全文获取类型
收费全文 | 321242篇 |
免费 | 3508篇 |
国内免费 | 942篇 |
专业分类
化学 | 176412篇 |
晶体学 | 3843篇 |
力学 | 13751篇 |
综合类 | 11篇 |
数学 | 32612篇 |
物理学 | 99063篇 |
出版年
2018年 | 2599篇 |
2017年 | 2537篇 |
2016年 | 4439篇 |
2015年 | 3045篇 |
2014年 | 4522篇 |
2013年 | 13313篇 |
2012年 | 9444篇 |
2011年 | 11900篇 |
2010年 | 8073篇 |
2009年 | 8052篇 |
2008年 | 10875篇 |
2007年 | 11079篇 |
2006年 | 10508篇 |
2005年 | 9604篇 |
2004年 | 8740篇 |
2003年 | 7765篇 |
2002年 | 7683篇 |
2001年 | 9351篇 |
2000年 | 7167篇 |
1999年 | 5650篇 |
1998年 | 4625篇 |
1997年 | 4622篇 |
1996年 | 4417篇 |
1995年 | 4111篇 |
1994年 | 4010篇 |
1993年 | 3765篇 |
1992年 | 4455篇 |
1991年 | 4249篇 |
1990年 | 4076篇 |
1989年 | 4095篇 |
1988年 | 3995篇 |
1987年 | 3923篇 |
1986年 | 3669篇 |
1985年 | 5029篇 |
1984年 | 5162篇 |
1983年 | 4202篇 |
1982年 | 4547篇 |
1981年 | 4392篇 |
1980年 | 4231篇 |
1979年 | 4530篇 |
1978年 | 4908篇 |
1977年 | 4655篇 |
1976年 | 4642篇 |
1975年 | 4427篇 |
1974年 | 4439篇 |
1973年 | 4467篇 |
1972年 | 2924篇 |
1968年 | 2881篇 |
1967年 | 3096篇 |
1966年 | 2627篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
101.
102.
103.
It is known that a distance-regular graph with valency k at least three admits at most two Qpolynomial structures. We show that all distance-regular graphs with diameter four and valency at least three admitting two Q-polynomial structures are either dual bipartite or almost dual bipartite. By the work of Dickie(1995) this implies that any distance-regular graph with diameter d at least four and valency at least three admitting two Q-polynomial structures is, provided it is not a Hadamard graph, either the cube H(d, 2)with d even, the half cube 1/2H(2d + 1, 2), the folded cube?H(2d + 1, 2), or the dual polar graph on [2A2d-1(q)]with q 2 a prime power. 相似文献
104.
Nonlinear Dynamics - Introduction of stiffness nonlinearities to broaden the frequency bandwidth of vibratory energy harvesters has the adverse influence of complicating the response behavior of... 相似文献
105.
Robin F. Weitkamp Beate Neumann Hans‐Georg Stammler Berthold Hoge 《Angewandte Chemie (International ed. in English)》2020,59(14):5494-5499
We report on the first examples of isolated silanol–silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol–silanolate anions are postulated intermediates in the hydroxide‐mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization. 相似文献
106.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
107.
108.
109.
ABSTRACTQM(UB3LYP)/MM(AMBER) calculations were performed for the locations of the transition structure (TS) of the oxygen–oxygen (O–O) bond formation in the S4 state of the oxygen-evolving complex (OEC) of photosystem II (PSII). The natural orbital (NO) analysis of the broken-symmetry (BS) solutions was also performed to elucidate the nature of the chemical bonds at TS on the basis of several chemical indices defined by the occupation numbers of NO. The computational results revealed a concerted bond switching (CBS) mechanism for the oxygen–oxygen bond formation coupled with the one-electron transfer (OET) for water oxidation in OEC of PSII. The orbital interaction between the σ-HOMO of the Mn(IV)4–O(5) bond and the π*-LUMO of the Mn(V)1=O(6) bond plays an important role for the concerted O–O bond formation for water oxidation in the CaMn4O6 cluster of OEC of PSII. One electron transfer (OET) from the π-HOMO of the Mn(V)1=O(6) bond to the σ*-LUMO of the Mn(IV)4–O(5) bond occurs for the formation of electron transfer diradical, where the generated anion radical [Mn(IV)4–O(5)]-? part is relaxed to the ?Mn(III)4?…?O(5)- structure and the cation radical [O(6)=Mn(V)1]+ ? part is relaxed to the +O(6)–Mn(IV)1? structure because of the charge-spin separation for the electron-and hole-doped Mn–oxo bonds. Therefore, the local spins are responsible for the one-electron reductions of Mn(IV)4->Mn(III)4 and Mn(V)1->Mn(IV)1. On the other hand, the O(5)- and O(6)+ sites generated undergo the O–O bond formation in the CaMn4O6 cluster. The Ca(II) ion in the cubane- skeleton of the CaMn4O6 cluster assists the above orbital interactions by the lowering of the orbital energy levels of π*-LUMO of Mn(V)1=O(6) and σ*-LUMO of Mn(IV)4–O(5), indicating an important role of its Lewis acidity. Present CBS mechanism for the O–O bond formation coupled with one electron reductions of the high-valent Mn ions is different from the conventional radical coupling (RC) and acid-base (AB) mechanisms for water oxidation in artificial and native photosynthesis systems. The proton-coupled electron transfer (PC-OET) mechanism for the O–O bond formation is also touched in relation to the CBS-OET mechanism. 相似文献
110.