全文获取类型
收费全文 | 2462篇 |
免费 | 53篇 |
国内免费 | 11篇 |
专业分类
化学 | 1840篇 |
晶体学 | 9篇 |
力学 | 61篇 |
数学 | 320篇 |
物理学 | 296篇 |
出版年
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 25篇 |
2018年 | 24篇 |
2016年 | 34篇 |
2015年 | 36篇 |
2014年 | 38篇 |
2013年 | 141篇 |
2012年 | 115篇 |
2011年 | 108篇 |
2010年 | 87篇 |
2009年 | 89篇 |
2008年 | 103篇 |
2007年 | 111篇 |
2006年 | 117篇 |
2005年 | 122篇 |
2004年 | 105篇 |
2003年 | 100篇 |
2002年 | 95篇 |
2001年 | 39篇 |
2000年 | 42篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 31篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 34篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 31篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1985年 | 37篇 |
1984年 | 43篇 |
1983年 | 27篇 |
1982年 | 39篇 |
1981年 | 35篇 |
1980年 | 46篇 |
1979年 | 42篇 |
1978年 | 52篇 |
1977年 | 38篇 |
1976年 | 32篇 |
1975年 | 36篇 |
1974年 | 36篇 |
1973年 | 37篇 |
1972年 | 15篇 |
1966年 | 13篇 |
排序方式: 共有2526条查询结果,搜索用时 78 毫秒
901.
Claude Bardos Irene M. Gamba François Golse C. David Levermore 《Communications in Mathematical Physics》2016,341(2):435-489
We consider the random regular k-nae- sat problem with n variables, each appearing in exactly d clauses. For all k exceeding an absolute constant \({{\it k}_0}\), we establish explicitly the satisfiability threshold \({{{d_\star} \equiv {d_\star(k)}}}\). We prove that for \({{d < d_\star}}\) the problem is satisfiable with high probability, while for \({{d > d_\star}}\) the problem is unsatisfiable with high probability. If the threshold \({{d_\star}}\) lands exactly on an integer, we show that the problem is satisfiable with probability bounded away from both zero and one. This is the first result to locate the exact satisfiability threshold in a random constraint satisfaction problem exhibiting the condensation phenomenon identified by Krz?aka?a et al. [Proc Natl Acad Sci 104(25):10318–10323, 2007]. Our proof verifies the one-step replica symmetry breaking formalism for this model. We expect our methods to be applicable to a broad range of random constraint satisfaction problems and combinatorial problems on random graphs. 相似文献
902.
Canard G Koeller S Bernardinelli G Piguet C 《Journal of the American Chemical Society》2008,130(3):1025-1040
The beneficial entropic effect, which may be expected from the connection of three tridentate binding units to a strain-free covalent tripod for complexing nine-coordinate cations (Mz+ = Ca2+, La3+, Eu3+, Lu3+), is quantitatively analyzed by using a simple thermodynamic additive model. The switch from pure intermolecular binding processes, characterizing the formation of the triple-helical complexes [M(L2)3]z+, to a combination of inter- and intramolecular complexation events in [M(L8)]z+ shows that the ideal structural fit observed in [M(L8)]z+ indeed masks large energetic constraints. This limitation is evidenced by the faint effective concentrations, ceff, which control the intramolecular ring-closing reactions operating in [M(L8)]z+. This predominence of the thermodynamic approach over the usual structural analysis agrees with the hierarchical relationships linking energetics and structures. Its simple estimation by using a single microscopic parameter, ceff, opens novel perspectives for the molecular tuning of specific receptors for the recognition of large cations, a crucial point for the programming of heterometallic f-f complexes under thermodynamic control. 相似文献
903.
Prudent R Moucadel V Laudet B Barette C Lafanechère L Hasenknopf B Li J Bareyt S Lacôte E Thorimbert S Malacria M Gouzerh P Cochet C 《Chemistry & biology》2008,15(7):683-692
Protein kinase CK2 is a multifunctional kinase of medical importance that is dysregulated in many cancers. In this study, polyoxometalates were identified as original CK2 inhibitors. [P2Mo18O62](6-) has the most potent activity. It inhibits the kinase in the nanomolar range by targeting key structural elements located outside the ATP- and peptide substrate-binding sites. Several polyoxometalate derivatives exhibit strong inhibitory efficiency, with IC50 values < or = 10 nM. Furthermore, these inorganic compounds show a striking specificity for CK2 when tested in a panel of 29 kinases. Therefore, polyoxometalates are effective CK2 inhibitors in terms of both efficiency and selectivity and represent nonclassical kinase inhibitors that interact with CK2 in a unique way. This binding mode may provide an exploitable mechanism for developing potent drugs with desirable properties, such as enhanced selectivity relative to ATP-mimetic inhibitors. 相似文献
904.
Goubard F Aubert PH Boukerma K Pauthe E Chevrot C 《Chemical communications (Cambridge, England)》2008,(27):3139-3141
A method for the elaboration of a heterojunction composed on n-type inorganic semiconducting nanoparticles, TiO(2), and a p-type organic semiconducting polymer poly(3,4-ethylene dioxythiophene) by UV illumination is described. 相似文献
905.
Geraud E Prevot V Forano C Mousty C 《Chemical communications (Cambridge, England)》2008,(13):1554-1556
Formation of new bio-nanohybrid material was obtained by immobilization of alkaline phosphatase within a Mg(2)Al LDH by "soft chemistry" coprecipitation synthesis, resulting in an original spongy gel-like morphology allowing the preservation of the enzyme structure and activity even at low pH values thanks to the buffering property of the basic host structure. 相似文献
906.
Cencek W Szalewicz K Leforestier C van Harrevelt R van der Avoird A 《Physical chemistry chemical physics : PCCP》2008,10(32):4716-4731
The ab initio water dimer interaction energies obtained from coupled cluster calculations and used in the CC-pol water pair potential (Bukowski et al., Science, 2007, 315, 1249) have been refitted to a site-site form containing eight symmetry-independent sites in each monomer and denoted as CC-pol-8s. Initially, the site-site functions were assumed in a B-spline form, which allowed a precise optimization of the positions of the sites. Next, these functions were assumed in the standard exponential plus inverse powers form. The root mean square error of the CC-pol-8s fit with respect to the 2510 ab initio points is 0.10 kcal mol(-1), compared to 0.42 kcal mol(-1) of the CC-pol fit (0.010 kcal mol(-1) compared to 0.089 kcal mol(-1) for points with negative interaction energies). The energies of the stationary points in the CC-pol-8s potential are considerably more accurate than in the case of CC-pol. The water dimer vibration-rotation-tunneling spectrum predicted by the CC-pol-8s potential agrees substantially and systematically better with experiment than the already very accurate spectrum predicted by CC-pol, while specific features that could not be accurately predicted previously now agree very well with experiment. This shows that the uncertainties of the fit were the largest source of error in the previous predictions and that the present potential sets a new standard of accuracy in investigations of the water dimer. 相似文献
907.
Stability of [MeBu3N][Tf2N] under gamma irradiation 总被引:1,自引:0,他引:1
Bossé E Berthon L Zorz N Monget J Berthon C Bisel I Legand S Moisy P 《Dalton transactions (Cambridge, England : 2003)》2008,(7):924-931
The stability of the ionic liquid [MeBu3N][Tf2N], dry or after contact with water (where [MeBu3N]+ is the methyltributylammonium cation and [Tf2N](-) is the bistriflimide anion), was studied under 137Cs gamma irradiation in argon and in air. In a quantitative study with an absorbed dose of 2 MGy this ionic liquid was highly stable regardless of the radiolysis conditions. The radiolytic disappearance yields determined by ESI-MS were -0.38 and -0.25 micromol J(-1) for the cation and anion, respectively. ESI-MS, NMR, and liquid chromatography coupled with ESI-MS identified a large number of degradation products in very small quantities for the same dose. The cation radicals were formed by the loss of a Bu group, the Me group, or two H atoms to form a double bond with the butyl chain. Radiolysis of the anion produced mainly F and CF3 radicals. The anion radicals recombined with the cation to form a wide range of secondary degradation products regardless of the radiolysis conditions. 相似文献
908.
Riis-Johannessen T Dupont N Canard G Bernardinelli G Hauser A Piguet C 《Dalton transactions (Cambridge, England : 2003)》2008,(28):3661-3677
The mononuclear Os(II) complex [Os()(3)](PF(6))(2) ( = 5-methyl(1-methylbenzimidazol-2-yl)pyridine) is an obvious candidate for the design of an inert d-block-based tripodal receptor capable of binding and photosensitizing trivalent lanthanides (Ln(III)). It has thus been prepared and its two enantiomeric meridional (Delta-mer and Lambda-mer) and facial (rac-fac) isomers have been separated by ion-exchange chromatography. The optical isomers have been characterized by CD spectroscopy and assignments of absolute configuration confirmed by an X-ray crystallographic study of Lambda-mer-[Os()(3)](PF(6))(2).1.5MeCN (monoclinic, P2(1), Z = 4). Comparison of the latter structure with that of racemic fac-[Os()(3)](PF(6))(2) (monoclinic, C2/c, Z = 8) and [Os(bipy)(3)](PF(6))(2) (where bipy = 2,2'-bipyridine) shows minimal structural variations, but differences are observed in the photophysical and electrochemical properties of the respective compounds. Luminescence emissions from Os(II) complexes of are typically lower in energy, with shorter lifetimes and lower quantum yields than their bipy analogues, whilst metal-centred oxidation processes are more facile due to the enhanced pi-donor ability of . The key relationships between these parameters are discussed. Finally, though challenged by (i) the low reactivity of many osmium precursors and (ii) the irreversible formation of competing side products, the synthesis and purification of the heterobimetallic triple-stranded helicate HHH-[OsLu()(3)](CF(3)SO(3))(5) has been realised, in which is a segmental ligand containing the same bidentate unit as that found in further connected to a tridentate binding site adapted for complexing Ln(III). Its solid-state structure has been established by X-ray crystallography (triclinic, P1, Z = 2). 相似文献
909.
Franco L. Molina Dr. Rafael A. Jara-Toro Dr. Jennifer A. Noble Dr. Claude Dedonder-Lardeux Dr. Christophe Jouvet Prof. Gustavo A. Pino 《Chemphyschem》2023,24(1):e202200324
The photodetachment and stability of R-Mandelate, the deprotonated form of the R-Mandelic acid, was investigated by observing the neutral species issued from either simple photodetachment or dissociative photodetachment in a cold anions set-up. R-Mandalate has the possibility to form an intramolecular ionic hydrogen-bond between adjacent hydroxyl and carboxylate groups. The potential energy surface along the proton transfer (PT) coordinate between both groups (O−…H+…−OCO) features a single local minima, with the proton localized on the O− group (OH…−OCO). However, the structure with the proton localized on the −OCO group (O−…HOCO) is also observed because it falls within the extremity of the vibrational wavefunction of the OH…−OCO isomer along the PT coordinate. The stability of the corresponding radicals, produced upon photodetachment, is strongly dependent on the position of the proton in the anion: the radicals produced from the OH…−OCO isomer decarboxylate without barrier, while the radicals produced from the O−…HOCO isomer are stable. 相似文献
910.
Bossé E Den Auwer C Berthon C Guilbaud P Grigoriev MS Nikitenko S Le Naour C Cannes C Moisy P 《Inorganic chemistry》2008,47(13):5746-5755
The complexes [MeBu 3N] 2[UCl 6] and [BuMe 2Im] 2[UCl 6] were characterized in the solid state and in solution of [MeBu 3N][Tf 2N], [BuMe 2Im][Tf 2N], and [BuMeIm][Tf 2N] room-temperature ionic liquids using single-crystal XRD, EXAFS, electrochemistry, UV-visible absorption spectroscopy, and NMR. In the solid state and in solution, the existence of hydrogen bonding between the UCl 6 (2-) complex and the ionic liquid cations was revealed by these techniques. The MeBu 3N (+) cation interacts with UCl 6 (2-) via the protons on the alpha-carbon atoms of nitrogen. The protons of the imidazolium ring account for the interaction between the BuMe 2Im (+) cation and the UCl 6 (2-) anion. For the BuMeIm (+) cation the major interaction was confirmed between the most acidic proton on C(2) and the chlorides of UCl 6 (2-). The experimental results also show that the intensity of the interaction between the UCl 6 (2-) anion and the cation varies with the ionic liquid cation in the following order: MeBu 3N (+) approximately BuMe 2Im (+) < BuMeIm (+). 相似文献