全文获取类型
收费全文 | 281篇 |
免费 | 5篇 |
专业分类
化学 | 179篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 48篇 |
物理学 | 52篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 13篇 |
2012年 | 23篇 |
2011年 | 23篇 |
2010年 | 5篇 |
2009年 | 8篇 |
2008年 | 7篇 |
2007年 | 25篇 |
2006年 | 8篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 6篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1962年 | 3篇 |
1960年 | 2篇 |
1959年 | 2篇 |
1955年 | 2篇 |
1954年 | 1篇 |
1948年 | 9篇 |
1947年 | 2篇 |
1946年 | 1篇 |
1945年 | 2篇 |
1941年 | 1篇 |
1940年 | 1篇 |
1939年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有286条查询结果,搜索用时 15 毫秒
61.
The propagation of a first-order electromagnetic discontinuity is discussed. Expressions are obtained for the possible velocities of propagation as functions of the field strengths ahead of the surface of discontinuity. Expressions are also obtained for the growth in the magnitude of the discontinuity as the wave progresses. 相似文献
62.
18‐Crown‐6 Catalyzed Microwave‐mediated Synthesis of Symmetric Bis‐Heterocyclic Compounds under Solvent‐free Condition 下载免费PDF全文
Rathnasamy Rishikesan Kamalakannan Prabakaran Rajamani Murugesan Ramaswamy Venkataraman Pakkath Karuvalam Ranjith Sivasubramanian Arvind Sathiah Thennarasu 《Journal of heterocyclic chemistry》2015,52(5):1321-1330
An efficient, solvent‐free and 18‐crown‐6 catalyzed method for the synthesis of N‐alkyl‐4‐(4‐(5‐(2‐(alkyl‐amino)thiazol‐4‐yl)pyridin‐3‐yl)phenyl)thiazol‐2‐amine, N‐alkyl‐4‐(5‐(2‐alkyamino)thiazol‐4‐yl)pyridine‐3‐yl)thiazol‐2‐amine, and 4,4′‐bis‐{2‐[amino]‐4‐thiazolyl}biphenyl bis‐heterocyclic derivatives via microwave accelerated cyclization is presented. 相似文献
63.
Manojit Pal Venkataraman SubramanianKaruppasamy Parasuraman Koteswar Rao Yeleswarapu 《Tetrahedron》2003,59(48):9563-9570
(S)-Prolinol facilitated the coupling reaction of terminal alkynes with 3-iodoflavone under palladium-copper catalysis in aqueous DMF affording a mild and convenient method for the synthesis of 3-alkynyl substituted flavones of potential biological interest. 相似文献
64.
Let G be a finite group andA be a normal subgroup ofG. We denote by ncc(A) the number ofG-conjugacy classes ofA andA is calledn-decomposable, if ncc(A)= n. SetK
G = {ncc(A)|A ⊲ G}. LetX be a non-empty subset of positive integers. A groupG is calledX-decomposable, ifK
G =X.
Ashrafi and his co-authors [1-5] have characterized theX-decomposable non-perfect finite groups forX = {1, n} andn ≤ 10. In this paper, we continue this problem and investigate the structure ofX-decomposable non-perfect finite groups, forX = {1, 2, 3}. We prove that such a group is isomorphic to Z6, D8, Q8, S4, SmallGroup(20, 3), SmallGroup(24, 3), where SmallGroup(m, n) denotes the mth group of ordern in the small group library of GAP [11]. 相似文献
65.
A 3,4-O-bisacetal 2,6-di-O-benzyl protected thioglucoside is converted to the corresponding glucosyl triflate with 1-benzenesulfinyl piperidine and trifluoromethanesulfonic anhydride. The moderate to excellent β-selectivity exhibited with this glucosyl triflate with a range of alcohols is generally higher than that observed with the more electronically disarmed corresponding 3,4-O-carbonate, for which a possible reason is advanced. 相似文献
66.
K. N. Venkataraman K. Suresh Chandra 《Annals of the Institute of Statistical Mathematics》1984,36(1):101-118
Summary LetX(t) be a linear autoregressively generated explosive time series, with autoregressive coefficientsb
1,…,bq, and a constant termb
0, and an error term
; a0=1. Where ε(t),t≧1 are independent, Eε(t)=0, and Eε
2(t)=σ2 is positive and finite. In this paper two categories of
-consisent and asymptotically singularly normal estimators are proposed for (b
1,…,bq, b0) thus settling an open problem since the publication of the paper (Venkataraman [5]). Based on these estimators several additional
limit theorems based on estimated error residuals are proved. The parameter-free limit theorems of Spectral and Quenouille
types of this paper serve as asymptotic goodness of fit tests for the model generatingX(t). 相似文献
67.
Kwong-Kit Choi Carlos Monroy Venkataraman Swaminathan Theodor Tamir Ming Leung John Devitt David Forrai Darrel Endres 《Infrared Physics & Technology》2007,50(2-3):124-135
Previously, we demonstrated a large format 1024 × 1024 corrugated quantum well infrared photodetector focal plane array (C-QWIP FPA). The FPA has a cutoff at 8.6 μm and is BLIP at 76 K with f/1.8 optics. The pixel had a shallow trapezoidal geometry that simplified processing but limited the quantum efficiency QE. In this paper, we will present two approaches to achieve a larger QE for the C-QWIPs. The first approach increases the size of the corrugations for more active volume and adopts a nearly triangular pixel geometry for larger light reflecting surfaces. With these improvements, QE is predicted to be about 35% for a pair of inclined sidewalls, which is more than twice the previous value. The second approach is to use Fabry–Perot resonant oscillations inside the corrugated cavities to enhance the vertical electric field strength. With this approach, a larger QE of 50% can be achieved within certain spectral regions without using either very thick active layers or anti-reflection coatings. The former approach has been adopted to produce two FPAs, and the preliminary experimental results will be discussed. In this paper, we also describe using voltage tunable detector materials to achieve multi-color capability for these FPAs. 相似文献
68.
Cetyl trimethyl ammonium (CTA) ions have been confined within galleries of layered CdPS3 at two different grafting densities. Low grafting densities are obtained on direct intercalation of CTA ions into CdPS3 to give Cd0.93PS3(CTA)0.14. Intercalation occurs with a lattice expansion of 4.8 ? with the interlamellar surfactant ion lying flat forming a monolayer.
Intercalation at higher grafting densities was effected by a two-step ion-exchange process to give Cd0.83PS3(CTA)0.34, with a lattice expansion of 26.5 ?. At higher grafting densities the interlamellar surfactant ions adopt a tilted bilayer
structure.13C NMR and orientation-dependent IR vibrational spectroscopy on single crystals have been used to probe the conformation and
orientation of the methylene ‘tail’ of the intercalated surfactant in the two phases. In the monolayer phase, the confined
methylene chain adopts an essentially all-trans conformation with most of the trans chain aligned parallel to the gallery
walls. On lowering the temperature, molecular plane aligns parallel, so that the methylene chain lies flat, rigid and aligned
to the confining surface. In the bilayer phase, most bonds in the methylene chain are in trans conformation. It is possible
to identify specific conformational sequences containing a gauche bond, in the interior and termini of the intercalated methylene.
These high energy conformers disappear on cooling leaving all fifteen methylene units of the intercalated cetyl trimethyl
ammonium ion in trans conformational registry at 40 K. 相似文献
69.
70.