全文获取类型
收费全文 | 14358篇 |
免费 | 2518篇 |
国内免费 | 3532篇 |
专业分类
化学 | 11203篇 |
晶体学 | 286篇 |
力学 | 866篇 |
综合类 | 292篇 |
数学 | 1882篇 |
物理学 | 5879篇 |
出版年
2024年 | 27篇 |
2023年 | 275篇 |
2022年 | 541篇 |
2021年 | 550篇 |
2020年 | 627篇 |
2019年 | 631篇 |
2018年 | 512篇 |
2017年 | 587篇 |
2016年 | 685篇 |
2015年 | 754篇 |
2014年 | 857篇 |
2013年 | 1168篇 |
2012年 | 1098篇 |
2011年 | 1214篇 |
2010年 | 1040篇 |
2009年 | 1020篇 |
2008年 | 1134篇 |
2007年 | 959篇 |
2006年 | 873篇 |
2005年 | 851篇 |
2004年 | 664篇 |
2003年 | 556篇 |
2002年 | 577篇 |
2001年 | 521篇 |
2000年 | 501篇 |
1999年 | 346篇 |
1998年 | 239篇 |
1997年 | 169篇 |
1996年 | 192篇 |
1995年 | 141篇 |
1994年 | 171篇 |
1993年 | 137篇 |
1992年 | 104篇 |
1991年 | 123篇 |
1990年 | 116篇 |
1989年 | 76篇 |
1988年 | 67篇 |
1987年 | 57篇 |
1986年 | 52篇 |
1985年 | 46篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 19篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1966年 | 5篇 |
1965年 | 4篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
使用分子图形软件设计出多种CnP-4(n =1~ 7)的结构模型 ,并进行B3LYP密度泛函几何构型优化和振动频率计算 .最稳定的CP-4和C2 P-3 都是平面环状结构 .最稳定的CnP-4(n =3 ,5 ,7)结构在直碳链的一端连接 1个磷原子且另一端是P3 C的四元环的平面结构 .最稳定的CnP-4(n =4,6)结构在直碳链的一端连接 1个磷原子且另一端是P3 的三元环的锄状结构 .直碳链可与平面环的磷原子生成大π键 .大多数构型是由C2 ,C3 ,C4子结构以环状或链状方式组成的 .碳原子与磷原子以交替方式排列的结构数量少、能量高 . 相似文献
102.
M. Carme Calderer M. Gregory Forest Qi Wang 《ournal of non Newtonian Fluid Mechanics》2004,120(1-3):69
We present a systematic derivation of hydrodynamic theories for nonhomogeneous nematic liquid crystal polymers (LCPs) by approximating the molecules as rigid ellipsoids, which can be either uniaxial molecules (spheroids) or biaxial ones. The short range interaction is assumed to be dominated by the excluded volume effect. Additional molecular properties with ellipsoidal molecules, e.g., a dipole–dipole interaction in extended nematics and chiral molecular structure in cholesterics, are accounted for through additional intermolecular potentials. Long-range molecular interaction is implemented through an averaged mean-field potential characterized by interaction functions. The extra elastic stress tensor is calculated using an extended virtual work principle consistent with conservation of angular momentum on the material volume, whereas the extra viscous stress is obtained by Batchelor’s volume averaging method. In the isothermal case, the theories are shown to satisfy the second law of thermodynamics, i.e., they admit positive production of entropy or energy dissipation. In the case of cholesterics, the kinetic theory reduces to the Leslie–Ericksen theory in the limit of weak translational diffusion, weak long range interaction, and weak flow. 相似文献
103.
LIANG Liang 《原子与分子物理学报》2003,20(4):575-578
By using the multichannel quantum defect theory(MQDT),we have evaluated the energy levels and lifetimes of 2sns ^3 S1,2snd ^3D(n=3-25)of BeI and 1 sns ^3s1,1snd ^3D(n=3-25)of BeⅢ,These energies and lifetimes that we have calculated not only agree with the recent measurements and theoretical calculation of Ref.4 and Ref.3, but also predict the lifetimes of 66 other highly excited states. 相似文献
104.
105.
πNN过程对Gottfried求和规则破坏的贡献 总被引:2,自引:0,他引:2
指出在计算πNN过程对核子结构函数的贡献时,将反冲核子视为物理核子更为合理.对Gottfried求和规则破坏、对质子中海夸克分布u和d不对称u(x)–d(x)等方面的贡献给出了详细的计算,与已有实验进行比较.结果表明π介子交换不是导致这一破坏以及影响核子结构函数的效应的惟一来源. 相似文献
106.
Lanthanide Complexes for Oligomerization of Phenyl Isocyanate 总被引:1,自引:0,他引:1
IntroductionThestudyonthereactivitiesoflanthanidecomplexesto wardisocyanateshasattractedmuchattention .Ithasbeenre portedthatlanthanidealkoxides,1anddivalentdiaza pentadi enyllanthanidecomplexes2 canbeusedasthesinglecompo nentinitiatorsforisocyanatespolymerization .Recentlyourre searchgrouphasalsofoundthatlanthanoceneamide ,3diva lentaryloxideofsamarium4 ,5anddivalentsamarocene6 areallactivefortheoligomerizationofphenylisocyanate,andtheactivespeciesforthesethreesystemswereallsuccessfullyisolat… 相似文献
107.
Strong limit-point criteria for singular Hamiltonian differential expressions with complex coefficients are obtained. The main results are extensions of the previous results due to Everitt, Giertz, and Weidmann for scalar differential expressions.
108.
109.
Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of thestationary laser intensity distribution Pst(Ⅰ) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationarylaser intensity distribution Pst(Ⅰ) by cross-correlation between noises and “color“ of noises (non-Markovian effect) whenthe laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(τ1 = τ2 = τ3 = τ). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect thatonly when λ≠ 0 can the noise-induced transition occur in the Pst(Ⅰ) curve, and only when τ≠ 0 and λ≠ 0, can the“reentrant noise-induced transition“ occur. The other case is that the three correlation times are not the same value,τ1 ≠τ2 ≠τ3. For this case, we find that the noise-induced transition occurring in the Pst (Ⅰ) curve is entirely differentwhen the values of τ1, τ2, and τ3 are changed respectively. In particular, when τ2 (self-correlation time of additivenoise) is changing, the ratio of the two maximums of the Pst(Ⅰ) curve R exhibits an interesting phenomenon, “reentrantnoise-induced transition“, which demonstrates the effect of noise “color“ (non-Markovian effect). 相似文献
110.