全文获取类型
收费全文 | 46177篇 |
免费 | 18144篇 |
国内免费 | 66篇 |
专业分类
化学 | 57560篇 |
晶体学 | 58篇 |
力学 | 2095篇 |
数学 | 3153篇 |
物理学 | 1521篇 |
出版年
2024年 | 157篇 |
2023年 | 4084篇 |
2022年 | 1439篇 |
2021年 | 2489篇 |
2020年 | 4639篇 |
2019年 | 2334篇 |
2018年 | 2293篇 |
2017年 | 611篇 |
2016年 | 5641篇 |
2015年 | 5566篇 |
2014年 | 4992篇 |
2013年 | 5234篇 |
2012年 | 3325篇 |
2011年 | 1257篇 |
2010年 | 3490篇 |
2009年 | 3443篇 |
2008年 | 1222篇 |
2007年 | 919篇 |
2006年 | 291篇 |
2005年 | 244篇 |
2004年 | 225篇 |
2003年 | 164篇 |
2002年 | 150篇 |
1997年 | 144篇 |
1996年 | 131篇 |
1995年 | 197篇 |
1994年 | 154篇 |
1993年 | 274篇 |
1992年 | 134篇 |
1988年 | 168篇 |
1987年 | 136篇 |
1985年 | 150篇 |
1984年 | 143篇 |
1983年 | 142篇 |
1982年 | 168篇 |
1981年 | 203篇 |
1980年 | 225篇 |
1979年 | 212篇 |
1978年 | 210篇 |
1977年 | 332篇 |
1976年 | 393篇 |
1975年 | 482篇 |
1974年 | 490篇 |
1973年 | 305篇 |
1972年 | 376篇 |
1971年 | 372篇 |
1970年 | 553篇 |
1969年 | 422篇 |
1968年 | 462篇 |
1967年 | 129篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
992.
993.
994.
Metal‐pernitride compounds belong to a class of chemical systems in which both the complex ions and the non‐bonding electrons may play roles in the formation of their modified crystalline structures. To investigate this issue, the energy landscapes of pernitrides of metals with different maximum valence (M=Ca, Sr, Ba, La, and Ti) were globally explored on the ab initio level at standard and high pressures, thereby yielding possible (meta)stable modifications in these systems together with information on how the landscape changed as function of the valence of the metal cation. For all of the systems in which no compounds had been synthesized so far, we predicted the existence of kinetically stable modifications that should, in principle, be experimentally accessible. In particular, TiN2 should crystallize in a new structure type, TiN2‐I. 相似文献
995.
Asymmetric Michael Addition of Aldimino Esters with Chalcones Catalyzed by Silver/Xing‐Phos: Mechanism‐Oriented Divergent Synthesis of Chiral Pyrrolines 下载免费PDF全文
Xing‐Feng Bai Dr. Li Li Dr. Zheng Xu Dr. Zhan‐Jiang Zheng Prof. Dr. Chun‐Gu Xia Dr. Yu‐Ming Cui Prof. Dr. Li‐Wen Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10399-10404
The mechanism‐oriented reaction design for the divergent synthesis of chiral molecules from simple starting materials is highly desirable. In this work, aromatic amide‐derived nonbiarylatropisomer/silver (silver/Xing‐Phos) complex was used to catalyze the Michael addition of glycine aldimino esters to chalcones and successfully applied to the subsequent cyclocondensation to afford substituted cis‐Δ(1)‐pyrroline derivatives with up to 98 % ee. Besides the inherent performance of the chiral Ag/Xing‐Phos catalyst system, it was found that the workup of such reactions played an important role for the stereoselective construction of stereodivergent Δ(1)‐pyrrolines, in which an epimerization of the cis‐Δ(1)‐pyrrolines to the trans‐isomers during was revealed. 相似文献
996.
A Phosphorescent Platinum(II) Bipyridyl Supramolecular Polymer Based on Quadruple Hydrogen Bonds 下载免费PDF全文
Fang‐Wei Liu Dr. Li‐Ya Niu Prof. Yong Chen Prof. Vaidhyanathan Ramamurthy Prof. Li‐Zhu Wu Prof. Chen‐Ho Tung Prof. Yu‐Zhe Chen Prof. Qing‐Zheng Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18132-18139
A platinum(II) bipyridyl complex bearing bis‐ureidopyrimidinone (Pt‐bisUPy) has been designed and its self‐assembling behavior has been thoroughly investigated by 1H NMR, DOSY NMR, Ubbelohde viscometry analysis, UV/Vis, and emission spectroscopies. Pt‐bisUPy underwent concentration‐dependent ring‐chain polymerization in apolar solvents. Hydrogen‐bonding interactions play an important role during the formation of the supramolecular polymers. Hydrogen‐bonded supramolecular polymers were transformed to nanoparticles in water through the miniemulsion method. These nanoparticles showed strong π–π excimeric emission. Metal‐metal‐to‐ligand charge transfer (MMLCT) from Pt–Pt interactions was not significant in the emission spectrum. The phosphorescence of the nanoparticle persisted even under aerobic conditions. The triplet state of these phosphorescent nanomaterials were long‐lived and possessed moderate emission quantum yields. Furthermore, the low toxicity of these materials promises a place for them in in vitro and in vivo bioimaging. 相似文献
997.
Fluorinated Musk Fragrances: The CF2 Group as a Conformational Bias Influencing the Odour of Civetone and (R)‐Muscone 下载免费PDF全文
Dr. Ricardo Callejo Dr. Michael J. Corr Mingyan Yang Prof. Mingan Wang Dr. David B. Cordes Prof. Alexandra M. Z. Slawin Prof. David O'Hagan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(24):8137-8151
The difluoromethylene (CF2) group has a strong tendency to adopt corner over edge locations in aliphatic macrocycles. In this study, the CF2 group has been introduced into musk relevant macrocyclic ketones. Nine civetone and five muscone analogues have been prepared by synthesis for structure and odour comparisons. X‐ray studies indeed show that the CF2 groups influence ring structure and they give some insight into the preferred ring conformations, triggering a musk odour as determined in a professional perfumery environment. The historical conformational model of Bersuker and co‐workers for musk fragrance generally holds, and structures that become distorted from this consensus, by the particular placement of the CF2 groups, lose their musk fragrance and become less pleasant. 相似文献
998.
999.
Inside Back Cover: Synthesis and Isolation of the Titanium–Scandium Endohedral Fullerenes—Sc2TiC@Ih‐C80, Sc2TiC@D5h‐C80 and Sc2TiC2@Ih‐C80: Metal Size Tuning of the TiIV/TiIII Redox Potentials (Chem. Eur. J. 37/2016) 下载免费PDF全文
1000.
Mixed Polymer‐Coated Magnetic Nanoparticles as Forward Osmosis Draw Agents of Tuned Hydrophilicity 下载免费PDF全文
Dr. Priyanka Dey Dr. Emad L. Izake 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11253-11260
We recently reported a polymer‐coated magnetic nanoparticle (MNP) draw agent for the forward osmosis (FO) water desalination process. The water flux was found to increase when the polymer poly(sodium acrylate) (PSA) was anchored to the MNP surface as compared to the polymer (or polyelectrolyte solution) alone, due to the polymer chains being stretched out and most of the hydrophilic groups on the polymer contributing to water flux. We herein report the use of a secondary polymer poly(N‐isopropylacrylamide) PNIPAM to manipulate the PSA polymer conformation and influence inter‐ and intrachain interactions to enhance the efficiency of the FO draw agent. These PSA–PNIPAM‐coated MNPs generated a much higher water flux of ~11.66 LMH when compared to the 100 % PSA‐coated MNPs featuring a value of ~5.32 LMH under identical FO conditions. The osmotic pressure and water flux driven by the mixed polymer‐coated MNPs were found to be a strong function of the net polymer coverage on MNPs, that is, net available hydrophilic groups. Our new draw agent demonstrates potential for use in the water industry due to its improved efficiency and cost effectiveness as it uses only ~0.062 % (w/v) of the draw agent solution. 相似文献