全文获取类型
收费全文 | 835篇 |
免费 | 31篇 |
国内免费 | 9篇 |
专业分类
化学 | 502篇 |
晶体学 | 1篇 |
力学 | 17篇 |
数学 | 124篇 |
物理学 | 231篇 |
出版年
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 37篇 |
2012年 | 42篇 |
2011年 | 40篇 |
2010年 | 27篇 |
2009年 | 18篇 |
2008年 | 54篇 |
2007年 | 47篇 |
2006年 | 31篇 |
2005年 | 40篇 |
2004年 | 44篇 |
2003年 | 25篇 |
2002年 | 45篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1971年 | 4篇 |
排序方式: 共有875条查询结果,搜索用时 31 毫秒
161.
Wesley A. Chalifoux Michael J. Ferguson Robert McDonald Frederic Melin Luis Echegoyen Rik R. Tykwinski 《Journal of Physical Organic Chemistry》2012,25(1):69-76
Polyynes spanning from a diyne to a dodecayne with adamantyl endgroups have been synthesized using the Fritsch–Buttenberg–Wiechell rearrangement as a key step to construct the acetylenic framework. Molecular properties as a function of polyyne length have been analyzed by UV–Vis spectroscopy, cyclic voltammetry, differential scanning calorimetry, and X‐ray crystallography. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
162.
Harbron RL McDonald TO Rannard SP Findlay PH Weaver JV 《Chemical communications (Cambridge, England)》2012,48(10):1592-1594
Multi-purpose amphiphilic branched copolymer surfactants can be used to simultaneously stabilise and cross-link emulsion droplets to produce encapsulated spheres and hollow capsules. 相似文献
163.
McDonald KP Hua Y Lee S Flood AH 《Chemical communications (Cambridge, England)》2012,48(42):5065-5075
Triazolophanes have recently surfaced as a new class of shape-persistent macrocycles that bind anions. Bearing only triazole- and phenyl-derived CH hydrogen bond donors, these receptors have shown extraordinary Cl(-) binding strengths (>10(6) M(-1), CH(2)Cl(2)). The attributes of the triazolophane that are responsible are presented herein alongside recent literature accounts that have utilized similar strategies in new and exciting supramolecular systems. This review describes how triazolophanes leverage the structural pre-organization characteristic of spherands to take advantage of non-traditional hydrogen bonds originating from extrinsic CH donors. 相似文献
164.
UV irradiation of a dipeptide gelator in solution with a photoacid generator (PAG) results in the formation of a hydrogel. We demonstrate that photopatterning of these gels using a UV mask is possible. 相似文献
165.
Michael E. Slaney D. Jason Anderson Dusan Ristic‐Petrovic Dr. Robert McDonald Prof. Dr. Martin Cowie 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(15):4723-4737
The bridging fluoroolefin ligands in the complexes [Ir2(CH3)(CO)2(μ‐olefin)(dppm)2][OTf] (olefin=tetrafluoroethylene, 1,1‐difluoroethylene; dppm=μ‐Ph2PCH2PPh2; OTf?=CF3SO3?) are susceptible to facile fluoride ion abstraction. Both fluoroolefin complexes react with trimethylsilyltriflate (Me3SiOTf) to give the corresponding fluorovinyl products by abstraction of a single fluoride ion. Although the trifluorovinyl ligand is bound to one metal, the monofluorovinyl group is bridging, bound to one metal through carbon and to the other metal through a dative bond from fluorine. Addition of two equivalents of Me3SiOTf to the tetrafluoroethylene‐bridged species gives the difluorovinylidene‐bridged product [Ir2(CH3)(OTf)(CO)2(μ‐OTf)(μ‐C?CF2)(dppm)2][OTf]. The 1,1‐difluoroethylene species is exceedingly reactive, reacting with water to give 2‐fluoropropene and [Ir2(CO)2(μ‐OH)(dppm)2][OTf] and with carbon monoxide to give [Ir2(CO)3(μ‐κ1:η2‐C?CCH3)(dppm)2][OTf] together with two equivalents of HF. The trifluorovinyl product [Ir2(κ1‐C2F3)(OTf)(CO)2(μ‐H)(μ‐CH2)(dppm)2][OTf], obtained through single C? F bond activation of the tetrafluoroethylene‐bridged complex, reacts with H2 to form trifluoroethylene, allowing the facile replacement of one fluorine in C2F4 with hydrogen. 相似文献
166.
167.
M. Cavers S.M. Cioabă S. Fallat D.A. Gregory W.H. Haemers S.J. Kirkland J.J. McDonald M. Tsatsomeros 《Linear algebra and its applications》2012,436(12):4512-4529
The spectra of the skew-adjacency matrices of a graph are considered as a possible way to distinguish adjacency cospectral graphs. This leads to the following topics: graphs whose skew-adjacency matrices are all cospectral; relations between the matchings polynomial of a graph and the characteristic polynomials of its adjacency and skew-adjacency matrices; skew-spectral radii and an analogue of the Perron–Frobenius theorem; and, the number of skew-adjacency matrices of a graph with distinct spectra. 相似文献
168.
We study the partition function of the Potts model in an external (magnetic) field, and its connections with the zero-field
Potts model partition function. Using a deletion-contraction formulation for the partition function Z for this model, we show that it can be expanded in terms of the zero-field partition function. We also show that Z can be written as a sum over the spanning trees, and the spanning forests, of a graph G. Our results extend to Z the well-known spanning tree expansion for the zero-field partition function that arises though its connections with the
Tutte polynomial. 相似文献
169.
Thode AM Kim KH Blackwell SB Greene CR Nations CS McDonald TL Macrander AM 《The Journal of the Acoustical Society of America》2012,131(5):3726-3747
An automated procedure has been developed for detecting and localizing frequency-modulated bowhead whale sounds in the presence of seismic airgun surveys. The procedure was applied to four years of data, collected from over 30 directional autonomous recording packages deployed over a 280 km span of continental shelf in the Alaskan Beaufort Sea. The procedure has six sequential stages that begin by extracting 25-element feature vectors from spectrograms of potential call candidates. Two cascaded neural networks then classify some feature vectors as bowhead calls, and the procedure then matches calls between recorders to triangulate locations. To train the networks, manual analysts flagged 219 471 bowhead call examples from 2008 and 2009. Manual analyses were also used to identify 1.17 million transient signals that were not whale calls. The network output thresholds were adjusted to reject 20% of whale calls in the training data. Validation runs using 2007 and 2010 data found that the procedure missed 30%-40% of manually detected calls. Furthermore, 20%-40% of the sounds flagged as calls are not present in the manual analyses; however, these extra detections incorporate legitimate whale calls overlooked by human analysts. Both manual and automated methods produce similar spatial and temporal call distributions. 相似文献
170.
A. David McDonald Anthony D.M. Smith Andre E. Punt Geoffrey N. Tuck Adam J. Davidson 《Natural Resource Modeling》1997,10(1):3-29
An approach to incorporating new information using Bayes' theorem is applied to obtain estimates of expected returns from research on stock structure for determination of total allowable catch (TAC). Expected returns are measured relative to quantitative performance criteria that are inferred from fishery management objectives. Principles of the approach are outlined and a detailed case study of Tasmanian orange roughy is reported. 相似文献