全文获取类型
收费全文 | 89928篇 |
免费 | 16885篇 |
国内免费 | 9192篇 |
专业分类
化学 | 61491篇 |
晶体学 | 915篇 |
力学 | 5746篇 |
综合类 | 512篇 |
数学 | 10092篇 |
物理学 | 37249篇 |
出版年
2024年 | 344篇 |
2023年 | 2043篇 |
2022年 | 3294篇 |
2021年 | 3453篇 |
2020年 | 3927篇 |
2019年 | 3509篇 |
2018年 | 3216篇 |
2017年 | 2867篇 |
2016年 | 4582篇 |
2015年 | 4362篇 |
2014年 | 5321篇 |
2013年 | 6766篇 |
2012年 | 8209篇 |
2011年 | 8397篇 |
2010年 | 5546篇 |
2009年 | 5379篇 |
2008年 | 5779篇 |
2007年 | 5063篇 |
2006年 | 4760篇 |
2005年 | 3818篇 |
2004年 | 2940篇 |
2003年 | 2294篇 |
2002年 | 2107篇 |
2001年 | 1816篇 |
2000年 | 1604篇 |
1999年 | 1840篇 |
1998年 | 1592篇 |
1997年 | 1577篇 |
1996年 | 1563篇 |
1995年 | 1322篇 |
1994年 | 1151篇 |
1993年 | 996篇 |
1992年 | 860篇 |
1991年 | 783篇 |
1990年 | 644篇 |
1989年 | 501篇 |
1988年 | 371篇 |
1987年 | 308篇 |
1986年 | 323篇 |
1985年 | 261篇 |
1984年 | 151篇 |
1983年 | 117篇 |
1982年 | 100篇 |
1981年 | 57篇 |
1980年 | 42篇 |
1979年 | 15篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
The grain-boundary-related optical and electrical properties in polycrystalline p-type ZnO films 总被引:3,自引:0,他引:3
C.Y. Zhang X.M. Li X.D. Gao J.L. Zhao K.S. Wan J.M. Bian 《Chemical physics letters》2006,420(4-6):448-452
Cathodoluminescence spectra and electrical properties of the N doped and N–Al codoped p-type ZnO films and the dependence of these two properties on the post-annealing were investigated. Spectral analyses show that the intensity of the green emission strongly depends on the annealing ambient and closely relates with the width of the electron depletion region at the particle boundary. The conducting type and electrical properties of N doped and N–Al codoped ZnO films are greatly affected by the annealing process. The grain boundary effect was proposed to explain the green emission behavior and the p-type conduction in polycrystalline ZnO based films. 相似文献
932.
Ya‐Ping Du Ya‐Wen Zhang Prof. Dr. Zheng‐Guang Yan Dr. Ling‐Dong Sun Prof. Dr. Song Gao Prof. Dr. Chun‐Hua Yan Prof. Dr. 《化学:亚洲杂志》2007,2(8):965-974
We report the synthesis of single‐crystalline and near‐monodispersed NaMF3 (M=Mn, Co, Ni, Mg), LiMAlF6 (M=Ca, Sr), and NaMgF3:Yb,Er nanocrystals (quasisquare nanoplates, nanorods, and nanopolygons) by the cothermolysis of multiple trifluoroacetates in hot combined organic solvents (oleic acid, oleylamine, and 1‐octadecene). The nanocrystals were characterized by XRD, TEM, superconductive quantum interference device (SQUID), and upconversion luminescence spectroscopy. By regulating the polarity of the dispersant, the NaMF3 (M=Mn, Co, Ni) nanoplates were partially aligned to form nanoarrays on copper TEM grids. The sizes of the NaMF3 nanocrystals were easily tuned by the use of proper synthetic conditions such as reaction temperature and time and solvent composition. On the basis of a series of experiments in which the reaction conditions were varied, together with GC–MS and FTIR analysis, the reaction pathways for the formation of these nanocrystals from trifluoroacetate precursors were proposed. The magnetic measurements showed that the differently sized NaMnF3 square plates displayed interesting weak ferromagnetic behavior on the nanometer scale. The strong red upconversion luminescence emitted from the NaMgF3:Yb,Er nanorods under 980‐nm near‐IR laser excitation suggests that NaMgF3 may be a good candidate host material for red upconversion luminescence. 相似文献
933.
Chiral fluorous imidazolidinone catalyst 2 provides consistently high enantioselectivities in Diels–Alder reactions of dienes and ,β-unsaturated aldehydes. The catalyst can be readily separated from the reaction products by fluorous solid-phase extraction, and recovered in excellent purity for direct reuse. 相似文献
934.
Qing‐Xiang Liu Feng‐Bo Xu Qing‐Shan Li Xian‐Shun Zeng Xue‐Bing Leng Zheng‐Zhi Zhang 《中国化学》2002,20(9):878-883
Dinuclear silver (I) six‐membered ring complex [Ag2 (bta)2 ‐(hmbta)2] (ClO4)2 (3) has been synthesized by the reaction of benzotriazole (bta) (1) and 1‐hydroxymethyl benzotriazole (hmbta) (2) with Ag (CH3CN)4ClO4. The structures of compound 2 and Complex 3 have been studied by single crystal X‐ray diffraction analysis. The change of luminescent intensity of 1, 2 and 3 was reported. Compound 2 crystallizes in the monoclinic system with space group P2 (1)/c, a = 0.7655 (10) nm, b = 1.0126 (14) nm, c =0.9502 (13) nm, β = 95.07 (2)°, V = 0.7337 (17) nm3 and Z = 4. Complex 3 crystallizes in the triclinic system with space group P1, a = 0.73611 (18) nm, b = 0.9152 (2) nm, c = 1.2277 (3) nm, β = 87.170 (5)°, V = 0.8221 (3) nm3 and Z = 1. The main structural feature of complex 3 is a symmetric dinuclear six‐membered ring formed by two silver (I) atoms and four N‐atoms from two benzotriazoles. The second structural feature of complex 3 is the τ‐τ stacking interaction between two adjacent molecular planes, which forms the two‐dimentional layer structure. Besides, compared with 2, the luminescent intensity of complex 3 shows a remarkable enhancement. 相似文献
935.
The effect of antimony concentration (C(Sb)/mass%) on the surface tension of molten silicon has been determined with the sessile drop method in the temperature range from 1693 to 1773 K and in the range of the oxygen partial pressure, Po(2), in an Ar atmosphere from 10(-23) to 10(-21) MPa. The results show that the surface tension of molten silicon decreases with increasing Sb concentration in the range of C(Sb)<0.9 mass%, which indicates positive adsorption of Sb in molten silicon and can be fairly described with the Szyszkowski's equation. The maximum decrease rate of surface tension is about 65 mN m(-1) (mass% C(Sb))(-1), and the temperature coefficient of surface tension, (partial differential sigma/ partial differential T)C(Sb), increases with increasing C(Sb). The evaporation of the systems was only observed between the melting points of antimony (904 K) and silicon (1683 K), and the surface tension presents no dependence on measuring time above the melting point of silicon. 相似文献
936.
Differential-pulse voltammetric determination of trace formaldehyde using magnetic microspheres and magnetic electrode 总被引:2,自引:0,他引:2
A new type of magnetic polymer microsphere containing acylhydrazine groups on the surface was synthesized. They can be reacted with formaldehyde to produce an electroactive adduct. Reduction of these derivatives following aggregation on a magnetic electrode is possible and is effective in the indirect determination of formaldehyde. The experimental conditions and electrode structure are discussed. Under the optimum conditions, it was found that the peak potential (Ep) of formaldehyde is -1.01 V (vs. Ag/AgCl). Formaldehyde in the range 1-1000 micrograms l-1 can be determined. The detection limit for formaldehyde is 0.3 microgram l-1 and the relative standard deviation for the determination of 100 micrograms l-1 formaldehyde was 2.26%. The method was applied to the determination of formaldehyde in environmental samples with satisfactory results. 相似文献
937.
A protein array for cell detection was fabricated by spotting different antibodies on modified glass slides. Glass slides were modified to allow antibodies to be immobilized on it and to selectively bind antigens. Antibodies were specially selected with the cells to be detected as targets, which permitted target cells in samples to bind specifically to the array with little nonspecific binding. Results can be obtained by directly putting the samples onto the array for 1 h or a little longer to let the cells specifically interact with the antibodies. After washing the unbound samples away, images were observed with a microscope and captured with a CCD camera. The assessment of antibody-cell binding was evaluated by capturing red blood cells (RBCs) in human blood with blood group antibodies (anti-A and anti-B). Blood group antibodies were spotted on the modified glass slide and kept at 4<.deg> degrees C overnight for immobilization. Human blood samples diluted to different concentrations were used to examine the sensitivity and specificity of the method. 相似文献
938.
压力流驱动电色谱分析方法及其若干色谱行为 总被引:1,自引:0,他引:1
压力流驱动电色谱分析方法是一种新型色谱技术。它组合了HPLC和电泳两种技术,为分离提供了更多可控制的因素。介绍了压力流驱动电色谱的装置和毛细管电色谱柱的装置方法,从理论上讨论了影响电色谱分离的因素并用实验数据加以证明。最后尝试性地将电色谱法用于测定香蕉样品中萨索啉(Salsolinol)等的含量。 相似文献
939.
在358K下用200ml/min的空气氧化碱性悬浮液合成了MFe_2O_(4+δ)(δ≥0,M=Fe、Co、Ni、Mn),并在573K下用40ml/min的H_2还原MFe_2O_(4+δ)制备了氧缺位铁酸盐MFe_2O_(4-δ)(δ>0)。用XRD、Mssbauer谱等测试方法对铁酸盐的结构进行了表征,考察了铁酸盐的组成及第二金属组分(Co、Ni、Mn)对铁酸盐还原性能的影响。在H_2还原3h内,铁酸盐氧缺位程度随还原时间增加而增大,晶格常数也相应增大;5h以上,铁酸盐将被还原为MO-FeO或α-Fe,晶格常数几乎不变。按Fe、Co、Ni、Mn顺序,MO与FeO的相互作用能力、MO-FeO固溶体的稳定性及铁酸盐还原为MO-FeO的能力均增强,MO-FeO进一步还原为α-Fe的能力却减弱。 相似文献
940.