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991.
992.
993.
从传统中药罗汉果中分离得到一系列三萜皂苷类化合物,其苷元为罗汉果醇,应用1D和2D NMR脉冲梯度场反相技术(gCOSY,gNOESY,gHMQC,gHMBC) 研究了罗汉果醇及其苷的结构,对其碳氢NMR信号进行了全归属,应用gNOESY技术研究了罗汉果醇的立体构型,并探讨了取代基对苷元质子和碳化学位移的影响. 相似文献
994.
黄芩的1H NMR指纹图谱研究 总被引:3,自引:0,他引:3
利用PFT-NMR 核磁共振波谱仪测定了黄芩提取物的1H NMR图谱,对黄芩提取物的1H NMR指纹图谱进行了解析,并与黄芩苷元、千层纸素A、汉黄芩素和黄芩苷进行了比较,获得了黄芩提取物的特征峰,并利用向量夹角法计算了不同指纹图谱的相似度;结果表明不同黄芩提取物的1H NMR指纹图谱都显示出黄酮类有效成分特征共振峰,并具有很好的重现性和高度的特征性,可以成为黄芩真伪鉴别的依据;不同黄芩的1H NMR指纹图谱的相似度计算结果定量地评价了不同指纹图谱的相似性. 相似文献
995.
Dr. Irán Rojas-León Gelen Gómez-Jaimes Dr. Pedro Montes-Tolentino Prof. Dr. Wolf Hiller Dr. Hazem Alnasr Prof. Dr. Braulio Rodríguez-Molina Dr. Irán F. Hernández-Ahuactzi Prof. Dr. Hiram Beltrán Prof. Dr. Klaus Jurkschat Prof. Dr. Herbert Höpfl 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(48):12276-12283
Hydrolysis reactions of di- and trinuclear organotin halides yielded large novel cage compounds containing Sn−O−Sn bridges. The molecular structures of two octanuclear tetraorganodistannoxanes showing double-ladder motifs, viz., [{Me3SiCH2(Cl)SnCH2YCH2Sn(OH)CH2SiMe3}2(μ-O)2]2 [ 1 , Y=p-(Me)2SiC6H4-C6H4Si(Me)2] and [{Me3SiCH2(I)SnCH2YCH2Sn(OH)CH2SiMe3}2(μ-O)2]2 ⋅ 0.48 I2 [ 2⋅ 0.48 I2, Y=p-(Me)2SiC6H4-C6H4Si(Me)2], and the hexanuclear cage-compound 1,3,6-C6H3(p-C6H4Si(Me)2CH2Sn(R)2OSn(R)2CH2Si(Me)2C6H4-p)3C6H3-1,3,6 ( 3 , R=CH2SiMe3) are reported. Of these, the co-crystal 2⋅ 0.48 I2 exhibits the largest spacing of 16.7 Å reported to date for distannoxane-based double ladders. DFT calculations for the hexanuclear cage and a related octanuclear congener accompany the experimental work. 相似文献
996.
Dr. Selina Beatrice van der Meer Theresa Seiler Christin Buchmann Georgia Partalidou Dr. Sophia Boden Dr. Kateryna Loza Dr. Marc Heggen Dr. Jürgen Linders Dr. Oleg Prymak Prof. Dr. Cristiano L. P. Oliveira Prof. Dr. Laura Hartmann Prof. Dr. Matthias Epple 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(4):1451-1464
Ultrasmall gold nanoparticles (diameter about 2 nm) were surface-functionalized with cysteine-carrying precision macromolecules. These consisted of sequence-defined oligo(amidoamine)s (OAAs) with either two or six cysteine molecules for binding to the gold surface and either with or without a PEG chain (3400 Da). They were characterized by 1H NMR spectroscopy, 1H NMR diffusion-ordered spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy. The number of precision macromolecules per nanoparticle was determined after fluorescent labeling by UV spectroscopy and also by quantitative 1H NMR spectroscopy. Each nanoparticle carried between 40 and 100 OAA ligands, depending on the number of cysteine units per OAA. The footprint of each ligand was about 0.074 nm2 per cysteine molecule. OAAs are well suited to stabilize ultrasmall gold nanoparticles by selective surface conjugation and can be used to selectively cover their surface. The presence of the PEG chain considerably increased the hydrodynamic diameter of both dissolved macromolecules and macromolecule-conjugated gold nanoparticles. 相似文献
997.
Triple resonance solid-state NMR experiments using the spin combination 1H–13C–29Si are still rarely found in the literature. This is due to the low natural abundance of the two heteronuclei. Such experiments are, however, increasingly important to study hybrid materials such as biosilica and others. A suitable model substance, ideally labeled with both 13C and 29Si, is thus very useful to optimize the experiments before applying them to studies of more complex samples such as biosilica. Tetraphenoxysilane could be synthesized in an easy, two-step synthesis including double isotope labelling. Using tetraphenoxysilane, we established a 1H–13C–29Si double CP-based HETCOR experiment and applied it to diatom biosilica from the diatom species Thalassiosira pseudonana. Furthermore, we carried out 1H–13C{29Si} CP-REDOR experiments in order to estimate the distance between the organic matrix and the biosilica. Our experiments on diatom biosilica strongly indicate a close contact between polyamine-containing parts of the organic matrix and the silica. This corroborates the assumption that the organic matrix is essential for the control of the cell wall formation. 相似文献
998.
999.
This work is motivated by the recent developments in online minerals analysis in the mining and minerals processing industry via nuclear quadrupole resonance (NQR). Here we describe a nuclear magnetic resonance (NMR) and NQR study of the minerals tennantite (Cu12As4S13) and tetrahedrite (Cu12 Sb4S13). In the first part NQR lines associated with 75As in tennantite and 121,123Sb isotopes in tetrahedrite are reported. The spectroscopy has been restricted to an ambient temperature studies in accord with typical industrial conditions. The second part of this contribution reports nuclear quadrupole-perturbed NMR findings on further, only partially characterised, metal arsenides. The findings enhance the detection capabilities of NQR based analysers for online measurement applications and may aid to control arsenic and antimony concentrations in metal processing stages. 相似文献
1000.
Comparison of the 13C (C = N) chemical shifts of substituted N‐(phenyl‐ethylene)‐anilines and substituted N‐(benzylidene)‐anilines
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Comparison of 13C NMR of C = N bond chemical shifts δC(C = N) in substituted N‐(phenyl‐ethylene)‐anilines XArC(Me) = NArY (XPEAYs) with that in substituted N‐(benzylidene)‐anilines XArCH = NArY (XBAYs) was carried out. The δC(C = N) of 61 samples of XPEAYs were measured, and the substituent effect on their δC(C = N) were investigated. The results show the factors affecting the δC(C = N) of XPEAYs are quite different from that of XBAYs. A penta‐parameter correlation equation was obtained for the 61 compounds, which has correlation coefficient 0.9922 and standard error 0.12 ppm. The result indicates that, in XPEAYs, the inductive effects of substituents X and Y are major factors affecting the δC(C = N), while the conjugative effect of them have very little effect on the δC(C = N) and can be ignored. The substituent‐specific cross‐interaction effects between X and Y and between Me of C = N bond and substituent Y are important factors affecting the δC(C = N). Also, the excited‐state substituent parameter of substitute Y has certain contribution to the δC(C = N). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献