全文获取类型
收费全文 | 2714篇 |
免费 | 87篇 |
国内免费 | 15篇 |
专业分类
化学 | 1897篇 |
晶体学 | 32篇 |
力学 | 73篇 |
数学 | 179篇 |
物理学 | 399篇 |
无线电 | 236篇 |
出版年
2024年 | 6篇 |
2023年 | 18篇 |
2022年 | 68篇 |
2021年 | 75篇 |
2020年 | 59篇 |
2019年 | 73篇 |
2018年 | 59篇 |
2017年 | 59篇 |
2016年 | 121篇 |
2015年 | 80篇 |
2014年 | 148篇 |
2013年 | 228篇 |
2012年 | 188篇 |
2011年 | 213篇 |
2010年 | 119篇 |
2009年 | 102篇 |
2008年 | 155篇 |
2007年 | 145篇 |
2006年 | 136篇 |
2005年 | 137篇 |
2004年 | 84篇 |
2003年 | 70篇 |
2002年 | 60篇 |
2001年 | 39篇 |
2000年 | 25篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 20篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 15篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1964年 | 5篇 |
排序方式: 共有2816条查询结果,搜索用时 9 毫秒
81.
A Suresh Dinesh K Patre T G Srinivasan P R Vasudeva Rao 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(2):341-347
Spectrophotometric determination of microgram amounts of U(VI) with 2-(5-Bromo-2-Pyridylazo)-5-diethylaminophenol (Br-PADAP), originally developed by Johnson and Florence has been modified to enable the determination of U(VI) in the presence of a large excess of Th(IV). The effects of thorium, tri-n-butyl phosphate (TBP) and ethanol on the estimation of uranium have been studied in detail and are presented in this paper. This modified method can be applied for the analysis of U(VI) both in aqueous and organic samples containing a large excess of Th(IV) (Th:U = 10000:1). 相似文献
82.
This paper reports the study of backbone cleavages in the collision-induced negative-ion mass spectra of the [M - H](-) anions of some synthetic modifications of the bioactive amphibian peptide citropin 1 (GLFDVIKKVASVIGGL-NH(2)). The peptides chosen for study contain no amino acid residues which could effect facile side-chain cleavage, i.e. Ser (-CH(2)O, side-chain cleavage) and Asp (-H(2)O) are replaced by Ala or Lys. We expected that such peptides should exhibit standard and pronounced peaks due to alpha cleavage ions (and to a lesser extent beta cleavage ions) in their collision-induced negative-ion spectra. This expectation was realised, but the spectra also contained peaks formed by a new series of cleavage anions. These are produced following cyclisation of the C-terminal CONH(-) moiety at carbonyl functions of amide groups along the peptide backbone; effectively transferring the NH of the C-terminal CONH(-) group to other amino acid residues. We have called the product anions of these processes beta' ions, in order to distinguish them from standard beta ions. Some beta' ions also fragment directly to some other beta' ions of smaller mass. The reaction coordinates of alpha,beta and beta' backbone processes have been calculated at the HF/6-31G*//AM1 level theory for simple model systems. The initial cyclisation step of the beta' sequence is barrierless and exothermic. Subsequent steps have a maximum barrier of +40 kcal mol(-1), with the overall reaction being endothermic by some 30 kcal mol(-1) at the level of theory used. These calculations take no account of the complexity of the conformationally flexible peptide system, and it is surprising that each of the two reacting centres can 'find' each other in such a large system. 相似文献
83.
Vartika Srivastava Manukonda Suresh Kumar Puthiya Veetil Nidheesh Carlos A. Martínez-Huitle 《Current Opinion in Electrochemistry》2021
Use of robust and safe water disinfection technologies which are inexpensive and energy-efficient are need of the hour to combat the problem of inadequate access of safe and clean drinking water. Energy and chemically intensive water treatment technologies warrant the need for a safe and environmentally sound treatment technology. Electrochemical disinfection or electrodisinfection (ED) is experiencing a great resurgence among the scientific communities owing to its novel use of electrode materials and electric current in an inexpensive and energy-efficient way for achieving the inactivation of microorganisms. Among the various electrodes used in the ED, boron-doped diamonds emerge as a sustainable alternate for their ability to electro generate strong potent oxidants which result in effective pathogen control in drinking water. ED for disinfecting waters occurs via generation of the reactive species which act in the bacterial inactivation mechanisms. In this mini-review, a critical discussion on the fundamentals and applications of promising electrochemical methods using boron-doped diamond anodes (namely electrochemical oxidation), evidencing their advantages for the remediation of drinking water infected with waterborne agents, is given. 相似文献
84.
Pawar Arvind Gajare Shivanand Patil Audumbar Kurane Rajanikant Rashinkar Gajanan Patil Suresh 《Research on Chemical Intermediates》2021,47(7):2801-2820
Research on Chemical Intermediates - Magnetic separable nanoparticles-decorated N-heterocyclic carbene complex with copper (MNP[1-Methyl benzimidazole]NHC@Cu) has been prepared by covalent grafting... 相似文献
85.
The inhibition of mild steel corrosion in aerated acid mixture of 0.5 N H2SO4 and 0.5 N HCl solution was investigated using potentiodynamic polarization studies, linear polarization studies, electrochemical impedance spectroscopy, adsorption, and surface morphological studies. The effect of inhibitor concentration on corrosion rate, degree of surface coverage, adsorption kinetics, and surface morphology is investigated. The inhibition efficiency increased markedly with increase in additive concentration. The presence of PEG and PVP decreases the double-layer capacitance and increases the charge-transfer resistance. The inhibitor molecules first adsorb on the metal surface following a Langmuir adsorption isotherm. Both PEG and PVP offer good inhibition properties for mild steel and act as mixed-type inhibitors. Surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that PVP offers better protection than PEG. 相似文献
86.
Synthesis and cytotoxicity study of pyrazoline derivatives of methoxy substituted naphthyl chalcones
K. R. Ethiraj P. Nithya V. Krishnakumar A. Jesil Mathew F. Nawaz Khan 《Research on Chemical Intermediates》2013,39(4):1833-1841
2-Acetyl naphthalene reacts with various methoxy substituted benzaldehyde in the presence of 10 % sodium hydroxide solution giving functionalized chalcones. The synthesized chalcones when further reacted with hydrazine hydrate in the presence of acetic acid afforded N-acetyl pyrazolines. All the synthesized products were confirmed by various spectral data such as FTIR, 1H NMR, 13C NMR, and HRMS studies. All the synthesized compounds were screened for cytotoxicity against various cell lines. 相似文献
87.
88.
Jinesh M. Kuthanapillil A. Nijamudheen Nayana Joseph Praveen Prakash E. Suresh Ayan Datta K.V. Radhakrishnan 《Tetrahedron》2013
A detailed investigation on the effect of solvent polarity, temperature, and microwave irradiation on periselectivity in cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaine is described. The base catalyzed generation of 3-oxidopyrylium betaine in CHCl3 resulted in the exclusive formation of [6+3] adducts. With increase in solvent polarity and temperature, mixtures of [6+3] and [3+2] adducts were formed, where as under microwave irradiation, [3+2] adducts were formed exclusively. The experimental results have been rationalized on the basis of theoretical calculations. 相似文献
89.
An efficient superparamagnetic Pd–ZnFe2O4 solid catalyst has been synthesized by loading Pd(0) species on zinc ferrite nanoparticles. Sonogashira cross couplings between terminal alkynes and aryl halides were achieved in the absence of any Cu co-catalyst. A Heck–Matsuda coupling reaction of structurally different aryldiazonium tetrafluoroborate substrates was preceded at 40 °C in water. Cyanation of aryl halides was successfully done using K4[Fe(CN)6] as the cyanide source over Pd–ZnFe2O4. The catalyst was also employed for Ullmann type cross coupling reactions. Excellent yield of the products, reusability, and uncomplicated work-up make this catalyst efficient for C–C and C–O coupling reactions. Good yield of products, easy separation, and negligible leaching of Pd from the catalyst surface confirm the true heterogeneity in these catalytic reactions. 相似文献
90.
A new, simple, and efficient protocol is developed for the synthesis of 2-substituted benzoxazole derivatives through N–C–O bond formation using Al3+-exchanged K10 clay (Al3+-K10) as catalyst. A wide range of benzoxazole derivatives are synthesized in high yields without affecting many functional groups. Hot filtration experiments showed the absence of metal leaching and catalyst can be reused for five times with only a slight decrease in yield. 相似文献