全文获取类型
收费全文 | 4839篇 |
免费 | 910篇 |
国内免费 | 753篇 |
专业分类
化学 | 3626篇 |
晶体学 | 91篇 |
力学 | 230篇 |
综合类 | 58篇 |
数学 | 588篇 |
物理学 | 1909篇 |
出版年
2024年 | 12篇 |
2023年 | 128篇 |
2022年 | 170篇 |
2021年 | 210篇 |
2020年 | 288篇 |
2019年 | 257篇 |
2018年 | 234篇 |
2017年 | 216篇 |
2016年 | 273篇 |
2015年 | 301篇 |
2014年 | 312篇 |
2013年 | 349篇 |
2012年 | 412篇 |
2011年 | 411篇 |
2010年 | 342篇 |
2009年 | 329篇 |
2008年 | 352篇 |
2007年 | 269篇 |
2006年 | 257篇 |
2005年 | 218篇 |
2004年 | 148篇 |
2003年 | 108篇 |
2002年 | 124篇 |
2001年 | 78篇 |
2000年 | 77篇 |
1999年 | 75篇 |
1998年 | 52篇 |
1997年 | 69篇 |
1996年 | 91篇 |
1995年 | 75篇 |
1994年 | 48篇 |
1993年 | 41篇 |
1992年 | 23篇 |
1991年 | 36篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 3篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有6502条查询结果,搜索用时 15 毫秒
61.
A purification method to remove the metal catalysts and impurity carbon materials from arc-discharge-grown single-walled carbon nanotubes (SWCNTs) has been developed. Microporous membrane and the oxidation in the air for the crude SWCNTs were used to eliminate the coexisting metal catalysts nanoparticles,carbon nanoparticles and amorphous carbon. Then we used the high resolution transmission electron microscopy (HRTEM) to characterize the crude SWCNTs prepared by arc-discharge method and the purified SWCNTs. The Raman spectra and the thermogravimetric analysis (TGA) were also utilized to analyze the approach of our purification for SWCNTs. With this method the SWCNTs with the purity more than 95% could be obtained. 相似文献
62.
合成了螺[异苯并呋喃-1(3H),9'-(9H)-2'-N,N-二苄胺基-6'-二乙胺基占吨]-酮-3,C_(37)H_(34)N_2O_3,单斜晶系,空间群Cc,晶体学参数为a=16.826(4),b=10.648(4),c=17.618(7),β=92.25(2)°,V=3154(2),Z=4,M_r=566.7,D_x=1.19g/cm3,F(000)=1200。结构由直接法解出,偏离因子R=0.080。分子由占吨和异苯并呋喃两部分组成Y形结构,占吨部分相连的苄基的两个苯环位于占吨部分的两侧。 相似文献
63.
Intracellular delivery of enzymes is essential for protein-based diagnostic and therapeutic applications. Protein-spherical nucleic acids (ProSNAs) defined by protein core and dense shell of oligonucleotides have been demonstrated as a promising vehicle-free enzyme delivery platform. In this work, we reported a crosslinking strategy to vastly improve both delivery efficiency and intracellular sensor performance of ProSNA. By assembling individual ProSNA with lactate oxidase (LOX) core into a nanoscale particle, termed as crosslinked SNA (X-SNA), the enzyme delivery efficiency increased up to 5–6 times higher. The LOX X-SNA was later demonstrated as a ratiometric probe for quantitative detection of lactate in living cells. More importantly, X-SNA probe showed significantly improved sensor performance with signal-to-noise ratio 4 times as high as ProSNA when detecting intracellular lactate.By crosslinking protein spherical nucleic acid (SNA) into a supramolecular architecture X-SNA, the intracellular enzyme delivery efficiency was significantly enhanced, showing 3–4 times higher signal-to-noise ratio in detecting intracellular lactate. 相似文献
64.
A new potential tetradentate ligand, 1,4-bis(N-1-methylimidazol-2-ylmethyl)-1,4-diazacycloheptane (l), together with its CuII complex [CulCl]ClO4 (1), has been reported. The crystal structure of 1, determined by single-crystal X-ray analysis, shows that it is in chiral P212121 space group. The CuII centre is penta-coordinated in square pyramidal geometry and the diazacycloheptane (DACH) ring adopts normal boat configuration. The most striking feature of this complex is the formation of a 3D network bridged through the C-H?Cl hydrogen bonds with the perchlorate anions in the cavities, and stabilized via π-π stacking interactions along the a-direction. The solution behaviour of 1 has been further investigated by UV/Vis and ESR techniques. 相似文献
65.
66.
La2O3对Ni/γ-Al2O3甲烷化催化剂的助催化作用 总被引:14,自引:0,他引:14
我国将稀土作为助剂引入镍基甲烷化催化剂,大大提高了催化剂的活性和热稳定性,并已投入工业应用[1-3].稀土对不同镍催化剂反应性能及其作用机理的研究已有一些报导[3-7].谢有畅等观察到镍负载在经单层La2O3改性的γ-Al2O3表面,其晶粒要比没有La2O3时小得多.Rotgerink等认为添加La后反应速率的增加不只是由于几何效应,而是La对甲烷化本身有促进作用,单位镍表面的活性是随La含量不同而改变的,活性增加的同时表观活化能也增加[5].作为助剂的La2O3在氢还原和反应过程中的变化及其作用的研究和讨论较少,目前一般认为添… 相似文献
67.
68.
The thermal decomposition of ammonium vanadyl oxalate supported on La2O3, MgO, SiO2, Al2O3, ZrO2, TiO2, SAPO-5, and ZSM-5 oxides in a dynamic atmosphere of dry air was compared by thermal gravimetric analysis (TG) and differential thermal analysis (DTA). The calcined catalysts were characterized by X-ray diffractometry (XRD). The TG and DTA results demonstrate that the surface acid-base properties of the oxides play a significant role in the decomposition behaviour of the supported ammonium vanadyl oxalate, i.e. the basic oxides exhibit an endothermic effect and the acidic oxides show an exothermic effect. Two mechanisms are suggested for thermal decomposition of ammonium vanadyl oxalate on basic and acidic oxides, respectively. After transformation of the ammonium vanadyl oxalate to vanadia, subsequent rearrangement of the vanadia on the surface of the supports was also observed. During the thermal treatment or calcination in air, solid state reactions of vanadia with the surface of oxides such as La2O3, ZrO2 and TiO2 took place to form new phases. 相似文献
69.
Ionic-liquid-supported peptide synthesis demonstrated by the synthesis of Leu(5)-enkephalin 总被引:1,自引:0,他引:1
A new strategy for the synthesis of oligopeptides was developed using an ionic liquid as a soluble support. The efficiency of this ionic liquid-phase approach was demonstrated by the synthesis of a bioactive pentapeptide, Leu(5)-enkephalin, in good yield and reasonable purity. The structures and purities of the reaction intermediates in each step were verified easily by routine spectroscopic analysis, and no chromatographic procedures were needed during the synthesis. 相似文献
70.
Xin Sheng Li Yao Jun Zhang Qin Xin Chun Xin Ji Yan Fen Miao Li Wang 《Reaction Kinetics and Catalysis Letters》1996,57(1):177-182
Volumetric H2-uptake measurements on an Mo2N (79 m2g–1) sample reduced at 673 K have been carried out and the uptake isotherms in the temperature range of 308–623 K have been determined. Both the total and reversible hydrogen uptake increased with the uptake temperature. The irreversible hydrogen uptake increased abruptly when the uptake temperature was raised up to 423 K. The maximum of irreversible hydrogen uptake was measured at 473 K. The HIR/Mo ratio calculated from the uptakes obtained in the temperature range of 308–623 K varies in the range of 0.0010–0.0202. One possible mechanism for hydrogen adsorption is proposed to be heterolytic dissociation on Mo-N paris, in which the molybdenum atoms are in unsaturated coordination. 相似文献