全文获取类型
收费全文 | 26858篇 |
免费 | 4585篇 |
国内免费 | 3156篇 |
学科分类
数理化 | 34599篇 |
出版年
2024年 | 90篇 |
2023年 | 539篇 |
2022年 | 962篇 |
2021年 | 1069篇 |
2020年 | 1113篇 |
2019年 | 1122篇 |
2018年 | 986篇 |
2017年 | 852篇 |
2016年 | 1363篇 |
2015年 | 1299篇 |
2014年 | 1538篇 |
2013年 | 2010篇 |
2012年 | 2407篇 |
2011年 | 2337篇 |
2010年 | 1704篇 |
2009年 | 1637篇 |
2008年 | 1744篇 |
2007年 | 1563篇 |
2006年 | 1484篇 |
2005年 | 1298篇 |
2004年 | 975篇 |
2003年 | 819篇 |
2002年 | 868篇 |
2001年 | 621篇 |
2000年 | 500篇 |
1999年 | 504篇 |
1998年 | 421篇 |
1997年 | 418篇 |
1996年 | 376篇 |
1995年 | 322篇 |
1994年 | 273篇 |
1993年 | 206篇 |
1992年 | 195篇 |
1991年 | 181篇 |
1990年 | 145篇 |
1989年 | 124篇 |
1988年 | 91篇 |
1987年 | 59篇 |
1986年 | 77篇 |
1985年 | 62篇 |
1984年 | 38篇 |
1983年 | 31篇 |
1982年 | 29篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1972年 | 9篇 |
1965年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Hong Wang Jian Hua Dong Kun Yuan Qiu 《Journal of polymer science. Part A, Polymer chemistry》1998,36(5):695-702
ABA-type block copolymers of poly(trimethylene carbonate) with poly(ethylene glycol) (Mn 6820), PTMC-b-PEG-b-PTMC, were synthesized by the ring-opening polymerization of 1,3-dioxan-2-one (trimethylene carbonate) in the presence of poly-(ethylene glycol) with stannous octoate catalyst, and the copolymers with various compositions were obtained. The PTMC-b-PEG-b-PTMC copolymers were characterized with Fourier transform infrared and nuclear magnetic resonance spectroscopies. The intrinsic viscosities of resulting copolymers increased with the increase of 1,3-dioxan-2-one content in feed while the molar ratio of monomer over catalyst kept constant. It has been observed that the glass transition temperature (Tg) of the PTMC segments in copolymers, recorded from differential scanning calorimetry, was dependent on the composition of copolymers. The melting temperature (Tm) of PEG blocks in copolymer was lower than that of PEG polymer, and then disappeared as the length of PTMC blocks increased. The results of dynamic contact angle measurement clearly revealed that the hydrophilicity of resulting copolymers increased greatly with the increase of PEG content in copolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 695–702, 1998 相似文献
993.
994.
995.
微乳液介质-对乙酰基偶氮氯膦光度法测定微量的锆 总被引:1,自引:0,他引:1
研究了在微乳液介质中锆与对乙酰基偶氮氯膦显色反应的条件。络合物的最大吸收波长在685nm处,锆含量在0~30μg/25mL的范围内符合比尔定律,表观摩尔吸光系数为3.0×10~4L/(mol·cm),络合物的络合比为1:1。对乙酰基偶氮氯膦与锆的显色反应体系稳定性及重现性较好。直接用于实际样品的测定,结果较好。 相似文献
996.
Dong Wenming Wang Xiangke Du Jinzhou Wang Dongqi Tao Zuyi 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(3):715-719
The effect of organic matter and iron oxides as solid components of the red earth on the retention of SeO3 has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO3 on the untreated red earth and the three treated soils were determined at 20°C, pH 6.8 or 7.2 and in the presence of 0.01M
CaCl2. It was found that the sorption-desorption hysteresis for untreated an treated soils is obvious and the clays play an important
role in the sorption-desorption hysteresis, and that the retention of SeO3 on red earth is attributed to the iron oxides to a great extent. 相似文献
997.
碳酸二苯酯中微量杂质的高效液相色谱分析 总被引:10,自引:0,他引:10
碳酸二苯酯和双酚A产生酯交换和缩聚反应,制得聚碳酸酯.聚碳酸酯耐压、透明性好,在机械制造、电子电器、军事及照明工业.安全与医疗器械等许多方面有着广泛的用途,是一种性能优良的工程塑料.聚碳酸酯的色泽与许多因素有关.由于原料碳酸二苯酯在制造过程中,一些沸点与之相近的杂质极易残留在产品里.要想得到高质量的聚碳酸酯,必须使其每一种杂质含量控制在100μg/g以下.至今未见报道同时检测碳酸二苯酯中3种微量杂质的分析方法.因此,本文结合单位工艺研究建立了一种用液相色谱进行分析的方法. 相似文献
998.
Prof. Dr. Yuandong Xu Binyang Liu Chaoyang Dong Haoyang Feng Prof. Dr. Yajun Wei Prof. Dr. Xia Zhang 《欧洲无机化学杂志》2023,26(1):e202200569
Three-dimensional (3D) heterostructured molybdenum disulfide (MoS2) is used as base materials for aniline monomer in situ polymerization on its surface. It is found that the aniline addition has a remarkable effect on the energy storage of the final compounds due to the improvement of the conductivity and structure stability combined with the synergistic effect between the two types of species. The optimal compound of PANI@MoS2-150 not only shows a high capacitance value of 801.4 F ⋅ g−1 at a current density of 0.5 A ⋅ g−1 but also provides a high retention rate of 77.4 % after 10,000 cycles. The capacitance fading may be due to the increase of the internal resistance analyzed by EIS. Furthermore, a flexible symmetric supercapacitor based on PANI@MoS2-150 has also been fabricated and the specific capacitance reaches 105 F ⋅ g−1 at a current density of 1 A ⋅ g−1. Impressively, the capacitance retention is larger than 100 % undergoing 10,000 cycles. Besides, the highest energy density of 21 Wh ⋅ kg−1 was obtained. Additionally, the fabricated symmetric supercapacitor demonstrates excellent flexibility. 相似文献
999.
Miancheng Zou Pengkun Zhao Jilin Fan Robert Göstl Andreas Herrmann 《Journal of polymer science. Part A, Polymer chemistry》2022,60(12):1864-1870
The ultrasound-induced cleavage of covalent and non-covalent bonds to activate drugs (sonopharmacology) is a promising concept to gain control over the action of active pharmaceutical ingredients by an external trigger. Previously, linear polymer architectures bearing drug payloads were exploited for drug release by using the principles of polymer mechanochemistry. In this work, the carrier design is altered by the polymer topology to improve the ultrasound-triggered release of covalently anchored drugs from polymer scaffolds. We use microgels crosslinked by mechanoresponsive disulfides and copolymerized with Diels-Alder adducts of furylated payload molecules and acetylenedicarboxylate. Force-induced thiol formation induces a Michael-type addition liberating the payload from the microgels. The use of microgels significantly reduces sonication times compared to linear polymer chains and shields the cargo efficiently from non-triggered activation using ultrasound that produces inertial cavitation at a frequency of 20 kHz as model condition. 相似文献
1000.
Nan Zhang Fan Li Yuanyuan Yu Ping Wang Man Zhou Qiang Wang 《Surface and interface analysis : SIA》2022,54(3):246-253
Natural fibers containing components with phenolic hydroxyl groups, such as jute, wool, and silk, can be directly modified by laccase-catalyzed grafting. However, cellulosic fibers like cotton cannot be functionalized in this manner. In this work, we developed a facile two-step method to graft polymers on cotton fabric via laccase catalysis. First, polydopamine (PDA) coating was deposited on the surface of the cotton fabrics via catalysis of laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) system. Then, the newly formed PDA coating acted as the secondary reaction platform for subsequent laccase-mediated grafting of hydrophobic monomer dodecyl gallate (DG). The oxidation of dopamine (DA) catalyzed with the laccase/TEMPO system was investigated using UV–visible (UV–vis) spectroscopy. The scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results verified that the PDA was coated on the surface of cotton fibers. Fourier transform infrared (FTIR) spectra indicated that the PDA-coated cotton was successfully grafted with DG (DG-PDA-cotton). According to the weighting method, the grafting percentage was about 1.06%. The hydrophobicity of the DG-PDA-cotton fabrics was greatly improved with a contact angle of 133°. Also, the grafted cotton fabrics show repellency of water-soluble stains like coffee, milk, and tea. This study provides a new strategy for surface modification of cotton by laccase-mediated grafting, which offers the references for the green fabrication of cotton fabrics with improved functionalization. 相似文献