全文获取类型
收费全文 | 239500篇 |
免费 | 2455篇 |
国内免费 | 820篇 |
专业分类
化学 | 121138篇 |
晶体学 | 4038篇 |
力学 | 10992篇 |
综合类 | 2篇 |
数学 | 26564篇 |
物理学 | 80041篇 |
出版年
2020年 | 1933篇 |
2019年 | 2196篇 |
2018年 | 2864篇 |
2017年 | 2794篇 |
2016年 | 4209篇 |
2015年 | 2590篇 |
2014年 | 4190篇 |
2013年 | 10499篇 |
2012年 | 7979篇 |
2011年 | 9901篇 |
2010年 | 7054篇 |
2009年 | 6962篇 |
2008年 | 9151篇 |
2007年 | 9127篇 |
2006年 | 8579篇 |
2005年 | 7788篇 |
2004年 | 7158篇 |
2003年 | 6329篇 |
2002年 | 6240篇 |
2001年 | 7223篇 |
2000年 | 5484篇 |
1999年 | 4319篇 |
1998年 | 3642篇 |
1997年 | 3528篇 |
1996年 | 3366篇 |
1995年 | 3065篇 |
1994年 | 3009篇 |
1993年 | 3094篇 |
1992年 | 3199篇 |
1991年 | 3376篇 |
1990年 | 3120篇 |
1989年 | 3053篇 |
1988年 | 3096篇 |
1987年 | 2975篇 |
1986年 | 2820篇 |
1985年 | 3843篇 |
1984年 | 4037篇 |
1983年 | 3220篇 |
1982年 | 3425篇 |
1981年 | 3356篇 |
1980年 | 3258篇 |
1979年 | 3353篇 |
1978年 | 3447篇 |
1977年 | 3362篇 |
1976年 | 3466篇 |
1975年 | 3159篇 |
1974年 | 3164篇 |
1973年 | 3212篇 |
1972年 | 2244篇 |
1971年 | 1854篇 |
排序方式: 共有10000条查询结果,搜索用时 869 毫秒
81.
82.
Jigneshkumar P. Patel Zou Guo Xiang Shaw Ling Hsu Andrew B. Schoch Sena Ada Carleen Dean Matsumoto 《Journal of Polymer Science.Polymer Physics》2015,53(21):1519-1526
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1519–1526 相似文献
83.
S. V. Panin I. V. Vlasov V. P. Sergeev B. B. Ovechkin P. O. Marushchak Sunder Ramasubbu P. S. Lyubutin V. V. Titkov 《Physical Mesomechanics》2015,18(3):261-272
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method. 相似文献
84.
85.
86.
87.
88.
Crosslinked poly(ethylene oxide) containing siloxanes fabricated through thiol‐ene photochemistry
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Victor A. Kusuma Elliot A. Roth William P. Clafshenkel Steven S. Klara Xu Zhou Surendar R. Venna Erik Albenze David R. Luebke Meagan S. Mauter Richard R. Koepsel Alan J. Russell David Hopkinson Hunaid B. Nulwala 《Journal of polymer science. Part A, Polymer chemistry》2015,53(13):1548-1557
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557 相似文献
89.
András Gy. Németh Renáta Szabó Dr. Attila Domján Prof. György M. Keserű Dr. Péter Ábrányi-Balogh 《ChemistryOpen》2021,10(1):16-27
The development of a new three-component chromatography-free reaction of isocyanides, amines and elemental sulfur allowed us the straightforward synthesis of thioureas in water. Considering a large pool of organic and inorganic bases, we first optimized the preparation of aqueous polysulfide solution from elemental sulfur. Using polysulfide solution, we were able to omit the otherwise mandatory chromatography, and to isolate the crystalline products directly from the reaction mixture by a simple filtration, retaining the sulfur in the solution phase. A wide range of thioureas synthesized in this way confirmed the reasonable substrate and functional group tolerance of our protocol. 相似文献
90.
Fernando Bento Cunha Karina Torres Pomini Ana Maria de Guzzi Plepis Virgínia da Conceio Amaro Martins Eduardo Gomes Machado Renato de Moraes Marcelo de Azevedo e Souza Munhoz Michela Vanessa Ribeiro Machado Marco Antonio Hungaro Duarte Murilo Priori Alcalde Daniela Vieira Buchaim Rogrio Leone Buchaim Victor Augusto Ramos Fernandes Eliana de Souza Bastos Mazuqueli Pereira Andr Antonio Pelegrine Marcelo Rodrigues da Cunha 《Molecules (Basel, Switzerland)》2021,26(6)
Autologous bone grafts, used mainly in extensive bone loss, are considered the gold standard treatment in regenerative medicine, but still have limitations mainly in relation to the amount of bone available, donor area, morbidity and creation of additional surgical area. This fact encourages tissue engineering in relation to the need to develop new biomaterials, from sources other than the individual himself. Therefore, the present study aimed to investigate the effects of an elastin and collagen matrix on the bone repair process in critical size defects in rat calvaria. The animals (Wistar rats, n = 30) were submitted to a surgical procedure to create the bone defect and were divided into three groups: Control Group (CG, n = 10), defects filled with blood clot; E24/37 Group (E24/37, n = 10), defects filled with bovine elastin matrix hydrolyzed for 24 h at 37 °C and C24/25 Group (C24/25, n = 10), defects filled with porcine collagen matrix hydrolyzed for 24 h at 25 °C. Macroscopic and radiographic analyses demonstrated the absence of inflammatory signs and infection. Microtomographical 2D and 3D images showed centripetal bone growth and restricted margins of the bone defect. Histologically, the images confirmed the pattern of bone deposition at the margins of the remaining bone and without complete closure by bone tissue. In the morphometric analysis, the groups E24/37 and C24/25 (13.68 ± 1.44; 53.20 ± 4.47, respectively) showed statistically significant differences in relation to the CG (5.86 ± 2.87). It was concluded that the matrices used as scaffolds are biocompatible and increase the formation of new bone in a critical size defect, with greater formation in the polymer derived from the intestinal serous layer of porcine origin (C24/25). 相似文献