全文获取类型
收费全文 | 56356篇 |
免费 | 9665篇 |
国内免费 | 7749篇 |
专业分类
化学 | 40525篇 |
晶体学 | 879篇 |
力学 | 3225篇 |
综合类 | 549篇 |
数学 | 6774篇 |
物理学 | 21818篇 |
出版年
2024年 | 122篇 |
2023年 | 1109篇 |
2022年 | 1756篇 |
2021年 | 2127篇 |
2020年 | 2383篇 |
2019年 | 2259篇 |
2018年 | 1898篇 |
2017年 | 1981篇 |
2016年 | 2671篇 |
2015年 | 2775篇 |
2014年 | 3311篇 |
2013年 | 4226篇 |
2012年 | 5179篇 |
2011年 | 5239篇 |
2010年 | 3791篇 |
2009年 | 3606篇 |
2008年 | 3910篇 |
2007年 | 3443篇 |
2006年 | 3129篇 |
2005年 | 2675篇 |
2004年 | 2044篇 |
2003年 | 1608篇 |
2002年 | 1481篇 |
2001年 | 1220篇 |
2000年 | 1108篇 |
1999年 | 1194篇 |
1998年 | 946篇 |
1997年 | 868篇 |
1996年 | 844篇 |
1995年 | 779篇 |
1994年 | 658篇 |
1993年 | 571篇 |
1992年 | 469篇 |
1991年 | 426篇 |
1990年 | 363篇 |
1989年 | 272篇 |
1988年 | 215篇 |
1987年 | 194篇 |
1986年 | 185篇 |
1985年 | 167篇 |
1984年 | 101篇 |
1983年 | 107篇 |
1982年 | 64篇 |
1981年 | 44篇 |
1980年 | 35篇 |
1979年 | 19篇 |
1976年 | 24篇 |
1975年 | 22篇 |
1973年 | 18篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Rapid Synthesis of Lead Oxide Nanorods by One-step Solid-state Chemical Reaction at Room Temperature
A simple and facile method was reported to synthesize lead oxide nanorods. Nanorods of lead oxide were obtained directly from grinding solid metal salt and sodium hydroxide in agate mortar with the assistance of a suitable nonionic surfactant in only one step, which is different from the result of hydroxide in solution. The product has been characterized by XRD, TEM and SEM. The formation mechanism of rod-like morphology is discussed and the surfactant plays an important soft-template role in modifying the interface of solid-state reaction and according process of rod-formation. 相似文献
922.
A novel TPPTS-Rh/SiO2 catalyst, prepared by directly modifying a heterogeneous high-surface-area Rh/SiO2 catalyst with water-soluble TPPTS ligands, could decrease the resistance of masstransfer in water/oil biphasic media for the hydroformylation of higher olefins. The catalytic performancefor hydroformylation on this biphasic TPPTS-Rh/SiO2 catalyst system was higher than those of thetraditional biphasic HRhCO(TPPTS)3 systems, owing to the chemical bonds between the highly dispersedRh metal particles and the TPPTS ligands. The catalyst system is applicable for hydroformylation ofhigher olefins such as 1-dodecene. 相似文献
923.
用高效毛细管电泳前沿分析法研究了酸性药物那格列奈与人血浆白蛋白的结合常数、结合位点和结合率。使用未涂层的毛细管柱 (4 0cm× 5 0 μmi.d .;有效柱长 32cm) ,磷酸盐缓冲溶液 (pH 7.4 ,离子强度0 .17)为背景溶液 ,在紫外检测波长 2 14nm、运行电压 18kV和重力进样 10 0s的条件下 ,利用那格列奈谱峰的平台高度和游离药物浓度的良好线性关系 (r>0 .999,n =6 ) ,测定了那格列奈的游离药物浓度。固定药物浓度 (2 0 0 μmol L ,2 5 0 μmol L) ,考察不同的蛋白质浓度对结合的影响 ;固定蛋白质浓度 (10 0 μmol L) ,考察不同的药物浓度对结合的影响。实验数据采用非线性拟和程序进行处理 ,得到了那格列奈的蛋白质结合参数。高效毛细管电泳前沿分析法测定的数据重现性良好 (RSD <2 .5 % ,n =3) ,在药代动力学和药效学研究方面具有简便、准确的优点。 相似文献
924.
925.
926.
The geometries of van der Waals complex CO2…CO were optimized at DFT and second-order Moller-Plesset perturbation(MP2) levels with the large basis set,three stable structures were found.The most stable structure has a T-shape geometry in which the CO lies along the C2 axis of CO2,with the two C atoms direct contact and R(C…C)=0.3227nm.The corresponding energies of the most stable structure were calculated by means of MP2,MP4D,MP4DQ,MP4SDTQ,MP4SDQ,CCSD and CCSD(T) methods,The BSSE (basis set superposition error) wads eliminated by the Boys-Bernardi counterpoise correction(CP) method.According to thermodynamics data.van der Waals complex CO2…CO can found at a low temperature and or a high pressure,There is a little charge transferred between the two interacted subunits.In the most stable structure,CO2 is the acceptor and CO is the donor. 相似文献
927.
Amorphous poly(ethylene terephthalate) was annealed at temperatures around the glass transition temperature and then heated up in differential scanning calorimeter at 20 °C min−1. It was found that the annealing favored the subsequent cold crystallization and this effect became stronger with increasing annealing temperature. The experimental results were explained by considering the structural change during the annealing. 相似文献
928.
The use of poly(maleic acid–styrene)-encapsulated silica for the determination of monovalent and divalent cations is well accepted in ion chromatography. The separation of Mn2+, alkali and alkaline earth metal cations is obtained under the same chromatographic conditions. The influences of pH and the concentration of eluent on the retention of cations have been studied. The preparation conditions of packings were studied. The metal ions in the boiler water samples from a thermal power plant were quantitatively determined using this column. The results are in agreement with those determined by ICP and Volumetric analysis methods. 相似文献
929.
Poon KW Liu W Chan PK Yang Q Chan TW Mak TC Ng DK 《The Journal of organic chemistry》2001,66(5):1553-1559
Up to eight redox-active ferrocenyl units have been incorporated, through the unsaturated ethynyl linkers, on the periphery of a series of cyclic tetrapyrrole derivatives including zinc(II) phthalocyanine and 2,3-naphthalocyanine, and nickel(II) meso-diphenylporphyrin. The synthesis of the former two macrocycles 4 and 7 involves the Sonogashira coupling reaction of ferrocenylethyne with 4,5-dichlorophthalonitrile (1) or 6,7-dibromonaphthalonitrile (5), respectively, followed by a base-promoted cyclization. The meso-bis(ferrocenylethynyl)porphyrin 11 has been prepared from the dibromo analogue 10 also by a palladium-catalyzed coupling reaction. These novel macrocyclic compounds have been spectroscopically and electrochemically characterized. As revealed by cyclic voltammetry, the ferrocenyl moieties appear to be electrochemically independent in these complexes and there is no significant electronic coupling among the iron(II) centers. 相似文献
930.