全文获取类型
收费全文 | 34963篇 |
免费 | 5791篇 |
国内免费 | 4339篇 |
专业分类
化学 | 25562篇 |
晶体学 | 355篇 |
力学 | 2257篇 |
综合类 | 355篇 |
数学 | 3916篇 |
物理学 | 12648篇 |
出版年
2024年 | 112篇 |
2023年 | 695篇 |
2022年 | 1180篇 |
2021年 | 1289篇 |
2020年 | 1461篇 |
2019年 | 1481篇 |
2018年 | 1185篇 |
2017年 | 1009篇 |
2016年 | 1708篇 |
2015年 | 1778篇 |
2014年 | 1988篇 |
2013年 | 2530篇 |
2012年 | 3026篇 |
2011年 | 3143篇 |
2010年 | 2128篇 |
2009年 | 2011篇 |
2008年 | 2149篇 |
2007年 | 1934篇 |
2006年 | 1815篇 |
2005年 | 1563篇 |
2004年 | 1382篇 |
2003年 | 1168篇 |
2002年 | 1243篇 |
2001年 | 1117篇 |
2000年 | 834篇 |
1999年 | 761篇 |
1998年 | 568篇 |
1997年 | 488篇 |
1996年 | 470篇 |
1995年 | 441篇 |
1994年 | 380篇 |
1993年 | 303篇 |
1992年 | 327篇 |
1991年 | 294篇 |
1990年 | 255篇 |
1989年 | 192篇 |
1988年 | 126篇 |
1987年 | 110篇 |
1986年 | 101篇 |
1985年 | 96篇 |
1984年 | 60篇 |
1983年 | 52篇 |
1982年 | 39篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
养殖池塘沉积物的重金属分布及污染特征 总被引:3,自引:0,他引:3
浙江省淅西北地区淡水养殖池塘沉积物重金属调查研究表明,养殖池塘沉积物中7种重金属元素分布不均衡,差异也较大,除Hg和Cr元素外,其余重金属元素已大大超过土壤本底值.虽然其实测含量都未超出国家规定的标准值范围,但沉积物中重金属元素对养殖水环境、养殖品种存在的潜在污染与危害值得关注.污染指数评价显示,养殖池塘沉积物中主要污染物质为Cu和Cr,而Hg、Pb污染程度相对较轻. 相似文献
42.
Precise measurement of magnetic moment of short-lived β-emitting nuclei12B ( I π=1+, T 1/2=20.18 ms)
Zhou Dongmei Zheng Yongnan Du Enpeng Xu Yongjun Zhu Jiazheng Yuan Daqing Wang Zhiqiang Luo Hailong Zuo Yi Ma Ruigang Duan Xiao M. Mihara M. Fukuda K. Matsuta T. Minamisono Zhu Shengyun 《中国科学G辑(英文版)》2004,47(5):531-539
The spin polarized β-emitting nuclei12B (I
π=1+,T
1/2=20.18 ms) were produced by the nuclear reaction11B(d, p)12B and by the selection technique of the incident deuteron energy and the12B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei12B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment
of12B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift. 相似文献
43.
44.
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
45.
We establish a self-improving property of the Hardy inequality and an estimate on the size of the boundary of a domain supporting a Hardy inequality.
46.
47.
HaiHuiXIE XiaoYiWEI JiDongWANG MeiFangLIU RenZhouYANG 《中国化学快报》2003,14(6):588-590
A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines. 相似文献
48.
Jianhu Yang Shixun Dai Nengli Dai Lei Wen Lili Hu Zhonghong Jiang 《Journal of luminescence》2004,106(1):9-14
Nonradiative decay of 4I13/2→4I15/2 transition of Er3+ has been investigated in a series of oxide glasses. For Er3+-doped glass samples, the Judd-Ofelt analysis on absorption spectra was performed and the fluorescence lifetime was determined by extrapolating to zero Er3+ concentration limit. Infrared spectra were measured in order to investigate the influence of OH− groups in different glasses. The effects of glass matrix on the decay rate were discussed from the viewpoint of phonon energy, variations of effective fields, and OH− groups. Compared to other glasses, phosphate glass presents low quantum efficiency and large nonradiative decay rate due to its high phonon energy and hygroscopic behavior. 相似文献
49.
A. M. Povolotsky V. B. Priezzhev Chin-Kun Hu 《Journal of statistical physics》2003,111(5-6):1149-1182
An asymmetric stochastic process describing the avalanche dynamics on a ring is proposed. A general kinetic equation which incorporates the exclusion and avalanche processes is considered. The Bethe ansatz method is used to calculate the generating function for the total distance covered by all particles. It gives the average velocity of particles which exhibits a phase transition from an intermittent to continuous flow. We calculated also higher cumulants and the large deviation function for the particle flow. The latter has the universal form obtained earlier for the asymmetric exclusion process and conjectured to be common for all models of the Kardar–Parisi–Zhang universality class. 相似文献
50.
A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6. 相似文献