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121.
《Analytical letters》2012,45(18):2879-2889
A method for basic nitrogen determination in residues of crude oil distillation using infrared spectroscopy and chemometrics algorithms was developed. Interval partial least squares, synergy interval partial least squares, and backward interval partial least squares were evaluated for calibration model construction. The samples were divided into a calibration and prediction set containing 40 and 15 samples, respectively. The first derivative with a Savitzky-Golay filter and the mean centered data showed the best results and were used in all calibration models. The backward interval partial least squares algorithm with spectra divided in 60 intervals and combinations of 4 intervals (1407 to 1372; 1117 to 1082; 971 to 936; 914 to 879 cm?1) showed the best root mean square error of prediction of 0.016 wt%. This calibration model displayed a suitable correlation coefficient between reference and predicted values. 相似文献
122.
An efficient and convenient approach for preparing a giant polypeptide–poly(ethylene oxide) triblock copolymer architecture of defined structure and composition is reported. This copolymer consists of two long polypeptide chains derived from bovine serum albumin of distinct lengths with stabilizing poly(ethylene oxide) side‐chains, a connecting poly(ethylene oxide) block, and the presence of secondary structure elements along the polypeptide backbone. It is synthesized from the abundant plasma protein serum albumin and the polypeptide backbone is fully biodegradable. This approach represents a convenient and efficient strategy for preparing giant polypeptide‐based block copolymers of defined structure via a semi‐synthetic strategy. Such high‐molecular‐weight, biodegradable copolymers are attractive for various biomedical applications 相似文献
123.
In this paper, a modified SIS model with an infective vector on complex networks is proposed and analyzed, which incorporates some infectious diseases that are not only transmitted by a vector, but also spread by direct contacts between human beings. We treat direct human contacts as a social network and assume spatially homogeneous mixing between vector and human populations. By mathematical analysis, we obtain the basic reproduction number R0 and study the effects of various immunization schemes. For the network model, we prove that if R0<1, the disease-free equilibrium is globally asymptotically stable, otherwise there exists an unique endemic equilibrium such that it is globally attractive. Our theoretical results are confirmed by numerical simulations and suggest a promising way for the control of infectious diseases. 相似文献
124.
Summary The pK
a
*
values of 10 nitrogen-containing basic drugs in non-aqueous acetonitrile were determined from the pH* dependence of their electrophoretic mobilities. The pH* scale in the organic solvent was established using background electrolytes with known conventional pK
a
*
values, making further calibration with reference pH electrodes unnecessary. In acetonitrile the pK
a
*
values of analytes (or their conjugated cation acids, BH+, respectively) were 5.2±8.9 pK units>those in water. The observed change in pK
a
*
values of cationic analytes was, however, much less than the known respective change for neutral acids type HA. From the
pK
a
*
values and the actual mobilities, it is possible to predict pH* conditions to enable separation of analytes, and this was demonstrated for two pairs of common drugs. 相似文献
125.
Summary A novel bonded phase for reversed-phase HPLC was synthesized in two steps. Octylamine was first reacted with β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane
(β-ECTS) and then the intermediate product was coupled onto porous silica. The prepared packing was characterized by elemental
analysis, solid-state13C NMR and Fourier transform infrared (FT-IR). Chromatographic evaluations were carried out by using a mixture of organic compounds
including acidic, basic and neutral analytes and methanol-water as binary mobile phase. The results showed that the stationary
phase has excellent chromatographic properties and is resistant to hydrolysis between pH=2≈8. It can be used efficiently for
the separation of basic compounds. 相似文献
126.
Summary The chromatographic properties of an alkylphosphonate-modified magnesia-zirconia composite stationary phase have been investigated
by reversed-phase high-performance liquid chromatography with basic compounds as probes. The influence of organic modifier
composition and mobile phase pH was studied. The new stationary phase, similar to a silica-based reversed-phase stationary
phase, has hydrophobic properties, but greater pH stability. Use of the phase results in more symmetric peaks for basic compounds.
A possible mechanism of retention of basic solutes on the new stationary phase is discussed. The chromatographic behavior
of the basic solutes depends mainly on hydrophobic interactions between the solutes and the hydrophobic moiety of the stationary
phase. Br?nsted acidic and basic sites on the surface of the new stationary phase play an important role in the retention
of ionized solutes by ion-exchange interaction. Promising separations of some basic compounds have been achieved by use of
methanolic TRIS buffer, pH 10.0, as the mobile phase. 相似文献
127.
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130.
多肽聚合物是以多肽为主链的合成聚合物,由于其固有的生物相容性和生物降解性,在生物医学领域展现出广阔的应用前景,然而多肽聚合物的高效、快速、简便合成仍然具有很大挑战。近年来随着合成化学的快速发展,基于α-氨基酸的N-羧基环内酸酐(NCA)开环聚合法制备多肽聚合物取得了突破性进展,合成了大量基于多肽聚合物的新型材料。本文首先介绍了NCA单体的合成机理及最新改进,然后重点介绍了近年来新发展的NCA开环聚合快速、高效制备多肽聚合物的不同引发或催化体系,最后简要介绍了多肽聚合物在抗菌剂、药物递送及组织工程等领域的应用,并提出了多肽聚合物材料在生物医学领域应用所面临的挑战。 相似文献