全文获取类型
收费全文 | 28045篇 |
免费 | 3328篇 |
国内免费 | 1769篇 |
专业分类
化学 | 19344篇 |
晶体学 | 235篇 |
力学 | 167篇 |
综合类 | 71篇 |
数学 | 59篇 |
物理学 | 13266篇 |
出版年
2024年 | 40篇 |
2023年 | 201篇 |
2022年 | 675篇 |
2021年 | 763篇 |
2020年 | 881篇 |
2019年 | 845篇 |
2018年 | 721篇 |
2017年 | 844篇 |
2016年 | 1341篇 |
2015年 | 1287篇 |
2014年 | 1362篇 |
2013年 | 2355篇 |
2012年 | 1713篇 |
2011年 | 1876篇 |
2010年 | 1555篇 |
2009年 | 1988篇 |
2008年 | 1865篇 |
2007年 | 1978篇 |
2006年 | 1810篇 |
2005年 | 1443篇 |
2004年 | 1245篇 |
2003年 | 1044篇 |
2002年 | 814篇 |
2001年 | 654篇 |
2000年 | 585篇 |
1999年 | 528篇 |
1998年 | 451篇 |
1997年 | 399篇 |
1996年 | 337篇 |
1995年 | 276篇 |
1994年 | 214篇 |
1993年 | 194篇 |
1992年 | 155篇 |
1991年 | 121篇 |
1990年 | 79篇 |
1989年 | 69篇 |
1988年 | 116篇 |
1987年 | 59篇 |
1986年 | 35篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 9篇 |
1982年 | 28篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1976年 | 8篇 |
1973年 | 10篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Solid state NMR spectroscopy is swiftly emerging as useful tool to characterize the structure, composition and dynamic properties of lead halide perovskites. On the other hand, interpretation of solid state NMR signatures is often challenging, because of the potential presence of many overlapping signals in small range of chemical shifts, hence complicating the extraction of detailed structural features. Here, we demonstrate the reliability of periodic Density Functional Theory in providing theoretical support for the NMR characterization of halide perovskite compounds, considering nuclei with spin I=1/2. For light 1H and 13C nuclei, we predict NMR chemical shifts in good agreement with experiment, further highlighting the effects of motional narrowing. Accurate prediction of the NMR response of 207Pb nuclei is comparably more challenging, but we successfully reproduce the downshift in frequency when changing the halide composition from pure iodine to pure bromine. Furthermore, we confirm NMR as ideal tool to study mixed halide perovskite compounds, currently at the limelight for tandem solar cells and color-tunable light emission. 相似文献
982.
Dr. Nicoló Zuin Fantoni Dr. Zara Molphy Sinéad O'Carroll Dr. Georgia Menounou Dr. George Mitrikas Dr. Marios G. Krokidis Dr. Chryssostomos Chatgilialoglu Dr. John Colleran Dr. Anna Banasiak Prof. Martin Clynes Dr. Sandra Roche Suainibhe Kelly Prof. Vickie McKee Prof. Andrew Kellett 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):971-983
We report a series of copper(II) artificial metallo-nucleases (AMNs) and demonstrate their DNA damaging properties and in-vitro cytotoxicity against human-derived pancreatic cancer cells. The compounds combine a tris-chelating polypyridyl ligand, di-(2-pycolyl)amine (DPA), and a DNA intercalating phenanthrene unit. Their general formula is Cu-DPA-N,N' (where N,N'=1,10-phenanthroline (Phen), dipyridoquinoxaline (DPQ) or dipyridophenazine (DPPZ)). Characterisation was achieved by X-ray crystallography and continuous-wave EPR (cw-EPR), hyperfine sublevel correlation (HYSCORE) and Davies electron-nuclear double resonance (ENDOR) spectroscopies. The presence of the DPA ligand enhances solution stability and facilitates enhanced DNA recognition with apparent binding constants (Kapp) rising from 105 to 107 m −1 with increasing extent of planar phenanthrene. Cu-DPA-DPPZ, the complex with greatest DNA binding and intercalation effects, recognises the minor groove of guanine–cytosine (G-C) rich sequences. Oxidative DNA damage also occurs in the minor groove and can be inhibited by superoxide and hydroxyl radical trapping agents. The complexes, particularly Cu-DPA-DPPZ, display promising anticancer activity against human pancreatic tumour cells with in-vitro results surpassing the clinical platinum(II) drug oxaliplatin. 相似文献
983.
Absorption spectrum of NbN has been obtained in the 560–670 nm region by intracavity laser spectroscopy. Vibrational and rotational analyses of 3φ - 3Δ transition has been caried out. Molecular constants for the upper (3φ) and ground (3Δ) states have been determined. 相似文献
984.
985.
986.
987.
988.
989.
Jianhuai Ye Dr. Sayaka Hatano Prof. Dr. Manabu Abe Prof. Dr. Ryohei Kishi Yusuke Murata Prof. Dr. Masayoshi Nakano Prof. Dr. Waldemar Adam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(7):2299-2306
In the photochemical denitrogenation of 1,4‐diaryl‐2,3‐diazabicyclo[2.2.1]heptane ( AZ6 ) bearing sterically hindered substituents, a curious new absorption band at about 450 nm was observed under low‐temperature matrix conditions, together with the previously well‐characterized planar singlet diradical pl‐1 DR6 with λmax=≈580 nm. The 450 nm species was electron paramagnetic resonance (EPR)‐silent. Instead of generating the planar diradical pl‐1 DR6 and the precursor azoalkane AZ6 upon warming, the ring‐closed bicyclo[2.1.0]pentane derivative SB6 , that is, the AZ6 denitrogenation product was identified. Based on product analysis, low‐temperature spectroscopic observations, high‐level quantum‐mechanical computations, viscosity effect, and laser‐flash photolysis, the puckered singlet diradicaloid puc‐1 DR6 was assigned to the new 450 nm absorption. The latter was detected experimentally at the same time as the planar singlet diradical pl‐1 DR6 . Sterically demanding substituents as well as viscosity impediments were essential for the detection of the experimentally hitherto unknown puckered singlet cyclopentane‐1,3‐diyl diradicaloid puc‐1 DR6 , that is, the third isomer in homolysis. The present findings should stimulate future work on the mechanistically fascinating stereoselectivity documented in the formation of bicyclo[2.1.0]pentanes during the 2,3‐diazabicyclo[2.2.1]heptane denitrogenation. 相似文献
990.
Copolymer composition, distribution and molecular size of the comonomer influence the final properties of polymer materials. Such influence can be followed from the effect on the chain conformation in solution determined from the scaling law between radius of gyration and molecular weight. 相似文献