全文获取类型
收费全文 | 9124篇 |
免费 | 1484篇 |
国内免费 | 1147篇 |
专业分类
化学 | 6567篇 |
晶体学 | 85篇 |
力学 | 414篇 |
综合类 | 102篇 |
数学 | 1039篇 |
物理学 | 3548篇 |
出版年
2024年 | 15篇 |
2023年 | 194篇 |
2022年 | 213篇 |
2021年 | 303篇 |
2020年 | 390篇 |
2019年 | 381篇 |
2018年 | 310篇 |
2017年 | 311篇 |
2016年 | 430篇 |
2015年 | 427篇 |
2014年 | 522篇 |
2013年 | 641篇 |
2012年 | 843篇 |
2011年 | 829篇 |
2010年 | 550篇 |
2009年 | 494篇 |
2008年 | 635篇 |
2007年 | 610篇 |
2006年 | 499篇 |
2005年 | 448篇 |
2004年 | 306篇 |
2003年 | 251篇 |
2002年 | 237篇 |
2001年 | 212篇 |
2000年 | 223篇 |
1999年 | 190篇 |
1998年 | 175篇 |
1997年 | 146篇 |
1996年 | 161篇 |
1995年 | 146篇 |
1994年 | 109篇 |
1993年 | 100篇 |
1992年 | 80篇 |
1991年 | 61篇 |
1990年 | 63篇 |
1989年 | 40篇 |
1988年 | 38篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 34篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1962年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
建立了土壤中8种羟基化多溴联苯醚(Hydroxylated polybrominated diphenyl ethers,OH-PBDEs)的Qu ECh ERS-超高效液相色谱串联质谱(UPLC-MS/MS)分析方法。样品前处理采用Qu ECh ERS方法,土壤样品用水浸润之后,以甲酸和乙腈提取目标物,C18填料和正丙基乙二胺(PSA)净化,C18色谱柱分离,乙腈和水梯度洗脱,多反应监测负离子模式扫描。在最佳实验条件下,8种目标物在9 min内分离良好,并在2~200μg/L范围内线性良好,相关系数范围在0.9936~0.9990,检出限范围为0.23~1.21 ng/g。在5.0和50 ng/g 2个浓度水平6次平行加标实验中,8种OH-PBDEs平均回收率为73.2%~117.7%,相对标准偏差为5.6%~19.7%。本方法操作简便,灵敏度高,适用于大批量样品的快速分析。 相似文献
992.
993.
A simple and sensitive voltammetric sensor for esculetin, based on electrochemically reduced graphene oxide film modified glassy carbon electrode, was reported for the quantitative determination of esculetin in the Chinese traditional herbal drug Viola yedoensis Makino. Electrochemical impedance spectroscopy and scanning electron microscopy were employed to study the characteristic of the graphene oxide film. The electrochemical behavior of esculetin on this sensor was investigated in pH 3.0 phosphate buffer solution by cyclic voltammetry. Significant advantages were achieved by the excellent conductivity and the high surface‐to‐volume ratio of electrochemically reduced graphene oxide. A calibration plot of oxidation peak currents versus esculetin concentrations was linear in the range of 4.0 ξ 10‐8 mol L‐1 to 5.0 ξ 10‐6 mol L‐1 with a detection limit of 2.0 ξ 10‐8 mol L‐1. The practical application of the present sensor was demonstrated by determining the concentration of esculetin in real sample with no interference. 相似文献
994.
Shao‐Fu Yu Xiao‐Jun Huang Shu‐Na Fu Chun Wu Wen‐Cai Ye Guang‐Xiong Zhou 《Helvetica chimica acta》2015,98(9):1267-1272
One new lactone, cyclopentanepyrone A ( 1 ), and two new monoterpenoids, gardeterpenone A ( 2 ) and jasminoside V ( 3 ), were isolated from the fruits of Gardenia jasminoides var. radicans, along with four known monoterpenoids, 4 – 7 , which were isolated from this plant for the first time. The structures of the isolates were elucidated by extensive spectroscopic studies, including UV, IR, 1D‐ and 2D‐NMR, ESI‐MS, HR‐ESI‐MS, and CD experiments. 相似文献
995.
Facile Synthesis of the Pentasaccharide Repeating Unit of the Exopolysaccharide from Cryptococcus neoformans Serotype D 下载免费PDF全文
Sheng‐Jun Huang Jun Liao Hong‐Gang Hu Qing‐Jie Zhao Qiu‐Ye Wu 《Helvetica chimica acta》2015,98(5):618-626
β‐D ‐GlcpA‐(1→2)‐[β‐D ‐Xylp‐(1→2)‐α‐D ‐Manp‐(1→3)]‐α‐D ‐Manp‐(1→3)‐α‐D ‐Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serotype D, was synthesized as its 4‐methoxyphenyl glycoside. The approach presented here also provides a route to the synthesis of more complex repeating units of glucuconoxylomannan (GXM) of C. neoformans serotypes A–C. 相似文献
996.
997.
998.
Unexpectedly Simple Synthesis of Benzazoles by tBuONa‐Catalyzed Direct Aerobic Oxidative Cyclocondensation of o‐Thio/Hydroxy/Aminoanilines with Alcohols under Air 下载免费PDF全文
Xinkang Shi Junmei Guo Dr. Jianping Liu Prof. Mingde Ye Prof. Dr. Qing Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):9988-9993
tBuONa‐catalyzed direct aerobic oxidative cyclocondensation reactions of readily available alcohols and o‐thio/hydroxy/aminoanilines under air have been developed and provide an efficient, practical, and green method for the synthesis of benzazoles. Mechanistic studies revealed that o‐substituted anilines promote the initial aerobic alcohol‐oxidation step, which explains the high reactivity and success of this unexpectedly simple and practical cyclocondensation method. 相似文献
999.
Postfunctionalization of BN‐Embedded Polycyclic Aromatic Compounds for Fine‐Tuning of Their Molecular Properties 下载免费PDF全文
Dr. Xiao‐Ye Wang Dong‐Chu Yang Fang‐Dong Zhuang Jia‐Jie Liu Dr. Jie‐Yu Wang Prof. Jian Pei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(24):8867-8873
New BN‐embedded, thiophene‐fused, polycyclic aromatic compounds with planar geometry were designed and synthesized. The molecules showed excellent stability and chemical robustness. Postfunctionalization on this skeleton was demonstrated with a series of electrophilic bromination, palladium‐catalyzed cross‐coupling, and Knoevenagel condensation reactions. The π skeleton remained intact during these late‐stage transformations. The optical and electronic properties have been well tuned through incorporation of electron‐rich and ‐deficient groups on the backbone. This work shows the great advantage of the postfunctionalization strategy on BN‐containing polycyclic aromatic compounds for fast diversification and materials screening. 相似文献
1000.
Ai‐Hua Zhou Fei Pan Dr. Chunyin Zhu Prof. Dr. Long‐Wu Ye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(29):10278-10288
Fluorenes are a commonly encountered structural motif in materials science, pharmaceutical chemistry, and organic synthesis. Among various strategies towards the synthesis of this unique structure, transition metal‐catalyzed functionalization has emerged as one of the most efficient methods. This Minireview presents an overview of the recent advances in this emerging area by highlighting the reactions’ specificity and applicability and, where possible, provides a mechanistic rationale. 相似文献