全文获取类型
收费全文 | 4077篇 |
免费 | 800篇 |
国内免费 | 360篇 |
专业分类
化学 | 847篇 |
晶体学 | 40篇 |
力学 | 712篇 |
综合类 | 131篇 |
数学 | 1232篇 |
物理学 | 2275篇 |
出版年
2024年 | 14篇 |
2023年 | 48篇 |
2022年 | 123篇 |
2021年 | 149篇 |
2020年 | 155篇 |
2019年 | 105篇 |
2018年 | 120篇 |
2017年 | 153篇 |
2016年 | 184篇 |
2015年 | 139篇 |
2014年 | 261篇 |
2013年 | 296篇 |
2012年 | 234篇 |
2011年 | 279篇 |
2010年 | 189篇 |
2009年 | 231篇 |
2008年 | 267篇 |
2007年 | 276篇 |
2006年 | 241篇 |
2005年 | 223篇 |
2004年 | 186篇 |
2003年 | 202篇 |
2002年 | 179篇 |
2001年 | 130篇 |
2000年 | 107篇 |
1999年 | 124篇 |
1998年 | 88篇 |
1997年 | 95篇 |
1996年 | 68篇 |
1995年 | 61篇 |
1994年 | 45篇 |
1993年 | 40篇 |
1992年 | 48篇 |
1991年 | 23篇 |
1990年 | 37篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
排序方式: 共有5237条查询结果,搜索用时 78 毫秒
31.
本文采用解析的方法计算了应变Si1-xGex层中p型杂质电离度与Ge组分x、温度T以及掺杂浓度N的关系.发现常温时,在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度的先变小,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加先变大,而后几乎不变;重掺杂时,杂质电离能变为0后,杂质电离度为1.低温下,轻掺杂时,载流子低温冻析效应较为明显,杂质的电离度普遍较小,当掺杂浓度大于Mott转换点时,载流子冻析效应不再明显,电离率迅速上升到1.在同一Ge组分下,随着掺杂浓度的升高,杂质的电离度先变小,后变大,而后又迅速上升到1.在同一掺杂浓度下,轻掺杂时,杂质的电离度随Ge组分的增加变大;重掺杂时,杂质电离能变为0后,杂质电离度为1. 相似文献
32.
33.
Considering a plane hyperbolic system with time-periodic coefficients, we construct a version of the direct Lyapunov method with the condition on the derivative of the Lyapunov functional along the trajectories of the system which is weakened by use of periodicity of the coefficients. We exhibit an illustrative example. 相似文献
34.
We propose objectives consisting of two mirrors with central holes for passage of a light beam. The optical layout ensures
multiple reflection of rays from both mirrors. We consider several approaches to calculating the design parameters for which
three and four aberrations do not occur. The objectives can be used in optical devices operating in the UV and IR regions
of the spectrum.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 267–270, March–April, 2007. 相似文献
35.
36.
Sarah Josefsson Rikard Westbom Lennart Mathiasson Erland Bjrklund 《Analytica chimica acta》2006,560(1-2):94-102
Pressurized liquid extractions were performed on eight sediments in order to investigate if a modified US EPA method (100 °C, 100 bar, n-heptane/acetone (1:1), 2 × 5 min) provided exhaustive extractions of polychlorinated biphenyls (PCBs) from sediment, and to study if the extractability of PCBs from the different sediments was affected by characteristics of the sediment. The recovery from the eight native sediments, contaminated in nature, was between 96.4% and 98.9%, as an average of the recoveries from 10 PCB congeners. Hundred percent recovery was defined as the sum of two consecutive extractions (2 × 5 min each) at the stated conditions. The recoveries of the individual congeners were above 94%, except for one congener in one sediment, which had a recovery of 92%. When the recoveries and different characteristics of the sediments were compared, no correlation appeared between recoveries and sediment PCB concentration, total organic carbon (TOC), soot carbon (SC) or amorphous carbon (AC). The fact that carbon did not influence the extractions was somewhat surprising, since previous experiments have indicated a connection. Instead, statistically significant (p < 0.05) correlations were observed for water content and carbon/nitrogen (C/N) ratio. The decrease in recoveries with decreased water content was attributed to less access of the solvent to the analytes due to less matrix swelling. The lowered recoveries with increased C/N ratio can indicate that a difference in structure of the organic matter exists, which influences the binding strength between the analytes and the matrix. The difference in structure can possibly be explained by different origin of the organic matter or by aging effects. Overall the method was found to be exhaustive and the excellent recoveries show that sediment characteristics do not influence the extractions markedly. 相似文献
37.
本文在M ogens B ladt和T ina H av iid R ydberg无市场假设,仅利用价格过程的实际概率的期权保险精算定价模型的基础上,得出了标的资产服从几何分数布朗运动的欧式期权定价公式,并说明了几何布朗运动是本文的一种特殊情况. 相似文献
38.
教学研究:介绍量子力学几个基本概念——兼答《关于量子几何相位的评注》中的几个主要问题 总被引:4,自引:4,他引:0
介绍了量子绝热定理的物理含义及成立的条件,认为有关主要献(Aharonov-Anandan,Bohm,孙昌璞等)的表述是正确的,而《关于量子几何相位的评注》^[1](以下简称《评注》)相应的表述不完全正确。在此基础上,认为这些献和教材(R.Shankar)得出的涉及Berry绝热相位的一些论述(不含Berry绝热相因子的瞬时能量本征态不满足含时Schroedinger方程等)也是正确的,而《评注》的论述与此相反。《评注》认为只有γn(C)才是Berry相位。本作则倾向于把γn(t)叫做Berry绝热相位,而把γn(C)=γn(T)-γn(0)叫做几何相位(geometric phase)^[2]。 相似文献
39.
40.