全文获取类型
| 收费全文 | 55937篇 |
| 免费 | 5857篇 |
专业分类
| 化学 | 59097篇 |
| 晶体学 | 28篇 |
| 力学 | 1110篇 |
| 数学 | 1119篇 |
| 物理学 | 440篇 |
出版年
| 2024年 | 422篇 |
| 2023年 | 4307篇 |
| 2022年 | 2476篇 |
| 2021年 | 3924篇 |
| 2020年 | 6585篇 |
| 2019年 | 4086篇 |
| 2018年 | 2366篇 |
| 2017年 | 597篇 |
| 2016年 | 5525篇 |
| 2015年 | 5500篇 |
| 2014年 | 4916篇 |
| 2013年 | 5028篇 |
| 2012年 | 3030篇 |
| 2011年 | 955篇 |
| 2010年 | 3301篇 |
| 2009年 | 3241篇 |
| 2008年 | 987篇 |
| 2007年 | 679篇 |
| 2006年 | 107篇 |
| 2005年 | 73篇 |
| 2004年 | 53篇 |
| 2003年 | 59篇 |
| 1997年 | 47篇 |
| 1996年 | 48篇 |
| 1995年 | 112篇 |
| 1994年 | 70篇 |
| 1993年 | 187篇 |
| 1992年 | 68篇 |
| 1991年 | 57篇 |
| 1989年 | 47篇 |
| 1988年 | 75篇 |
| 1987年 | 60篇 |
| 1985年 | 57篇 |
| 1984年 | 59篇 |
| 1983年 | 64篇 |
| 1982年 | 73篇 |
| 1981年 | 84篇 |
| 1980年 | 103篇 |
| 1979年 | 94篇 |
| 1978年 | 96篇 |
| 1977年 | 162篇 |
| 1976年 | 181篇 |
| 1975年 | 186篇 |
| 1974年 | 194篇 |
| 1973年 | 110篇 |
| 1972年 | 153篇 |
| 1971年 | 122篇 |
| 1970年 | 207篇 |
| 1969年 | 125篇 |
| 1968年 | 147篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
91.
Natalie R. Altvater Rick W. Dorn Melissa C. Cendejas William P. McDermott Dr. Brijith Thomas Prof. Dr. Aaron J. Rossini Prof. Dr. Ive Hermans 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(16):6608-6612
Boron-containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron-containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B2(OH)xO(3−x/2) (x=0–6) layer. Yet, the precise nature of the active site(s) remains elusive. In this Communication, we provide a detailed characterization of zeolite MCM-22 isomorphously substituted with boron (B-MWW). Using 11B solid-state NMR spectroscopy, we show that the majority of boron species in B-MWW exist as isolated BO3 units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B-MWW for ODH of propane falsifies the hypothesis that site-isolated BO3 units are the active site in boron-based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium-based catalysts and provides an important piece of the mechanistic puzzle. 相似文献
92.
Dou Ma Ping Li Xiangyu Duan Jiazhen Li Pengpeng Shao Dr. Zhongling Lang Lixia Bao Dr. Yuanyuan Zhang Dr. Zhengguo Lin Prof. Dr. Bo Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(10):3933-3937
Metal–organic frameworks (MOFs) with long-term stability and reversible high water uptake properties can be ideal candidates for water harvesting and indoor humidity control. Now, a mesoporous and highly stable MOF, BIT-66 is presented that has indoor humidity control capability and a photocatalytic bacteriostatic effect. BIT-66 (V3(O)3(H2O)(BTB)2), possesses prominent moisture tunability in the range of 45–60 % RH and a water uptake and working capacity of 71 and 55 wt %, respectively, showing good recyclability and excellent performance in water adsorption–desorption cycles. Importantly, this MOF demonstrates a unique photocatalytic bacteriostatic behavior under visible light, which can effectively ameliorate the bacteria and/or mold breeding problem in water adsorbing materials. 相似文献
93.
Yukako Yoshinaga Dr. Takeshi Yamamoto Prof. Dr. Michinori Suginome 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(18):7318-7322
Enantiospecific intramolecular Suzuki–Miyaura-type coupling with α-(2-halobenzoylamino)benzylboronic esters to give 3-substituted isoindolinones is achieved by using copper catalysts with 2,2′-bipyridine-based achiral ligands. Enantioenriched α-aminobenzylboron reactants bearing a hydrogen atom at the boron-bound stereogenic carbons undergo stereoinvertive coupling in the presence of a 6-phenyl-2,2′-bipyridine ligand with high enantiospecificity. α-Aminobenzylboronates bearing fully substituted boron-bound stereogenic centers also gave the 3,3-disubstituted isoindolinones with stereospecific stereochemical inversion in the presence of simple 2,2′-bipyridine as a ligand. 相似文献
94.
Dr. Jin-Xia Liang Prof. Dr. Jian Lin Prof. Dr. Jingyue Liu Prof. Dr. Xiaodong Wang Prof. Dr. Tao Zhang Prof. Dr. Jun Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12968-12975
Herein, we report a theoretical and experimental study of the water-gas shift (WGS) reaction on Ir1/FeOx single-atom catalysts. Water dissociates to OH* on the Ir1 single atom and H* on the first-neighbour O atom bonded with a Fe site. The adsorbed CO on Ir1 reacts with another adjacent O atom to produce CO2, yielding an oxygen vacancy (Ovac). Then, the formation of H2 becomes feasible due to migration of H from adsorbed OH* toward Ir1 and its subsequent reaction with another H*. The interaction of Ir1 and the second-neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe3+−O⋅⋅⋅Ir2+−Ovac to Fe2+−Ovac⋅⋅⋅Ir3+−O with the involvement of Ovac. The redox mechanism for WGS reaction through a dual metal active site (DMAS) is different from the conventional associative mechanism with the formation of formate or carboxyl intermediates. The proposed new reaction mechanism is corroborated by the experimental results with Ir1/FeOx for sequential production of CO2 and H2. 相似文献
95.
96.
97.
Wu Wen Shengsheng Yu Chaoqun Zhou Prof. Hao Ma Prof. Zhongyue Zhou Chuangchuang Cao Dr. Jiuzhong Yang Minggao Xu Prof. Fei Qi Prof. Guobin Zhang Prof. Yang Pan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4903-4908
HCHO has been confirmed as an active intermediate in the methanol-to-hydrocarbon (MTH) reaction, and is critical for interpreting the mechanisms of coke formation. Here, HCHO was detected and quantified during the MTH process over HSAPO-34 and HZSM-5 by in situ synchrotron radiation photoionization mass spectrometry. Compared with conventional methods, excellent time-resolved profiles were obtained to study the formation and fate of HCHO, and other products during the induction, steady-state reaction, and deactivation periods. Similar formation trends of HCHO and methane, and their close correlation in yields suggest that they are derived from disproportionation of methanol at acidic sites. In the presence of Y2O3, the amount of HCHO changes, affecting the hydrogen-transfer processes of olefins into aromatics and aromatics into cokes. The yield of HCHO affects the aromatic-based cycle and the formation of ethylene, indicating that ethylene is mainly formed from the aromatic-based cycle. 相似文献
98.
Ye Xu Dr. Huifeng Yao Lijiao Ma Ling Hong Jiayao Li Qing Liao Yunfei Zu Jingwen Wang Mengyuan Gao Prof. Long Ye Prof. Jianhui Hou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9089-9095
Decreasing the energy loss is one of the most feasible ways to improve the efficiencies of organic photovoltaic (OPV) cells. Recent studies have suggested that non-radiative energy loss ( ) is the dominant factor that hinders further improvements in state-of-the-art OPV cells. However, there is no rational molecular design strategy for OPV materials with suppressed . Herein, taking molecular surface electrostatic potential (ESP) as a quantitative parameter, we establish a general relationship between chemical structure and intermolecular interactions. The results reveal that increasing the ESP difference between donor and acceptor will enhance the intermolecular interaction. In the OPV cells, the enhanced intermolecular interaction will increase the charge-transfer (CT) state ratio in its hybridization with the local exciton state to facilitate charge generation, but simultaneously result in a larger . These results suggest that finely tuning the ESP of OPV materials is a feasible method to further improve the efficiencies of OPV cells. 相似文献
99.
Hee-Jeong Cha Se-Yeun Hwang Da-Som Lee Dr. Akula Ravi Kumar Prof. Dr. Yong-Uk Kwon Moritz Voß Eva Schuiten Prof. Dr. Uwe T. Bornscheuer Prof. Dr. Frank Hollmann Prof. Dr. Deok-Kun Oh Prof. Dr. Jin-Byung Park 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(18):7090-7094
Long-chain aliphatic amines such as (S,Z)-heptadec-9-en-7-amine and 9-aminoheptadecane were synthesized from ricinoleic acid and oleic acid, respectively, by whole-cell cascade reactions using the combination of an alcohol dehydrogenase (ADH) from Micrococcus luteus, an engineered amine transaminase from Vibrio fluvialis (Vf-ATA), and a photoactivated decarboxylase from Chlorella variabilis NC64A (Cv-FAP) in a one-pot process. In addition, long chain aliphatic esters such as 10-(heptanoyloxy)dec-8-ene and octylnonanoate were prepared from ricinoleic acid and oleic acid, respectively, by using the combination of the ADH, a Baeyer–Villiger monooxygenase variant from Pseudomonas putida KT2440, and the Cv-FAP. The target compounds were produced at rates of up to 37 U g−1 dry cells with conversions up to 90 %. Therefore, this study contributes to the preparation of industrially relevant long-chain aliphatic chiral amines and esters from renewable fatty acid resources. 相似文献
100.
Dr. Shuo Tao Dr. Xiaolei Li Dr. Xiaoge Wang Dr. Ying Wei Yunling Jia Dr. Jing Ju Dr. Yuanhui Cheng Prof. Huaisheng Wang Prof. Shuwen Gong Dr. Xingjun Yao Haixu Gao Cunyin Zhang Qiqi Zang Prof. Zhijian Tian 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3483-3487
The synthesis of hierarchical nanosized zeolite materials without growth modifiers and mesoporogens remains a substantial challenge. Herein, we report a general synthetic approach to produce hierarchical nanosized single-crystal aluminophosphate molecular sieves by preparing highly homogeneous and concentrated precursors and heating at elevated temperatures. Accordingly, aluminophosphate zeotypes of LTA (8-rings), AEL (10-rings), AFI (12-rings), and -CLO (20-rings) topologies, ranging from small to extra-large pores, were synthesized. These materials show exceptional properties, including small crystallites (30–150 nm), good monodispersity, abundant mesopores, and excellent thermal stability. A time-dependent study revealed a non-classical crystallization pathway by particle attachment. This work opens a new avenue for the development of hierarchical nanosized zeolite materials and understanding their crystallization mechanism. 相似文献