全文获取类型
收费全文 | 225篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 186篇 |
力学 | 6篇 |
数学 | 7篇 |
物理学 | 31篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2015年 | 6篇 |
2013年 | 6篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 15篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1943年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有230条查询结果,搜索用时 15 毫秒
31.
32.
The syntheses of tetraamines 10 (Scheme 3) and 17 (Scheme 4), which might be useful as rigid organizing scaffolds in dynamic or standard combinatorial chemistry, are described. The Diels‐Alder reaction of the electron‐rich dienophile 1,3‐diacetyl‐2,3‐dihydro‐1H‐imidazol‐2‐one ( 5 ) with benzo[c]thiophene or 2H‐pyran‐2‐one is the key step in their preparation. The intermediate fused cyclic diureas 9 and 16 are dimethylglycoluril analogues, and their crystal structures are examined. Diurea 9 (Fig. 2) crystallizes as a hydrate and forms undulating chains through a network of H‐bonds. These chains are interconnected through H‐bonds to the H2O molecules. H2O Molecules are not incorporated in the crystal of `bis‐urea' 16 (Fig. 3), the molecules of which associate through an extended three‐dimensional H‐bonding network. 相似文献
33.
34.
We prepared the PLGA‐loaded anti‐cancer drug and coated it with quantum dots to make it a dual‐function nanoparticles, and analyzed its potential use in cellular imaging and curing cancers. Two cancer cell lines, paclitaxel‐sensitive KB and paclitaxel‐resistant KB paclitaxel‐50 cervical carcinoma cells, were the relativistic models for analysis of the cytotoxicity of free paclitaxel and paclitaxel‐loaded PLGA conjugated with quantum‐dot nanoparticles. The paclitaxel‐loaded PLGA conjugated with quantum dots nanoparticles were significantly more cytotoxic than the free paclitaxel drug in paclitaxel‐resistant KB paclitaxel‐50 cells. This might have been because the cancer cells developed multi‐drug resistance (MDR), which hampered the action of free paclitaxel by pumping its molecules to extracellular areas. Addition of verapamil, a P‐glycoprotein inhibitor, reversed the MDR mechanism and significantly reduced KB paclitaxel‐50 cell viability. As a result, KB paclitaxel‐50 was highly associated with MDR on the cell membrane. The cytotoxicity results indicated that PLGA nanoparticles served as drug carriers and protected the drugs from MDR‐accelerated efflux. Combined quantum dots with PLGA nanoparticles allowed additional functionality for cellular imaging. 相似文献
35.
袁勤勤 杨正 李仁忠 Wesley J. Transue 李志鹏 江凌 Niranjan Govin Christopher C. Cummins 王学斌 《化学物理学报》2018,31(4):463-470
Gaseous dibenzo-7-phosphanorbornadiene P-sulfide anions APS-(A=C14H10 or anthracene) were generated via electrospray ionization, and characterized by magnetic-bottle photoelectron spectroscopy, velocity-map imaging (VMI) photoelectron spectroscopy, and quantum chemical calculations. The electron affinity (EA) and spin-orbit (SO) splitting of the APS· radical are determined from the photoelectron spectra and Franck-Condon factor simulations to be EA=(2.62±0.05) eV and SO splitting=(43±7) meV. VMI photoelectron images show strong and sharp peaks near the detachment threshold with an identical electron kinetic energy (eKE) of 17.9 meV at three different detachment wavelengths, which are therefore assigned to autodetachment from dipole-bound anion states. The B3LYP/6-31++G(d,p) calculations indicate APS· has a dipole moment of 3.31 Debye, large enough to support a dipole-bound electron. 相似文献
36.
Diuranium μ-η(6),η(6)-arene complexes supported by ketimide ligands were synthesized and characterized. Disodium or dipotassium salts of the formula M(2)(μ-η(6),η(6)-arene)[U(NC(t)BuMes)(3)](2) (M = Na or K, Mes = 2,4,6-C(6)H(2)Me(3)) and monopotassium salts of the formula K(μ-η(6),η(6)-arene)[U(NC(t)BuMes)(3)](2) (arene = naphthalene, biphenyl, trans-stilbene, or p-terphenyl) were both observed. Two different salts of the monoanionic, toluene-bridged complexes are also described. Density functional theory calculations have been employed to illuminate the electronic structure of the μ-η(6),η(6)-arene diuranium complexes and to facilitate the comparison with related transition-metal systems, in particular (μ-η(6),η(6)-C(6)H(6))[VCp](2). It was found that the μ-η(6),η(6)-arene diuranium complexes were isolobal with (μ-η(6),η(6)-C(6)H(6))[VCp](2) and that the principal arene-binding interaction was a pair of δ bonds (total of 4e) involving both metals and the arene lowest unoccupied molecular orbital. Reactivity studies have been carried out with the mono- and dianionic μ-η(6),η(6)-arene diuranium complexes, revealing contrasting modes of redox chemistry as a function of the system's state of charge. 相似文献
37.
Brillouin and Raman scattering studies of salol from room temperature to within 5 mK of the melting transition at Tm = 40.97°C are reported. Changes in the Brillouin shifts and linewidths were accurately determined by nonlinear least-squares fitting and deconvolution. A marked increase in the deconvoluted Brillouin linewidth (~400%) and a gradual softening (~20%) of the transverse acoustic modes were observed very close to Tm. The increase of the Brillouin linewidths was analyzed by a simple dislocation model assuming the hypersonic attenuation to be proportional to the concentration of thermally generated defects near Tm. The defect formation energy ED(T) was computed from the temperature-dependent linewidth data, and was found to decrease significantly (~60%) near Tm, suggesting a cooperative effect producing a catastrophic growth of defects which brings about melting by destroying the long range order of the crystal. The conclusion that melting is mediated by a sudden growth of defect concentration near Tm was further strengthened by Raman scattering experiments in which 13 new Raman modes appeared close to Tm. These new modes are believed to be defect activated through breaking of the local symmetry of the crystal. A slight softening of the Raman modes (~5%) was observed close to the melting point. 相似文献
38.
Comparing Classes of Finite Structures 总被引:3,自引:0,他引:3
We compare classes of structures using the notion of a computable embedding, which is a partial order on the classes of structures. Our attention is mainly, but not exclusively, focused on classes of finite structures. Also, a number of problems are formulated. 相似文献
39.
40.