全文获取类型
收费全文 | 184540篇 |
免费 | 1097篇 |
国内免费 | 310篇 |
专业分类
化学 | 93202篇 |
晶体学 | 2688篇 |
力学 | 9577篇 |
综合类 | 7篇 |
数学 | 21385篇 |
物理学 | 59088篇 |
出版年
2020年 | 2049篇 |
2019年 | 2466篇 |
2018年 | 3612篇 |
2017年 | 3686篇 |
2016年 | 4402篇 |
2015年 | 2058篇 |
2014年 | 3812篇 |
2013年 | 7481篇 |
2012年 | 5852篇 |
2011年 | 6935篇 |
2010年 | 5728篇 |
2009年 | 5812篇 |
2008年 | 6535篇 |
2007年 | 6507篇 |
2006年 | 5754篇 |
2005年 | 5110篇 |
2004年 | 4911篇 |
2003年 | 4452篇 |
2002年 | 4605篇 |
2001年 | 5056篇 |
2000年 | 3738篇 |
1999年 | 2877篇 |
1998年 | 2634篇 |
1997年 | 2482篇 |
1996年 | 2294篇 |
1995年 | 2086篇 |
1994年 | 2031篇 |
1993年 | 2067篇 |
1992年 | 2103篇 |
1991年 | 2416篇 |
1990年 | 2328篇 |
1989年 | 2403篇 |
1988年 | 2291篇 |
1987年 | 2319篇 |
1986年 | 2149篇 |
1985年 | 2687篇 |
1984年 | 2692篇 |
1983年 | 2338篇 |
1982年 | 2395篇 |
1981年 | 2288篇 |
1980年 | 2106篇 |
1979年 | 2415篇 |
1978年 | 2573篇 |
1977年 | 2667篇 |
1976年 | 2746篇 |
1975年 | 2543篇 |
1974年 | 2475篇 |
1973年 | 2642篇 |
1972年 | 2157篇 |
1971年 | 1976篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
102.
103.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and... 相似文献
104.
Siberian Mathematical Journal - Under study are the right-symmetric algebras over a field $ F $ which possess a “unital” matrix subalgebra $... 相似文献
105.
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
106.
N. I. Golovina G. N. Nechiporenko G. G. Nemtsev G. P. Dolganova V. P. Roshchupkin D. B. Lempert G. B. Manelis 《Russian Journal of Applied Chemistry》2007,80(1):24-30
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined. 相似文献
107.
In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K+-Na+. atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange. 相似文献
108.
Experimental data on the effect of thallium and sodium impurities on the lattice heat conductivity of PbTe at room temperature
are reported. Because the lattice of lead chalcogenides is strongly polarized near charged impurities, the effect of impurities
on the lattice heat conductivity depends substantially on their charge state. This property of the material has been used
to determine the charge state of the thallium impurity in PbTe. The results obtained argue for a model of quasi-local thallium-impurity
states which assumes low electron-correlation energy at an impurity center.
Fiz. Tverd. Tela (St. Petersburg) 40, 1206–1208 (July 1998) 相似文献
109.
We use the eikonal approximation to develop a general formula for the cross sections of inelastic collisions of multicharged
fast ions (including relativistic ions) with atoms that is applicable within a broad range of collision energies, has the
standard nonrelativistic limit, and becomes, in the ultrarelativistic case, the well-known result that follows from the exact
solution of the Dirac equation. As an example we study the excitation and ionization of a hydrogenlike atom, the single and
double excitation and ionization of a heliumlike atom, and multiple (up to the eighth order) ionization of the neon atom and
(up to eighteenth order) ionization of the argon atom. We derive simple analytical expressions for the inelastic cross sections
and establish recurrence relations linking the cross sections of ionization of different orders. Finally, we compare our results
with the experimental data.
Zh. éksp. Teor. Fiz. 114, 1646–1660 (November 1998) 相似文献
110.