全文获取类型
收费全文 | 8496篇 |
免费 | 1275篇 |
国内免费 | 1095篇 |
专业分类
化学 | 6120篇 |
晶体学 | 57篇 |
力学 | 555篇 |
综合类 | 73篇 |
数学 | 961篇 |
物理学 | 3100篇 |
出版年
2024年 | 22篇 |
2023年 | 155篇 |
2022年 | 268篇 |
2021年 | 315篇 |
2020年 | 334篇 |
2019年 | 330篇 |
2018年 | 240篇 |
2017年 | 217篇 |
2016年 | 344篇 |
2015年 | 406篇 |
2014年 | 434篇 |
2013年 | 562篇 |
2012年 | 662篇 |
2011年 | 766篇 |
2010年 | 497篇 |
2009年 | 497篇 |
2008年 | 550篇 |
2007年 | 488篇 |
2006年 | 464篇 |
2005年 | 449篇 |
2004年 | 318篇 |
2003年 | 279篇 |
2002年 | 276篇 |
2001年 | 233篇 |
2000年 | 182篇 |
1999年 | 192篇 |
1998年 | 177篇 |
1997年 | 150篇 |
1996年 | 160篇 |
1995年 | 172篇 |
1994年 | 126篇 |
1993年 | 111篇 |
1992年 | 81篇 |
1991年 | 103篇 |
1990年 | 66篇 |
1989年 | 61篇 |
1988年 | 51篇 |
1987年 | 37篇 |
1986年 | 25篇 |
1985年 | 21篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Capillary electrophoresis with amperometric detection of curcumin in Chinese herbal medicine pretreated by solid-phase extraction 总被引:1,自引:0,他引:1
In the present study, curcumin from Chinese herbal medicine turmeric was determined by capillary electrophoresis with amperometric detection (CE-AD) pretreated by a self-designed, simple, inexpensive solid-phase extraction (SPE) cartridge based on the material of tributyl phosphate resin. An average concentration factor of 9 with the recovery of > 80% was achieved when applied to the analysis of curcumin in extracts of tumeric. Under the optimized CE-AD conditions: a running buffer composed of 15 mM phosphate buffer at a pH 9.7, separation voltage at 16 kV, injection for 6 s at 9 kV and detection at 1.20 V, CE-AD with SPE exhibited low detection limit as 3 x 10(-8) mol/l (S/N = 3), high efficiency of 1.0 x 10(5) N, linear range of 7 x 10(-4) -3 x 10(-6) mol/l (r = 0.9986) for curcumin extracted from light petroleum. The method developed resulted in enhancement of the detection sensitivity and reduction of interference from sample matrix in complicated samples and exhibited the potential application for routine analysis, especially in food, because a relatively complete process of sample treatment and analysis was described. 相似文献
62.
Determination of tripolyphosphate in frozen cod and scallop adductor by ion chromatography 总被引:4,自引:0,他引:4
We introduce a method for the determination of tripolyphosphate in frozen cod and scallop adductor by using ion chromatography. The tripolyphosphate was extracted from minced cod and scallop adductor with deionized water by ultrasonic leaching, and then the proteins soluble in water were precipitated with trichloroacetic acid and removed by filtering. An ion chromatograph with an ionpac AS11-HC anion-exchange column, an ASRS (Anion Self Regenerating Suppression), a conductivity detector and a gradient pump (sodium hydroxide gradient) was used. The detection limit was below 5 mg tripolyphosphate/kg cod or scallop adductor. This method is applicable to the determination of polyphosphates in aquatic products and the procedures are easy to implement. 相似文献
63.
The dependence of the frequency factor on the temperature (A=A
0
T
m) has been examined and the errors involved in the activation energy calculated from some integral methods without considering
such dependence have been estimated. Investigated integral methods are the Coats-Redfern method, the Gorbachev-Lee-Beck method,
the Wanjun-Yuwen method and the Junmeng-Fusheng method. The results have shown that the error in the determination of the
activation energy calculated ignoring the dependence of the frequency factor on the temperature can be rather large and it
is dependent on x=E/RT and the exponent m. 相似文献
64.
65.
对已经商品化的Perkin-Elmer TMS-2型热机分析仪进行改进,用来测量聚合物材料的热释蠕变行为。按照7SCr分步加载的程序,用弯曲法测量了-83~300℃温度范围内低密度聚乙烯的玻璃化转变松弛过程,并从TSCr谱上计算其相应的分子参数,实验结果与用扭转的TSCr方法所得结果相等,因此这是一种研究聚合物材料松弛行为的方便可行的技术。 相似文献
66.
本文综述了前列环素及其类似物的合成。类似物包括有7-羰基—、10,10-二氟—、5-氯—,4-羰基—、6,9-硫—、6,9-氮—,6 a-碳—前列环素以及苯前列环素等。前列环素及其类似物是一类具有抑制血小板聚集的生物活性化合物。 相似文献
67.
Binyuan Liu Yang Li Boo-gyo Shin Li Zhang Weidong Yan 《Polymer Degradation and Stability》2007,92(5):868-875
The thermal properties and degradation behaviors of poly(norbornene-2,3-dicarboxylic acid dialkyl esters) (PNB-dialkyl esters) (alkyl = Me (PNB-Me), Et (PNB-Et), Pr (PNB-Pr), and Bu (PNB-Bu)) were investigated by thermogravimetric analysis (TGA) in dynamic conditions and by infrared (IR) spectroscopy. The PNB-dialkyl esters show good thermal stability up to 350 °C, and the thermal stability decreases in the order Me > Et > Pr > Bu with the increase in size of side chain. The effect of side-chain size on the thermal degradation behaviors of PNB-dialkyl esters is evidenced by one-step thermal degradation profile for PNB-Me while two-step thermal degradation profile for PNB-Et, PNB-Pr, and PNB-Bu. Transformation is deduced to undergo β-hydrogen elimination and formation of anhydride group in the first stage of thermal degradation reaction according to TGA and IR results for PNB-Et, PNB-Pr, and PNB-Bu. The apparent activation energy and thermal degradation model of PNB-dialkyl esters are estimated by means of Ozawa-Flynn-wall method and Phadnis-Deshpande method, respectively. 相似文献
68.
Jijun Qiu Weidong Yu Xiangdong Gao Xiaomin Li 《Journal of Sol-Gel Science and Technology》2007,44(3):235-239
Ordered porous TiO2 films, including TiO2 nanotube arrays, are fabricated by a sol-gel dip-coating approach via ZnO nanorod templates obtained from aqueous solution
approach. The results indicate that the morphologies of ordered porous TiO2 films have been great affected by the sol-gel dip-coating cycle number. Open-ended TiO2 nanotube arrays can be obtained in optimum dip-coating cycle numbers. The TiO2 nanotubes with the inner diameter matching well with the diameters of ZnO nanorods, are well assembled and separate each
other. When the cycle number is less than this optimum value, no intact porous TiO2 film can be obtained. As the cycle number is larger than this optimum value, an ordered porous TiO2 film with many throughout holes is formed. The evolutive mechanism of ordered porous TiO2 films is proposed. 相似文献
69.
Adsorption, desorption and activities of acid phosphatase on various colloidal particles from an Ultisol 总被引:1,自引:0,他引:1
Adsorption, desorption and activity of acid phosphatase on various soil colloidal particles and pure clay minerals were studied. Higher adsorption amounts and low percentage of desorption of acid phosphatase were found on fine soil clays (<0.2 μm). Electrostatic force and ligand exchange are the major driving forces that are involved in the adsorption of enzymes on soil clays. More enzyme molecules were adsorbed on soil clays in the presence of organic components. However, enzymes on organic clays were more easily released. One-third of the enzyme on goethite was adsorbed via ligand exchange process. Some other interactions, such as van der Waals force, hydrophobic force and hydrogen bonding may be more important in the adsorption of enzyme on kaolinite and the enzyme in this system cannot be easily removed. Coarse clays (0.2–2 μm) and inorganic soil clays had higher affinities for enzyme molecules than fine clays and organic clays, respectively. The activity of enzyme bound on soil clays was inhibited and the thermal stability was increased in the presence of organic matter. Data obtained in this study are helpful for a better understanding of the interactions of enzymes with inorganic and organic constituents in soil and associated environments. 相似文献
70.
A new quantum scattering approach (linear combination of arrangement channels-scattering wavefunction, LCAC-SW) proposed by Deng and his co-workers is used to calculate collinear state-to-state reaction probabilities for the F + H2(v) → HF(v') + H system. Several interesting problems such M threshold energy, compound states and enhance by translational energy of the reactants and the vibration excitation of products are discussed and they are compared with other theoretical investigations reported in the literature. It is shown that the LCAC-SW approach is the successful one of quantum scattering methods. 相似文献