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排序方式: 共有693条查询结果,搜索用时 15 毫秒
1.
Gruber JW Kittipongpatana N Bloxton JD Der Marderosian A Schaefer FT Gibbs R 《Journal of chromatographic science》2004,42(4):196-199
Devil's root, Oplopanax horridus, is a widely used folk medicine in Alaska and British Columbia. The inner bark of the root and stem has been used to treat colds, cough, fever, and diabetes. The present study involves the development of high-pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC) methods to detect the presence of trans-nerolidol and sterols in the root bark. The HPLC and TLC analytical methods presented are suitable for the characterization and identification of Oplopanax horridus. 相似文献
2.
E. M. Araújo Renata Barbosa Amanda D. Oliveira Crislene R. S. Morais T. J. A. deMélo A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(3):811-814
Polyethylene/montmorillonite clay nanocomposites were obtained via direct
melt intercalation. The clay was organically modified with four different
types of quaternary ammonium salts. The objective of this work is to study
the use of montmorillonite clay in the production of nanocomposites by means
on rheological, mechanical and crystallization properties of nanocomposites
and to compare to the properties of the matrix and PE/unmodified clay nanocomposites.
In general, the tensile test showed that the yield strength and modulus of
the nanocomposites are close to the pure PE. Apparently, the mixture with
Dodigen salt seems to be more stable than the pure PE and PE/unmodified clay. 相似文献
3.
Sérgio L. C. Ferreira Neyla M. L. Araújo Adriana B. Santos Alailson F. Dantas A. C. Spinola Costa 《Mikrochimica acta》1995,118(1-2):123-129
TAN reacts with zinc(II) forming a red complex with composition 1:2 Zn(II)-TAN and absorption maximum at 582 nm. Zinc can be determined with this reagent in the presence of Triton X-100, in the pH range 6.20-8.00 with a molar absorptivity of 4.5×104 l/mol/cm Beer's Law was obeyed up to least 1.55 g/ml. Copper interference was eliminated with a mixture of thiosulfate and ascorbic acid and nickel separated by precipitation with dimethylglyoxime. The proposed method was used for zinc determination in several copper-base alloys and the results of analysis in comparison with certified values indicated that the procedure was accurate and precise. A derivative procedure is also proposed, allowing zinc determination with high sensitivity (5-400 ng/ml). 相似文献
4.
Araúzo-Bravo MJ Fujii S Kono H Ahmad S Sarai A 《Journal of the American Chemical Society》2005,127(46):16074-16089
Sequence dependence of DNA conformation plays a crucial role in its recognition by proteins and ligands. To clarify the relationship between sequence and conformation, it is necessary to quantify the conformational energy and specificity of DNA. Here, we make a systematic analysis of dodecamer DNA structures including all the 136 unique tetranucleotide sequences at the center by molecular dynamics simulations. Using a simplified conformational model with six parameters to describe the geometry of adjacent base pairs and harmonic potentials along these coordinates, we estimated the equilibrium conformational parameters and the harmonic potentials of mean force for the central base-pair steps from many trajectories of the simulations. This enabled us to estimate the conformational energy and the specificity for any given DNA sequence and structure. We tested our method by using sequence-structure threading to estimate the conformational energy and the Z-score as a measure of specificity for many B-DNA and A-DNA crystal structures. The average Z-scores were negative for both kinds of structures, indicating that the potential of mean force from the simulation is capable of predicting sequence specificity for the crystal structures and that it may be used to study the sequence specificity of both types of DNA. We also estimated the positional distribution of conformational energy and Z-score within DNA and showed that they are strongly position dependent. This analysis enabled us to identify particular conformations responsible for the specificity. The presented results will provide an insight into the mechanisms of DNA sequence recognition by proteins and ligands. 相似文献
5.
F. Lieneweg J. Guzmán A. Ara J. W. Teiss O. R. Wagner C. del Fresno L. Valdés und Je. I. Denissow 《Fresenius' Journal of Analytical Chemistry》1941,122(7-8):291-292
Ohne Zusammenfassung 相似文献
6.
Diphenylphosphine oxidatively adds to the ReRe bonds of Re2
X
4(-dppm)2 (X=Cl or Br; dppm=Ph2PCH2PPh2) and Re2Cl4(-dpam)2 (dpam=Ph2AsCH2AsPh2) to afford the dirhenium(III) complexes Re2(-X)(-PPh2)HX
3(-LL)2. The dppm complexes have also been prepared from the reactions of Re2(-O2CCH3)X
4(-dppm)2 with Ph2PH, and a similar strategy has been used to prepare Re2(-Cl)(-PPh2)HCl3(-dmpm)2 (dmpm=Me2PCH2PMe2) from Re2(-O2CCH3)Cl4(dmpm)2. Phenylphosphine likewise reacts with Re2
X
4(-dppm)2 to give Re2(-X)(-PHPh)HX
3(-dppm)2. An X-ray crystal structure determination on Re2(-Cl)(-PPh2)HCl3(-dppm)2 confirms its edge-shared bioctahedral structure. This complex crystallizes in the space group
(No. 148) witha=21.699(3) Å, =84.50(4)°,V=10084(5) Å3, andZ=6. The structure was refined toR=0.049 (R
w
0.069) for 5770 data withI>3.0(I). The Re-Re distance is 2.5918(7) Å. Oxidation of the bromide complex Re2(-Br)(-PPh2)HBr3(-dppm)2 with NOPF6 produces the unusual dirhenium(III, II) cation [Re2(-H)(-Br)[P(O)Ph2]Br2(NO)(-dppm)2]+ which has been structurally characterized as its perrhenate salt, [Re2(-H)(-Br)[P(O)Ph2]Br2(NO)(-dppm)2]ReO4 · 2CH2Cl2. This complex crystallizes in the space group
(No. 2) witha=14.187(7) Å,b=16.419(5) Å,c=16.729(5) Å, =98.76(2)°, =110.11(3)°, =104.66(3)°,V=3414(6) Å3,Z=2. The structure was refined toR=0.040 (R
w
=0.051) for 5736 data withI>3.0(I). The presence of a phosphorus-bound [P(O)Ph2]– ligand, a linear nitrosyl and a bridging hydrido ligand has been confirmed. The Re-Re distance is 2.6273(8) Å. 相似文献
7.
Santos EM Araújo AN Couto CM Montenegro MC 《Analytical and bioanalytical chemistry》2006,384(4):867-875
The construction and general performance of new valproate-selective electrodes based on manganese(III) tetraphenylporphyrin
[Mn(III)TPP-Cl], as an ionophore, are presented. The ionophore was incorporated into PVC and ceramic membranes (sol–gel) based
on methyltriethoxysilane. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives
in PVC membranes were investigated concerning their influence on the slope, response time, selectivity and lifetime of the
electrodes. The PVC membrane without additive and the sol–gel membrane presented slopes and practical limits of detection
of −60.8 mV dec−1 and 5x10−6 mol l−1 and −60.3 mV dec−1 and 1×10−4 mol l−1, respectively. The sol–gel membranes displayed higher selectivity for valproate when compared with PVC membranes. These two
types of electrodes were coupled to a sequential-injection analysis (SIA) system for the direct determination of valproate
in pharmaceutical formulations. The association of Mn(III)TPP-Cl with the sol–gel support inserted in a SIA system provided
potentiometric sensors with an analytical range of 1x10−3–5x10−2 mol l−1, with a sample rate of 55 samples per hour and a sample and carrier consumption of 140 and 2,500 μl per determination, respectively. 相似文献
8.
Hellyda K. T. A. Silva Thiago Chellappa Fabíola C. Carvalho Edjane F. B. Silva Tarcísio A. Nascimento Antônio S. Araújo Valter J. FernandesJr. 《Journal of Thermal Analysis and Calorimetry》2011,106(3):731-733
Biodiesel is defined as a mixture of mono- or di-alquil esters of vegetable oil or animal fats. During long-term storage,
oxidation caused by contact with air (autoxidation) presents a legitimate concern in relation to monitoring and maintaining
fuel quality. Extensive oxidative degradation may compromise the quality by adversely affecting kinematic viscosity, acid
value, or peroxide value. The oxidation susceptibility of biodiesel, due to the presence of triacilglycerides of poly-unsaturated
fatty acids, was evaluated in this study. Samples of sunflower, castor, and soybean biodiesels were obtained through the transesterification
reaction, with the intention of achieving the thermal stability study through thermogravimetrical analyses and differential
scanning calorimetry high pressure. It was furthermore observed through thermogravimetry and pressure differential scanning
calorimetry curves that castor biodiesel exhibited the highest thermal and oxidative stability. 相似文献
9.
A glucose biosensor with enzyme immobilised by sol–gel technology was constructed and evaluated. The glucose biosensor reported is based on encapsulated GOX within a sol–gel glass, prepared with 3-aminopropyltriethoxy silane, 2-(3,4-epoxycyclohexyl)-ethyltrimetoxy silane and HCl. A flow system incorporating the amperometric biosensor constructed was developed for the determination of glucose in the 1×10−4–5×10−3 mol l−1 range with a precision of 1.5%. The results obtained for the analysis of electrolytic solution for iv administration and human serum samples showed good agreement between the proposed method and the reference procedure, with relative error <5%. 相似文献
10.
Spisso BF de Oliveira e Jesus AL de Araújo MA Monteiro MA 《Analytica chimica acta》2007,581(1):108-117
A high-performance liquid chromatography-fluorescence detection method was optimized and validated to determine tetracyclines residues in bovine milk. Post-column derivatization using metal complexation in non-aqueous reagent increased the fluorescence of chelates by a factor up to 2.54 compared to water (signal-to-noise ratio enhancement). Overall recoveries ranged from 61 to 115%, with RSDr from 5 to 15% (n = 54). Detection limits ranged from 5 to 35 μg kg−1. Limits of quantification were established at 50 μg kg−1. Decision limits (CCα) were 109, 108 and 124 μg kg−1 and detection capabilities (CCβ) 119, 117 and 161 μg kg−1 for oxytetracycline, tetracycline and chlortetracycline, respectively. The method was applied successfully in a national monitoring program. 相似文献