全文获取类型
收费全文 | 5511篇 |
免费 | 1151篇 |
国内免费 | 1878篇 |
专业分类
化学 | 3974篇 |
晶体学 | 263篇 |
力学 | 338篇 |
综合类 | 302篇 |
数学 | 822篇 |
物理学 | 2841篇 |
出版年
2024年 | 4篇 |
2023年 | 41篇 |
2022年 | 189篇 |
2021年 | 205篇 |
2020年 | 211篇 |
2019年 | 185篇 |
2018年 | 175篇 |
2017年 | 269篇 |
2016年 | 175篇 |
2015年 | 278篇 |
2014年 | 316篇 |
2013年 | 428篇 |
2012年 | 469篇 |
2011年 | 482篇 |
2010年 | 469篇 |
2009年 | 467篇 |
2008年 | 554篇 |
2007年 | 522篇 |
2006年 | 493篇 |
2005年 | 431篇 |
2004年 | 389篇 |
2003年 | 223篇 |
2002年 | 268篇 |
2001年 | 254篇 |
2000年 | 308篇 |
1999年 | 149篇 |
1998年 | 61篇 |
1997年 | 51篇 |
1996年 | 37篇 |
1995年 | 53篇 |
1994年 | 57篇 |
1993年 | 57篇 |
1992年 | 42篇 |
1991年 | 24篇 |
1990年 | 43篇 |
1989年 | 21篇 |
1988年 | 26篇 |
1987年 | 13篇 |
1986年 | 24篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有8540条查询结果,搜索用时 46 毫秒
21.
22.
Cationic polymer as a kind of flocculant is widely applied in purification treatment of waste water. Because it has positive charge group, it is able to connect strongly the suspended matters, short cellulose and other microparticles. The research on synthesis of cationic polymer and application in treatment of waste water is very universal abroad. But domestic research on those is not general. The technology of synthesis of PEM is simple, and the production cost is low. It is easy to apply in treatment of waste water.Synthesis of PEM Emulsion FlocculantSome distilled water, PVA(poly(vinyl alcohol)), EA(ethyl acrylate), and K2S2O8(potassium persulfate) were put into reaction vessel. Kept stirring up under nitrogen. When heated the solution to 40℃, dropped the water solution of MTA[(2-methacryloxylethyl)trimethyl ammonium].Maintained the temperature at 70℃, reacted about 7-8 hours. Then got the PEM emulsion. Changed the ratio of EA and MTA. Obtained a series of PEM emulsions.Stability and Convertibility of PEM EmulsionThe test results showed that when the EA/MTA was 85/15, the PEM emulsion was most stable.When the total monomer quantity was 35%, the convertibility of PEM emulsion was the highest,i.e.98.6%.The MTA Copolymerization Ratio and Morphology of PEM EmulsionWhen the monomers EA/MTA=85/15 and total monomer quantity was 35%, the MTA copolymerization ratio of PEM emulsion was 95.15%(the highest), and the PEM emulsion was some microspheres with 100-180nm of diameter.The Test Results of PEM Emulsion in Treatment of Waste Water The PEM emulsion flocculant was applied in treatment of waste water of paper mill, and measured the precipitation time(t) and transmittancy(T). The test results were showed in table 1. The optimum value of PEM which was able to make the waste water of paper mill into clear water was 0.008%. 相似文献
23.
JianXinCAO YiFengWANG GuoFangLAI ShiDeLUO 《中国化学快报》2004,15(7):797-800
From the dried aerial part ofParepigynumfuningesis Tsiang et P. T. Li (Apocynaceae),a new cardiac glucoside, named parefuningoside (1) had been isolated. Its structure was determined by means of hydrolysis and spectral analysis. 相似文献
24.
The paper discusses the relationship between weights and control vertices of two rational NURBS curves of degree two or three with all weights larger than zero when they represent the same curve parametrically and geometrically, and gives sufficient and necessary conditions for coincidence of two rational NURBS curves in non-degeneracy case. 相似文献
25.
德国夏洛滕堡物理技术研究所(The Physikallisch-Technische Reichanstalt,简称PTR)是世界上第一个国家级的物理技术研究所,它开创了科学研究和技术研究相结合,服务于工业和国家经济之先河。文章从PTR建立的历史背景、早期研究工作和所产生的影响等方面作较为全面的讨论。 相似文献
26.
27.
激光相位成像雷达的研究 总被引:1,自引:0,他引:1
利用无合作目标漫反射激光相位测距的原理,对关键单元技术进行分析和设计,研制成一种用于自主式车辆视觉导引的激光相位成像雷达的原理样机. 相似文献
28.
Using the path integral method we derive quantum wave function and quantum fluctuations of charge andcurrent in the mesoscopic RLC circuit. We find that the quantum fluctuation of charge decreases with time, oppositely,the quantum fluctuation of current increases with time monotonously. Therefore there is a squeezing effect in the circuit.If some more charge devices are used in the mesoscopic-damped circuit, the quantum noise can be reduced. We also findthat uncertainty relation of charge and current periodically varies with the period π/2 in the under-damped case. 相似文献
29.
根据碳氢燃料化学反应系统具有层次结构的特性,本文通过分析二甲醚(DME)与液化石油气(LPG)的详细化学反应机理,构建了反映DME/LPG混合燃料均质压燃(HCCI)燃烧的详细化学反应机理.采用该机理应用单区燃烧模型对DME/LPG混合燃料HCCI燃烧的化学反应动力学过程进行了数值计算.计算结果与试验结果对比表明,所构建的DME/LPG混合燃料氧化的详细化学反应机理能够准确预测DME/LPG混合燃料的两阶段放热特性,对低温和高温着火始点的预测很好;但高温反应过程预测欠佳,高温反应机理需要改进. 相似文献
30.