全文获取类型
收费全文 | 4374篇 |
免费 | 270篇 |
国内免费 | 164篇 |
专业分类
化学 | 2772篇 |
晶体学 | 53篇 |
力学 | 134篇 |
综合类 | 12篇 |
数学 | 801篇 |
物理学 | 1036篇 |
出版年
2023年 | 51篇 |
2022年 | 45篇 |
2021年 | 91篇 |
2020年 | 105篇 |
2019年 | 88篇 |
2018年 | 89篇 |
2017年 | 80篇 |
2016年 | 161篇 |
2015年 | 144篇 |
2014年 | 178篇 |
2013年 | 260篇 |
2012年 | 301篇 |
2011年 | 300篇 |
2010年 | 197篇 |
2009年 | 182篇 |
2008年 | 245篇 |
2007年 | 251篇 |
2006年 | 225篇 |
2005年 | 211篇 |
2004年 | 159篇 |
2003年 | 109篇 |
2002年 | 131篇 |
2001年 | 66篇 |
2000年 | 75篇 |
1999年 | 56篇 |
1998年 | 44篇 |
1997年 | 53篇 |
1996年 | 59篇 |
1995年 | 37篇 |
1994年 | 41篇 |
1993年 | 46篇 |
1992年 | 41篇 |
1991年 | 34篇 |
1990年 | 26篇 |
1989年 | 24篇 |
1988年 | 21篇 |
1987年 | 21篇 |
1986年 | 28篇 |
1985年 | 26篇 |
1984年 | 19篇 |
1983年 | 25篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 27篇 |
1978年 | 23篇 |
1977年 | 36篇 |
1976年 | 22篇 |
1975年 | 23篇 |
1974年 | 13篇 |
排序方式: 共有4808条查询结果,搜索用时 171 毫秒
61.
Bis-(2,4,5-triphenylimidazolyls) result from the dimerization of 2,4,5-triphenylimidazolyls and from the nucleophilic attack of 2,4,5-triphenylimidazole anions upon 2,4,5-triphenylimidazolylium cations. The isomeric bis-imidazolyls consist of imidazole and isoimidazole systems. Imidazoles undergo only anodic oxidation, isoimidazoles only cathodic reduction. Therefore the bis-imidazolyls may be analyzed from their electrochemical behaviour. Bis-(2,4,5-triphenylimidazolyl)-1,2′ and bis-(2,4,5-triphenylimidazolyl)-1,4′ undergo reductive bond cleavage in an ē.c?.ē. mechanism from which 2,4,5-triphenyl-imidazole anions result. The electrochemical properties of one of the bis-imidazolyls agree with that of 1,4,5-triphenyl-2-(2,4,5-triphenylisoimidazolyl-4)-imidazole and not with that of bis-(2,4,5-triphenylimidazolyl)-2,4′ as reported in literature. 相似文献
62.
Addition-elimination reactions from germanium heterocycles . III. 2,2-Diethyl-2-germa-1,-3-oxazolidines (R = Et; X = O; Y = NH, NMe) . The reactions of 2,2-diethyl-2-germa-1,3-oxazolidines with heterocumulenes (PhNCO, PhNCS, CS2, CO2, CH2?C?O) and carbonyl compounds (aldehydes and ketones) are studied. Generally, monoinsertion derivatives are formed by addition of one molecule of the unsaturated compound accross the Ge? N bond. This bond is always the most reactive center of the molecule. In the case of the carbonyl compounds used, diinsertion may occur in a second step by a further addition across a Ge? O bond. Generally, this latter reaction is reversible. By thermal eliminat on of (Et2GeO)n or (Et2GeS)3 the monoaddition derivatives yield the corresponding oxazolidines and thiooxazolidines. The mechanisms of these reactions are discussed. 相似文献
63.
M. Weiden J. Köhler G. Sparn M. Köppen M. Lang C. Geibel F. Steglich 《Zeitschrift für Physik B Condensed Matter》1995,98(2):167-169
We present an investigation of the spin-Peierls transition atT
SP=14.5 K in polycrystalline CuGeO3 through specific-heat and thermal-expansion measurements. Clear second-order phase-transition anomalies are found in both properties atT
SP, although only a small entropy of S0.1 Rn2 is released at the transition. Most of the entropy is released atT
SP<T<150 K, where the temperature dependence of the magnetic contribution to the specific heat as well as the thermal expansion exhibit extrema atT
*40 K. These are caused by one-dimensional antiferromagnetic fluctuations along the Cu chains, possibly accompanied by structural fluctuations. Using Ehrenfest's relation, a hydrostatic pressure coefficient (T
SP/p)p0 (0.45±0.06) K/kbar is derived. 相似文献
64.
Bai JZ Bardon O Blum I Breakstone A Burnett T Chen GP Chen HF Chen J Chen SJ Chen SM Chen Y Chen YB Chen YQ Cheng BS Cowan RF Cui HC Cui XZ Ding HL Du ZZ Dunwoodie W Fan XL Fang J Fero M Gao CS Gao ML Gao SQ Gao WX Gratton P Gu JH Gu SD Gu WX Gu YF Guo YN Han SW Han Y Harris FA Hatanaka M He J He KR He M Hitlin DG Hu GY Hu HB Hu T Hu XQ Huang DQ Huang YZ Izen JM Jia QP Jiang CH Jin Y Jones L Kang SH Kelsey MH Kim BK Lai YF Lan HB Lang PF Lankford A Li F Li J Li PQ Li Q Li RB 《Physical review D: Particles and fields》1995,52(7):3781-3784
65.
Gabriel P. Paternain 《Bulletin of the Brazilian Mathematical Society》1994,25(2):207-211
LetT
* M denote the cotangent bundle of a manifoldM endowed with a twisted symplectic structure [1]. We consider the Hamiltonian flow generated (with respect to that symplectic structure) by a convex HamiltonianH: T
* M, and we consider a compact regular energy level ofH, on which this flow admits a continuous invariant Lagrangian subbundleE. When dimM3, it is known [9] that such energy level projects onto the whole manifoldM, and thatE is transversal to the vertical subbundle. Here we study the case dimM=2, proving that the projection property still holds, while the transversality property may fail. However, we prove that in the case whenE is the stable or unstable subbundle of an Anosov flow, both properties hold. 相似文献
66.
67.
68.
69.
Dasu S de Barbaro P Bodek A Harada H Krasny MW Lang K Riordan EM Andivahis L Arnold R Benton D Bosted P deChambrier G Lung A Rock SE Szalata ZM Walker RC Filippone BW Jourdan J Milner R McKeown R Potterveld D Para A Dietrich F Van Bibber K Button-Shafer J Debebe B Hicks RS Gearhart R Whitlow LW Alster J 《Physical review D: Particles and fields》1994,49(11):5641-5670
70.