全文获取类型
收费全文 | 429篇 |
免费 | 14篇 |
专业分类
化学 | 336篇 |
晶体学 | 4篇 |
力学 | 1篇 |
数学 | 43篇 |
物理学 | 59篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 23篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 19篇 |
2015年 | 15篇 |
2014年 | 25篇 |
2013年 | 23篇 |
2012年 | 35篇 |
2011年 | 55篇 |
2010年 | 24篇 |
2009年 | 16篇 |
2008年 | 22篇 |
2007年 | 23篇 |
2006年 | 17篇 |
2005年 | 12篇 |
2004年 | 15篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有443条查询结果,搜索用时 15 毫秒
91.
Brgles M Bertoša B Winkler W Kurtović T Allmaier G Marchetti-Deschmann M Halassy B 《Analytical and bioanalytical chemistry》2012,402(9):2737-2748
The ammodytoxins (Atxs) are neurotoxic phospholipases which occur in Vipera ammodytes ammodytes (Vaa) snake venom. There are three Atx isoforms, A, B, and C, which differ in only five amino acid positions at the C-terminus
but differ substantially in their toxicity. The objective of this study was to establish an analytical method for unambiguous
identification of all three isoforms and to use the method to assess a procedure for purification of the most toxic phospholipase,
AtxA, from the venom. Isolation procedure for AtxA consisted of isolation of Atx-cross-reactive material (proteins recognized
by anti-Atx antibodies), by use of an affinity column, then cation exchange on CIM (Convective Interaction Media) disks. The
purification procedure was monitored by means of reversed-phase chromatography (RPC) and mass spectrometry (MS). Although
previous cation exchange of the pure isoforms enabled separate elution of AtxA from B and C, separation of AtxA from Atxs
mixture was not accomplished. RPC was not able to separate the Atx isoforms, whereas an MS based approach proved to be more
powerful. Peptides resulting from tryptic digestion of Atxs which enable differentiation between the three isoforms were successfully
detected and their sequences were confirmed by post-source decay (PSD) fragmentation. Separation of Atx isoforms by ion-exchange
chromatography is most presumably prevented by Atxs heterodimer formation. The tendency of Atxs to form homodimers and heterodimers
of similar stability was confirmed by molecular modeling. 相似文献
92.
Gas-phase conjugation to unprotonated arginine side-chains via N-hydroxysuccinimide (NHS) esters is demonstrated through both charge reduction and charge inversion ion/ion reactions. The unprotonated guanidino group of arginine can serve as a strong nucleophile, resulting in the facile displacement of NHS from NHS esters with concomitant covalent modification of the arginine residue. This reactivity is analogous to that observed with unprotonated primary amines such as the N-terminus or ε-amino group of lysine. In solution, however, the arginine residues tend to be protonated at pH values low enough to prevent hydrolysis of NHS esters, which would render them relatively unreactive with NHS esters. This work demonstrates novel means for gas-phase conjugation to arginine side chains in polypeptide ions. 相似文献
93.
Kroflič A Sarac B Bešter-Rogač M 《Langmuir : the ACS journal of surfaces and colloids》2012,28(28):10363-10371
A systematic investigation of the micellization process of a biocompatible zwitterionic surfactant 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) has been carried out by isothermal titration calorimetry (ITC) at temperatures between 278.15 K and 328.15 K in water, aqueous NaCl (0.1, 0.5, and 1 M), and buffer solutions (pH = 3.0, 6.8, and 7.8). The effect of different cations and anions on the micellization of CHAPS surfactant has been also examined in LiCl, CsCl, NaBr, and NaI solutions at 308.15 K. It turned out that the critical micelle concentration, cmc, is only slightly shifted toward lower values in salt solutions, whereas in buffer media it remains similar to its value in water. From the results obtained, it could be assumed that CHAPS behaves as a weakly charged cationic surfactant in salt solutions and as a nonionic surfactant in water and buffer medium. Conventional surfactants alike, CHAPS micellization is endothermic at low and exothermic at high temperatures, but the estimated enthalpy of micellization, ΔHM0, is considerably lower in comparison with that obtained for ionic surfactants in water and NaCl solutions. The standard Gibbs free energy, ΔGM0, and entropy, ΔSM0, of micellization were estimated by fitting the model equation based on the mass action model to the experimental data. The aggregation numbers of CHAPS surfactant around cmc, obtained by the fitting procedure also, are considerably low (nagg ≈ 5 ± 1). Furthermore, some predictions about the hydration of the micelle interior based on the correlation between heat capacity change, Δcp,M0, and changes in solvent-accessible surface upon micelle formation were made. CHAPS molecules are believed to stay in contact with water upon aggregation, which is somehow similar to the micellization process of short alkyl chain cationic surfactants. 相似文献
94.
Chang DP Jankunec M Barauskas J Tiberg F Nylander T 《Langmuir : the ACS journal of surfaces and colloids》2012,28(29):10688-10696
Controlling the interfacial behavior and properties of lipid liquid crystalline nanoparticles (LCNPs) at surfaces is essential for their application for preparing functional surface coatings as well as understanding some aspects of their properties as drug delivery vehicles. Here we have studied a LCNP system formed by mixing soy phosphatidylcholine (SPC), forming liquid crystalline lamellar structures in excess water, and glycerol dioleate (GDO), forming reversed structures, dispersed into nanoparticle with the surfactant polysorbate 80 (P80) as stabilizer. LCNP particle properties were controlled by using different ratios of the lipid building blocks as well as different concentrations of the surfactant P80. The LCNP size, internal structure, morphology, and charge were characterized by dynamic light scattering (DLS), synchrotron small-ange X-ray scattering (SAXS), cryo-transmission electron microscopy (cryo-TEM), and zeta potential measurements, respectively. With increasing SPC to GDO ratio in the interval from 35:65 to 60:40, the bulk lipid phase structure goes from reversed cubic micellar phase with Fd3m space group to reversed hexagonal phase. Adding P80 results in a successive shift toward more disorganized lamellar type of structures. This is also seen from cryo-TEM images for the LCNPs, where higher P80 ratios results in more extended lamellar layers surrounding the inner, more dense, lipid-rich particle core with nonlamellar structure. When put in contact with a solid silica surface, the LCNPs adsorb to form multilayer structures with a surface excess and thickness values that increase strongly with the content of P80 and decreases with increasing SPC:GDO ratio. This is reflected in both the adsorption rate and steady-state values, indicating that the driving force for adsorption is largely governed by attractive interactions between poly(ethylene oxide) (PEO) units of the P80 stabilizer and the silica surface. On cationic surface, i.e., silica modified with 3-aminopropltriethoxysilane (APTES), the slightly negatively charged LCNPs give rise to a very significant adsorption, which is relatively independent of LCNP composition. Finally, the dynamic thickness measurements indicate that direct adsorption of intact particles occurred on the cationic surface, while a slow buildup of the layer thickness with time is seen for the weakly interacting systems. 相似文献
95.
Radoslava Stojanović Vesna Ilić Verica Manojlović Diana Bugarski Marija Dević Branko Bugarski 《Applied biochemistry and biotechnology》2012,166(6):1491-1506
In this work, we describe an optimized procedure based on gradual hemolysis for the isolation of hemoglobin derived from bovine
slaughterhouse erythrocytes in a membrane bioreactor. The membrane bioreactor system that provided high yields of hemoglobin
(mainly oxyhemoglobin derivate) and its separation from the empty erythrocyte membranes (ghosts) was designed at a pilot scale.
Ten different concentrations of hypotonic media were assessed from the aspect of the extent of hemolysis, hematocrit values
of the erythrocyte suspensions, cell swelling, and membrane deformations induced by decreased salt concentration. Effective
gradual osmotic hemolysis with an extent of hemolysis of 88% was performed using 35 mM Na-phosphate/NaCl buffer of pH 7.2–7.4.
Under these conditions most of the cell membranes presented the appearance of the normal ghosts under phase contrast microscope.
The hemoglobin purity of >80% was confirmed by SDS-PAGE. Kinetic studies showed that maximal concentration of hemoglobin was
reached after 40 min, but the process cycle at which recovery of 83% was achieved lasted for 90 min. The dynamics of both
steps, (1) transport through the membrane of erythrocytes during process of hemolysis and (2) transport through the reactor
filters, were evaluated. 相似文献
96.
Sebastjan Glin?ek Iztok Ar?on Barbara Mali? Alojz Kodre Marija Kosec 《Journal of Sol-Gel Science and Technology》2012,62(1):1-6
The KTa0.6Nb0.4O3 sols for chemical solution deposition of thin films were prepared from potassium acetate and transition metal ethoxides by
the 2-methoxyethanol based route. The local environment of both transition metals after reflux times 1, 4, 24, and 48 h, whereby
the crystallization behavior of the films was strongly affected, was monitored by extended X-ray absorption fine structure
spectroscopy, at Ta L3 and Nb K edges. The Ta species existed in the sols as monomers, remaining stable even with prolonged reflux time. The Ta–O–K
correlations were confirmed in all cases. In contrast, the Nb-alkoxide formed dimers, with a gradual formation of oligomeric
species with prolonged refluxing. The Nb–O–K correlations were present after all reflux times. The number of K neighbours
around Nb increased upon refluxing, saturating at 24 h. 相似文献
97.
Marija Matković Krešimir Molčanov Robert Glaser Kata Mlinarić-Majerski 《Tetrahedron》2012,68(42):8795-8804
2-(1-Adamantyl)-β-butyrolactones 3a and 3b were synthesized using very common peptide coupling reagents under mild conditions and their ring-opening reactions were then studied. These novel lactones showed pronounced stability and were resistant to cleavage upon acidic water extraction and column chromatographic purification. The adamantane moiety plays an important function in lowering the lactone reactivity by protecting the electrophilic sites on the four membered ring via steric hindrance. However under certain conditions, both O–C(carbonyl) and O–C(alkyl) bond-cleavage ring-opening reactions were observed. Bond-cleavage at physiological temperature makes these novel lactones especially noteworthy. Novel adamantyl-β-butyrolactones have a potential to act as biomembrane soluble amphiphiles that might exhibit a combination of stability and biological activity with the latter hopefully predominating. 相似文献
98.
99.
Functionalized 1,2-dithioles have been synthesized by a ring opening-closing process of 5-substituted- and 5-unsubstituted-2-alkylidene-4-oxothiazolidines with Lawesson's reagent. The 13C NMR data confirmed the meso-ionic structure of these aromatic-type 1,2-dithioles. 相似文献
100.
JPC – Journal of Planar Chromatography – Modern TLC - Quantitative determination of the pesticides alachlor, atrazine and α-cypermethrin in aquatic samples is reported. The method... 相似文献