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991.
992.
A pair of MnIII(quinazolinone) complexes was prepared and evaluated in the catalytic epoxidation of the chiral allylic alcohols and unfunctionalised alkenes with iodosylbenzene. Epoxidation of chiral allylic alcohols with 1,3-allylic strain proceeded chemo- and diastereoselectively to give threo-epoxy alcohol (up to 99% d.r). Epoxidation of unfunctionalised alkenes by the proposed catalyst system proceeded nonselectively, as evidenced by the formation of isomerization and rearrangement products in the epoxidation of (Z)-stilbene. A three-step pathway involving a cationic intermediate is proposed for the formation of isomerization and rearrangement products. The fact that only products resulting from the cationic intermediate were detected in the oxidation of a mechanistic probe, (2-methoxy-3-vinylcyclopropyl)benzene, with MnIII(quinazolinone) and PhIO substantiated the cationic oxygen transfer mechanism. 相似文献
993.
Paul G. Mezey 《Theoretical chemistry accounts》1981,58(4):309-330
The space of internal coordinates of a molecular system is partitioned into catchment regions of various critical points of the energy hypersurface. The partitioning is based on an ordering of steepest descent paths into equivalence classes. The properties of these catchment regions and their boundaries are analyzed and the concepts of chemical structure, reaction path and reaction mechanism are discussed within the framework of the Born-Oppenheimer and energy hypersurface approximations. Relations between catchment regions and the chemically important reactive domains of energy hypersurfaces, as well as models for branching of reaction mechanisms, caused by instability domainsD
, 1, are investigated. 相似文献
994.
Alessandro Cembran Remedios González-Luque Luis Serrano-Andrés Manuela Merchán Marco Garavelli 《Theoretical chemistry accounts》2007,118(1):173-183
CASPT2//CASSCF/6-31G* computations are used on the singlet S
1 and S
2 states to map the photoisomerization process of the 11-cis retinal protonated Schiff base in vacuo and to characterize its
optical properties. It is shown that the spectroscopic observations recorded in Rhodopsin are reproduced quite well, calling
for a substantially neutral effect of the protein. Furthermore, a rationale is proposed for the unreactive population recently
observed in Rhodopsin, which is here addressed to the accessible S
2 state, behaving as a trap. The experimental transient absorption and (absorption-wavelength dependent) emission are discussed
and interpreted under the light of this novel model. Finally, a planarization of the β-ionone ring is observed on S
1, which may cause a steric lever effect into the protein pocket, thus assisting photoisomerization catalysis. The reported
results constitute a solid reference for further studies aimed to rationalize the effect of the environment on the photochemical
reactivity of retinal chromophores.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary
material, which is available to authorized users.
Contribution to the Fernando Bernardi Memorial Issue. 相似文献
995.
V/Sb催化剂上丙烷氨氧化反应机理的Monte Carlo模拟 总被引:1,自引:0,他引:1
本文应用Monte Carlo方法对丙烷氨氧化的反应机理进行了初步研究。首先在分析了V/Sb金红石构催化剂的各个晶面之后,以100面为模板建立了V/Sb双活性中心模型。在此基础上,对丙烷,氨及氧的不同进料摩尔比率对丙烯腈,丙烯及COX三种产物的影响规律进行了详细考察。 相似文献
996.
将含有多乙烯基的聚硅氧烷与菲式环戊二烯酮和苊式环戊二烯酮分别在α-氯萘中进行Diels-Alder反应,生成含有稠环侧链的聚硅氧烷.该聚硅氧烷具有较好的耐热性.将其作为组分制成高温加成型硅橡胶,综合性能达到较高水平(高模量).随着其用量的增加,可使其耐热性能得到较大改善。 相似文献
997.
998.
Summary Hydrogenation degradation of hexane, 2-methylpentane, 2,2-dimethylbutane, trans 2-hexene, cyclohexane and benzene on a nickel catalyst was studied. The degradation products were separated in a capillary column with squalane and identified using the appropriate retention indices. The results obtained (the degree of conversion and the relative content of the individual products) are discussed in connection with the thermal degradation of these substances in an inert atmosphere. 相似文献
999.
1000.
高分子凝胶化反应对功能高分子骨架结构有重要影响,它经历溶胶一凝胶的不可逆转变(sol-geltransition);导致高分子网络结构及分子尺寸的突变,动力学过程和机理十分复杂,因此,人们对这一领域的研究始终贯注了巨大兴趣.追溯过去,人们对高分子凝胶化过程的研究经历了由未考虑环化、搭环的Flory-stockmayer理论问;静态渗流理论[’]到动态凝胶化模型*三个发展阶段·后者除克报了前两种的不足外,还引入了与几何形状密切相关的动态标度处理方法.近年来,分形概念的产生更激励了动态标度的发展,这种增长模型的研究方法考虑了增长… 相似文献