全文获取类型
收费全文 | 17544篇 |
免费 | 3998篇 |
国内免费 | 7262篇 |
专业分类
化学 | 13214篇 |
晶体学 | 987篇 |
力学 | 1364篇 |
综合类 | 877篇 |
数学 | 3028篇 |
物理学 | 9334篇 |
出版年
2024年 | 51篇 |
2023年 | 151篇 |
2022年 | 620篇 |
2021年 | 605篇 |
2020年 | 591篇 |
2019年 | 553篇 |
2018年 | 535篇 |
2017年 | 788篇 |
2016年 | 566篇 |
2015年 | 895篇 |
2014年 | 1012篇 |
2013年 | 1424篇 |
2012年 | 1375篇 |
2011年 | 1496篇 |
2010年 | 1509篇 |
2009年 | 1672篇 |
2008年 | 1964篇 |
2007年 | 1698篇 |
2006年 | 1664篇 |
2005年 | 1425篇 |
2004年 | 1170篇 |
2003年 | 879篇 |
2002年 | 808篇 |
2001年 | 896篇 |
2000年 | 967篇 |
1999年 | 592篇 |
1998年 | 313篇 |
1997年 | 248篇 |
1996年 | 273篇 |
1995年 | 253篇 |
1994年 | 228篇 |
1993年 | 222篇 |
1992年 | 180篇 |
1991年 | 145篇 |
1990年 | 148篇 |
1989年 | 155篇 |
1988年 | 127篇 |
1987年 | 103篇 |
1986年 | 81篇 |
1985年 | 50篇 |
1984年 | 76篇 |
1983年 | 74篇 |
1982年 | 64篇 |
1981年 | 49篇 |
1980年 | 36篇 |
1979年 | 28篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
关于Banach空间中凸泛函的广义次梯度不等式 总被引:2,自引:0,他引:2
本文在前人^[1,2]的基础之上,以凸泛函的次梯度不等式为工具,将Jensen不等式推广到Banach空间中的凸泛函,导出了Banach空间中的Bochner积分型的广义Jensen不等式,给出其在Banach空间概率论中某些应用,从而推广了文献[3—6]的工作. 相似文献
33.
34.
Radiative lifetimes of two short-lived levels (i.e. 4f^8 (TF6)6p^1/2 (6, 1/2)11/2,13/2) in Tb Ⅲ are measured by time-resolved laser-induced fluorescence (LIE) technique with a two-step excitation process. Free Tb Ⅲ ions are produced in a laser-induced plasma. Lifetime values are evaluated with a deconvolution procedure of the timeresolved fluorescence signal with the temporal shape of second-step excitation pulse (about 1 ns). The lifetimes of the 4f^8 (^7F6)6p^1/2 (6, 1/2)11/2 and 4f^8(^7F6)6p^1/2 (6, 1/2)13/2 levels are determined to be 1.9 (2) and 2.0 (2)ns, respectively. 相似文献
35.
36.
研究了不同衬底-阴极距离、直流电压和H2流量对a-CH薄膜沉积速率的影响。结果表明:衬底-阴极距离必须大于0.5cm,随着该距离的增加,薄膜的沉积速率减少;直流电压达550V时沉积速率最大;随着H2含量的增加,CH4含量相对减少,沉积速率随之降低。用AFM观察了以该方法制得的448.4nm CH薄膜的表面形貌,表面粗糙度约为10nm。最后测出了不同条件下CH薄膜的UV-VIS谱,由此可以计算得到薄膜的禁带宽度及折射率。 相似文献
37.
38.
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
39.
A New Triterpene from the Orchid Pholidota yunnanensis 总被引:2,自引:0,他引:2
ZhiMingBI ZhengTaoWANG LuoShanXU 《中国化学快报》2004,15(10):1179-1181
A new triterpene, 25-methylenecyclopholidonyl p-hydroxy-trans-cinnamate, was isolated from a orchid Pholidota yunnanensis. The structure elucidation and ^1H, ^13C-NMR assignments were achieved by spectral and chemical method. 相似文献
40.
WeiMingXU LuLingWU XianHUANG 《中国化学快报》2004,15(11):1279-1280
A mild, regioselective 1, 3-dipolar cycloaddition protocol for the preparation ofphenylselenomethyl isoxazolines through substituted allyl phenyl selenides and nitrile oxides wasreported. 相似文献