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941.
A Grignard reaction of reactantA and phenyl magnesium chloride is used to make a pharmaceutical intermediate at the production scale. The elimination of protecting groups onA was proposed as a means to reduce synthesis costs. This new synthesis route, however, had process efficiency and safety issues associated with it: (1) build-up of unreactedA in the reactor, (2) influence ofA's particle size on the reaction rate, (3) the sensitivity of the reaction rate to the reaction temperature and to the (changing) solvent composition, and (4) the highly exothermic nature of the reaction.The Mettler RC1 Reaction Calorimeter was used to quantify the influence of solvent composition, temperature, and particle size on the reaction rate. Results indicated a dramatic effect of solvent composition and reaction temperature on the reaction rate; for example, over a temperature range of just 30°C, the reaction time decreased from more than a day to just a few minutes. At such high reaction rates, the vessel jacket could not remove the reaction heat sufficiently and the internal temperature rose adiabatically.These results were used to make process design and operation recommendations for safe and efficient plant operation with this modified Grignard reaction system.The authors would like to thank the following for their assistance in this work: E. Daugs for preparing the Grignard reagents, K.L. Gonzales for her help in running the experiments and in the subsequent data work-up; P.M. Russell for his assistance in the design of the slurry addition assembly, and K. Chritz and J. Engel for performing the HPLC analyses of the samples. 相似文献
942.
XU Ying ② CHEN Wen-Kai CAO Mei-Juan LIU Shu-Hong LI Jun-Qian 《结构化学》2007,26(3):361-366
The plane-wave pseudopotential function method,based on density-functional theory,has been used to calculate the adsorption,electronic band structures,orbitals and optical absorption spectrum of [Fe(CN)6]4-on TiO2 anatase(101) surface. Our calculations reveal that the surface-modified anatase system has large adsorption energy and a much narrower band gap. [Fe(CN)6]4-adsorption on the (101) surface could lead to a large red shift of the anatase optical absorption threshold,which extends into a visible region significantly. The calculated results are in agreement with the experiment and other theoretical studies reasonably. It is very important for the understanding and further development of photovoltaic materials that are active under visible light. 相似文献
943.
Summary In this work we establish the basic layout of IONICS, an expert system for optimizing the separation of ionogenic solutes in Reversed-Phase Liquid Chromatography, using the pH and the organic-modifier concentration of the mobile phase as parameters. We also present REMO, a front-end system that automates the retention modelling stage, based on a 9-parameter model. This system uses a scale transformation to suppress several numerical problems previously observed and features a strategy for automatic calculation of an initial approximation to the model optimum. The successful application of this system to a set of seven drugs is described. The final models are accurate and have smaller numerical problems. We also describe the use of a genetic algorithm instead of classical non-linear least-squares for fitting the model to the experimental data. Results indicate that genetic algorithms are a valuable, complementary tool for retention modelling. 相似文献
944.
We describe a three-step method development/optimization strategy for HPLC assay/impurity methods for pharmaceuticals, which include multiple-column/mobile phase screening using a system equipped with a column-switching device, further optimization of separation by using multiple organic modifiers in the mobile phase, and multiple-factor method optimization using Plackett-Burman experimental designs. In the first two steps, commercially available chromatography optimization software, DryLab, was used to perform computer simulations. This allows the method developer to evaluate each condition (one column/mobile phase combination) with retention data from two scouting gradient runs. This approach significantly reduces the number of runs in method development. After a satisfactory separation was obtained, we used a method optimization step with Plackett-Burman experimental designs. The purpose of the 16-injection set experiments was to evaluate nine method factors with regard to method precision, accuracy, sensitivity and specificity. The results provided logical justifications in selecting method parameters such as column temperature, detection wavelength, injection volume, and sample solvent, etc. In data analysis, instead of the traditional mathematical manipulations, we used the graphical methods to examine and present data by creating the so-called main effect plots. Because replicates of design points were not run, the data did not allow the testing of statistical significance. However, it provided visual presentations in a way that is easy to understand for the method developer and end user alike. 相似文献
945.
G. Matysik 《Chromatographia》1996,43(5-6):301-303
Summary A mixture of 13 DABS-amino acids has been chromatographed on high-performance silica gel layers developed with eluents containing increasing concentrations of ethyl acetate in heptane + chloroform, using a modification of stepwise multiple development MGD described in a earlier paper. Densitograms were obtained at 485 nm. The MGD method was very efficient, separating all 13 DABS-amino acids, and rapid, owing to the use of a non-aqueous mobile phase. 相似文献
946.
947.
The reactivity of tetraethoxysilane (TEOS) used in many sol-gel syntheses can be increased by prehydrolysis. In contrast to one-step prehydrolysis acidic two-step prehydrolysis causes an increase of the reactivity of the low molecular species provided the total water/TEOS ratios are the same in both cases. By choice of the processing conditions of the hydrolysis—shown on variation of water content, hydrolysis steps and heat treatment—the degree of condensation, the ratio of hydrolyzable (-OC2H5) and hydrolyzed groups (-OH) and the structure of the low molecular species (short chains, 3-membered and 4-membered rings) can be influenced systematically. The development of the building units formed in the early reaction stages is ascertained by molybdate method and 29Si NMR measurements. 相似文献
948.
统计了美国高中化学教科书《化学:概念与应用》中氧化还原反应的知识内容所包含的图片类型,分析研究其作用,同时针对我国化学教科书图片设计提出了建议。 相似文献
949.
950.
Proteomics is a research field aiming to characterize molecular and cellular dynamics in protein expression and function on a global level. The introduction of proteomics has been greatly broadening our view and accelerating our path in various medical researches. The most significant advantage of proteomics is its ability to examine a whole proteome or sub-proteome in a single experiment so that the protein alterations corresponding to a pathological or biochemical condition at a given time c… 相似文献