全文获取类型
收费全文 | 1170篇 |
免费 | 59篇 |
国内免费 | 25篇 |
专业分类
化学 | 985篇 |
晶体学 | 8篇 |
力学 | 14篇 |
数学 | 92篇 |
物理学 | 155篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 46篇 |
2021年 | 50篇 |
2020年 | 77篇 |
2019年 | 75篇 |
2018年 | 109篇 |
2017年 | 76篇 |
2016年 | 80篇 |
2015年 | 57篇 |
2014年 | 91篇 |
2013年 | 119篇 |
2012年 | 98篇 |
2011年 | 77篇 |
2010年 | 55篇 |
2009年 | 45篇 |
2008年 | 58篇 |
2007年 | 43篇 |
2006年 | 19篇 |
2005年 | 20篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1254条查询结果,搜索用时 0 毫秒
101.
Razieh FAZAELI Hamid ALIYAN Shadpour MALLAKPOUR Zahra RAFIEE Maryam BORDBAR 《催化学报》2011,32(4):582-588
A novel compound constructed from polyoxometalate (H3PW12O40,PW12) and poly(amidoamine) (PA) was prepared at room temperature in an aqueous solution by an impregnation method.A series of novel 1,3,5-triaryl-2-pyrazoline derivatives was synthesized by the reaction between chalcone and phenylhydrazine in the presence of the title compound,PW12/PA,in high yields.The structures of the compounds obtained were determined by IR and 1H NMR spectra. 相似文献
102.
103.
Gas sensing is one of the most promising applications for graphene. Using molecular dynamics simulation method, adsorption isotherm of xenon (Xe) gas on defected and perfect graphene is studied in order to investigate sensing properties of graphene for Xe gas. In this method, first generation of Brenner many-body potential is used to simulate the interaction of carbon–carbon (C) atoms in graphene, and Lennard–Jones two-body potential is used to simulate interaction of Xe–Xe and Xe–C atoms. In the simulated systems, adsorption coverage, radial distribution function, heat of adsorption, binding energy and specific heat capacity at constant volume are calculated for several temperatures between 90 K and 130 K, and various pressures. It was found that both of the defected and perfect graphene could be introduced as very good candidates for adsorption of Xe gas. 相似文献
104.
The isomorphic substitution of boron into ZSM‐5 zeolite under static hydrothermal condition was investigated. Evaluation of hydrothermal synthesis of BZSM‐5 was performed by treating the synthesis mixture by different aging processes, namely, ultrasonic, static, stirring, and microwave‐assisted aging prior to the conventional hydrothermal treatment. The synthetic processes with different techniques of aging prior to the onset of conventional hydrothermal crystallization were compared with a process without any prior aging. The obtained results showed that the ultrasonic and microwave assisted aging shortened the crystallization time and altered the crystal size and the morphology of the obtained products. The characteristics of the synthesized products were obtained by FT‐IR spectroscopic, XRD and SEM techniques. 相似文献
105.
Maryam?FaizEmail author Laia?Acarin Bernardo?Castellano Berta?Gonzalez 《BMC neuroscience》2005,6(1):26
Background
The forebrain subventricular zone (SVZ)-olfactory bulb pathway and hippocampal subgranular zone (SGZ) generate neurons into adulthood in the mammalian brain. Neurogenesis increases after injury to the adult brain, but few studies examine the effect of injury on neural and glial precursors in the postnatal brain. To characterize the spatio-temporal dynamics of cell proliferation in the germinative zones, this study utilized a model of postnatal damage induced by NMDA injection in the right sensorimotor cortex at postnatal day 9. 相似文献106.
Shi W Shafaei-Fallah M Anson CE Rothenberger A 《Dalton transactions (Cambridge, England : 2003)》2005,(24):3909-3912
The investigation presents new synthetic methods for the generation of tripodal P/S ligands by reactions of metal alkoxides and carboxylates with the organoperthiophosphinic acid anhydride Lawesson's reagent. Four new transition-metal complexes containing various tripodal ligand sets were synthesised and characterised. 相似文献
107.
Ansari M Kazemipour M Khosravi F Baradaran M 《Chemical & pharmaceutical bulletin》2004,52(10):1166-1170
Losartan, a highly effective blood pressure-lowering agent, has been widely used for the treatment of hypertension. A fast and reliable method for the determination of losartan was highly desirable to support formulation screening and quality control. A first-derivative UV spectroscopic method and HPLC were developed for the determination of losartan in the tablet dosage form. The first-derivative spectrum recorded between 220 and 320 nm and a zero-crossing technique for first-derivative measurement at 232.5 nm were selected. The selectivity and sensitivity of the method was in desirable range. In comparison with the direct UV method, first-derivative UV spectroscopy has a definite trough without any interference from UV absorbing-excipients. This method is also fast and economical in comparison with the more time-consuming HPLC method regularly used for formulation screening and quality control and can be used routinely by any laboratory possessing a spectrophotometer with a derivative accessory. The linear concentration ranges were 2-50 microg ml(-1), (D(1)=-0.0159C-0.0056, r=0.9994, n=6). Between-days CV of < or =2.9%, within-day CV of < or =2.1%, and analytical recovery close to 98.1% show the suitability of the method for determination in quality control. 相似文献
108.
Rezaee Elham Amrolah Somayeh Minaei Nazari Maryam Tabatabai Sayyed Abbas 《Molecular diversity》2021,25(1):45-53
Molecular Diversity - Soluble epoxide hydrolase (sEH) enzyme plays an important role in the metabolism of endogenous chemical mediators, epoxyeicosatrienoic acids, which are involved in the... 相似文献
109.
Let R be a commutative Noetherian ring. It is shown that the finitely generated R-module M with finite Gorenstein dimension is reflexive if and only if M p is reflexive for p ∈ Spec(R) with depth(R p) ? 1, and $G - {\dim _{{R_p}}}$ (M p) ? depth(R p) ? 2 for p ∈ Spec(R) with depth(R p) ? 2. This gives a generalization of Serre and Samuel’s results on reflexive modules over a regular local ring and a generalization of a recent result due to Belshoff. In addition, for n ? 2 we give a characterization of n-Gorenstein rings via Gorenstein dimension of the dual of modules. Finally it is shown that every R-module has a k-torsionless cover provided R is a k-Gorenstein ring. 相似文献
110.
Hossaini Z Rostami-Charati F Firoziyan S Sabbaghan M Khalilzadeh MA 《Combinatorial chemistry & high throughput screening》2012,15(6):503-508
An efficient synthesis of dialkyl pyrrolo[2,1-a]isoquinoline-2,3-dicarboxylates, pyrrolo[1,2-a]quinoline-1,2- dicarboxylates and indolizines is described via one-pot reactions of isoquinoline, quinoline or pyridine and phenacyl bromids with dialkyl acetylenedicarboxylates or diaryloylacetylene under solvent-free conditions at 50°C. The mild reaction conditions and high yields of the products exhibit the good synthetic advantage of these methods. 相似文献