全文获取类型
收费全文 | 73496篇 |
免费 | 12837篇 |
国内免费 | 7301篇 |
专业分类
化学 | 50884篇 |
晶体学 | 658篇 |
力学 | 4741篇 |
综合类 | 312篇 |
数学 | 8199篇 |
物理学 | 28840篇 |
出版年
2024年 | 279篇 |
2023年 | 1603篇 |
2022年 | 2717篇 |
2021年 | 2836篇 |
2020年 | 3107篇 |
2019年 | 2908篇 |
2018年 | 2566篇 |
2017年 | 2337篇 |
2016年 | 3570篇 |
2015年 | 3474篇 |
2014年 | 4142篇 |
2013年 | 5311篇 |
2012年 | 6733篇 |
2011年 | 6727篇 |
2010年 | 4470篇 |
2009年 | 4256篇 |
2008年 | 4595篇 |
2007年 | 4109篇 |
2006年 | 3755篇 |
2005年 | 3133篇 |
2004年 | 2425篇 |
2003年 | 1920篇 |
2002年 | 1751篇 |
2001年 | 1472篇 |
2000年 | 1357篇 |
1999年 | 1533篇 |
1998年 | 1306篇 |
1997年 | 1292篇 |
1996年 | 1290篇 |
1995年 | 1050篇 |
1994年 | 921篇 |
1993年 | 763篇 |
1992年 | 675篇 |
1991年 | 581篇 |
1990年 | 501篇 |
1989年 | 384篇 |
1988年 | 335篇 |
1987年 | 274篇 |
1986年 | 249篇 |
1985年 | 204篇 |
1984年 | 143篇 |
1983年 | 102篇 |
1982年 | 80篇 |
1981年 | 67篇 |
1980年 | 65篇 |
1979年 | 33篇 |
1978年 | 30篇 |
1977年 | 40篇 |
1976年 | 30篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Xiaohui Yang Xiaoying Sun Jiajia Shao Yunhang Liu Xinling Wang 《Journal of Polymer Science.Polymer Physics》2004,42(22):4195-4198
A series of polymer electrolytes based on multiarm polymers and lithium salt complexes were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and impedance measurement. The relationships of conductivity with salt concentration, temperature, and arm numbers are discussed. It is suggested that the star polymer has a higher solvency and ion transfer ability on lithium salts than on linear polymers. The conductivity maximum appeared at a higher salt concentration ([EO]/[Li] = 4). Impedance measurement suggested that the optimum conductivity was 2 × 10?4 s · cm?1. The conductivity increased with temperature and the dependence of ionic conductivity on temperature fits the Arrhenius equation. Among the studied systems, the star polymer with a five arm number performs better than other structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4195–4198, 2004 相似文献
82.
Hydrogels containing benzo-18-crown-6 were used to modify microcantilevers for measurements of the concentration of Pb2+ in aqueous solutions. These microcantilevers undergo bending deflection upon exposure to solutions containing various Pb2+ concentrations as the result of a swelling of the hydrogels. It was found that a concentration of 10(-6) M Pb2+ can be detected using this technology. Other cations, such as Na+, have no effect on the deflection of this cantilever. The cation K+, which also complexes with benzo-18-crown-6, could interfere with Pb2+ detection, but only at high concentrations (> 10(-4) M). 相似文献
83.
Xiao Xiaohua Cao Yuguan Liu Xia Jiang Shengxiang 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(3-4):111-115
A PM3 calculation in vacuum of the inclusion complexation ofo-, m-, p-nitro-phenol with calix[n]arenes is performedsuccessfully. The pathways for inclusion process are describedand the most probable structures of the 1:1 complex are soughtthrough a potential energy scan. The energy differences betweenthe inclusion complexes and the hosts, by calculation, show thatthe most stable complexation is calix[4]-p-nitro phenol andcalix[6]-m-nitro phenol. 相似文献
84.
85.
86.
In-time motion adjustment in laser cladding manufacturing process for improving dimensional accuracy and surface finish of the formed part 总被引:2,自引:0,他引:2
This paper presents in-time motion adjustment in laser cladding manufacturing process as a means to improve dimensional accuracy and surface finish of the built part. Defects occurring during laser cladding degrade the part quality such as dimensional accuracy and surface finish. In this paper, in-time motion adjustment strategy was presented to remedy and eliminate defects occurring during laser cladding to improve the dimensional accuracy and surface finish. Based on the relationship between the motion of laser head relative to the growing part and other parameters in effects on clad profile, the laser traverse speed, stand-off distance and laser approach orientation to the existing clad layer were adjusted by instructions from a close-loop control system in real time to remedy and eliminate defects. The results of the experiments verified the effects of in-time motion adjustment on dimensional accuracy and surface finish. 相似文献
87.
微模塑法制备PMMA/SiO2二氧化硅杂化材料微结构 总被引:1,自引:0,他引:1
以摩尔比为 1∶1的甲基丙烯酸甲酯 (MMA)、甲基丙烯酸 (3 三乙氧基硅烷基 )丙酯 (ESMA)单体、0 .2 %(单体总量的质量分数 )的偶氮二异丁腈AIBN引发剂和四氢呋喃 (THF)溶剂 ,及 2 0 % (总质量分数 )的正硅酸乙酯TEOS合成出PMMA/SiO2 有机 无机杂化的杂化溶胶 .将溶胶在洗净的普通光学玻璃基片表面甩膜 .利用软刻蚀中的微模塑法 ,把有机硅弹性印章复制有精细图纹一面轻放在杂化溶胶膜上进行微模塑 ,外加 1N压力于12 0℃下处理 2h使溶胶凝胶化 .印章剥离后在基片表面就形成了PMMA/SiO2 有机 无机杂化材料的微图纹结构 .从微图纹的光学显微镜照片可以看出微模塑方法制备杂化材料复制的图纹精细度高 ,操作简单易行 ,是一类比较理想的微细图纹结构加工的方法 . 相似文献
88.
内部审核在计量体系中的作用 总被引:1,自引:0,他引:1
介绍内部审核制度在计量测试工作中的目的和作用,提出了内部审核工作应注意的事项,如内部审核工作计划的完整性,内部审核工作的有效性,管理者工作内容的全面性,以及后续工作的完善性。 相似文献
89.
The main purpose of this paper is to use a mean value theorem of Dirichlet L-functions to study the asymptotic property of a hybrid mean value of a generalized Cochrane sum, and give an interesting mean value formula.2000 Mathematics Subject Classification: Primary—11F20; Secondary—11F99 相似文献
90.