全文获取类型
收费全文 | 57046篇 |
免费 | 9435篇 |
国内免费 | 6143篇 |
专业分类
化学 | 40079篇 |
晶体学 | 682篇 |
力学 | 3395篇 |
综合类 | 351篇 |
数学 | 6534篇 |
物理学 | 21583篇 |
出版年
2024年 | 204篇 |
2023年 | 1199篇 |
2022年 | 2210篇 |
2021年 | 2303篇 |
2020年 | 2422篇 |
2019年 | 2295篇 |
2018年 | 1973篇 |
2017年 | 1889篇 |
2016年 | 2839篇 |
2015年 | 2820篇 |
2014年 | 3305篇 |
2013年 | 4269篇 |
2012年 | 5241篇 |
2011年 | 5169篇 |
2010年 | 3582篇 |
2009年 | 3351篇 |
2008年 | 3606篇 |
2007年 | 3169篇 |
2006年 | 2861篇 |
2005年 | 2460篇 |
2004年 | 1902篇 |
2003年 | 1531篇 |
2002年 | 1384篇 |
2001年 | 1119篇 |
2000年 | 979篇 |
1999年 | 1140篇 |
1998年 | 918篇 |
1997年 | 869篇 |
1996年 | 861篇 |
1995年 | 782篇 |
1994年 | 650篇 |
1993年 | 561篇 |
1992年 | 457篇 |
1991年 | 428篇 |
1990年 | 364篇 |
1989年 | 265篇 |
1988年 | 190篇 |
1987年 | 174篇 |
1986年 | 173篇 |
1985年 | 157篇 |
1984年 | 96篇 |
1983年 | 103篇 |
1982年 | 62篇 |
1981年 | 42篇 |
1980年 | 30篇 |
1979年 | 18篇 |
1977年 | 18篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
By constructing close-one-cochain density Ω^12n in the gauge group space we get the Wess-Zumino-Witten (WZW) effective Lagrangian on high-dimensional noncommutative space.Especially consistent anomalies derived from this WZW effective action in noncommutative four-dimensional space coincide with those obtained by L.Bonora etc.(het-th/0002210). 相似文献
73.
74.
许多乙酰芳胺类化合物具有优异的生物活性,例如除草剂苯噻草胺,可抑制细胞生长和分裂,防除稻田中禾本科杂草[1];杀菌剂甲霜灵可防治作物霜霉病[2]。本文将具有多种生物活性的嘧啶基团引入到乙酰芳胺结构中[3],合成下列10个未见文献报道的标题化合物Ⅰ,通... 相似文献
75.
The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth. 相似文献
76.
本文以fp 同伦方法为工具,借助于一些适当的变换,研究有序的(B)空间中的集值映象方程的多正解问题;在文中的有关工作中,还使用了集值映象的拟导数的某些性质. 相似文献
78.
79.
In theory, both polarity and steric hindrance are basic factors which affect molecular interactions. To investigate the optical properties and steric structures of chiral compounds having different chiral moieties which affect the wavelength of light reflection in liquid crystal (LC) cells, a series of novel chiral compounds and azobenzene derivatives were synthesized. The liquid crystalline phases of the compounds were identified using small angle X-ray diffraction, differential scanning calorimetry and polarizing optical microscopy. Cholesteric LC cells with various synthesized chiral dopants which selectively reflect visible light were first prepared, the photochemical switching behaviour of colours was then investigated, with special reference to the change in transmittance in cholesteric LC cells containing an azobenzene derivative as a photoisomerizable guest molecule. Reversible isomerization of azobenzene molecules occurred in the cholesteric systems, resulting in a depression of TChI and a shift of the selectively reflected wavelength. We discuss the photochemically driven change in the helical pitch of the cholesteric LCs with respect to structural effects involving the chiral moieties. Molecular interactions caused by the added dopants, reliability and stability of the photoisomerization, and UV irradiation effects on the cholesteric LC cells were also investigated. A real image was recorded through a mask on a cholesteric LC cell fabricated in this investigation. 相似文献
80.
Chii-Wann Lin Kuo-Ping Chen Ming-Chii Su Chih-Kung Lee Chih-Chung Yang 《Optical and Quantum Electronics》2005,37(13-15):1423-1437
We have reported a novel design of surface plasmon resonance (SPR) device, which uses alternating dielectric layers to enhance the SPR signal quality and modulate its resonant position. Admittance loci method of thin film design has been used in the design of such a device. The use of biomolecular thin film, such as DNAs or Porteins, in this design can result in resonant condition of wavelength changes as well. Bio-plasmonics is proposed for the research and development of novel devices, which use biomolecules as a part of the plasmon oscillation system to actively interact with nano/micro structure. 相似文献