全文获取类型
收费全文 | 7536篇 |
免费 | 1333篇 |
国内免费 | 1194篇 |
专业分类
化学 | 6089篇 |
晶体学 | 81篇 |
力学 | 392篇 |
综合类 | 83篇 |
数学 | 793篇 |
物理学 | 2625篇 |
出版年
2024年 | 31篇 |
2023年 | 151篇 |
2022年 | 326篇 |
2021年 | 326篇 |
2020年 | 360篇 |
2019年 | 412篇 |
2018年 | 306篇 |
2017年 | 286篇 |
2016年 | 404篇 |
2015年 | 423篇 |
2014年 | 463篇 |
2013年 | 591篇 |
2012年 | 731篇 |
2011年 | 669篇 |
2010年 | 423篇 |
2009年 | 429篇 |
2008年 | 459篇 |
2007年 | 371篇 |
2006年 | 359篇 |
2005年 | 324篇 |
2004年 | 276篇 |
2003年 | 242篇 |
2002年 | 326篇 |
2001年 | 267篇 |
2000年 | 168篇 |
1999年 | 150篇 |
1998年 | 128篇 |
1997年 | 74篇 |
1996年 | 84篇 |
1995年 | 64篇 |
1994年 | 64篇 |
1993年 | 51篇 |
1992年 | 77篇 |
1991年 | 49篇 |
1990年 | 50篇 |
1989年 | 30篇 |
1988年 | 22篇 |
1987年 | 24篇 |
1986年 | 24篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Ji XY Zhong ZJ Xue ST Meng S He WY Gao RM Li YH Li ZR 《Chemical & pharmaceutical bulletin》2010,58(11):1436-1441
A series of novel glutarimide compounds were synthesized and their antiviral activities were evaluated. The compounds displaying the strongest antiviral activities included 5, 6f, 7e and 9 against coxsackievirus B3 (Cox B3), 10 and 6f against influenza virus A (influenza A) and 7a against herpes simplex virus 2 (HSV-2). However, most of the synthetic glutarimides showed comparatively much weaker activity against influenza A, Cox B3 and HSV-2 than the natural glutarimide compounds tested. Based on the results, it seemed likely that a conjugated system at the β-substituted moiety provides stronger antiviral activity. 相似文献
992.
An easy-to-prepare chemosensor, 2-(4-formylphenyl)phenanthroimidazole 1, synthesized by facile one-step condensation under microwave irradiation, has been indicated to be a colorimetric and fluorometric
probe for fluoride anion with good sensitivity and high selectivity. This probe shows obvious red shift and absorbance intensity
changes in UV absorption and fluorescence spectra in the presence of fluoride anions. Such color and absorbance intensity
changes are attributed to the deprotonation of N-H on the imidazole moiety with fluoride anion. 相似文献
993.
In this note,we obtain some a-priori estimates for gradient of weak solutions to a class of subelliptic quasilinear equations constructed by Ho¨rmander’s vector fields,and then prove local uniqueness of weak solutions.A key ingredient is the estimated about kernel on metirc "annulus". 相似文献
994.
995.
The omni-directional reflection characteristics of one-dimensional photonic crystals composed of Ta 2 O 5 /MgF 2 multi-quantum well (MQW) are studied using the transfer matrix method. An omni-directional reflector consisting of three and four Ta 2 O 5 /MgF 2 MQWs is investigated. Results show that the photonic band gap of the photonic crystal composed of three and four Ta 2 O 5 /MgF 2 MQWs, which are within the wavelength ranges of 402–712 and 412–1,023 nm, respectively, could cover the entire visible region. The relationship among the width of the band gap, its location, reflectivity rate, and incident angle of the incident light is analyzed. The optimal structural parameters of the MQW of the omni-directional reflector in the visible region are also calculated. The calculations provide a guide for the design of omni-directional reflection devices in the visible region. 相似文献
996.
利用EDXRF探针无损分析技术,分析了河南禹县阳翟遗址出土的一批金元时期的玻璃样品,以研究这批古玻璃的工艺技术特点.分析显示,所有蓝色玻璃样品的呈色剂均为CuO,而非CoO.从化学组成来看,这批古玻璃的种类较为复杂,主要包括钾钙玻璃、钠钙玻璃和铅钾钙玻璃等. 相似文献
997.
998.
A Mach-Zehnder structure with modulation in one arm and dispersive time delay in the other is proposed to implement highly flexible single-bandpass chirped microwave photonic filters based on broadband optical sources. Both the amplitude response and the time delay slope can be fully reconfigured via control of the optical spectra and dispersion. The passband can also be widely tuned without changing the shape. A chirped filter with a bandwidth of ~4?GHz, a delay slope of ~-0.6?ns/GHz, and a tunability up to 40?GHz is demonstrated experimentally. 相似文献
999.
We propose a novel structure of a photonic RF phase shifter based on the vector-sum principle. The optical signal with quadrature double-sideband modulation passes through a dual-output Mach-Zehnder interferometer (MZI), and the two outputs are differentially detected. Two phase-quadrature RF terms are generated, and their amplitudes can be controlled in a triangularly complementary way by changing the phase of the MZI. A full tuning range of 0°-360° at 14?GHz is demonstrated experimentally accompanied by nearly constant RF amplitude. The validity of using our scheme in all-optical RF phase modulation is also verified. 相似文献
1000.
Two kinds of nano TiO2-polyacrylate hybrid dispersions, TBM-w and TBM-e were synthesized by in-situ suspension polymerization and solution polymerization respectively, in order to fix the nano TiO2 on fabrics. The photocatalytic self-cleaning fabrics have received much attention in recent years for its water-saving and environment-protection advantages. However, the fixation of the photocatalyst on fabrics is still a key problem that inhibits industrialization of these eco-friendly fabrics. The cotton fabric was treated by the two hybrid dispersions. The photocatalytic self-cleaning property was characterized. Infrared spectroscopy, burning loss test and thermogravimetry showed that some copolymer chains entangled with the nano TiO2. Transmission electron microscope illustrated that there was a polymeric layer on the surface of nano TiO2. The average diameter of TBM-w was smaller than that of TBM-e based on size analysis. The photocatalytic decoloration of the grape syrup indicated that the fabric with TiO2-polymer hybrid had excellent self-cleaning property. 相似文献