全文获取类型
收费全文 | 103954篇 |
免费 | 5360篇 |
国内免费 | 3982篇 |
专业分类
化学 | 44415篇 |
晶体学 | 1109篇 |
力学 | 8135篇 |
综合类 | 273篇 |
数学 | 34714篇 |
物理学 | 24650篇 |
出版年
2024年 | 54篇 |
2023年 | 530篇 |
2022年 | 609篇 |
2021年 | 874篇 |
2020年 | 1185篇 |
2019年 | 1240篇 |
2018年 | 11189篇 |
2017年 | 10904篇 |
2016年 | 7354篇 |
2015年 | 2266篇 |
2014年 | 1915篇 |
2013年 | 2373篇 |
2012年 | 6229篇 |
2011年 | 12789篇 |
2010年 | 7329篇 |
2009年 | 7658篇 |
2008年 | 8366篇 |
2007年 | 10315篇 |
2006年 | 1732篇 |
2005年 | 2589篇 |
2004年 | 2635篇 |
2003年 | 2920篇 |
2002年 | 2105篇 |
2001年 | 1188篇 |
2000年 | 918篇 |
1999年 | 713篇 |
1998年 | 586篇 |
1997年 | 512篇 |
1996年 | 538篇 |
1995年 | 384篇 |
1994年 | 299篇 |
1993年 | 274篇 |
1992年 | 225篇 |
1991年 | 222篇 |
1990年 | 209篇 |
1989年 | 164篇 |
1988年 | 134篇 |
1987年 | 107篇 |
1986年 | 128篇 |
1985年 | 101篇 |
1984年 | 86篇 |
1983年 | 64篇 |
1982年 | 57篇 |
1981年 | 53篇 |
1980年 | 63篇 |
1979年 | 57篇 |
1978年 | 57篇 |
1914年 | 45篇 |
1913年 | 42篇 |
1909年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
41.
42.
Facile fabrication of fast recyclable and multiple self‐healing epoxy materials through diels‐alder adduct cross‐linker 下载免费PDF全文
Xiao Kuang Guoming Liu Xia Dong Xianggui Liu Jianjun Xu Dujin Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(18):2094-2103
A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2094–2103 相似文献
43.
44.
Jinke Bai Linfeng Wang Wenyong Chen Xiao Jin Qinghua Li Yuxiao Wang Xueru Zhang Yinglin Song 《Particle & Particle Systems Characterization》2020,37(8):2000115
Device grade quantum dots (QDs) require QDs ensembles to retain their original superior optical properties as in solution. QDs with thick shells are proven effective in suppressing the inter-dot interaction and preserving the emission properties for QDs solids. However, lattice strain–induced defects may form as the shell grows thicker, resulting in a notable photoluminescence quenching. Herein, a well-type CdxZn1−xS/CdSe/CdyZn1−yS QDs is proposed, where ternary alloys CdZnS are adopted to match the lattice parameter of intermediate CdSe by separately adjusting the x and y parameters. The resultant thick-shell Cd0.5Zn0.5S/CdSe/Cd0.73Zn0.27S QDs reveal nonblinking properties with a high PL QY of 99% in solution and 87% in film. The optimized quantum dot light-emitting diodes (QLEDs) exhibit a luminance of 31547.5 cd m−2 at the external quantum efficiency maximum of 21.2% under a bias of 4.0 V. The shell thickness shows great impact on the degradation of the devices. The T50 lifetime of the QLEDs with 11.2 nm QDs reaches 251 493 h, which is much higher than that of 6.5 and 8.4 nm QDs counterparts. The performances of the well-type thick-shell QLEDs are comparable to state-of-the-art devices, suggesting that this type of QDs is a promising candidate for efficient optoelectronic devices. 相似文献
45.
46.
47.
Xiao Sun Li Zhang Yu Cao Jinhua Li Atanas G. Atanasov Linfang Huang 《Biomedical chromatography : BMC》2020,34(12):e4949
Balanophora involucrata J. D. Hooker has been known to possess potential anti-inflammatory and antibacterial activities; however, its antiviral activity has not been evaluated so far. In order to find new neuraminidase inhibitors (NAIs), the neuraminidase (NA) inhibition activity of different B. involucrata extracts was evaluated. In this study, an in vitro NA inhibition assay was performed to identify which extract of B. involucrata exhibits (maximal) inhibitory activity against NA. Ultra high performance liquid chromatography/quadrupole time-of-flight–tandem mass spectroscopy (MS/MS) and molecular docking techniques were used to identify the specific compounds responsible for the anti-influenza activity of the extract, and to explore the potential natural NAIs. The ethyl acetate extract of B. involucrata exhibited significant inhibitory activity against NA with 50% inhibitory concentration (IC50) value of 159.5 μg/mL. Twenty compounds were identified according to the MS/MS spectra; among them two compounds (quercitrin and phloridzin) showed obvious inhibitory activity against NA, with IC50 of 311.76 and 347.32 μmol/L, respectively. This study suggested that B. involucrata can be a potential natural source of NAIs and may be useful in the fight against ferocious influenza viruses. 相似文献
48.
49.
Thomas Wittmann Dr. Renée Siegel Nele Reimer Dr. Wolfgang Milius Prof. Dr. Norbert Stock Prof. Dr. Jürgen Senker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):314-323
The resistance of metal–organic frameworks towards water is a very critical issue concerning their practical use. Recently, it was shown for microporous MOFs that the water stability could be increased by introducing hydrophobic pendant groups. Here, we demonstrate a remarkable stabilisation of the mesoporous MOF Al‐MIL‐101‐NH2 by postsynthetic modification with phenyl isocyanate. In this process 86 % of the amino groups were converted into phenylurea units. As a consequence, the long‐term stability of Al‐MIL‐101‐URPh in liquid water could be extended beyond a week. In water saturated atmospheres Al‐MIL‐101‐URPh decomposed at least 12‐times slower than the unfunctionalised analogue. To study the underlying processes both materials were characterised by Ar, N2 and H2O sorption measurements, powder X‐ray diffraction, thermogravimetric and chemical analysis as well as solid‐state NMR and IR spectroscopy. Postsynthetic modification decreased the BET equivalent surface area from 3363 to 1555 m2 g?1 for Al‐MIL‐101‐URPh and reduced the mean diameters of the mesopores by 0.6 nm without degrading the structure significantly and reducing thermal stability. In spite of similar water uptake capacities, the relative humidity‐dependent uptake of Al‐MIL‐101‐URPh is slowed and occurs at higher relative humidity values. In combination with 1H‐27Al D ‐HMQC NMR spectroscopy experiments this favours a shielding mechanism of the Al clusters by the pendant phenyl groups and rules out pore blocking. 相似文献
50.