全文获取类型
收费全文 | 16540篇 |
免费 | 2629篇 |
国内免费 | 2546篇 |
专业分类
化学 | 12371篇 |
晶体学 | 151篇 |
力学 | 953篇 |
综合类 | 165篇 |
数学 | 2100篇 |
物理学 | 5975篇 |
出版年
2024年 | 22篇 |
2023年 | 370篇 |
2022年 | 419篇 |
2021年 | 626篇 |
2020年 | 760篇 |
2019年 | 689篇 |
2018年 | 573篇 |
2017年 | 571篇 |
2016年 | 825篇 |
2015年 | 814篇 |
2014年 | 941篇 |
2013年 | 1262篇 |
2012年 | 1351篇 |
2011年 | 1481篇 |
2010年 | 1063篇 |
2009年 | 962篇 |
2008年 | 1123篇 |
2007年 | 956篇 |
2006年 | 889篇 |
2005年 | 766篇 |
2004年 | 615篇 |
2003年 | 508篇 |
2002年 | 533篇 |
2001年 | 447篇 |
2000年 | 399篇 |
1999年 | 365篇 |
1998年 | 286篇 |
1997年 | 221篇 |
1996年 | 274篇 |
1995年 | 213篇 |
1994年 | 202篇 |
1993年 | 163篇 |
1992年 | 142篇 |
1991年 | 150篇 |
1990年 | 160篇 |
1989年 | 95篇 |
1988年 | 73篇 |
1987年 | 57篇 |
1986年 | 57篇 |
1985年 | 55篇 |
1984年 | 31篇 |
1983年 | 34篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1975年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
61.
On Polynomial Functions over Finite Commutative Rings 总被引:1,自引:0,他引:1
Jian Jun JIANG Guo Hua PENG Qi SUN Qi Fan ZHANG 《数学学报(英文版)》2006,22(4):1047-1050
Let R be an arbitrary finite commutative local ring. In this paper, we obtain a necessary and sufficient condition for a function over R to be a polynomial function. Before this paper, necessary and sufficient conditions for a function to be a polynomial function over some special finite commutative local rings were obtained. 相似文献
62.
63.
It is well known that topology and dynamics are two major aspects to determine the function of a network. We study one of the dynamic properties of a network: trajectory convergence, i.e. how a system converges to its steady state. Using numerical and analytical methods, we show that in a logical-like dynamical model, the occurrence of convergent trajectory in a network depends mainly on the type of the fixed point and the ratio between activation and inhibition links. We analytically proof that this property is induced by the competition between two types of state transition structures in phase space: tree-like transition structure and star-like transition structure. We show that the biological networks, such as the cell cycle network in budding yeast, prefers the tree-like transition structures and suggest that this type of convergence trajectories may be universal. 相似文献
64.
65.
Chirped fiber grating was used in dispersion compensator. We tried to use the same phase mask to write fiber grating of different wavelength with two methods to reduce the price of the fiber grating. 相似文献
66.
A one-pot procedure for the conversion of mono-substituted arenes and heteroarenes into the ortho-cyano derivatives was achieved through directed lithiation followed by electrophilic cyanation with phenyl cyanate. This reaction method proved to be applicable to halogen-lithium exchanged intermediates, so especially useful for the synthesis of benzonitriles. The scope of the reaction sequence was explored using a number of substrates. 相似文献
67.
Using the theoretically calculated point-defect total-energy values of Baraff and Schlüter in GaAs, anamphoteric-defect model has been proposed by Walukiewicz to explain a large number of experimental results. The suggested amphoteric-defect system consists of two point-defect species capable of transforming into each other: the doubly negatively charged Ga vacancyV
Ga
2–
and the triply positively charged defect complex (ASGa+V
As)3+, with AsGa being the antisite defect of an As atom occupying a Ga site andV
As being an As vacancy. When present in sufficiently high concentrations, the amphoteric defect systemV
Ga
2–
/(AsGa+V
As)3+ is supposed to be able to pin the GaAs Fermi level at approximately theE
v
+0.6 eV level position, which requires that the net free energy of theV
Ga/(AsGa+V
As) defect system to be minimum at the same Fermi-level position. We have carried out a quantitative study of the net energy of this defect system in accordance with the individual point-defect total-energy results of Baraff and Schlüter, and found that the minimum net defect-system-energy position is located at about theE
v
+1.2 eV level position instead of the neededE
v
+0.6 eV position. Therefore, the validity of the amphoteric-defect model is in doubt. We have proposed a simple criterion for determining the Fermi-level pinning position in the deeper part of the GaAs band gap due to two oppositely charged point-defect species, which should be useful in the future. 相似文献
68.
超软X射线流气式正比计数管 总被引:2,自引:0,他引:2
介绍了一种用于测量183~933eV超软X射线的圆柱形、侧窗式、流气式正比计数管,工作气体是0.11MPa的P-10气体或氦气-丙烷混合气体。计数管内径为φ25mm,直径为φ0.3mm的入射窗是由厚度80~90μgcm~2聚乙烯甲醛制成的。该计数管的特点:(1)薄窗,对软X射线透过率高。(2)流气式,工作寿命长。(3)能量分辨率好。(4)计数率高(1×10~(14)个/s)。(5)可测能区宽(0.183~10keV)。(6)可以方便更换窗膜材料、厚度及窗口直径。近几年来该计数管已经为高强度低能X光源提供较好监测。 相似文献
69.
在异源四倍体棉种中现已鉴定出22个芽黄突变体、26个芽黄基因,其中V1与V7、V2之间存在着部分同源关系。重叠牙黄基因V16V17的遗传主式独特,单体1测验的分离世代F2和BC恢复产生了黄化的单体株。鉴于杂中子生产现状,俄系统阐述了以芽黄作为指示性进行棉花杂种优势利用的可行性。 相似文献
70.
单模光纤中皮秒啁啾脉冲压缩 总被引:11,自引:2,他引:9
对单模光纤正群速色散区秒啁啾脉冲的非线性传进行了近似的解析分析和定量的数值计算。结果表明,负啁啾脉冲在传输过程中能得到有效压缩。压缩比与脉冲初始峰值功率和初始啁啾程度有关。初始峰值功率一定的脉冲,其压缩比随初始啁啾程度的增大面大,初始啁啾程度一定的脉冲,压缩比随初始峰值功率的增大而减小,表明自相位调制效应导致脉冲压缩效果变差。计算结果还表明,在脉冲时域宽度得到压缩的同时,光谱宽度也能得到同步压缩。 相似文献