全文获取类型
收费全文 | 4571篇 |
免费 | 140篇 |
国内免费 | 6篇 |
专业分类
化学 | 3333篇 |
晶体学 | 62篇 |
力学 | 49篇 |
综合类 | 2篇 |
数学 | 161篇 |
物理学 | 1110篇 |
出版年
2023年 | 31篇 |
2022年 | 32篇 |
2021年 | 37篇 |
2020年 | 68篇 |
2019年 | 69篇 |
2018年 | 52篇 |
2016年 | 80篇 |
2015年 | 101篇 |
2014年 | 83篇 |
2013年 | 220篇 |
2012年 | 217篇 |
2011年 | 222篇 |
2010年 | 140篇 |
2009年 | 151篇 |
2008年 | 209篇 |
2007年 | 252篇 |
2006年 | 222篇 |
2005年 | 240篇 |
2004年 | 193篇 |
2003年 | 173篇 |
2002年 | 174篇 |
2001年 | 114篇 |
2000年 | 119篇 |
1999年 | 75篇 |
1998年 | 55篇 |
1997年 | 42篇 |
1996年 | 78篇 |
1995年 | 53篇 |
1994年 | 48篇 |
1993年 | 67篇 |
1992年 | 65篇 |
1991年 | 64篇 |
1990年 | 52篇 |
1989年 | 54篇 |
1988年 | 50篇 |
1987年 | 57篇 |
1986年 | 49篇 |
1985年 | 88篇 |
1984年 | 69篇 |
1983年 | 42篇 |
1982年 | 51篇 |
1981年 | 46篇 |
1980年 | 54篇 |
1979年 | 56篇 |
1978年 | 46篇 |
1977年 | 32篇 |
1976年 | 38篇 |
1975年 | 23篇 |
1974年 | 28篇 |
1973年 | 26篇 |
排序方式: 共有4717条查询结果,搜索用时 15 毫秒
991.
The long-range correction (LC) scheme of density-functional theory (DFT) was applied to the calculation of the pi-aromatic interaction of the benzene dimer and naphthalene dimer. In previous calculations, it was confirmed that the LC scheme [Iikura et al., J. Chem. Phys. 115, 3540 (2001)] gives very accurate potential- energy surfaces (PESs) of small van der Waals (vdW) complexes by combining with the Anderson-Langreth-Lundqvist (ALL) vdW correlation functional [Andersson et al., Phys. Rev. Lett. 76, 102 (1996)] (LC-DFT + ALL). In this study, LC-DFT+ALL method was examined by calculating a wide range of PES of the benzene dimer including parallel, T-shaped, and parallel-displaced configurations. As a result, we succeeded in reproducing very accurate PES within the energy deviance of less than 1 kcalmol in comparison with the results of high-level ab initio molecular-orbital methods at all reference points on the PES. It was also found that LC-DFT + ALL gave accurate results independent of exchange-correlation functional used, in contrast with the strong functional dependencies of conventional pure functionals. This indicates that both exchange repulsion and van der Waals attractive interactions should be correctly incorporated in conventional pure functionals in order to calculate accurate pi-aromatic interactions. We also found that LC-DFT + ALL method has a low basis-set dependency in the calculations of pi-aromatic interactions. The present scheme was also successfully applied to the pi,[ellipsis (horizontal)],pi stacking interactions of naphthalene dimer. This may suggest that LC-DFT + ALL method would be a powerful tool in the calculations of large molecules such as biomolecules. 相似文献
992.
Hirokazu Tsukamoto Takamichi Suzuki Masanori Sato Yoshinori Kondo 《Tetrahedron letters》2007,48(48):8438-8441
Polystyrene-bound diethanolamine (PS-DEAM) work-up for a newly developed Pd(PPh3)4-catalyzed cleavage of allylic alkyl ethers using phenylboronic acid can effectively release Pd-free parent alcohols. Furthermore, chromatography-free deallylation can be conducted by using vinylboronic anhydride pyridine complex as an allyl scavenger with a catalytic amount of Pd(OAc)2 and 4-(diphenylphosphino)benzoic acid instead of Pd(PPh3)4 to yield the desired products in high purities and yields after removal of volatile byproducts and the phosphine-derived contaminants by evaporation and sequestration through acid-base interaction with PS-DEAM, respectively. 相似文献
993.
A very sensitive, selective and simple method for extraction and spectrophotometric determination of titanium(IV) with an alpha-hydroxy acid has been developed. p-Chloromandelic acid reacts with titanium in weakly acidic aqueous solution at room temperature to form a complex anion extractable into chlorobenzene with Malachite Green as counter-ion. Titanium is determined indirectly by measuring the absorbance of Malachite Green in the extract at 630 nm. The calibration graph is linear for titanium(IV) over the range 0.25-7.5muM (0.05-1.44 mug); the apparent molar absorptivity is 1.31 x 10(5) l.mole(-1).cm(-1). The method has been successfully applied to the determination of titanium in mild steels. 相似文献
994.
S Nochi N Shimomura T Hattori T Sato Y Miyake K Tanizawa 《Chemical & pharmaceutical bulletin》1989,37(10):2855-2857
It was found that [4-(2-succinimidoethylthio)phenyl 4-guanidinobenzoate]methanesulfonate (E-3123) inhibits trypsin, thrombin and kallikrein, and its inhibitory activity is most potent toward trypsin. The interactions of these enzymes with E-3123 were studied mainly by using stopped-flow spectrophotometry. E-3123 behaved as a quasi-substrate of the enzymes and the inhibitory property was due to the efficient production of the stable acyl-enzyme. The acylation process with trypsin was exceedingly effective, and the resulting acyl-enzyme was the most stable among the three enzymes tested. This observation affords a rational basis for explaining the action of E-3123, which is a transient inhibitor most active toward trypsin. 相似文献
995.
The synthesis and coordination chemistry of two chiral tetradentate pyridylimine Schiff base ligands are reported. The ligands were prepared by the nucleophilic displacement of both bromides of 1,3-bis(bromomethyl)benzene (2) or 3,5-bis(bromomethyl)toluene (3) by the anion of (S)-valinol, followed by capping of both amine groups with pyridine-2-carboxaldehyde. Both ligands react with CoCl(2) and NiCl(2) to give [M(2)L(2)Cl(2)](2+) complexes. Remarkably, neither fluoride nor bromide ions can act as bridging ligands. The formation of [Co(2)((S)-3)(2)Cl(2)](2+) is highly diastereoselective, and X-ray crystallography shows that both metal centers in the [Co(2)((S)-3)(2)Cl(2)](CoCl(4)) complex adopt the lambda configuration (crystal data: [Co(2)(C(31)H(40)N(4)O(2))(2)Cl(2)](CoCl(4)).(CH(3)CN)(3), monoclinic, P2(1), a = 11.595(2) A, b = 22.246(4) A, c = 15.350(2) A, V = 3705(1) A(3), beta = 110.643(3) degrees, Z = 2). Structurally, the dinuclear complex can be viewed as a helicate with the helical axis running perpendicular to the [Co(2)Cl(2)] plane. The reaction of racemic 2 with CoCl(2) was shown by (1)H NMR spectroscopy to yield a racemic mixture of Lambda,Lambda-[Co(2)((S)-2)(2)Cl(2)](2+) and delta,delta-[Co(2)((R)-2)(2)Cl(2)](2+) complexes; that is, a homochiral recognition process takes place. Spectrophotometric titrations were performed by titrating (S)-3 with Co(ClO(4))(2) followed by Bu(4)NCl, and the global stability constants of [Co((S)-3)](2+) (log beta(110) = 5.7), [Co((S)-3)(2)](2+) (log beta(120) = 11.6), and [Co(2)((S)-3)(2)Cl(2)](2+) (log beta(110) = 23.8) were calculated. The results revealed a strong positive cooperativity in the formation of [Co(2)((S)-3)(2)Cl(2)](2+). Variable-temperature magnetic susceptibility curves for [Co(2)((S)-2)(2)Cl(2)](BPh(4))(2) and [Co(2)((S)-3)(2)Cl(2)](BPh(4))(2) are very similar and indicate that there are no significant magnetic interactions between the cobalt(II) centers. 相似文献
996.
Takayuki Chujo Isao Saraoka Shinobu Kato Hiroyasu Sato Koichi Fukuhara Hiroatsu Matsuura 《Journal of inclusion phenomena and macrocyclic chemistry》1995,22(1):41-58
Three sodium complexes (bromide, iodide and thiocyanate) of 4,13-diaza-18-crown-6 were studied using Raman and IR spectroscopy and normal coordinate calculations to probe the stoichiometry of the complexes and the variation in the conformation of azacrown moiety on complex formation. complex formation is accompanied by characteristic shifts of the bands, especially of those in the 800–900 cm–1 region. Complexes of both 11 and 21 stoichiometry were observed. Normal coordinate calculations showed the reduction of symmetry of azacrown moiety toC
i
, in contrast to theC
2h
symmetry known for the parent azacrown and potassium thiocyanate complex. 相似文献
997.
Rare earth elements react with HFNO2 solution to produce nitrosylium fluorometallates (NO)xLnFx+3. The value of x is 1.0 or 1.5 for light rare earth elements and 0.5 or 1.0 for heavy rare earths. Nitrosylium fluorometallates of rare earth elements can be decomposed into the simple fluoride and nitrosyl fluoride at low temperatures (46–68°C). 相似文献
998.
Ikeda A Sato T Kitamura K Nishiguchi K Sasaki Y Kikuchi J Ogawa T Yogo K Takeya T 《Organic & biomolecular chemistry》2005,3(16):2907-2909
Various types of lipid membrane-incorporated C60 with high C60 concentrations can be prepared easily in several hours using the C60 exchange method and the photocleaving activity of cationic lipid membrane-incorporated C60 was appreciably higher than that of the C60.gamma-CDx complex. 相似文献
999.
Sato T 《Langmuir : the ACS journal of surfaces and colloids》2004,20(4):1095-1099
Association-dissociation equilibria and the static scattering function were formulated using precise thermodynamic functions for nonionic surfactant solutions including long, stiff, threadlike micelles. The present theory is applicable for micellar solutions with the surfactant concentration much higher than the critical micelle concentration and containing highly growing threadlike micelles. The scattering function formulated was compared with experimental light scattering data for aqueous solutions of a nonionic surfactant, penta(oxyethylene glycol) n-decyl ether (C12E5), at different surfactant concentrations and also temperatures. 相似文献
1000.