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31.
用CeO2作为铈源,采用可重复利用的H3PO4及非模板剂的情况下,用低温超声法成功合成了六方结构的CePO4一维纳米线材料。用X-射线粉末衍射(XRD)、透射电镜(TEM)和荧光分光光度计(FL)测试样品的物相结构、微观形貌、颗粒尺寸和发光性能;并研究超声时间和PO3-4/Ce3+摩尔比对产物的形貌和荧光性能的影响。结果表明:实验所做出的样品全部是六方晶系的结构,形貌都为一维纳米线,其纳米线长50~200nm,宽5~40nm左右;不同超声时间和PO3-4/Ce3+摩尔比的纳米线长径比不同,随超声时间的延长和PO3-4/Ce3+摩尔比增大纳米线出现团聚现象,产物在250~300nm处有宽的激发峰,在378nm处有一个发射峰,是属于Ce3+的5d-4f能级跃迁。 相似文献
32.
Prathibha Kumari Weiwei Liu Cheng-Jie Wang Jun Dai Mei-Xin Wang Qi-Qiong Yang Yu-Hua Deng Zhihui Shao 《中国化学》2020,38(2):151-157
Summary of main observation and conclusion A Pd-catalyzed asymmetric aromative[4+3]-cyclization reaction of amino-trimethylenemethanes(TMM,1d,ip3-oles)with fused 1-azadienes has been developed.This method enables access to the synthetically importance and biologically active benzofuran fused azepines and indeno-azepines in excellent efficiency and stereoselectivity(up to 95%yield,99%ee,>19:1 dr). 相似文献
33.
Moritz Balkenhohl Harish Jangra Ilya S. Makarov Shu‐Mei Yang Hendrik Zipse Paul Knochel 《Angewandte Chemie (International ed. in English)》2020,59(35):14992-14999
The development of a predictive model towards site‐selective deprotometalation reactions using TMPZnCl?LiCl is reported (TMP=2,2,6,6‐tetramethylpiperidinyl). The pKa values of functionalized N‐, S‐, and O‐heterocycles, arenes, alkenes, or alkanes were calculated and compared to the experimental deprotonation sites. Large overlap (>80 %) between the calculated and empirical deprotonation sites was observed, showing that thermodynamic factors strongly govern the metalation regioselectivity. In the case of olefins, calculated frozen state energies of the deprotonated substrates allowed a more accurate prediction. Additionally, various new N‐heterocycles were analyzed and the metalation regioselectivities rationalized using the predictive model. 相似文献
34.
Caiyun Xu Haihong Wu Zhanrong Zhang Bingxiao Zheng Jianxin Zhai Kaili Zhang Wei Wu Xuelei Mei Mingyuan He Buxing Han 《Chemical science》2022,13(6):1629
Effective hydrodeoxygenation (HDO) of aromatic alcohols is very attractive in both conventional organic synthesis and upgrading of biomass-derived molecules, but the selectivity of this reaction is usually low because of the competitive hydrogenation of the unsaturated aromatic ring and the hydroxyl group. The high activity of noble metal-based catalysts often leads to undesired side reactions (e.g., saturation of the aromatic ring) and excessive hydrogen consumption. Non-noble metal-based catalysts suffer from unsatisfied activity and selectivity and often require harsh reaction conditions. Herein, for the first time, we report chemoselective HDO of various aromatic alcohols with excellent selectivity, using porous carbon–nitrogen hybrid material-supported Co catalysts. The C–OH bonds were selectively cleaved while leaving the aromatic moiety intact, and in most cases the yields of targeted compounds reached above 99% and the catalyst could be readily recycled. Nitrogen doping on the carbon skeleton of the catalyst support (C–N matrix) significantly improved the yield of the targeted product. The presence of large pores and a high surface area also improved the catalyst efficiency. This work opens the way for efficient and selective HDO reactions of aromatic alcohols using non-noble metal catalysts.Porous carbon–nitrogen hybrid material-supported Co catalysts can effectively promote the chemoselective hydrodeoxygenation reaction of a various of aromatic alcohols in ethanol and hydrogen atmosphere, under relatively mild conditions. 相似文献
35.
Dong-Zhao Yang Zhen-Zhen Chen Mei Chi Ying-Ying Dong Shou-Zhi Pu Qi Sun 《Molecules (Basel, Switzerland)》2022,27(3)
5-Hydroxymethyl-2′-deoxycytidine (5hmdC) phosphoramidite and triphosphate are important building blocks in 5hmdC-containing DNA synthesis for epigenetic studies. However, efficient and practical methods for the synthesis of these compounds are still limited. The current research provides an intensively improved synthetic method that enables the preparation of commercially available cyanoethyl-protected 5hmdC phosphoramidite with an overall yield of 39% on 5 g scale. On the basis of facile and efficient accesses to cyanoethyl protected-5hmdU and 5hmdC intermediates, two efficient synthetic routes for 5hmdC triphosphate were also developed. 相似文献
36.
Nonlinear Dynamics - In this paper, a novel fixed-time second-order sliding mode (SOSM) controller has been developed for a class of nonlinear systems with output constraints. Based on the output... 相似文献
37.
利用Sinc-Galerkin法数值求解Burgers方程的初边值问题。首先,用Hopf-Cole变换将二阶非线性的Burgers方程变换为二阶线性方程,同时把第一类边界条件变为第二类边界条件。时间上的导数采用θ加权格式离散,空间导数采用Sinc-Galerkin法离散,端点处分别引入权函数处理变换后的第二类边界条件。最后,通过数值算例验证了Sinc-Galerkin法的指数收敛性,与精确解相比,本文构造的数值格式精度高,能够有效捕捉激波等物理现象。 相似文献
38.
多媒体在目前教学中扮演一个很重要的角色,但做一个好的课件,是件很不容易的事。笔者通过Authorware6.5简体中文版制作课件,现将制作过程中有关细节拿出来供大家参考,希望大家在遇到类似问题时,能少走弯路,节约时间。1对视频文件的处理中常见问题化学课件中常需要插入一些视频, 相似文献
39.
40.
The optimization of nutrient levels for the production of pristinamycins by Streptomyces pristinaespiralis CGMCC 0957 in submerged fermentation was carried out using the statistical methodologies based on the Plackett–Burman design,
the steepest ascent method, and the central composite design (CCD). First, the Plackett–Burman design was applied to evaluate
the influence of related nutrients in the medium. Soluble starch and MgSO4·7H2O were then identified as the most significant nutrients with a confidence level of 99%. Subsequently, the concentrations
of the two nutrients were further optimized using response surface methodology of CCD, together with the steepest ascent method.
Accordingly, a second-order polynomial regression model was finally fitted to the experimental data. By solving the regression
equation from the model and analyzing the response surface, the optimal levels for soluble starch and MgSO4·7H2O were determined as 20.95 and 5.67g/L, respectively. Under the optimized medium, the yield of pristinamycins in the shake
flask and 5-L bioreactor could reach 1.30 and 1.01g/L, respectively, which is the highest yield reported in literature to
date. 相似文献