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排序方式: 共有342条查询结果,搜索用时 31 毫秒
1.
Beads prepared from a thermosensitive polymer, hydroxypropylcellulose, exhibit temperature-dependent porosity. At temperatures below 40°C the beads are swollen having large pores, while at temperatures above 45°C the beads are in a shrunken state having smaller pores. In the presence of 1 M NaCl the transition temperature decreased to about 30°C. In a swollen state the size of pore is large enough to accommodate lysozyme (mol. mass 14 400) and -chymotrypsin (mol. mass 21 600) but not bovine serum albumin (mol. mass 67 000). When the beads are shrunken, all the proteins are eluted from the column packed with hydroxypropylcellulose beads in the volume close to the void volume of the column. 相似文献
2.
Oxidation of cysteine to cysteic acid in proteins by peroxyacids, as monitored by immobilized pH gradients. 总被引:1,自引:0,他引:1
It has often been debated whether the presence of persulfate in a polyacrylamide gel could lead to the oxidation of cysteine (Cys) in proteins to cysteic acid. In fact, direct incubation of bovine serum albumin (BSA) with peroxodisulfate and periodate barely alters the isoelectric point (pI) and does not produce any cysteic acid. In contrast, caroate (peroxomonosulfate) and perphthalate strongly lower the pI of BSA. In the former case it as demonstrated that 4-Cys (of a total of 35) were converted into cysteic acid. Perphthalate was found to be, by far, the strongest oxidant: 15 (of 35) Cys residues were oxidized to cysteic acid and all methionine groups were destroyed. 相似文献
3.
[reaction: see text] A new mild method for protecting alcohols as t-butyl ethers is reported. The reaction proceeds with Mg(ClO4)2 and Boc2O and shows general applicability. The deprotection of t-butyl ethers has also been revisited. Preliminary results indicate the CeCl3 x 7H2O/NaI system is a very suitable catalyst for their removal. 相似文献
4.
Use of high-molecular-mass polyacrylamides as matrices for microchip electrophoresis of DNA fragments 总被引:1,自引:0,他引:1
DNA fragment analysis requires the use of polymer solutions as sieving matrices. Generally, such matrices are constituted of high-molar-weight polymers employed at a concentration higher than their entanglement threshold concentration. These polymer solutions are highly viscous and difficult to use in the narrow channels of a microchip. Ultralarge polyacrylamides synthesized via a nonconventional method, being the low-temperature plasma-induced polymerization (PIP), were used as DNA sieving matrices for microchip electrophoresis. The distinctive features of these polymers (ultralarge molecular mass and linearity) allow their use at a dilute concentration. Dilute PIP polyacrylamides revealed a constant value of resolution in a broad range of DNA fragment sizes (123 bp-1353 bp), thus proving to be effective in common genotyping applications. Moreover, the low viscosity of the dilute solutions enable it to be easier and faster in filling the channel between runs, thus enhancing the throughput of the microchip devices. 相似文献
5.
The impedance of the cell Au/HClO4-5.5 H2O/Au was investigated in the frequency range 1 to 105 Hz between 4.2 and 300 K. The analysis of the data enables an evaluation of important electrolyte properties such as conductivity and dielectric constant in a wide range of temperatures, predominantly in the solid state of the electrolyte HClO4-5.5 H2O (Tf = 228 K). The double layer capacity of the gold electrodes was also determined; it shows a qualitatively similar result compared with previous measurements. In the solid state, the ionic conductivity exhibits two distinct activation energies of 0.37 and 0.54 eV corresponding to the two phases present in HClO4-5.5 H2O above and below 170 K. Below 120 K the activation energy becomes very small and tends to zero around 80 K indicating possible tunneling processes in the rigid H2O structure. At about the same temperature the dielectric constant reaches its low temperature limit with a value ∞ ≈ 11 which is considerably higher than the value of pure ice of ∞ ≈ 3. 相似文献
6.
Bartoli G Bartolacci M Bosco M Foglia G Giuliani A Marcantoni E Sambri L Torregiani E 《The Journal of organic chemistry》2003,68(11):4594-4597
Alkylation of indoles by means of the Michael addition has been the subject of a number of investigation. It is well established that regioselectivity in the additions of indoles to electron-deficient alkenes is strongly controlled by the reaction medium. In a continuation of the work on developing greener and cleaner technologies, the cerium(III) chloride heptahydrate and sodium iodide combination supported on silica gel catalyzes the alkylation of various indoles with alpha,beta-unsaturated ketones giving 3-(3-oxoalkyl)indole derivatives in good yields. The substitution on the indole nucleus occurred exclusively at the 3-position, and N-alkylation products have not been observed. 相似文献
7.
Piergiorgio Pecorari Marcella Rinaldi Maria Paola Costi 《Journal of heterocyclic chemistry》1989,26(6):1701-1705
Derivatives of two new molecular structures, namely, [1,3]thiazino[3,2-a]purine and [1,2,3]triazolo[4,5-d]-[1,3]thiazino[3,2-a]pyrimidine, were synthesized together with other heterocyclic compounds. Retrosynthetic analysis of their molecular skeletons suggested a simple way of obtaining 3,4-dihydro-7,8-diamino-2H,6H-pyrimido[2,1-b][1,3]thiazin-6-one, which is a useful intermediate for their synthesis. This intermediate and the thiazole homologue were obtained directly by reaction of 5,6-diamino-2,3-dihydro-2-thioxo-4(lH)-pyrimidi-none with 1,3- or 1,2-dibromoalkane, respectively. 相似文献
8.
Marcella Massacesi Rosalba Pinna Gerolamo Devoto Ermanno Barni Piero Savarino Liliana Strinna Erre 《Transition Metal Chemistry》1984,9(9):351-355
Summary Complexes of general formula MLmCl2 · nH2O, where M=cobalt(II) or nickel(II); L=2-(4-methyl, 2-pyridyl)-benzimidazole (mpbi), 2-(4-methyl, 2-pyridyl)benzothiazole (mpbt), 2-(4-methyl, 2-pyridyl)benzoxazole (mpbo), 2-(4-methyl, 2-quinolyl)benzoxazole (mqbo), or 2-(4-methyl, 8-quinolyl)benzoxazole (mqbo); m=1,2; n=0–3, were prepared and characterized by t.g.a., conductance and magnetic measurements, i.r. and diffuse-reflectance electronic spectra.All the ligands behave as bidentate and coordinate through the pyridine- and isoxazole-nitrogen atoms.The nickel complexes have distorted octahedral or fivecoordinate structures. The cobalt complexes arepseudo-tet- rahedral except Co(mpbo)2Cl2·2H2O where the metal is six-coordinate. 相似文献
9.
Serenella Medici Marcella Gagliardo ScottB. Williams PrestonA. Chase Serafino Gladiali Martin Lutz AnthonyL. Spek GerardP.M. vanKlink Gerard vanKoten 《Helvetica chimica acta》2005,88(3):694-705
Achiral P‐donor pincer‐aryl ruthenium complexes ([RuCl(PCP)(PPh3)]) 4c , d were synthesized via transcyclometalation reactions by mixing equivalent amounts of [1,3‐phenylenebis(methylene)]bis[diisopropylphosphine] ( 2c ) or [1,3‐phenylenebis(methylene)]bis[diphenylphosphine] ( 2d ) and the N‐donor pincer‐aryl complex [RuCl{2,6‐(Me2NCH2)2C6H3}(PPh3)], ( 3 ; Scheme 2). The same synthetic procedure was successfully applied for the preparation of novel chiral P‐donor pincer‐aryl ruthenium complexes [RuCl(P*CP*)(PPh3)] 4a , b by reacting P‐stereogenic pincer‐arenes (S,S)‐[1,3‐phenylenebis(methylene)]bis[(alkyl)(phenyl)phosphines] 2a , b (alkyl=iPr or tBu, P*CHP*) and the complex [RuCl{2,6‐(Me2NCH2)2C6H3}(PPh3)], ( 3 ; Scheme 3). The crystal structures of achiral [RuCl(equation/tex2gif-sup-3.gifPCP)(PPh3)] 4c and of chiral (S,S)‐[RuCl(equation/tex2gif-sup-6.gifPCP)(PPh3)] 4a were determined by X‐ray diffraction (Fig. 3). Achiral [RuCl(PCP)(PPh3)] complexes and chiral [RuCl(P*CP*)(PPh3)] complexes were tested as catalyst in the H‐transfer reduction of acetophenone with propan‐2‐ol. With the chiral complexes, a modest enantioselectivity was obtained. 相似文献
10.
A nanosize material composed of 330 nm glass beads coated with a copolymer of N,N-dimethylacrylamide (DMA), N,N-acryloyloxysuccinimide (NAS) and [3-(methacryloyl-oxy)propyl]trimethoxysilane (MAPS) was developed to improve the protein immobilization on biochips. The developed material, bearing rabbit-IgG proteins, was arrayed as 150 μm spots trapped at the surface of a poly(dimethylsiloxane) elastomer (PDMS), and compared to copoly(DMA-NAS-MAPS)-coated glass slides and latex beads based biochips. Evidences were made through scanning electron microscopy that the newly developed material based microarray exhibited surface irregularities at the submicron level leading to high specific area.The combination of such large immobilization area with the highly efficient protein immobilization of the copoly(DMA-NAS-MAPS) polymer, enabled the achievement of microarrays exhibiting good performances both in pure media and complex samples (human sera). Indeed, high specific/non-specific signal ratio was found using this optimized immobilization procedure.Chemiluminescent detection of anti-rabbit-IgG was obtained through peroxidase labeled antibodies in the 5 μg/l to 10 mg/l range. Application of the developed system to real samples was achieved for the detection of rheumatoid factor (RF) through a capture assay. Interesting results were obtained, with a RF detection over the 5.3-485 IU/ml range and without measurable matrix effect or non-specific signal. 相似文献