全文获取类型
收费全文 | 15961篇 |
免费 | 3012篇 |
国内免费 | 2061篇 |
专业分类
化学 | 11594篇 |
晶体学 | 216篇 |
力学 | 1011篇 |
综合类 | 137篇 |
数学 | 1627篇 |
物理学 | 6449篇 |
出版年
2024年 | 69篇 |
2023年 | 358篇 |
2022年 | 694篇 |
2021年 | 647篇 |
2020年 | 755篇 |
2019年 | 784篇 |
2018年 | 662篇 |
2017年 | 620篇 |
2016年 | 856篇 |
2015年 | 921篇 |
2014年 | 1016篇 |
2013年 | 1251篇 |
2012年 | 1526篇 |
2011年 | 1473篇 |
2010年 | 991篇 |
2009年 | 1086篇 |
2008年 | 1137篇 |
2007年 | 949篇 |
2006年 | 887篇 |
2005年 | 741篇 |
2004年 | 558篇 |
2003年 | 400篇 |
2002年 | 366篇 |
2001年 | 315篇 |
2000年 | 254篇 |
1999年 | 255篇 |
1998年 | 195篇 |
1997年 | 193篇 |
1996年 | 160篇 |
1995年 | 155篇 |
1994年 | 117篇 |
1993年 | 120篇 |
1992年 | 97篇 |
1991年 | 84篇 |
1990年 | 64篇 |
1989年 | 42篇 |
1988年 | 43篇 |
1987年 | 34篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1965年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
用金属蒸汽真空弧源,以40kV加速电压对纯锆样品分别进行了1016—1017/cm2的钇、镧离子注入,注入温度约为130℃.然后对注入样品进行表面分析.x射线光电子能谱分析表明,注入的钇以Y2O3形式存在,镧以La2O3形式存在.俄歇电子能谱表明,纯锆基体表面的氧化膜厚度随着离子注入剂量的增加而增加,当离子注入剂量达到1017/cm2时,氧化膜的厚度达到了最大值.卢瑟福背散射显示镧层的厚度约为30nm,同时直接观察到当离子注入剂量为(La+Y)1017/cm2时,纯锆样品表面发生了严重的溅射.
关键词:
纯锆
钇和镧离子共注入
卢瑟福背散射
x射线光电子能谱 相似文献
82.
Kan‐Yi Pu Yi Chen Xiao‐Ying Qi Chun‐Yang Qin Qing‐Quan Chen Hong‐Yu Wang Yun Deng Qu‐Li Fan Yan‐Qin Huang Shu‐Juan Liu Wei Wei Bo Peng Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3776-3787
In this contribution, we demonstrate a new effective methodology for constructing highly efficient and durable poly(p‐phenyleneethynylene) (PPE) containing emissive material with nonaggregating and hole‐facilitating properties through the introduction of hole‐transporting blocks into the PPE system as the grafting coils as well as building the energy donor–acceptor architecture between the grafting coils and the PPE backbone. Poly(2‐(carbazol‐9‐yl)ethyl methacrylate) (PCzEMA), herein, is chosen as the hole‐transporting blocks, and incorporated into the PPE system as the grafting coils via atom transfer radical polymerization. The chemical structure of the resultant copolymer, PPE‐g‐PCzEMA, was characterized by NMR and gel permeation chromatography, showing that the desirable copolymer was obtained with the narrow polydispersity. The increased thermal stability of PPE‐g‐PCzEMA was confirmed by thermogravimetric analysis and differential scanning calorimetry along with its macroinitiator. The optoelectronic properties of this copolymer were studied in detail by ultraviolet‐visible absorption, photoluminescence emission and excitation spectra, and cyclic voltammogram (CV). The results indicate that PPE‐g‐PCzEMA exhibits the solid‐state luminescent property dominated by individual lumophores, and also the energy transfer process from the PCzEMA blocks to the PPE backbone with a relatively higher energy transfer efficiency in the solid‐state compared to that of the solution state. Additionally, the hole‐injection property is greatly facilitated due to the presence of PCzEMA, as confirmed by CV profiles. All these data indicate that PPE‐g‐PCzEMA is a good candidate for use in optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3776–3787, 2007 相似文献
83.
以MCl2和配体L(L=1,10-菲罗啉-5,6-二酮)为原料,合成了标题配合物MLCl2,M=NiⅡ,CuⅡ,ZnⅡ,并经元素分析、热谱、IR和摩尔电导表征.三者均为四配位的电中性配合物,热稳定性高于500K,易溶于DMF、DMSO和吡啶,可溶于乙腈和水.它们在DMF中于350nm和315nm附近显示出强的M-L荷移跃迁 相似文献
84.
采用气相色谱-质谱(GC-MS)选择离子监测法(SIM),建立了准确可靠、灵敏度高、快速简便的测定维生素C泡腾片中甜蜜素含量的新方法.样品中的甜蜜素衍生后用有机试剂提取,在选择离子模式下进行测定,以保留时间和特征离子比例进行定性,单离子定量.甜蜜素的线性范围为0.05-10mg/L,检出限为0.6mg/kg,回收率为90.5%-96.9%,相对标准偏差小于4.4%.方法分析所用时间短,结果准确可靠,选择性好,适用于维生素C泡腾片中甜蜜素含量的检验. 相似文献
85.
Buckling and free vibration analyses of stiffened plates using the FSDT mesh-free method 总被引:1,自引:0,他引:1
This paper presents a mesh-free Galerkin method for the free vibration and stability analyses of stiffened plates via the first-order shear deformable theory (FSDT). The model of a stiffened plate is formed by (1) regarding the plate and the stiffener separately, (2) imposing displacement compatible conditions between the plate and the stiffener so that displacement fields of the stiffener can be expressed in terms of the mid-surface displacement of the plate, and (3) superimposing the strain energy of plate and stiffener. Because there are no meshes used in this method, the stiffeners can be placed anywhere on the plate and need not be placed along the mesh lines. Several numerical examples are computed by this method to show its accuracy and convergence. The present results demonstrate good agreement with the existing solutions given by other researchers and the ANSYS. Influences of support size and order of the complete basis functions on the numerical accuracy are also investigated. 相似文献
86.
基于专家动态权重的群组AHP交互式决策方法 总被引:2,自引:0,他引:2
为了能在群组决策中得到更为客观和准确的决策结果,在把专家权重划分为静态权重和动态权重的基础上,研究了在交互式决策中专家动态权重的确定方法,给出了共识度的一个定义.在此基础上,研究了群组AHP交互式决策方法中的一致性和相容性检验,给出了基于专家动态权重的群组AHP交互式决策方法流程,最后用一个示例说明了该方法的应用步骤. 相似文献
87.
A simple and rapid method is developed to determine the high acidity and the basicity of solutions by chronopotentiometry with a platinum working electrode. The acidity range from 5.0 mol/l H+ to 1.0 mol/l OH− can be measured by the adjustment of deposition potential and time. The response mechanism to acidity and basicity has been explored. The transition potential plateau in chronopotentiograms is caused from the oxidation of hydrogen adsorbed on electrode surface. 相似文献
88.
Measurement of small-signal and large-signal responses of packaged laser modules at high temperature
Ning Hua Zhu Ji Min Wen Hai Peng Song Shang Jian Zhang Liang Xie 《Optical and Quantum Electronics》2006,38(15):1245-1257
In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules,
such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained
by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide
temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different
chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In
the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the
laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different
red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved
at higher temperature. 相似文献
89.
Peng Xu Haitao Wang Rui Lv Qiangguo Du Wei Zhong Yuliang Yang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(12):3911-3920
A novel microphase‐inversion method was proposed for the preparation of TiO2–SiO2/poly(methyl methacrylate) core–shell nanocomposite particles. The inorganic–polymer nanocomposites were first synthesized via a free‐radical copolymerization in a tetrahydrofuran solution, and the poor solvent was added slowly to induce the microphase separation of the nanocomposite and result in the formation of nanoparticles. The average particle sizes of the microspheres ranged from 70 to 1000 nm, depending on the reaction conditions. Transmission electron microscopy and scanning electron microscopy indicated a core–shell morphology for the obtained microspheres. Thermogravimetric analysis and X‐ray photoelectron spectroscopy measurements confirmed that the surface of the nanocomposite microspheres was polymer‐rich, and this was consistent with the core–shell morphology. The influence of the synthetic conditions, such as the inorganic composition and the content of the crosslinking monomer, on the particle properties was studied in detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3911–3920, 2006 相似文献
90.
Peng Chen Jun Chen Baoqing Zhang Jun Zhang Jiasong He 《Journal of Polymer Science.Polymer Physics》2006,44(6):1020-1030
Polycarbonate (PC) was melt blended with small amount of liquid‐crystalline polymer (LCP) and various contents of glass beads (GB) having different diameters. The rheological measurements indicated that the GB addition increased the viscosity ratio and seemed unfavorable to the LCP fibrillation. However, the morphological observation showed that the LCP fibrillation was promoted by the GB addition and varied with the GB packing. With the increased GB packing by increasing the GB content and/or decreasing the GB diameter, LCP deformed from spheres and ellipsoids into stretched ellipsoids at lower shear rates and into long fibrils at higher shear rates. Although higher content of smaller GB jammed into the larger LCP droplets and inhibited the LCP fibrillation, very long LCP fibrils formed at higher shear rates at a high enough packing of GB. The relationship between GB packing and LCP fibrillation revealed two kinds of hydrodynamic effects of GB promoting the LCP fibrillation: at lower GB packing, the shear flow was enhanced by the high local shear between GB, in quantity; and for a high enough GB packing, the shear flow was changed, in quality, into elongational flow, which was more effective for the LCP fibrillation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1020–1030, 2006 相似文献