全文获取类型
收费全文 | 23073篇 |
免费 | 3927篇 |
国内免费 | 2667篇 |
专业分类
化学 | 16334篇 |
晶体学 | 243篇 |
力学 | 1343篇 |
综合类 | 138篇 |
数学 | 2387篇 |
物理学 | 9222篇 |
出版年
2024年 | 93篇 |
2023年 | 514篇 |
2022年 | 788篇 |
2021年 | 916篇 |
2020年 | 935篇 |
2019年 | 885篇 |
2018年 | 824篇 |
2017年 | 733篇 |
2016年 | 1114篇 |
2015年 | 1095篇 |
2014年 | 1334篇 |
2013年 | 1635篇 |
2012年 | 2049篇 |
2011年 | 1964篇 |
2010年 | 1391篇 |
2009年 | 1290篇 |
2008年 | 1391篇 |
2007年 | 1320篇 |
2006年 | 1213篇 |
2005年 | 1086篇 |
2004年 | 799篇 |
2003年 | 645篇 |
2002年 | 658篇 |
2001年 | 518篇 |
2000年 | 460篇 |
1999年 | 543篇 |
1998年 | 449篇 |
1997年 | 434篇 |
1996年 | 409篇 |
1995年 | 338篇 |
1994年 | 306篇 |
1993年 | 253篇 |
1992年 | 212篇 |
1991年 | 192篇 |
1990年 | 191篇 |
1989年 | 163篇 |
1988年 | 113篇 |
1987年 | 89篇 |
1986年 | 73篇 |
1985年 | 73篇 |
1984年 | 39篇 |
1983年 | 38篇 |
1982年 | 34篇 |
1981年 | 27篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1957年 | 4篇 |
1930年 | 2篇 |
1916年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
31.
32.
LIZHIBIN SHIHE 《高校应用数学学报(英文版)》1996,11(1):1-6
Abstract. We consider the following simplified model for the Belousou-Zhabotinskii(B-Z)reaction: 相似文献
33.
34.
35.
36.
37.
On-line photochemical reaction of reserpine in the presence of acetone was investigated. Acetone was found to speed up the on-line photochemical conversion of reserpine into an intensively fluorescent compound. Not only reaction acidity but also the acetate buffer concentration affected the on-line photochemical induced fluorescence signal. Based on the observation an automated flow injection photochemical fluorimetric approach was developed. An injected sample zone was carried by a water stream to be merged with a acetate buffer (pH 3.4) solution containing 0.02% acetone in a knotted PTFE reactor (KR), which was freely coiled around a 6-W low pressure mercury lamp. While passing the KR, reserpine was transformed into an intensively fluorescent compound. It was on-line detected in a flow-through cell at the emission wavelength of 490 nm and excitation wavelength of 386 nm. At optimized conditions, a detection limit 0.45 mug l(-1) was achieved at a sampling rate of 90 h(-1). Eleven determinations of a 0.5 mg l(-1) reserpine standard solution gave a R.S.D. of 0.3%. The linear dynamic range of reserpine calibration curve was 0.01-0.75 mg l(-1). The proposed method was applied to assay the reserpine content in tablets and to monitor the dissolution profile of reserpine tablets. Satisfactory results were obtained for both the assays and dissolution studies. 相似文献
38.
The thermal reaction of HNCO has been studied in a static cell at temperatures between 873 and 1220 K and a constant pressure of 800 torr under highly diluted conditions. The reaction was measurable above 1000 K by FTIR spectrometry. The products detected include CO, CO2, HCN, NH3, and the unreacted HNCO. In this moderate temperature regime, the rates of product formation and HNCO decay cannot be accounted for by a previously established high-temperature mechanism, assuming HNCO → NH + CO (1) as the initiation process. Instead, a new bimolecular reaction, 2HNCO → CO2 + HNCNH (2), has been invoked to interpret the disappearance of HNCO as well as the formation of various products, most importantly CO2. The concentration profiles of all measured species can be quantitatively modeled, throughout the temperature range analyzed, by varying k2 using a modified mechanism. The kinetically modeled values of k2 can be effectively represented by This result agrees closely with that computed with the conventional transition-state theory using the TST parameters predicted by the BAC-MP4 method: The bimolecular reaction takes place via a stable 4-membered ring intermediate which is isoelectronic with diketene; viz. 相似文献
39.
本文把单个分子链的横截面积与聚合物的玻璃化转变温度联系起来,发现对于所讨论的聚合物,考虑了分子链间的相互作用以后,上面二者之间有一一对应的关系。认为单个分子链的横截面积与聚合物分子链柔顺性有关。同时采用文献[17]的方法,得到了1,2-聚丁二烯的分子链的内旋转异构化能,比较所得结果,证实了上面的看法。 相似文献
40.
Jun-hua Shi Yuxun Zhou Ming-lei He Jian Jin Yi-chuan Xiao Jun-hua Xiao Dong-zhi Wei 《Chemistry of Natural Compounds》2006,42(3):325-327
A novel compound, biotinylated 18β-glycyrrhetinic acid (BGA), was synthesized. It is a compound of 18β-glycyrrhetinic acid linked with biotin.
Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 266–267, May–June, 2006.
An erratum to this article is available at . 相似文献