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排序方式: 共有1499条查询结果,搜索用时 62 毫秒
991.
Torbjörn Wixe Dr. Carl‐Johan Wallentin Dr. Magnus T. Johnson Dr. Peter Fristrup Prof. Sven Lidin Prof. Kenneth Wärnmark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14963-14969
The synthesis of an orthogonal topological pentamer analogue of helicene is presented. This analogue forms a tubular structure with its aromatic systems directed parallel to the axis of propagation, which creates a cavity with the potential to function as a host molecule. The synthetic strategy reported, based on a series of repeating Friedländer condensations that utilize pyrido[3,2‐d]pyrimidine moieties as protected amino aldehydes, allows for the facile access of higher generations of helical, tubular structures. As a result of the synthetic strategy, only a helical isomer of the pentamer is possible. The structure and absolute configuration of the pentamer were elucidated from a combination of NMR spectroscopic data, optical properties, X‐ray structures, and by comparison of an experimental electronic circular dichroism spectrum to a calculated spectrum. 相似文献
992.
通过溶胶-凝胶法以十八烷基三甲基溴化铵(STAB)自组装体为模板和非离子型联二萘酚衍生物(S)作为手性添加剂制备螺旋介孔二氧化硅。样品利用扫描电镜、透射电镜、X-光衍射以及氮气吸附-脱附进行了表征。结果表明:反应混合物中S与STAB的物质的量之比对介孔二氧化硅的形貌及孔结构有很大影响。改变nS:nSTAB比,从0.1:1到0.4:1时,其结构从螺旋纳米棒状变为表面具有环形层状孔的纳米棒,孔道由沿着纳米棒长轴方向转变为同心环状。当nS:nSTAB=0.5:1时,得到类似皱缩花瓣的纳米颗粒。该手性添加剂的引入并没有改变左右手螺旋纳米棒的比例。 相似文献
993.
通过乳酸衍生物和3-溴-4-羟基苯甲酸的组合得到对映体3-溴-4-(((1R)-1-羧基乙基)氧基)苯甲酸(R-H2bba)和3-溴-4-(((1S)-1-羧基乙基)氧基)苯甲酸(S-H2bba)。以其为手性合成子在水热条件下分别与1,3-二(吡啶-4-基)丙烷(1,3-dpp)和Ni2+反应,构建了对映手性配位聚合物{[Ni(R-bba)(1,3-dpp)(H2O)0.5]·1.5H2O}n (HU12-R)和{[Ni(S-bba)(1,3-dpp)(H2O)0.5]·1.5H2O}n (HU12-S)。结构分析揭示HU12-R和HU12-S是具有dia网络特征的三维螺旋骨架。在骨架中,阴离子配体R-bba2-和S-bba2-分别与Ni2+中心连接在一起围绕21螺旋轴得到一对小的对映螺旋链,而1,3-dpp与Ni2+中心则围绕41螺旋轴构建出另外一对大的对映螺旋链。电化学测试显示HU12-R属n型半导体,具有低阻抗性质,对紫外可见光有很强的吸收能力。进一步光催化实验证实在紫外光照射下所得配合物对染料降解有明显催化效果。 相似文献
994.
Young‐Jae Jin Toshiki Aoki Giseop Kwak 《Angewandte Chemie (International ed. in English)》2020,59(5):1837-1844
A substituted poly(phenylacetylene) derivative (PPAHB) with two hydroxymethyl groups at the meta position of the side phenyl ring was examined as a conformation‐switchable helical spring polymer that responds to solvent and heat stimuli in a precisely controlled manner. Intramolecular hydrogen bonds, which cause the helical structure of the polymer, were broken and re‐formed by adjusting the hydrogen‐bonding strength values (pKHB) of various combinations of solvents or by varying the temperature. In this process, a reversible conformational change from cis–cisoid to cis–transoid, accompanied by a phase transition in the form of a helix‐coil transformation occurred, with the polymer exhibiting critical changes of color fading and recovery in specific environments. These results demonstrate that PPAHB can be used as either a pKHB indicator or a thermometer. The color changes of the polymer solution are described in detail based on spectroscopic analyses and thermodynamic considerations. 相似文献
995.
胆甾相液晶结构色的光调控 总被引:1,自引:0,他引:1
胆甾相液晶是一类具有周期性螺旋超结构的软光子晶体,能够选择性地反射不同波长的光产生结构色.在向列相液晶中掺杂光响应手性分子是制备光响应胆甾相液晶的普遍方法.在外界光源的刺激下,光响应手性分子的空间结构改变,诱导螺旋超结构的螺距发生变化,从而调控胆甾相液晶的结构色,因此光响应胆甾相液晶在滤光器、传感器、可调光学激光器和动态显示等领域具有广阔的应用前景.总结了不同光响应手性分子构筑的胆甾相液晶体系,分析了手性分子结构设计对胆甾相液晶结构色调控的影响,最终讨论了光响应胆甾相液晶目前面临的挑战以及未来的发展方向. 相似文献
996.
Pedro Mateus Nagula Chandramouli Cameron D. Mackereth Brice Kauffmann Yann Ferrand Ivan Huc 《Angewandte Chemie (International ed. in English)》2020,59(14):5797-5805
The recognition of either homomeric or heteromeric pairs of pentoses in an aromatic oligoamide double helical foldamer capsule was evidenced by circular dichroism (CD), NMR spectroscopy, and X‐ray crystallography. The cavity of the host was predicted to be large enough to accommodate simultaneously two xylose molecules and to form a 1:2 complex (one container, two saccharides). Solution and solid‐state data revealed the selective recognition of the α‐4C1‐d ‐xylopyranose tautomer, which is bound at two identical sites in the foldamer cavity. A step further was achieved by sequestering a heteromeric pair of pentoses, that is, one molecule of α‐4C1‐d ‐xylopyranose and one molecule of β‐1C4‐d ‐arabinopyranose despite the symmetrical nature of the host and despite the similarity of the guests. Subtle induced‐fit and allosteric effects are responsible for the outstanding selectivities observed. 相似文献
997.
Chang‐Bo Huang Artur Ciesielski Paolo Samorì 《Angewandte Chemie (International ed. in English)》2020,59(19):7319-7330
Molecular/supramolecular springs are artificial nanoscale objects possessing well‐defined structures and tunable physicochemical properties. Like a macroscopic spring, supramolecular springs are capable of switching their nanoscale conformation as a response to external stimuli by undergoing mechanical spring‐like motions. This dynamic action offers intriguing opportunities for engineering molecular nanomachines by translating the stimuli‐responsive nanoscopic motions into macroscopic work. These nanoscopic objects are reversible dynamic multifunctional architectures which can express a variety of novel properties and behave as adaptive nanoscopic systems. In this Minireview, we focus on the design and structure–property relationships of supramolecular springs and their (self‐)assembly as a prerequisite towards the generation of novel dynamic materials featuring controlled movements to be readily integrated into macroscopic devices for applications in sensing, robotics, and the internet of things. 相似文献
998.
Chiral Overpass Induction in Dynamic Helical Polymers Bearing Pendant Groups with Two Chiral Centers
Esteban Surez‐Picado Emilio Quio Ricardo Riguera Flix Freire 《Angewandte Chemie (International ed. in English)》2020,59(11):4537-4543
The dynamic behavior of helical polymers bearing pendant groups with two chiral centers was studied. Controlled conformational changes at the chiral units placed either closer to or further away from the main chain promote different helical structures. Although the first residue is usually responsible for determining a specific helicity (P or M), we now found that the second chiral center is also able to induce a preferred helical sense when it is located closer in space to the main chain, thereby cancelling the order from the first chiral moiety. This result was achieved through proper coordination with a metal cation. As proof of concept, poly(phenylacetylene)s (PPAs) that bear one and two chiral amino acid units of different sizes and configuration combinations (l /d ‐alanine and l /d ‐phenylalanine) as pendants were evaluated. In total, ten polymers were studied. This constitutes the first report of axial control from a remote stereocenter in polymers bearing complex chiral pendants. 相似文献
999.
Rafael Rodríguez Esteban Surez‐Picado Emilio Quio Ricardo Riguera Flix Freire 《Angewandte Chemie (International ed. in English)》2020,59(22):8616-8622
Herein, macromolecular gears composed of helical poly(phenylacetylenes) (PPAs) bearing short oligopeptides as pendant groups are described, in which the two structural motifs (framework and substituents) are combined. These gears are obtained by polymerization of the acetylene groups introduced at the C‐terminus of short oligopeptides formed by achiral (Aib)n units (n=1–3) derivatized at the N‐terminus by a single enantiomer (R or S) of α‐methoxy‐α‐trifluoromethylphenylacetic acid (MTPA, Mosher's reagent). The chiral information of the MTPA is transmitted to the achiral Aib fragments and, through either chiral tele‐induction and/or chiral harvesting mechanisms, is further transferred to the polyene backbones, which adopt preferentially P or M helical senses. Moreover, these materials also show dynamic behavior and respond to the action of external stimuli by either inverting the P/M sense and/or modifying the elongation in fully reversible processes. 相似文献
1000.
Aromaticity and Chemical Bonding of Chalcogen-Bonded Capsules Featuring Enhanced Magnetic Anisotropy
Prof. Demeter Tzeli Dr. Ioannis D. Petsalakis Dr. Giannoula Theodorakopoulos Dr. Faiz-Ur Rahman Prof. Pablo Ballester Prof. Julius Rebek Jr. Prof. Yang Yu 《Chemphyschem》2020,21(19):2187-2195
We present a theoretical study of chalcogen bonded container capsules ( AX+AX ) where X=O, S, Se, and Te, and their encapsulation complexes with n-C9H20 (n-C9H20@ AX+AX ). Both Se and Te encapsulation complexes have significant experimental and computed binding energies, analogous to the hydrogen bonded counterparts, while the S and O capsules and their encapsulation complexes show only weak binding energies, which are attributed to different types of bonding: chalcogen S⋅⋅⋅N bonds for S-capsules and π–π stacking and weak hydrogen bonds for the O case. All AX+AX and C9H20@ AX+AX present unusually high magnetic anisotropies in their interiors. The 1H NMR spectra of the encapsulation complexes display the proton signals of the encapsulated n-nonane highly upfield shifted, in agreement with the available experimental data for the Se capsule. We found that different factors contribute to the observed magnetic anisotropy of the capsule's interior: for the Te capsule the most important factor is Te's large polarizability; for the O analogue the inductive effects produced by the electronegative nature of the O and N heteroatoms; and for the S and Se capsules, the polarizability of the heteroatoms combines with electric field effects. 相似文献