全文获取类型
收费全文 | 14349篇 |
免费 | 2655篇 |
国内免费 | 2023篇 |
专业分类
化学 | 11597篇 |
晶体学 | 158篇 |
力学 | 741篇 |
综合类 | 164篇 |
数学 | 1613篇 |
物理学 | 4754篇 |
出版年
2024年 | 32篇 |
2023年 | 306篇 |
2022年 | 352篇 |
2021年 | 471篇 |
2020年 | 664篇 |
2019年 | 733篇 |
2018年 | 525篇 |
2017年 | 434篇 |
2016年 | 778篇 |
2015年 | 775篇 |
2014年 | 866篇 |
2013年 | 1047篇 |
2012年 | 1301篇 |
2011年 | 1289篇 |
2010年 | 931篇 |
2009年 | 865篇 |
2008年 | 966篇 |
2007年 | 862篇 |
2006年 | 736篇 |
2005年 | 679篇 |
2004年 | 586篇 |
2003年 | 578篇 |
2002年 | 690篇 |
2001年 | 621篇 |
2000年 | 384篇 |
1999年 | 332篇 |
1998年 | 195篇 |
1997年 | 170篇 |
1996年 | 140篇 |
1995年 | 130篇 |
1994年 | 84篇 |
1993年 | 73篇 |
1992年 | 84篇 |
1991年 | 89篇 |
1990年 | 76篇 |
1989年 | 41篇 |
1988年 | 35篇 |
1987年 | 21篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1959年 | 1篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Three new compounds, 2‐methoxy‐3,4‐(methylenedioxy)benzophenone ( 1 ), 4‐hydroxy‐2,3‐dimethoxybenzophenone ( 2 ), and 3‐hydroxy‐4,6‐dimethoxy‐9H‐xanthen‐9‐one ( 3 ), besides three known compounds were isolated from the roots of Securidaca inappendiculata. Their structures were established by spectroscopic means and X‐ray crystallographic diffraction analysis. The biogenetic relationships among these six compounds are discussed. 相似文献
992.
993.
Systematic NMR characterization of 4‐thio‐5‐furan‐pyrimidine nucleosides or 4‐thio‐5‐thiophene‐pyrimidine nucleosides (ribonucleosides and 2′‐deoxynucleosides) was performed. All proton and carbon signals of 4‐thio‐5‐thiophene‐ribouridine and related analogues were unambiguously assigned. The orientations of the base (4‐thiouridine or its deoxy analogue) relative to the ring (furan or thiophene) are explored by a NMR approach and further supported by X‐ray crystallographic studies. The procedures presented here would be applicable to other modified nucleosides and nucleotides. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
994.
995.
L LinHui Ye YanLin Jiang DongXing Hua Hui Zheng Tao Li ZhiHuan Ge YuCheng Li XiangQing Lou JianLing Cao ZhongXin Song YuShou Xiao Jun Li QiTe Qiao Rui You HaiBo Chen RuiJiu Xu HuShan Wang JianSong Guo ZhongYan Zhang XueYing Li Chen Hu ZhengGuo Chen RuoFu Wang Meng Xu ZhiGuo Yue Ke Tang Bin Zang YongDong Zhang XueHeng Yao XiangWu Chen JinDa Bai Zhen 《中国科学:物理学 力学 天文学(英文版)》2011,54(1):136-140
Knockout reaction experiment was carried out by using the 6He beams at 61.2 MeV/u impinging on a CH2 target. The α core fragments at forward angles were detected in coincidence with the recoiled protons at larger angles. From this exclusive measurement the valence nucleon knockout mechanism and the core knockout mechanism can be distinguished by the relation between the polar angles of the core fragments and the recoiled protons, respectively. It is demonstrated that the core knockout mechanism may result in some strong contamination to the real invariant mass spectrum.
相似文献996.
Reduced Graphene‐Wrapped MnO2 Nanowires Self‐Inserted with Co3O4 Nanocages: Remarkable Enhanced Performances for Lithium‐Ion Anode Applications 下载免费PDF全文
Qi Zhu Yunhui Li Prof. Ying Gao Prof. Xiao Wang Prof. Shuyan Song 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6876-6880
A simple synthetic approach for graphene‐templated nanostructured MnO2 nanowires self‐inserted with Co3O4 nanocages is proposed in this work. The Co3O4 nanocages were penetrated in situ by MnO2 nanowires. As an anode, the as‐obtained MnO2–Co3O4–RGO composite exhibits remarkable enhanced performance compared with the MnO2–RGO and Co3O4–RGO samples. The MnO2–Co3O4–RGO electrode delivers a reversible capacity of up to 577.4 mA h g?1 after 400 cycles at 500 mA g?1 and the Coulombic efficiency of MnO2–Co3O4–RGO is about 96 %. 相似文献
997.
Ultrathin Co3S4 Nanosheets that Synergistically Engineer Spin States and Exposed Polyhedra that Promote Water Oxidation under Neutral Conditions 下载免费PDF全文
Youwen Liu Dr. Chong Xiao Mengjie Lyu Dr. Yue Lin Weizheng Cai Pengcheng Huang Prof. Wei Tong Prof. Youming Zou Prof. Yi Xie 《Angewandte Chemie (International ed. in English)》2015,54(38):11231-11235
Development of efficient and affordable electrocatalysts in neutral solutions is paramount importance for the renewable energy. Herein, we report that the oxygen evolution reaction (OER) performance of Co3S4 under neutral conditions can be enhanced by exposed octahedral planes and self‐adapted spin states in atomically thin nanosheets. A HAADF image clearly confirmed that the active octahedra with Jahn–Teller distortions were exposed exclusively. Most importantly, in the atomically thin nanosheets, the spin states of Co3+ in the octahedral self‐adapt from low‐spin to high‐spin states. As a result, the synergistic effect endow the Co3S4 nanosheets with superior OER performance, with exceptional low onset overpotentials of circa 0.31 V in neutral solutions, which is state‐of‐the‐art among inorganic non‐noble metal compounds. 相似文献
998.
999.
Soluble guanylate cyclase(sGC) is a critical heme-containing enzyme involved in NO signaling.The dimerization of sGC subunits is necessary for its bioactivity and its mechanism is a striking and an indistinct issue.The roles of heme domain cysteines of the sGC on the dimerization and heme binding were investigated herein.The site-directed mutations of three conserved cysteines(C78A,C122A and C174S) were studied systematically and the three mutants were characterized by gel filtration analysis,UV-vis spectroscopy and heme transfer examination.Cys78 was involved in heme binding but not referred to the dimerization,while Cys174 was demonstrated to be involved in the homodimerization.These results provide new insights into the cysteine-related dimerization regulation of sGC. 相似文献
1000.
Dean Shi Xiao‐Yang Wang Hengchong Shi Jing‐Hua Yin Robert K. Y. Li Guo‐Hua Hu 《Journal of Polymer Science.Polymer Physics》2010,48(1):65-73
TEM micrographs show that the PA grafts of PS‐g‐PA6 graft copolymers, which are obtained directly by extracting homo‐PA6 out from the homo‐PA6/PS‐g‐PA6 blends, are in the form of wormlike structure. The wormlike PA6 domains can shrink into droplets after annealing at 250 °C for 15 min. The diameter of the droplet determined by TEM and SAXS is in the range of 50–60 nm. This article reports on a unique crystallization behavior of the PA6 grafts in PS‐g‐PA6 graft copolymers. In a DSC cooling scan, PA6 grafts do not crystallize from the melt with a cooling rate of 10 °C/min. However, there is a cold crystallization peak around 65 °C in the subsequent heating scan. This cold crystallization phenomenon, which has not yet been reported in the literature till now, follows well the homogeneous nucleation mechanism and is depressed at relatively slow cooling rates (2 °C/min) or even completely eliminated after annealing within a specific temperature range. It may be caused by the slow diffusion or transport rate of the less flexible PA6 grafts to the crystal fronts when crystallization takes place around its glass transition temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 65–73, 2010 相似文献