首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   875篇
  免费   53篇
  国内免费   5篇
化学   590篇
力学   16篇
数学   143篇
物理学   184篇
  2023年   9篇
  2022年   11篇
  2021年   7篇
  2020年   18篇
  2019年   21篇
  2018年   8篇
  2017年   13篇
  2016年   41篇
  2015年   31篇
  2014年   32篇
  2013年   55篇
  2012年   49篇
  2011年   76篇
  2010年   37篇
  2009年   43篇
  2008年   52篇
  2007年   26篇
  2006年   40篇
  2005年   31篇
  2004年   34篇
  2003年   26篇
  2002年   16篇
  2001年   11篇
  2000年   11篇
  1998年   9篇
  1997年   7篇
  1996年   10篇
  1995年   7篇
  1993年   5篇
  1992年   6篇
  1989年   5篇
  1988年   6篇
  1987年   9篇
  1986年   6篇
  1985年   7篇
  1984年   4篇
  1983年   7篇
  1982年   5篇
  1980年   5篇
  1978年   5篇
  1977年   11篇
  1976年   9篇
  1975年   6篇
  1934年   4篇
  1927年   4篇
  1926年   7篇
  1925年   5篇
  1924年   4篇
  1923年   6篇
  1899年   4篇
排序方式: 共有933条查询结果,搜索用时 15 毫秒
1.
While titanium‐based metal–organic frameworks (MOFs) have been widely studied for their (photo)catalytic potential, only a few TiIV MOFs have been reported owing to the high reactivity of the employed titanium precursors. The synthesis of COK‐47 is now presented, the first Ti carboxylate MOF based on sheets of TiIVO6 octahedra, which can be synthesized with a range of different linkers. COK‐47 can be synthesized as an inherently defective nanoparticulate material, rendering it a highly efficient catalyst for the oxidation of thiophenes. Its structure was determined by continuous rotation electron diffraction and studied in depth by X‐ray total scattering, EXAFS, and solid‐state NMR. Furthermore, its photoactivity was investigated by electron paramagnetic resonance and demonstrated by catalytic photodegradation of rhodamine 6G.  相似文献   
2.
3.
From the early precipitation-based techniques, introduced more than a century ago, to the latest development of enzymatic bio- and nano-sensor applications, the analysis of phytic acid and/or other inositol phosphates has never been a straightforward analytical task. Due to the biomedical importance, such as antinutritional, antioxidant and anticancer effects, several types of methodologies were investigated over the years to develop a reliable determination of these intriguing analytes in many types of biological samples; from various foodstuffs to living cell organisms. The main aim of the present work was to critically overview the development of the most relevant analytical principles, separation and detection methods that have been applied in order to overcome the difficulties with specific chemical properties of inositol phosphates, their interferences, absence of characteristic signal (e.g., absorbance), and strong binding interactions with (multivalent) metals and other biological molecules present in the sample matrix. A systematical and chronological review of the applied methodology and the detection system is given, ranging from the very beginnings of the classical gravimetric and titrimetric analysis, through the potentiometric titrations, chromatographic and electrophoretic separation techniques, to the use of spectroscopic methods and of the recently reported fluorescence and voltammetric bio- and nano-sensors.  相似文献   
4.
5.
A series of non-fullerene acceptors based on perylene monoimides coupled in the peri position through phenylene linkers were synthesized via Suzuki-coupling reactions. Various substitution patterns were investigated using density functional theory (DFT) calculations in combination with experimental data to elucidate the geometry and their optical and electrochemical properties. Further investigations of the bulk properties with grazing incidence wide angle X-ray scattering (GIWAXS) gave insight into the stacking behavior of the acceptor thin films. Electrochemical and morphological properties correlate with the photovoltaic performance of devices with the polymeric donor PBDB-T and a maximum efficiency of 3.17 % was reached. The study gives detailed information about structure–property relationships of perylene-linker-perylene compounds.  相似文献   
6.
Maggis  Marco  Meyer-Brandis  Thilo  Svindland  Gregor 《Positivity》2019,23(1):247-247
Positivity - There is an error in Proposition 3.10. In fact, the stated proof only shows  相似文献   
7.
Pulsed EPR dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling and thus the distance between electron-spin centers. To date, PDS measurements to metal centers were limited to ions that adhere to the high-field approximation. Here, the PDS methodology is extended to cases where the high-field approximation breaks down on the example of the high-spin Fe3+/nitroxide spin-pair. First, the theory developed by Maryasov et al. (Appl. Magn. Reson. 2006 , 30, 683–702) was adapted to derive equations for the dipolar coupling constant, which revealed that the dipolar spectrum does not only depend on the length and orientation of the interspin distance vector with respect to the applied magnetic field but also on its orientation to the effective g-tensor of the Fe3+ ion. Then, it is shown on a model system and a heme protein that a PDS method called relaxation-induced dipolar modulation enhancement (RIDME) is well-suited to measuring such spectra and that the experimentally obtained dipolar spectra are in full agreement with the derived equations. Finally, a RIDME data analysis procedure was developed, which facilitates the determination of distance and angular distributions from the RIDME data. Thus, this study enables the application of PDS to for example, the highly relevant class of high-spin Fe3+ heme proteins.  相似文献   
8.
9.
Synthesis of 1,1′‐bifunctional aminophosphane complexes 3 a–e was achieved by the reaction of Li/Cl phosphinidenoid complex 2 with various primary amines (R=Me, iPr, tBu, Cy, Ph). Deprotonation of complex 3 a (R=Me) with potassium hexamethyldisilazide yielded a mixture of K/NHMe phosphinidenoid complex 4 a and potassium phosphanylamido complex 4 a′ . Treatment of complex 3 c (R=tBu) and e (R=Ph) with KHMDS afforded the first examples of K/NHR phosphinidenoid complexes 4 c and e . The reaction of complex 3 c with 2 molar equivalents of KHMDS followed by PhPCl2 afforded complexes 5 c,c′ , which possess a P2N‐ring ligand. All complexes were characterized by NMR, IR, MS, and microanalysis, and additionally, complexes 3 b – e and 5 c′ were scrutinized by single‐crystal X‐ray crystallography.  相似文献   
10.
To summarize some of the most important findings in the field of ultrasonic (US) testing of early age hydration and formation of structure of different cement based materials (CBMs), a review of literature with focus on US P-wave transmission and S-wave reflection methods is presented in this paper. The review shows a great ability of both US techniques to observe setting phenomena and to determine different milestones during the early age formation of CBM’s microstructure. Clear physical basis, high accuracy, and non-destructive nature of the method indicate that US methods could become standardized in the near future.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号