全文获取类型
收费全文 | 12050篇 |
免费 | 1796篇 |
国内免费 | 1054篇 |
专业分类
化学 | 7438篇 |
晶体学 | 193篇 |
力学 | 218篇 |
综合类 | 72篇 |
数学 | 242篇 |
物理学 | 6737篇 |
出版年
2024年 | 32篇 |
2023年 | 106篇 |
2022年 | 300篇 |
2021年 | 322篇 |
2020年 | 341篇 |
2019年 | 300篇 |
2018年 | 317篇 |
2017年 | 404篇 |
2016年 | 440篇 |
2015年 | 423篇 |
2014年 | 531篇 |
2013年 | 975篇 |
2012年 | 834篇 |
2011年 | 712篇 |
2010年 | 547篇 |
2009年 | 723篇 |
2008年 | 694篇 |
2007年 | 889篇 |
2006年 | 725篇 |
2005年 | 666篇 |
2004年 | 609篇 |
2003年 | 545篇 |
2002年 | 457篇 |
2001年 | 404篇 |
2000年 | 358篇 |
1999年 | 362篇 |
1998年 | 296篇 |
1997年 | 272篇 |
1996年 | 238篇 |
1995年 | 179篇 |
1994年 | 165篇 |
1993年 | 154篇 |
1992年 | 122篇 |
1991年 | 107篇 |
1990年 | 66篇 |
1989年 | 65篇 |
1988年 | 36篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 21篇 |
1984年 | 27篇 |
1983年 | 6篇 |
1982年 | 18篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1974年 | 8篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Hamid Berriche 《International journal of quantum chemistry》2013,113(9):1349-1357
The potential energy curves and spectroscopic constants of the ground and many excited states of the FrAr van der Waals system have been determined using a one‐electron pseudopotential approach. The Fr+ core and the electron–Ar interactions are replaced by effective potentials. The Fr+Ar core–core interaction is incorporated using the accurate CCSD(T) potential of Hickling et al. (Phys. Chem. Chem. Phys. 2004, 6, 4233). This approach reduces the number of active electrons of the FrAr van der Waals system to only one valence electron, which permits the use of very large basis sets for the Fr and Ar atoms. Using this technique, the potential energy curves of the ground and many excited states are calculated at the self consistent field (SCF) level. In addition, the spin–orbit interaction is also considered using the semiempirical scheme for the states dissociating into Fr (7p) and Fr (8p). The FrAr system is not studied previously and its potential interactions, spectroscopic constants and dipole functions are presented here for the first time. Furthermore, we have predicted the X2Σ+–A2Π1/2, X2Σ+–AΠ3/2, X2Σ+–B2Σ1/2+, X2Σ+–32Π1/2, X2Σ+–32Π3/2, and X2Σ+–52Σ1/2+ absorption spectra. © 2012 Wiley Periodicals, Inc. 相似文献
972.
The infrared spectra of 4-Cl 2-Me, 4-Cl 3-Me and 6-Cl 3-Me phenols have been recorded. The vibrational spectrum has been analysed
assuming that the molecules belong toC
s
point group and a tentative assignment of the observed frequencies to various modes of vibration has been proposed. The near
ultraviolet absorption spectrum of these compounds has also been recorded. Assuming the transition to be electronically allowed
the strongest band on the longer wavelength side has been assigned as the (0, 0) band in each case. The spectrum has been
analysed in terms of several excited state frequencies which have been correlated with the ground state frequencies observed
in the infrared spectrum. 相似文献
973.
Using electron spectroscopy, X-ray photoelectron spectroscopy, and ESR spectroscopy, the blue forms of bisphthalocyanines of rare-earth elements were found to have structures of sandwich-type complexes with isoelectronic phthalocyanine ligands linked with tetravalent metal ions, [Pc2–Ln4+Pc2–]0. A comparative spectral and electrochemical study of the blue and green forms oftert-butyl-substituted bisphthalocyanines was carried out for almost the whole series of rare-earth metals. Lutetium octa(perfluoro-tert-butyl)- and perchlorobisphthalocyanines were synthesized for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 425–430, March, 1995.This study was financially supported by the Russian Foundation for Basic Research (grant No. 94-03-08903). 相似文献
974.
Yousry M. Issa Hosny Ibrahim Adel F. Shoukry Sabry K. Mohamed 《Mikrochimica acta》1995,118(3-4):257-263
Ion-association complexes of antazoline HCl [I], hydralazine HCl [II], amiloride HCl [III] and quinine sulphate [IV] with [Co(SCN)4]2– and [Co(NO2)6]3– were precipitated and the excess unreacted cobalt complex was determined. A new method using atomic emission and atomic absorption spectrometry for the determination of the above drugs in pure solutions and pharmaceutical preparations is given. The drugs can be determined in the ranges 0.3–3.0, 0.19–1.96, 0.3–3.0, and 0.78–7.82 mg/25 ml solutions of I, II, III, and IV, respectively, with mean relative standard deviations of 0.65–2.03 % and recovery values of 95.76–101.2% indicating high precision and accuracy. 相似文献
975.
D. Gozzi R. Caputo P. Luigi Cignini M. Tomellini G. Gigli G. Balducci E. Cisbani S. Frullani F. Garibaldi M. Jodice G. Maria Urciuoli 《Journal of Electroanalytical Chemistry》1995,380(1-2)
We present the results of a new experiment with our multicell set-up implemented with mass spectrometric measurements of4He and a highly improved neutron detector. The excess heat measured is comparable with the results of other laboratories, but no neutrons were found and the tritium excess was lower than expected from the power excess. 4He has been measured in the electrolysis gases and a tentative correlation of 4He with excess power is presented and discussed. 相似文献
976.
原子吸收法在有机分析中的应用(Ⅲ):茶叶中茶多酚的测定 总被引:14,自引:0,他引:14
研究了间接测定茶叶中茶多酚的原子吸收,用甲基异丁酮和丁醇的混合溶剂萃取茶汤中的茶多酚,与氨基酸分离后,加入碱性Cu3(PO4)2悬浮液反萃取并同茶多酚作用,离心沉降未作用的Cu3(PO4)2后,用原子吸收法测定Cu,可求得茶多酚的含量,本法可消除茶叶共存氨基酸的干扰,测定结果同标准方法一致,回收率范围为94%-104%,平均标准偏差为3.1%。 相似文献
977.
石墨探针—原子吸收光谱法测定人发中痕量铟的研究 总被引:2,自引:0,他引:2
探针原子化技术是一种实现等温原子化,改善灵敏度的行之有效的方法。本文采用此方法对痕量钿进行了一系列条件试验,峰面积与钿浓度在0~50ng·ml~(-1)范围内呈线性关系,其特征量4.8pg,检出限21.5pg,相对标准偏差5.7%,并成功地测定了成人发中铟的含量,范围在12~159pg·g~(-1),回收率96.4%~103.2%。该方法灵敏度高,操作简单、快速,结果满意。 相似文献
978.
J. Li S. Wang G. Sun H. Gao X. Yu S. Tang X. Zhao Z. Yi Y. Wang Y. Wei 《Materials Today Chemistry》2021
Novel Mn3O4-promoted double p?n junction MgAl2O4/CeO2/Mn3O4 heterojunction photocatalyst was constructed by one-step synthesis method and two-step synthesis method. The X-ray powder diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, optical and photoluminescence demonstrated that the MgAl2O4/CeO2/Mn3O4 heterojunction photocatalyst was synthesized by the two-step synthesis method comprehends a high crystallinity, charge carrier migration and separation efficiency, and relatively low optical absorption coefficient. The MgAl2O4/CeO2/Mn3O4 heterojunction photocatalysts were efficiently used as simulated sunlight-driven n-n and p-n double junction photocatalyst for the simultaneous degradation of methylene blue (MB) dye. The continuous double p?n junction MgAl2O4/CeO2/Mn3O4 heterojunctions strengthened the function of single n-n or p-n junction and guided the charge carrier migration and separation direction; thus, the oxidation and reduction reactions occur at the active site of spatial separation and prevent the recombination of electrons and holes. The results suggest that the continuous double p?n junction MgAl2O4/CeO2/Mn3O4 heterojunctions are very promising candidate material for enhancing the photocatalytic activity in the photocatalytic degradation of MB dye. 相似文献
979.
Can Ren Shuyu Xiao Junzi Li Prof. Lin Ma Prof. Rui Chen Dr. Chuanxiang Ye Prof. Yang Gao Prof. Chenliang Su Prof. Tingchao He 《化学:亚洲杂志》2021,16(4):309-314
Although the production of near-infrared (NIR)-absorbing organic polymers with an excellent nonlinear optical (NLO) response is vital for various optoelectronic devices and photodynamic therapy, the molecular design and relevant photophysical investigation still remain challenging. In this work, large NLO activity is observed for an NIR-absorbing bithiophene-based polymer with a unique head-to-head linkage in the NIR region. The saturable absorption coefficient and modulation depth of the polymer are determined as ∼−3.5×105 cm GW−1 and ∼32.43%, respectively. Notably, the polymer exhibits an intrinsic nonlinear refraction index up to ∼−9.36 cm2 GW−1, which is six orders of magnitude larger than that of CS2. The maximum molar-mass normalized two-photon absorption cross-section (σ2/M) of this polymer can be up to ∼14 GM at 1200 nm. Femtosecond transient absorption measurements reveal significant spectral overlap between the 2PA and excited state absorption in the 1000–1400 nm wavelength range and an efficient triplet quantum yield of ∼36.7%. The results of this study imply that this NIR-absorbing polymer is promising for relevant applications. 相似文献
980.
Dr. Zeyu Liu Dr. Tian Lu Prof. Aihua Yuan Xia Wang Qinxue Chen Dr. Xiufen Yan 《化学:亚洲杂志》2021,16(16):2267-2271
Inspired by recent experimental observation of molecular morphology and theoretical predictions of multiple properties of cyclo[18]carbon, we systematically studied the photophysical and nonlinear optical properties of cyclo[2N]carbons (N=3–15) allotropes through density functional theory. This work unveils the unusual optical properties of the sp-hybridized carbon rings with different sizes. The remarkable size dependence of the optical properties of these systems and their underlying nature are profoundly explored, and the relevance between aromaticity and optical properties are highlighted. The extrapolation curves fitted for energy level of frontier molecular orbitals, maximum absorption wavelength, and (hyper)polarizability of considered carbon rings are presented, which can be used to reliably predict corresponding properties for arbitrarily large carbon rings. The findings in this study will facilitate the exploration of potential application of cyclocarbons in the field of optical materials. 相似文献