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971.
共价有机框架(Covalent Organic Frameworks, COFs)是一种新型的多孔材料,具有结构规整、骨架稳定、孔径结构可调等特点,被视为固定化酶的理想载体。我们主要总结了近10年来COFs材料作为载体,通过物理吸附、共价连接、包埋的固定化策略制备固定化酶的研究进展与应用,并讨论了COFs材料在酶固定化领域所面临的机遇和挑战。 相似文献
972.
973.
Covalent bonding and J–J mixing effects on the EPR parameters of Er~(3+) ions in GaN crystal
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The EPR parameters of trivalent Er~(3+) ions doped in hexagonal Ga N crystal have been studied by diagonalizing the 364×364 complete energy matrices. The results indicate that the resonance ground states may be derived from the Kramers doublet Γ_6. The EPR g-factors may be ascribed to the stronger covalent bonding and nephelauxetic effects compared with other rare-earth doped complexes, as a result of the mismatch of ionic radii of the impurity Er~(3+)ion and the replaced Ga~(3+) ion apart from the intrinsic covalency of host Ga N. Furthermore, the J–J mixing effects on the EPR parameters from the high-lying manifolds have been evaluated. It is found that the dominant J–J mixing contribution is from the manifold ~2K_(15/2), which accounts for about 2.5%. The next important J–J contribution arises from the crystal–field mixture between the ground state ~4I_(15/2) and the first excited state~4I_(13/2), and is usually less than 0.2%. The contributions from the rest states may be ignored. 相似文献
974.
The electronic energy spectrum and wavefunction of a quantum-dot molecule are studied by means of the finite-element solution of the single electron Schr?dinger equation. We find that the nature of the coupling can be covalent, ionic, or "intermediate" new mixed states, depending on various parameters such as the separation distance between two dots, the height of potential barrier, matching of the energies and parities of the orbital localized on each dot. The bond property can be used to explain the experimental result obtained by Oosterkamp et al. (1998 Nature 395 873). 相似文献
975.
Elizabeth C. King William J. Watkins A. John Blacker Timothy D. H. Bugg 《Journal of polymer science. Part A, Polymer chemistry》1998,36(12):1995-1999
Methods for the covalent modification in aqueous solution of poly-γ-D-glutamic acid from Bacillus licheniformis have been studied. Co-derivatization of a synthetic UV-absorbent amine and ethanolamine, using a water-soluble carbodi-imide coupling agent, yielded a water-soluble modified polymer. Derivatization of the polymer was accompanied by cleavage of the γ-linked polypeptide backbone, and a reduction in molecular mass from 170 to 10 kDa. A procedure was developed for the removal of noncovalently bound ligands by treatment with 5 M CaCl2. The polymer sidechains also reacted in aqueous solution with p-nitrophenyl acetate to form covalent linkages. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 1995–1999, 1998 相似文献
976.
动态共价交联聚合物的研究具有悠久的历史,其早期的工作着眼于如何解决应力松弛带来的聚合物材料力学性能降低的问题.20世纪90年代以来,利用动态共价键来主动设计聚合物网络的特殊可适性逐渐成为研究主流,其中包括自修复和重加工性.然而,受到动态共价键的种类、通用性及所实现功能的特异性等限制,对于动态共价交联聚合物网络的研究尚停留在基础阶段.本文以本课题组近期在动态共价交联形状记忆聚合物的研究为基础,结合其他相关工作,展示了通用共价键(酯键及氨酯键)的动态可逆性,并利用其设计了具有特殊性能和潜在商业化价值的形状记忆聚合物.在此基础上,我们提出分子结构设计及宏观性能均不同于传统热塑性和热固性形状记忆聚合物的第3类形状记忆聚合物,即热适性形状记忆聚合物. 相似文献
977.
978.
用2,5-二(2-甲氧基-乙氧基)对苯二甲酰肼(BMTH)和1,3,5-三甲氧基-2,4,6-三甲酰基苯(TpOMe)缩聚,基于界面聚合法,在多孔三氧化二铝(AAO)基底上制备出一种二维共价有机骨架(COF)膜TpOMe-BMTH,并研究了所得膜材料对锂、镁离子的分离性能。结果显示,TpOMe-BMTH/AAO膜具有高的结晶性和良好的稳定性,并表现出优异的金属离子选择性,在LiCl(0.1 mol·L-1)和MgCl2(0.1 mol·L-1)组成的二元混合离子体系中,对Li+/Mg2+的分离因子高达258。基于密度泛函理论的平面波赝势方法计算表明,材料孔道中的富氧低聚醚链对 Li+和 Mg2+的结合能分别为-282.69和-13.46 kJ·mol-1,使材料表现出强的亲锂特性,促进了Li+沿着COF膜的一维孔道进行吸附扩散,最终实现锂、镁离子的高效分离。 相似文献
979.
980.
Ahmed Temirak Jonathan G. Schlegel Jan H. Voss Victoria J. Vaaßen Christin Vielmuth Tobias Claff Christa E. Müller 《Molecules (Basel, Switzerland)》2022,27(12)
Blockade of the adenosine A2B receptor (A2BAR) represents a potential novel strategy for the immunotherapy of cancer. In the present study, we designed, synthesized, and characterized irreversible A2BAR antagonists based on an 8-p-sulfophenylxanthine scaffold. Irreversible binding was confirmed in radioligand binding and bioluminescence resonance energy transfer(BRET)-based Gα15 protein activation assays by performing ligand wash-out and kinetic experiments. p-(1-Propylxanthin-8-yl)benzene sulfonyl fluoride (6a, PSB-21500) was the most potent and selective irreversible A2BAR antagonist of the present series with an apparent Ki value of 10.6 nM at the human A2BAR and >38-fold selectivity versus the other AR subtypes. The corresponding 3-cyclopropyl-substituted xanthine derivative 6c (PSB-21502) was similarly potent, but was non-selective versus A1- and A2AARs. Attachment of a reactive sulfonyl fluoride group to an elongated xanthine 8-substituent (12, Ki 7.37 nM) resulted in a potent, selective, reversibly binding antagonist. Based on previous docking studies, the lysine residue K2697.32 was proposed to react with the covalent antagonists. However, the mutant K269L behaved similarly to the wildtype A2BAR, indicating that 6a and related irreversible A2BAR antagonists do not interact with K2697.32. The new irreversible A2BAR antagonists will be useful tools and have the potential to be further developed as therapeutic drugs. 相似文献