全文获取类型
收费全文 | 17006篇 |
免费 | 2856篇 |
国内免费 | 4608篇 |
专业分类
化学 | 12955篇 |
晶体学 | 539篇 |
力学 | 1155篇 |
综合类 | 358篇 |
数学 | 2221篇 |
物理学 | 7242篇 |
出版年
2024年 | 69篇 |
2023年 | 281篇 |
2022年 | 695篇 |
2021年 | 665篇 |
2020年 | 704篇 |
2019年 | 740篇 |
2018年 | 570篇 |
2017年 | 764篇 |
2016年 | 694篇 |
2015年 | 896篇 |
2014年 | 1099篇 |
2013年 | 1388篇 |
2012年 | 1457篇 |
2011年 | 1511篇 |
2010年 | 1311篇 |
2009年 | 1306篇 |
2008年 | 1487篇 |
2007年 | 1185篇 |
2006年 | 1172篇 |
2005年 | 998篇 |
2004年 | 793篇 |
2003年 | 597篇 |
2002年 | 636篇 |
2001年 | 573篇 |
2000年 | 589篇 |
1999年 | 382篇 |
1998年 | 203篇 |
1997年 | 194篇 |
1996年 | 184篇 |
1995年 | 174篇 |
1994年 | 172篇 |
1993年 | 155篇 |
1992年 | 137篇 |
1991年 | 86篇 |
1990年 | 89篇 |
1989年 | 93篇 |
1988年 | 74篇 |
1987年 | 53篇 |
1986年 | 49篇 |
1985年 | 51篇 |
1984年 | 39篇 |
1983年 | 33篇 |
1982年 | 32篇 |
1981年 | 25篇 |
1980年 | 19篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1959年 | 6篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
A new family of photonucleases, naphthalimide-thiazoles was synthesized and evaluated. These compounds intercalated into DNA efficiently and damaged DNA photochemically at concentrations as low as 5 μM. Mechanistic experiment suggests that a novel naphthalimide-thiazole radical produced via an excited triple state might be involved in the DNA photodamage. Different activity may arise from the impact of substituents at 2-phenyl ring of thiazole on the electron population of excited triple state according to AM1 semi-empirical calculation. 相似文献
22.
乌桕类可可脂结晶过程中表现体积变化 总被引:1,自引:0,他引:1
为了解乌桕类可可脂(CTCBE)缓冷结晶横向胀罐爆裂原因,研究CTCBE结晶过程中的膨胀特性,采用流体静力法测试了不同等温结晶条件下CTCBE结晶形成的表观密度和表观体积及其横纵向膨胀状况。结果表明,CTCBE缓冷结晶后形成外部和中部两个晶区。在5-25℃的各等温结晶范围内,当结晶温度增加时,外部结晶区域减小、表观密度变化不大;中部结晶区域增大、表观密度明显减小,CTCBE的表观体积、横向、纵向膨胀率均增大,膨胀横向大于纵向。进一步表明CTCBE在自然缓冷固化的表观体积根本上由其结晶温度决定。为有效防止横向胀罐,自然缓冷固化温度应低于10℃。 相似文献
23.
一种小波域音频信息隐藏方法 总被引:1,自引:0,他引:1
提出了一种基于量化的小波域音频隐藏算法,将保密语音隐藏到载体音频中.为提高隐藏重和保密语音传输的安全性,对保密语音进行了小波域压缩编码和m序列的扩频调制,生成待隐藏的比特序列;通过量化方法,将编码和调制后的保密语音隐藏到载体音频的小波系数中;保密语音的恢复过程不需要使用原始音频、仿真结果表明,隐藏有保密语音的载体音频听觉质量没有明显下降,提取的保密语音感知质量较好;该算法对重量化、加噪、低通滤波等攻击均有良好的鲁棒性. 相似文献
24.
25.
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
26.
Gujie Qian S. Baccaro M. Falconieri Jiafang Bei A. Cecilia Guorong Chen 《Journal of Non》2008,354(40-41):4626-4629
Glasses in SiO2–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF2/BaO ratio on structure of glasses. 相似文献
27.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献
28.
29.
30.