全文获取类型
收费全文 | 452篇 |
免费 | 17篇 |
国内免费 | 24篇 |
专业分类
化学 | 336篇 |
晶体学 | 19篇 |
力学 | 10篇 |
数学 | 48篇 |
物理学 | 80篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 26篇 |
2011年 | 42篇 |
2010年 | 24篇 |
2009年 | 26篇 |
2008年 | 40篇 |
2007年 | 35篇 |
2006年 | 30篇 |
2005年 | 25篇 |
2004年 | 20篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有493条查询结果,搜索用时 15 毫秒
1.
Chee Sing Yap 《The Journal of the Operational Research Society》1989,40(7):649-658
This paper describes three case studies which investigated issues relating to the implementation and management of advanced information technology. The benefits derived from information technology were found to vary from one organization to another. These studies provide further evidence to support earlier research findings that senior management has an important role to play in the effective exploitation of information technology, and that the investment approach taken by an organization has a significant effect on the development of computer-based information systems. The effectiveness of a system depends not only on applying the appropriate technology, but also on how successfully technical and behavioural issues are resolved. 相似文献
2.
To date, ten experimental measurements of the asymmetry parameter have been made for the positron decay of52Mn. The Fermi to Gamow-Teller mixing ratioy can be deduced from such measurements and this quantity is important because the time-reversal violating amplitude is proportional toy/(1+y2). Our theoretical calculation using the Collective Model yieldsy=? 3.5×10?4 for the deformation parameterβ=0.1 andy=? 4.6×10?4 forβ=0.2. Such small values ofy are consistent with time-reversal invarisance. 相似文献
3.
Chun-Wei Hsu 《Journal of Non》2008,354(34):4037-4042
A sol-gel method has been used to fabricate a cholesterol MIP for application in polar solutions. In this study, (cholesteryl propylcarbamate)triethoxysilane and tetraethyl orthosilicate were used as the hydrophobic monomer and crosslinker, respectively. The MIP had a larger pore volume when formation of the polymer was catalyzed at a higher pH than when it was formed at lower pH values, with the pore diameters being 3.5 nm and 2 nm, respectively for materials formed at high and low pH values. Both of these pore volumes were greater than those found for the respective control polymers formed without template. However, only the polymers formed at low pH values showed an imprinting effect. Compared with other methods explored, the sol-gel procedure gave only a small amount of non-specific binding for both the MIP and NIP when synthesized at low pH values. The largest imprinting-induced promotion of binding (IPB) value of the MIP (13 650%) was obtained with [HCl] = 0.01 M in the sol-gel solution. The MIP showed high selectivity towards cholesterol in comparison with other steroid hormones, and also to a lesser extent recognized vitamin D3 in methanol solution containing 5 vol.% water. 相似文献
4.
Two graphsG andH of the same order are packable ifG can be embedded in the complement
ofH. In this paper we give a complete characterization of two graphs of ordern having total size at most 2n – 2 which are packable. This result extends an earlier result of B. Bollobás and S.E. Eldridge. 相似文献
5.
Dubé T Conoci S Gambarotta S Yap GP Vasapollo G 《Angewandte Chemie (International ed. in English)》1999,38(24):3657-3659
The cooperative attack of four (dipyrromethanyl)Sm(II) units on dinitrogen resulted in a novel tetranuclear samarium dinitrogen complex (shown schematically). The presence of halogen atoms inhibited reactivity with dinitrogen through the assembly of divalent samarium clusters. dipyrr=diphenylmethyldipyrrolide dianion. 相似文献
6.
Alexandra M. Antonio Kyle J. Korman Glenn P. A. Yap Eric D. Bloch 《Chemical science》2020,11(46):12540
Diverse strategies for the preparation of mixed-metal three-dimensional porous solids abound, although many of them lend themselves only moderate levels of tunability. Herein, we report the design and synthesis of surface functionalized permanently microporous coordination cages and their use in the isolation of mixed metal solids. Judicious alkoxide-based ligand functionalization was utilized to tune the solubility of starting copper(ii)-based cages and their resulting compatibility with the mixed-cage approach described here. We further prepared a family of isostructural molybdenum(ii) cages for a subset of the ligands. The preparation of mixed-metal cage solids proceeds under facile conditions where solutions of parent cages are mixed and product phases isolated. A suite of spectroscopic and characterization tools confirm the starting cages are intact in the amorphous product. Finally, we show that utilization of precise ligand functional groups can be used to prepare mixed cage solids that can be easily and cleanly separated into their constituent components through simple solvent washing or solvent extraction techniques.Surface-functionalized porous coordination cages can be used to create homogeneous mixed-cage alloys with high levels of tunability and processability. 相似文献
7.
Pradeep Mathur Bala Manimaran Md. Munkir Hossain Arnold L. Rheingold Louise M. Liable-Sands Glenn P.A. Yap 《Journal of organometallic chemistry》1997,540(1-2):165-168
The tris-methylene bridged compound (NO)4Fe2Se(μ-CH2)3 has been isolated. It has been characterised by IR and 1H, 13C, and 77Se NMR spectroscopy. Its structure has been determined by single-crystal X-ray diffraction methods. The structure consists of a heavy atom triangle consisting of one Se and two Fe atoms. The Fe-Fe and the two Fe-Se edges are bridged by methylene groups. 相似文献
8.
Huang W Todaro L Yap GP Beer R Francesconi LC Polenova T 《Journal of the American Chemical Society》2004,126(37):11564-11573
Vanadium environments in Keggin oxopolytungstates were characterized by (51)V solid-state MAS NMR spectroscopy. (C(4)H(9))(4)N(+)-, K(+)-, Cs(+)-, as well as mixed Na(+)/Cs(+)- salts of the mono-, di-, and trivanadium substituted oxotungstates, [VW(11)O(40)](4-), [V(2)W(10)O(40)](5-), and [V(3)W(9)O(40)](6-), have been prepared as microcrystalline and crystalline solids. Solid-state NMR spectra report on the local environment of the vanadium site in these Keggin ions via their anisotropic quadrupolar and chemical-shielding interactions. These (51)V fine structure constants in the solid state are determined by the number of vanadium atoms present in the oxoanion core. Surprisingly, the quadrupolar anisotropy tensors do not depend to any significant extent on the nature of the countercations. On the other hand, the chemical-shielding anisotropy tensors, as well as the isotropic chemical shifts, display large variations as a function of the cationic environment. This information can be used as a probe of the local cationic environment in the vanadium-substituted Keggin solids. 相似文献
9.
A lactone ring confers unusual stability to a diphenylmethyl-like radical that is virtually unreactive toward oxygen. Thus, the radical derived from HP-136 is about 10,000 times less reactive than typical carbon-centered radicals. A reversible reaction with oxygen is proposed by analogy with triphenylmethyl; however, the association constant is about 1000 times smaller for HP-136 than for triphenylmethyl. While the lactone ring greatly influences the reactivity, the spectroscopy of the HP-136-derived radical is in line with that expected for a substituted diphenylmethyl radical. 相似文献
10.