全文获取类型
收费全文 | 22994篇 |
免费 | 3332篇 |
国内免费 | 2450篇 |
专业分类
化学 | 16160篇 |
晶体学 | 276篇 |
力学 | 1355篇 |
综合类 | 187篇 |
数学 | 2299篇 |
物理学 | 8499篇 |
出版年
2024年 | 67篇 |
2023年 | 426篇 |
2022年 | 742篇 |
2021年 | 846篇 |
2020年 | 851篇 |
2019年 | 833篇 |
2018年 | 714篇 |
2017年 | 738篇 |
2016年 | 1016篇 |
2015年 | 1038篇 |
2014年 | 1172篇 |
2013年 | 1610篇 |
2012年 | 1873篇 |
2011年 | 1996篇 |
2010年 | 1298篇 |
2009年 | 1270篇 |
2008年 | 1469篇 |
2007年 | 1355篇 |
2006年 | 1224篇 |
2005年 | 973篇 |
2004年 | 776篇 |
2003年 | 658篇 |
2002年 | 635篇 |
2001年 | 465篇 |
2000年 | 457篇 |
1999年 | 486篇 |
1998年 | 423篇 |
1997年 | 423篇 |
1996年 | 463篇 |
1995年 | 367篇 |
1994年 | 381篇 |
1993年 | 272篇 |
1992年 | 255篇 |
1991年 | 233篇 |
1990年 | 166篇 |
1989年 | 129篇 |
1988年 | 117篇 |
1987年 | 97篇 |
1986年 | 95篇 |
1985年 | 85篇 |
1984年 | 58篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
A novel and practical procedure was developed for the abnormal Beckmann rearrangement of steroid 17-oximes. Treatment of the 17-oximes with TFA/CH(OMe)(3) in boiling THF for 2 h gives the corresponding 13,17-seco alkene nitrile products in unprecedented high yields (70-92%). Since the alkene nitriles can be subsequently converted into 18-norsteroids, this general method provides a highly efficient route to these biologically important compounds and, by extension, to other structurally related natural products. 相似文献
92.
Chen YW Liu YC Lu SX Xu CS Shao CL Wang C Zhang JY Lu YM Shen DZ Fan XW 《The Journal of chemical physics》2005,123(13):134701
Self-assembled zinc oxide (ZnO) and indium-doping zinc oxide (ZnO:In) nanorod thin films were synthesized on quartz substrates without catalyst in aqueous solution by sol-gel method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), Raman-scattering spectroscopy, room-temperature photoluminescence (PL) spectra, and temperature-dependent PL spectra measurements. XRD and Raman spectra illustrated that there were no single In2O3 phase in ZnO lattice after indium doping. The PL spectra of ZnO showed a strong UV emission band located at 394 nm and a very weak visible emission associated with deep-level defects. Indium incorporation induced the shift of optical band gap, quenching of the near-band-edge photoluminescence and enhanced LO mode multiphonon resonant Raman scattering in ZnO crystals at different temperatures. Abnormal temperature dependence of UV emission integrated intensity of ZnO and ZnO:In samples is observed. The local state emission peak of ZnO:In samples at 3.37 eV is observed in low-temperature PL spectra. The near-band-edge emission peak at room temperature was a mixture of excitons and impurity-related transitions for both of two samples. 相似文献
93.
Yu-min?SongEmail author Xiao-lin?Lu Mei-ling?Yang Xiu-rong?Zheng 《Transition Metal Chemistry》2005,30(4):499-502
Fluorescence, absorption spectra have been produced by the interaction of platinum(IV), silver(I) and gold(III) ions with the berberine–DNA system (berberine, Scheme 1). Platinum(IV) and gold(III) ions show different effects from that of silver(I) ion on the spectral characteristics of the berberine–DNA system. Quenching fluorescence is seen with platinum(IV) and gold(III) ions addition, whereas increasing fluorescence is observed for silver(I) ions. The addition of gold(III) and silver(I) ions cause an increase in absorption of the berberine–DNA system. The above results suggest that different metal ions exhibit different affinities when binding to DNA correlates well with the ions’ charge, structure and the coordination ability. 相似文献
94.
WEI Ping-Rong JIA Lu LIU Chang-Rang FAN Yao-TingDepartment of Chemistry Zhengzhou University Zhengzhou Henan ChinaGAO SongResearch Center of Rare Earth Chemistry Peking University Beijing China 《中国化学》1994,12(6):503-508
The two complexes [Ni(oxen)Cu(L)2](ClO4)2.xH2O (L=2,2'-bipyridyl(bpy), 1,10-phenanthroline(phen)) have been synthesized, where oxen is N,N'-bis(2-aminoethyl)oxamido di-anion. The crystal structure of [Ni(oxen)Cu(bpy)2](ClO4)2.CH3OH has been determined by X-ray diffraction method. The crystal is triclinic system, space group P1 with a=12.179(1),b=12.298(2), c=11.476(2) A, a=97.57(1), B=97.52(1), 7=80.29(2), V=1669.04(67) A3, Z=2, Dcalcd=1.667 g/cm3. The structure has been refined to final R of 0.076 and Rw of 0.080, respectively. The complexes have an extended oxamido-bridged structure and consist of Ni(Ⅱ) ion in a square planar environment and Cu(Ⅱ) ion in a distorted octahedral environment. 相似文献
95.
The rate of electron transfer from organic sulfides to [CrV(ehba)2]− (ehba-2-ethyl-2-hydroxy butyric acid) decreases with a decrease in the polarity of the medium. The anionic surfactant, SDS and the cationic surfactant, CTAB have different effects on the kinetics of this reaction. The micellar inhibition observed in the presence of SDS is probably due to the decrease in the polarity and the electrostatic repulsion faced by the anionic oxidant from the anionic micelle and the partition of the hydrophobic substrate between the aqueous and micellar phases. The micellar catalysis in the presence of CTAB is attributed to the increase in the concentration of both reactants in the micellar phase. This micellar catalysis is observed to offset the retarding effects of the less polar micellar medium and the unfavorable charge-charge interaction between the + charge developed on S center in the transition state and the cationic micelle. This catalysis is contrary to the enormous micellar inhibition observed with IO4−, HSO5− and HCO4− oxidation of organic sulfides. 相似文献
96.
97.
98.
99.
100.
Y. -F. Lu M. Takai T. Nakata S. Nagatomo S. Namba 《Applied Physics A: Materials Science & Processing》1991,52(2):129-134
Maskless deposition of nickel lines on single crystalline Mn-Zn ferrite (MnO:ZnO:Fe2O3=31:17:52) has been investigated in a NiSO4 aqueous solution by Ar+ laser irradiation. A high deposition rate of up to 36.4m/s was achieved by a single scan of laser beam. The purity of deposited nickel layers is up to 86%. In particular, well-defined values of laser power and laser irradiation time were necessary for effective deposition. The deposition process was found to be a thermochemical process.On leave from D. S. Scanner Co., Ltd., 5-3-7. Fukushima, Osaka 553, Japan 相似文献