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831.
Das B Krishnaiah M Laxminarayana K Nandankumar D 《Chemical & pharmaceutical bulletin》2008,56(7):1049-1051
Silica supported phosphomolybdic acid, an eco-friendly heterogeneous catalyst, has been found to be highly efficient for Friedlander synthesis of quinolines in excellent yields. A variety of ketones afford the quinolines smoothly. The catalyst can be easily recovered and reused. 相似文献
832.
The Effects of a Consumer Chemistry Intervention on Urban At‐Risk High School Students’ Performance,Utility Value,and Intentions to Pursue STEM
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Lisa C. Duffin Michael P. Starling Martha M. Day Jennifer D. Cribbs 《School science and mathematics》2016,116(7):356-365
The main purpose of this quantitative study was to examine the degree to which a three‐week intervention in an urban high‐needs high school science classroom would influence students’ (n = 51) interest, utility value, content knowledge, and intentions for future study in chemistry. The intervention consisted of an authentic, inquiry‐based chemistry project where students worked cooperatively to investigate core chemistry concepts and connect them to real‐world consumer products and careers in manufacturing that required chemistry knowledge. Findings indicated that students improved their chemistry knowledge, found greater relevance for chemistry, and intend to take more chemistry in the future. Interest in chemistry did not statistically significantly increase as a result of the intervention; however, students’ interest levels remained consistently moderate from pre‐test to post. This study adds to the current body of literature in three ways. First, the intervention showcased positive outcomes with students from an urban, high‐needs high school who lacked motivation and academic proficiency in science. Second, using an authentic, inquiry‐based utility value intervention is a viable alternative to previous successful interventions that involved writing tasks. Finally, the study was the result of a high school teacher's advanced training in research where important evaluation skills were cultivated and advanced. 相似文献
833.
Mawji E Gledhill M Worsfold PJ Achterberg EP 《Rapid communications in mass spectrometry : RCM》2008,22(14):2195-2202
The behaviour of a series of hydroxamate siderophores--microbially produced iron complexes - was investigated using electrospray ionisation mass spectrometry (ESI-MS). Three groups of iron hydroxamate siderophores, namely the ferrioxamines, ferrichromes and coprogens/fusigens, were separated by high-performance liquid chromatography (HPLC) prior to ESI and MS(2) fragmentation. For the majority of the siderophores, both protonated molecules and sodium adducts were observed. The most abundant ion was selected for collision-induced fragmentation. Potential fragmentation mechanisms are postulated and discussed. Fragmentation patterns differed between siderophore groups; however, common fragmentation patterns were observed for siderophore ions within the groups examined. Cleavage frequently occurred at carbon-nitrogen or carbon-oxygen bonds. Fragmentation of the ions also involved cleavage of iron-oxygen bonds and transfer of the charge to iron. 相似文献
834.
Quiñones W Vicente B Torres F Archbold R Murillo W Londoño M Echeverri F 《Molecules (Basel, Switzerland)》2008,13(1):190-194
Ground pearl (Eurhizococcus colombianus) is a crop pest in Colombia, with special impact on fig, grass, rubus and tomato plants. The insect is resistant to external insecticide application because it produces a thick waxy shell that isolates it from the environment. The composition of this shell was determined by NMR and MS as a triglyceride, whose fatty acid is transformed into other products with the metamorphosis of the insect. Additionally, several enzymatic inhibitors were assayed to control the insect with negative results. 相似文献
835.
Hsun‐Lien Lin Tsung‐Yi Chao Yeng‐Fong Shih Shenghong A. Dai Wen‐Chiung Su Ru‐Jong Jeng 《先进技术聚合物》2008,19(8):984-992
A series of thermally stable organic/inorganic second‐order nonlinear optical (NLO) composites via sequential self‐repetitive reaction (SSRR) and sol–gel process has been developed. This SSRR is based on carbodiimide (CDI) chemistry. The difunctional azo chromophores (2,4‐diamino‐4′‐(4‐ nitrophenyl‐diazenyl)azobenzene (DNDA)) was reacted with excessive amount of 4, 4′‐methylene‐ diphenylisocyanate (MDI) to form poly‐CDI, and subsequently trimellitic anhydride (TMA) was added to obtain poly(N‐acylurea). The organic/inorganic composites containing prepolymer of phenyltriethoxysilane (PTEOS) and poly(N‐acylurea) in different weight ratios (10:90, 30:70, 50:50, 70:30, 90:10 wt%) were prepared, respectively. The moderate glass transition temperature (Tg) characteristic of the poly(N‐acylurea) allows the NLO‐active polymer to achieve high poling efficiency. After in situ poling and curing process, the Tgs of the composites were elevated, and higher than that of the pristine poly(amide–imide) sample. Electro‐optical (EO) coefficients (r33) of about 5.5 ~ 18.0 pm/V at 830 nm were obtained. Excellent temporal stability at 100°C, and waveguide characteristics (3.1–4.2 dB/cm at 830 nm) were also obtained for these composites. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
836.
Jeng-Yu Lin Chih-Heng Lien Shu-Wei Chou 《Journal of Solid State Electrochemistry》2012,16(4):1415-1421
In this study, electrophoretic deposition (EPD) was employed to fabricate multi-wall carbon nanotube (MWCNT) counter electrodes
(CEs) for dye-sensitized solar cells (DSSCs). Firstly, raw MWCNTs were functionalized by means of an acid mixture solution
and then subjected to EPD. The results obtained from Raman spectroscopy, Fourier transform infrared spectroscopy, field-emission
scanning electron microscope, and cyclic voltammogram demonstrated that the defects and open ends on the MWCNTs can be obtained
via chemical functionalization and thus facilitate the enhancement in the electrocatalytic activity for I3− reduction of MWCNT CEs. In addition to optimizing chemical functionalization of MWCNTs surface, the optimal thickness of
MWCNT CEs prepared by EPD was also investigated. Additionally, consecutive cyclic voltammetric tests demonstrated that the
MWCNT CE fabricated by EPD possessed excellent electrochemical stability. In comparison with MWCNT CEs fabricated by tape-casting
approach, MWCNT CEs prepared by EPD presented a superior adhesion between MWCNT deposits and conducting glass substrates.
Therefore, MWCNT CEs fabricated by EPD can be of great potential for use in low-cost plastic DSSCs. 相似文献
837.
838.
Serine-Proline (SP) dipeptide motifs have been shown to form unique hydrogen-bonding patterns in protein crystal structures. Peptides were designed to mimic these patterns by forming the 6 + 10 and the 9 + 10 hydrogen-bonded rings. Factors that contribute to the formation of SP turns include controlling backbone flexibility and amino acid chirality along with creating a hydrophobic environment around the intramolecular hydrogen bonds. 相似文献
839.
Zahuiti Hernández-Monta?ez Margarita Juárez-Montiel Martha Velázquez-ávila Eliseo Cristiani-Urbina César Hernández-Rodríguez Lourdes Villa-Tanaca Griselda Chávez-Camarillo 《Applied biochemistry and biotechnology》2012,167(7):2117-2129
A yeast isolate able to produce high levels of extracellular ??-amylase was selected from a collection of 385 yeasts and identified as Wickerhamia sp. by the sequence of the D1/D2 domain of the 26?S rDNA gene. Part of the nucleotide sequence of the amy1-W gene was cloned, and a sequence of 191 amino acids deduced from this gene was analyzed. The peptide contains three characteristic well-conserved regions in the active sites of ??-amylases (EC 3.2.1.1). The enzyme was purified and in situ activity showed only one band with amylolytic activity. The molecular mass of the ??-amylase was estimated at 54?kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Enzymatic activity on soluble starch as substrate was optimal at pH 5?C6 and 50 °C. This thermostable enzyme was inhibited by EDTA?CNa2 and 1,10-phenanthroline; the activity of the dialyzed enzyme was reactivated with Ca2+ and Mg2+ cations, which indicates that the ??-amylase is a metalloenzyme. ??-Amylase production was induced by starch and maltose and repressed by glucose. The high yield and productivity found in this work makes this Wickerhamia sp. strain a promising candidate for the biotechnological production of ??-amylase. 相似文献
840.
Mohrig JR Beyer BG Fleischhacker AS Ruthenburg AJ John SG Snyder DA Nyffeler PT Noll RJ Penner ND Phillips LA Hurley HL Jacobs JS Treitel C James TL Montgomery MP 《The Journal of organic chemistry》2012,77(6):2819-2828
As part of a comprehensive investigation on the stereochemical aspects of base-catalyzed 1,2-elimination reactions, we have studied a set of acyclic carbonyl substrates that react by an irreversible E1cB mechanism with largely anti stereospecificity. (2)H NMR data show that these reactions using KOH in EtOH/H(2)O under non-ion-pairing conditions produce a minimum of 85-89% anti elimination on stereospecifically labeled tert-butyl (2R*,3R*)- and (2R*,3S*)-3-(3-trifluoromethylphenoxy)-2,3-(2)H(2)-butanoate, S-tert-butyl (2R*,3R*)- and (2R*,3S*)-3-(3-trifluoromethylphenoxy)-2,3-(2)H(2)-butanethioate, and the related ketones, (4R*,5R*)- and (4R*,5S*)-5-(3-trifluoromethylphenoxy)-4,5-(2)H(2)-3-hexanone. With both diastereomers of each substrate available, the KIEs can be calculated and the innate stereoselectivities determined. The elimination reactions of the β-3-trifluoromethylphenoxy substrates occur by E1cB mechanisms with diffusionally equilibrated enolate-anion intermediates. Thus, it is clear that anti elimination does not depend solely upon concerted E2 mechanisms. Negative hyperconjugation provides a satisfactory explanation for the anti stereospecificity exhibited by our carbonyl substrates, where the leaving group activates the anti proton, leading to the enolate intermediate. The activation of the anti proton by negative hyperconjugation may also play a role in the concerted pathways of E2 mechanisms. We have also measured the rates of the hydroxide-catalyzed elimination reactions of butanoate, thiobutanoate, and ketone substrates in EtOH/H(2)O, with β-tosyloxy, acetoxy, and 3-trifluoromethylphenoxy nucleofuges. 相似文献