全文获取类型
收费全文 | 9014篇 |
免费 | 299篇 |
国内免费 | 603篇 |
专业分类
化学 | 5031篇 |
晶体学 | 50篇 |
力学 | 95篇 |
综合类 | 4篇 |
数学 | 127篇 |
物理学 | 4609篇 |
出版年
2024年 | 8篇 |
2023年 | 142篇 |
2022年 | 95篇 |
2021年 | 94篇 |
2020年 | 168篇 |
2019年 | 139篇 |
2018年 | 116篇 |
2017年 | 166篇 |
2016年 | 184篇 |
2015年 | 159篇 |
2014年 | 309篇 |
2013年 | 512篇 |
2012年 | 501篇 |
2011年 | 676篇 |
2010年 | 555篇 |
2009年 | 651篇 |
2008年 | 573篇 |
2007年 | 730篇 |
2006年 | 568篇 |
2005年 | 495篇 |
2004年 | 435篇 |
2003年 | 339篇 |
2002年 | 262篇 |
2001年 | 232篇 |
2000年 | 197篇 |
1999年 | 206篇 |
1998年 | 166篇 |
1997年 | 170篇 |
1996年 | 148篇 |
1995年 | 122篇 |
1994年 | 109篇 |
1993年 | 125篇 |
1992年 | 85篇 |
1991年 | 89篇 |
1990年 | 63篇 |
1989年 | 43篇 |
1988年 | 48篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 23篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 27篇 |
1981年 | 23篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 13篇 |
排序方式: 共有9916条查询结果,搜索用时 15 毫秒
31.
Interface properties of BCN/GaN metal-insulator-semiconductor (MIS) structures are investigated by X-ray photoelectron spectroscopy (XPS) and capacitance versus voltage (C-V) characteristics measurements. The BCN/GaN samples are fabricated by in situ process consisting of plasma treatment and deposition of BCN film in the plasma-assisted chemical vapor deposition (PACVD) apparatus. XPS measurement shows that the oxide formation at the BCN/GaN interface is suppressed by nitrogen (N2) and hydrogen (H2) plasma treatment. The interface state density is estimated from C-V characteristics measured at 1 MHz using Terman method. The minimum interface state density appears from 0.2 to 0.7 eV below the conduction band edge of GaN. The minimum value of the interface state density is estimated to be 3.0 × 1010 eV−1 cm−2 for the BCN/GaN structure with mixed N2 and H2 plasma treatment for 25 min. Even after annealing at 430 °C for 10 min, the interface state density as low as 6.0 × 1010 eV−1 cm−2 is maintained. 相似文献
32.
A plasma reactor that has a transient traveling arc has been used to study hydrogen in relation to in-flight reduction of metal oxide particles. Experiments were done to determine the nature of the arc and its interaction with the reactor gas. The lifetime of the excited atomic hydrogen was measured and it was found to be more than 4 ms after the arc had ceased. Powders and tablets of oxides were exposed to the pulsed-arc treated hydrogen and found to react much more rapidly and intensely than when exposed to hot molecular hydrogen. The results suggest that atomic hydrogen will exist throughout the volume of such a reactor for a period that is sufficient to reduce particles of FeO, Cr2O3, and TiO2. 相似文献
33.
34.
Saeed Balalaie Elahe Kowsari Mehri S. Hashtroudi 《Monatshefte für Chemie / Chemical Monthly》2003,134(3):453-456
Summary. Three component condensation of alkylacetoacetates, primary amines, and alkyl cyanoacetates catalyzed by solid supports under
microwave irradiation gave N-alkyl 3-cyano-6-hydroxy-2(1H)-pyridinones with high yields. Upon carrying out the reaction under the same condition on acidic alumina, zeolite HY, silica
gel, and montmorillonite K-10, the best yields were achieved by silica gel.
Corresponding author. E-mail: balalaie@yahoo.com
Received August 28, 2002; accepted September 3, 2002 相似文献
35.
A closed microwave digestion method followed by inductively coupled plasma spectrometric (ICP-MS) analysis was evaluated for the determination of trace impurities in photoresist. To optimize the digestion procedure, several digestion parameters such as acid, heating temperature and heating time were evaluated. Besides, the digestion efficiency of used photoresist material and the recovery of analyte elements obtained by the use of gravimetric method and ICP-MS measurement, individually, were also compared to clarify the completeness of digestion. According to our experiments, the gravimetric method was found to be not so relevant to the completeness of digestion, because the remaining sample matrix could cause suppression effect in the subsequent ICP-MS measurement. In view of minimizing blank value and working time, a simple single-step heating program was proposed to mineralize 0.25 ml of photoresist material with 5 ml of nitric acid at 180 °C for 10 min. Based on the comparative study of the analytical results obtained by instrumental neutron activation analysis (INAA) and proposed method, the reliability of proposed method for the determination of trace metallic impurities in photoresist material has been confirmed. 相似文献
36.
钛酸钾晶须通常是直径和长度在微米量级的无机晶须 ,可用K2 O·nTiO2 表示其组成 ,n =1,2 ,4 ,6 ,8,[1] .六钛酸钾晶须具有耐高温、耐腐蚀、纤维拉伸强度高、导热系数小、红外反射率高 ,硬度低的特点 .在民用及工业方面有很多应用 .如催化剂载体、离子吸附交换材料、高温过滤器、绝热材料、耐摩擦材料等[2~ 5] .钛酸钾纳米线的合成尚未见报道 .我们在用电弧产生的N2 等离子体热解焦油时 ,生成了一种直径 9~ 2 0nm长约几百纳米线 .X射线能谱定量分析表明这种纳米线化学组成为K2 Ti8O15,是一种新的非化学计量化合物 .试验装… 相似文献
37.
F.O. Borges G.H. Cavalcanti A.G. Trigueiros 《Journal of Quantitative Spectroscopy & Radiative Transfer》2003,78(1):119-129
The weighted oscillator strengths (gf) and the lifetimes presented in this work were carried out in a multi configuration Hartree-Fock relativistic (HFR) approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure, in order to improve the adjustment to experimental energy levels. This method produces gf-values that are in better agreement with intensity observations and lifetime values that are closer to the experimental ones. In this work, we presented all the experimentally known electric dipole S IX and S X spectral lines. 相似文献
38.
We have observed three-dimensional sponge-like structures as well as strips of connecting pits on the surface of the LR 115 detector after etching, which can be confused with the small tracks formed after short etching time. We have employed an atomic force microscope (AFM) to study these “damages” as well as genuine alpha tracks for short etching time. It was found that while the track and damage openings could be similar in size and shape, the depths for the damages were consistently smaller. Therefore, the depth of the pits will serve as a clear criterion to differentiate between tracks and other damages. The ability to discriminate between genuine tracks from other damages is most important for etching for short time intervals. 相似文献
39.
Summary Vezetéknév 相似文献
40.
Ekatherina A. Karatsuba 《Numerical Algorithms》2007,45(1-4):127-137
A new approach to the study of the Jaynes–Cummings sum, which determines the atomic inversion in quantum model of a single
two-level atom interacting with a single mode of the quantized radiation field, based on the number theory theorems on approximation
of trigonometric sums is presented.
相似文献