全文获取类型
收费全文 | 23243篇 |
免费 | 2430篇 |
国内免费 | 2956篇 |
专业分类
化学 | 9502篇 |
晶体学 | 223篇 |
力学 | 930篇 |
综合类 | 185篇 |
数学 | 1778篇 |
物理学 | 5112篇 |
综合类 | 10899篇 |
出版年
2024年 | 111篇 |
2023年 | 393篇 |
2022年 | 684篇 |
2021年 | 742篇 |
2020年 | 718篇 |
2019年 | 659篇 |
2018年 | 613篇 |
2017年 | 655篇 |
2016年 | 777篇 |
2015年 | 990篇 |
2014年 | 1233篇 |
2013年 | 1561篇 |
2012年 | 1729篇 |
2011年 | 1777篇 |
2010年 | 1508篇 |
2009年 | 1493篇 |
2008年 | 1715篇 |
2007年 | 1482篇 |
2006年 | 1426篇 |
2005年 | 1157篇 |
2004年 | 916篇 |
2003年 | 723篇 |
2002年 | 796篇 |
2001年 | 668篇 |
2000年 | 585篇 |
1999年 | 584篇 |
1998年 | 378篇 |
1997年 | 336篇 |
1996年 | 343篇 |
1995年 | 320篇 |
1994年 | 252篇 |
1993年 | 235篇 |
1992年 | 192篇 |
1991年 | 176篇 |
1990年 | 159篇 |
1989年 | 143篇 |
1988年 | 121篇 |
1987年 | 77篇 |
1986年 | 44篇 |
1985年 | 47篇 |
1984年 | 26篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1971年 | 3篇 |
1957年 | 3篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
YaoKui ChenZhixiang 《分析论及其应用》2003,19(2):115-120
This paper gives the weighted Lp convergence rate estimations of the Gruenwald interpolatory polynomials based on the zeros of Chebyshev polymomials of the first kind,and proves that the order of the estimations is optimal for p≥1. 相似文献
22.
Pyroelectricity and Spontaneous Polarization in [111] Oriented 0.955 Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 Single Crystals 下载免费PDF全文
We report that the measurements of the pyroelectric current of the pre-poled [111]-oriented 0.955 Pb(Zn1/3Nb2/3) O3-0.045 PbTiO3 (PZN-4.5%PT) single crystals can shed some light on the phase transition and spontaneous polarization characters of this material in a similar way to measures of remanent polarization and dielectric properties. The pyroelectric current is measured and the corresponding spontaneous polarization is calculated as a function of temperature with various poling fields added during cooling the sample from 200℃ to room temperature. Critical electric field of 0.061 k V/cm is found to be essential to induce the intermediate ferroelectric orthorhombic phase between the ferroelectric rhombohedral and tetragonal phases. Below the critical field, the polarization increases almost linearly with the increase of poling field. At the critical field, the polarization at 30OC increases abruptly from 14μC/cm^2 for a poling field of O.06kV/cm to 29.5μC/cm^2 for a poling field of 0.061 kV/cm, and afterwards, increases slowly and saturates to 31 μC/cm^2 for poling fields beyond 0.55 kV/cm. 相似文献
23.
Yu‐Hsiang Hu Chuh‐Yung Chen Chen‐Chien Wang Yao‐Hui Huang Shao‐Ping Wang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4976-4993
The bulk polymerization of styrene initiated by ?‐caprolactam (CL) and n‐dodecyl mercaptan (RSH) has been explored. This novel polymerization system shows living characteristics. For example, the molecular weight of the resulting polymers increases with conversion, and the system has the ability to form diblock copolymers and so forth. The polymer chain end contains thiol and lactam structures, which we have investigated with Fourier transform infrared, 1H NMR, and 13C NMR techniques. Electron spin resonance spectra and theoretical calculations by the Hartree–Fock methods have been used to examine the mechanism. The results reveal that the initial polymerization starts from thiol via a chain‐transfer reaction, and the propagation proceeds by the insertion of a monomer between the terminal group and the intermediate structure of lactam. Finally, the polymerization kinetics have been examined. The polymerization rate varies linearly with the concentration of CL and RSH, and this confirms the mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4976–4993, 2004 相似文献
24.
25.
Introduction In the previous studies on the oxidation reaction,peroxydisulfate was widely used as an oxidizingagent.1-5 One of the advantages of this oxidant lies in itsstability in a wide range of pH values. The reaction be-tween Fe(CN)5L3- (L=N-aromatic heterocyclic li-gands) and S2O8 2- has been proved to proceed throughan outer-sphere electron transfer mechanism.5 For a re-action [(Eq. (1)] to be under an outer-sphere mechanismthe steps involved are the formation of a reactant … 相似文献
26.
Ming Zhao WANG Guan Liang CAI Ling XIA Jun Jian YAO Hong Yan CHEN Zhao Xing MENG Bo Li LIUDepartment of Chemistry Beijing Normal University Beijing Chemical Defense Institute PLA Beijing 《中国化学快报》2004,15(4):495-497
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents. 相似文献
27.
MENG Yuan-yao 《广西民族大学学报》2008,(2)
壮语里t-(t‘-)>s-的音变现象是存在的,不论是汉语,或者是壮语,它们的内部或两者之间都存在着s-与t-(t‘-)对应的规律。 相似文献
28.
Yao Ping HOU 《数学学报(英文版)》2005,21(4):955-960
A signed graph is a graph with a sign attached to each edge. This paper extends some fundamental concepts of the Laplacian matrices from graphs to signed graphs. In particular, the relationships between the least Laplacian eigenvalue and the unbalancedness of a signed graph are investigated. 相似文献
29.
30.