全文获取类型
收费全文 | 40062篇 |
免费 | 4828篇 |
国内免费 | 3851篇 |
专业分类
化学 | 21450篇 |
晶体学 | 371篇 |
力学 | 1436篇 |
综合类 | 234篇 |
数学 | 3610篇 |
物理学 | 9321篇 |
无线电 | 12319篇 |
出版年
2024年 | 82篇 |
2023年 | 735篇 |
2022年 | 889篇 |
2021年 | 1240篇 |
2020年 | 1234篇 |
2019年 | 1235篇 |
2018年 | 1062篇 |
2017年 | 1072篇 |
2016年 | 1453篇 |
2015年 | 1577篇 |
2014年 | 1870篇 |
2013年 | 2466篇 |
2012年 | 2975篇 |
2011年 | 3176篇 |
2010年 | 2377篇 |
2009年 | 2410篇 |
2008年 | 2638篇 |
2007年 | 2499篇 |
2006年 | 2260篇 |
2005年 | 1984篇 |
2004年 | 1560篇 |
2003年 | 1305篇 |
2002年 | 1259篇 |
2001年 | 1053篇 |
2000年 | 904篇 |
1999年 | 843篇 |
1998年 | 732篇 |
1997年 | 671篇 |
1996年 | 688篇 |
1995年 | 574篇 |
1994年 | 528篇 |
1993年 | 480篇 |
1992年 | 446篇 |
1991年 | 377篇 |
1990年 | 327篇 |
1989年 | 242篇 |
1988年 | 207篇 |
1987年 | 144篇 |
1986年 | 164篇 |
1985年 | 176篇 |
1984年 | 117篇 |
1983年 | 75篇 |
1982年 | 81篇 |
1981年 | 59篇 |
1980年 | 58篇 |
1979年 | 62篇 |
1978年 | 49篇 |
1976年 | 46篇 |
1974年 | 48篇 |
1973年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
881.
Commercial poly(ethylene terephthalate) (PET) was treated at R. H.>80% and room temperature for a set time. The glass transition
temperature (Tg) decreases with the time of exposure to high humidity. The decrease in Tg is a result of plasticization. Our
data indicate that the Tg of dry PET of 76-78°C may decrease to as low a temperature as 65-67°C when it is wet. Induced crystallization
of PET in the presence of water reduces the cold crystallization temperature (Tc). The structure of water-induced crystals
is imperfect and can be improved in perfection by annealing.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
882.
Poor sensitivity and low phase ratio are the main drawbacks of open tubular capillary electrochromatography (OTCEC). The poor sensitivity results from the use of narrow bore size capillary, whereas the low phase ratio, which limits the separation capability, is caused by the limited surface area of conventional capillary. Two strategies may be useful to overcome these disadvantages. First, an extended light path (ELP) capillary, which has a bubble cell at the detection point, is used to improve the sensitivity. Secondly, an etched capillary of a 1,000-fold increased surface area is used to enhance the phase ratio. In this work, use of an ELP capillary and an etched capillary in OTCEC was evaluated with a chiral stationary phase of avidin prepared with the physical adsorption method. With a 20 microm I.D. ELP capillary with a 150 microm bubble cell, the peak height was enhanced by 4-10-fold and the corrected peak area was increased by 12-fold relative to a 20 microm I.D. conventional capillary. However, the peak efficiency and resolution decreased noticeably. The phase ratio on the etched capillary was slightly enhanced, by a factor of 1.64 relative to an unetched capillary. Consequently, the separation capability was slightly improved. The increase in the phase ratio was much lower than that expected from the increase in surface area, the reason for which is probably the reduced density of surface silanol group and the generation of nitrogen-containing groups due to the etching process. 相似文献
883.
Hua Lin XIE Yu Jie LI Xi Du NIE Li Bo LI 《中国化学快报》2006,17(7):945-948
Because of its high sensitivity, wide dynamic range and relative freedom from interferences, inductively coupled plasma mass spectrometry (ICP-MS) has been developed for the determination of trace and ultra-trace levels of elements in various fields1. Due… 相似文献
884.
885.
886.
887.
888.
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
889.
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
890.