全文获取类型
收费全文 | 2497篇 |
免费 | 479篇 |
国内免费 | 642篇 |
专业分类
化学 | 1938篇 |
晶体学 | 74篇 |
力学 | 209篇 |
综合类 | 79篇 |
数学 | 369篇 |
物理学 | 949篇 |
出版年
2024年 | 5篇 |
2023年 | 42篇 |
2022年 | 84篇 |
2021年 | 104篇 |
2020年 | 107篇 |
2019年 | 106篇 |
2018年 | 93篇 |
2017年 | 76篇 |
2016年 | 117篇 |
2015年 | 161篇 |
2014年 | 141篇 |
2013年 | 202篇 |
2012年 | 188篇 |
2011年 | 184篇 |
2010年 | 185篇 |
2009年 | 200篇 |
2008年 | 216篇 |
2007年 | 187篇 |
2006年 | 193篇 |
2005年 | 167篇 |
2004年 | 124篇 |
2003年 | 113篇 |
2002年 | 97篇 |
2001年 | 89篇 |
2000年 | 102篇 |
1999年 | 59篇 |
1998年 | 39篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 14篇 |
1993年 | 17篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1965年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有3618条查询结果,搜索用时 15 毫秒
101.
The synthesis of some new N‐[1‐(2,5‐dichlorophenyl)‐5‐methyl‐1,2,3‐triazol‐4‐yl]‐carbamic acid ester derivatives are reported in this paper. The yielded products 6a‐l were confirmed by Elemental analyses, NMR, MS, and IR spectra. 相似文献
102.
103.
104.
The enolates produced from the conjugate addition reaction of lithium dialkylcuprates with α,β- unsaturated ketones react with aldehydes in the presence of zinc chloride to give overall β-alkyl α-hydroxyalkyl addition to the original alkene. Reaction of these enolates with carbon dioxide and ethyl formate is also reported. 相似文献
105.
Yu H Li J Loomis RA Gibbons PC Wang LW Buhro WE 《Journal of the American Chemical Society》2003,125(52):16168-16169
Soluble CdSe quantum wires are prepared by the solution-liquid-solid mechanism, using monodisperse bismith nanoparticles to catalyze wire growth. The quantum wires have micrometer lengths, diameters in the range of 5-20 nm, and diameter distributions of +/-10-20%. Spectroscopically determined wire band gaps compare closely to those calculated by the semiemipirical pseudopotential method, confirming 2D quantum confinement. The diameter dependence of the quantum wire band gaps is compared to that of CdSe quantum dots and rods. Quantum rod band gaps are shown to be delimited by the band gaps of dots and wires of like diameter, for short and long rods, respectively. The experimental data suggest that a length of ca. 30 nm is required for the third dimension of quantum confinement to fully vanish in CdSe rods. That length is about six times the bulk CdSe exciton Bohr radius. 相似文献
106.
芳基三氮烯4-位取代基对抗癌活性影响的构象分析 总被引:1,自引:0,他引:1
传统的药物设计和新药开发主要是依靠随机筛选,这种方法误差大,且需要费大量时间和经费,其结果也经常不能达到预期的设想。即使是一个国际性的大制药集团,每年平均要合成上万个化合物才能从中筛选出一个可以成为商品的新药。这种状况迫使我们去寻找一条新的打破常规的途径研究新药。近年来,随着计算机图形系统的广泛应用,对药物构效关系的研究得到了卓有成效的发展,取得了一些成功的例子。如抗菌抗癌琥珀酰-L脯氨酸就是计算化学与分子图形技术相结合的成果,目前已投放市场。 相似文献
107.
Meng Chen Heng Jiang Yafei Feng Yuren Wang 《Applied Physics A: Materials Science & Processing》2014,117(4):2067-2072
We experimentally and theoretically investigated the mechanisms of acoustic absorption in phononic glass to optimize its properties. First, we experimentally studied its locally resonant absorption mechanism. From these results, we attributed its strong sound attenuation to its locally resonant units and its broadband absorption to its networked structure. These experiments also indicated that the porosity and thickness of the phononic glass must be tuned to achieve the best sound absorption at given frequencies. Then, using lumped-mass methods, we studied how the absorption bandgaps of the phononic glass were affected by various factors, including the porosity and the properties of the coating materials. These calculations gave optimal ranges for selecting the porosity, modulus of the coating material, and ratio of the compliant coating to the stiff matrix to achieve absorption bandgaps in the range of 6–30 kHz. This paper provides guidelines for designing phononic glasses with proper structures and component materials to work in specific frequency ranges. 相似文献
108.
Yuliang Zhang Leishan Shao Jingjing Li Qi Xu Lulu Liu Heng Zhang 《Liquid crystals》2013,40(10):1428-1435
In this study, we demonstrated that doping polymer matrix with a small amount of reduced graphene oxide (rGO) component (0.05–0.2%) had significant influence on the polymerisation kinetics and electro-optical performances of polymer-dispersed liquid crystal films (PDLCs) fabricated with macro reversible addition-fragmentation chain transfer agents. The effects of rGO content were studied in terms of morphology, compound viscosity, polymer conductivity, polymerisation kinetics and driving voltage of PDLCs. The results exhibited that higher rGO content increased the compound viscosity and the entire process proceeded slowly. Furthermore, the addition of rGO increased the polymer conductivity and local electric field, and reduced the saturation voltage as well as the threshold voltage from 27.3 to 19.5 V and 13.2 to 6.41 V, respectively. 相似文献
109.
We consider the augmented Lagrangian method (ALM) as a solver for the fused lasso signal approximator (FLSA) problem. The ALM is a dual method in which squares of the constraint functions are added as penalties to the Lagrangian. In order to apply this method to FLSA, two types of auxiliary variables are introduced to transform the original unconstrained minimization problem into a linearly constrained minimization problem. Each updating in this iterative algorithm consists of just a simple one-dimensional convex programming problem, with closed form solution in many cases. While the existing literature mostly focused on the quadratic loss function, our algorithm can be easily implemented for general convex loss. We also provide some convergence analysis of the algorithm. Finally, the method is illustrated with some simulation datasets. 相似文献
110.
Thermoresponsive poly(ionic liquid): Controllable RAFT synthesis,thermoresponse, and application in dispersion RAFT polymerization 下载免费PDF全文
Chonggao Liu Shuang Wang Heng Zhou Chengqiang Gao Wangqing Zhang 《Journal of polymer science. Part A, Polymer chemistry》2016,54(7):945-954
The thermoresponsive poly(ionic liquid) of poly[1‐(4‐vinylbenzyl)‐3‐methylimidozolium tetrafluoroborate] trithiocarbonate (P[VBMI][BF4]‐TTC) showing the soluble‐to‐insoluble phase transition in the methanol/water mixture at the upper critical solution temperature (UCST) was synthesized by solution RAFT polymerization and the synthesized P[VBMI][BF4]‐TTC was employed as macro‐RAFT agent to mediate the RAFT polymerization under dispersion condition to afford the thermoresponsive diblock copolymer nanoparticles of poly[1‐(4‐vinylbenzyl)‐3‐methylimidozolium tetrafluoroborate]‐b‐polystyrene (P[VBMI][BF4]‐b‐PS). The controllable solution RAFT polymerization was achieved as indicated by the linearly increasing polymer molecular weight with the monomer conversion and the narrow molecular weight distribution. The P[VBMI][BF4]‐TTC macro‐RAFT agent mediated dispersion polymerization afforded the P[VBMI][BF4]‐b‐PS nanoparticles, the size of which was uncorrelated with the polymerization degree of the P[VBMI][BF4] block. Several parameters including the polymerization degree, the polymer concentration and the water content in the solvent of the methanol/water mixture were found to be correlated with the UCST of the poly(ionic liquid). The synthesized poly(ionic liquid) is believed to be a new thermos‐responsive polymer and will be useful in material science. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 945–954 相似文献