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51.
Cardin Pedro Toniol Teixeira Marco Antonio 《Journal of Dynamics and Differential Equations》2022,34(2):775-787
Journal of Dynamics and Differential Equations - In this paper we focus on a class of symmetric vector fields in the context of singularly perturbed fast-slow dynamical systems. Our main question... 相似文献
52.
53.
Dr. Arianna Melillo Dr. Antonio Franconetti Prof. Dr. Mercedes Alvaro Prof. Dr. Belen Ferrer Prof. Hermenegildo Garcia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2023,29(1):e202202625
Hydrogenation of multiple bonds are among the most general and important organic reactions. Typical heterogeneous catalysts are based on transition metal nanoparticles, including noble metals. Data are presented here showing that metal nodes of MIL-101(Cr) and UiO-66 in the absence of occluded metal nanoparticles can promote hydrogenation of polarized X=Y double bonds of nitro and carbonyl groups. The catalytic activity is a function of the composition of the metal node and the organic linker. It is proposed that the reaction mechanism is based on the operation of frustrated Lewis acid/base pairs. 相似文献
54.
Antonio J. LaPorte Jack E. Feldner Jan C. Spies Tom J. Maher Prof. Martin D. Burke 《Angewandte Chemie (International ed. in English)》2023,62(40):e202309566
Multifunctional organoboron compounds increasingly enable the simple generation of complex, Csp3-rich small molecules. The ability of boron-containing functional groups to modify the reactivity of α-radicals has also enabled a myriad of chemical reactions. Boronic esters with vacant p-orbitals have a significant stabilizing effect on α-radicals due to delocalization of spin density into the empty orbital. The effect of coordinatively saturated derivatives, such as N-methyliminodiacetic acid (MIDA) boronates and counterparts, remains less clear. Herein, we demonstrate that coordinatively saturated MIDA and TIDA boronates stabilize secondary alkyl α-radicals via σB-N hyperconjugation in a manner that allows site-selective C−H bromination. DFT calculated radical stabilization energies and spin density maps as well as LED NMR kinetic analysis of photochemical bromination rates of different boronic esters further these findings. This work clarifies that the α-radical stabilizing effect of boronic esters does not only proceed via delocalization of radical character into vacant boron p-orbitals, but that hyperconjugation of tetrahedral boron-containing functional groups and their ligand electron delocalizing ability also play a critical role. These findings establish boron ligands as a useful dial for tuning reactivity at the α-carbon. 相似文献
55.
Dr. Xiaona Li Cristina Di Carluccio He Miao Lvfeng Zhang Jintao Shang Prof. Dr. Antonio Molinaro Prof. Dr. Peng Xu Prof. Dr. Alba Silipo Prof. Dr. Biao Yu Prof. Dr. You Yang 《Angewandte Chemie (International ed. in English)》2023,62(43):e202307851
Cyclodextrins are widely used as carriers of small molecules for drug delivery owing to their remarkable host properties and excellent biocompatibility. However, cyclic oligosaccharides with different sizes and shapes are limited. Cycloglycosylation of ultra-large bifunctional saccharide precursors is challenging due to the constrained conformational spaces. Herein we report a promoter-controlled cycloglycosylation approach for the synthesis of cyclic α-(1→6)-linked mannosides up to a 32-mer. Cycloglycosylation of the bifunctional thioglycosides and (Z)-ynenoates was found to be highly dependent on the promoters. In particular, a sufficient amount of a gold(I) complex played a key role in the proper preorganization of the ultra-large cyclic transition state, providing a cyclic 32-mer polymannoside, which represents the largest synthetic cyclic polysaccharide to date. NMR experiments and a computational study revealed that the cyclic 2-mer, 4-mer, 8-mer, 16-mer, and 32-mer mannosides adopted different conformational states and shapes. 相似文献
56.
Llorenç Rubert Dr. Md Faizul Islam Dr. Andrew B. Greytak Rahul Prakash Mark D. Smith Dr. Rosa Maria Gomila Prof. Dr. Antonio Frontera Prof. Dr. Linda S. Shimizu Dr. Bartolome Soberats 《Angewandte Chemie (International ed. in English)》2023,62(46):e202312223
We report on a dendronized bis-urea macrocycle 1 self-assembling via a cooperative mechanism into two-dimensional (2D) nanosheets formed solely by alternated urea-urea hydrogen bonding interactions. The pure macrocycle self-assembles in bulk into one-dimensional liquid-crystalline columnar phases. In contrast, its self-assembly mode drastically changes in CHCl3 or tetrachloroethane, leading to 2D hydrogen-bonded networks. Theoretical calculations, complemented by previously reported crystalline structures, indicate that the 2D assembly is formed by a brick-like hydrogen bonding pattern between bis-urea macrocycles. This assembly is promoted by the swelling of the trisdodecyloxyphenyl groups upon solvation, which frustrates, due to steric effects, the formation of the thermodynamically more stable columnar macrocycle stacks. This work proposes a new design strategy to access 2D supramolecular polymers by means of a single non-covalent interaction motif, which is of great interest for materials development. 相似文献
57.
Dr. Cristina Di Carluccio Dr. Francesco Milanesi Dr. Monica Civera Celeste Abreu Prof. Sara Sattin Prof. Oscar Francesconi Prof. Antonio Molinaro Dr. Ondřej Vaněk Prof. Roberta Marchetti Prof. Alba Silipo 《European journal of organic chemistry》2023,26(40):e202300644
We investigated two recently synthesized and characterized sialyl derivatives, bearing the Neu5Ac-α-(2-6)-Gal epitope, as promising binders for Siglec-7, an inhibitory Siglec mainly found on natural killer cells. A variety of sialoglycan structures can be recognized by Siglec-7 with implications in the modulation of immune responses. Notably, overexpression of sialylated glycans recognized by Siglec-7 can be associated with the progression of several tumors, including melanoma and renal cell carcinoma. NOE-based NMR techniques, including Saturation Transfer Difference and transferred-NOESY NMR, together with molecular docking and dynamic simulations were combined to shed light on the molecular basis of Siglec-7 recognition of two conformationally constrained Sialyl-Tn antigen analogs. We, therefore, identify the ligands epitope mapping and their conformational features and propose 3D models accurately describing the protein-ligand complexes. We found that the binding site of Siglec-7 can accommodate both synthetic analogs, with the sialic acid mainly involved in the interaction. Moreover, the flexibility of Siglec-7 loops allows a preferred accommodation of the more rigid compound bearing a biphenyl moiety at position 9 of the sialic acid that contributed to the interaction to a large extent. Our findings provided insights for developing potential novel high affinity ligands for Siglec-7 to hinder tumor evasion. 相似文献
58.
Some literature reports have shown the existence of short Hg(II)⋅⋅⋅d8[M] (M=Pd, Pt) contacts between linear Hg(II) and square planar d8[M] complexes that have been defined as heterometallophilic interactions. Linear L−Hg(II)−L complexes exhibit a π-hole or positive belt of electrostatic potential at the Hg atom, whereas late transition metals can serve as effective electron donors through their filled dz2 orbitals. This study provides compelling evidence that Hg(II)⋅⋅⋅d8[M] interactions should be more appropriately termed spodium bonds. 相似文献
59.
Prof. Lorenzo Franco Prof. Abdirisak Ahmed Isse Prof. Antonio Barbon Prof. Lina Altomare MSc. Viivi Hyppönen Dr. Jessica Rosa Dr. Venla Olsson Prof. Mikko Kettunen Prof. Lucio Melone 《Chemphyschem》2023,24(19):e202300100
This paper reports the synthesis, characterization and in vivo application of water-soluble supramolecular contrast agents (Mw: 5–5.6 kDa) for MRI obtained from β-cyclodextrin functionalized with different kinds of nitroxide radicals, both with piperidine structure ( CD2 and CD3 ) and with pyrrolidine structure ( CD4 and CD5 ). As to the stability of the radicals in presence of ascorbic acid, CD4 and CD5 have low second order kinetic constants (≤0.05 M−1 s−1) compared to CD2 (3.5 M−1 s−1) and CD3 (0.73 M−1 s−1). Relaxivity (r1) measurements on compounds CD3 - CD5 were carried out at different magnetic field strength (0.7, 3, 7 and 9.4 T). At 0.7 T, r1 values comprised between 1.5 mM−1 s−1 and 1.9 mM−1 s−1 were found while a significant reduction was observed at higher fields (r1≈0.6-0.9 mM−1 s−1 at 9.4 T). Tests in vitro on HEK293 human embryonic kidney cells, L929 mouse fibroblasts and U87 glioblastoma cells indicated that all compounds were non-cytotoxic at concentrations below 1 μmol mL−1. MRI in vivo was carried out at 9.4 T on glioma-bearing rats using the compounds CD3 - CD5 . The experiments showed a good lowering of T1 relaxation in tumor with a retention of the contrast for at least 60 mins confirming improved stability also in vivo conditions. 相似文献
60.
Miriam Calabrese Andrea Pizzi Roberta Beccaria Antonio Frontera Giuseppe Resnati 《Chemphyschem》2023,24(16):e202300298
Single crystal X-ray diffraction of iodate and bromate salts shows that the I and Br atoms in IO3− and BrO3− anions form short and linear O−I/Br ⋅⋅⋅ O contacts with the O atoms of nearby anions. Non-centrosymmetric systems are formed wherein anions are orderly aligned into supramolecular 1D and 2D networks. Theoretical evidences, namely the outcome of QTAIM and NCIplot studies, prove the attractive nature of these contacts and the ability of iodate and bromate anions to act as robust halogen bond (HaB) donors. The HaB is proposed as a general and effective assisting tool to control the architecture of acentric iodate salts. 相似文献