全文获取类型
收费全文 | 2705篇 |
免费 | 67篇 |
国内免费 | 16篇 |
专业分类
化学 | 1976篇 |
晶体学 | 30篇 |
力学 | 45篇 |
数学 | 447篇 |
物理学 | 290篇 |
出版年
2022年 | 28篇 |
2021年 | 27篇 |
2020年 | 49篇 |
2019年 | 45篇 |
2018年 | 34篇 |
2017年 | 16篇 |
2016年 | 55篇 |
2015年 | 67篇 |
2014年 | 63篇 |
2013年 | 96篇 |
2012年 | 153篇 |
2011年 | 161篇 |
2010年 | 84篇 |
2009年 | 82篇 |
2008年 | 157篇 |
2007年 | 134篇 |
2006年 | 139篇 |
2005年 | 142篇 |
2004年 | 117篇 |
2003年 | 125篇 |
2002年 | 90篇 |
2001年 | 38篇 |
2000年 | 39篇 |
1999年 | 22篇 |
1998年 | 22篇 |
1997年 | 34篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 28篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 29篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 48篇 |
1984年 | 39篇 |
1983年 | 43篇 |
1982年 | 50篇 |
1981年 | 39篇 |
1980年 | 43篇 |
1979年 | 24篇 |
1978年 | 31篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1974年 | 15篇 |
1973年 | 16篇 |
排序方式: 共有2788条查询结果,搜索用时 31 毫秒
1.
2.
3.
Carey Lea 《Fresenius' Journal of Analytical Chemistry》1867,6(1):95-96
Ohne Zusammenfassung 相似文献
4.
Inhibition of the reduction of Cr(VI) at the magnetite–water interface by calcium carbonate coatings
The effect of calcium carbonate coatings on the reduction of aqueous chromate on the magnetite(1 1 1) surface has been investigated using a combination of synchrotron based X-ray photoemission spectroscopy (PES) and X-ray absorption near edge structure (XANES) spectroscopy, along with laboratory-based powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO3 coatings (dominantly calcite with minor quantities of aragonite and vaterite) of thicknesses ranging from 10 Å to 20 m were grown on magnetite(1 1 1) surfaces by exposure to supersaturated aqueous solutions followed by evaporation of the solution—a process that mimics pore-water evaporation in vadose zones leading to the formation of caliche and calcium carbonate coatings on mineral grains. Coating thicknesses were determined from attenuation of the Fe 2p photoemission signal by the carbonate coating. For coatings less than 15 Å thick, Cr 2p photoemission and Cr LII, LIII-edge XANES spectra show that chromate is reduced by the underlying magnetite surface; however, as the minimum coating thickness increases beyond 15 Å, the magnetite surface becomes passivated and further chromate reduction ceases. Our findings suggest that carbonate coatings on natural magnetite grains can significantly reduce or eliminate their ability to reduce Cr(VI), which is a toxic and highly mobile environmental contaminant. 相似文献
5.
6.
Raymond G. Plevey Richard W. Rendell John Colin Tatlow 《Journal of fluorine chemistry》1982,21(2):159-169
Pyridine has been fluorinated over caesium tetrafluorocobaltate(III) (CsCoIIIF4) at 300–400°C to give a mixture of undecafluoro-N-methylpyrrolidine, bis(trifluoromethyl)amine, pentafluoropyridine and several polyfluoropyridines; the product composition depended to some extent on the geometry of the reactor. The fluorinations of pentafluoropyridine, piperidine and undecafluoropiperidine were also investigated. 相似文献
7.
Peter G. Doyle Colin Mallows Alon Orlitsky Larry Shepp 《Israel Journal of Mathematics》1989,67(1):34-42
Letn cells be arranged in a ring, or alternatively, in a row. Initially, all cells are unmarked. Sequentially, one of the unmarked
cells is chosen at random and marked until, aftern steps, each cell is marked. After thekth cell has been marked the configuration of marked cells defines some number of islands: maximal sets of adjacent marked
cells. Let ξ
k
denote the random number of islands afterk cells have been marked.
We give explicit expressions for moments of products of ξ
k
’s and for moments of products of 1/ξ
k
’s.
These are used in a companion paper to prove that if a random graph on the natural number is made by drawing an edge betweeni≧1 andj>i with probabilityλ/j, then the graph is almost surely connected ifλ>1/4 and almost surely disconnected ifλ≦1/4. 相似文献
8.
We see that the entropy method yields strong concentration results for general self‐bounding functions of independent random variables. These give an improvement of a concentration result of Talagrand much used in discrete mathematics. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献
9.
The self-organizing map (a neural network) was applied to the spectral pattern recognition of voice quality in 34 subjects: 15 patients operated on because of insufficient glottal closure and 19 subjects not treated for voice disorders. The voice samples, segments of sustained /a/, were perceptually rated by six experts. A self-organized acoustic feature map was first computed from tokens of /a/ and then used for the analysis of the samples. The locations of the samples on the map were determined and the distances from a normal reference were compared with the perceptual ratings. The map locations corresponded to the degree of audible disorder: the samples judged as normal were overlapping or close to the normal reference, whereas the samples judged as dysphonie were located further away from it. The comparison of pre- and postoperative samples of the patients showed that the perceived improvement of voice quality was also detected by the map. 相似文献
10.
We describe a method for searching for ideal symmetric solutions to the Prouhet-Tarry-Escott Problem. We report results of extensive searches for solutions of sizes up to 12. We found two solutions of size 10 that are smaller by two orders of magnitude than the solution found by A. Letac in the 1940s, which was the smallest size 10 solution known before our search.