全文获取类型
收费全文 | 5569篇 |
免费 | 281篇 |
国内免费 | 68篇 |
专业分类
化学 | 3444篇 |
晶体学 | 52篇 |
力学 | 239篇 |
综合类 | 1篇 |
数学 | 1089篇 |
物理学 | 1093篇 |
出版年
2023年 | 48篇 |
2022年 | 45篇 |
2021年 | 72篇 |
2020年 | 90篇 |
2019年 | 97篇 |
2018年 | 162篇 |
2017年 | 126篇 |
2016年 | 188篇 |
2015年 | 188篇 |
2014年 | 220篇 |
2013年 | 450篇 |
2012年 | 471篇 |
2011年 | 463篇 |
2010年 | 302篇 |
2009年 | 232篇 |
2008年 | 351篇 |
2007年 | 378篇 |
2006年 | 297篇 |
2005年 | 296篇 |
2004年 | 240篇 |
2003年 | 188篇 |
2002年 | 176篇 |
2001年 | 54篇 |
2000年 | 56篇 |
1999年 | 42篇 |
1998年 | 29篇 |
1997年 | 29篇 |
1996年 | 54篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 26篇 |
1992年 | 28篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 31篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有5918条查询结果,搜索用时 31 毫秒
971.
972.
Dumas D Fendler M Berger F Cloix B Pornin C Baier N Druart G Primot J le Coarer E 《Optics letters》2012,37(4):653-655
Design of miniature and light cameras requires an optical design breakthrough to achieve good optical performance. Solutions inspired by animals' eyes are the most promising. The curvature of the retina offers several advantages, such as uniform intensity and no field curvature, but this feature is not used. The work presented here is a solution to spherically bend monolithic IR detectors. Compared to state-of-the-art methods, a higher fill factor is obtained and the device fabrication process is not modified. We made an IR eye camera with a single lens and a curved IR bolometer. Images captured are well resolved and have good contrast, and the modulation transfer function shows better quality when comparing with planar systems. 相似文献
973.
Mehdi Zeghal Loïc Auvray Mondher Jebbari Abdelhafidh Gharbi 《Macromolecular Symposia》2005,222(1):149-156
We study by SANS the structure of intermolecular complexes formed through hydrogen bonding and hydrophobic interactions between poly(methacrylic acid) (PMA) and a neutral copolymer surfactant (PEO-PPO-PEO). The contrast variation method enables us to probe the structure factor of each polymer in the complex and their cross structure factor. The number of copolymer chains, which results from the cooperative action of hydrogen bonding and hydrophobic interactions increases as the charge of the polyacid decreases. The aggregation preserves the micellar core-corona organization of the copolymer and shrinks the polyacid chains which adopt a similar compact structure. Finally, the structure of the aggregates is compared to that of PEO-PMA homopolymer complex observed by SANS. 相似文献
974.
Analysis for the Data of Singly Strange Particle Production in 200AGeVpp,pS and SS Reactions
下载免费PDF全文
![点击此处可从《中国物理C(英文版)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We have used the event generator LUCIAE to analyse the data of singly strange particle production in pp,pS,and SS reactions at 200AGeV.The results seem to indicate that in comparing with the pp and the pS minimum bias event,the SS center collision seems having stronger final state interaction,shorter fomation time of strange particles,and larger s quark pair suppression factor.The strangeness enhancement evidence from pp to pS and to SS could be explained without the introduction of quark-gluon plasma formation. 相似文献
975.
当前,我国的现代化建设事业已进入了全面发展的局面。在新的形势下,现代科学的特点不但是科学知识彼此之间的紧密联系、互相渗透。边缘科学层出不穷,而且作为知识体系的自然科学理论也同社会的其它各项事业以大跨度地结网,凝结在尘产力的基本因素之中,空前的发挥着它的社会职能。 相似文献
976.
Soukaina Faarasse Nabil El Brahmi Grald Guillaumet Saïd El Kazzouli 《Molecules (Basel, Switzerland)》2021,26(19)
The regioselective C-H functionalization of the five-membered ring of the 6,5-fused heterocyclic systems is nowadays well documented due to its high reactivity compared to the six-membered ring. So, developing new procedures of C-H functionalization of the six-membered ring “by thinking out of the box” is extremely challenging, which explains the limited number of reports published to date. This review paper aims to highlight advances achieved in this emerging chemistry research and discusses recently reported methods. 相似文献
977.
探讨了利用HMBC及TOCSY相结合等二维核磁共振技术确定人参皂甙类化合物结构中糖链连接顺序的方法,并用该方法测定了胶股蓝皂甙ⅩⅦ(1)和西洋参皂甙L3(2)中二个糖链的连接顺序,并通过化学方法得以确定.其结构分别为3-O-β-D-吡喃葡萄糖基20-O[β-D-吡喃葡萄糖基(1-6)-β-D-吡喃葡萄糖基]-20(S)-达玛-24-烯3,12,20三醇(1)和3-O-β-D-吡喃葡萄糖基-20-O-[β-D-吡喃木糖基(1-6)-β-D-吡喃葡萄糖基]-20(S)-达玛-23-烯-3,12,20,25-四醇(2). 相似文献
978.
C. Cantin J. Kliava A. Marbeuf D. Mikaïlitchenko 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):525-540
A new thermodynamic model is proposed in order to account for the high spin low spin conversion in metal-organic polymers. The model, based on the idea that the spin conversion occurs in interacting
domains of like-spin metal ions, allows to explain most of the important features of various types of spin conversion. The
sine qua non condition of the existence of spin transitions with hysteresis is obtained. In the case of very large cooperativity, the
model predicts unusual behaviour of the spin conversion system due to a low-temperature metastable high spin state. Existence
of such a state is interesting in the context of the light induced excited spin state trapping recently observed in some ferrous
compounds. The model is applied to interpret the spin transition in polycrystalline ferrous polymer [Fe
1-y
Cu
y
(Htrz)2
trz] (BF
4) with y = 0.00, 0.01 and 0.10, detected by differential scanning calorimetry, optical reflectivity and electron paramagnetic resonance.
The domain size and the interaction energy between the domains are estimated as, respectively, n = 11 and for the y = 0 compound. As the copper content is growing, n and tend to decrease, resulting in transformations of the shape of hysteresis loop which becomes less steep, narrows and shifts
to lower temperatures. The electron paramagnetic resonance gives further evidence of the presence of like-spin domains.
Received 27 November 1998 and Received in final form 19 April 1999 相似文献
979.
Caroline Piffet Bénédicte Vertruyen Frédéric Hatert Rudi Cloots Frédéric Boschini Abdelfattah Mahmoud 《Journal of Energy Chemistry》2022,(2):210-218
Na2Ti3O7 has attracted much attention in the field of anode materials for Na-ion batteries thanks to its non-toxicity and very low working potential of 0.3 V vs Na0/Na+.Building a clearer picture of its formation from cheap Na2CO3 and TiO2 starting materials is therefore of obvious interest.Here,we report new insights from an in-situ high temperature X-ray diffraction study conducted from room temperature to 800°C,complemented by ex-situ characterizations.We were thereby able to position the previously reported Na4Ti5O12 and Na2Ti6O13 intermediate phases in a reaction scheme involving three successive steps and temperature ranges.Shifts and/or broadening of a subset of the Na2Ti6O13 reflections suggested a combination of intra-layer disorder with the well-established ordering of successive layers.This in-situ study was carried out on reproducible mixtures of Na2CO3 and TiO2 in 1:3 molar ratio prepared by spraydrying of mixed aqueous suspensions.Single-phase Na2Ti3O7 was obtained after only 8 h at 800°C in air,instead of a minimum of 20 h for a conventional solid-state route using the same precursors.Microstructure analysis revealed~15 mm diameter granules made up from rectangular rods of a fewmm length presenting electrochemical properties in line with expectations.In the absence of grinding or formation of intimate composites with conductive carbon,the specific capacity of 137 m Ah/g at C/5 decreased at higher rates. 相似文献
980.
We report a rheological study on the effect of adding organic salts [sodium tosylate (NaTos) and benzoic acid potassium salt
(BaPs)] on the micellar growth and structure of aqueous solutions of cethyltrimethylammonium chloride (CTAC) at a constant
molar concentration ratio [salt]/[CTAC]. The rheological data show two well-defined domains of growth characterized by scaling
laws for the surfactant concentration. The addition of NaTos leads to an unusual maximum in the viscosity-surfactant concentration
curve. Before the maximum (domain 1), the analysis of the data (η0, τR and G
0) suggests the presence of branched micelles (connections). After the maximum (domain 2), however, the exponents of the scaling
laws do not reflect either the relaxation of this branched structure or that of an entangled transient network structure.
A faster mechanism of relaxation, not yet elucidated governs their dynamics. The exponents of the power laws in the presence
of the BaPs are found, however, to be in accordance with the theory of equilibrium polymers.
Received: 15 April 1998 Accepted in revised form: 20 October 1998 相似文献