全文获取类型
收费全文 | 54497篇 |
免费 | 4661篇 |
国内免费 | 3080篇 |
专业分类
化学 | 27636篇 |
晶体学 | 504篇 |
力学 | 3227篇 |
综合类 | 229篇 |
数学 | 12276篇 |
物理学 | 18366篇 |
出版年
2023年 | 574篇 |
2022年 | 655篇 |
2021年 | 840篇 |
2020年 | 1104篇 |
2019年 | 1014篇 |
2018年 | 2087篇 |
2017年 | 2304篇 |
2016年 | 1965篇 |
2015年 | 1750篇 |
2014年 | 1917篇 |
2013年 | 2591篇 |
2012年 | 5446篇 |
2011年 | 4700篇 |
2010年 | 3410篇 |
2009年 | 3106篇 |
2008年 | 2258篇 |
2007年 | 2064篇 |
2006年 | 1936篇 |
2005年 | 5544篇 |
2004年 | 4715篇 |
2003年 | 2943篇 |
2002年 | 1035篇 |
2001年 | 775篇 |
2000年 | 577篇 |
1999年 | 774篇 |
1998年 | 609篇 |
1997年 | 571篇 |
1996年 | 508篇 |
1995年 | 497篇 |
1994年 | 423篇 |
1993年 | 362篇 |
1992年 | 449篇 |
1991年 | 403篇 |
1990年 | 370篇 |
1989年 | 290篇 |
1988年 | 243篇 |
1987年 | 180篇 |
1986年 | 133篇 |
1985年 | 130篇 |
1984年 | 90篇 |
1983年 | 76篇 |
1982年 | 70篇 |
1981年 | 40篇 |
1976年 | 80篇 |
1975年 | 37篇 |
1974年 | 40篇 |
1973年 | 48篇 |
1972年 | 39篇 |
1969年 | 37篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
21.
Yongxing Tang Yajun Yu Xinyu Wei Jin Yang Yeting Zhu Yun-Hui Zhao Zilong Tang Zhihua Zhou Xiaofang Li Xianyong Yu 《Tetrahedron letters》2019,60(43):151187
A novel 6-endo-dig cyclization followed by oxidation/elimination of o-alkynylarylaldimines with 4-hydroxybenzylamine was developed for preparation of isoquinolines. The intermediates of this tandem reaction were monitored by mass spectroscopy (MS) to confirm the reaction pathway. This methodology was further applied to the design and synthesis of a novel ratiometric chemosensor for determination of fluoride. 相似文献
22.
Nonlinear Dynamics - In this paper, we mainly propose a chaotic secure communication scheme which is based on the synchronization of double-layered and multiple complex dynamical networks. Compared... 相似文献
23.
Pengfei Xie Jiao Wang Jianbo Li Qian Cheng Keyu Zhou Jie Ren 《Journal of polymer science. Part A, Polymer chemistry》2019,57(7):814-826
The miktoarm star‐shaped poly(lactic acid) (PLA) copolymer, (PLLA)2‐core‐(PDLA)2, was synthesized via stepwise ring‐opening polymerization of lactide with dibromoneopentyl glycol as the starting material. 1H NMR and FTIR spectroscopy proved the feasibility of synthetic route and the successful preparation of star‐shaped PLA copolymers. The results of FTIR spectroscopy and XRD showed that the stereocomplex structure of the copolymer could be more perfect after solvent dissolution treatment. Effect of chain architectures on crystallization was investigated by studying the nonisothermal and isothermal crystallization of the miktoarm star‐shaped PLA copolymer and other stereocomplexes. Nonisothermal differential scanning calorimetry and polarizing optical microscopy tests indicated that (PLLA)2‐core‐(PDLA)2 exhibited the fastest formation of a stereocomplex in a dynamic test due to its special structure. In isothermal crystallization tests, the copolymer exhibited the fast crystal growth rate and the most perfect crystal morphology. The results reveal that the unique molecular structure has an important influence on the crystallization of the miktoarm star‐shaped PLA copolymer. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 814–826 相似文献
24.
The combinatorial object named -spontaneous emission error design (-SEED) was proposed by Beth et al. in 2003 in order to correct errors caused by quantum jumps. The newly rising category of -SEEDs has been studied extensively in recent years. Especially, the maximal possible dimensions for 2-SEEDs with block size 3 were determined completely; lower bounds on 2-SEEDs were established by applying affine groups. In this paper we utilize the action of twisted affine groups on finite fields and obtain new lower bounds on the dimensions of 2- SEEDs, some of which outperform the known ones. 相似文献
25.
Shehzad Hamza Zhou Limin Wang Yun Ouyang Jinbo Huang Guolin Liu Zhirong Li Zhao 《Journal of Radioanalytical and Nuclear Chemistry》2019,322(2):605-611
Journal of Radioanalytical and Nuclear Chemistry - The kinetics of Co ions sorption on CoTreat® was investigated in the 5–40 mg/L concentration range at a bulk temperature of... 相似文献
26.
Crystallography Reports - A coordination polymer, [CuL]n (HL = 1H-benzimidazole-2-methanol), has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction.... 相似文献
27.
Dr. Xiaoyan Sun Prof. Dr. Shaodong Zhou Dr. Lei Yue Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(14):3550-3559
Thermal gas-phase reactions of the ruthenium-oxide clusters [RuOx]+ (x=1–3) with methane and dihydrogen have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. For methane activation, as compared to the previously studied [RuO]+/CH4 couple, the higher oxidized Ru systems give rise to completely different product distributions. [RuO2]+ brings about the generations of [Ru,O,C,H2]+/H2O, [Ru,O,C]+/H2/H2O, and [Ru,O,H2]+/CH2O, whereas [RuO3]+ exhibits a higher selectivity and efficiency in producing formaldehyde and syngas (CO+H2). Regarding the reactions with H2, as compared to CH4, both [RuO]+ and [RuO2]+ react similarly inefficiently with oxygen-atom transfer being the main reaction channel; in contrast, [RuO3]+ is inert toward dihydrogen. Theoretical analysis reveals that the reduction of the metal center drives the overall oxidation of methane, whereas the back-bonding orbital interactions between the cluster ions and dihydrogen control the H−H bond activation. Furthermore, the reactivity patterns of [RuOx]+ (x=1–3) with CH4 and H2 have been compared with the previously reported results of Group 8 analogues [OsOx]+/CH4/H2 (x=1–3) and the [FeO]+/H2 system. The electronic origins for their distinctly different reaction behaviors have been addressed. 相似文献
28.
Zhu Hong Zeng Xiangbing Han Tianli Li Xuexue Zhu Shuguang Sun Bai Zhou Ping Liu Jinyun 《Journal of Solid State Electrochemistry》2019,23(7):2173-2180
Journal of Solid State Electrochemistry - Since conventional graphite-based anode possesses a low capacity, seeking for high-capacity anode candidates becomes significant for constructing emerging... 相似文献
29.
Meng-Meng Zhao Lin Zhou Ping-Ping Shi Xuan Zheng Xiao-Gang Chen Ji-Xing Gao Lei He Prof. Dr. Qiong Ye Prof. Dr. Cai-Ming Liu Prof. Dr. Da-Wei Fu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(25):6447-6454
Organic–inorganic hybrid perovskite-type multiferroics have attracted considerable research interest owing to their fundamental scientific significance and promising technological applications in sensors and multiple-state memories. The recent achievements with divalent metal dicyanamide compounds revealed such malleable frameworks as a unique platform for developing novel functional materials. Herein, two 3D organic–inorganic hybrid perovskites [Et3P(CH2)2F][Mn(dca)3] ( 1 ) and [Et3P(CH2)2Cl][Mn(dca)3] ( 2 ) (dca=dicyanamide, N(CN)2−) are presented. Accompanying the sequential phase transitions, they display a broad range of intriguing physical properties, including above room temperature ferroelastic behavior, switchable dielectricity, and low-temperature antiferromagnetic ordering (Tc=2.4 K for both 1 and 2 ). It is also worth noting that the spontaneous strain value of 1 is far beyond that of 2 in the first ferroelastic phase, as a result of the precise halogen substitution. From the point view of molecular design, this work should inspire further exploration of multifunctional molecular materials with desirable properties. 相似文献
30.
高能重带电粒子能直接穿透靶原子核外电子层,与原子核发生直接碰撞,发生散裂反应,产生一系列具有放射性的剩余产物核.重带电粒子诱发靶材放射性剩余核与辐射防护和人员安全有着密切联系,当前,大部分剩余核产额主要依靠蒙特卡罗粒子输运程序进行模拟计算,其准确程度亟需通过实验测量进行准确评估.本文利用能量为80.5 MeV/u的(12)^C6+粒子对薄铜靶开展了辐照实验与伽玛射线测量,结合伽玛谱学分析方法,得出了辐照产生的18种放射性剩余产物的初始活度和产生截面值,并与PHITS模拟结果进行对比.结果表明,PHITS模拟程序对放射性剩余核种类的估计具有较高可靠性,在其绝对产额方面,与实验测量仍具有较大偏差. 相似文献