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991.
992.
在数学教学中,教师掌握了学生学习各个知识点的思维过程与知识间的相互干扰,采用相应的教学方法,对杜绝不当的知识干扰,排除解题障碍,提高教学效果,有着重要的作用. 一、局部出发,轻易判断 学生解题过程中,对一些数学概念或数学原理的发生、发展过程没有深刻的理解,往往根据某些局部特征不作深入的审题,不弄清命题的本质涵义,没有摆脱局部事实的片面性而把握事物的本质,产生解题的片面性与主观性,造成解题的不当与失误.例如:  相似文献   
993.
We show that the Hausdorff dimension of quasi-circles of polygonal mappings is one.Furthermore,we apply this result to the theory of extremal quasiconformal mappings.Let [μ] be a point in the universal Teichmller space such that the Hausdorff dimension of fμ(Δ) is bigger than one.We show that for every kn∈(0,1) and polygonal differentials ψn,n=1,2,...,the sequence {[kn ψn/|ψn|]} cannot converge to [μ] under the Teichmer metric.  相似文献   
994.
本文首先引入了由广义微分算子定义的某些$p$叶解析函数新子类$S_{p,q,\lambda}^{m,j,l}[A,B;\gamma]$ 和 $H_{p,q,\lambda}^{m,j,l}(\alpha,\beta)$, 然后研究了该子类的优化性质, 所得结果推广了某些已知结论.  相似文献   
995.
 制备了 SiO2 负载的壳聚糖席夫碱钯催化剂, 利用 X 射线衍射、红外光谱和热重等方法对催化剂进行了表征, 并考察了该催化剂催化羰基加氢为亚甲基的反应性能, 以二苯甲酮为底物, 系统地研究了反应时间、反应温度和催化剂用量等因素对反应性能的影响. 结果表明, 该催化剂具有较高的催化芳香羰基加氢为亚甲基的活性和选择性, 且反应可在较低的温度和常压的温和条件下进行. 关键词:壳聚糖; 席夫碱;  相似文献   
996.
A new chitosan imprinting adsorbent using diatomite as core material was prepared by using the surface molecular imprinting technology with the Pb2+ as imprinted ion. The preparation process conditions of the surface molecular imprinting adsorbent were studied. The adsorbent was characterized by using Fourier transform infrared (FTIR) spectrum. FTIR spectrum indicated that it was cross-linked by epichlorohydrin. The new imprinting adsorbent could provide a higher adsorption capacity for Pb2+, which reached 139.6 mg/g increasing 32.3% compared with cross-linking chitosan adsorbent (the initial Pb2+ concentration of 600 mg/L). The adsorption velocity was quick and the equilibration time of the imprinting adsorbent for Pb2+ was 3 h that shortened about 40% compared with cross-linking chitosan adsorbent. It had a more wide pH range of 5–7 than that of cross-linking chitosan adsorbent. The new imprinting adsorbent can be reused for up to ten cycles without loss of adsorption capacity. In the kinetics and isotherm study, the pseudosecond order model and Langmuir model could represent the adsorption process.  相似文献   
997.
Densities of ionic liquids at different temperature and pressure were collected from 84 references. The collection contains 7381 data points derived from 123 pure ionic liquids and 13 kinds of binary ionic liquids mixtures. In terms of the collected database, a group contribution method based on 51 groups was used to predict the densities of ionic liquids. In group partition, the effect of interaction among several substitutes on the same center was considered. The same structure in different substitutes may have different group values. According to the estimation of pure ionic liquids’ densities, the results show that the average relative error is 0.88% and the standard deviation (S) is 0.0181. Using the set of group values three pure ionic liquids densities were predicted, the average relative error is 0.27% and the S is 0.0048. For ionic liquid mixtures, they are thought considered as idea mixtures, so the group contribution method was used to estimate their densities and the average relative error is 1.22% with S is 0.0607. And the method can also be used to estimate the densities of MClx type ionic liquids which are produced by mixing an ionic liquid with a Cl? anion and a kind of metal chloride.  相似文献   
998.
设计合成了一种C60-苯并噻吩吡咯烷衍生物(2),以1HNMR、13CNMR、FTIR、UV-Vis和FAB-MS进行了结构表征。由其在甲苯溶液中的紫外光谱和荧光发射光谱测得,在最大发射波长下的荧光寿命为5.34ns。Z-扫描技术测得其分子三阶非线性极化率γ(3)为1.82×10-33esu,大于C60的文献报道值7.5×10-34esu,表明在激光激发下苯并噻吩与C60之间发生了分子内能量转移和电荷传递。理论计算结果进一步佐证了电荷转移的发生。  相似文献   
999.
通过实验对不同温度条件下半胱氦酸抑制盐酸对碳钢腐蚀的性能进行评价,并采用分子动力学模拟(Molecular Dynamics Simulation,简称MD)方法,从缓蚀剂膜抑制腐蚀粒子扩散的角度对其缓蚀机理进行深入研究.静态失重实验显示:随温度的升高(25~65℃),半胱氨睃缓蚀剂的缓蚀效率呈逐渐下降趋势,其数值从88.36%降至61.64%.MD模拟发现:随温度升高,半胱氨酸缓蚀剂膜的自由体积逐渐增大,且腐蚀粒子与缓蚀剂膜的相互作用也逐渐减弱,更有利于腐蚀粒子在膜中的主动扩散;同时膜内半胱氨酸分子的自扩散能力也随温度升高而增强,腐蚀粒子在缓蚀剂膜携带下被动迁移的过程也随之加剧.主动扩散和被动迁移两方面的变化表明,腐蚀粒子在缓蚀剂膜中扩散能力随温度升高而增大;也就是说,随温度升高,半胱氨酸缓蚀剂膜对腐蚀粒子的扩散抑制能力逐渐降低,腐蚀粒子更易扩散运移至金属表面,导致半胱氨酸缓蚀剂缓蚀效率的降低.  相似文献   
1000.
Monophosphine‐o‐carborane has four competitive coordination modes when it coordinates to metal centers. To explore the structural transitions driven by these competitive coordination modes, a series of monophosphine‐o‐carborane Ir,Rh complexes were synthesized and characterized. [Cp*M(Cl)2{1‐(PPh2)‐1,2‐C2B10H11}] (M=Ir ( 1 a ), Rh ( 1 b ); Cp*=η5‐C5Me5), [Cp*Ir(H){7‐(PPh2)‐7,8‐C2B9H11}] ( 2 a ), and [1‐(PPh2)‐3‐(η5‐Cp*)‐3,1,2‐MC2B9H10] (M=Ir ( 3 a ), Rh ( 3 b )) can be all prepared directly by the reaction of 1‐(PPh2)‐1,2‐C2B10H11 with dimeric complexes [(Cp*MCl2)2] (M=Ir, Rh) under different conditions. Compound 3 b was treated with AgOTf (OTf=CF3SO3?) to afford the tetranuclear metallacarborane [Ag2(thf)2(OTf)2{1‐(PPh2)‐3‐(η5‐Cp*)‐3,1,2‐RhC2B9H10}2] ( 4 b ). The arylphosphine group in 3 a and 3 b was functionalized by elemental sulfur (1 equiv) in the presence of Et3N to afford [1‐{(S)PPh2}‐3‐(η5‐Cp*)‐3,1,2‐MC2B9H10] (M=Ir ( 5 a ), Rh ( 5 b )). Additionally, the 1‐(PPh2)‐1,2‐C2B10H11 ligand was functionalized by elemental sulfur (2 equiv) and then treated with [(Cp*IrCl2)2], thus resulting in two 16‐electron complexes [Cp*Ir(7‐{(S)PPh2}‐8‐S‐7,8‐C2B9H9)] ( 6 a ) and [Cp*Ir(7‐{(S)PPh2}‐8‐S‐9‐OCH3‐7,8‐C2B9H9)] ( 7 a ). Compound 6 a further reacted with nBuPPh2, thereby leading to 18‐electron complex [Cp*Ir(nBuPPh2)(7‐{(S)PPh2}‐8‐S‐7,8‐C2B9H10)] ( 8 a ). The influences of other factors on structural transitions or the formation of targeted compounds, including reaction temperature and solvent, were also explored.  相似文献   
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