全文获取类型
收费全文 | 31798篇 |
免费 | 501篇 |
国内免费 | 512篇 |
专业分类
化学 | 12441篇 |
晶体学 | 273篇 |
力学 | 1529篇 |
综合类 | 34篇 |
数学 | 9410篇 |
物理学 | 9124篇 |
出版年
2023年 | 62篇 |
2022年 | 53篇 |
2021年 | 88篇 |
2020年 | 111篇 |
2019年 | 98篇 |
2018年 | 1252篇 |
2017年 | 1497篇 |
2016年 | 823篇 |
2015年 | 647篇 |
2014年 | 606篇 |
2013年 | 859篇 |
2012年 | 3396篇 |
2011年 | 2567篇 |
2010年 | 1991篇 |
2009年 | 1690篇 |
2008年 | 763篇 |
2007年 | 760篇 |
2006年 | 748篇 |
2005年 | 4569篇 |
2004年 | 4027篇 |
2003年 | 2424篇 |
2002年 | 586篇 |
2001年 | 375篇 |
2000年 | 156篇 |
1999年 | 232篇 |
1998年 | 153篇 |
1997年 | 123篇 |
1996年 | 103篇 |
1995年 | 87篇 |
1994年 | 84篇 |
1993年 | 57篇 |
1992年 | 194篇 |
1991年 | 170篇 |
1990年 | 159篇 |
1989年 | 122篇 |
1988年 | 113篇 |
1987年 | 70篇 |
1986年 | 55篇 |
1985年 | 54篇 |
1984年 | 50篇 |
1983年 | 39篇 |
1979年 | 43篇 |
1976年 | 87篇 |
1975年 | 42篇 |
1974年 | 45篇 |
1973年 | 49篇 |
1972年 | 42篇 |
1969年 | 38篇 |
1968年 | 37篇 |
1966年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
11.
通过调整Mn的成分,系统地研究了Ni81Fe19/Ni100-xMnx双层膜的磁学性质,特别是交换偏置场(Hex)的变化.当Ni100-xMnx中Mn的原子百分比在534%到600%之间时,对于150nm的Ni81Fe19,得到了最大的交换偏置场175kA/m,同时由于Mn对Ni81Fe19层的扩散所造成的磁矩的降低小于20%;高角x射线衍射证明Ni100-xMnx的晶格常数随着Mn成分的改变而变化,Mn含量越多,其晶格常数越大;制备态Ni100-xMnx膜晶格常数与θ相NiMn膜晶格常数的接近程度与NiMn膜θ相形成的容易程度相对应.也研究了交换偏置场随着Ni100-xMnx厚度的变化,第一次得到了当Ni100-xMnx中Mn的原子百分比为706%时,Ni81Fe19(150nm)/Ni100-xMnx(90nm)双层膜在经过240℃,5h退火后,可以有80kA/m的交换偏置场,此时铁磁层磁矩的大小几乎不变.
关键词:
Ni81Fe19/Ni100-xMnx
交换偏置场 相似文献
12.
Micha? Chmielewski 《Tetrahedron letters》2004,45(31):6007-6010
Comparison of the anion binding properties of a series of uncharged macrocyclic tetraamides reveal significant effects of the receptor's size on the strength of its anion complexes. This study allowed for estimation of the optimal size of a macroring for complexation of common anions. 相似文献
13.
M. Missous C. Mitchell J. Sly K. T. Lai R. Gupta S. K. Haywood 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):496
Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on InxGa(1−x)As−InyAl(1−y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of 420°C to produce structures that are suitable for both emission and detection in the 2–5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In0.84Ga0.16As/AlAs/In0.52Al0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ–Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2–7 μm) in three structures of differing In0.84Ga0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs–InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ–Γ bands and the Γ–X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated. 相似文献
14.
Fang‐Chyou Chiu Sun‐Mou Lai Jong‐Wu Chen Pei‐Hsien Chu 《Journal of Polymer Science.Polymer Physics》2004,42(22):4139-4150
The melt mixing technique was used to prepare various polypropylene (PP)‐based (nano)composites. Two commercial organoclays (denoted 20A and 30B) served as the fillers for the PP matrix, and two different maleated (so‐called) compatibilizers (denoted PP‐MA and SMA) were employed as the third component. The results from X‐ray diffraction (XRD) and transmission electron microscope (TEM) experiments revealed that 190 °C was an adequate temperature for preparing the nanocomposites. Nanocomposites were achieved only if specific pairs of organoclay and compatibilizer were simultaneously incorporated in the PP matrix. For example, PP/20A(5 wt %)/PP‐MA(10 wt %) and PP/30B(5 wt %)/SMA(5 wt %) composites exhibited nanoscaled dispersion of 20A or 30B in the PP matrix. Differential scanning calorimetry (DSC) results indicated that the organoclays served as nucleation agents for the PP matrix. Generally, their nucleation effectiveness increased with the addition of compatibilizers. The thermal stability enhancement of PP after adding 20A was confirmed with thermogravimetric analysis (TGA). The enhancement became more evident as a suitable compatibilizer was further added. However, for the 30B‐included composites, thermal stability enhancement was not evident. The dynamic mechanical properties (i.e., storage modulus and loss modulus) of PP increased as the nanocomposites were formed; the properties increment corresponded to the organoclay dispersion status in the matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4139–4150, 2004 相似文献
15.
Sándor G?r?g 《Analytical sciences》2004,20(5):767-782
The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis. 相似文献
16.
The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed. 相似文献
17.
JingXiaWANG ChengYouKAN DeShanLIU 《中国化学快报》2004,15(10):1161-1163
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA. 相似文献
18.
19.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
20.