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51.
C. Cismaş I. Grosu G. Plé E. Condamine Y. Ramondenc L. Toupet I. Silaghi-Dumitrescu G. Nemeş A. Terec L. Muntean 《Structural chemistry》2005,16(4):369-377
The synthesis and stereochemistry of some new bis(1,3-oxathian-2-yl) derivatives are reported. The conformational behavior of these compounds and the orientation of their substituents are deduced from the NMR spectra, from the X-ray crystal structures of two compounds and from the ab-initio level calculations. The epimerization of diastereoisomers and the chair ⇌ 22,5-twist equilibria were studied by variable temperature NMR. 相似文献
52.
Behzad Haghighi Mohammad Reza Hussaindokht Mohammad Reza Bozorgmehr Naser Seyed Matin 《中国化学快报》2007,18(9):1154-1158
In this paper five equations of state are tested for checking their ability to predict the Joule-Thomson inversion curve.These five equations of state are:Mohsennia-Modarres-Mansoori(MMM),Ji-Lemp(JL),modified Soave-Redlich-Kwang(SRK)equation of state by Graboski(MSRK1),modified SRK equation of state by Peneloux and Rauzy(MSRK2),and modified Peng-Robinson (PR)equation of state by Rauzy(PRmr).The investigated equations of state give good prediction of the low-temperature branch of the inversion curve,except for MMM equation of state.The high-temperature branch and the peak of the inversion curve have been observed,in general,to be sensitive to the applied equation of state.The values of the maximum inversion temperature and maximum inversion pressure are calculated for each component used in this work. 相似文献
53.
Shyh‐Jong Chen Cheng Chen Yaw‐Shun Hong 《International journal of quantum chemistry》2005,103(2):198-214
This investigation conducted reaction channels of weakly bound complexes CO2…HF, CO2…HF…NH3, CO2…HF…NH2CH3, CO2…HF…NH(CH3)2, and CO2…HF…N(CH3)3 systems, using the Gaussian 98 package at the B3LYP/6‐311++G(3df,2pd) level. The syn‐fluoroformic acid or syn‐fluoroformic acid plus NH3 or amine conformers are more stable than the related anti‐fluoroformic acid or anti‐fluoroformic acid plus NH3 or amine conformers. However, the above‐mentioned weakly bound complexes are more stable than both the related syn‐ and anti‐type fluoroformic acid or acid plus NH3 or amine conformers and their related decomposed into CO2 + HF or CO2 + NHR3F (R?H, CH3) combined molecular systems. Five reaction channels of the weakly bound complexes exist. Each channel includes weakly bound complexes and their related above‐mentioned systems. Moreover, each reaction channel contains two transition states. The transition state between the weakly bound complex and anti‐fluoroformic acid type structure (T13) is significantly higher than that of internal rotation (T23) between syn‐ and anti‐FCO2H (or FCO2H…NR3) structures. However, the above‐mentioned T13 can significantly decrease its energy by adding the third molecule NH3 or NR3 (R?H or CH3). The more CH3 that is substituted in NR3 of the reaction channel, the lower the activation energy of the transition state in the system is affected. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
54.
Ben-zhong Tang Xiang-xing Kong Xin-de Feng Department of Chemistry Hong Kong University of Science & Technology Clear Water Bay Kowloon Hong Kong China Department of Polymer Science & Engineering College of Chemistry Peking University Beijing China 《高分子科学》1999,(3):289-294
A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily "tunab1e" by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments. 相似文献
55.
56.
Xiao Zhen Liu Fei Wang Dong Dong Luo Xing Guo Guang Qing Lei 《中国化学快报》2007,18(11):1339-1341
The hydroxyl group of carbocyclic nucleosides was inversed when the compounds were treated with Me_3SiCl,KCN and a catalytic amount of NaI in DMF/CH_3CN. 相似文献
57.
Tomoyuki Yoshimura 《Tetrahedron letters》2004,45(50):9241-9244
Diastereoselective construction of the 19-epi-C18-C25 segment of (−)-lasonolide A was achieved using a 5-exo-trigonal mode of radical cyclization for the creation of the contiguous quaternary and tertiary stereogenic centers at C22 and C23 as the key reaction step. During the dehydration stage, it was found that an unusual inversion of configuration took place. 相似文献
58.
烃类选择氧化在石油化工中极其重要.近二十多年来,随着石油化工原料逐步从烯烃、芳烃等不饱和烃向资源丰富和价格相对低廉的烷烃的转化,研究烷烃的氧化活化和定向转化来取代相应的烯烃和芳烃工艺具有非常重要的学术意义和工业价值.因而,烷烃的选择活化和氧化得到了世界范围内的 相似文献
59.
60.
Toshiaki Sunazuka Masaki Handa Tatsuya Shirahata Kazuhiko Otoguro Satoshi ōmura 《Tetrahedron》2004,60(36):7845-7859
In the current studies, we used the Kakisawa-Kashman modification of the Mosher NMR method to determine the complete absolute stereochemistry of arisugacins. We also report the convergent total synthesis of (+)-arisugacins A and B by a sequence including (i) ruthenium complex-catalyzed asymmetric reduction of the cyclohexenone derivative; (ii) stereoselective construction of the arisugacin skeleton by a Knoevenagel-type reaction of an α,β-unsaturated aldehyde derivative with production of a 4-hydroxy-2-pyrone derivative as a key reaction; and (iii) stereoselective dihydroxylation to give the diol derivative, followed by deoxygenation. Accordingly, we defined the absolute structures of arisugacins A and B as 4a-(R),6a-(R),12a-(R), and 12b-(S). Finally, we characterized the bioactivities of the synthetic intermediates to understand the structure-activity relationships of the arisugacins. 相似文献