全文获取类型
收费全文 | 910篇 |
免费 | 50篇 |
国内免费 | 4篇 |
专业分类
化学 | 718篇 |
晶体学 | 6篇 |
力学 | 27篇 |
数学 | 41篇 |
物理学 | 172篇 |
出版年
2023年 | 10篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 30篇 |
2019年 | 30篇 |
2018年 | 29篇 |
2017年 | 27篇 |
2016年 | 45篇 |
2015年 | 31篇 |
2014年 | 38篇 |
2013年 | 72篇 |
2012年 | 67篇 |
2011年 | 84篇 |
2010年 | 37篇 |
2009年 | 30篇 |
2008年 | 56篇 |
2007年 | 55篇 |
2006年 | 42篇 |
2005年 | 52篇 |
2004年 | 28篇 |
2003年 | 24篇 |
2002年 | 31篇 |
2001年 | 11篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有964条查询结果,搜索用时 15 毫秒
1.
2.
Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex 下载免费PDF全文
Sandeep Suryabhan Gholap Dr. Masanori Takimoto Prof. Dr. Zhaomin Hou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8547-8552
The alkylative carboxylation of allenamide catalyzed by an N‐heterocyclic carbene (NHC)–copper(I) complex [(IPr)CuCl] with CO2 and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO2 (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)‐α,β‐dehydro‐β‐amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ‐carbon, and the carboxyl group introduced onto the β‐carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO2. A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β‐hydrogen atoms, such as Et2Zn or Bu2Zn, also gave the corresponding alkylative carboxylation products without β‐hydride elimination. The present methodology provides an easy route to alkyl‐substituted α,β‐dehydro‐β‐amino acid ester derivatives under mild reaction conditions with high regio‐ and stereoselectivtiy. 相似文献
3.
Kenchappa R. Bodke Yadav D. Telkar Sandeep Sindhe M. Aruna Giridhar M. 《Russian Journal of General Chemistry》2016,86(12):2827-2836
Russian Journal of General Chemistry - A novel series of (5-substituted-1-benzofuran-2-yl)(2,4-substituted phenyl)methanones (4a–4i) have been prepared by the Knoevenagel condensation of... 相似文献
4.
Sandeep Kumar 《Liquid crystals》2020,47(8):1195-1203
ABSTRACT Discotic liquid crystals (DLCs) have reached from curiosity to commodity in a short span of time. Tremendous development has been observed in the field of DLCs in the past few years due to their vide-viewing display and unidirectional conducting properties. In this article, I present some aspects of research carried out by me and my collaborators on DLCs. This work was presented at the Asian Conference on Liquid Crystals (ACLC 2019) at Shenzhen, China during January 17–18, 2019. 相似文献
5.
Nagaraju Kerru Lalitha Gummidi Surya Narayana Maddila Sandeep V.H.S. Bhaskaruni Sreekantha B. Jonnalagadda 《应用有机金属化学》2020,34(5):e5590
The bismuth loaded on fluorapatite (Bi2O3/FAp) proved to be an excellent catalyst for the synthesis of novel dihydro-[1,2,4]triazolo[1,5-a]pyrimidine derivatives via a three-component reaction involving the mixture of 1H-1,2,4-triazol-5-amine, ethyl cyanoacetate or ethyl acetoacetate, and different benzaldehydes in ethanol at room temperature. The catalyst material was characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, Fourier-transform infrared, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy techniques. The efficacy of Bi2O3/FAp as a heterogeneous catalyst was evaluated with the loading of different wt% of bismuth on FAp. The 2.5% bismuth on FAp performed extremely well as a catalyst with a high yield of products (92%–96%) in a short reaction time (25–35 min). The catalyst was recovered by simple filtration. It showed undiminished activity up to five runs. Simple work-up, room temperature reaction, short reaction time, high yields, no column chromatography, and good reusability of catalyst are the merits of the proposed protocol. In addition, this process offers 100% carbon efficiency and 98% atom economy with noteworthy fiscal and environmental benefits. 相似文献
6.
Rana Surjyakanta Varadwaj G. Bishwa Bidita Bhaskaruni Sandeep V. H. S. Jonnalagadda Sreekantha B. 《Research on Chemical Intermediates》2020,46(10):4465-4473
Research on Chemical Intermediates - We report the synthesis of 1, 5, 10 wt% cobalt oxide/reduced graphene oxide (CoO–RGO) composite materials by a simple solvothermal method. We assessed... 相似文献
7.
Megan Douglass Sean Hopkins Rashmi Pandey Priya Singha Megan Norman Hitesh Handa 《Macromolecular bioscience》2021,21(1)
The novel use of nanofibers as a physical barrier between blood and medical devices has allowed for modifiable, innovative surface coatings on devices ordinarily plagued by thrombosis, delayed healing, and chronic infection. In this study, the nitric oxide (NO) donor S‐nitrosoglutathione (GSNO) is blended with the biodegradable polymers polyhydroxybutyrate (PHB) and polylactic acid (PLA) for the fabrication of hemocompatible, antibacterial nanofibers tailored for blood‐contacting applications. Stress/strain behavior of different concentrations of PHB and PLA is recorded to optimize the mechanical properties of the nanofibers. Nanofibers incorporated with different concentrations of GSNO (10, 15, 20 wt%) are evaluated based on their NO‐releasing kinetics. PLA/PHB + 20 wt% GSNO nanofibers display the greatest NO release over 72 h (0.4–1.5 × 10?10 mol mg?1 min?1). NO‐releasing fibers successfully reduce viable adhered bacterial counts by ≈80% after 24 h of exposure to Staphylococcus aureus. NO‐releasing nanofibers exposed to porcine plasma reduce platelet adhesion by 64.6% compared to control nanofibers. The nanofibers are found noncytotoxic (>95% viability) toward NIH/3T3 mouse fibroblasts, and 4′,6‐diamidino‐2‐phenylindole and phalloidin staining shows that fibroblasts cultured on NO‐releasing fibers have improved cellular adhesion and functionality. Therefore, these novel NO‐releasing nanofibers provide a safe antimicrobial and hemocompatible coating for blood‐contacting medical devices. 相似文献
8.
Study of the forced degradation behavior of prasugrel hydrochloride by liquid chromatography with mass spectrometry and liquid chromatography with NMR detection and prediction of the toxicity of the characterized degradation products 下载免费PDF全文
Dilip Kumar Singh Archana Sahu Tarun Handa Mallikarjun Narayanam Saranjit Singh 《Journal of separation science》2015,38(17):2995-3005
Prasugrel was subjected to forced degradation studies under conditions of hydrolysis (acid, base, and neutral), photolysis, oxidation, and thermal stress. The drug showed liability in hydrolytic as well as oxidative conditions, resulting in a total of four degradation products. In order to characterize the latter, initially mass fragmentation pathway of the drug was established with the help of mass spectrometry/time‐of‐flight, multiple stage mass spectrometry and hydrogen/deuterium exchange data. The degradation products were then separated on a C18 column using a stability‐indicating volatile buffer method, which was later extended to liquid chromatography‐mass spectrometry studies. The latter highlighted that three degradation products had the same molecular mass, while one was different. To characterize all, their mass fragmentation pathways were established in the same manner as the drug. Subsequently, liquid chromatography‐nuclear magnetic resonance (NMR) spectroscopy data were collected. Proton and correlation liquid chromatography with NMR spectroscopy studies highlighted existence of diastereomeric behavior in one pair of degradation products. Lastly, toxicity prediction by computer‐assisted technology (TOPKAT) and deductive estimation of risk from existing knowledge (DEREK) software were employed to assess in silico toxicity of the characterized degradation products. 相似文献
9.
10.
Salahudeen Nurudeen Ahmed Abdulkarim S. Al-Muhtaseb Ala’a H. Dauda Mohammed Jibril Baba Y. Viswanadham Nagabhatla Saxena Sandeep K. 《Research on Chemical Intermediates》2017,43(1):467-479
Research on Chemical Intermediates - This study presents the synthesis of rare earth-doped Y (RE Y) zeolite, its application in formulation of a fluid catalytic cracking (FCC) catalyst and the... 相似文献