全文获取类型
收费全文 | 2009篇 |
免费 | 35篇 |
国内免费 | 1篇 |
专业分类
化学 | 1026篇 |
晶体学 | 29篇 |
力学 | 79篇 |
数学 | 538篇 |
物理学 | 373篇 |
出版年
2023年 | 14篇 |
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 24篇 |
2019年 | 38篇 |
2018年 | 41篇 |
2017年 | 24篇 |
2016年 | 47篇 |
2015年 | 39篇 |
2014年 | 42篇 |
2013年 | 96篇 |
2012年 | 72篇 |
2011年 | 668篇 |
2010年 | 82篇 |
2009年 | 70篇 |
2008年 | 81篇 |
2007年 | 58篇 |
2006年 | 51篇 |
2005年 | 50篇 |
2004年 | 52篇 |
2003年 | 43篇 |
2002年 | 29篇 |
2001年 | 43篇 |
2000年 | 29篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 23篇 |
1996年 | 15篇 |
1995年 | 23篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1989年 | 11篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 14篇 |
1971年 | 6篇 |
排序方式: 共有2045条查询结果,搜索用时 62 毫秒
41.
Joseph S. Alper Robert I. Gelb Marietta H. Schwartz 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(4):333-348
Complexation stoichiometries and formation constants of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with NO
3
–
, Cl–, IO
3
–
and SO
4
2–
ions are determined by pH potentiometric and13C NMR spectrometric measurements. Estimates of H and S are obtained from the values of the temperature dependent formation constants and acid dissociation constants. All four anions form only 1 : 1 complexes with the triprotonated amine species. NO
3
–
and Cl– form 1 : 1 complexes only with the tetraprotonated amine, while IO
3
–
and SO
4
2–
form both 1 : 1 and 2 : 1 complexes. The complexation behavior is interpreted in terms of solvation and internal hydrogen bonding interactions. 相似文献
42.
S. Matejcik A. Kiendler P. Stampfli J. D. Skalny A. Stamatovic T. D. Märk 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):70-74
Highly monochromatized electrons (with 30 meV FWHM) are used in a crossed beams experiment to investigate electron attachment to oxygen clusters (O2)n at electron energies from approximately zero eV up to 2 eV. At energies close to zero the attachment cross section for the reaction (O2)n +e → O 2 ? varies inversely with the electron energy, indicative of s-wave electron capture to (O2)n. Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion. The vibrational spacings observed can be quantitatively accounted for. In addition electron attachment to mixed oxygen/ozone clusters has been studied in the energy range up to 4 eV. Despite the initially large excess of oxygen molecules in the neutral clusters the dominant attachment products are undissociated cluster ions (O3) m ? including the O 3 ? monomer while oxygen cluster ions (O2) n ? appear with comparatively low intensity. 相似文献
43.
44.
(1R,2R)-1,2-bis-(5-amino-1,3,4-thiadiazole-2-yl)ethane-1,2-diol (L) has been prepared by the reaction of thiosemicarbazide with (2R,3R)-(+)-tartaric
acid (I) and phosphorous oxychloride, and its complexes with Co(II), Ni(II) and Cu(II) have been obtained. The structures
of the ligand and its complexes have been established by i. r., 1H- and 13C-n.m.r. spectra, u.v.–vis–nir spectroscopy, elemental analyses, T.g.-D.t.a. and magnetic susceptibility measurements. 相似文献
45.
Fatma Alper 《Journal of organometallic chemistry》2006,691(12):2734-2738
Pentacarbonylpyrazinetungsten(0), (CO)5W(pyz), is not stable in solution in polar solvents such as acetone or dichloromethane and undergoes conversion to a bimetallic complex, (CO)5W(pyz)W(CO)5 plus free pyrazine. These three species exist at equilibrium. Using the quantitative 1H NMR spectroscopy, the equilibrium constant could be determined to be Keq = (5.9 ± 0.8) × 10−2 at 25 °C. Introducing a second pyrazine ligand into the molecule does not stabilize the complex, as cis-W(CO)4(pyz)2 was found to be less stable than W(CO)5(pyz) and, therefore, could not be isolated. However, introducing trimethylphosphite as a donor ligand into the complex leads to the stabilization of the carbonyl-pyrazine-metal(0) complexes, as shown by the synthesis of cis-W(CO)4[P(OCH3)3](pyz). This complex could be isolated from the reaction of the photogenerated W(CO)4[P(OCH3)3](tetrahydrofuran) with trimethylphosphite upon mixing for 2 h at 10 °C in tetrahydrofuran and characterized by elemental analysis, IR, MS, 1H, 13C, and 31P NMR spectroscopy. 相似文献
46.
H. Göktürk C. Eylem S. Hatipoĝlu H. N. Erten 《Journal of Radioanalytical and Nuclear Chemistry》1995,198(2):449-456
The sorption behavior of strontium and barium on kaolinite, bentonite and chlorite-illite mixed clay was studied by radioanalytical techniques using the batch method.90Sr (29.1 y) and133Ba (10.5 y) were used as radiotracers. Characterization of the solid matrices was done by FTIR and XRD spectrometries and specific surface area measurements. Synthetic groundwater was used as the aqueous phase. The variation of the distribution ratioR
d, as a function of metal ion loading was examined. The sorption isotherms were fitted to various isotherm models. The sorption energies were calculated to be in the range of 8–10 kJ/mol suggesting an ion exchange type of sorption mechanism. In detailed experiments, chlorite-illite mixed clay was first presaturated with K+, Sr2+, Ca2+ and Al3+ ions, respectively, prior to sorption studies with Ba2+ ions. The results of Ca2+ pretreated chlorite-illite were very similar to those of natural chlorite-illite, suggesting that the Ba2+ ion exchanges primarily with the Ca2+ ion on the clay minerals. 相似文献
47.
The π-π stacking interactions between maleimide's and nitrone's aromatic rings during the 1,3-dipolar cycloaddition were assumed to control the exo-endo selectivity of the reaction. The exo-endo ratios change during the reactions until they reach a constant value, which depends on the substituent. Electron-withdrawing groups favour the exo adduct while electron-donating groups favour the endo adduct. The nitrone ZnBr2 complexes react much more slowly than the free nitrone and the cycloaddition is exo selective in all cases independent of the substituents on the maleimide's aromatic ring. Thermal retrocycloaddition of the cycloadducts produce the corresponding nitrones. The ring opening in the presence of secondary amines did not induce imine formation. endo Adducts were shown for the first time to be the stable paramagnetic compounds. 相似文献
48.
Tuncer??aykaraEmail author Recai??nam Zülfiye??ztürk Olgun?Güven 《Colloid and polymer science》2004,282(11):1282-1285
The formation of metal complexes between water-soluble polymers, poly(vinyl alcohol) [PVA], poly(N-vinylpyrrolidone) [PVP], poly(acrylamide) [PAAm] and poly(ethylene oxide) [PEO] with trivalent metal ions, Fe3+, Cr3+, and V3+ were studied by using differential pulse polarography (DPP). The general experimental observation is the shift of totally reversible reduction peaks (M3++Hg+e–M2++Hg) towards more negative potentials when the complexing water-soluble polymers are added to the solution of trivalent metal ions. The negative shift in potential permitted the determination of complex formation constants (Kf) between trivalent metal ions and water soluble polymers. The complex formation constants for Fe3+, Cr3+, and V3+ ions with these polymers increased in the order of V3+>Cr3+>Fe3+. 相似文献
49.
Howard Alper 《Journal of organometallic chemistry》1975,96(1):95-98
(N-Carboalkoxy-1,2-dihydropyridine)iron tricarbonyl complexes have been isolated by treatment of either N-carboalkoxy-1,2 or -1,4-dihydropyridines with diiron ennecarbonyl. The organic ligand was liberated from these complexes by use of trimethylamine oxide. 相似文献
50.