全文获取类型
收费全文 | 44859篇 |
免费 | 7568篇 |
国内免费 | 5629篇 |
专业分类
化学 | 32775篇 |
晶体学 | 779篇 |
力学 | 2563篇 |
综合类 | 404篇 |
数学 | 5058篇 |
物理学 | 16477篇 |
出版年
2024年 | 73篇 |
2023年 | 771篇 |
2022年 | 1419篇 |
2021年 | 1414篇 |
2020年 | 1679篇 |
2019年 | 1765篇 |
2018年 | 1408篇 |
2017年 | 1347篇 |
2016年 | 2023篇 |
2015年 | 2048篇 |
2014年 | 2370篇 |
2013年 | 3187篇 |
2012年 | 4183篇 |
2011年 | 4235篇 |
2010年 | 3045篇 |
2009年 | 2941篇 |
2008年 | 3256篇 |
2007年 | 2878篇 |
2006年 | 2759篇 |
2005年 | 2408篇 |
2004年 | 1853篇 |
2003年 | 1433篇 |
2002年 | 1448篇 |
2001年 | 1101篇 |
2000年 | 969篇 |
1999年 | 927篇 |
1998年 | 686篇 |
1997年 | 630篇 |
1996年 | 626篇 |
1995年 | 511篇 |
1994年 | 466篇 |
1993年 | 361篇 |
1992年 | 308篇 |
1991年 | 291篇 |
1990年 | 226篇 |
1989年 | 188篇 |
1988年 | 139篇 |
1987年 | 128篇 |
1986年 | 114篇 |
1985年 | 114篇 |
1984年 | 62篇 |
1983年 | 59篇 |
1982年 | 46篇 |
1981年 | 34篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
912.
913.
Jun Chen 《European Polymer Journal》2007,43(4):1188-1194
γ-Ray-induced polymerization of methyl methacrylate was conducted in a microemulsion stabilized by a mixture of sodium of 12-acryloxy-9-octadecenoic acid (AOA) and sodium dodecyl sulfate (SDS) with various weight ratios at room temperature. The experimental data showed that the mixture of AOA and SDS with a weight ratio 2 was an efficient surfactant system for the microemulsion containing 38.6 wt% MMA and 5.5 wt% surfactant. The effects of MMA concentration and dose rate on the polymerization kinetics and particle size are discussed. 相似文献
914.
Experimental and modeling study on decomposition kinetics of methane hydrates in different media 总被引:6,自引:0,他引:6
Liang M Chen G Sun C Yan L Liu J Ma Q 《The journal of physical chemistry. B》2005,109(40):19034-19041
The decomposition kinetic behaviors of methane hydrates formed in 5 cm3 porous wet activated carbon were studied experimentally in a closed system in the temperature range of 275.8-264.4 K. The decomposition rates of methane hydrates formed from 5 cm3 of pure free water and an aqueous solution of 650 g x m(-3) sodium dodecyl sulfate (SDS) were also measured for comparison. The decomposition rates of methane hydrates in seven different cases were compared. The results showed that the methane hydrates dissociate more rapidly in porous activated carbon than in free systems. A mathematical model was developed for describing the decomposition kinetic behavior of methane hydrates below ice point based on an ice-shielding mechanism in which a porous ice layer was assumed to be formed during the decomposition of hydrate, and the diffusion of methane molecules through it was assumed to be one of the control steps. The parameters of the model were determined by correlating the decomposition rate data, and the activation energies were further determined with respect to three different media. The model was found to well describe the decomposition kinetic behavior of methane hydrate in different media. 相似文献
915.
916.
917.
由RhCl_3·xH_2O制备了不同Rh含量的Rh/SiO_2和Rh-V/SiO_2催化剂,采用化学吸附和原位TPD-IR方法考察钒助剂对Rh/SiO_2催化剂在常温和高温的H_2和CO化学吸附的影响。结果再次表明:1)不同Rh中心对H_2和CO的化学吸附性能不同,钒助剂对不同Rh中心的H_2和CO吸附的影响也不同。H_2主要吸附在Rh~Ⅱ和Rh~Ⅲ中心上,而在Rh~Ⅰ中心上的吸附弱。2)Rh-钒助剂的强相互作用主要是Rh~Ⅱ和Rh~Ⅲ与钒助剂之间的相互作用,H_2吸附受到比CO吸附更强烈的抑制。钒助剂对Rh/SiO_2的H_2和CO吸附性能的影响可用覆盖模型解释。 相似文献
918.
919.
Spectrophotometric determination of procaine hydrochloride is described. The procaine hydrochloride reacts with p-dimethylaminobenzalhyde in glacial acetic acid to form an Schiff base which is a yellow compound, and its maximum absorption wavelength is at 455nm, 455=3.46×104. The absorbance for procaine hydrochloride from 0.2 to 15 μg ml−1 obeys Beer's law. The linear regression equation of the calibration graph is C=5.866A−0.02, with a linear regression correlative coefficient is 0.9994 and relative standard deviation (RSD) of 1.7%; the detection limit is 0.1 μg ml−1; recovery is from 92.0 to 110.0%. Effects of reaction medium, temperature, gentamycin, beneylpenicillin, kanamycin, streptomycin, foreign ions, and stand for time on the determination of procaine hydrochloride have been examined. The results obtained by this method agreed with those by the official method (dead-stop titration). This method is rapid and simple, and can be used for the determination of procaine hydrochloride in injection solution of procaine hydrochloride. 相似文献
920.
烷基醇聚氧乙烯醚中二噁烷的测定 总被引:6,自引:2,他引:6
采用顶空气相色谱法测定了烷基醇聚氧乙烯醚中的二口恶烷。研究了顶空条件,标准曲线的相关系数为0.9989,检出限为20μg/L,回收率为91.6%~97.6%,相对标准偏差小于2.5%。 相似文献