全文获取类型
收费全文 | 10004篇 |
免费 | 1666篇 |
国内免费 | 2255篇 |
专业分类
化学 | 7967篇 |
晶体学 | 275篇 |
力学 | 591篇 |
综合类 | 261篇 |
数学 | 1261篇 |
物理学 | 3570篇 |
出版年
2024年 | 10篇 |
2023年 | 131篇 |
2022年 | 286篇 |
2021年 | 298篇 |
2020年 | 358篇 |
2019年 | 354篇 |
2018年 | 293篇 |
2017年 | 343篇 |
2016年 | 438篇 |
2015年 | 489篇 |
2014年 | 586篇 |
2013年 | 762篇 |
2012年 | 830篇 |
2011年 | 901篇 |
2010年 | 793篇 |
2009年 | 732篇 |
2008年 | 827篇 |
2007年 | 828篇 |
2006年 | 769篇 |
2005年 | 571篇 |
2004年 | 568篇 |
2003年 | 402篇 |
2002年 | 435篇 |
2001年 | 387篇 |
2000年 | 302篇 |
1999年 | 211篇 |
1998年 | 149篇 |
1997年 | 122篇 |
1996年 | 101篇 |
1995年 | 67篇 |
1994年 | 71篇 |
1993年 | 79篇 |
1992年 | 65篇 |
1991年 | 50篇 |
1990年 | 59篇 |
1989年 | 40篇 |
1988年 | 31篇 |
1987年 | 25篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 17篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1974年 | 4篇 |
1969年 | 3篇 |
1928年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Baijun Liu Gilles P. Robertson Michael D. Guiver Yi‐Ming Sun Yin‐Ling Liu Juin‐Yih Lai Serguei Mikhailenko Serge Kaliaguine 《Journal of Polymer Science.Polymer Physics》2006,44(16):2299-2310
A series of sulfonated poly(aryl ether ether ketone ketone)s statistical copolymers with high molecular weights were synthesized via an aromatic nucleophilic substitution polymerization. The sulfonation content (SC), defined as the number of sulfonic acid groups contained in an average repeat unit, could be controlled by the feed ratios of monomers. Flexible and strong membranes in sodium sulfonate form could be prepared by the solution casting method, and readily transformed to their proton forms by treating them in 2 N sulfuric acid. The polymers showed high Tgs, which increased with an increase in SC. Membranes prepared from the present sulfonated poly(ether ether ketone ketone) copolymers containing the hexafluoroisopropylidene moiety (SPEEKK‐6F) and copolymers containing the pendant 3,5‐ditrifluoromethylphenyl moiety (SPEEKK‐6FP) had lower water uptakes and lower swelling ratios in comparison with previously prepared copolymers containing 6F units. All of the polymers possessed proton conductivities higher than 1 × 10?2 S/cm at room temperature, and proton conductivity values of several polymers were comparable to that of Nafion at high relative humidity. Their thermal stability, oxidative stability, and mechanical properties were also evaluated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2299–2310, 2006 相似文献
82.
83.
A single hair sample preparation protocol modified from reported method was developed and used to prepare longitudinally sectioned hair for ToF-SIMS analysis. Preliminary results demonstrate that ToF-SIMS is capable of providing molecular distribution of fragment ions from intrinsic constituents as well as external chemicals like the hair dye ingredients used in this study. The observation of pPDA and H2PO4− penetrating into the internal region of hair might initiate a renewed interest in exposure study. 相似文献
84.
7-Hydroxyderivativesofcholesteroldisplayawidevarietyofbiologicalactivities'-',mostofwhicharerelatedtothephysiologicalcontrolofcholesterolbiosynthesisandantitumoractivity.Inearlyreports',the7-hydroxycholesterolswerepreparedbythesequenceofacetylation,allylicchromicoxidation,andhydridereduction.Generally,theproductisamixtureof7a-and76-epimerswhichisdifficulttobeseparated.V.Kumaretal5improvedthisprocedurebyusingstereospecificreducingreagentsinsteadofthesimplehydride.7a-and7o-epimerscouldbeobtained… 相似文献
85.
Conflict resolution methodology is discussed with fuzzified Pareto frontier. Four solution concepts, namely, the Nash solution, the generalized Nash solution, the Kalai-Smorodinsky concept, and a solution method based on a special bargaining process are examined. The solutions are also fuzzy, the corresponding payoff values are fuzzy numbers, the membership functions of which are determined. Three particular cases are considered in the paper. Linear, quadratic, and general nonlinear Pareto frontiers with known shape are examined. 相似文献
86.
87.
88.
Gabriel M. Rebeiz Curtis C. Ling David B. Rutledge 《International Journal of Infrared and Millimeter Waves》1989,10(8):931-936
An accurate monolithic power meter has been developed for millimeter-wave applications. The detector is a large-area Bismuth bolometer, integrated on a fused-Quartz substrate. It simply measures the temperature change caused by the absorption of millimeter-wave radiation. The power meter is simple to fabricate, inexpensive, and can be easily calibrated using a low-frequency network. The measured responsivity for a 50 bolometer, with an area of 1×1cm, at a bias of 1V. and a video modulation of 100Hz, is 1mV/W. The noise spectrum exhibits a 1/f rolloff till 1KHz, and is limited by the Johnson noise for higher frequencies. The NEP of the detector is 3WHz–1/2 at a video modulation of 1KHz. It is possible to decrease the current NEP by fabricating bolometers with higher responsivities. Possible application areas are absolute power calibration and localized power density measurements at millimeter and submillimeter wavelengths. 相似文献
89.
90.
A novel method for preparing silver nanoelectrode ensembles(SNEEs) and gold nanoelectrode ensembles (GNEEs) has been developed. Silver colloid particles were first absorbed to the gold electrode surface to form a monolayer silver colloid. N-hexadecyl nercaptan was then assembled on the electrode to form a thoil monolayer on which hydrophilic ions cannot be transfered. The SNEEs was prepared by removing thiol from silver colloid surface through applying and AC voltage with increasing frequency at 0.20V(vs.SCE). Finally,GNEEs was obtained by immersing a SNEEs into 6 mol/L HNO3 to remove the silver colloid particles. By comparison with other methods such as template method ect., this method enjoys some advantages of lower resistance, same diameter,easy preparation,controllable size and density. 相似文献