全文获取类型
收费全文 | 8229篇 |
免费 | 1294篇 |
国内免费 | 1442篇 |
专业分类
化学 | 6682篇 |
晶体学 | 192篇 |
力学 | 404篇 |
综合类 | 117篇 |
数学 | 858篇 |
物理学 | 2712篇 |
出版年
2024年 | 14篇 |
2023年 | 110篇 |
2022年 | 257篇 |
2021年 | 304篇 |
2020年 | 360篇 |
2019年 | 399篇 |
2018年 | 319篇 |
2017年 | 308篇 |
2016年 | 437篇 |
2015年 | 460篇 |
2014年 | 545篇 |
2013年 | 669篇 |
2012年 | 754篇 |
2011年 | 797篇 |
2010年 | 584篇 |
2009年 | 622篇 |
2008年 | 621篇 |
2007年 | 572篇 |
2006年 | 457篇 |
2005年 | 425篇 |
2004年 | 356篇 |
2003年 | 236篇 |
2002年 | 264篇 |
2001年 | 198篇 |
2000年 | 147篇 |
1999年 | 166篇 |
1998年 | 114篇 |
1997年 | 92篇 |
1996年 | 90篇 |
1995年 | 58篇 |
1994年 | 54篇 |
1993年 | 39篇 |
1992年 | 29篇 |
1991年 | 16篇 |
1990年 | 23篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1973年 | 2篇 |
1959年 | 1篇 |
1935年 | 1篇 |
1909年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
制备了导电高分子聚苯胺与活性炭的复合载体(PAnC),用PAnC作为载体制备的钯催化剂性能优于单独活性炭作为载体制备的催化剂。此外掺杂十二烷基磺酸钠制备的聚苯胺碳载体(PAnC-S)具有比PAnC更低的电荷传递电阻,10~25 nm的介孔数量明显增加,比表面积增大到94.9 m2/g。PAnC-S与PAnC粒径均匀,粒径均在30 nm左右。以PAnC-S和 PAnC为载体制备的钯催化剂比活性炭作载体制备的钯催化剂具有更大的电化学比表面积,分别为84.7和62.6 m2/g。对甲酸的氧化具有更高的电化学活性和稳定性。 相似文献
972.
Hong-Tao Fan Yan Lu Ai-Juan Liu Bing Jiang Hua Shen Cong-Cong Huang Wen-Xiu Li 《Analytica chimica acta》2015
A diffusive gradients in thin films (DGT) device for the analysis of free Cd(II) species, based on Cd(II) ion-imprinted sorbent (IIS) as the binding agents and commercial polyethersulfone membrane (PES) as diffusion layer, was developed (PES/IIS-DGT). DGT time-series experiments showed that the mass of free Cd(II) species accumulated by PES/IIS-DGT was linear vs. time (R2 = 0.9953) and the concentration of free Cd(II) species by PES/IIS-DGT was in good agreement with the total dissolved concentrations of free Cd(II) species in simple synthetic solutions where free ionic species dominated. PES/IIS-DGT performance was independent in the range of pH 4.5–7.5 and ionic strength range from 1.0 × 10−3 to 0.7 mol L−1. The measurement of free Cd(II) species in synthetic solution containing different concentrations of ligands by PES/IIS-DGT showed an excellent agreement with the value measured by Cd(II) ion selective electrodes (Cd-ISE), indicating that PES/IIS-DGT method is more suitable than Cd-ISE for the measurement of low concentration of free Cd(II) species due to the enrichment of IIS for the analytes. 相似文献
973.
In this work, a novel sandwich-type electrochemical immunosensor based on host-guest interaction was fabricated for the detection of alpha-fetoprotein (AFP). Due to the large specific surface area of multiwalled carbon nanotubes and the unique supramolecular recognition ability of β-cyclodextrins, ferrocenecarboxylic acid (Fc) was incorporated into this sensor platform by host-guest interaction to generate an electrochemical signal. And β-cyclodextrins functionalized silver supported adamantine-modified glucose oxidase (GOD-CD-Ag), was used as a label to improve the analytical performance of the immunosensor by the dual amplification strategy. The obtained GOD-CD-Ag conjugates could convert glucose into gluconic acid with the formation of hydrogen peroxide (H2O2). And then silver nanoparticles could in situ catalyze the reduction of the generated H2O2, dramatically improving the oxidation reaction of Fc. The developed immunosensor shows a wide linear calibration range from 0.001 to 5.0 ng/mL with a low detection limit (0.2 pg/mL) for the detection of AFP. The method, with ideal reproducibility and selectivity, has a wide application prospect in clinical research. 相似文献
974.
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
975.
976.
高效液相色谱串联质谱法测定玉米及植株中胺唑草酮及其代谢物 总被引:1,自引:0,他引:1
建立了同时测定玉米及玉米植株中胺唑草酮及其两个代谢物残留量的液相色谱串联质谱分析方法.样品采用乙腈提取,石墨化炭黑(GCB)和C18分散固相萃取净化,以甲醇-5 mmol/L乙酸铵溶液为流动相,液相色谱串联质谱分析测定.在1 ~ 1000 μg/L的浓度范围内,3种目标化合物的响应值与浓度呈良好的线性关系,在3个添加水平下,玉米籽粒及植株中胺唑草酮及其代谢物的平均添加回收率为85%~111%,相对标准偏差(RSD)为2.3%~11.0%.方法定量限(LOQ)为5μg/kg.采用本方法监测15例市售玉米样品,样品中目标物均低于方法检出限.本方法简单,快速,灵敏度高,可完全满足国外胺唑草酮相关现行法规的限量要求. 相似文献
977.
Guapsidial A and Guadials B and C: Three New Meroterpenoids with Unusual Skeletons from the Leaves of Psidium guajava
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yu‐Qing Jian Dr. Xiao‐Jun Huang Dr. Dong‐Mei Zhang Prof. Dr. Ren‐Wang Jiang Min‐Feng Chen Dr. Bing‐Xin Zhao Prof. Dr. Ying Wang Prof. Dr. Wen‐Cai Ye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9022-9027
A novel sesquiterpene‐based Psidium meroterpenoid, possessing an unusual coupling pattern, and two new monoterpene‐based meroterpenoids with unprecedented skeletons were isolated from the leaves of Psidium guajava. Their structures and absolute configurations were elucidated by spectroscopic, X‐ray diffraction, and computational methods. The plausible biosynthetic pathway of these meroterpenoids as well as their cytotoxicities toward HepG2 and HepG2/ADM cells were also discussed. 相似文献
978.
A Convenient Palladium‐Catalyzed Carbonylative Suzuki Coupling of Aryl Halides with Formic Acid as the Carbon Monoxide Source
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Xinxin Qi Li‐Bing Jiang Hao‐Peng Li Prof. Dr. Xiao‐Feng Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17650-17656
A practical palladium‐catalyzed carbonylative Suzuki coupling of aryl halides under carbon monoxide gas‐free conditions has been developed. Here, formic acid was utilized as the carbon monoxide source for the first time with acetic anhydride as the additive. A variety of diarylketones were produced in moderate to excellent yields from the corresponding aryl halides and arylboronic acids. 相似文献
979.
980.
采用超高效液相色谱法同时测定脐橙中的橘红2号和苏丹红染料。样品经乙腈超声提取,氨基固相萃取小柱净化后,用Waters ACQUITY UPLC BEH C18色谱柱分离,以乙腈-水为流动相进行梯度洗脱,采用二极管阵列检测器检测,检测波长分别为478 nm和515 nm。5种染料的质量浓度在0.20~20 mg·L-1范围内呈线性,检出限(3S/N)在0.31~0.53μg·kg-1之间。加标回收率在87.8%~99.4%之间,测定值的相对标准偏差(n=5)在0.54%~3.1%之间。 相似文献