全文获取类型
收费全文 | 77616篇 |
免费 | 334篇 |
国内免费 | 374篇 |
专业分类
化学 | 23890篇 |
晶体学 | 787篇 |
力学 | 6719篇 |
数学 | 31939篇 |
物理学 | 14989篇 |
出版年
2018年 | 10431篇 |
2017年 | 10259篇 |
2016年 | 6050篇 |
2015年 | 834篇 |
2014年 | 280篇 |
2013年 | 297篇 |
2012年 | 3750篇 |
2011年 | 10471篇 |
2010年 | 5613篇 |
2009年 | 6026篇 |
2008年 | 6566篇 |
2007年 | 8728篇 |
2006年 | 197篇 |
2005年 | 1281篇 |
2004年 | 1508篇 |
2003年 | 1953篇 |
2002年 | 998篇 |
2001年 | 239篇 |
2000年 | 284篇 |
1999年 | 149篇 |
1998年 | 189篇 |
1997年 | 142篇 |
1996年 | 194篇 |
1995年 | 114篇 |
1994年 | 74篇 |
1993年 | 92篇 |
1992年 | 52篇 |
1991年 | 62篇 |
1990年 | 49篇 |
1989年 | 58篇 |
1988年 | 58篇 |
1987年 | 57篇 |
1986年 | 57篇 |
1985年 | 46篇 |
1984年 | 42篇 |
1983年 | 36篇 |
1982年 | 41篇 |
1981年 | 38篇 |
1980年 | 46篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1973年 | 25篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1910年 | 24篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 136 毫秒
101.
We prove Schauder estimates for solutions to both divergence and non-divergence type higher-order parabolic systems in the whole space and a half space. We also provide an existence result for the divergence type systems in a cylindrical domain. All coefficients are assumed to be only measurable in the time variable and Hölder continuous in the spatial variables. 相似文献
102.
103.
104.
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
105.
106.
107.
Kätlin Kaare Ivar Kruusenberg Maido Merisalu Leonard Matisen Väino Sammelselg Kaido Tammeveski 《Journal of Solid State Electrochemistry》2016,20(4):921-929
Manganese phthalocyanine (MnPc) and copper phthalocyanine (CuPc)-modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) as a support material. The catalyst materials were heat treated at four different temperatures to investigate the effect of pyrolysis on the oxygen reduction reaction (ORR) activity of these electrocatalysts. The MWCNT to metal phthalocyanine ratio was varied. Scanning electron microscopy (SEM) was employed to visualise the surface morphology of the electrodes and the x-ray photoelectron spectroscopic (XPS) study was carried out to analyse the surface composition of the most active catalyst materials. The ORR was studied in 0.1 M KOH solution employing the rotating disk electrode (RDE) method. Glassy carbon (GC) electrodes were modified with carbon nanotube-supported metal phthalocyanine catalysts using Tokuyama AS-4 ionomer. The RDE results revealed that the highest electrocatalytic activity for ORR was achieved upon heat treatment at 800 °C. CuPc-derived catalyst demonstrated lower catalytic activity as compared to the MnPc-derived counterpart, which is in good agreement with previous literature, whereas the activity of MnPc-based catalyst was higher than that reported earlier. 相似文献
108.
109.
110.