全文获取类型
收费全文 | 329篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 257篇 |
力学 | 5篇 |
数学 | 57篇 |
物理学 | 25篇 |
出版年
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 22篇 |
2015年 | 8篇 |
2014年 | 5篇 |
2013年 | 17篇 |
2012年 | 21篇 |
2011年 | 26篇 |
2010年 | 12篇 |
2009年 | 12篇 |
2008年 | 19篇 |
2007年 | 23篇 |
2006年 | 22篇 |
2005年 | 13篇 |
2004年 | 18篇 |
2003年 | 17篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 0 毫秒
41.
42.
43.
In the first part of this paper, we enumerate exactly walks on the square lattice that start from the origin, but otherwise
avoid the half-line . We call them walks on the slit plane. We count them by their length, and by the coordinates of their endpoint. The corresponding three variable is algebraic of
degree 8. Moreover, for any point (i, j), the length for walks of this type ending at (i, j) is also algebraic, of degree 2 or 4, and involves the famous Catalan numbers.
Our method is based on the solution of a functional equation, established via a simple combinatorial argument. It actually
works for more general models, in which walks take their steps in a finite subset of ℤ2 satisfying two simple conditions. The corresponding are always algebraic.
In the second part of the paper, we derive from our enumerative results a number of probabilistic corollaries. For instance,
we can compute exactly the probability that an ordinary random walk starting from (i, j) hits for the first time the half-line at position (k, 0), for any triple (i, j, k). This generalizes a question raised by R. Kenyon, which was the starting point of this paper.
Taking uniformly at random all n-step walks on the slit plane, we also compute the probability that they visit a given point (k, 0), and the average number of visits to this point. In other words, we quantify the transience of the walks. Finally, we derive
an explicit limit law for the coordinates of their endpoint.
Received: 22 December 2001 / Revised version: 19 February 2002 / Published online: 30 September 2002
Both authors were partially supported by the INRIA, via the cooperative research action Alcophys.
Mathematics Subject Classification (2000): O5A15-60C05 相似文献
44.
45.
Gam-Derouich S Gosecka M Lepinay S Turmine M Carbonnier B Basinska T Slomkowski S Millot MC Othmane A Ben Hassen-Chehimi D Chehimi MM 《Langmuir : the ACS journal of surfaces and colloids》2011,27(15):9285-9294
Homopolymer grafts from α-tert-butoxy-ω-vinylbenzyl-polyglycidol (PGL) were prepared on gold and stainless steel (SS) substrates modified by 4-benzoyl-phenyl (BP) moieties derived from the electroreduction of the parent salt 4-benzoyl benzene diazonium tetrafluoroborate. The grafted BP aryl groups efficiently served to surface-initiate photopolymerization (SIPP) of PGL. In similar conditions, SIPP of hydroxyethyl methacrylate (HEMA) permitted the production of PHEMA grafts as model surfaces. Water contact angles were found to be 66°, 15°, and 0° for SS-BP, SS-PHEMA, and SS-PPGL, respectively. The spontaneous spreading of water drops on SS-PPGL was invariably observed with 1.5 μL water drops. PPGL thus appears as a superhydrophilic polymer. Resistance to nonspecific adsorption of proteins of PPGL and PHEMA grafts on gold was evaluated by surface plasmon resonance (SPR) using antibovine serum albumin (anti-BSA). The results conclusively show that PPGL-grafts exhibit enhanced resistance to anti-BSA adsorption compared to the well-known hydrophilic PHEMA. PPGL grafts were further modified with BSA through the carbonyldiimidazole activation of the OH groups providing immunosensing surfaces. The so-prepared PPGL-grafted BSA hybrids specifically interacted with anti-BSA in PBS as compared to antimyoglobin. It is clear that the superhydrophilic character of PPGL grafts opens new avenues for biomedical applications where surfaces with dual functionality, namely, specific protein grafting together with resistance to biofouling, are required. 相似文献
46.
The effect of confinement within some zeolitic structures on the activity and selectivity of metallocene catalysts for the ethylene oligomerization has been investigated using grand canonical Monte Carlo simulations (GCMC). The following zeolite (host) frameworks displaying different pore sizes, have been studied as solid hosts: mazzite (MAZ), AIPO-8 (AET), UTD-1F (DON), faujasite (FAU), and VPI-5 (VFI). Intermediates and transition states involved in the ethylene trimerization reaction catalyzed by a Ti-based catalyst [(η(5)-C(5)H(4)CMe(2)C(6)H(5))TiCl(3)/MAO] have been used as sorbates (guests). We have demonstrated linear correlations with slope a(H,j) between the adsorption enthalpy and the molecular volume V(m) of the sorbates, each holding for a given microporous host below a host-specific threshold V(mmax,j). Beyond this maximal molecular volume, the adsorption vanishes due to steric exclusion. a(H,j) increases, and V(mmax,j) decreases with decreasing host pore size, in line with the confinement concept. We moreover showed that, in the limit of vanishing loading (Henry regime), the enthalpies and entropies of adsorption in a given host are linearly correlated. We have defined a host-specific confinement compensation temperature a(j), which refers to a temperature where the stabilizing adsorption enthalpic interactions are canceled out against the loss in entropy. However, calculated a(j) are much larger than the operating temperatures. With a setup microkinetic model, we predict that the activity and selectivity of the confined Ti-catalyst in ethylene oligomerization can be significantly altered with respect to homogeneous phase conditions, since the adsorption free energies of transition states and intermediates also become functions of a(H,j) and V(m). We have applied this theory to predict the optimum host pore size to get maximum α-octene production, instead of α-hexene, which is primarily produced in the homogeneous phase. We also predict a significantly increased activity for confined catalysts. 相似文献
47.
Seguin J Moutiez M Li Y Belin P Lecoq A Fonvielle M Charbonnier JB Pernodet JL Gondry M 《Chemistry & biology》2011,18(11):1362-1368
Cyclodipeptide synthases (CDPSs) are small enzymes structurally related to class-I aminoacyl-tRNA synthetases (aaRSs). They divert aminoacylated tRNAs from their canonical role in ribosomal protein synthesis, for cyclodipeptide formation. All the CDPSs experimentally characterized to date are?bacterial. We show here that a predicted CDPS from the sea anemone Nematostella vectensis is an active CDPS catalyzing the formation of various cyclodipeptides, preferentially containing tryptophan. Our findings demonstrate that eukaryotes encode active CDPSs and suggest that all CDPSs have?a similar aminoacyl-tRNA synthetase-like architecture and ping-pong mechanism. They also raise questions about the biological roles of the cyclodipeptides produced in bacteria and eukaryotes. 相似文献
48.
Ferreira BS de Almeida CG Faza LP de Almeida A Diniz CG da Silva VL Grazul RM Le Hyaric M 《Molecules (Basel, Switzerland)》2011,16(7):5875-5885
Pequi (Caryocar brasiliense Camb.), baba?u (Orbignya phalerata Mart.), buriti (Mauritia flexuosa), and passion fruit (Passiflora edulis) oils were studied to determine their antibacterial, antioxidant and cytotoxic activities, as well as their total phenol and carotenoid contents. The fatty acid contents were determined by GC-MS. The three types of passion fruit oils studied were refined, cold pressed or extracted from seeds in a Soxhlet apparatus. The oils thus obtained showed differences in antioxidant activity and carotenoid content, but were similar in regard to total phenols. Buriti and pequi had the highest carotenoid contents, while refined and cold pressed passion fruit oil displayed the highest antioxidant activity. Pequi oil was the only oil to display antibacterial and cytotoxic activity. 相似文献
49.
Mireille Bossy Jean-François Jabir 《Stochastic Processes and their Applications》2011,121(12):2751-2775
We construct a confined Langevin type process aimed to satisfy a mean no-permeability condition at the boundary. This Langevin process lies in the class of conditional McKean Lagrangian stochastic models studied by Bossy, Jabir and Talay (2010) [5]. The confined process considered here is a first construction of solutions to the class of Lagrangian stochastic equations with boundary condition issued by the so-called PDF methods for Computational Fluid Dynamics. We prove the well-posedness of the confined system when the state space of the Langevin process is a half-space. 相似文献
50.
Mireille Bousquet-Mélou 《Journal of Algebraic Combinatorics》2011,33(4):571-608
We recover Gessel’s determinantal formula for the generating function of permutations with no ascending subsequence of length
m+1. The starting point of our proof is the recursive construction of these permutations by insertion of the largest entry.
This construction is of course extremely simple. The cost of this simplicity is that we need to take into account in the enumeration
m−1 additional parameters—namely, the positions of the leftmost increasing subsequences of length i, for i=2,…,m. This yields for the generating function a functional equation with m−1 “catalytic” variables, and the heart of the paper is the solution of this equation. 相似文献