全文获取类型
收费全文 | 2011篇 |
免费 | 66篇 |
国内免费 | 14篇 |
专业分类
化学 | 1430篇 |
晶体学 | 10篇 |
力学 | 52篇 |
数学 | 208篇 |
物理学 | 391篇 |
出版年
2022年 | 13篇 |
2021年 | 23篇 |
2020年 | 25篇 |
2019年 | 36篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 37篇 |
2015年 | 36篇 |
2014年 | 71篇 |
2013年 | 90篇 |
2012年 | 102篇 |
2011年 | 139篇 |
2010年 | 58篇 |
2009年 | 63篇 |
2008年 | 111篇 |
2007年 | 105篇 |
2006年 | 100篇 |
2005年 | 84篇 |
2004年 | 69篇 |
2003年 | 46篇 |
2002年 | 57篇 |
2001年 | 28篇 |
2000年 | 34篇 |
1999年 | 28篇 |
1998年 | 19篇 |
1997年 | 14篇 |
1996年 | 27篇 |
1995年 | 21篇 |
1994年 | 25篇 |
1993年 | 20篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 29篇 |
1989年 | 15篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 24篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 25篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 32篇 |
1978年 | 35篇 |
1977年 | 35篇 |
1976年 | 20篇 |
1975年 | 24篇 |
1974年 | 25篇 |
1973年 | 25篇 |
排序方式: 共有2091条查询结果,搜索用时 93 毫秒
11.
DEBACHE Abdelmadjid BOULCINA Raouf TAFER Radia BELFAITAH Ali RHOUATI Salah CARBONI Bertrand 《中国化学》2008,26(11):2112-2116
The synthesis of 1,2,3,4-dihydropyrimidinone/thione derivatives was achieved in good to excellent yields using calcium(II) nitrate as catalyst to promote the Biginelli three-component condensation reaction from a diversity of aromatic aldehydes, β-keto compounds and urea or thiourea. The reaction was carried out under solvent-free conditions. 相似文献
12.
Ge segregation during the growth of Si1 − xGex alloys (x = 5, 10, 20, and 40%) was studied using X-ray photoelectron spectroscopy. The alloys were grown in thicknesses up to 20.0 nm at 500°C to measure quantitatively the amount of segregated surface Ge. The length of alloy needed to reach steady-state growth edge was found to decrease with increasing alloy concentration (4.8, 2.8, 2.4, and 2.0 nm, respectively). It was found that each alloy had a complete monolayer of Ge on the surface and an increasing amount of segregated Ge in the second layer (20, 55, 80, and 95%, respectively) during steady-state growth. An increase in the temperature of alloy growth (400–750°C) resulted in an increase in the leading edge of alloy growth but did not change the amount of segregated Ge during steady-state growth. We propose that film stress is responsible for the amount of Ge segregation. 相似文献
13.
The flat rank of a totally disconnected locally compact group G, denoted flat-rk(G), is an invariant of the topological group
structure of G. It is defined thanks to a natural distance on the space of compact open subgroups of G. For a topological
Kac-Moody group G with Weyl group W, we derive the inequalities alg-rk(W) ≤ flat-rk(G) ≤ rk(|W|0). Here, alg-rk(W) is the maximal Z-rank of abelian subgroups of W, and rk(|W|0) is the maximal dimension of isometrically embedded flats in the CAT0-realization |W|0. We can prove these inequalities under weaker assumptions. We also show that for any integer n ≥ 1 there is a simple, compactly
generated, locally compact, totally disconnected group G, with flat-rk(G) = n and which is not linear. 相似文献
14.
15.
16.
17.
18.
Two Optically Active Luteochromes: Preparation, Spectra and Chiroptical and Chromatographic Properties Selective rearrangement of (5R,6S,5′ R,6′S)-5,6:5′, 6′ -diepoxy-5,6,5′, 6′ -tetrahydro- β,β -carotene with the aid ofan ethereal solution of malonic acid leads to the mixture of the C(8′)-epimeric luteochromes. HPLC separation gave the pure isomers. This is the first report on th preparation of optically active luteochromes. 相似文献
19.
Alan D. Potoff Bertrand L. Chamberland Lewis Katz 《Journal of solid state chemistry》1973,8(3):234-237
A single crystal study of hydrothermally prepared eight-layer BaMnO3 has been carried out which confirms the (Zhdanov notation) 121121 layer stacking scheme for the BaO3 layers. The MnO6 octahedra share faces in strings of four, and these strings are connected to each other by corner sharing. The compound has an hexagonal unit cell of dimensions a = 5.667 ± 0.003 and c = 18.738 ± 0.009 Å, probable space group . Its structure has been determined from 352 independent reflections, of which 242 were considered observed, collected manually by a counter technique and refined to a conventional R value of 0.079. 相似文献
20.
Volatile hydrides of As, Se, Sb, Sn and Bi were generated from aqueous sample solutions using a tetrahydroborate reductant. The gaseous analytes were transferred to the inner wall of an electrothermal vaporizer (graphite furnace) and preconcentrated on a 1.25 μg thin-film of reduced palladium at 400°C. The furnace comprised the sample introduction unit of an inductively coupled plasma mass spectrometric detection system. Absolute limits of detection (3σB) were 2.9, 3.3, 54, 5 and 1980 pg for As, Sb, Sn, Bi and Se, respectively. System efficiency for the generation and sequestration of the hydrides averaged, with the exception of Se, better than 75%. Multielement determinations of As, Se and Bi were possible using the same experimental conditions, those for Sn and Sb were accomplished in a separate run. The efficacy of this analytical approach was verified by the analysis of several marine reference materials using simple calibration standards prepared in the same manner as the samples. Good agreement with certified values was achieved for As, Sn, Sb and Se; no reference materials were available for assessment of accuracy in the case of Bi. 相似文献