全文获取类型
收费全文 | 1210篇 |
免费 | 157篇 |
国内免费 | 331篇 |
专业分类
化学 | 1264篇 |
晶体学 | 41篇 |
力学 | 5篇 |
综合类 | 9篇 |
数学 | 27篇 |
物理学 | 352篇 |
出版年
2023年 | 21篇 |
2022年 | 30篇 |
2021年 | 48篇 |
2020年 | 59篇 |
2019年 | 45篇 |
2018年 | 48篇 |
2017年 | 39篇 |
2016年 | 42篇 |
2015年 | 37篇 |
2014年 | 53篇 |
2013年 | 99篇 |
2012年 | 134篇 |
2011年 | 71篇 |
2010年 | 65篇 |
2009年 | 84篇 |
2008年 | 81篇 |
2007年 | 77篇 |
2006年 | 77篇 |
2005年 | 66篇 |
2004年 | 60篇 |
2003年 | 61篇 |
2002年 | 68篇 |
2001年 | 40篇 |
2000年 | 33篇 |
1999年 | 43篇 |
1998年 | 18篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 12篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有1698条查询结果,搜索用时 62 毫秒
991.
992.
Both experimental and computer-simulated magneto-optical (MO) and optical spectroscopies of Co/Pt multilayered films (MLF) with a nearly constant Pt sublayer thickness and variable Co sublayer thickness, as well as pure Co and Pt, and Co0.51Pt0.49 alloy films, have been performed in the energy range 1.1–4.7 eV. The simulations were achieved by solving the multireflection task for various models of the MLF. The comparison between experimental and computer-simulated optical properties of the Co/Pt MLF allowed us to evaluate the thickness of the interfacial regions with the alloyed components. The diagonal and off-diagonal components of the optical conductivity tensor were calculated not only for the pure Co and Co0.51Pt0.49 alloy films, and the whole Co/Pt MLF, but also for the spin-polarized Pt layers in the Co/Pt MLF. 相似文献
993.
对比研究了熔体旋淬和常规熔铸合金Zr0 .9Ti0 .1(Ni,Co ,Mn ,V) 2 .1的微结构和电化学性能 .XRD分析表明 :熔体旋淬合金在退火前后的晶体结构和铸态合金一样 ,均为面心立方结构 ,由LaveC15相组成 ;并且随旋淬速度的增加 ,旋淬合金中的非晶成分越多 .电化学测试表明 :旋淬合金有较好的活化性能 ,但其最大放电容量较低 ,小于 2 80mAh/g ;而退火后的旋淬合金需经 30次循环才能完全活化 ,其最大放电容量皆为 34 0mAh/g左右 ,高于铸态合金和退火前的旋淬合金 ;在电流密度为 30 0mA/g下进行充放电循环 ,发现退火后的旋淬合金循环稳定性明显高于铸态合金电极 ,并且随旋淬速度的增加 ,循环稳定性越好 ,经过 80 0次循环后 ,退火后的 4 0m/s合金容量保持率高达 85 % ,容量衰减率只有 6.9% 相似文献
994.
According to a uniform and simple method
of calculating spin-lattice coupling coefficients and the perturbation
formulas of gi factors and hyperfine structure constants
Ai based on the cluster approach for 3d7 ions in cubic, tetragonal and trigonal octahedral crystal fields, the spin-lattice coupling coefficients Fij (F11, F12, F44), Zij (Z11, Z12, Z44) and also
g factor and hyperfine constant A for MgO:Co2+ are calculated
by using the parameters obtained from the optical spectra without adjustable parameters. The calculated results
show good agreement with the observed values. The difficulty
in explaining the coefficients
Fij and Zij is therefore removed. 相似文献
995.
Jae-Dong Kim Yong-Il Park Koichi Kobayashi Masayuki Nagai Masayuki Kunimatsu 《Solid State Ionics》2001,140(3-4):313-325
The CO tolerance of a proton exchange membrane fuel cell (PEMFC) was investigated by ac impedance spectroscopy. The impedance of the fuel cell could be obtained by feeding oxygen into the cathode side and simulated gas into anode side. Furthermore, the anode impedance could be obtained by feeding hydrogen into the cathode side and simulated gas into anode side. The CO gas had a greater effect on the charge transfer reaction (high frequency arc) and hydrogen dissociative chemisorption (medium frequency arc) but little effect on the low frequency arc. Although the cathode impedance is a main part at high temperature, irrespective of CO concentration (≤100 ppm), the impedance of the full cell depends on anode impedance at low temperature and high CO concentration. It was found that CO gas has little effect on cathode impedance. 相似文献
996.
电感耦合等离子体原子发射光谱法定量测试明胶中的微量元素Co和Bi——应用IEC模型校正Fe对Co的光谱干扰 总被引:1,自引:0,他引:1
应用电感耦合等离子体原子发射光谱法(ICP-AES),建立了定量测试明胶中微量金属元素Co, Bi的方法。采用湿法消解对明胶样品进行了前处理, 对仪器的测试条件进行了优化。讨论了用ICP-AES同时测定明胶中Co和Bi时,应用光谱干扰系数校正法(IEC)模型校正了Fe在特定波长下对Co的光谱干扰。结果表明,Fe对Co的光谱干扰可以应用IEC模型进行有效的消除, 进行光谱校正后的结果明显优于未加校正的实验结果。建立的方法准确、快速、高效、线性范围宽。被测元素工作曲线的线性相关系数r≥0.999 90。结果的相对标准偏差RSD%≤2.00。加标回收率为98%~107%。 相似文献
997.
The title compound [Co(IM2-Py)(PCA)(N3)2] (IM2-Py = 2-(2'-pyridyl)-4,4,5,5-te-
tramethylimidazoline-1-oxyl, PCA = 2-pyridine carboxylic acid) has been prepared and structurally
characterized by elemental analysis, IR spectra and X-ray diffraction. It crystallizes in monoclinic,
space group P21/c with a = 13.169(3), b = 11.235(2), c = 15.596(3) (A), β = 104.70(3)°, V = 2232.0(8) (A)3, C18H21CoN1oO3, Mr = 484.38, Z = 4, Dc = 1.441 g/cm3,μ(MoKα) = 0.811 mm-1, F(000) = 1000,the final R = 0.0563 and wR = 0.1010. The nitronyl nitroxide (NIT2Py) was reduced to IM2-Py, and another NIT2Py oxidated to PCA. The self-redox reaction between the radicals was observed. The cobalt(Ⅱ) ion is six-coordinated into a distorted octahedral geometry. Meanwhile, the intermolecular hydrogen bonds result in the dimer. 相似文献
998.
999.
CO和H_2在非晶态合金Ni-B、Co-B催化剂上的吸附及其作用的TPD-MS研究张菊,郑小明,周烈华(杭州大学催化研究所,杭州,310028)关键词非晶态Ni(Co)-B合金,H_2、CO吸附,TPD-MS非晶态合金作为一种新型催化材料在加氢反应中表... 相似文献
1000.
A pair of cobalt(II)-based hydrogen-bonded organic frameworks (HOFs), [Co(pca)2(bmimb)]n (1) and [Co2(pca)4(bimb)2] (2), where Hpca = p-chlorobenzoic acid, bmimb = 1,3-bis((2-methylimidazol-1-yl)methyl)benzene, and bimb = 1,4-bis(imidazol-1-ylmethyl)benzene were hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. X-ray diffraction structural analysis revealed that 1 has a one-dimensional (1D) infinite chain network through the deprotonated pca− monodentate chelation and with a μ2-bmimb bridge Co(II) atom, and 2 is a binuclear Co(II) complex construction with a pair of symmetry-related pca− and bimb ligands. For both 1 and 2, each cobalt atom has four coordinated twisted tetrahedral configurations with a N2O2 donor set. Then, 1 and 2 are further extended into three-dimensional (3D) or two-dimensional (2D) hydrogen-bonded organic frameworks through C–H···Cl interactions. Topologically, HOFs 1 and 2 can be simplified as a 4-connected qtz topology with a Schläfli symbol {64·82} and a 4-connected sql topology with a Schläfli symbol {44·62}, respectively. The fluorescent sensing application of 1 was investigated; 1 exhibits high sensitivity recognition for Fe3+ (Ksv: 10970 M−1 and detection limit: 19 μM) and Cr2O72− (Ksv: 12960 M−1 and detection limit: 20 μM). This work provides a feasible detection platform of HOFs for highly sensitive discrimination of Fe3+ and Cr2O72− in aqueous media. 相似文献