全文获取类型
收费全文 | 272348篇 |
免费 | 8487篇 |
国内免费 | 4106篇 |
专业分类
化学 | 151627篇 |
晶体学 | 4011篇 |
力学 | 11656篇 |
综合类 | 138篇 |
数学 | 29999篇 |
物理学 | 87510篇 |
出版年
2022年 | 2372篇 |
2021年 | 2805篇 |
2020年 | 3144篇 |
2019年 | 3386篇 |
2018年 | 3627篇 |
2017年 | 3441篇 |
2016年 | 5390篇 |
2015年 | 4084篇 |
2014年 | 5815篇 |
2013年 | 13503篇 |
2012年 | 10884篇 |
2011年 | 12800篇 |
2010年 | 8392篇 |
2009年 | 8203篇 |
2008年 | 10911篇 |
2007年 | 10803篇 |
2006年 | 9943篇 |
2005年 | 9067篇 |
2004年 | 7925篇 |
2003年 | 6940篇 |
2002年 | 6864篇 |
2001年 | 7748篇 |
2000年 | 5806篇 |
1999年 | 4793篇 |
1998年 | 4053篇 |
1997年 | 4061篇 |
1996年 | 3772篇 |
1995年 | 3551篇 |
1994年 | 3282篇 |
1993年 | 3270篇 |
1992年 | 3562篇 |
1991年 | 3546篇 |
1990年 | 3339篇 |
1989年 | 3243篇 |
1988年 | 3249篇 |
1987年 | 3108篇 |
1986年 | 3027篇 |
1985年 | 4058篇 |
1984年 | 4178篇 |
1983年 | 3441篇 |
1982年 | 3776篇 |
1981年 | 3667篇 |
1980年 | 3524篇 |
1979年 | 3553篇 |
1978年 | 3777篇 |
1977年 | 3606篇 |
1976年 | 3815篇 |
1975年 | 3388篇 |
1974年 | 3516篇 |
1973年 | 3819篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
A. Lashgari S. Ghammamy R. Ramirez-Tagle G. Salgado-Moran 《Journal of Structural Chemistry》2015,56(8):1505-1513
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data. 相似文献
52.
Khusnutdinov R. I. Shchadneva N. A. Mayakova Yu. Yu. Aminov R. I. 《Russian Journal of Organic Chemistry》2021,57(6):950-953
Russian Journal of Organic Chemistry - Binder-free iron- and nickel-containing micro-, meso-, and macroporous zeolites FeHY and NiHY were found to effectively catalyze Knoevenagel condensation of... 相似文献
53.
Farsi R. Mohammadi M. K. Saghanezhad S. J. 《Russian Journal of Organic Chemistry》2021,57(12):2002-2009
Russian Journal of Organic Chemistry - Herein, we report the sulfonamide-functionalized covalent organic framework (COF-SO3H), prepared by condensation of melamine and terephthalaldehyde and... 相似文献
54.
The biodegradability of phtalic acid esters in marine and freshwater environments was characterized by their binding free energy with corresponding degrading enzymes. According to comprehensive biodegradation effects weights, the binding free energy values were converted into dimensionless efficacy coefficient using ratio normalization method. Then, considering comprehensive dual biodegradation effects value and the structural parameters of PAEs in both marine and freshwater environments, a 3D-QSAR pharmacophore model was constructed, five PAE derivatives (DBP−COOH, DBP−CHO, DBP−OH, DINP−NH2, and DINP−NO2) were screened out based on their environmental friendliness, functionality and stability. The prediction of biodegradation effects on five PAE derivatives by biodegradation models in marine and freshwater environment increased by 15.90 %, 15.84 %, 27.21 %, 12.33 %, and 8.32 %, and 21.57 %, 15.21 %, 20.99 %, 15.10 %, and 9.74 %, respectively. By simulating the photodegradation path of the PAE derivative molecular, it was found that DBP−OH can generate .OH and provides free radicals for the photodegradation of microplastics in the environment. 相似文献
55.
56.
57.
58.
59.
Terahertz(THz) wave emission from argon atom in a two-color laser pulses is studied numerically by solving the one-dimensional(1D) time-dependent Schr ¨odinger equation. The THz spectra we obtained include both discontinuous and continuum ones. By using the special basis functions that we previously proposed, our analysis points out that the discontinuous and continuum parts are contributed by bound–bound and continuum–continuum transition of atomic energy levels. Although the atomic wave function is strongly dressed during the interaction with laser fields, our identification for the discontinuous part of the THz wave shows that the transition between highly excited bound states can still be well described by the field-free basis function in the tunneling ionization regime. 相似文献
60.
Rajkumar P. Diwakar K. Subadevi R. Gnanamuthu R. M. Wang Fu-Ming Liu Wei-Ren Sivakumar M. 《Journal of Solid State Electrochemistry》2021,25(3):939-948
Journal of Solid State Electrochemistry - The “shuttle effect” of polysulfides is a serious issue, resulting in a decrease in the life-cycle of lithium-sulfur (Li-S) batteries. To... 相似文献