全文获取类型
收费全文 | 4990篇 |
免费 | 595篇 |
国内免费 | 355篇 |
专业分类
化学 | 1342篇 |
晶体学 | 130篇 |
力学 | 318篇 |
综合类 | 40篇 |
数学 | 1561篇 |
物理学 | 2549篇 |
出版年
2024年 | 6篇 |
2023年 | 81篇 |
2022年 | 89篇 |
2021年 | 114篇 |
2020年 | 142篇 |
2019年 | 122篇 |
2018年 | 133篇 |
2017年 | 155篇 |
2016年 | 171篇 |
2015年 | 144篇 |
2014年 | 219篇 |
2013年 | 538篇 |
2012年 | 222篇 |
2011年 | 259篇 |
2010年 | 203篇 |
2009年 | 295篇 |
2008年 | 321篇 |
2007年 | 308篇 |
2006年 | 261篇 |
2005年 | 255篇 |
2004年 | 202篇 |
2003年 | 191篇 |
2002年 | 229篇 |
2001年 | 158篇 |
2000年 | 164篇 |
1999年 | 134篇 |
1998年 | 141篇 |
1997年 | 99篇 |
1996年 | 69篇 |
1995年 | 60篇 |
1994年 | 73篇 |
1993年 | 52篇 |
1992年 | 40篇 |
1991年 | 42篇 |
1990年 | 18篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 23篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有5940条查询结果,搜索用时 468 毫秒
11.
The essential self-adjointness on a natural domain of the sharp-time Wick powers of the relativistic free field in two space-time dimension is proven. Other results on Wick powers are reviewed and discussed. 相似文献
12.
德国夏洛滕堡物理技术研究所(The Physikallisch-Technische Reichanstalt,简称PTR)是世界上第一个国家级的物理技术研究所,它开创了科学研究和技术研究相结合,服务于工业和国家经济之先河。文章从PTR建立的历史背景、早期研究工作和所产生的影响等方面作较为全面的讨论。 相似文献
13.
We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules. 相似文献
14.
15.
Hiromichi Kurosu Mizuyo Kikuchi Isao Ando 《Journal of Polymer Science.Polymer Physics》1995,33(5):769-775
The solid-state 15N CP/MAS NMR spectra and 15N spin-lattice relaxation times (T1) of doped and dedoped 15N-labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high-resolution solid-state 15N NMR. The 15N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half-width of the 15N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wiley & Sons, Inc. 相似文献
17.
Jrg Winkelmann 《Mathematische Nachrichten》1997,186(1):285-302
We investigate under which conditions an algebraic group G defined over a locally compact field k admitr a subgroup Γ? G(k) which is dense in the Zariski topology, but discerte in the topology induced by the locally compact topology on k. For non—solvable groups we provide a complete answer. 相似文献
18.
Montgomery Multiplication in GF(2k) 总被引:8,自引:0,他引:8
We show that the multiplication operation c=a · b · r-1 in the field GF(2k can be implemented significantly faster in software than the standard multiplication, where r is a special fixed element of the field. This operation is the finite field analogue of the Montgomery multiplication for modular multiplication of integers. We give the bit-level and word-level algorithms for computing the product, perform a thorough performance analysis, and compare the algorithm to the standard multiplication algorithm in GF(2k. The Montgomery multiplication can be used to obtain fast software implementations of the discrete exponentiation operation, and is particularly suitable for cryptographic applications where k is large. 相似文献
19.
应用七级目测法对浙江中部地区27个夏熟作物田样点的杂草进行了优势等级调查,将所得数据转换成重要值,以杂草在27个样点中的重要值为运算指标,应用主成分分析法和图论聚类中的最小生成树法,对24种杂草的生态学相似性进行了比较,指出了长期使用单一的除草剂导致农田杂草种群迅速更迭的原因:杂草对除草剂的敏感性差异及不同杂草间的生态学特性的差异。 相似文献
20.
Temperature effects on deposition rate of silicon nitride films were characterized by building a neural network prediction model. The silicon nitride films were deposited by using a plasma enhanced chemical vapor deposition system and process parameter effects were systematically characterized by 26−1 fractional factorial experiment. The process parameters involved include a radio frequency power, pressure, temperature, SiH4, N2, and NH3 flow rates. The prediction performance of generalized regression neural network was drastically improved by optimizing multi-valued training factors using a genetic algorithm. Several 3D plots were generated to investigate parameter effects at various temperatures. Predicted variations were experimentally validated. The temperature effect on the deposition rate was a complex function of parameters but N2 flow rate. Larger decreases in the deposition rate with the temperature were only noticed at lower SiH4 (or higher NH3) flow rates. Typical effects of SiH4 or NH3 flow rate were only observed at higher or lower temperatures. A comparison with the refractive index model facilitated a selective choice of either SiH4 or NH3 for process optimization. 相似文献