are produced but with lower signal intensities; For C n Sb?, the signal intensity of clusters does not show even/odd alternation; Finally, for C n Bi?, the intensities of cluster anions with evenn are higher than those with oddn. This parity effect can be attributed to the linear structure of the cluster anions, and the parity reversal of C n X? from C n N? to C n Bi? can be explained from the electronegativity decreasing of the heteroatom X as it descends in the group. The Hückel model was applied to account the structural feature of these clusters. 相似文献
165.
合成甲醇的催化剂Rh-ZnO/MWNTs的研究 总被引:2,自引:0,他引:2
研究新型的由多壁碳纳米管(MWNTs)负载的, ZnO助催的铑基甲醇合成催化剂. 当铑含量达到4%(w)时,催化剂具有较高的比表面积(99.6 m2•g-1), 催化剂的反应活化能为68.8 kJ•mol-1.在563 K, 1 MPa下,催化剂的最高催化活性和甲醇选择性分别为411.4 mg/gcat.•h和96.7%. TEM、TPR和TPD等表征结果显示,碳纳米管能增加Rh在催化剂表面的分散度,提高催化剂的还原温度并能增加氢物种的吸附量,这些结果将有助于更好地了解催化剂中各组分间的协同作用和催化活性中心本质. 相似文献
166.
《Fluid Phase Equilibria》2006,248(2):181-190
The vapor pressures of liquid hex-1-yne or hex-2-yne + methyl 1,1-dimethylethyl ether (MTBE) binary mixtures and of the three pure components were measured by a static method at several temperatures between 263 and 343 K. These data were correlated with the Antoine equation. Excess molar Gibbs energies GE were calculated for several constant temperatures, taking into account the vapor-phase imperfection in terms of the second molar virial coefficients, and were fitted to the Redlich–Kister equation. Calorimetric excess enthalpy HE measurements, for these binary mixtures, are also reported at 298.15 K. The experimental VLE and HE data were used, examining the binary mixtures hex-1-yne or hex-2-yne + MTBE in the framework of the DISQUAC and modified UNIFAC (Do) models. The DISQUAC calculations, reporting a new set of interaction parameters for the contact carbon–carbon triple bond/oxygen ether, is regarded as a preliminary approach. 相似文献
167.
We present a comprehensive survey of different C-H activation pathways over various kinds of active sites of terminal oxygens [=O] and bridge oxygens [-O-] by using Mo3O9 model systems. This allows us to provide some insights into fundamental issues concerning C-H activation by metal oxo species involved in many heterogeneous, homogeneous, and enzymatic processes. We show that H abstraction is the most feasible reaction pathway for the activation of a C-H bond on molybdenum oxides; and that [=O] is more active than [-O-]. Our calculations also suggest that (2+2) can be an alternative if M=O bond possesses a high polarity, while (5+2) can provide another effective pathway if two M=O bonds are in close proximity. Implications for the related heterogeneous, homogeneous, and enzymatic processes are discussed. 相似文献
168.
在镍电极表面制备了γ-氨丙基三甲摒在硅烷膜并对其形成和结构进行了研究 。镍电极表面有机官能团硅烷膜的X射线光电子能谱(XPS)结果表明氮、硅等元素 在电极表面的存在,并且氨基在膜中有若干种存在方式,包括自由氨基和质子化的 氨基。通过对表面增强拉曼散射光谱(SERS)谱图的分析,发现与电极表面作用的 吸附基团硅醇羟基和氨基发生了竞争吸附,它们及其邻近基团的拉曼谱几随着电位 的负称除了相对强度发生变化以外,还发生了一定的位移,这缘于吸咐基团吸附的 量和吸附取向随电极电位发生了变化并形成的更为复杂的界面结构;氨基不同存在 方式之间也会随之发生转变,这一结果与X射线光电子能谱分析的结果相符合。原 子力显微镜(AFM)结果表明镍电极表面的有机官能团硅烷膜呈现为一种较规则的 多孔结构。 相似文献
169.
Macromonomers bearing tridentate 2,6-bis(1,2,3-trizol-4-yl)pyridine (BTP) ligand unit synthesized via CuAAC “click” chemistry in the middle of the chain and two ureidopyrimidinone (UPy) motifs on the ends linked to the central BTP unit via PEGs of various lengths were synthesized and used for the study of gelation both with and without the presence of Eu(III) ions. Various interesting gelation behaviors were found. Gels exhibited various multi-responsive properties, including photoluminescence, mechanoresponsive properties, self-healing abilities, thermorepsonsive properties and chemoresponsive properties. The different gelation abilities and multi-responsive properties for different systems were shown to be resulted from difference in PEG linker lengths and the introduction of orthogonal metal–ligand coordination and hydrogen bonding interactions. The selective responsiveness to different chemicals would allow the development of modular sensory systems that utilize a combination of orthogonal supramolecular interactions. 相似文献
170.
Ho3+ doped TTB–BaTa2O6 phosphors were produced by the solid state reaction method. XRD analysis confirmed the formation of BaTa2O6 single phase which was accomplished by heat treatment at 1425 °C for 20 h. The crystal structure of TTB–BaTa2O6 allowed doping concentration of Ho3+ ions up to 10 mol%, maintaining a single phase composition. A second phase of HoTaO4 begins to appear at 15 mol%. The lattice structure and the crystallite sizes changed with the concentration of Ho3+. In SEM analysis, it was also shown that BaTa2O6 grain sizes changed with the concentration of Ho3+. EDS analysis revealed that the Ta/Ba ratio increased on the grains depending on Ho3+ concentration. Charge balance of the structure was formulated through the EDS results. In fluorometer analysis, a strong green emission (λem = 546.9 nm) was observed in the visible spectral region. The emission increased with the doping concentration of up to 2.5 mol%, and above this level decreased due to concentration quenching. 相似文献