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991.
This study examines the reagent gas pressure and ion source temperature dependence for dimethyl ether chemical ionization (DME CI) mass spectra recorded with an external source ion trap mass spectrometer (ITMS). Information for better controls of the reagent gas pressure in order to obtain fair CI spectra is provided. The origin of M+? ions observed in DME CIMS is discussed in detail. Furthermore, the ion source temperature effect on the DME CI is also investigated. 相似文献
992.
[reaction: see text] Anodic intramolecular cyclization of alpha-(phenylthio)acetamides using a fluoride ion mediator was realized. Under ultrasonic irradiation, cyclization was accelerated markedly to give desired cyclized products in moderate to good yields. The local heating effect of ultrasonic irradiation seems to be more advantageous than usual heating. 相似文献
993.
The starting electrophoretic motion of a porous, uniformly charged, spherical particle, which models a solvent-permeable and ion-penetrable polyelectrolyte coil or floc of nanoparticles, in an arbitrary electrolyte solution due to the sudden application of an electric field is studied for the first time. The unsteady Stokes/Brinkman equations with the electric force term governing the fluid velocity fields are solved by means of the Laplace transform. An analytical formula for the electrophoretic mobility of the porous sphere is obtained as a function of the dimensionless parameters , , , and , where a is the radius of the particle, κ is the Debye screening parameter, λ is the reciprocal of the square root of the fluid permeability in the particle, ρp and ρ are the mass densities of the particle and fluid, respectively, ν is the kinematic viscosity of the fluid, and t is the time. The electrophoretic mobility normalized by its steady-state value increases monotonically with increases in and , but decreases monotonically with an increase in , keeping the other parameters unchanged. In general, a porous particle with a high fluid permeability trails behind an identical porous particle with a lower permeability and a corresponding hard particle in the growth of the normalized electrophoretic mobility The normalized electrophoretic acceleration of the porous sphere decreases monotonically with an increase in the time and increases with an increase in from zero at . 相似文献
994.
ZnSn(OH)6的热分解动力学 总被引:1,自引:0,他引:1
用TG/DTG联用技术, 在2.5、5.0、10.0、15.0、20.0 K·min-1不同线性升温条件下, 研究了ZnSn(OH)6的热分解过程. 结果表明, 在氮气气氛下, ZnSn(OH)6在298-873 K范围内发生了一步分解. 其失重率与理论计算值相符. 应用非等温多重扫描速率法对热分解过程进行了动力学分析, ZnSn(OH)6在氮气中分解的活化能E=128.77 kJ·mol-1, 指前因子lg(A/s-1)=10.61, 机理函数为Mample单行法则. 相似文献
995.
采用浸渍法制备了一系列Ag/ZrO2催化剂, 考察了Ag/ZrO2催化剂对1,2-丙二醇选择性氧化合成丙酮醛反应的催化性能. 实验结果表明: 在原料气配比为V(N2)∶V(O2)=300∶19, n(O2)/n(alcohol)=1.2, 反应物液时空速为3.2 g/(g•h), 反应温度为673 K时, 1,2-丙二醇选择性氧化合成丙酮醛反应的转化率为95.7%, 选择性为55.3%, 高于传统电解银催化剂. UV-Vis DRS和XPS的研究结果表明: 在Ag/ZrO2催化剂上存在大量的Ag+和Agnδ+有利于促进催化活性的提高. 相似文献
996.
Systematic Study of Ti‐Distribution in Titanosilicate *BEA Zeolites via Symmetry‐Adapted Enumeration
The high performance of titanosilicate zeolites in various industrial oxidation reactions is highly affected by the distribution of Ti atoms in their frameworks. Because of their structural complexity, previous theoretical studies mainly focus on the preferential location of single Ti atoms within the unit cells of titanosilicate zeolites. When multiple Ti atoms are required, conventional approaches consider only symmetrically related T sites to reduce the computation complexity. Such symmetry‐constrained approaches obviously overlooked many possible configurations. Herein, we conduct a systematic study on the distribution of two Ti atoms in the unit cell of titanosilicate zeolite *BEA . Different from conventional symmetry‐constrained approaches, we introduce two Ti atoms simultaneously without any constraint and adopt a symmetry‐adapted algorithm to enumerate all possible configurations for double‐Ti introduction. We generate a total of 273 distinct configurations and analyze the Ti‐distribution via Boltzmann statistics. We find that many of the configurations overlooked by conventional symmetry‐constrained approaches indeed exhibit more feasible energies, which may lead to different Ti‐distributions. Our study indicates the necessity of unconstrained introduction of Ti atoms when multiple‐Ti atoms are considered for calculations. 相似文献
997.
998.
Wang F Han MY Mya KY Wang Y Lai YH 《Journal of the American Chemical Society》2005,127(29):10350-10355
A novel class of monodisperse conjugated polymer nanoparticles have been readily prepared by the facile reprecipitation of poly{1,3-bis[2-(3-alkylthienyl)]azulene} or poly{1,3-bis[2-(3-alkoxythienyl)]azulene}. The multicomponent poly(bithiophene-alt-azulene) macromolecules were efficiently self-assembled into a wide range of size-tunable nanoparticles from a few tens to five hundred nanometers via the hydrophobic and pi-stacking effects in the mixed chloroform/methanol solutions. Electronically altered polymer structures with different alkyl or alkoxy substitutes exhibited variable self-assembling behaviors to precisely tune the size and the optical/electronic properties of nanoparticles. A strong size dependence of continuous bathochromic absorption and significant enhanced emission were observed with the increase of particle size. A linear relationship between the absorption or fluorescence intensities and the particle size was demonstrated as well, and this is very useful to probe the intermolecular interactions and the size evolutions of conjugated polymer nanoparticles. After the size-dependent optical and electronic properties are created, they can be further optimized to improve the performance of materials prior to the use in novel organic nanodevices in a cost-effective way. 相似文献
999.
利用酯基锡与缺位Keggin结构杂多阴离子PW9O9-34反应,合成了6种新的杂多阴离子--有机金属配合物M9[(R'OOCCHR"CH2SnOH2)3(PW9O34)2]·xH2O(M=(CH3)4N+,K+;R'=CH3-,CH3CH2-;R"=H,CH3-),通过元素分析、IR光谱、紫外电子光谱、1H
NMR、31P NMP、183w NMR和TGA-DSC热分析等测试手段对标题配合物进行了表征和性质研究,确定该系列配合物为A-β-PW9
型夹心配合物结构. 相似文献
1000.
Zhixia Zhuang Chenglong Yang Xioaru Wang Pengyuan Yang Benli Huang 《Fresenius' Journal of Analytical Chemistry》1996,355(3-4):277-280
Palladium salts can be used as a coprecipitation carrier for the preconcentration of trace elements from natural water prior to their measurement by atomic spectrometry (AAS). The palladium is subsequently reduced by the introduction of hydrogen gas into the sample solution. The procedure is applied to the determination of Cu, Pb and Cd in seawater (enrichment factor 50) and synthetic water samples. Operating conditions have been optimized for the analysis of real samples. With the technique established an enrichment factor (500 fold) is feasible in synthetic samples. The recoveries of Cu, Cd and Pb from seawater are 95, 103 and 100%, respectively. This simple and rapid method can be applied in a wide pH-range and with complex matrices. 相似文献