全文获取类型
收费全文 | 346篇 |
免费 | 20篇 |
国内免费 | 9篇 |
专业分类
化学 | 240篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 21篇 |
物理学 | 101篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 8篇 |
2016年 | 17篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 36篇 |
2012年 | 28篇 |
2011年 | 28篇 |
2010年 | 26篇 |
2009年 | 17篇 |
2008年 | 17篇 |
2007年 | 12篇 |
2006年 | 22篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 4篇 |
排序方式: 共有375条查询结果,搜索用时 15 毫秒
111.
Research on Chemical Intermediates - HZSM-5 (HZ(1) and HZ(2)) zeolites synthesized with various framework aluminum distributions and also cobalt-modified H-form zeolites (Co/HZ(1) and Co/HZ(2))... 相似文献
112.
Badrnezhad Ramin Pourfarzad Hamed Madram Ali Reza Ganjali Mohammad Reza 《Russian Journal of Electrochemistry》2019,55(4):272-280
Russian Journal of Electrochemistry - The present paper aims to compare the corrosion protection performance of electrodeposited Ni?P with Ni–P–C nanocomposite coatings in 3.5 wt... 相似文献
113.
Ramin Ghorbani-Vaghei 《Tetrahedron letters》2003,44(40):7529-7532
N,N′-Diiodo-N,N′-1,2-ethanediylbis(p-tolouenesulphonamide) [NIBTS] and catalytic trifluoroacetic acid can be used for the regioselective iodination of aromatic compounds in acetonitrile under mild conditions in excellent yields. 相似文献
114.
A clique covering of a simple graph G is a collection of cliques of G covering all the edges of G such that each vertex is contained in at most k cliques. The smallest k for which G admits a clique covering is called the local clique cover number of G and is denoted by lcc(G). Local clique cover number can be viewed as the local counterpart of the clique cover number that is equal to the minimum total number of cliques covering all edges. In this article, several aspects of the local clique covering problem are studied and its relationships to other well‐known problems are discussed. In particular, it is proved that the local clique cover number of every claw‐free graph is at most , where Δ is the maximum degree of the graph and c is a constant. It is also shown that the bound is tight, up to a constant factor. Moreover, regarding a conjecture by Chen et al. (Clique covering the edges of a locally cobipartite graph, Discrete Math 219(1–3)(2000), 17–26), we prove that the clique cover number of every connected claw‐free graph on n vertices with the minimum degree δ, is at most , where c is a constant. 相似文献
115.
A new solid-phase microextraction fiber based on alumina/titania sol-gel-coated on copper wire for headspace sampling of chlorinated organic solvents (chloroform, carbon tetrachloride, trichloroethene, and tetrachloroethene) from urine samples is introduced. The influences of fiber coating composition and microextraction conditions (extraction temperature, extraction time, and ionic strength of the sample matrix) on the fiber performance were investigated. Also, the influence of temperature and time on desorption of analytes from fiber was studied. The proposed fiber has high capacity and demonstrates fast sampling of chlorinated organic solvents from urine samples with high sensitivity. The relative standard deviation (RSD, n=5) for all analytes was below 6.5%. 相似文献
116.
Ramin Rabbani Sima Saeedi Md Nazimuddin Hctor Barbero Nathalie Kyritsakas Travis A. White Eric Masson 《Chemical science》2021,12(46):15347
A cucurbit[8]uril (CB[8])-secured platinum terpyridyl chloride dimer was used as a photosensitizer and hydrogen-evolving catalyst for the photoreduction of water. Volumes of produced hydrogen were up to 25 and 6 times larger than those obtained with the corresponding free and cucurbit[7]uril-bound platinum monomer, respectively, at equal Pt concentration. The thermodynamics of the proton-coupled electron transfer from the Pt(ii)–Pt(ii) dimer to the corresponding Pt(ii)–Pt(iii)–H hydride key intermediate, as quantified by density functional theory, suggest that CB[8] secures the Pt(ii)–Pt(ii) dimer in a particularly reactive conformation that promotes hydrogen formation.The cucurbit[8]uril macrocycle can secure a platinum terpyridyl complex into a particularly reactive dimer that catalyzes the photoreduction of water. 相似文献
117.
S. C. Tsou P. H. Tsien M. Takai D. Röschenthaler M. Ramin H. Ryssel I. Ruge 《Applied Physics A: Materials Science & Processing》1980,23(2):163-168
The annealing behavior of arsenic-implanted silicon under scanned cw CO2-laser irradiation from front and back surfaces is investigated. Ellipsometry, Hall effect, Rutherford backscattering measurements
and neutron activation analysis indicate an enhancement of annealing efficiency by laser irradiation from the back surface,
which provides complete recovery of crystal damage, high substitutionality and electrical activation of implanted arsenic
atoms without redistribution of concentration profile. The enhancement of annealing efficiency under back-surface irradiation
is explained by the difference in laser reflection from the front and back surface of silicon wafers. No differences in the
results are found for scanned and static annealing. 相似文献
118.
Maximum trapping efficiency in optical tweezers occurs close to the coverslip because spherical aberration owing to a mismatch in the refractive indices of the specimen (water) and the immersion oil dramatically decreases the trap efficiency as the trap depth increases. Measuring the axial trap efficiency at various tube lengths by use of an oil-immersion objective has shown that such an aberration can be balanced by another source of spherical aberration, leading to a shift in the position of the maximum efficiency in the Z direction. For a 1.1 microm polystyrene bead we could achieve the maximal efficiency at a depth of 70 microm, whereas the trap was stable up to a depth of 100 microm. 相似文献
119.
Various aryl aldehydes underwent prompt one pot conversion into the corresponding nitriles in high yields by reacting with hydroxylamine hydrochloride supported on melamine formaldehyde under microwave irradiation in the presence of ammonium acetate as catalyst. 相似文献