全文获取类型
收费全文 | 3581篇 |
免费 | 80篇 |
国内免费 | 12篇 |
专业分类
化学 | 2405篇 |
晶体学 | 21篇 |
力学 | 99篇 |
数学 | 363篇 |
物理学 | 785篇 |
出版年
2021年 | 25篇 |
2020年 | 34篇 |
2019年 | 37篇 |
2018年 | 27篇 |
2017年 | 22篇 |
2016年 | 48篇 |
2015年 | 48篇 |
2014年 | 50篇 |
2013年 | 127篇 |
2012年 | 171篇 |
2011年 | 225篇 |
2010年 | 106篇 |
2009年 | 81篇 |
2008年 | 180篇 |
2007年 | 179篇 |
2006年 | 202篇 |
2005年 | 166篇 |
2004年 | 160篇 |
2003年 | 118篇 |
2002年 | 137篇 |
2001年 | 89篇 |
2000年 | 94篇 |
1999年 | 45篇 |
1998年 | 56篇 |
1997年 | 39篇 |
1996年 | 76篇 |
1995年 | 43篇 |
1994年 | 58篇 |
1993年 | 80篇 |
1992年 | 56篇 |
1991年 | 35篇 |
1990年 | 37篇 |
1989年 | 39篇 |
1988年 | 31篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 57篇 |
1984年 | 34篇 |
1983年 | 23篇 |
1982年 | 52篇 |
1981年 | 36篇 |
1980年 | 47篇 |
1979年 | 32篇 |
1978年 | 49篇 |
1977年 | 38篇 |
1976年 | 29篇 |
1975年 | 47篇 |
1974年 | 31篇 |
1973年 | 36篇 |
1972年 | 19篇 |
排序方式: 共有3673条查询结果,搜索用时 46 毫秒
991.
A generalized geometric model is presented which describes the collision efficiency factor of aggregation (the probability of a binary particle or aggregate collision resulting in adhesion) for systems comprised of two oppositely charged species. Application of the general model to specific systems requires calculation of the area of each species available for collision with a second species. This is in contrast to previous models developed for polymer-particle flocculation that are based on the fractional surface coverage of adsorbed polymer. The difference between these approaches is suggested as an explanation for previously observed discrepancies between theory and observation. In the current work the specific case of oppositely charged nondeformable spherical particles (heteroaggregation) is quantitatively addressed. The optimum concentration of oppositely charged particles for rapid aggregation (maximum collision efficiency) as a function of relative particle size is calculated and an excellent correlation is found with data taken from literature. 相似文献
992.
The photochemistry of 1,2-dihydronaphthalene oxide (254 nm) was reexamined and indan was found to be a primary photoproduct, as well as the traditionally assumed secondary photoproduct. Quenching studies demonstrated that indan, as a primary photoproduct, is derived from a triplet pathway, competing with a singlet route, back to the ground state surface. CASSCF calculations strongly suggest that the triplet pathway consists of a dissociation of the oxirane moiety to give a triplet carbene and aldehyde, which via hydrogen abstraction-decarbonylation-ISC recloses to give indan. Conical intersections corresponding to the presumed 1,2-hydrogen shift and 1,2-alkyl shift to give 2-tetralone and 1-indancarbaldehyde, respectively, were located computationally. 相似文献
993.
Wehlan H Jezek E Lebrasseur N Pavé G Roulland E White AJ Burrows JN Barrett AG 《The Journal of organic chemistry》2006,71(21):8151-8158
A concise and efficient synthesis of the tetracyclic CDEF ring system of lactonamycin (1) is described. The key step involved the Lewis acid mediated, intramolecular Friedel-Crafts acylation of carboxylic acid 6 to produce the tetracyclic CDEF core structure of target 1. The synthesis of 6 was carried out using a high-yielding Negishi coupling of benzyl bromide 7 with triflate 8, which was accessible in 11 steps and 31% overall yield on a multigram scale starting from trihydroxy acid 9. 相似文献
994.
Peng C Snook GA Fray DJ Shaffer MS Chen GZ 《Chemical communications (Cambridge, England)》2006,(44):4629-4631
The amphiphobic nature of carbon nanotubes allows them to stabilise droplets of water-insoluble monomers dispersed in the aqueous nanotube suspension, leading to a flexible route to electrochemical synthesis of useful nanoporous composites of nanotube doped conducting polymers, and potentially to other chemistry involving reactants incompatible in the same medium. 相似文献
995.
A Pd(II)/sulfoxide-catalyzed sequential allylic C-H oxidation/vinylic C-H arylation of alpha-olefins to furnish E-arylated allylic esters in high regio- and E:Z selectivities (>20:1) is reported. The broad scope of this method with respect to the alpha-olefin, carboxylic acid, and aryl boronic acid enables the rapid assembly of densely functionalized fragments for complex molecule synthesis from cheap, abundant hydrocarbon starting materials. The Pd(II)/sulfoxide-catalyzed vinylic C-H arylation of electronically unbiased olefins with aryl boronic acids proceeds under oxidative, acidic conditions and mild temperatures (room temperature to 45 degrees C). 相似文献
996.
Doonan CJ Nielsen DJ Smith PD White JM George GN Young CG 《Journal of the American Chemical Society》2006,128(1):305-316
Atom transfer reactions have been employed to convert Tp(i)(Pr)MoO(2)(OAr) into monomeric cis-oxosulfido-Mo(VI) and dimeric mu-disulfido-Mo(V) species, [Tp(i)(Pr)MoOS(OAr)](n)() (Tp(i)(Pr) = hydrotris(3-isopropylpyrazol-1-yl)borate; OAr = phenolate or naphtholate derivative; n = 1 and 2, respectively). Dark red, monomeric Tp(i)(Pr)MoOS(OAr) complexes contain distorted octahedral cis-oxosulfido-Mo(VI) centers, with d(Mo=O) = 1.692(5) A, d(Mo=S) = 2.132(2) A, and angle(O=Mo=S) = 103.68(16) degrees for the 2-sec-butylphenolate derivative. Dark red-purple, dimeric [Tp(i)(Pr)MoOS(OAr)](2) complexes undergo S-S bond cleavage forming monomeric oxosulfido-Mo(VI) species in solution. In the solid state, the 3,5-di-tert-butylphenolate derivative exhibits a centrosymmetric structure, with distorted octahedral anti oxo-Mo(V) centers bridged by a disulfido-kappaS,kappaS' ligand. Hydrolysis of the oxosulfido-Mo(VI) complexes results in the formation of [Tp(i)(Pr)MoO](2)(mu-S(2))(mu-O). In anaerobic solutions, certain oxosulfido-Mo(VI) complexes convert to molybdenyl complexes bearing bidentate 2-mercaptophenolate or related naphtholate ligands formed via intramolecular attack of the sulfido ligand on a coligand C-H group. The oxosulfido-Mo(VI) complexes serve as precursors to biologically relevant Mo(V) and heterobimetallic MoO(mu-S)Cu species and undergo a range of biomimetic reactions. 相似文献
997.
Gourlay C Nielsen DJ White JM Knottenbelt SZ Kirk ML Young CG 《Journal of the American Chemical Society》2006,128(7):2164-2165
New paramagnetic, heterobimetallic Mo/Cu complexes featuring the Mo(=O)(mu-S)Cu core of O. carboxidovorans carbon monoxide dehydrogenase have been synthesized and structurally and spectroscopically characterized. The complexes exhibit EPR spectra (left graphic) indicative of extensive electron delocalization across the Mo-S-Cu core, in agreement with computational studies identifying the singly-occupied molecular orbital (right graphic). 相似文献
998.
Barrett AG Gray AA Hill MS Hitchcock PB Procopiou PA White AJ 《Inorganic chemistry》2006,45(8):3352-3358
The new imino sulfinamidine ligand PhS(NHt-Bu)=NC(Me)=N(C6H3-2,6-iPr2), LH (11) was synthesized from N-(2,6-diisopropylphenyl)acetamidine (9) and N-tert-butyl phenylsulfinimidoyl chloride (10). Reaction of LH (11) with ZnEt2 or AlMe3 gave the complexes LZnEt (12) and LAlMe2 (13), respectively. The structures of 12 and 13 were determined by X-ray diffraction and were shown to contain L as a kappa2-N1,N5 bidentate ligand in a six-membered chelate. Formation of the magnesium complex (LMgN(TMS)2 x L2Mg) (14) from 11, MgI2, and KN(SiMe3)2 highlighted a secondary coordination mode of L, binding through the sulfinamidine nitrogens in a four-membered chelate. 相似文献
999.
Gregson CK Gibson VC Long NJ Marshall EL Oxford PJ White AJ 《Journal of the American Chemical Society》2006,128(23):7410-7411
The activity of a single-site titanium-based lactide polymerization initiator supported by a ferrocenyl-derivatized salen ligand is shown to be modulated by a chemical redox switch; a substantially higher rate of propagation is found for the neutral catalyst compared to its oxidized dicationic ferrocenium counterpart. 相似文献
1000.
Larrosa I Da Silva MI Gómez PM Hannen P Ko E Lenger SR Linke SR White AJ Wilton D Barrett AG 《Journal of the American Chemical Society》2006,128(43):14042-14043
The first total synthesis of (+)-clavilactone B, a potent antifungal agent and novel tyrosine kinase inhibitor, is described. The absolute configuration of clavilactones has been unambiguously established by using Sharpless asymmetric epoxidation to generate the enantiomerically pure substrate. The strategy highlights the use of a powerful and convergent three-component benzyne coupling with a methylallyl Grignard and a chiral epoxy-aldehyde to generate two C-C bonds and install the carbon skeleton of clavilactone. Oxidative lactonization, ten-membered ring construction by ring closing metathesis, and oxidation gave clavilactone B. 相似文献