全文获取类型
收费全文 | 5755篇 |
免费 | 1037篇 |
国内免费 | 566篇 |
专业分类
化学 | 3741篇 |
晶体学 | 53篇 |
力学 | 258篇 |
综合类 | 30篇 |
数学 | 746篇 |
物理学 | 2530篇 |
出版年
2024年 | 23篇 |
2023年 | 132篇 |
2022年 | 198篇 |
2021年 | 212篇 |
2020年 | 226篇 |
2019年 | 196篇 |
2018年 | 181篇 |
2017年 | 176篇 |
2016年 | 293篇 |
2015年 | 256篇 |
2014年 | 319篇 |
2013年 | 387篇 |
2012年 | 481篇 |
2011年 | 550篇 |
2010年 | 337篇 |
2009年 | 334篇 |
2008年 | 360篇 |
2007年 | 331篇 |
2006年 | 320篇 |
2005年 | 261篇 |
2004年 | 193篇 |
2003年 | 169篇 |
2002年 | 193篇 |
2001年 | 151篇 |
2000年 | 124篇 |
1999年 | 158篇 |
1998年 | 132篇 |
1997年 | 108篇 |
1996年 | 105篇 |
1995年 | 72篇 |
1994年 | 53篇 |
1993年 | 53篇 |
1992年 | 47篇 |
1991年 | 59篇 |
1990年 | 31篇 |
1989年 | 28篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7358条查询结果,搜索用时 0 毫秒
991.
In this work, photovoltaic properties of the PBDB-T:ITIC based-NF-PSCs were fully optimized and characterized by tuning the morphology of the active layers and changing the device architecture. First, donor/acceptor (D/A) weight ratios were scanned, and then further optimization was performed by using different additives, i.e. 1,8-diiodooctane (DIO), diphenyl ether (DPE), 1-chloronaphthalene (CN) and N-methyl-2-pyrrolidone (NMP), on the basis of best D/A ratio (1:1, w/w), respectively. Finally, the conventional or inverted device architectures with different buffer layers were employed to fabricate NF-PSC devices, and meanwhile, the morphology of the active layers was further optimized by controlling annealing temperature and time. As a result, a record efficiency of 11.3% was achieved, which is the highest result for NF-PSCs. It’s also remarkable that the inverted NF-PSCs exhibited long-term stability, i.e. the best-performing devices maintain 83% of their initial PCEs after over 4000 h storage. 相似文献
992.
993.
Chao Xie Qi-Meng Wu Ruo-Ning Li Gao-Chen Gu Xue Zhang Na Li Richard Berndt J rg Kr ger Zi-Yong Shen Shi-Min Hou Yong-Feng Wang 《中国化学快报》2016,27(6):807-812
To date, supramolecular chemistry is an ever growing research field owing to its crucial role in molecular catalysis, recognition, medicine, data storage and processing as well as artificial photosynthetic devices.Different isolated supramolecules were prepared by molecular self-assembly on surfaces. This review mainly focuses on supramolecular aggregations on noble metal surfaces studied by scanning tunneling microscopy, including dimers, trimers, tetramers, pentamers, wire-like assemblies and Sierpin′ ski triangular fractals. The variety of self-assembled structures reflects the subtle balance between intermolecular and molecule–substrate interactions, which to some extent may be controlled by molecules, substrates and the molecular coverage. The comparative study of different architectures helps identifying the operative mechanisms that lead to the structural motifs. The application of these mechanisms may lead to novel assemblies with tailored physicochemical properties. 相似文献
994.
995.
目的观察不同浓度高糖对小鼠足细胞活性的抑制作用,以及不同浓度雷公藤内酯醇(TP)和缬沙坦(Val)对高糖抑制后小鼠足细胞活性的影响,探讨高糖对足细胞的损伤作用,以及有效的药物干预浓度范围。方法将培养成熟的小鼠足细胞随机分为对照组(11.1mmol/L葡萄糖)和不同浓度高糖组(16.1、21.1、26.1、31.1、36.1mmol/L),以上述浓度培养48h后采用CCK-8检测足细胞活性的变化。取活性变化最大的浓度为高糖诱导浓度,在此基础上随机分为不同浓度的TP组(4、8、16、32、64ng/ml)和Val组(2×10-8、2×10-7、2×10-6、2×10-5、2×10-4mol/L),以上述浓度干预48h后,采用CCK-8检测足细胞活性的变化。结果(1)与对照组相比,除16.1mmol/L高糖组外,其余各高糖组的足细胞活性显著减少,其中以26.1mmol/L葡萄糖组减少最为明显(P<0.01)。(2)与26.1mmol/L葡萄糖组相比,TP组(除4ng/ml组外)和Val组(除2×10-8mol/L组外)足细胞活性部分恢复,其中以16ng/mlTP组和2×10-5mol/LVal组足细胞活性恢复最为明显(P<0.01)。结论一定浓度范围的TP和Val可部分恢复受高糖抑制的小鼠足细胞活性。 相似文献
996.
997.
998.
Synthesis of Lithium Boracarbonate Ion Pairs by Copper‐Catalyzed Multi‐Component Coupling of Carbon Dioxide,Diboron, and Aldehydes 下载免费PDF全文
Béatrice Carry Dr. Liang Zhang Dr. Masayoshi Nishiura Prof. Dr. Zhaomin Hou 《Angewandte Chemie (International ed. in English)》2016,55(21):6257-6260
The catalytic selective multi‐component coupling of CO2, bis(pinacolato)diboron, LiOtBu, and a wide range of aldehydes has been achieved for the first time by using an NHC‐copper catalyst. This transformation has efficiently afforded a series of novel lithium cyclic boracarbonate ion pair compounds in high yields from readily available starting materials. This protocol has not only provided a new catalytic process for the utilization of CO2, but it has also constituted a novel route for the efficient synthesis of a new class of lithium borate compounds that might be of interest as potential electrolyte candidates for lithium ion batteries. 相似文献
999.
Electrochemical C−H/N−H Functionalization for the Synthesis of Highly Functionalized (Aza)indoles 下载免费PDF全文
Zhong‐Wei Hou Zhong‐Yi Mao Huai‐Bo Zhao Yared Yohannes Melcamu Prof. Dr. Xin Lu Dr. Jinshuai Song Prof. Dr. Hai‐Chao Xu 《Angewandte Chemie (International ed. in English)》2016,55(32):9168-9172
Indoles and azaindoles are among the most important heterocycles because of their prevalence in nature and their broad utility in pharmaceutical industry. Reported herein is an unprecedented noble‐metal‐ and oxidant‐free electrochemical method for the coupling of (hetero)arylamines with tethered alkynes to synthesize highly functionalized indoles, as well as the more challenging azaindoles. 相似文献
1000.
Yang-Rong Xu Jing-Jing Yang Juan Liu Gui-Ge Hou Qing-Guo Meng 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(6):498-503
Ocotillol‐type saponins have a wide spectrum of biological activities. Previous studies indicated that the configuration at the C24 position may be responsible for their stereoselectivity in pharmacological action and pharmacokinetics. Natural ocotillol‐type saponins share a 20(S)‐form but it has been found that the 20(R)‐stereoisomers have different pharmacological effects. The semisynthesis of 20(R)‐ocotillol‐type saponins has not been reported and it is therefore worthwhile clarifying their crystal structures. Two C24 epimeric 20(R)‐ocotillol‐type saponins, namely (20R,24S)‐20,24‐epoxydammarane‐3β,12β,25‐triol, C30H52O4, (III), and (20R,24R)‐20,24‐epoxydammarane‐3β,12β,25‐triol monohydrate, C30H52O4·H2O, (IV), were synthesized, and their structures were elucidated by spectral studies and finally confirmed by single‐crystal X‐ray diffraction. The (Me)C—O—C—C(OH) torsion angle of (III) is 146.41 (14)°, whereas the corresponding torsion angle of (IV) is −146.4 (7)°, indicating a different conformation at the C24 position. The crystal stacking in (III) generates an R44(8) motif, through which the molecules are linked into a one‐dimensional double chain. The chains are linked via nonclassical C—H…O hydrogen bonds into a two‐dimensional network, and further stacked into a three‐dimensional structure. In contrast to (III), epimer (IV) crystallizes as a hydrate, in which the water molecules act as hydrogen‐bond donors linking one‐dimensional chains into a two‐dimensional network through intermolecular O—H…O hydrogen bonds. The hydrogen‐bonded chains extend helically along the crystallographic a axis and generate a C44(8) motif. 相似文献