全文获取类型
收费全文 | 27060篇 |
免费 | 4781篇 |
国内免费 | 4702篇 |
专业分类
化学 | 20905篇 |
晶体学 | 433篇 |
力学 | 1432篇 |
综合类 | 466篇 |
数学 | 3094篇 |
物理学 | 10213篇 |
出版年
2024年 | 93篇 |
2023年 | 492篇 |
2022年 | 915篇 |
2021年 | 959篇 |
2020年 | 1130篇 |
2019年 | 1252篇 |
2018年 | 948篇 |
2017年 | 900篇 |
2016年 | 1309篇 |
2015年 | 1483篇 |
2014年 | 1660篇 |
2013年 | 2059篇 |
2012年 | 2422篇 |
2011年 | 2393篇 |
2010年 | 1865篇 |
2009年 | 1811篇 |
2008年 | 1999篇 |
2007年 | 1763篇 |
2006年 | 1557篇 |
2005年 | 1330篇 |
2004年 | 1175篇 |
2003年 | 966篇 |
2002年 | 1075篇 |
2001年 | 977篇 |
2000年 | 716篇 |
1999年 | 611篇 |
1998年 | 368篇 |
1997年 | 313篇 |
1996年 | 301篇 |
1995年 | 269篇 |
1994年 | 214篇 |
1993年 | 186篇 |
1992年 | 181篇 |
1991年 | 159篇 |
1990年 | 148篇 |
1989年 | 104篇 |
1988年 | 106篇 |
1987年 | 70篇 |
1986年 | 54篇 |
1985年 | 63篇 |
1984年 | 40篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1965年 | 4篇 |
1959年 | 4篇 |
1955年 | 2篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Martin E. V. Pedersen Lars S. Rishøj Henrik Steffensen Sanshui Xiao Niels Asger Mortensen 《Optical and Quantum Electronics》2007,39(10-11):903-911
Slow-light enhanced optical detection in liquid-infiltrated photonic crystals is theoretically studied. Using a scattering-matrix approach and the Wigner–Smith delay time concept, we show that optical absorbance benefits both from slow-light phenomena as well as a high filling factor of the energy residing in the liquid. Utilizing strongly dispersive photonic crystal structures, we numerically demonstrate how liquid-infiltrated photonic crystals facilitate enhanced light–matter interactions, by potentially up to an order of magnitude. The proposed concept provides strong opportunities for improving existing miniaturized absorbance cells for optical detection in lab-on-a-chip systems. 相似文献
52.
A Novel and Efficient Catalytic System for Aerobic Oxidative Coupling of 2-Naphthol Derivatives 总被引:2,自引:0,他引:2
LiCHEN JingBoLAN ZhiHuaMAO XiaoQiYU RuGangXIE 《中国化学快报》2004,15(8):903-906
The paper reported a novel and efficient aerobic oxidative coupling reaction of 2-naphthol derivatives catalyzed by CuCu (Ⅰ or Ⅱ)N-alkylimidazole complexes in excellent yields. The crystal structure of CuCu(Ⅱ)N-methylimidazole complex to be determined by X-Ray. 相似文献
53.
Zhi‐Yong Huang Jin‐Can Shen Zhi‐Xia Zhuang Xiao‐Ru Wang Frank S. C. Lee 《应用有机金属化学》2004,18(6):255-261
Cinnabar, as one of the most widely used mineral drugs in traditional Chinese medicines, has been proven to have prominent curative effects in clinical use for more than 2000 years. But the safety and toxicity of the drug has been under constant debate in clinic usage. Metallothionein (MT) contains about 30% of cysteine in the molecule, and plays an important detoxification role against heavy metals. In this study, it was used as a biomarker to assess mercurial accumulation in rats fed orally with cinnabar. After feeding rats with cinnabar by gastric gavage at different dosages and at different times, the distribution of heavy metals (including mercury, copper and zinc) and MT was investigated among rat tissues, including liver, kidney, heart, brain, testis and blood. Metals and MT determinations were carried out using inductively coupled plasma mass spectrometry (ICP‐MS) and a modified mercury saturation assay technique respectively. The results indicated that mercury was easily accumulated in the tissues of rats exposed to cinnabar, especially in kidney. For example: at a feeding dosage of 5 g kg?1 (bw) for 4 weeks, the mercury concentrations in kidney were 13, 8.7, 21.6 and 26 times those in liver, testis, brain and heart respectively; and at 2.5 g kg?1 (bw) for 2 weeks, the mercury concentrations in kidney were 21, 2.1, 3 and 21 times those in liver, testis, brain and heart respectively. In addition, mercury in kidney and liver of all cinnabar groups was significantly higher than that of the control group (P < 0.01). A high positive correlation observed between MT concentrations and mercury levels in both liver and kidney (R2 = 0.9299, P < 0.02 for liver; R2 = 0.9923, P < 0.0008 for kidney) indicated that MT could be used as a biomarker for mercury in tissues. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
54.
采用MTT比色法对体外培养的肿瘤细胞进行细胞毒作用实验,验证槲寄生蛋白注射液体外抗肿瘤效果.并且鉴定这种检测方法的有效性。实验结果表明槲寄生蛋白注射液有一定的体外抗肿瘤效果;MTT比色法是一种可用的体外细胞毒作用检测法,为新药品的开发提供了实验依据。 相似文献
55.
Triterpenoid Constituents of Huperzia miyoshiana 总被引:1,自引:0,他引:1
Thirteen triterpenoids, including three new ones, miyoshianois A (1), B (2) and C (3), were isolated from Huperzia miyoshiana. The structures of these new compounds were established as 3-O-dihydroferuloyltohogenol (1), 16-oxo-3β,21β-dihydrox-y-serrat-14-en-24-ferulate (2) and 16-oxo-3a, 21β-dihydroxy-serrat-14-en-24-ferulate (3), respectively, on the basis of their spectroscopic analysis. 相似文献
56.
This paper firstly examines the value of optical bypass scheme in packet ring networks. An Integer Linear Program (ILP) formulation is presented and analytical results under different traffic patterns are given. 相似文献
57.
58.
35Cr25Ni12奥氏体耐热钢中碳化物的电子显微分析 总被引:1,自引:0,他引:1
应用扫描电镜(SEM)和透射电镜(TEM)研究了长期使用前后的35Cr25Ni12奥氏体耐热钢中的碳化物演变行为;该钢固溶时效后的组织由初晶奥氏体及M23C6共晶碳化物组成,奥氏体基体中析出了二次M23C6,二次碳化物总是与基体保持立方-立方取向关系;长期使用(3、5年)后,奥氏体中析出的二次碳化物量明显增加,部分M23C6已转变为M6C,M6C与奥氏体基体以及二次碳化物M23C6保持[001]M6C//[221]A//[221]M23C6孪晶取向关系。 相似文献
59.
具有两台专用机,两台通用机的Q4//Cmax问题的近似算法 总被引:8,自引:1,他引:7
本文讨论具有两台专用机、两台通用机的两组工件的同种类平行机的Q4//Cmax问题,对这类特殊的排序问题,提出一种启发式算法,得到了最差情况下性能指标的严格的界. 相似文献
60.
J. P. Bucher D. C. Douglass P. Xia B. Haynes L. A. Bloomfield 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,19(4):251-254
A new apparatus for measuring the magnetic properties of metal clusters has been constructed. The technique involves the conventional Stern-Gerlach deflection scheme together with modern pulsed laser vaporization source technology and time of flight mass spectrometry. High field seeking monodirectional deflections have been measured for cobalt clusters containing between 40 and 400 atoms. The measured magnetic moments per atom are found to be lower than the known values for the bulk. Special attention has been given to velocity measurements of the metal clusters and the carrier gas atoms in the beam. The residence time of the particles in the source cavity has been measured. 相似文献