全文获取类型
收费全文 | 5548篇 |
免费 | 184篇 |
国内免费 | 23篇 |
专业分类
化学 | 4231篇 |
晶体学 | 143篇 |
力学 | 221篇 |
数学 | 330篇 |
物理学 | 830篇 |
出版年
2023年 | 34篇 |
2022年 | 67篇 |
2021年 | 96篇 |
2020年 | 116篇 |
2019年 | 124篇 |
2018年 | 131篇 |
2017年 | 114篇 |
2016年 | 184篇 |
2015年 | 129篇 |
2014年 | 225篇 |
2013年 | 540篇 |
2012年 | 367篇 |
2011年 | 341篇 |
2010年 | 210篇 |
2009年 | 191篇 |
2008年 | 298篇 |
2007年 | 297篇 |
2006年 | 243篇 |
2005年 | 225篇 |
2004年 | 219篇 |
2003年 | 184篇 |
2002年 | 155篇 |
2001年 | 59篇 |
2000年 | 61篇 |
1999年 | 53篇 |
1998年 | 31篇 |
1997年 | 34篇 |
1996年 | 56篇 |
1995年 | 36篇 |
1994年 | 45篇 |
1993年 | 45篇 |
1992年 | 44篇 |
1991年 | 38篇 |
1990年 | 50篇 |
1989年 | 43篇 |
1988年 | 40篇 |
1987年 | 44篇 |
1986年 | 39篇 |
1985年 | 51篇 |
1984年 | 56篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 37篇 |
1980年 | 50篇 |
1979年 | 37篇 |
1978年 | 29篇 |
1977年 | 38篇 |
1976年 | 33篇 |
1975年 | 25篇 |
1974年 | 16篇 |
排序方式: 共有5755条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
B. D. Reddy 《Numerische Mathematik》1988,53(6):687-699
Summary The stability and convergence of mixed finite element methods are investigated, for an equilibrium problem for thin shallow elastic arches. The problem in its standard form contains two terms, corresponding to the contributions from the shear and axial strains, with a small parameter. Lagrange multipliers are introduced, to formulate the problem in an alternative mixed form. Questions of existence and uniqueness of solutions to the standard and mixed problems are addressed. It is shown that finite element approximations of the mixed problem are stable and convergent. Reduced integration formulations are equivalent to a mixed formulation which in general is distinct from the formulation shown to be stable and convergent, except when the order of polynomial interpolationt of the arch shape satisfies 1tmin (2,r) wherer is the order of polynomial approximation of the unknown variables. 相似文献
45.
46.
Summary Complexes of nickel(II) with N-(2-carboxyphenyl)benzamide (CPBH), 2-amino-N-(2-carboxyphenyl)benzamide (ACPBH), N-isoxazolyl benzamide (IB), N-anilinobenzamide (AB), N-(2-pyridyl)-3-carboxypropanamide (PCPA) and N-(2-pyridyl)-2-carboxybenzamide (PCBA) have been isolated and characterized by elemental analyses, magnetic susceptibility measurements, thermal studies, i.r. and electronic spectral studies. The electrochemical behaviour of some complexes has also been investigated. 相似文献
47.
Indoles undergo smooth alkylation with cyclopropyl ketones in the presence of the CeCl3·7H2O/LiI reagent system in refluxing acetonitrile under neutral conditions to produce the corresponding C-3 substituted indole derivatives in good to high yields and with high selectivity. The use of CeCl3·7H2O/LiI makes this method simple, convenient, and cost-effective. 相似文献
48.
The true potential energy curves for different electronic states of diatomic molecules have been constructed by a simplified and modified form of the Jarmain method. To check the validity of this new procedure potential energy curves are constructed for NO+, VO, Si2, AsO, AsO+, PF+, CO and Bi2. The results are in good agreement with the Jarmain, RKRV and Lakshman and Rao methods. 相似文献
49.
M. V. Reddy B. Pecquenard P. Vinatier A. Levasseur 《Surface and interface analysis : SIA》2007,39(8):653-659
We prepared stoichiometric lithium nickel vanadate amorphous thin films by using r.f. magnetron sputtering under controlled oxygen partial pressure. The amorphous films were heated at various temperatures, 300–600 °C, for 8 h. The as‐deposited and annealed thin films were characterized by Rutherford backscattering spectroscopy, nuclear reaction analysis, Auger electron spectroscopy, X‐ray diffraction, scanning electron microscopy and atomic force microscopy. The electrochemical behavior of the various films was studied by the galvanostatic method. The cells were tested in a liquid electrolyte at room temperature, with lithium metal used as the counter and reference electrode. The best electrochemical storage value was obtained with the thin film annealed at 300 °C, which showed superior capacity and small capacity loss during cycling. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
50.
Anzalone PW Baru AR Danielson EM Hayes PD Nguyen MP Panico AF Smith RC Mohan RS 《The Journal of organic chemistry》2005,70(6):2091-2096
[reaction: see text] Three one-pot methods for the conversion of aldehydes to homoallyl ethers catalyzed by Bi(OTf)(3).xH(2)O (1 < x < 4) have been developed. The one-pot synthesis of homoallyl ethers can be achieved either by in situ generation of the acetal followed by its reaction with allyltrialkylsilane or by a three-component synthesis in which the aldehyde, trimethylorthoformate or an alkoxytrimethylsilane and allyltrimethylsilane are mixed together in the presence of bismuth triflate (0.1-1.0 mol %). In addition, a three-component synthesis of homoallyl acetates, which is achieved by reacting the aldehyde, acetic anhydride, and allyltrimethylsilane in the presence of bismuth triflate (3.0-5.0 mol %), has been developed. The use of a relatively nontoxic, easy to handle, and inexpensive catalyst adds to the versatility of these methods. 相似文献