全文获取类型
收费全文 | 2814篇 |
免费 | 487篇 |
国内免费 | 345篇 |
专业分类
化学 | 1223篇 |
晶体学 | 150篇 |
力学 | 282篇 |
综合类 | 12篇 |
数学 | 363篇 |
物理学 | 1616篇 |
出版年
2024年 | 4篇 |
2023年 | 73篇 |
2022年 | 110篇 |
2021年 | 97篇 |
2020年 | 101篇 |
2019年 | 96篇 |
2018年 | 105篇 |
2017年 | 96篇 |
2016年 | 126篇 |
2015年 | 106篇 |
2014年 | 168篇 |
2013年 | 311篇 |
2012年 | 186篇 |
2011年 | 252篇 |
2010年 | 157篇 |
2009年 | 204篇 |
2008年 | 211篇 |
2007年 | 173篇 |
2006年 | 156篇 |
2005年 | 115篇 |
2004年 | 106篇 |
2003年 | 76篇 |
2002年 | 65篇 |
2001年 | 58篇 |
2000年 | 60篇 |
1999年 | 60篇 |
1998年 | 67篇 |
1997年 | 52篇 |
1996年 | 42篇 |
1995年 | 27篇 |
1994年 | 21篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 6篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有3646条查询结果,搜索用时 218 毫秒
921.
Vukadin M. Leovac Ljiljana S. Jovanović Violeta S. Jevtović Giorgio Pelosi Franco Bisceglie 《Polyhedron》2007
Reaction of aqueous solutions of Ni(NO3)2 and pyridoxal semicarbazone (PLSC) in the presence of NaN3 afforded two complexes, viz. green, paramagnetic binuclear octahedral [Ni2(PLSC)2(μ1,1-N3)2(N3)2] · 2H2O (1) and, as admixture, red, octahedral [Ni(PLSC–H)2] · 2H2O (2) complex. Under the same reaction conditions, pyridoxal thiosemicarbazone (PLTSC) gave only one diamagnetic square-planar, red complex [Ni(PLTSC–H)N3] · H2O (3). In the absence of NaN3, the reaction of PLTSC and Ni(NO3)2 yielded brown paramagnetic octahedral complex [Ni(PLTSC)2](NO3)2 · H2O (4). 相似文献
922.
R.K. Mandal S. Lele 《Progress in Crystal Growth and Characterization of Materials》1997,34(1-4):183-190
In spite of various models being available for the icosahedral quasicrystal structure in Al-Mn(Fe)-Si system, a consistent model for describing the simple cubic approximant and icosahahedral structure in terms of rational and irrational sections of the same six dimensional cubic crystal seems to be lacking. Such a model is presented and the subtle difference between the present model and the previous ones is discussed. The necessity of such considerations is spelt out while accomplishing the partitioning of the tricontahedral motif (with extension in three dimensional pseudo direct space) based on the chemistry of the alloy. An algorithm for generating the required polyhedra for partitioning is also presented. 相似文献
923.
记忆是学生进行其他认知活动的基础,因记忆容量以及保持时间等限制具有一些缺陷,表现为分心、暗示、健忘、纠缠、空白、错认、偏颇等7种类型。记忆缺陷影响着学生的化学学习,了解化学学习中学生记忆的7种缺陷,可以精准地把握学生化学学习产生困难的原因,并采取一定的教学方法改进教学。 相似文献
924.
固-固掺杂结构声子晶体中弹性波的缺陷模 总被引:5,自引:4,他引:5
为了研究弹性波在固-固掺杂结构声子晶体中缺陷模的特性,推导出弹性波斜入射固-固掺杂结构声子晶体的转移矩阵。利用它计算了固-固掺杂结构声子晶体中弹性波的透射系数,得到由于掺杂在禁带的中间出现了多条缺陷模透射峰带,缺陷模透射峰带随杂质厚度的变化呈周期性地出现,在同一缺陷模透射峰带上缺陷模的频率随杂质厚度增加近似呈线性减少。缺陷模的这些特征可以作为设计声子晶体滤波器的理论依据。 相似文献
925.
Xin-Jun Wang Zhi-Qiang Gong Meng-dong He Ke-Qiu Chen Lingling Wang 《Physica E: Low-dimensional Systems and Nanostructures》2008,40(9):3014-3019
Using the scattering-matrix cascading method, we investigate the effect of structural defect on the acoustic phonon transmission quantization in a low-dimensional superlattice quantum waveguide. In the present system, the phonon transmission exhibits rather complex resonant behaviors. It is found that a lateral defect in an otherwise periodic structure modifies the transversal phonon transmission spectra nontrivially and completely washes away the transmission quantization due to the strong additional scattering by defect. However, the appreciable quantization survives in the presence of a longitudinal defect. Our results also show that by adjusting the geometric parameters of the structural defect, one can control the phonon transport of the structure to match practical requirements in devices. 相似文献
926.
This paper addresses the optimization problem of a spot-welded structure under fatigue life consideration. The so-called umbrella model of spot welds and the radial stresses around a spot weld were introduced into the optimization process. The idea was to study the optimization problem using the type of analysis which is now considered to be valid for fatigue life prediction. Two formations were considered: one maximizes the stiffness of a structure under fatigue life constraints and the other seeks the maximum fatigue life of the structure. The optimization results show that the optimization process has successfully found the global minimum values of the corresponding objective functions for both the formations. 相似文献
927.
928.
929.
铁基非晶稀土合金的结构转变和结构弛豫 总被引:1,自引:0,他引:1
通过对铁基非晶稀土合金结构转变和结构弛豫过程特征的研究,讨论了该材料的稳定性;认为稀土成份是影响合金品质和应用前景的关键因素。 相似文献
930.
Fatma Fakhfakh 《Journal of Mathematical Analysis and Applications》2008,347(1):235-242
In the present paper we investigate the stability of closed densely defined semi-Browder operators under operator perturbations that belong to a perturbation class related to compact operators. Furthermore, we apply the obtained results to give a characterization and to study the stability of Browder's essential approximate point spectrum and Browder's essential defect spectrum. 相似文献