全文获取类型
收费全文 | 1086篇 |
免费 | 54篇 |
国内免费 | 22篇 |
专业分类
化学 | 765篇 |
晶体学 | 7篇 |
力学 | 47篇 |
综合类 | 3篇 |
数学 | 71篇 |
物理学 | 269篇 |
出版年
2024年 | 5篇 |
2023年 | 12篇 |
2022年 | 38篇 |
2021年 | 36篇 |
2020年 | 50篇 |
2019年 | 43篇 |
2018年 | 55篇 |
2017年 | 61篇 |
2016年 | 68篇 |
2015年 | 46篇 |
2014年 | 62篇 |
2013年 | 130篇 |
2012年 | 93篇 |
2011年 | 69篇 |
2010年 | 44篇 |
2009年 | 52篇 |
2008年 | 58篇 |
2007年 | 50篇 |
2006年 | 24篇 |
2005年 | 19篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 15篇 |
2001年 | 14篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有1162条查询结果,搜索用时 15 毫秒
101.
The nanocatalyst-assisted sonodegradation of Basic Blue 41 (BB41) dye in aqueous medium was modeled and optimized using response
surface method (RSM) based on Box-Behnken design. The studied variables included pH, initial dye concentration, H2O2 concentration and sonolysis time while each factor varied at three levels: Low level (−1), Medium level (0) and High level
(+1). The ultrasound -assisted degradation was well described by developing quadratic model with correlation value squared
(R2) of 0.9114. Factor effects along with interaction effects were evaluated. The graphical optimization step was conducted to
achieve the best experimental condition in dye removal. pH, H2O2 concentration and initial dye concentration of the reaction were investigated. It was recognized that at lower pH values
the dye removal rate decreased. However, dye removal rate increased (82.5%) by increasing the concentration of H2O2 and by lowering the initial dye concentration.
相似文献
102.
The aim of this review is to provide an overview of the contributions and recent advances made by Iranian scientists in the
field of isocyanide-based reactions between 1999 and 2009. With over 100 publications during this period, Iranians are responsible
for approximately 10% of all publications in the world involving isocyanide-based multicomponent reactions (IMCRs). Some important
aspects of these IMCRs include the execution of reactions in green reaction mediums like water or ethanol, high atom economies,
mild reaction conditions, high yields, and catalyst-free processes. On the other hand, in most of these reactions, new classes
of heterocyclic compounds with potential biological and medicinal activities have been reported. 相似文献
103.
Parvin Farshchi Seyed Khatiboleslam Sadrnezhaad Naser Moharram Nejad Mahmood Mahmoodi Leila Ibrahimi Ghavam Abadi 《Journal of nanoparticle research》2011,13(8):3511-3519
Using survey data, public awareness of and attitudes toward nanotechnology are examined in Iran (N = 759). Iran is a developing country with a national nanotechnology action plan for a ten year period starting from 2003
and has been active in the field of research and development of nanotechnology meanwhile. First, the results show that majority
of people are still not familiar with nanotechnology and perceived risks posed by this technology are not considered to be
a lot and most people feel its benefits outweigh the risks. The emotions toward this technology are of a hopeful and positive
nature and this technology is looked upon favorably in Iran. In particular, our results reveals that although the level of
trust is high specially in scientists to communicate the risks with the public, there are a great number who just have some
trust not quite a lot of it. Knowing that it is a hard and time-consuming effort to manage a nation’s view on nanotechnology,
extensive research as well as collaboration with other countries is needed to effectively communicate the risks in time. 相似文献
104.
Mahmood Alaghmandan Yemon Choi Ebrahim Samei 《Journal of Mathematical Analysis and Applications》2014
Let G be a restricted direct product of finite groups {Gi}i∈I, and let Z?1(G) denote the centre of its group algebra. We show that Z?1(G) is amenable if and only if Gi is abelian for all but finitely many i , and characterize the maximal ideals of Z?1(G) which have bounded approximate identities. We also study when an algebra character of Z?1(G) belongs to c0 or ?p and provide a variety of examples. 相似文献
105.
106.
107.
Aflatoxin determination is imperative among agricultural and food products as the pollution of the toxic aflatoxin could cause severe hazards towards animals and human beings. Here, we prepared Elaeagnus gum derived porous carbon material as electrode modified material. In situ electropolymerization of molecularly imprinted polymer utilizing phenol as monomer and aflatoxin B1 as target template was further processed onto the porous carbon surface to achieve aflatoxin B1 sensing ability. This sensitive MIP sensor has a detection range from 5 pM to 100 pM of aflatoxin B1, an electrochemical sensitivity of 82.4 μA log(pM)−1 cm−2 with a detection limit of 1.7 pM, and a recovery rate of real sample measurement is 98.21 %. Good selectivity, fair repeatability and stability was confirmed. This work demonstrates the promising application of Elaeagnus gum derived porous carbon modified electrode sensor for food and drug monitoring. 相似文献
108.
Edwards HG Mohsin MA Sadooni FN Nik Hassan NF Munshi T 《Analytical and bioanalytical chemistry》2006,385(1):46-56
The Raman spectroscopic biosignatures of halotrophic cyanobacterial extremophiles from sabkha evaporitic saltpans are reported for the first time and ideas about the possible survival strategies in operation have been
forthcoming. The biochemicals produced by the cyanobacteria which colonise the interfaces between large plates of clear selenitic
gypsum, halite, and dolomitized calcium carbonates in the centre of the salt pans are identifiably different from those which
are produced by benthic cyanobacterial mats colonising the surface of the salt pan edges in the intertidal zone. The prediction
that similar geological formations would have been present on early Mars and which could now be underlying the highly peroxidised
regolith on the surface of the planet has been confirmed by recent satellite observations from Mars orbit and by localised
traverses by robotic surface rovers. The successful adoption of miniaturised Raman spectroscopic instrumentation as part of
a scientific package for detection of extant life or biomolecular traces of extinct life on proposed future Mars missions
will depend critically on interpretation of data from terrestrial Mars analogues such as sabkhas, of which the current study is an example. 相似文献
109.
Two‐dimensional (2D) magnetosonic wave propagation in magnetized quantum dissipative plasmas is studied. The plasma system is comprised of inertial ions, inertia‐less electrons, and positrons. The multi‐fluid quantum hydrodynamic model is used, in which quantum statistical and quantum tunnelling effects of electrons and positrons are included. Reductive perturbation analysis is performed to derive the Zabolotskaya–Khokhlov equation for the 2D propagation of a magnetosonic shock wave in a magnetized qauntum plasma. The effects of varying the different plasma parameters such as positron density and magnetic field intensity on the propagation characteristics of magnetosonic shock waves are discussed with non‐relativistic degenerate plasma parameters in astrophysical plasma situations. 相似文献
110.
Shaukat Mahmood Nek M. Shaikh M.A. Kalyar M. Rafiq N.K. Piracha M.A. Baig 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(17):1840-1850
In the present work emission and absorption spectroscopy have been used to determine the plasma parameters of neon in a hollow cathode discharge lamp. The excitation temperature is determined using the intensity ratio method and Boltzmann's plot method whereas the electron density is determined from the Stark broadening of the spectral lines. The behavior of the optogalvanic signal as a function of laser energy has been studied for three transitions from the 2p53s [1/2]2 metastable state following ΔJ=ΔK=0, ±1 dipole selection rules. The saturation technique has been used to measure the photoionization cross section from three intermediate states 2p53p′ [1/2]1, 2p53p′ [3/2]2 and 2p53p [5/2]3 up to the 2p5 2P1/2 ionization threshold. 相似文献