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21.
Wojciech Dmowski Anna Ja?mu?na Z. Urbańczyk-Lipkowska 《Journal of fluorine chemistry》2007,128(12):1431-1438
Sodium dithionite effectively promotes the addition of dibromodifluoromethane to the exocyclic double bond of β-pinene. The reaction proceeded in a MeCN/H2O system to give almost quantitatively an adduct, 1-(2-bromo-2,2-difluoroethyl)-4-(2-bromoisopropyl)-cyclohexene, as the sole product. On treatment of the adduct with 2,2,6,6-tetramethylpiperidine elimination of HBr only from the (CH3)2CHBr group occurred to give a mixture of regioisomeric dienes, while treatment with 50% KOH under phase transfer catalysis conditions or with K2CO3 in DMF resulted in total dehydrobromination to give trienes possessing an exocyclic CHCF2 group. Surprisingly, the main course of the reactions of the adduct with DBU (1,8-diazabicyclo[5.4.0]undece-7-ene) and also with t-BuOK in THF was elimination of HBr only from the CH2CF2Br group to afford 1-(2,2-difluorovinyl)-4-(2-bromoisopropyl)cyclohexene as the main product. Catalytic hydrogenation of the adduct followed by treatment with DBU afforded a conjugated diene, 1-(2,2-difluorovinyl)-4-isopropylcyclohexene. Compounds bearing the CHCF2 group are new 1,1-difluorodienes which readily reacted with 4-phenyl-3H-1,2,4-triazoline-3,5-dione to give cycloadducts, derivatives of triazolo[1,2-α]cinnoline. 相似文献
22.
We consider equations of modified gravity with critical accelerations and find its solutions for the point-like source by suggesting the appropriate symmetry of metrics in empty space-time. 相似文献
23.
24.
Mészáros Szécsényi K. Leovac V. M. Jaćimović Ž. K. Češljević V. I. Kovács A. Pokol G. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):573-581
The synthesis of copper(II) chloride complexes with 3,5-dimethylpyrazole, 1-carboxamidine-3,5-dimethylpyrazole, 5-amino-4-carboxamide-1-phenylpyrazole
and 4-acetyl-3-amino-5-methylpyrazole is described. The compounds are characterized by elemental analysis, FT-IR spectroscopy,
thermal methods, magnetic moment and molar conductivity measurements. Thermal decomposition of the dichloro-(3,5-dimethylpyrazole)-copper(II)
complex results in an unstable intermediate with a stochiometric composition. The decomposition of the other compounds is
continuous.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
25.
Preparation of the enantiomeric pair of 3‐[2‐(3‐benzenesulfonylamino‐7‐oxabicyclo[2.2.1]hept‐2‐yl‐methyl)phenyl] propionic acid, a novel thromboxane antagonist is reported. They are synthesized from either enantiomers of known (1R,2R,3R,4S)‐3‐[2‐(3‐carboxy‐7‐oxabicyclo[2,2,1]hept‐2‐yl‐methyl)phenyl]‐propionic acid methyl ester via epimerization, modified Curtius' rearrangement and sulfonylamino formation. Other derivatives may be prepared similarly. 相似文献
26.
Chester M. Mikulski Scott Grossman Chung Ja Lee Nicholas M. Karayannis 《Transition Metal Chemistry》1987,12(1):21-25
Summary Complexes of the general types Pd(L)(LH)Cl (LH=hxH, xnH, or tbH) and Pt(L)(LH)Cl3 (LH=hxH, or xnH) are formed by boiling under reflux 21 molar mixtures of hypoxanthine (hxH), xanthine (xnH) or theobromine (tbH) and PdCl2 or PtCl4 in ethanol-triethyl orthoformate. These complexes appear to be linear chain polymeric species, characterized by single monoanionic L– ligands bridging between adjacent Pd2+ or Pt4+ ions. Inclusion of one terminal neutral LH and one terminal chloro-ligand completes the coordination sphere in the square-planar Pd2+ complexes, while the Pt4+ complexes aretrans-octahedral, involving three terminal chloro and one terminal LH ligand per platinum. The possible binding sites of the bidentate bridging L– and the unidentate terminal LH are discussed. 相似文献
27.
R. Jaćimović P. Makreski V. Stibilj T. Stafilov 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(3):795-799
Major and trace element contents in iron ore reference materials were investigated using k
0-instrumental neutron activation analysis (k
0-INAA). To avoid iron interferences, radiochemical separation was developed (k
0-RNAA). The determination of the investigated elements in the inorganic phase from hydrochloric acid solution was performed
after radiochemical separation of iron by diisopropyl ether. It was found that after the Fe elimination, the limit of detection
for some elements was much lower that enables their direct determination. The distribution of 39 elements (with intermediate/medium
and long half-life radionuclides) after Fe removal was investigated. 相似文献
28.
Mathias B. Danielsen Dr. Chenguang Lou Jolanta Lisowiec-Wachnicka Prof. Anna Pasternak Per T. Jørgensen Prof. Jesper Wengel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1368-1379
Off-target effects remain a significant challenge in the therapeutic use of gapmer antisense oligonucleotides (AONs). Over the years various modifications have been synthesized and incorporated into AONs, however, precise control of RNase H-induced cleavage and target sequence selectivity has yet to be realized. Herein, the synthesis of the uracil and cytosine derivatives of a novel class of 2′-deoxy-2′-fluoro-3′-C-hydroxymethyl-β-d -lyxo-configured nucleotides has been accomplished and the target molecules have been incorporated into AONs. Experiments on exonuclease degradation showed improved nucleolytic stability relative to the unmodified control. Upon the introduction of one or two of the novel 2′-fluoro-3′-C-hydroxymethyl nucleotides as modifications in the gap region of a gapmer AON was associated with efficient RNase H-mediated cleavage of the RNA strand of the corresponding AON:RNA duplex. Notably, a tailored single cleavage event could be engineered depending on the positioning of a single modification. The effect of single mismatched base pairs was scanned along the full gap region demonstrating that the modification enables a remarkable specificity of RNase H cleavage. A cell-based model system was used to demonstrate the potential of gapmer AONs containing the novel modification to mediate gene silencing. 相似文献
29.
Paulina Mierzejewska Michal Kunc Magdalena Agnieszka Zabielska-Kaczorowska Barbara Kutryb-Zajac Iwona Pelikant-Malecka Alicja Braczko Patrycja Jablonska Pawel Romaszko Patrycja Koszalka Jolanta Szade Ryszard Tomasz Smolenski Ewa Maria Slominska 《Experimental & molecular medicine》2021,53(9):1402
Our recent studies identified a novel pathway of nicotinamide metabolism that involves 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) and demonstrated its endothelial cytotoxic effect. This study tested the effects of 4PYR and its metabolites in experimental models of breast cancer. Mice were divided into groups: 4T1 (injected with mammary 4T1 cancer cells), 4T1 + 4PYR (4PYR-treated 4T1 mice), and control, maintained for 2 or 21 days. Lung metastasis and endothelial function were analyzed together with blood nucleotides (including 4PYR), plasma amino acids, nicotinamide metabolites, and vascular ectoenzymes of nucleotide catabolism. 4PYR metabolism was also evaluated in cultured 4T1, MDA-MB-231, MCF-7, and T47D cells. An increase in blood 4PYR in 4T1 mice was observed at 2 days. 4PYR and its metabolites were noticed after 21 days in 4T1 only. Higher blood 4PYR was linked with more lung metastases in 4T1 + 4PYR vs. 4T1. Decreased L-arginine, higher asymmetric dimethyl-L-arginine, and higher vascular ecto-adenosine deaminase were observed in 4T1 + 4PYR vs. 4T1 and control. Vascular relaxation caused by flow-dependent endothelial activation in 4PYR-treated mice was significantly lower than in control. The permeability of 4PYR-treated endothelial cells was increased. Decreased nicotinamide but enhanced nicotinamide metabolites were noticed in 4T1 vs. control. Reduced N-methylnicotinamide and a further increase in Met2PY were observed in 4T1 + 4PYR vs. 4T1 and control. In cultured breast cancer cells, estrogen and progesterone receptor antagonists inhibited the production of 4PYR metabolites. 4PYR formation is accelerated in cancer and induces metabolic disturbances that may affect cancer progression and, especially, metastasis, probably through impaired endothelial homeostasis. 4PYR may be considered a new oncometabolite.Subject terms: Mechanisms of disease, Pathogenesis, Breast cancer 相似文献
30.