全文获取类型
收费全文 | 18937篇 |
免费 | 2859篇 |
国内免费 | 2460篇 |
专业分类
化学 | 10911篇 |
晶体学 | 176篇 |
力学 | 814篇 |
综合类 | 142篇 |
数学 | 1866篇 |
物理学 | 4993篇 |
无线电 | 5354篇 |
出版年
2024年 | 46篇 |
2023年 | 475篇 |
2022年 | 495篇 |
2021年 | 669篇 |
2020年 | 748篇 |
2019年 | 690篇 |
2018年 | 558篇 |
2017年 | 501篇 |
2016年 | 804篇 |
2015年 | 828篇 |
2014年 | 1050篇 |
2013年 | 1344篇 |
2012年 | 1529篇 |
2011年 | 1568篇 |
2010年 | 1149篇 |
2009年 | 1048篇 |
2008年 | 1215篇 |
2007年 | 1106篇 |
2006年 | 1047篇 |
2005年 | 939篇 |
2004年 | 704篇 |
2003年 | 687篇 |
2002年 | 704篇 |
2001年 | 612篇 |
2000年 | 474篇 |
1999年 | 464篇 |
1998年 | 402篇 |
1997年 | 340篇 |
1996年 | 364篇 |
1995年 | 291篇 |
1994年 | 260篇 |
1993年 | 220篇 |
1992年 | 182篇 |
1991年 | 155篇 |
1990年 | 117篇 |
1989年 | 107篇 |
1988年 | 76篇 |
1987年 | 53篇 |
1986年 | 42篇 |
1985年 | 52篇 |
1984年 | 48篇 |
1983年 | 24篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 851 毫秒
911.
Highly Enantioselective Kinetic Resolution of Axially Chiral BINAM Derivatives Catalyzed by a Brønsted Acid
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Dao‐Juan Cheng Liang Yan Prof. Dr. Shi‐Kai Tian Ming‐Yue Wu Lu‐Xin Wang Zi‐Li Fan Dr. Sheng‐Cai Zheng Prof. Dr. Xin‐Yuan Liu Prof. Dr. Bin Tan 《Angewandte Chemie (International ed. in English)》2014,53(14):3684-3687
A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid‐catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities. 相似文献
912.
Fan Shi Aaron M. Coffey Assist. Prof. Kevin W. Waddell Assist. Prof. Eduard Y. Chekmenev Assoc. Prof. Boyd M. Goodson 《Angewandte Chemie (International ed. in English)》2014,53(29):7495-7498
A novel variant of an iridium‐based organometallic catalyst was synthesized and used to enhance the NMR signals of pyridine in a heterogeneous phase by immobilization on polymer microbead solid supports. Upon administration of parahydrogen (pH2) gas to a methanol mixture containing the HET‐SABRE catalyst particles and the pyridine, up to fivefold enhancements were observed in the 1H NMR spectra after sample transfer to high field (9.4 T). Importantly, enhancements were not due to any residual catalyst molecules in solution, thus supporting the true heterogeneity of the SABRE process. Further significant improvements may be expected by systematic optimization of experimental parameters. Moreover, the heterogeneous catalyst is easy to separate and recycle, thus opening a door to future potential applications varying from spectroscopic studies of catalysis, to imaging metabolites in the body without concern of contamination from expensive and potentially toxic metal catalysts or accompanying organic molecules. 相似文献
913.
Jinrong Yang Dr. Guosheng Shi Dr. Yusong Tu Prof. Haiping Fang 《Angewandte Chemie (International ed. in English)》2014,53(38):10190-10194
Recent experiments have shown the coexistence of both large unoxidized and oxidized regions on graphene oxide (GO), but the underlying mechanism for the formation of the GO atomic structure remains unknown. Now, using density functional calculations, 52 oxidation pathways for local pyrene structures on GO were identified, and a kinetic profile for graphene oxidation with a high correlation between oxidation loci was proposed, which is different from the conventional view, which entails a random distribution of oxidation loci. The high correlation is an essential nature of graphene oxidation processes and can be attributed to three crucial effects: 1) breaking of delocalized π bonds, 2) steric hindrance, and 3) hydrogen‐bond formation. This high correlation leads to the coexistence of both large unoxidized and oxidized regions on GO. Interestingly, even in oxidized regions on GO, some small areas of sp2‐hybridized domains, similar to “islands”, can persist because of steric effects. 相似文献
914.
Lysosomal pH Rise during Heat Shock Monitored by a Lysosome‐Targeting Near‐Infrared Ratiometric Fluorescent Probe
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Qiongqiong Wan Prof. Dr. Suming Chen Prof. Dr. Wen Shi Lihong Li Prof. Dr. Huimin Ma 《Angewandte Chemie (International ed. in English)》2014,53(41):10916-10920
Heat stroke is a life‐threatening condition, featuring a high body temperature and malfunction of many organ systems. The relationship between heat shock and lysosomes is poorly understood, mainly because of the lack of a suitable research approach. Herein, by incorporating morpholine into a stable hemicyanine skeleton, we develop a new lysosome‐targeting near‐infrared ratiometric pH probe. In combination with fluorescence imaging, we show for the first time that the lysosomal pH value increases but never decreases during heat shock, which might result from lysosomal membrane permeabilization. We also demonstrate that this lysosomal pH rise is irreversible in living cells. Moreover, the probe is easy to synthesize, and shows superior overall analytical performance as compared to the existing commercial ones. This enhanced performance may enable it to be widely used in more lysosomal models of living cells and in further revealing the mechanisms underlying heat‐related pathology. 相似文献
915.
Yingbo Shi Baochao Yang Shujun Cai Prof. Dr. Shuanhu Gao 《Angewandte Chemie (International ed. in English)》2014,53(36):9539-9543
The total synthesis of gracilamine, a pentacyclic Amaryllidaceae alkaloid, was achieved from simple building blocks. The synthesis features a mild photo‐Nazarov reaction, intramolecular 1,4‐addition, and an intramolecular Mannich reaction. This approach not only confirms the C6 stereochemistry of natural gracilamine, and also provides a novel solution to prepare its derivatives and structurally related natural products. 相似文献
916.
A Small‐Molecule FRET Reporter for the Real‐Time Visualization of Cell‐Surface Proteolytic Enzyme Functions
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jing Mu Dr. Fang Liu Muhammad Shafiq Rajab Meng Shi Shuang Li Chiching Goh Prof. Lei Lu Prof. Qing‐Hua Xu Prof. Bin Liu Dr. Lai Guan Ng Prof. Bengang Xing 《Angewandte Chemie (International ed. in English)》2014,53(52):14357-14362
Real‐time imaging of cell‐surface‐associated proteolytic enzymes is critical to better understand their performances in both physiological and pathological processes. However, most current approaches are limited by their complexity and poor membrane‐anchoring properties. Herein, we have designed and synthesized a unique small‐molecule fluorescent probe, which combines the principles of passive exogenous membrane insertion and Förster resonance energy transfer (FRET) to image cell‐surface‐localized furin‐like convertase activities. The membrane‐associated furin‐like enzymatic cleavage of the peptide probe leads to an increased fluorescence intensity which was mainly localized on the plasma membrane of the furin‐expressed cells. This small‐molecule fluorescent probe may serve as a unique and reliable reporter for real‐time visualization of endogenous cell‐surfaceassociated proteolytic furin‐like enzyme functions in live cells and tissues using one‐photon and two‐photon microscopy. 相似文献
917.
Sulfonamide‐Promoted Palladium(II)‐Catalyzed Alkylation of Unactivated Methylene C(sp3)H Bonds with Alkyl Iodides
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kai Chen Prof. Dr. Bing‐Feng Shi 《Angewandte Chemie (International ed. in English)》2014,53(44):11950-11954
The alkylation of unactivated β‐methylene C(sp3)? H bonds of α‐amino acid substrates with a broad range of alkyl iodides using Pd(OAc)2 as the catalyst is described. The addition of NaOCN and 4‐Cl‐C6H4SO2NH2 was found to be crucial for the success of this transformation. The reaction is compatible with a diverse array of functional groups and proceeds with high diastereoselectivity. Furthermore, various β,β‐hetero‐dialkyl‐ and β‐alkyl‐β‐aryl‐α‐amino acids were prepared by sequential C(sp3)? H functionalization of an alanine‐derived substrate, thus providing a versatile strategy for the stereoselective synthesis of unnatural β‐disubstituted α‐amino acids. 相似文献
918.
Phosphate Monoester Hydrolysis by Trinuclear Alkaline Phosphatase; DFT Study of Transition States and Reaction Mechanism
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alkaline phosphatase (AP) is a trinuclear metalloenzyme that catalyzes the hydrolysis of a broad range of phosphate monoesters to form inorganic phosphate and alcohol (or phenol). In this paper, by using density functional theory with a model based on a crystal structure, the AP‐catalyzed hydrolysis of phosphate monoesters is investigated by calculating two substrates, that is, methyl and p‐nitrophenyl phosphates, which represent alkyl and aryl phosphates, respectively. The calculations confirm that the AP reaction employs a “ping‐pong” mechanism involving two chemical displacement steps, that is, the displacement of the substrate leaving group by a Ser102 alkoxide and the hydrolysis of the phosphoseryl intermediate by a Zn2‐bound hydroxide. Both displacement steps proceed via a concerted associative pathway no matter which substrate is used. Other mechanistic aspects are also studied. Comparison of our calculations with linear free energy relationships experiments shows good agreement. 相似文献
919.
12 perfluorinated compounds(PFCs) in human blood from workers in a textile mill in Shandong province and several barbershops in Tianjin were analyzed in this study. It was found that perfluorooctanesulfonate(PFOS) and perfluorooctanoate(PFOA) were the most prominent PFCs, with average concentrations of 5.73 mg/L and 5.46 mg/L for textile workers, and 2.55 mg/L and 2.84 mg/L for barbers.PFOS and perfluorohexanesulfonate(PFHxS) concentrations revealed a positive correlation in blood samples(p 〈 0.01), and concentrations among PFOS, perfluorononanoic acid(PFNA) and perfluorodecanoic acid(PFDA) also revealed positive correlations(p 〈 0.01). The influence of gender and age on PFC concentration in blood was also investigated, and the results showed that there was no statistically significant difference between the male and female samples, as well as in samples from people with different ages. Generally speaking, the textile workers 相似文献
920.
Min-Jie Shi Sheng-Zhong Kou Bao-Shou Shen Jun-Wei Lang Zhi Yang Xing-Bin Yan 《中国化学快报》2014,25(6):859-864
Ionic liquid gel polymers have widely been used as the electrolytes in all-solid-state supercapacitors, but they suffer from low ionic conductivity and poor electrochemical performance. Arc discharge is a fast, low-cost and scalable method to prepare multi-layered graphene nanosheets, and as-made graphene nanosheets (denoted as ad-GNSs) with few defects, high electrical conductivity and high thermal stability should be favorable conductive additive materials. Here, a novel ionic liquid gel polymer electrolyte based on an ionic liquid (EM1MNTF2) and an copolymer (P(VDF-HFP)) was modified by the addition of ad-GNSs as an ionic conducting promoter. This modified gel electrolyte shows excellent thermal stability up to 400 ℃ and a wide electrochemical window of 3 V. An all-solid-state supercapacitor based on commercial activated carbon was fabricated using this modified ionic liquid gel polymer electrolyte, which shows obviously improved electrochemical behaviors compared with those of the corresponding all-solid-state supercapacitor using pure ionic liquid gel polymer electrolyte. Specially, smaller internal resistance, higher specific capacitance, better rate performance and cycling stability are achieved. These results indicate that the ionic liquid gel polymers modified by ad-GNSs would be promising and suitable gel electrolytes for high performance all-solid-state electrochemical devices. 相似文献