全文获取类型
收费全文 | 5423篇 |
免费 | 1066篇 |
国内免费 | 1842篇 |
专业分类
化学 | 3814篇 |
晶体学 | 253篇 |
力学 | 505篇 |
综合类 | 176篇 |
数学 | 715篇 |
物理学 | 2868篇 |
出版年
2024年 | 16篇 |
2023年 | 65篇 |
2022年 | 192篇 |
2021年 | 185篇 |
2020年 | 215篇 |
2019年 | 205篇 |
2018年 | 205篇 |
2017年 | 251篇 |
2016年 | 222篇 |
2015年 | 270篇 |
2014年 | 334篇 |
2013年 | 455篇 |
2012年 | 473篇 |
2011年 | 490篇 |
2010年 | 466篇 |
2009年 | 532篇 |
2008年 | 503篇 |
2007年 | 508篇 |
2006年 | 429篇 |
2005年 | 366篇 |
2004年 | 276篇 |
2003年 | 233篇 |
2002年 | 200篇 |
2001年 | 210篇 |
2000年 | 249篇 |
1999年 | 164篇 |
1998年 | 68篇 |
1997年 | 56篇 |
1996年 | 66篇 |
1995年 | 52篇 |
1994年 | 47篇 |
1993年 | 49篇 |
1992年 | 36篇 |
1991年 | 26篇 |
1990年 | 36篇 |
1989年 | 32篇 |
1988年 | 23篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有8331条查询结果,搜索用时 15 毫秒
1.
The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr2·6H2O formed. In addition to this double salt, the three single salts LiBr·2H2O, KBr and MgBr2·6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer's electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones. 相似文献
2.
WANG Zhong HONG Haitao XIAO Hai SUN Changku MENG Yan YE Shenghua 《Chinese Journal of Lasers》1997,6(5):435-440
1.IntroductionAbsolutedistancemeasurementisfarfromanewtopic.However,itisstillafieldstimulatinggreatinterestsnowadaysduetoitSimportantroleinmanufacturingandassembly['J.SincethegreatsuccessachievedbyMichelsonandBenoitwhentheyfirstdevelopedaninterferometertodeterminethestandardmeterintermsofthemonochromaticredcadmiumline,theopticinterferometerhasbeenprovedtobeoneofthemostpreciseandefficientwayindisplacementmeasurementbecauseofitshighdiscriminationandsimplestructure.However,thetraditionalinterfe… 相似文献
3.
4.
5.
6.
Haitao Qian Edith Mathiowitz 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5899-5915
We succeeded in developing the acyl chloride‐facilitated condensation polymerization method for the synthesis of new poly(anhydride‐ester)s with aromatic side groups, which cannot be polymerized by the classic melt condensation polymerization method. Using chlorinated and acylated carboxylic acids as the intermediates, the polymerization was carried out at low temperatures of 120 or 135 °C to yield pure poly(anhydride‐ester)s of molecular weights as high as 1.55 × 105 with minimal side‐reactions. A homogeneous route of preparation was developed and optimized, using butyric anhydride as the acylating reagent and oxalyl chloride as the chlorinating reagent. A comparison of the mechanisms of the classic method and the new method indicates that the effects of transacylation—cyclization and oligomer formation—were greatly reduced due to the high reactivity of carboxylic acid chloride and the steric effect of bulky acyl groups. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5899–5915, 2007 相似文献
7.
8.
9.
The catalytic activities of SO42-/TiO2-MoO3 in synthesizing cyclohexanone ethylene ketal,cyclohexanone 1,2-propanediol ketal, 2-propyl-1,3-dioxolane, 4-methyl-2-isopropyl-1,3-dioxolane,2-isopropyl-1,3-dioxolane, 4-methyl-2-isopropyl-1,3-dioxolane, butanone ethy-lene ketal and butanone 1,2-propanediol ketal were reported. It has been demonstrated that SO42-/TiO2-MoO3 is an excellent catalyst. Various factors concerned in this reaction have been investigated. The optimum conditions have been found, that is, the molar ratio of aldehyde/ketone to alcohol was 1:1.5 or 1:1.3,the mass ratio of the catalyst used to the reactants was 0.25~1.5%, and the reaction time was 45~60 min. Under this conditions, the yield of cyclohexanone ethylene ketal is 82.7%, cyclohexanone 1,2-propanediol ketal is 83.4%, the yield of 2-propyl-1,3-dioxolane is 68.1%,4-methyl-2-isopropyl-1,3-dioxolane is 87.5%, the yield of 2-isopropyl-1,3-dioxolane is 70.7%,4-methyl-2-isopropyl-1,3-dioxolane is 82.5%, the yield of butanone ethylene ketal is 74.1%, and butanone 1,2-propanediol ketal is 94.9%.Some equation and experiment results concerned of the synthetic acetals or ketals were listed as follows. 相似文献
10.