全文获取类型
收费全文 | 3009篇 |
免费 | 118篇 |
国内免费 | 28篇 |
专业分类
化学 | 1746篇 |
晶体学 | 68篇 |
力学 | 123篇 |
综合类 | 1篇 |
数学 | 594篇 |
物理学 | 623篇 |
出版年
2023年 | 30篇 |
2022年 | 59篇 |
2021年 | 71篇 |
2020年 | 89篇 |
2019年 | 90篇 |
2018年 | 136篇 |
2017年 | 132篇 |
2016年 | 158篇 |
2015年 | 110篇 |
2014年 | 162篇 |
2013年 | 359篇 |
2012年 | 224篇 |
2011年 | 190篇 |
2010年 | 174篇 |
2009年 | 113篇 |
2008年 | 187篇 |
2007年 | 154篇 |
2006年 | 114篇 |
2005年 | 72篇 |
2004年 | 78篇 |
2003年 | 57篇 |
2002年 | 49篇 |
2001年 | 27篇 |
2000年 | 40篇 |
1999年 | 21篇 |
1998年 | 22篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 13篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1972年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有3155条查询结果,搜索用时 15 毫秒
1.
2.
Analysis Mathematica - We introduce and study the k-Hankel Gabor transform. We investigate the localization operators for this transform. In particular, we study their trace class properties and we... 相似文献
3.
4.
5.
6.
Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m2/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon. 相似文献
7.
Muhammad Usman Khan Muhammad Yasir Mehboob Riaz Hussain Zainab Afzal Muhammad Khalid Muhammad Adnan 《International journal of quantum chemistry》2020,120(22):e26377
The development of organic electron acceptor materials is one of the key factors for realizing high-performance organic solar cells (OSCs). Nonfullerene electron acceptors, compared to traditional fullerene acceptor materials, have gained much impetus owing to their better optoelectronic tunabilities and lower cost, as well as higher stability. Therefore, 5 three-dimensional (3D) cross-shaped acceptor materials having a spirobifullerene core flanked with 2,1,3-benzothiadiazole are designed from a recently synthesized highly efficient acceptor molecule SF(BR) 4 and are investigated in detail with regard to their use as acceptor molecules in OSCs. The density functional theory (DFT) and time-dependent DFT (TDDFT) calculations have been performed for the estimation of frontier molecular orbital (FMO) analysis, density of states analysis, reorganization energies of electron and hole, dipole moment, open-circuit voltage, photo-physical characteristics, and transition density matrix analysis. In addition, the structure-property relationship is studied, and the influence of end-capped acceptor modifications on photovoltaic, photo-physical, and electronic properties of newly selected molecules ( H1-H5 ) is calculated and compared with reference ( R ) acceptor molecule SF(BR) 4 . The structural tailoring at terminals was found to effectively tune the FMO band gap, energy levels, absorption spectra, open-circuit voltage, reorganization energy, and binding energy value in selected molecules H1 to H5 . The 3D cross-shaped molecules H1 to H5 suppress the intermolecular aggregation in PTB7-Th blend, which leads to high efficiency of acceptor material H1 to H5 in OSCs. Consequently, better optoelectronic properties are achieved from designed molecules H1 to H5 . It is proposed that the conceptualized molecules are superior than highly efficient spirobifullerene core-based SF(BR) 4 acceptor molecules and, thus, are recommended to experiments for future developments of highly efficient solar cells. 相似文献
8.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
9.
The dynamics of multiphoton transitions in a two-level spin system excited by transverse microwave and longitudinal RF fields with the frequencies ωmw and ωrf, respectively, is analyzed. The effective time-independent Hamiltonian describing the “dressed” spin states of the “spin + bichromatic field” system is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The direct detection of the time behavior of the spin system by the method of nonstationary nutations makes it possible to identify the multiphoton transitions for resonances ω0 = ωmw + rωrf (ω0 is the central frequency of the EPR line, r = 1, 2), to measure the amplitudes of the effective fields of these transitions, and to determine the features generated by the inhomogeneous broadening of the EPR line. It is shown that the Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening of spectral lines reduce only the nutation amplitude but do not change their frequencies. 相似文献
10.