全文获取类型
收费全文 | 1193篇 |
免费 | 47篇 |
国内免费 | 4篇 |
学科分类
数理化 | 1244篇 |
出版年
2023年 | 11篇 |
2022年 | 6篇 |
2021年 | 34篇 |
2020年 | 42篇 |
2019年 | 29篇 |
2018年 | 29篇 |
2017年 | 17篇 |
2016年 | 37篇 |
2015年 | 35篇 |
2014年 | 35篇 |
2013年 | 49篇 |
2012年 | 63篇 |
2011年 | 63篇 |
2010年 | 33篇 |
2009年 | 32篇 |
2008年 | 33篇 |
2007年 | 52篇 |
2006年 | 63篇 |
2005年 | 44篇 |
2004年 | 28篇 |
2003年 | 30篇 |
2002年 | 25篇 |
2001年 | 17篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 21篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1986年 | 7篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1977年 | 9篇 |
1975年 | 7篇 |
1966年 | 10篇 |
1964年 | 8篇 |
1963年 | 7篇 |
1957年 | 6篇 |
1956年 | 6篇 |
1922年 | 6篇 |
1888年 | 5篇 |
排序方式: 共有1244条查询结果,搜索用时 390 毫秒
61.
Isaiah Adelabu Patrick TomHon Mohammad S. H. Kabir Shiraz Nantogma Mustapha Abdulmojeed Iuliia Mandzhieva Dr. Jessica Ettedgui Dr. Rolf E. Swenson Dr. Murali C. Krishna Prof. Thomas Theis Prof. Boyd M. Goodson Prof. Eduard Y. Chekmenev 《Chemphyschem》2022,23(2):e202100839
Signal Amplification By Reversible Exchange in SHield Enabled Alignment Transfer (SABRE-SHEATH) is investigated to achieve rapid hyperpolarization of 13C1 spins of [1-13C]pyruvate, using parahydrogen as the source of nuclear spin order. Pyruvate exchange with an iridium polarization transfer complex can be modulated via a sensitive interplay between temperature and co-ligation of DMSO and H2O. Order-unity 13C (>50 %) polarization of catalyst-bound [1-13C]pyruvate is achieved in less than 30 s by restricting the chemical exchange of [1-13C]pyruvate at lower temperatures. On the catalyst bound pyruvate, 39 % polarization is measured using a 1.4 T NMR spectrometer, and extrapolated to >50 % at the end of build-up in situ. The highest measured polarization of a 30-mM pyruvate sample, including free and bound pyruvate is 13 % when using 20 mM DMSO and 0.5 M water in CD3OD. Efficient 13C polarization is also enabled by favorable relaxation dynamics in sub-microtesla magnetic fields, as indicated by fast polarization buildup rates compared to the T1 spin-relaxation rates (e. g., ∼0.2 s−1 versus ∼0.1 s−1, respectively, for a 6 mM catalyst-[1-13C]pyruvate sample). Finally, the catalyst-bound hyperpolarized [1-13C]pyruvate can be released rapidly by cycling the temperature and/or by optimizing the amount of water, paving the way to future biomedical applications of hyperpolarized [1-13C]pyruvate produced via comparatively fast and simple SABRE-SHEATH-based approaches. 相似文献
62.
Svitlana O. Sotnik Artem M. Mishchenko Eduard B. Rusanov Andriy V. Kozytskiy Konstantin S. Gavrilenko Sergey V. Ryabukhin Dmitriy M. Volochnyuk Sergey V. Kolotilov 《Molecules (Basel, Switzerland)》2021,26(12)
The third generation Buchwald precatalysts Pd(ABP)(Phos)(OMs) (also known as Phos Pd G3)) with XPhos and RuPhos were prepared in multigram scale by a modified procedure (ABP = fragment of C-deprotonated 2-aminobiphenyl, XPhos = 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl, RuPhos = 2-dicyclohexylphosphino-2′,6′-diisopropoxybiphenyl, OMs− = CH3SO3−). The 1H- and 31P-NMR spectra of the title complexes and some impurities, measured by various 1D and 2D techniques, were analyzed in detail. The solvent-dependent isomerization of Pd(ABP)(XPhos)(OMs) was studied by NMR, and the X-ray structures of two isomers were determined. The impurities in precatalysts, such as Pd(ABP)(HABP)(OMs) (HABP—neutral 2-aminobiphenyl coordinated to Pd2+ in N-monodentate mode) and PdCl2(XPhos)2, were identified and characterized by single crystal X-ray diffraction. A simple method for the quick quality control (QC) of the precatalysts, suitable for routine use, was proposed. The method was based on the assessment of the impurity content on the basis of the 1H-NMR spectra analysis. 相似文献
63.
Patrick M. TomHon Dr. Suyong Han Dr. Sören Lehmkuhl Prof. Stephan Appelt Prof. Eduard Y. Chekmenev Prof. Milad Abolhasani Prof. Thomas Theis 《Chemphyschem》2021,22(24):2526-2534
We introduce a Spin Transfer Automated Reactor (STAR) that produces continuous parahydrogen induced polarization (PHIP), which is stable for hours to days. We use the PHIP variant called signal amplification by reversible exchange (SABRE), which is particularly well suited to produce continuous hyperpolarization. The STAR is operated in conjunction with benchtop (1.1 T) and high field (9.4 T) NMR magnets, highlighting the versatility of this system to operate with any NMR or MRI system. The STAR uses semipermeable membranes to efficiently deliver parahydrogen into solutions at nano to milli Tesla fields, which enables 1H, 13C, and 15N hyperpolarization on a large range of substrates including drugs and metabolites. The unique features of the STAR are leveraged for important applications, including continuous hyperpolarization of metabolites, desirable for examining steady-state metabolism in vivo, as well as for continuous RASER signals suitable for the investigation of new physics. 相似文献
64.
Stephan Wasielewski Eduard Rott Ralf Minke Heidrun Steinmetz 《Molecules (Basel, Switzerland)》2021,26(1)
Sludge water (SW) arising from the dewatering of anaerobic digested sludge causes high back loads of ammonium, leading to high stress (inhibition of the activity of microorganisms by an oversupply of nitrogen compounds (substrate inhibition)) for wastewater treatment plants (WWTP). On the other hand, ammonium is a valuable resource to substitute ammonia from the energy intensive Haber-Bosch process for fertilizer production. Within this work, it was investigated to what extent and under which conditions Carpathian clinoptilolite powder (CCP 20) can be used to remove ammonium from SW and to recover it. Two different SW, originating from municipal WWTPs were investigated (SW1: c0 = 967 mg/L NH4-N, municipal wastewater; SW2: c0 = 718–927 mg/L NH4-N, large industrial wastewater share). The highest loading was achieved at 307 K with 16.1 mg/g (SW1) and 15.3 mg/g (SW2) at 295 K. Kinetic studies with different specific dosages (0.05 gCLI/mgNH4-N), temperatures (283–307 K) and pre-loaded CCP 20 (0–11.4 mg/g) were conducted. At a higher temperature a higher load was achieved. Already after 30 min contact time, regardless of the sludge water, a high load up to 7.15 mg/g at 307 K was reached, achieving equilibrium after 120 min. Pre-loaded sorbent could be further loaded with ammonium when it was recontacted with the SW. 相似文献
65.
Omer Anis Ajjampura C. Vinayaka Nurit Shalev Dvora Namdar Stalin Nadarajan Seegehalli M. Anil Ofer Cohen Eduard Belausov Jacob Ramon Einav Mayzlish Gati Hinanit Koltai 《Molecules (Basel, Switzerland)》2021,26(2)
Cannabis sativa contains more than 500 constituents, yet the anticancer properties of the vast majority of cannabis compounds remains unknown. We aimed to identify cannabis compounds and their combinations presenting cytotoxicity against bladder urothelial carcinoma (UC), the most common urinary system cancer. An XTT assay was used to determine cytotoxic activity of C. sativa extracts on T24 and HBT-9 cell lines. Extract chemical content was identified by high-performance liquid chromatography (HPLC). Fluorescence-activated cell sorting (FACS) was used to determine apoptosis and cell cycle, using stained F-actin and nuclei. Scratch and transwell assays were used to determine cell migration and invasion, respectively. Gene expression was determined by quantitative Polymerase chain reaction (PCR). The most active decarboxylated extract fraction (F7) of high-cannabidiol (CBD) C. sativa was found to contain cannabichromene (CBC) and Δ9-tetrahydrocannabinol (THC). Synergistic interaction was demonstrated between CBC + THC whereas cannabinoid receptor (CB) type 1 and type 2 inverse agonists reduced cytotoxic activity. Treatments with CBC + THC or CBD led to cell cycle arrest and cell apoptosis. CBC + THC or CBD treatments inhibited cell migration and affected F-actin integrity. Identification of active plant ingredients (API) from cannabis that induce apoptosis and affect cell migration in UC cell lines forms a basis for pre-clinical trials for UC treatment. 相似文献
66.
A particle phi coupling to two photons couples also radiatively to charged particles, like protons. If the particle is a light scalar, this induced coupling leads to spin-independent non-Newtonian forces. We show that the experimental constraints on exotic, fifth-type forces lead to stringent constraints on the phigammagamma coupling. We discuss the impact on the recent PVLAS results and the role of paraphoton models introduced to solve the PVLAS-CAST puzzle. 相似文献
67.
Valentinos Mouarrawis Eduard O. Bobylev Prof. Dr. Bas de Bruin Prof. Dr. Joost N. H. Reek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(32):8390-8397
Confinement of a catalyst can have a significant impact on catalytic performance and can lead to otherwise difficult to achieve catalyst properties. Herein, we report the design and synthesis of a novel caged catalyst system Co−G@Fe8(Zn−L ⋅ 1)6 , which is soluble in both polar and apolar solvents without the necessity of any post-functionalization. This is a rare example of a metal-coordination cage able to bind catalytically active porphyrins that is soluble in solvents spanning a wide variety of polarity. This system was used to investigate the combined effects of the solvent and the cage on the catalytic performance in the cobalt catalyzed cyclopropanation of styrene, which involves radical intermediates. Kinetic studies show that DMF has a protective influence on the catalyst, slowing down deactivation of both [Co(TPP)] and Co−G@Fe8(Zn−L ⋅ 1)6 , leading to higher TONs in this solvent. Moreover, DFT studies on the [Co(TPP)] catalyst show that the rate determining energy barrier of this radical-type transformation is not influenced by the coordination of DMF. As such, the increased TONs obtained experimentally stem from the stabilizing effect of DMF and are not due to an intrinsic higher activity caused by axial ligand binding to the cobalt center ([Co(TPP)(L)]) . Remarkably, encapsulation of Co−G led to a three times more active catalyst than [Co(TPP)] (TOFini) and a substantially increased TON compared to both [Co(TPP)] and free Co−G . The increased local concentration of the substrates in the hydrophobic cage compared to the bulk explains the observed higher catalytic activities. 相似文献
68.
69.
Raluca Nicoleta Darie Eduard Lack Franz Lang Jr. Martin Sova Alexandra Nistor Iuliana Spiridon 《International Journal of Polymer Analysis and Characterization》2014,19(5):453-467
New materials were obtained by incorporating in polypropylene (PP) matrix 60% wood wastes resulting after extraction with supercritical carbon dioxide, water, and ethanol. Structural, mechanical, thermal, and rheological characterizations, as well as moisture uptake of the composites, were evaluated before and after accelerated weathering. It was found that the extraction method influenced the composite properties due to the hydrophilic-hydrophobic balance. The addition of extracted fibers results in an increase in hardness and tensile properties and a decrease of impact strength as compared to PP. 相似文献
70.
Tânia Regina Silva Eduard Westphal Hugo Gallardo Iolanda Cruz Vieira 《Electroanalysis》2014,26(8):1801-1809
This paper describes the development of a new sensor based on an ionic organic film. The amphiphilic molecule, 4‐[(4‐decyloxyphenyl)‐ethynyl]‐1‐methylpyridinium iodide (10PyI), which has liquid‐crystalline properties, was synthesized and applied in the construction of a GCE/10PyI sensor. Analytical parameters for caffeic acid, repeatability (4.8 %), reproducibility (2.8 %), linearity (two ranges: 9.9×10?7 to 3.8×10?5 mol L?1 and 4.7×10?5 to 9.9×10?5 mol L?1) and detection limits (9.0×10?7 mol L?1 and 8.7×10?6 mol L?1), were determined. The method was successfully applied in the determination of total phenolic compounds (TPC) in mate herb extracts. 相似文献