全文获取类型
收费全文 | 43004篇 |
免费 | 7020篇 |
国内免费 | 4663篇 |
专业分类
化学 | 29712篇 |
晶体学 | 435篇 |
力学 | 3027篇 |
综合类 | 348篇 |
数学 | 5391篇 |
物理学 | 15774篇 |
出版年
2024年 | 103篇 |
2023年 | 852篇 |
2022年 | 1264篇 |
2021年 | 1453篇 |
2020年 | 1653篇 |
2019年 | 1603篇 |
2018年 | 1373篇 |
2017年 | 1372篇 |
2016年 | 1969篇 |
2015年 | 1898篇 |
2014年 | 2333篇 |
2013年 | 3033篇 |
2012年 | 3783篇 |
2011年 | 3873篇 |
2010年 | 2636篇 |
2009年 | 2460篇 |
2008年 | 2773篇 |
2007年 | 2429篇 |
2006年 | 2308篇 |
2005年 | 1912篇 |
2004年 | 1430篇 |
2003年 | 1220篇 |
2002年 | 1142篇 |
2001年 | 962篇 |
2000年 | 838篇 |
1999年 | 969篇 |
1998年 | 807篇 |
1997年 | 775篇 |
1996年 | 770篇 |
1995年 | 690篇 |
1994年 | 584篇 |
1993年 | 501篇 |
1992年 | 449篇 |
1991年 | 423篇 |
1990年 | 362篇 |
1989年 | 302篇 |
1988年 | 224篇 |
1987年 | 194篇 |
1986年 | 172篇 |
1985年 | 154篇 |
1984年 | 117篇 |
1983年 | 94篇 |
1982年 | 84篇 |
1981年 | 53篇 |
1980年 | 41篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 24篇 |
1974年 | 20篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
High-quality online course materials were reconstructed through feedback from undergraduate students and online data analysis regarding constructed learning materials on the Chao Xing Learning Platform. They were used for studying organic chemistry courses online and offline in university for nationalities. This model, based on student-centered teaching, can effectively transform students from passively accepting knowledge to actively learning and internalizing knowledge. This strategy can also enhance the students' learning initiative and the effects of learning, and hopefully be helpful to the universities in multi-ethnic areas in developing fundamental disciplined construction of organic chemistry and other courses. 相似文献
992.
The palladium-catalyzed reaction of simple arenes and nitriles provides good to excellent yields of aryl ketones or the corresponding hindered imines. The addition of a small amount of DMSO increases the yields dramatically. Both intermolecular and intramolecular examples of this process are successful. This novel chemistry is believed to involve palladium-catalyzed C-H activation, followed by carbopalladation of the nitrile. 相似文献
993.
本文用阴离子聚合方法,首先合成了线形‘活’的聚苯乙烯大分子阴离子,然后用二乙烯基苯为偶联成核剂,制备了十三个4-80臂较窄分子量分布的等臂长规则星形支化聚苯乙烯的模型化合物,并用GPC—粘度计联用装置对之进行了表征。 相似文献
994.
995.
巯基化合物的电位分析法研究 总被引:3,自引:0,他引:3
本文对用直接电位法测试巯基化合物的可行性进行了研究。发现由硫化银,硫化汞等金属难溶盐制成的膜电极对6-巯基嘌呤,高胱氨酸,1,4-二巯基苏糖经合物可产生响应,其斜率为30-110mV/pC,电极响应时间,则为十几秒至十几分钏,测试结果具有较好的重现性。因此,该方法可望得到应用。文中还对有关响应机理进行了探讨。 相似文献
996.
This paper restudies the method of direct chelatometric titration of V(IV) with N-benzoyl-N-phenylhydroxylamine (BPHA) as indicator. The indicator functions entirely differently from indicators hitherto used in chelatometry. The solution contains two independent systems – the indicator and the titrand-titrant system – without any color changing species. The BPHA-V(V) chelate once formed as the result of aerial oxidation constitutes the indicator system and does not react with EDTA. Its color therefore remains unchanged throughout titration. It is not a metallochromic indicator. Its function is that of color-screening. The color of the titrant system deepens during titration, but does not change. The end-point is indicated by one color completely covering up the other. Hence, this method is of purely empirical nature.Received July 5, 2002; accepted February 11, 2003
Published online July 16, 2003 相似文献
997.
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
998.
999.
Brownian dynamics simulations with hydrodynamic interactions are conducted to investigate the self-diffusion of charged tracer particles in a dilute solution of charged polymers, which are modeled by bead-spring chains. The Debye-Hückel approximation is used for the electrostatic interactions. The hydrodynamic interactions are implemented by the Ewald summation of the Rotne-Prager tensor. Our simulations find that the difference in short- and long-time diffusivities is very slight in uncharged short-chain solutions. For charged systems, to the contrary, the difference becomes considerable. The short-time diffusivity is found to increase with increasing chain length, while an opposite behavior is obtained for the long-time diffusivity. The former is attributed to the hydrodynamic screening among beads in a same chain due to the bead connectivity. The latter is explained by the memory effect arising from the electrostatic repulsion and chain length. The incorporation of hydrodynamic interactions improves the agreement between the simulation prediction and the experimental result. 相似文献
1000.
高效液相钴离子催化化学发光抑制法测定茶叶中的茶氨酸 总被引:5,自引:0,他引:5
研究了用高效液相分离、抑制化学发光测定茶叶中茶氨酸的分析方法。该法采用YWG C18(10μm,250mm×5 0mmi d )柱,以0 01mol·L-1醋酸钠 醋酸缓冲液(pH5 5)为流动相,流速为0 8mL·min-1。对茶氨酸抑制Co2+催化鲁米诺(luminol)与过氧化氢(H2O2)化学发光反应的条件进行了优化:Co2+的质量浓度为2μg·L-1,鲁米诺浓度为0 25mmol·L-1,H2O2浓度为0 5mmol·L-1。在茶氨酸的质量浓度为0 2g·L-1~5 0g·L-1时,茶氨酸抑制化学发光产生负峰的相对峰面积Y(将实际峰面积缩小至万分之一)与其质量浓度X(kg·L-1)的线性回归方程为Y=33862X+1 0605(r=0 9983)。 相似文献