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121.
Laura Herrero Sagrario CalvarroMario A. Fernández Jesús Eduardo Quintanilla-LópezMaría José González Belén Gómara 《Analytica chimica acta》2015
Phthalates (PAEs) are ubiquitous toxic chemical compounds. During the last few years, some phthalate metabolites (MPAEs) have been proposed as appropriate biomarkers in human urine samples to determine PAE human intake and exposure. So, it is necessary to have fast, easy, robust and validated analytical methods to determine selected MPAEs in urine human samples. Two different instrumental methods based on gas (GC) and ultra-high performance liquid (UHPLC) chromatography coupled to mass spectrometry (MS) have been optimized, characterized and validated for the simultaneous determination of nine primary and secondary phthalate metabolites in urine samples. Both instrumental methods have similar sensitivity (detection limits ranged from 0.03 to 8.89 pg μL−1 and from 0.06 to 0.49 pg μL−1 in GC–MS and UHPLC–MS2, respectively), precision (repeatability, expressed as relative standard deviation, which was lower than 8.4% in both systems, except for 5OH-MEHP in the case of GC–MS) and accuracy. But some advantages of the UHPLC–MS2 method, such as more selectivity and lower time in the chromatographic runs (6.8 min vs. 28.5 min), have caused the UHPLC–MS2 method to be chosen to analyze the twenty one human urine samples from the general Spanish population. Regarding these samples, MEP showed the highest median concentration (68.6 μg L−1), followed by MiBP (23.3 μg L−1), 5cx-MEPP (22.5 μg L−1) and MBP (19.3 μg L−1). MMP (6.99 μg L−1), 5oxo-MEHP (6.15 μg L−1), 5OH-MEHP (5.30 μg L−1) and MEHP (4.40 μg L−1) showed intermediate levels. Finally, the lowest levels were found for MBzP (2.55 μg L−1). These data are within the same order of magnitude as those found in other similar populations. 相似文献
122.
Michelle P. van der Helm Chang-Lin Wang Bowen Fan Mariano Macchione Eduardo Mendes Rienk Eelkema 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20785-20792
Signal transduction in living systems is the conversion of information into a chemical change, and is the principal process by which cells communicate. In nature, these functions are encoded in non-equilibrium (bio)chemical reaction networks (CRNs) controlled by enzymes. However, man-made catalytically controlled networks are rare. We incorporated catalysis into an artificial fuel-driven out-of-equilibrium CRN, where the forward (ester formation) and backward (ester hydrolysis) reactions are controlled by varying the ratio of two organocatalysts: pyridine and imidazole. This catalytic regulation enables full control over ester yield and lifetime. This fuel-driven strategy was expanded to a responsive polymer system, where transient polymer conformation and aggregation are controlled through fuel and catalyst levels. Altogether, we show that organocatalysis can be used to control a man-made fuel-driven system and induce a change in a macromolecular superstructure, as in natural non-equilibrium systems. 相似文献
123.
Dr. Stefano Elli Dr. Eduardo Stancanelli Dr. Zhangjie Wang Dr. Maurice Petitou Prof. Jian Liu Dr. Marco Guerrini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(51):11814-11818
Heparin binds to and activates antithrombin (AT) through a specific pentasaccharide sequence, in which a trisaccharide subsite, containing glucuronic acid (GlcA), has been considered as the initiator in the recognition of the polysaccharide by the protein. Recently it was suggested that sulfated iduronic acid (IdoA2S) could replace this “canonical” GlcA. Indeed, a heparin octasaccharidic sequence obtained by chemoenzymatic synthesis, in which GlcA is replaced with IdoA2S, has been found to similarly bind to and activate antithrombin. By using saturation-transfer-difference (STD) NMR, NOEs, transferred NOEs (tr-NOEs) NMR and molecular dynamics, we show that, upon binding to AT, this IdoA2S unit develops comparable interactions with AT as GlcA. Interestingly, two IdoA2S units, both present in a 1C4-2S0 equilibrium in the unbound saccharide, shift to full 2S0 and full 1C4 upon binding to antithrombin, providing the best illustration of the critical role of iduronic acid conformational flexibility in biological systems. 相似文献
124.
125.
Ion/molecule reactions of +CH2OCH2. with alpha-dicarbonyl compounds were performed via pentaquadrupole mass spectrometry. Besides the previously known [3+ + 2] 1,3-cycloaddition reaction that forms cyclic 1,3-dioxonium ions, an unprecedented reaction proceeding formally by [4 + 1+] cycloaddition of ionized methylene (CH2+.) to the alpha-dicarbonyl compounds occurs competitively, leading to the gas-phase synthesis of several ionized 2-unsubstituted 1,3-dioxoles. This novel cycloaddition reaction may therefore be added to the set of methods available for the synthesis of 1,3-dioxoles. 相似文献
126.
Jia Y Ma N Liu Z Bois-Choussy M Gonzalez-Zamora E Malabarba A Brunati C Zhu J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(20):5334-5351
16-membered meta,para-cyclophanes mimicking the vancomycin binding pocket (D-O-E ring) were designed and synthesized. The structural key features of these biaryl ether containing macrocycles are (1) the presence of beta-amino-alpha-hydroxy acid or alpha,beta-diamino acid as the C-terminal component of the cyclopeptide and (2) the presence of a hydrophobic chain or lipidated aminoglucose at the appropriate position. Cycloetherification by an intramolecular nucleophilic aromatic substitution reaction (S(N)Ar) is used as the key step for the construction of the macrocycle. The atropselectivity of this ring-closure reaction is found to be sensitive to the peptide backbone and chemoselective cyclization (phenol versus primary amine) is achievable. Glycosylation of phenol was realized with freshly prepared 3,4,6-tri-O-acetyl-2-N-lauroyl-2-amino-2-deoxy-alpha-D-glucopyranosyl bromide under phase-transfer conditions. Minimum inhibitory concentrations for all of the derivatives are measured by using a standard microdilution assay, and potent bioactivities against both sensitive and resistant strains are found for some of these compounds (MIC (minimum inhibitory concentration) = 4 microg mL(-1) against VRE). From these preliminary SAR studies, it was anticipated that both the presence of a hydrophobic substituent and an appropriate structure of the macrocycle were required for this series of compounds to be active against VRE. 相似文献
127.
An on-line preconcentration system for zinc determination in 24-h urine, blood plasma and erythrocyte matrices by flame atomic absorption spectrometry (FAAS) was used. This procedure was based on adsorption of Zn(II) ions onto a minicolumn filled with silica gel, chemically modified with niobium(V) oxide (Nb2O5-SiO2). The determination of the optimum conditions for Zn(II) preconcentration was done using two-level full factorial and Doehlert designs. In the optimization procedure, four variables (sample pH, eluent concentration, sample flow rate and eluent flow rate) were investigated. The results obtained from the full factorial design demonstrated that the sample pH and sample flow rate variables, and their interactions, were statistically significant. A Doehlert matrix was used in order to determine the optimum conditions for the sample pH and sample flow rate. The optimized conditions for sample pH and flow rate sampling were 6.6 and 7.1 ml min−1, respectively, to obtain the maximum Zn(II) preconcentration and determination in the biological samples studied. Parameters of analytical curve, precision, effect of other ions in the proposed system and accuracy were achieved to assess the proposed method. The accuracy was confirmed by analysis of certified reference materials (urine Seronorm™ Trace Elements) and recovery tests in blood plasma and erythrocyte samples. Detection limit (3σ/S) of 0.77 μg l−1, precision (calculated as relative standard deviation) of 1.5% for Zn(II) concentration of 10 μg l−1 (n = 7) and a sampling frequency of 27 samples/h were obtained from the proposed system. 相似文献
128.
Anayive Pérez-Rebolledo Nivaldo L. Speziali Eduardo E. Castellano Heloisa Beraldo 《Journal of organometallic chemistry》2006,691(18):3919-3930
Reaction of 2-benzoylpyridine thiosemicarbazone (H2Bz4DH, HL1) and its N(4)-methyl (H2Bz4Me, HL2) and N(4)-phenyl (H2Bz4Ph, HL3) derivatives with SnCl4 and diphenyltin dichloride (Ph2SnCl2) gave [Sn(L1)Cl3] (1), [Sn(L1)PhCl2] (2), [Sn(L2)Cl3] (3), (4) [Sn(L3)PhCl2] (5) and [Sn(L3)Ph2Cl] (6). Infrared and 1H, 13C and 119Sn NMR spectra of 1-3, 5 and 6 are compatible with the presence of an anionic ligand attached to the metal through the Npy-N-S chelating system and formation of hexacoordinated tin complexes. The crystal structures of 1-3, 5 and 6 show that the geometry around the metal is a distorted octahedron formed by the thiosemicarbazone and either chlorides or chlorides and phenyl groups. The crystal structure of 4 reveals the presence of and trans [Ph2SnCl4]2−. 相似文献
129.
Manfredo Hörner Gelson Manzoni de Oliveira Eduardo Giuliani Koehler Lorenzo do CantoVisentin 《Journal of organometallic chemistry》2006,691(6):1311-1314
Deprotonated 1,3-bis(3-acetylphenyl)triazene reacts with Hg(CH3COO)2 and pyridine to give light-yellow crystals of {[HgII(RC6H4NNNC6H4R)2Py]}n (R = acetyl). The tectons [HgII(RC6H4NNNC6H4R)2Py] [R = CH3C(O)] are linked to pairs as centrosymmetric dimers through reciprocal metal-η2-arene π-interactions. The dimeric units are operated by a screw axis 21 parallel to the crystallographic direction [0 1 0], also through a reflection-translation plane parallel to the c-axis, resulting a supramolecular bidimensional (2D) assembling of the dimeric tectons through non classical C-H?(O)CCH3 bonding. 相似文献
130.
Size,Charge, and Stability of Fully Serine‐Based Catanionic Vesicles: Towards Versatile Biocompatible Nanocarriers 下载免费PDF全文
Dr. Sandra G. Silva Prof. M. Luísa C. do Vale Prof. Eduardo F. Marques 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):4092-4101
Vesicles based on mixed cationic and anionic surfactants (catanionic vesicles) offer a number of advantageous colloidal features over conventional lipid‐based vesicles, namely spontaneity in formation, long‐term stability, and easy modulation of size and charge. If biocompatibility is added through rational design of the chemical components, the potential for biorelated applications further emerges. Here, we report for the first time on two catanionic vesicle systems in which both ionic amphiphiles are derivatized from the same amino acid—serine—with the goal of enhancing aggregate biocompatibility. Phase behavior maps for a mixture with chain length symmetry, 12Ser/12‐12Ser, and another with asymmetry, 16Ser/8‐8Ser, are presented, for which regions of vesicles, micelles, and coexisting aggregates are identified. For the asymmetric mixture, detailed phase behavior and microstructure characterization have been carried out based on surface tension, light microscopy, cryo‐SEM, cryo‐TEM, and dynamic light scattering analysis. Vesicles are found with tunable mean size, pH, and zeta potential. Changes in aggregate shape with varying composition and the effect of preparation methods and aging on vesicle features and stability have been investigated in detail. The results are discussed in the light of self‐assembly models and related catanionic systems reported before. A versatile system of robust vesicles is thus presented for potential applications. 相似文献