全文获取类型
收费全文 | 42872篇 |
免费 | 6303篇 |
国内免费 | 5555篇 |
专业分类
化学 | 31943篇 |
晶体学 | 544篇 |
力学 | 2057篇 |
综合类 | 487篇 |
数学 | 5081篇 |
物理学 | 14618篇 |
出版年
2024年 | 116篇 |
2023年 | 701篇 |
2022年 | 1246篇 |
2021年 | 1279篇 |
2020年 | 1489篇 |
2019年 | 1524篇 |
2018年 | 1297篇 |
2017年 | 1243篇 |
2016年 | 1871篇 |
2015年 | 1947篇 |
2014年 | 2231篇 |
2013年 | 3050篇 |
2012年 | 3536篇 |
2011年 | 3817篇 |
2010年 | 2690篇 |
2009年 | 2677篇 |
2008年 | 2939篇 |
2007年 | 2652篇 |
2006年 | 2464篇 |
2005年 | 2188篇 |
2004年 | 1738篇 |
2003年 | 1451篇 |
2002年 | 1455篇 |
2001年 | 1169篇 |
2000年 | 1015篇 |
1999年 | 887篇 |
1998年 | 693篇 |
1997年 | 614篇 |
1996年 | 642篇 |
1995年 | 519篇 |
1994年 | 484篇 |
1993年 | 437篇 |
1992年 | 390篇 |
1991年 | 324篇 |
1990年 | 273篇 |
1989年 | 225篇 |
1988年 | 188篇 |
1987年 | 155篇 |
1986年 | 165篇 |
1985年 | 174篇 |
1984年 | 109篇 |
1983年 | 72篇 |
1982年 | 76篇 |
1981年 | 59篇 |
1980年 | 56篇 |
1979年 | 60篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 42篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
将快速 Monte Carlo方法与分子动力学方法相结合 ,研究了不同种类有机分子在 Al3P4 O3- 1 6 计量比的二维层状磷酸铝形成中的模板能力 .依据主 -客体之间非键相互作用能 (包括范德华能、氢键能和库仑能 ) ,可合理地解释已知实验现象 ,并能有效地预测出适于形成某一特定无机层结构的有机胺模板剂 .通过选择理论预测的有机胺分子作为模板剂 ,成功地合成了二维层状磷酸铝化合物 Al3P4 O1 6 · 1 .5 H3NC6 H1 0 NH3. 相似文献
952.
953.
954.
955.
Lin Jiacheng Li Qianqian Zeng Xiaodong Chen Ziyang Ding Qihang Li Yang Zhou Hui Meng Xianli Chen Deliang Deng Zixin Hong Xuechuan Xiao Yuling 《中国科学:化学(英文版)》2020,63(6):766-770
Osteosarcoma is the most common primary malignant tumor of bone, particularly among children and adolescents. Advances in imaging, surgical techniques, and implants have dramatically reduced the need for amputation in the past three decades.Recently, in vivo fluorescence imaging in the second near-infrared window(NIR-II, 1,000–1,700 nm) shows impressive advantages of deeper tissue penetration and higher spatial resolution, which makes it a promising tool for the early diagnosis and post-operative observation of Osteosarcoma. To the best of our knowledge, this paper is the first time to develop a novel NIR-II fluorescence probe conjugated with an osteosarcoma targeted oligopeptide for molecular tumor imaging in a xenograft orthotopic osteosarcoma mouse model. 相似文献
956.
Conjugated linoleic acids (CLA) have been a subject of extensive investigation for their anticarcinogenic, hypolipidemic, antiatherosclerotic and immune-enhancing activities. Stability of CLA in foods has not received much attention by both academics and industry. Although CLA has shown many beneficial effects, its decomposition must be prevented when CLA in foods is processed, stored and transported. However, no study to date has addressed the stability of CLA in foods. The present study was carried out further to examine the stability of CLA in egg yolk during the storage and frying, using gas liquid chromatography (GLC) and silver ion high-performance liquid chromatography (Agt-HPLC). The eggs, containing 4.0% CLA per gramme of egg yolk, were 40s. Either storage for 6 months or frying for 40 s did not significantly change the composition of CLA in egg yolk. However, the degradation of CLA was statistically significant when the CLA components of egg yolk protected CLA from degradation. It is concluded that CLA is well preserved in egg before it is consumed. 相似文献
957.
958.
JinguangXu ZhijianTian JunweiWang YunpengXu ZhushengXu LiwuLin 《天然气化学杂志》2003,12(2):105-112
Conventional oven drying (COD) and supercritical drying (SCD) methods were applied to the preparation of Mn-substituted hexaaluminate (BaMnA111O19-α) catalysts. The effect of drying methods on phase composition, specific surface area, pore structure, reduction behavior of Mn^3 ions, and combus-tion activity of the samples was investigated. The homogenous mixing of the components in the sol-gel process could be maintained by SCD, and the hexaaluminate phase was almost the only phase of the resulting materials after calcination. H2-TPR revealed that the Mn^3 ions in the sample obtained by SCD were easier to be reduced than that by COD. Moreover, the samples obtained by SCD have higher surface area, narrower pore size distribution, and higher combustion activity than those obtained by COD. 相似文献
959.
利用波长为266nm的激光光解CHBr3产生CH自由基,其与NO反应作为NCO自由基的来源.在298K,总压2660Pa的条件下,采用激光诱导荧光的方法,研究了NCO自由基与SO2、CS2的反应.得到了NCO自由基与SO2、CS2双分子反应速率常数分别为(1.8±0.3)×10-11和(3.1±0.4)×10-12cm3·molecule-1·s-1.对这两个反应在B3LYP/6-31 G(d)的水平上进行理论研究的结果表明,NCO自由基与SO2、CS2的反应是加成反应,其机理是NCO自由基中的N原子攻击反应物的中心原子,得到加成产物. 相似文献
960.
Zhong Lin Wang 《Microscopy and microanalysis》2004,10(1):158-166
Characterizing the physical properties of individual nanostructures is challenging because of the difficulty in manipulating the objects of sizes from nanometers to micrometers. Most nanomeasurements have been carried using scanning probe microscopy. In this article, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements of the mechanical and electrical properties of a single nanostructure. Dual-mode resonance of an oxide nanobelt has been observed, and its bending modulus has been measured. An in situ technique was demonstrated for measuring the work function at the tip of a carbon nanotube. The ballistic quantum conductance of a multiwalled carbon nanotube was observed at room temperature using the setup in TEM. It is concluded that in situ measurement by directly linking structure with property is a future direction of electron microscopy. 相似文献