全文获取类型
收费全文 | 2999篇 |
免费 | 578篇 |
国内免费 | 719篇 |
专业分类
化学 | 1234篇 |
晶体学 | 64篇 |
力学 | 161篇 |
综合类 | 134篇 |
数学 | 232篇 |
物理学 | 794篇 |
无线电 | 1677篇 |
出版年
2024年 | 13篇 |
2023年 | 45篇 |
2022年 | 119篇 |
2021年 | 97篇 |
2020年 | 84篇 |
2019年 | 75篇 |
2018年 | 79篇 |
2017年 | 141篇 |
2016年 | 102篇 |
2015年 | 154篇 |
2014年 | 215篇 |
2013年 | 203篇 |
2012年 | 222篇 |
2011年 | 229篇 |
2010年 | 205篇 |
2009年 | 256篇 |
2008年 | 297篇 |
2007年 | 276篇 |
2006年 | 225篇 |
2005年 | 233篇 |
2004年 | 167篇 |
2003年 | 132篇 |
2002年 | 124篇 |
2001年 | 117篇 |
2000年 | 129篇 |
1999年 | 58篇 |
1998年 | 47篇 |
1997年 | 36篇 |
1996年 | 23篇 |
1995年 | 30篇 |
1994年 | 16篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1968年 | 2篇 |
1964年 | 1篇 |
1961年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有4296条查询结果,搜索用时 15 毫秒
1.
2.
在不同激光脉宽下的高次谐波 总被引:3,自引:2,他引:1
用数值计算方法计算了不同强激光脉冲宽度下高次谐波的产生.我们发现对于激光场强度不高,不能有效电离初态的激光场,长脉冲宽度可以更有效产生高次谐波;而对于高场强的激光场,由于它能够在几个光学周期之内把原子的初态全部电离,所以短脉冲的激光场能够更有效产生高次谐波. 相似文献
3.
ZHONG Hui WAN Mingxi JIANG Yifeng WANG Supin 《声学学报:英文版》2006,25(2):104-115
The present study was to investigate the differential imaging method for detecting HIFU (High Intensity Focused Ultrasound)-induced lesions and the estimation of variation of attenuation for lesion evaluation with log spectral difference algorithm. Experiment results of bovine muscle and liver in vitro were acquired. Several algorithms for lesion detection - Absolute Difference (AD), Sum Absolute Differences (SAD) and Sum Squared Differences (SSD) - were analyzed with several window sizes and threshold values. Then three attenuation parameters were compared to evaluate the degree of tissue damage. It was found that variation of the mean attenuation △α was an effective parameter to evaluate lesions. 相似文献
4.
毛细管气相色谱法测定中药中有机氯农药残留量 总被引:4,自引:0,他引:4
建立了江西省两种中药中有机氯农药残留量的气相色谱分析方法。样品以丙酮提取,在NaCl存在下,以正已烷进行液—液分配,提取液用H2SO4净化,采用DB—1701毛细管柱,GC—ECD检测有机氯农药残留量。最低检测限为1.0×10-3-5.0×10-3mg/kg,添加回收率为85.7%-115.2%,应用于实际样品中有机氯农药残留量的检测,获得了较为满意结果。 相似文献
5.
给出引理解决了方程非振动解与其各阶导数的符号关系,并由此得到了若干判别准则,用于判别三阶线性脉冲微分方程解的振动性与渐近性,举例说明了准则的有效性。本文推广了相关文献的结果。 相似文献
6.
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
7.
Zeolite A rods by self-assembly of zeolite A microcrystal were successfully synthesized by microwave-assisted hydrotherrnal synthesis. The average size of zeolite crystals consisting of self-assembling materials was about 300 nm and the length of zeolite rods was in the range of 15--30μm. 相似文献
8.
9.
罗尔定理证明一类存在性问题 总被引:1,自引:0,他引:1
提出罗尔定理证明一类存在性问题的方法,采用拉格朗日中值定理或柯西中值定理来证明这类问题往往需要构造精巧的辅助函数,我们还指出了这种方法的一般性. 相似文献
10.
CHEN Yue WANG Xuan-jun CONG Xian-ling ZHANG Pei-yin WU Xiu-li WEI Hong-fei WANG Li WAN Min WANG Li-ying YU Yong-li 《高等学校化学研究》2006,22(6):712-716
IntroductionClassical swine fever(CSF), included in the listA of the Office International des Epizooties(OIE), is ahighly contagious disease of domestic pigs and is con-sidered as the mostharmful disease occurring in pigs allover the world[1]. Outbreaks o… 相似文献