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181.
A.?Khanal K.?NakashimaEmail author N.?Kawasaki Y.?Oishi M.?Uehara H.?Nakamura Y.?Tajima 《Colloid and polymer science》2005,283(11):1226-1232
New organic–inorganic nano-complexes were produced from a micelle of tri-block polymers; poly(styrene)-b-poly(2-vinylpyridine)- b-poly (ethylene oxide) (PS-PVP-PEO) and tungsten compounds such as tungstate (W12−), undecatungstophospate (PW117−) and undecatungstosilicate (SiW118−) in acidic aqueous solutions. The size and morphology of the complexes were characterized by measurements of dynamic light
scattering, atomic force microscopy, and scanning electron microscopy. This complex is assembled mainly by the charge interaction
between the inorganic polyanions and the positively charged PVP block in the PS-PVP-PEO molecule, which was confirmed by zeta-potential
and fluorescence spectroscopic studies. In the absence of the inorganic anions, the zeta-potential of the micelle was +11 mV
at pH 3 due to the positive charge of the PVP block. When the inorganic anion was mixed with the PS-PVP-PEO micelle, decrease
in the zeta-potential due to charge neutralization occurred with incorporation of inorganic anions into the PS-PVP-PEO micelle.
The minimum zeta-potential was 0, −33, and −35 mV for W12− /PS-PVP-PEO, PW117− /PS-PVP-PEO, and SiW118− /PS-PVP-PEO complexes, respectively. Excess negative charge which occurred in the latter two complexes indicates that PS-PVP-PEO
molecules bound PW117− and SiW118− by forces other than charge interaction. In addition, the incorporation of an inorganic polyanion into the micelle gave a
new morphology to the micelle. In the absence of the polyanion, the PS-PVP-PEO micelles showed an extended conformation due
to repulsive forces working among the positively charged PVP blocks. Addition of the polyanion caused the formation of shrunken
forms of the micelles, since the charge repulsion was cancelled by the polyanion. This feature may be useful in developing
a new type of functioning micelle. 相似文献
182.
The intercalation of Co(2+), [Co(NH(3))(6)](3+), and [Co(NH(3))(5)Cl](2+) ions into layered manganese oxide (birnessite) was studied by chemical, XRD, SEM, IR, and DTA-TG analyses. The intercalation reaction progressed by a 2:1 or 3:1 ion-exchange mechanism depending on the valence of the starting ions. The oxidation state of cobalt did not change with the intercalation reaction. The intercalation of [Co(NH(3))(6)](3+) ions resulted in an increase of basal spacing from 0.716 to 0.956 nm, giving a layered structure material consisting mainly of platelike particles. The chemical analysis results showed that the structure of [Co(NH(3))(6)](3+) ions was maintained in the interlayer. On the other hand, an H(2)O/NH(3) ligand exchange reaction progressed for the intercalation of [Co(NH(3))(5)Cl](2+) ions, resulting in an increase in the basal spacing from 0.716 to 0.956 nm. 相似文献
183.
Otaka A Katagiri F Kinoshita T Odagaki Y Oishi S Tamamura H Hamanaka N Fujii N 《The Journal of organic chemistry》2002,67(17):6152-6161
Proline dipeptides (Xaa-Pro) exist as an equilibrium mixture of cis- and trans-rotamers, which depends on the energy barriers for imide isomerization. This conformation mixture contributes to both structure and function of proline-containing peptides and proteins. Structural motifs resembling these cis- or trans-conformers have served as useful tools for elucidating contributions of proline residues in the physicochemical and biological profiles of structures which contain them. Among such motifs are alkene dipeptide isosteres which mimic cis- or trans-imide using (Z)- or (E)-alkene, respectively. In this report, the first regio- and stereoselective syntheses of (E)-alkene dipeptide isosteres (20, 31, and 35) corresponding to trans-proline dipeptides are described. Key to the synthesis of these mimetics is the anti-S(N)2' reaction of vinyl aziridines such as 15 or vinyl oxazolidinones such as 28 and 32 with organocopper reagents "RCu" (R = CH(2)SiMe(2)(Oi-Pr)). Reaction of cis-vinylaziridine 15 derived from L-serine with organocopper reagent gave a precursor of the trans-L-Ser-D-Pro type alkene isosteres 20, accompanied by an S(N)2 side product. One limitation with the use of such aziridine-mediated methodology is formation of the corresponding trans-aziridine 22, which leads to L-L type isosteres, that is unstable and obtainable only in low yield. On the other hand, both isomers of oxazolidinone derivatives can be easily obtained from N-Boc-protected amino alcohols. The reaction of trans- 28 or cis-oxazolidinone derivative 32 with organocopper reagents proceeds quantitatively with high regio- and diastereoselectivities in anti-S(N)2' fashion. Subsequent oxidative treatment of the newly introduced isopropoxydimethylsilylmethyl group yields trans-L-Ser-L-Pro 31 or trans-L-Ser-D-Pro type isosteres 35, respectively. Of note, synthesized isostere 31 can also be converted to trans-phosphoSer-Pro 42 and trans-Cys-Pro mimetics 44. The present synthetic methodology affords trans-Xaa-Pro alkene-type dipeptide isosteres in high yield with relatively simple manipulation. 相似文献
184.
Ohno H Miyamura K Tanaka T Oishi S Toda A Takemoto Y Fujii N Ibuka T 《The Journal of organic chemistry》2002,67(4):1359-1367
A general and efficient synthesis of allenes using a palladium(0)/diethylzinc system is described. Treatment of mesylates or trichloroacetates of (E)- or (Z)-2-bromoalk-2-en-1-ols with diethylzinc in the presence of a catalytic amount of palladium(0) affords allenes bearing an aminoalkyl, alkyl, or aryl substituent(s) in good to high yields. No transfer of chirality from the stereogenic center carrying the mesyloxy group to the allene was observed. 相似文献
185.
(+)-Benzoylpedamide (5), a right half of (+)-pederin (1), was synthesized stereoselectively based on the newly developed method for the synthesis of 1,3--and 1,3--polyols. 相似文献
186.
Tadashi Nakata Takaaki Kuwabara Yōichirō Tani Takeshi Oishi 《Tetrahedron letters》1982,23(9):1015-1016
()-Oudemansin has been synthesized starting from -cinnamaldehyde by a route involving the stereoselective Zn(BH4)2 reduction of β-keto ester. 相似文献
187.
(+)-Benzoylselenopederic acid (1), a left half of (+)-pederin (3), was synthesized stereoselectively based on the Zn(BH4)2 reduction and total synthesis of (+)-pederin (3) was accomplished from 1 and the previously synthesized 2. 相似文献
188.
A sperm-activating and attracting factor (SAAF) was isolated from the eggs of the ascidian Ciona intestinalis, and its structure was deduced with only approximately 4 μg of the specimen. Based upon the proposed structure, two epimers were synthesized from chenodeoxycholic acid in 16 steps. Comparison between synthetic and natural compounds led to the unambiguous structure determination of SAAF to be (3R,4R,7R,25S)-3,4,7,26-tetrahydroxycholestane-3,26-disulfate. The synthetic pure specimen was also utilized to confirm that both sperm-activation and attraction were elicited by a single compound. 相似文献
189.
An iridoid glucoside dimer and a non-glycosidic iridoid from the leaves of Lasianthus wallichii 总被引:1,自引:0,他引:1
Takeda Y Shimidzu H Mizuno K Inouchi S Masuda T Hirata E Shinzato T Aramoto M Otsuka H 《Chemical & pharmaceutical bulletin》2002,50(10):1395-1397
A new iridoid glucoside dimer (1) and a non-glycosidic iridoid (2) was isolated together with the known compounds, asperuloside (3), paederoside (4), daphylloside (5), citroside A (6) and benzyl 6-O-alpha-L-rhamnopyranosyl-beta-D-glucopyranoside (7), from the leaves of Lasianthus wallichii. The structures of the new compounds were elucidated by spectroscopic and chemical evidence. 相似文献
190.