全文获取类型
收费全文 | 30656篇 |
免费 | 5278篇 |
国内免费 | 3977篇 |
专业分类
化学 | 22136篇 |
晶体学 | 354篇 |
力学 | 2023篇 |
综合类 | 329篇 |
数学 | 3631篇 |
物理学 | 11438篇 |
出版年
2024年 | 75篇 |
2023年 | 574篇 |
2022年 | 920篇 |
2021年 | 1081篇 |
2020年 | 1253篇 |
2019年 | 1211篇 |
2018年 | 1055篇 |
2017年 | 922篇 |
2016年 | 1398篇 |
2015年 | 1502篇 |
2014年 | 1699篇 |
2013年 | 2178篇 |
2012年 | 2660篇 |
2011年 | 2962篇 |
2010年 | 1968篇 |
2009年 | 1794篇 |
2008年 | 1968篇 |
2007年 | 1749篇 |
2006年 | 1663篇 |
2005年 | 1422篇 |
2004年 | 1237篇 |
2003年 | 1022篇 |
2002年 | 1075篇 |
2001年 | 896篇 |
2000年 | 697篇 |
1999年 | 648篇 |
1998年 | 529篇 |
1997年 | 432篇 |
1996年 | 495篇 |
1995年 | 453篇 |
1994年 | 392篇 |
1993年 | 297篇 |
1992年 | 312篇 |
1991年 | 259篇 |
1990年 | 242篇 |
1989年 | 189篇 |
1988年 | 117篇 |
1987年 | 113篇 |
1986年 | 90篇 |
1985年 | 103篇 |
1984年 | 52篇 |
1983年 | 54篇 |
1982年 | 44篇 |
1981年 | 30篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
光电效应是物理学中一个重要课问题,也是近代物理学几个重大的实验之一.一般物理学教材均要介绍光电效应.但是,在众多的教材中,对光电效应实验装置图的引入存在差异,有些有失科学性,因而引起广大物理学教育工作者的关注. 相似文献
123.
Baoqiang Li Dechang Jia Yu Zhou Qiaoling Hu Wei Cai 《Journal of magnetism and magnetic materials》2006
Chitosan/magnetite nanocomposite was synthesized induced by magnetic field via in situ hybridization in ambient condition. Results of XRD patterns and TEM micrographs indicated that magnetite particles with 10–20 nm were dispersed in chitosan homogeneously. An interesting result is that magnetite nanoparticles were assembled to form chain-like structures under the influence of the external magnetic field, which mimics the magnetite chains inside of magnetotatic bacteria. The saturated magnetization (Ms) of nano-magnetite in chitosan was 50.54 emu/g, which is as high as 54% of bulk magnetite. The remanence (Mr) and coercivity (Hc) were 4 emu/g and14.8 Oe, respectively, which indicated that magnetite nanoparticles were superparamagnetic. The key of route is that a pre-precipitated chitosan hydrogel membrane, used as chemical reactor, which controlled the precipitation of chitosan precipitation and in situ transformation of magnetite from the precursor simultaneously in the magnetic field environment. 相似文献
124.
125.
Han-xing Wang Xi Hu Qin Zhang 《应用数学学报(英文版)》2007,23(2):235-244
In this paper,we present a random graph model with spatial reuse for a mobile ad hoc network(MANET) based on the dynamic source routing protocol.Many important performance parameters of theMANET are obtained,such as the average flooding distance (AFD),the probability generating function of theflooding distance,and the probability of a flooding route to be symmetric.Compared with the random graphmodel without spatial reuse,this model is much more effective because it has a smaller value of AFD and alarger probability for finding a symmetric valid route. 相似文献
126.
127.
Leong‐Huat Gan Palaniswamy Ravi Bao Wei Mao Kam‐Chiu Tam 《Journal of polymer science. Part A, Polymer chemistry》2003,41(17):2688-2695
Polymerization of 2‐(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous atom transfer radical polymerization under various reaction conditions is described. The effects of the initiators and solvents were examined. With 1,1,4,7,10,10‐hexamethyl triethylenetetramine/copper(I) chloride/p‐toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, poly(DEAEMA) with a polydispersity index as low as 1.07 was synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well‐defined block copolymers of DEAEMA and tert‐butyl methacrylate (tBMA) were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either p(DEAEMA) or p(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well‐defined copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2688–2695, 2003 相似文献
128.
Wenbing Hu Alexander Buzin Jar‐Shyong Lin Bernhard Wunderlich 《Journal of Polymer Science.Polymer Physics》2003,41(4):403-417
The annealing at 373 K of ultrastrong, gel‐spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature‐modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small‐angle X‐ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi‐isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 403–417, 2003 相似文献
129.
Yingyu Hu Guoqiao Lai Yongjia Shen Yongfang Li 《Monatshefte für Chemie / Chemical Monthly》2004,33(2):1167-1172
Zinc(II) and magnesium(II) phthalocyanines bearing four substituted propylenedithiotetrathiafulvalene (PDT-TTF) units were synthesized and characterized by NMR, MS, EA, and UV/VIS spectra. The absorption peaks of two target molecules were hypsochromically shifted compared with the phthalocyanine parent compound. Studies using cyclic voltammetry indicated that introduction of Zn and Mg as central metals enhanced the electronwithdrawing between the phthalocyanine core and the PDT-TTF unit, thus losing one electron to form (PDT-TTF)+ becomes more difficult. 相似文献
130.