全文获取类型
收费全文 | 146483篇 |
免费 | 8302篇 |
国内免费 | 20464篇 |
专业分类
化学 | 124802篇 |
晶体学 | 2667篇 |
力学 | 2761篇 |
综合类 | 1381篇 |
数学 | 16087篇 |
物理学 | 27551篇 |
出版年
2024年 | 142篇 |
2023年 | 1144篇 |
2022年 | 3494篇 |
2021年 | 3315篇 |
2020年 | 3572篇 |
2019年 | 4479篇 |
2018年 | 3207篇 |
2017年 | 4987篇 |
2016年 | 4665篇 |
2015年 | 4085篇 |
2014年 | 5519篇 |
2013年 | 11056篇 |
2012年 | 9479篇 |
2011年 | 8223篇 |
2010年 | 7005篇 |
2009年 | 8872篇 |
2008年 | 9285篇 |
2007年 | 9677篇 |
2006年 | 8924篇 |
2005年 | 7755篇 |
2004年 | 7340篇 |
2003年 | 6062篇 |
2002年 | 6903篇 |
2001年 | 4478篇 |
2000年 | 4765篇 |
1999年 | 4061篇 |
1998年 | 3652篇 |
1997年 | 2677篇 |
1996年 | 2331篇 |
1995年 | 2157篇 |
1994年 | 1844篇 |
1993年 | 1538篇 |
1992年 | 1479篇 |
1991年 | 1054篇 |
1990年 | 815篇 |
1989年 | 814篇 |
1988年 | 610篇 |
1987年 | 451篇 |
1986年 | 390篇 |
1985年 | 356篇 |
1984年 | 382篇 |
1983年 | 189篇 |
1982年 | 300篇 |
1981年 | 293篇 |
1980年 | 283篇 |
1979年 | 273篇 |
1978年 | 239篇 |
1977年 | 160篇 |
1976年 | 135篇 |
1973年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Srinivasan G. 《物理学报》2006,55(5):2548-2552
讨论了Ni0.8Zn0.2Fe2O4 (NZFO)与锆钛酸铅(PZT)的双层膜结构样品的磁电(ME)效应.NZFO粉料由溶胶-凝胶法制成,再经900℃热压,并高温烧结.在该双层膜中测量到了很强的磁电相互作用.发现横向的磁电效应比纵向效应大一个数量级,并且随NZFO烧结温度的提高而增加.当烧结温度从950℃上升到1380℃时,横向ME电压系数(αE)的最大值变化范围为25.6 mV Am-2≤αE≤199.6 mV Am-2.理论分析显示NZFO-PZT双层膜样品中ME效应源于NZFO与PZT之间相对良好的磁电耦合.
关键词:
镍铁氧体
PZT
热压法
ME效应 相似文献
132.
meso-Tetra(n-hexyloxycarbonyl)porphyrin was found to be converted into porphine, the mother compound of porphyrins, in a 77% yield when heated in aqueous sulfuric acid at 180 °C over 30 min under an inert atmosphere. The observation demonstrates that the substituted porphyrin serves as a novel and useful precursor for porphine. 相似文献
133.
Juzo Oyamada 《Tetrahedron》2006,62(29):6918-6925
Synthesis of coumarins from phenols and propiolic acids was examined by using a Pt catalyst such as PtCl2/AgOTf, K2PtCl4/AgOTf, and K2PtCl4/AgOAc. Propiolic acid reacted even with less reactive phenols in trifluoroacetic acid to give coumarins and dihydrocoumarins. In the case of substituted propiolic acids, phenylpropiolic acid and 2-octynoic acid, the reactions proceeded selectively to afford coumarins in good to high yields. 相似文献
134.
135.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
136.
137.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
138.
139.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
140.
Proton conductivity of phosphoric acid derivative of fullerene 总被引:1,自引:0,他引:1
The proton conductive property of methano [60] fullerene diphosphoric acid has been investigated under various humidity conditions at the temperature range between 15 and 45 °C. It shows proton conductivity as high as 10−2 S cm−1 at 25 °C under relative humidity of 95%. Thermal analyses including TG–DTA and thermal desorption mass spectroscopy (TDS) confirm that the compound is thermally stable up to 200 °C. Proton conduction of the compound depends very much on humidity or water content. The logarithmic conductivity at 25 °C is increased linearly with increasing relative humidity. The activation energy (Ea) estimated from the slope of log(σT) vs. 1/T is decreased from 1.08 to 0.52 eV, as the relative humidity is increased from 40% to 75%. The humidity dependence of conductivity is discussed in the light of the observed hydration isotherm. 相似文献