全文获取类型
收费全文 | 8557篇 |
免费 | 1192篇 |
国内免费 | 761篇 |
专业分类
化学 | 5292篇 |
晶体学 | 164篇 |
力学 | 142篇 |
综合类 | 51篇 |
数学 | 105篇 |
物理学 | 4756篇 |
出版年
2024年 | 10篇 |
2023年 | 63篇 |
2022年 | 145篇 |
2021年 | 224篇 |
2020年 | 233篇 |
2019年 | 197篇 |
2018年 | 214篇 |
2017年 | 287篇 |
2016年 | 307篇 |
2015年 | 300篇 |
2014年 | 401篇 |
2013年 | 697篇 |
2012年 | 641篇 |
2011年 | 488篇 |
2010年 | 392篇 |
2009年 | 524篇 |
2008年 | 510篇 |
2007年 | 641篇 |
2006年 | 486篇 |
2005年 | 474篇 |
2004年 | 432篇 |
2003年 | 381篇 |
2002年 | 333篇 |
2001年 | 253篇 |
2000年 | 227篇 |
1999年 | 252篇 |
1998年 | 199篇 |
1997年 | 207篇 |
1996年 | 165篇 |
1995年 | 137篇 |
1994年 | 126篇 |
1993年 | 115篇 |
1992年 | 92篇 |
1991年 | 90篇 |
1990年 | 51篇 |
1989年 | 51篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 10篇 |
1984年 | 22篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 997 毫秒
41.
42.
Bi12TiO20纳米粉体的制备及其光吸收特性研究 总被引:3,自引:0,他引:3
以钛酸四丁酯和硝酸铋为原料 ,利用化学溶液分解法制备了Bi12 TiO2 0 纳米多晶粉体 .采用XRD和TEM对其结构和形貌进行了表征 .结合热重 差热 (TG DTA)分析 ,探讨了Bi12 TiO2 0 晶相的形成机理 .通过UV Vis漫反射谱的测定 ,研究了Bi12 TiO2 0 纳米晶粉体的光吸收特性 .结果显示 ,从组成为化学计量比的前驱液中可以很容易制得纯Bi12 TiO2 0 纳米晶粉体 ,该Bi12 TiO2 0 纳米晶粉体呈现了在很宽的波长范围内 (5 6 0~ 385nm )对光的吸收的特性 . 相似文献
43.
Fiber-Optic Backscattering Profile Measurements for Determination of the Optical Coefficients of Turbid Media 总被引:1,自引:0,他引:1
A. M. Maiorova S. P. Kotova M. A. Rakhmatulin V. V. Yakutkin 《Journal of Russian Laser Research》2003,24(1):1-13
The necessity of using anisotropic approximation in techniques for determining optical parameters from the backscattered radiation profile is shown. A fiber-optic technique for simultaneous determination of the anisotropy parameter as well as the scattering and absorption coefficients of turbid media is proposed. It is based on the comparison of the experimental backscattered radiation profiles and those obtained by the numerical Monte Carlo method. 相似文献
44.
A new method based on anion exchange resin separation and graphite furnace atomic absorption spectrometry (GFAAS) detection
is proposed for the determination of inorganic tin species. The result showed that Sn(IV) was quantitatively retained on the
resin when [HCl] = 9.0 mol · L−1, but Sn(II) could not be adsorbed on the resin under the same condition. Thus, a separation of Sn(II) and Sn(IV) has been
realized. When the concentration of NaOH solution was between 2.0–7.0 mol · L−1, Sn(IV) that adsorbed on the resin could be eluated from the resin completely. Meanwhile, under the atmosphere and the nitrogen
states, the translation between Sn(II) and Sn(IV) was investigated. Under the optimal conditions, the detection limit of Sn(IV)
is 0.40 μg · L−1 with RSD of 2.3% (n = 5, c = 2.0 μg · L−1). The proposed method was applied to the speciation analysis of tin in different water samples and the recovery of total
Sn was in the range of 98.7–101.7%. In order to verify the accuracy of the method, a certified reference water sample was
analyzed and the results obtained were in good agreement with the certified value. 相似文献
45.
Cordula Grüttner Knut Müller Joachim Teller Fritz Westphal Allan Foreman Robert Ivkov 《Journal of magnetism and magnetic materials》2007
Bionized nanoferrite (BNF) particles with high specific power absorption rates were synthesized in the size range of 20–100 nm by high-pressure homogenization for targeted cancer therapy with alternating magnetic fields. Several strategies were used to conjugate antibodies to the BNF particles. These strategies were compared using an immunoassay to find optimal conditions to reach a high immunoreactivity of the final antibody–particle conjugate. 相似文献
47.
半导体中多光子吸收跃迁速率的全量子理论分析 总被引:3,自引:3,他引:0
本文从非线性光学中辐射跃迁速率的表达式出发,在全量子理论下,导出了半导体中任意阶多光子吸收跃迁速率的一般表达式。理论分析结果表明,n光子吸收跃迁速率与光强的n次方和n阶光子相干度成正比。本文在多能带及二能带理论模型下,对多光子吸收跃迁速率的一般表达式进行了化简,并对非线性相互作用项对跃迁速率的贡献,作了讨论。 相似文献
48.
49.
将三阶微扰理论应用于单晶GaAs半导体,结合与实际相接近的能带结构,得到了GaAs中三光子吸收系数的解析式表达式,在考虑了激发电子的逃逸过程的情况下,进而推导了负电子亲和势GaAs光电阴极中三光子光电发射的发射系数的解析表达式.两表达式得到的理论数值分别与用ns量级脉宽、2.06μm波长的激光测得的GaAs中三光子吸收系数和GaAs(Cs,O)光电阴极中三光子发射系数的实验值相比较,吻合较好. 相似文献
50.
We have devised a new method for bis(tributyltin)oxide (TBTO) determination in marine sediments and mussels. This technique involves an n-hexane/methylene chloride mixture extraction and extract purification with a sodium hydroxide wash in order to eliminate interfering compounds. TBTO is then extracted again by nitric acid and converted into an inorganic tin species; the analysis has been effected using Zeeman graphite furnace-atomic absorption spectrophotometry. The method detection limit for the matrices examined is 0.004 μg TBTO g?1 (wet weight) and is sufficient for the analysis in real samples. The percentage recovery of TBTO from sediments and mussels samples is higher than 85% and 95% respectively. This method has been applied to TBTO level determination in sediments and mussels (Mytilus galloprovincialis) sampled in the harbour area in Taranto, where mussel culture activities are much developed; the TBTO levels obtained in sediments and mussels were in the range 15-47 ng g?1 (wet weight) and 11-30 ng g?1 (wet weight) respectively. Such values are comparable with those found in other harbour areas in the Mediterranean Sea. 相似文献