全文获取类型
收费全文 | 26352篇 |
免费 | 4591篇 |
国内免费 | 2816篇 |
专业分类
化学 | 17625篇 |
晶体学 | 250篇 |
力学 | 1868篇 |
综合类 | 217篇 |
数学 | 3411篇 |
物理学 | 10388篇 |
出版年
2024年 | 32篇 |
2023年 | 572篇 |
2022年 | 649篇 |
2021年 | 829篇 |
2020年 | 1089篇 |
2019年 | 1005篇 |
2018年 | 921篇 |
2017年 | 883篇 |
2016年 | 1287篇 |
2015年 | 1217篇 |
2014年 | 1470篇 |
2013年 | 1975篇 |
2012年 | 2370篇 |
2011年 | 2447篇 |
2010年 | 1640篇 |
2009年 | 1594篇 |
2008年 | 1740篇 |
2007年 | 1499篇 |
2006年 | 1373篇 |
2005年 | 1167篇 |
2004年 | 864篇 |
2003年 | 681篇 |
2002年 | 582篇 |
2001年 | 497篇 |
2000年 | 492篇 |
1999年 | 607篇 |
1998年 | 503篇 |
1997年 | 507篇 |
1996年 | 468篇 |
1995年 | 458篇 |
1994年 | 382篇 |
1993年 | 342篇 |
1992年 | 281篇 |
1991年 | 251篇 |
1990年 | 236篇 |
1989年 | 184篇 |
1988年 | 145篇 |
1987年 | 124篇 |
1986年 | 92篇 |
1985年 | 94篇 |
1984年 | 62篇 |
1983年 | 50篇 |
1982年 | 52篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1959年 | 1篇 |
1957年 | 7篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
102.
Namita Panda Mieon Kim Nobuyuki Aoki Zeyi Zhou Takuya Shimosaka Youngdoo Kim Sangil Lee Dalho Kim 《Accreditation and quality assurance》2016,21(4):295-304
A validation study for primary formaldehyde gas standards was performed at three National Metrology Institutes: the Korea Research Institute of Standards and Science (KRISS), the National Metrology Institute of Japan (NMIJ) and the National Institute of Metrology of China (NIM). The studied materials had a nominal amount fraction of 2 μmol/mol formaldehyde in nitrogen balance and were prepared in 10-L aluminum cylinders by KRISS. The impurities in the materials were analyzed using a gas chromatograph/atomic emission detector and a Fourier-transform infrared spectrometer (FTIR). The stability of the materials was assessed for 1 year by KRISS using paraformaldehyde as a source for the primary standard gas and a cavity ring-down spectrometer (CRDS) instrument as the measurement method. The amount fraction of formaldehyde in the materials decreased linearly by 0.74 % each month. The studied materials that exhibited similar linear rates of decline were distributed to the participants. After the measurement was completed by the participants, the materials were returned to KRISS and the stability analysis based on the primary standard maintained at KRISS was repeated. NMIJ analyzed the materials using paraformaldehyde as the source of the primary standard of formaldehyde and FTIR analysis, whereas NIM used trioxane as the primary standard gas source and CRDS analysis. The results of the comparison revealed good agreement between the results and were within the expanded uncertainty of 2 % although each of them used different combinations of methods in the generation of primary gas standards and measurements. 相似文献
103.
104.
Is PdII‐Promoted σ‐Bond Metathesis Mechanism Operative for the PdPEPPSI Complex‐Catalyzed Amination of Chlorobenzene with Aniline? Experiment and Theory 下载免费PDF全文
Feiqun Wang Lei Zhu Yunfei Zhou Prof. Xiaoguang Bao Prof. Henry F. Schaefer III 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):4153-4161
Reduction of the Pd?PEPPSI precatalyst to a Pd0 species is generally thought to be essential to drive Buchwald–Hartwig amination reactions through the well‐ documented Pd0/PdII catalytic cycle and little attention has been paid to other possible mechanisms. Considered here is the Pd?PEPPSI‐catalyzed aryl amination of chlorobenzene with aniline. A neat reaction system was used in new experiments, from which the potentially reductive roles of the solvent and labile ligand of the PEPPSI complex in leading to Pd0 species are ruled out. Computational results demonstrate that anilido‐containing PdII intermediates involving σ‐bond metathesis in pathways leading to the diphenylamine product have relatively low barriers. Such pathways are more favorable energetically than the corresponding reductive elimination reactions resulting in Pd0 species and other putative routes, such as the PdII/PdIV mechanism, single electron transfer mechanism, and halide atom transfer mechanism. In some special cases, if reactants/additives are inadequate to reduce a PdII precatalyst, a PdII‐involved σ‐bond metathesis mechanism might be feasible to drive the Buchwald–Hartwig amination reactions. 相似文献
105.
106.
107.
108.
Enhanced Peroxidase‐Like Properties of Graphene–Hemin‐Composite Decorated with Au Nanoflowers as Electrochemical Aptamer Biosensor for the Detection of K562 Leukemia Cancer Cells 下载免费PDF全文
Dr. Jing Liu Meirong Cui Dr. Li Niu Dr. Hong Zhou Prof. Dr. Shusheng Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18001-18008
Graphene composites with hemin and gold nanoparticles show a better performance for hydrogen peroxide decomposition compared to that of the three components alone or duplex/hybrid complexes. Our previous studies showed that the morphology of the Au nanoparticles may greatly influence the catalytic activity of graphene‐family peroxidase mimics. Recently, we found that Au nanoflowers could grow in situ and form on the surface of hemin/RGO (reduced graphene oxide). The prickly morphology of this Au nanoflower brought a higher catalytic ability with enhanced kinetic parameters than traditional Au nanoparticles that showed a smooth surface. Therefore, based on this discovery, a smart electrochemical aptamer biosensor for K562 leukemia cancer cells was further presented with good performance in selectivity and sensitivity attributed to the excellent mimetic peroxidase catalytic activity of this newly synthesized Au nanoflower decorated graphene–hemin composite (H‐RGO‐Au NFs). 相似文献
109.
Nonlinear Dynamics - Recently, COVID-19 has attracted a lot of attention of researchers from different fields. Wearing masks is a frequently adopted precautionary measure. In this paper, we... 相似文献