全文获取类型
收费全文 | 326920篇 |
免费 | 3305篇 |
国内免费 | 642篇 |
专业分类
化学 | 160776篇 |
晶体学 | 4926篇 |
力学 | 15300篇 |
综合类 | 4篇 |
数学 | 48590篇 |
物理学 | 101271篇 |
出版年
2018年 | 10810篇 |
2017年 | 11708篇 |
2016年 | 7305篇 |
2015年 | 3353篇 |
2014年 | 3361篇 |
2013年 | 9689篇 |
2012年 | 11069篇 |
2011年 | 21059篇 |
2010年 | 12794篇 |
2009年 | 12626篇 |
2008年 | 18475篇 |
2007年 | 22125篇 |
2006年 | 7480篇 |
2005年 | 13873篇 |
2004年 | 9581篇 |
2003年 | 8656篇 |
2002年 | 6439篇 |
2001年 | 6484篇 |
2000年 | 5205篇 |
1999年 | 3888篇 |
1998年 | 3081篇 |
1997年 | 3106篇 |
1996年 | 3310篇 |
1995年 | 2973篇 |
1994年 | 2879篇 |
1993年 | 2841篇 |
1992年 | 3229篇 |
1991年 | 3005篇 |
1990年 | 2990篇 |
1989年 | 2974篇 |
1988年 | 2927篇 |
1987年 | 2934篇 |
1986年 | 2723篇 |
1985年 | 3723篇 |
1984年 | 3744篇 |
1983年 | 3116篇 |
1982年 | 3317篇 |
1981年 | 3244篇 |
1980年 | 3146篇 |
1979年 | 3267篇 |
1978年 | 3548篇 |
1977年 | 3271篇 |
1976年 | 3182篇 |
1975年 | 3018篇 |
1974年 | 2974篇 |
1973年 | 3013篇 |
1972年 | 1903篇 |
1968年 | 2142篇 |
1967年 | 2272篇 |
1966年 | 2089篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
This article provides a status report on discrete mathematics in America's schools, including an overview of publications
and programs that have had major impact. It discusses why discrete mathematics should be introduced in the schools and the
authors' efforts to advocate, facilitate, and support the adoption of discrete mathematics topics in the schools. Their perspective
is that discrete mathematics should be viewed not only as a collection of new and interesting mathematical topics, but, more
importantly, as a vehicle for providing teachers with a new way to think about traditional mathematical topics and new strategies
for engaging their students in the study of mathematics. 相似文献
974.
In this paper, an interior point cutting plane method (IPCPM)is applied to solve optimal power flow (OPF) problems. Comparedwith the simplex cutting plane method (SCPM), the IPCPM is simpler,and efficient because of its polynomial-time characteristic.Issues in implementing IPCPM for OPF problems are addressed,including (1) how to generate cutting planes without using thesimplex tableau, (2) how to identify the basis variables inIPCPM, and (3) how to generate mixed integer cutting planes.The calculation speed of the proposed algorithm is further enhancedby utilizing the sparsity features of the OPF formulation. Numericalsimulations on IEEE 14-300-bus test systems have shown thatthe proposed method is effective. 相似文献
975.
976.
S.H Chen 《Journal of luminescence》2004,109(2):93-102
The ZnS:Cu,Al,Au (P22G) phosphor powder was bombarded by an electron beam in an O2 ambient, Ar ambient and other mixture of gases. These gases consisted of mixtures of O2 and COx, and O2, COx and Ar gas. Auger electron spectroscopy (AES) was used to monitor changes in the surface composition of the P22G phosphor during electron bombardment. When the P22G phosphor powder was exposed to the electron beam in a water-rich O2 ambient, a chemically limited ZnO layer was formed on the surface. The electron beam degradation of the P22G phosphor powder was also performed in a dry O2 ambient and a layer of ZnSO4 was formed on the surface. The ZnSO4 formation decayed exponentially with time and it is postulated that this was due to the diffusion of the charge reactants through the ZnSO4 film to the reaction interfaces. The P22G phosphor exposed to the electron beam in an Ar ambient and to the other gas mixtures degraded at a lower rate than in the case of the O2 ambient. This suggests that Ar and COx may suppress the degradation of the P22G phosphor powder. 相似文献
977.
978.
We synthesized TPP[FeIII(Pc)(CN)2]2, PTMAx[FeIII(Pc)(CN)2]·y(MeCN), and PXX [FeIII(Pc)(CN)2], a new series of charge-transfer salts containing the axially-substituted phthalocyanine (Pc), [FeIII(Pc)(CN)2]−. In this molecular unit, the π conduction electron derived from the Pc-ring coexists with the d electron which is a potential source of a local magnetic moment. Therefore various phenomena associated with the interplay between local magnetic moments and conduction electrons are expected. We observed the giant negative magnetoresistance (GNMR) in all the three salts. The GNMR is highly anisotropic for the magnetic-field direction, and reflects the g-tensor anisotropy of the local magnetic moment in the [FeIII(Pc)(CN)2]− unit. This indicates that the GNMR in these salts originates from the strong π-d interaction in the [FeIII(Pc)(CN)2]− unit. 相似文献
979.
The cation distribution in spinel-related titanium-substituted lithium ferrite, Li0.5+0.5xFe2.5−1.5xTixO4 has been explored using interatomic potential and ab initio calculations. The results suggest that the cation distribution with Ti4+ substituting for Fe3+ on octahedral B sites and excess Li+ substituting for Fe3+ on tetrahedral A sites is stabilised by the formation of clusters of two octahedrally coordinated Ti4+ ions and one tetrahedrally coordinated Li+ ion linked through a common oxygen. 相似文献