全文获取类型
收费全文 | 701篇 |
免费 | 26篇 |
专业分类
化学 | 451篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 169篇 |
物理学 | 104篇 |
出版年
2023年 | 7篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 30篇 |
2015年 | 17篇 |
2014年 | 32篇 |
2013年 | 60篇 |
2012年 | 46篇 |
2011年 | 49篇 |
2010年 | 35篇 |
2009年 | 27篇 |
2008年 | 56篇 |
2007年 | 32篇 |
2006年 | 24篇 |
2005年 | 47篇 |
2004年 | 35篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1975年 | 3篇 |
1967年 | 1篇 |
1952年 | 3篇 |
1936年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有727条查询结果,搜索用时 15 毫秒
41.
The title compound // may be transformed into the 3-/methylaminomethylene/--2,3,6,7,8,9-hexahydro-4H-pyrido[1,2-a]pyrimidine-2,4-dione /E, Z/ which is in equilibrium with the 1,2,3,6,7,8-hexahydro tautomer /E, Z/ in DMSO-d6. 相似文献
42.
Zoltán Kunszt 《Physics letters. [Part B]》1981,99(5):429-432
Using recent results of Ellis et al. I calculate the O(α2S) corrections to thrust distribution in e+e? annihilation. The numerical importance of the change of the four-momentum squared which determines the strength of the running coupling constant is studied in detail. 相似文献
43.
Kukovecz A Hodos M Horváth E Radnóczi G Kónya Z Kiricsi I 《The journal of physical chemistry. B》2005,109(38):17781-17783
We discuss the formation mechanism of titania nanotubes synthesized by the hydrothermal method. On the basis of a comprehensive analysis of TEM, HRTEM, FT-Raman, and N(2) adsorption data, we point out some major shortcomings of the currently accepted trititanate sheet rollup mechanism. We suggest that a novel formation mechanism, oriented nanotube crystal growth from nanoloop seeds, can explain the experimental findings better than the ones proposed so far. 相似文献
44.
Self-organized Monte Carlo simulations are suggested. Their essence is artificial dynamics consisting of the well-known single-spin-flip
Metropolis algorithm supplemented by biased random walk in temperature space. The action of walker is driven by feedback utilizing
the linear filtering recursion based on the instantaneous estimates of Binder cumulants. The simulation for 2d Ising model
demonstrates that the mean temperature typical for the steady noncanonical equilibrium regime properly approximates the true
critical temperature. The estimates of the critical Binder cumulants and critical exponents are also discussed. 相似文献
45.
Bartók M Kele Z Sutyinszki M Bucsi I Felföldi K 《Rapid communications in mass spectrometry : RCM》2004,18(12):1352-1360
The reaction mixture for the hydrogenation of ethyl pyruvate on Pt-alumina catalyst modified with isocinchona alkaloids (alpha-ICN (I) and beta-ICN (II)) was studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). It was established that part of the chiral modifiers themselves are converted into ions of m/z 299, 305 and 309 in the course of chiral hydrogenation. The experimental data allowed the determination of the probable structure of the ions mentioned. According to ESI-MS/MS spectra the structure of the new cinchona alkaloids was assumed: tetrahydro-isocinchonines (III-VI), decahydro-isocinchonines (VII, VIII) and hydrogenated compounds of VII and VIII by scission of their C--N and C--O bonds (IX/1, IX/2, X). Fragmentation pathways are proposed for these new compounds. 相似文献
46.
Gologan B Takáts Z Alvarez J Wiseman JM Talaty N Ouyang Z Cooks RG 《Journal of the American Society for Mass Spectrometry》2004,15(12):1874-1884
Protein ions, after mass spectrometric separation, can be soft-landed into liquid surfaces with preservation of their native structures. Retention of biological activity is strongly favored in glycerol-based surfaces but not in self-assembled monolayer solid surfaces. Soft-landing efficiency for multiply-charged hexokinase ions was found to be some four times higher for a glycerol/fructose liquid surface than for a fluorinated self-assembled monolayer surface. Soft-landing into liquid surfaces is also shown to allow (1) protein purification, (2) on-surface identification of the soft-landed material using MALDI, and (3) protein identification by in-surface tryptic digestion. Pure lysozyme was successfully isolated from different mixtures including an oxidized, partially decomposed batch of the protein and a partial tryptic digest. Liquid glycerol/carbohydrate mixtures could be used directly to record MALDI spectra on the soft-landed compounds provided they were fortified in advance with traditional MALDI matrices such as p-nitroaniline and alpha-cyano-4-hydroxycinnamic acid. Various proteins were soft-landed and detected on-target using these types of liquid surface. Soft-landing of multiply-charged lysozyme ions onto fluorinated self-assembled monolayer surfaces was found to occur with a limited amount of neutralization, and trapped multiply-charged ions could be desorbed from the surface by laser desorption. Initial data is shown for a new approach to protein identification that combines top-down and bottom-up approaches by utilizing protein ion soft-landing from a protein mixture, followed by tryptic digestion of the landed material and detection of characteristic tryptic fragments by MALDI. 相似文献
47.
Zoltán?M.?BaloghEmail author Kevin?Rogovin Thomas?Zürcher 《Journal of Geometric Analysis》2004,14(3):405-422
We extend Cheeger’s theorem on differentiability of Lipschitz functions in metric measure spaces to the class of functions
satisfying Stepanov’s condition. As a consequence, we obtain the analogue of Calderon’s differentiability theorem of Sobolev
functions in metric measure spaces satisfying a Poincaré inequality.
Communicated by Steven Krantz 相似文献
48.
A simple method capable of generating and investigating various solvent clusters and solvated ions was developed. The technique opens a door to studying these complexes on commercially available instruments. Formation of the desired solvated ion in the gas phase was achieved by introducing the appropriate volatile solvent vapour into the curtain gas stream. Capabilities of the technique are illustrated by generating alkali, alkaline earth and transition metal cations solvated by various volatile compounds such as water, methanol and acetonitrile. Depending on the ligands and on the experimental conditions, clusters of 2-100 molecules may be observed. Isotope labelling suggests that these are formed by a re-solvation process in the curtain gas region. 相似文献
49.
Kónya Z Zhu J Szegedi A Kiricsi I Alivisatos P Somorjai GA 《Chemical communications (Cambridge, England)》2003,(3):314-315
Branched mesoporous silica SBA-15 materials have been prepared in a simple process using non-ionic surfactant in acidic conditions in the presence of metal ions. 相似文献
50.
Structural isomers of [UO(2)(oxalate)(3)](4-), [UO(2)(oxalate)F(3)](3-), [UO(2)(oxalate)(2)F](3-), and [UO(2)(oxalate)(2)(H(2)O)](2-) have been studied by using EXAFS and quantum chemical ab initio methods. Theoretical structures and their relative energies were determined in the gas phase and in water using the CPCM model. The most stable isomers according to the quantum chemical calculations have geometries consistent with the EXAFS data, and the difference between measured and calculated bond distances is generally less than 0.05 A. The complex [UO(2)(oxalate)(3)](4-) contains two oxalate ligands forming five-membered chelate rings, while the third is bonded end-on to a single carboxylate oxygen. The most stable isomer of the other two complexes also contains the same type of chelate-bonded oxalate ligands. The activation energy for ring opening in [UO(2)(oxalate)F(3)](3-), deltaU++ = 63 kJ/mol, is in fair agreement with the experimental activation enthalpy, deltaH++ = 45 +/- 5 kJ/mol, for different [UO(2)(picolinate)F(3)](2-) complexes, indicating similar ring-opening mechanisms. No direct experimental information is available on intramolecular exchange in [UO(3)(oxalate)(3)](4-). The theoretical results indicate that it takes place via the tris-chelated intermediate with an activation energy of deltaU++ = 38 kJ/mol; the other pathways involve multiple steps and have much higher activation energies. The geometries and energies of dioxouranium(VI) complexes in the gas phase and solvent models differ slightly, with differences in bond distance and energy of typically less than 0.06 A and 10 kJ/mol, respectively. However, there might be a significant difference in the distance between uranium and the leaving/entering group in the transition state, resulting in a systematic error when the gas-phase geometry is used to estimate the activation energy in solution. This systematic error is about 10 kJ/mol and tends to cancel when comparing different pathways. 相似文献