全文获取类型
收费全文 | 186篇 |
免费 | 4篇 |
国内免费 | 14篇 |
专业分类
化学 | 105篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 59篇 |
物理学 | 34篇 |
出版年
2020年 | 1篇 |
2019年 | 5篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 1篇 |
2013年 | 7篇 |
2012年 | 7篇 |
2011年 | 18篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 19篇 |
2007年 | 9篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 13篇 |
2001年 | 3篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有204条查询结果,搜索用时 15 毫秒
91.
Patricia E. Simmons Tom Albers Debbie Barco Michelle Barker Ron Beer Cassandra Belton Betty Burris Hal Donovan Pili Dressel Ron Giesler Terri Gipson Neal Gleditsch Marian Heimbouch Lea Heintz Linda Kalinowski Kathy Ketterer Kit Klein Lebee Meehan Diane Miller Donna Northcott Barb Pollman Tom Potter Jeffrey Powell Dan Prater Doug Raney Chris Roman Beryl Rosenthal Brian Schaffer Joe Seidler Laura Sturmfels Mary Stewart Carey Tisdal Carol Valenta Suzanne Walton Ralph Wilke 《School science and mathematics》1998,98(7):354-356
92.
Christian Friesen Doug Hensley 《Proceedings of the American Mathematical Society》1996,124(9):2661-2673
Given a finite field of order and polynomials of degrees respectively, there is the continued fraction representation . Let denote the number of such pairs for which and for . We give both an exact recurrence relation, and an asymptotic analysis, for . The polynomial associated with the recurrence relation turns out to be of P-V type. We also study the distribution of . Averaged over all and as above, this presents no difficulties. The average value of is , and there is full information about the distribution. When is fixed and only is allowed to vary, we show that this is still the average. Moreover, few pairs give a value of that differs from this average by more than
93.
Doug Miller Suzanne Mamiche-Afara M.J. Dignam M. Moskovits 《Chemical physics letters》1983,100(3):236-240
The photoactivity of TiO2 produced by high-voltage anodization as described by Marchenoir et al. was compared to single-crystal TiO2. The anodic oxide film was found to be highly porous. The photocurrent and quantum yield of the anodic sample is markedly larger on the long-wavelength side of the action spectrum as compared to sinle-crystal rutile. We ascribe this behavior either to the formation of anatase “pockets” in the film or to the incomplete oxidation of Ti during the anodization process. 相似文献
94.
Diphenylpicrylhydrazyl (DPPH), a stable, intensely purple free radical, is used as a reagent in the quantitative determination of various aromatic and aliphatic thiols by indirect spectrophotometric analysis. Plots of degree of reaction vs. time show that thiophenol and its derivatives react more quickly than aliphatic thiols with DPPH. Calibration plots are linear over the concentration range 0.05-3.00 x 10(-5)M thiol. The average relative error is in the range 1-2% and the absolute standard deviations range up to 0.50 x 10(-6)M. 相似文献
95.
Mark R. Mason Doug Ogrin Bassam Fneich Thomas S. Barnard Kristin Kirschbaum 《Journal of organometallic chemistry》2005,690(1):157-162
Deprotonation of di(3-methylindol-2-yl)phenylmethane (L2H2) or with two equivalents of nBuLi, followed by reactions with Cp2TiCl2 or Cp2ZrCl2 yielded complexes . Compounds 1-4 were characterized by NMR spectroscopy, and compounds 1, 3, and 4 were further analyzed by X-ray crystallography and elemental analysis. The molecular structures of 1, 3, and 4 illustrate that chelating di(3-methylindol-2-yl)methanes have a structural relationship to coordinated bis(pyrazolyl)borates. 相似文献
96.
Recent comparability of oceanographic nutrients data: results of a 2003 intercomparison exercise using reference materials. 总被引:1,自引:0,他引:1
Michio Aoyama Susan Becker Minhan Dai Hideshi Daimon Louis I Gordon Hiromi Kasai Roger Kerouel Nurit Kress Doug Masten Akihiko Murata Naoki Nagai Hiroshi Ogawa Hidekazu Ota Hiroaki Saito Kazuhiro Saito Takao Shimizu Hiroyuki Takano Atsushi Tsuda Katsumi Yokouchi Agnes Youenou 《Analytical sciences》2007,23(9):1151-1154
An intercomparison exercise was conducted using the recently developed Reference Material for Nutrients in Seawater (RMNS). Discrepancies of reported values among laboratories were greater than the homogeneity of RMNS samples and the reported analytical precision of nutrients. The variability of in-house standards of the participating laboratories might be the most likely source of interlaboratory discrepancies. Therefore, the use of common reference materials, i.e. certified RM, is essential to establish and improve the comparability of nutrient data of the world's oceans. 相似文献
97.
The temperature dependence of the solution equilibrium constants for [((t)Bu)(2)Al(OPh)]2(mu-4,4'-bipy)(1a), [((t)Bu)2Al(OPh)](2)(mu-bipetha)(2a, bipetha = 1,2-bis(4-pyridyl)ethane), and [((t)Bu)(2)Al(OPh)]2(mu-bipethe)(3a, bipethe =trans-1,2-bis(4-pyridyl)ethylene) in C6D6 and CDCl(3) allow for the determination of DeltaH and DeltaS for the dissociation of one Al(tBu)2OPh moiety from the bridging ligand, i.e., 2[(tBu)2AL(OPh)]2(mu-L)<==>(K1)2AL(OPh)(tBu)2(L)+[(tBu)2Al(mu-OPh)]2. For compounds and the DeltaH values in C6D6[99(2) kJ mol(-1)(2a) and 109(5) kJ mol(-1)(3a)] and CDCl3[115(5) kJ mol(-1)(2a) and 139(7) kJ mol(-1)(3a)] were found to be inversely proportional with the dielectric constant of the solvent. In contrast, the DeltaH value for 1a in CDCl3 is surprisingly small [14.9(7) kJ mol(-1)] and does not fit with the trends adopted by the bipetha and bipethe derivatives or the value obtained in C6D6[110(2) kJ mol(-1)]. Unlike the other compounds and the C6D6 solutions, the CDCl3 solution of 1a allows for the observation of a second equilibrium 2Al(OPh)(tBu)2(L)<==>(K2)[(tBu)2Al(mu-OPh)]2+2L, for which the DeltaH has been determined [4.5(3) kJ mol(-1)]. This result suggests that in CDCl3 bonding of the second Al(tBu)2OPh moiety to Al(OPh)(tBu)2(4,4'-bipy)(1b) is stabilized by the presence of the first aluminium, which is counter to ab initio calculations that predicts the aluminium in Al(OPh)((t)Bu)2(L) should destabilize the Al-N interaction with a second Al(tBu)2OPh group. The BDE for dissociation of both Al(tBu)2OPh moieties from 1a-3a, and the energy of formation of hydrogen bond interactions with CHCl3, has been calculated by ab initio methods, and no unusual effects are inherent in 1a. 相似文献
98.
Woods M Kiefer GE Bott S Castillo-Muzquiz A Eshelbrenner C Michaudet L McMillan K Mudigunda SD Ogrin D Tircsó G Zhang S Zhao P Sherry AD 《Journal of the American Chemical Society》2004,126(30):9248-9256
Two gadolinium(III) chelates, GdNP-DO3A (1-methlyene-(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triAcetate) and GdNP-DO3AM (1-methlyene(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide), containing a single nitrophenolic pendant arm plus either three acetate or three amide pendant arms were synthesized and characterized. The properties of the gadolinium, terbium, and dysprosium complexes of these ligands were examined as a function of pH. The extent and mechanism of the changes in water relaxivity with pH of each gadolinium complex was found to differ substantially for the two complexes. The water relaxivity of Gd(NP-DO3A) increases from 4.1 mM(-1) s(-1) at pH 9 to 7.0 mM(-1) s(-1) at pH 5 as a result of acid-catalyzed dissociation of the nitrophenol from the lanthanide. The nitrophenol group in Gd(NP-DO3AM) does not dissociate from the metal center even at pH 5; therefore, the very modest increase in relaxivity in this complex must be ascribed to an increase in prototropic exchange rate of the bound water and/or phenolic protons. 相似文献
99.
[reaction: see text] A mild, efficient, and high-yielding method for the synthesis of N,N'-diaryl cyanoguanidines from their corresponding thioureas under microwave-assisted conditions is described. A series of cyanoguanidines were synthesized containing both electron-donating and electron-withdrawing substituents. The reactions were facilitated by the use of polar solvents along with moderate temperatures. 相似文献
100.
Iron‐Catalyzed Stereoselective Cross‐Coupling Reactions of Stereodefined Enol Carbamates with Grignard Reagents
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ana Cristina Parra Rivera Raymond Still Prof. Doug E. Frantz 《Angewandte Chemie (International ed. in English)》2016,55(23):6689-6693
A practical and highly stereoselective iron‐catalyzed cross‐coupling reaction of stereodefined enol carbamates and Grignard reagents to yield tri‐ and tetrasubstituted acrylates is reported. A facile method for the stereoselective generation of these enol carbamates has also been developed. 相似文献