全文获取类型
收费全文 | 16838篇 |
免费 | 3084篇 |
国内免费 | 6305篇 |
专业分类
化学 | 12122篇 |
晶体学 | 892篇 |
力学 | 1241篇 |
综合类 | 598篇 |
数学 | 2414篇 |
物理学 | 8960篇 |
出版年
2024年 | 29篇 |
2023年 | 128篇 |
2022年 | 612篇 |
2021年 | 582篇 |
2020年 | 593篇 |
2019年 | 557篇 |
2018年 | 542篇 |
2017年 | 840篇 |
2016年 | 628篇 |
2015年 | 928篇 |
2014年 | 1113篇 |
2013年 | 1384篇 |
2012年 | 1326篇 |
2011年 | 1535篇 |
2010年 | 1589篇 |
2009年 | 1651篇 |
2008年 | 1818篇 |
2007年 | 1547篇 |
2006年 | 1599篇 |
2005年 | 1335篇 |
2004年 | 986篇 |
2003年 | 710篇 |
2002年 | 635篇 |
2001年 | 707篇 |
2000年 | 771篇 |
1999年 | 382篇 |
1998年 | 216篇 |
1997年 | 169篇 |
1996年 | 152篇 |
1995年 | 128篇 |
1994年 | 135篇 |
1993年 | 132篇 |
1992年 | 163篇 |
1991年 | 59篇 |
1990年 | 82篇 |
1989年 | 63篇 |
1988年 | 81篇 |
1987年 | 56篇 |
1986年 | 44篇 |
1985年 | 36篇 |
1984年 | 37篇 |
1983年 | 42篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 8篇 |
1979年 | 30篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1971年 | 4篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
光参量啁啾脉冲放大(OPCPA)在饱和放大区存在一个增益稳定点,据此设计了一个输出稳定的三级OPCPA系统;第一、二、三级分别选用准相位匹配的周期极化钛氧磷酸钾(PPKTP)晶体、LBO晶体和KDP晶体作为增益介质。饱和放大时,增益随泵浦光强度变化时的增益输出稳定性明显改善,在泵浦光强度抖动低于6%的情况下,各级光参量放大器OPA输出的增益抖动小于1%。前级采用准相位匹配的PPKTP晶体作为增益介质,在远低于破坏阈值的30MW/cm2的泵浦功率密度下,可得到2×105的饱和放大增益和20%的能量转换效率。 相似文献
53.
54.
55.
56.
N- aryl substituted benzenesulfamides are often used as heating-sensitive recording material1, thermal printing material2, sensitizer3 and developer4. Moreover, some of the benzenesulfamides have antifungal activities5. Many methods have been described for preparation of sulfamides. They are used to carry out in solvent8 or in solid phase condition9. These methods required solvent or solid support and even required heating or cooling. At the same time, the process of these methods is complex. Now we have developed a new method to prepare N-aryl substituted toluenesulfamides under solvent-free conditions.In recent years, solvent-free technology has gained popularity in organic synthesis. For instance,solidstate reaction and microwave reaction have received considerable attention. Solvent-free synthesis of amides has been reported10-11. This technology has many advantages such as high efficiency and selectivity, easy separation and environmental acceptability. All these merits are in accord with green chemistry's requirements of energy-saving, high efficiency and environmental benefits.In our paper, we used a simple and efficient method for preparing N-aryl substituted toluenesulfamides under solvent-free conditions, as a replacement for classic solvent, which gives many environmental benefits.All reactions were completed at room temperature by co-grinding in an agate mortar for 3-20min and the results are shown in Table 1.In conclusion, we have developed an efficient and convenient method of preparation N-aryl substituted toluenesulfamides in high yields. It symbols an improvement for synthesis of benzenesulfamides. 相似文献
57.
YAN Xiaomin ZHAO Lin SHAO Jianhui TAN Xin SONG Zhengxiao School of Chemical Engineering Technology Tianjin University Tianjin China Slichem Liquid Material Co. Ltd. Shijiazhuang China 《Chinese Journal of Reactive Polymers》2004,(Z1)
1. INTRODUCTION Methionine, namely 2-amido-4-thiomethyl butyric acid with a structure of CH3SCH2CH2CHCOOH, is one of the essential amino acids and has two natural enantionmers, D and L-methionine. The mixture of L- and D-isomers can be used as analeptics or nutritive additives to maintain the equilibrium of amino acids of feed [1,2]. L-methionine can release active methyl and accelerate the synthesis of choline, which further speeds up the conversion of the lipid accumulated in liv… 相似文献
58.
Direct Observation of Non-covalent Complexes for Phosphorylated Flavonoid-protein Interaction by ESI
XiaoLanCHEN TingZHANG HongXiaLIU LingBoQU YouZhuYU YuFenZHAO 《中国化学快报》2004,15(3):343-346
Diethyl flavon-7-yl phosphate was synthesized by modified Atheron-Todd reaction. The result of ESI shows that the phosphated flavonoids possess stronger binding affinities toward proteins such as myoglobin, insulin and lysozyme and are easier to form the non-covalent complexes with them. 相似文献
59.
The First Intramolecular Charge Transfer Transition Based on 2-Ureido-4[1H]-pyrimidinone Binding Module 总被引:1,自引:0,他引:1
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported. 相似文献
60.
In this paper, we develop an approximation procedure for functionsof bounded variations. Our procedure cannot increase the variationof the function being approximated, and also avoids discontinuityof the interpolation function. 相似文献