全文获取类型
收费全文 | 10975篇 |
免费 | 2177篇 |
国内免费 | 2515篇 |
专业分类
化学 | 8702篇 |
晶体学 | 271篇 |
力学 | 709篇 |
综合类 | 227篇 |
数学 | 1327篇 |
物理学 | 4431篇 |
出版年
2024年 | 27篇 |
2023年 | 184篇 |
2022年 | 408篇 |
2021年 | 447篇 |
2020年 | 463篇 |
2019年 | 533篇 |
2018年 | 438篇 |
2017年 | 437篇 |
2016年 | 502篇 |
2015年 | 579篇 |
2014年 | 664篇 |
2013年 | 861篇 |
2012年 | 951篇 |
2011年 | 959篇 |
2010年 | 757篇 |
2009年 | 749篇 |
2008年 | 817篇 |
2007年 | 718篇 |
2006年 | 697篇 |
2005年 | 590篇 |
2004年 | 517篇 |
2003年 | 468篇 |
2002年 | 562篇 |
2001年 | 518篇 |
2000年 | 375篇 |
1999年 | 277篇 |
1998年 | 173篇 |
1997年 | 101篇 |
1996年 | 113篇 |
1995年 | 101篇 |
1994年 | 108篇 |
1993年 | 80篇 |
1992年 | 114篇 |
1991年 | 75篇 |
1990年 | 71篇 |
1989年 | 48篇 |
1988年 | 30篇 |
1987年 | 35篇 |
1986年 | 38篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1979年 | 3篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1959年 | 3篇 |
1957年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Amal A. El Daibani Yuecheng Xi Lijun Luo Xue Mei Chunyang Zhou Shin Yasuda 《Natural product research》2020,34(6):797-803
AbstractPrevious studies have revealed sulfation as a major pathway for the metabolism of hesperetin, naringenin and apigenin. The current study was designed to identify the human cytosolic sulfotransferase (SULT) enzyme(s) capable of sulfating these flavonoid compounds. Of the thirteen human SULTs, six (1A1, 1A2, 1A3, 1B2, 1C4, 1E1) displayed significant sulfating activity toward hesperetin, five (1A1, 1A2, 1A3, 1B2, 1C4) displayed sulfating activity towards naringenin, and four (1A1, 1A2, 1A3, 1C4) showed sulfating activity towards apigenin. Of the four human organ specimens tested, liver and intestine cytosols displayed much higher hesperetin-, naringenin- and apigenin-sulfating activity than lung and kidney cytosols. Moreover, sulfation of hesperetin, naringenin and apigenin was shown to take place in HepG2 human hepatoma cells and Caco-2 human colon adenocarcinoma cells under cultured conditions. Taken together, these results provided a biochemical basis underlying the metabolism of hesperetin, naringenin and apigenin through sulfation in humans. 相似文献
232.
Zhen‐Ting Du Guo‐Ren Yue An‐Pai Li Jun‐Ying Ma Tong‐Xing Wu Xue‐Gong She Xin‐Fu Pan 《中国化学会会志》2004,51(3):505-508
A facile total synthesis of (±)‐nimbiol 1 has been achieved. In order to decrease the dioxo byproduct 2a , an improved oxidation system of CrO3/H2O/HOAc/NaOAc was used. 相似文献
233.
正庚烷在超稳Y沸石(USY)负载超强酸催化剂上加氢异构化 总被引:6,自引:0,他引:6
The Pt-bearing SO42-/ZrO2 superacid catalysts supported on ultra stable Y (USY) zeolite were prepared by impregnation and characterized by X-ray diffraction, nitrogen adsorption and Hammett indicators. Their catalytic activities were evaluated in the hydroisomerization of n-heptane with an atmospheric fixed-bed reactor. The catalysts possessed a high surface area, superacidity and well maintained pore structure of USY support. The supported catalysts with a suitable SO42-/ZrO2 loading exhibited a higher catalytic activity and selectivity than the unsupported SO42-/ZrO2 catalyst or the Pt supported on USY catalyst without superacid. At the reaction temperature of 220 ℃, over the catalyst with a Pt loading of 0.8wt% and ZrO2 loading of 10wt%, the conversion of n-heptane could be as high as 35.2% with a selectivity of 87.9% for isomerization products. 相似文献
234.
235.
Studies on the Interaction of Beryllon Ш with Proteins by Voltammetric Technique and its Application 总被引:1,自引:0,他引:1
A new quantitative determination method of proteins using beryllon Ш by voltammetric technique was developed in this paper. In pH 3.5 Britton-Robinson (B-R) buffer solution, beryllon Ш can bind with human serum albumin (HSA) to form an electro-inactive supermolecular complex. Beryllon Ш has a well-defined voltammetric reduction peak at -0.38 V (vs. SCE) and the addition of protein in this solution can cause the decrease of the reductive peak current. Based on the decrease of the reduction peak current, a new electrochemical method for the determination of HSA was established with linear range of 1.0~40.0 mg/L and the detection limit of 1.0 mg/L. This method is further applied to the determination of real sample of healthy human serum. 相似文献
236.
采用循环伏安法,稳态法,计时电位法等研究了SO2在聚钴卟啉膜电极上的电化学氧化过程,并和SO2在贵金属电极上的行为进行了比较。 相似文献
237.
Determination of Partial Molar Volumes of EPA and DHA Ethyl Esters in Supercritical Carbon Dioxide 总被引:4,自引:0,他引:4
Mei HUANG Xian Da WANG Ren Tian XIONG Ping Dong WU Qi Long REN* National Laboratory of Secondary Resources Chemical Engineering Zhejiang University Hangzhou 《中国化学快报》2002,13(1)
The use of supercritical fluids (SCFs) as solvents has been attracting widespread interest in the research and commercial applications. The study of partial molar volumes of solutes at infinite dilution in the near-critical region is of considerable fundamental importance, as these data reflects the interactions occurring between the solute and the solvent. Experimental measurements of partial molar volumes may be divided into two categories: direct and indirect methods. The direct methods… 相似文献
238.
交联助剂对PPC/NBR弹性体结构和性能的影响 总被引:2,自引:1,他引:2
研究了马来酸酐(MA)及异氰脲酸三烯丙酯(TAIC)对聚丙撑碳酸酯/丁腈橡胶共混弹性体结构和性能的影响,发出加入MA或TAIC能有效地改善交联网络;加入适量MA能显著改善共混弹性体热氧老化稳定性;加入TAIC使共混弹性体具有优良的高弹特性和力学性能。 相似文献
239.
3He/4He ratios in samples of sea water obtained at depths from surface to 300 m in the upper layer of the Western Pacific Ocean were measured by a mass spectrometer VG5400. The lateral and vertical distribution of He isotopes in the studied area was discussed in detail on the basis of 3He/4He ratios. Excess and depleted 3He. in relation to δ3He value of surface water in equilibrium with air has been discussed in the area, which may be mainly attributed to the incorporation of the North Pacific Intermediate Water with the Equatorial Upwelling and the exchange of water masses between the South China Sea and the Western Pacific, respectively. The present work in Western Pacific has also indicated that He isotopes may be used as a tracer for mixing processes of water masses and oceanic circulation. 相似文献
240.
Rheological investigation on a series ot unvulcamzed polybutadiene elastomers of different processability has been carried out by means of a capillary extrusion rheometer. It is found that the processability of unvulcanized polybutadiene can be correlated with the occurrence of unsteady flow and the wall stress, dependence of the dimensionless number e characterizing the entrance elongational elasticity which has been found to be sensitive to the branching structure and the molecular weight distribution of the samples. Interpretations based on the structural data of unvulcanized polybutadiene were discussed. 相似文献