全文获取类型
收费全文 | 874篇 |
免费 | 136篇 |
国内免费 | 105篇 |
专业分类
化学 | 628篇 |
晶体学 | 10篇 |
力学 | 79篇 |
综合类 | 17篇 |
数学 | 81篇 |
物理学 | 300篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 22篇 |
2021年 | 27篇 |
2020年 | 27篇 |
2019年 | 36篇 |
2018年 | 32篇 |
2017年 | 23篇 |
2016年 | 39篇 |
2015年 | 42篇 |
2014年 | 60篇 |
2013年 | 76篇 |
2012年 | 60篇 |
2011年 | 68篇 |
2010年 | 40篇 |
2009年 | 46篇 |
2008年 | 48篇 |
2007年 | 73篇 |
2006年 | 63篇 |
2005年 | 47篇 |
2004年 | 35篇 |
2003年 | 32篇 |
2002年 | 32篇 |
2001年 | 25篇 |
2000年 | 24篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1115条查询结果,搜索用时 31 毫秒
991.
本文提出一种具有边缘效果的假彩色编码新方法,不仅能对黑白图像进行假彩色化处理,同时又能使图像边缘获得增强。并且处理的图像面积较大,可使用白光信息处理系统,操作方法简便。用以处理黑白X线胸片,对某些不易确诊的病症,如癌症等的鉴别诊断有很好的效果。 相似文献
992.
In this study, surface plasmon resonance (SPR) biosensor techniques were used to obtain quantitative information on the kinetics of the DNA and polymerase I (Klenow fragment) interaction. DNA duplexes containing different base compositions at the binding site were immobilized on the SPR sensor surface via biotin-streptavidin chemistry and the subsequent binding of the polymerase was measured in real time. Various kinetic models were tested and a translocation model was shown to provide the best fit for the binding and dissociation profiles. The results revealed that the enzyme binds to DNA at both the polymerase and the exonuclease domains with different association and dissociation rates as well as affinity constants, depending on the presence of mismatches near the primer 3'-end. Introduction of unpaired bases increases the DNA binding affinity towards the exonuclease domain and promotes the translocation of DNA from the polymerase site to the exonuclease site. The results also demonstrated that SPR biosensors may be used as a sensitive technique for studying molecular recognition events such as single-base discrimination involved in protein-DNA interaction. 相似文献
993.
不同来源壳聚糖的基本特性及红外光谱研究 总被引:16,自引:0,他引:16
用同一方法在相同条件下,分别以螯虾壳、河虾壳、对虾壳、海蟹壳和蚕蛹制备了壳聚糖,并对其多项特性进行了比较研究。壳聚糖的收率分别为螯虾13.6%、海蟹12.3%、对虾10.5%、河虾8.70%、蚕蛹1.8%;灰份含量接近(0.25~0.45%);脱乙酰度相近(76~80%);壳聚糖的粘均分子量分别为:螯虾12.8×106、河虾1.15×106、海蟹1.06×106、对虾0.96×106、蚕蛹0.91×106。五种壳聚糖的红外光谱基本相似,只存在个别峰值、峰位的差异,表明五种壳聚糖的基本结构相同,但其空间构象和结晶度等方面存在差异。 相似文献
994.
995.
Fengchun Wang Rui Yang Jian Gong Chunhong Sui Lunyu Qu 《European Polymer Journal》2006,42(9):2108-2113
In this paper, polyaniline (PANI) microfibers with average diameter of 250 nm were synthesized by utilizing H4SiW12O40/polyacrylamide (HPA/PAM) microfibers seeding template method. The PANI microfibers were characterized by element analyses, FT-IR spectra, X-ray diffraction pattern (XRD), and Scanning electron micrograph (SEM). The microfibers seeding template significantly affected the fibrous morphology of the resulting PANI. However, the diameter of the PANI microfibers was almost not affected by the diameter of the microfibers seeding template in the experimental range. In addition, the conductivity of the PANI microfibers was also investigated. The result showed that the best conductivity of the PANI microfibers doped with H4SiW12O40 was 27.1 S/cm. 相似文献
996.
997.
Hong Zheng Xijun Chang Ning Lian Jie Mao Sui Wang Yuming Dong 《Mikrochimica acta》2005,149(3-4):259-266
A novel poly(acryl-p-toluenesulfonamideamidine-p-toluenesulfonylamide) chelating fiber containing S, N and O elements was synthesized from polyacrylonitrile fiber and p-toluenesulfonamide and used for the preconcentration and separation for traces of Ru(III), Rh(III), Au(III) and Pd(IV) ions from waste water and ore sample solution. The synthesis of this fiber was simple and rapid. The results indicate that 100ngmL–1 of these ions can be quantitatively enriched by the chelating fiber at a flow rate of 6mLmin–1 and a pH of 4 and desorbed quantitatively with 20mL of 6molL–1 HCl and 5% CS(NH2)2 solution at 50°C (with recovery>95%). A 50 to 1000-fold excess of Ca2+, Mg2+, Mn2+, Co2+, Fe3+, Cu2+, Zn2+, and Al3+ ions caused little interference in the concentration and determination of the analyzed ions. When the fiber had been reused twenty times, the recoveries of the ions enriched by the fiber were still over 96%. The saturated adsorption capacities of the fiber were in the range of 22–96mgg–1. The relative standard deviation (RSD) of the method was between 0.70% and 0.84%. Recoveries of a standard added to actual samples were in range of 95–101%. The results obtained for these ions in real solution samples were basically in agreement with the given values, the average errors being below 5.0%. FT-IR spectra show that the existence of –SO2–Ar, HN=C–NH–, O=C–NH– and –NH–SO2 functional groups are verified in the chelating fiber. The experiments show that the method is rapid, precise, simple and convenient. 相似文献
998.
A new poly(acryl-p-nitrophenylamidrazone-p-nitrophenylhydrazide) chelating fibre was synthesized from polyacrylnitrile fibre, and the structure of the chelating fibre was determined with the help of the FT-IR spectrum. The parameters influencing the efficiency of the fibre for concentrating trace amounts of Bi3+, In3+, Sn4+, Ga3+ and Ti4+, including sample acidity during enrichment, flow rate, adsorptive capacity, re-usability, interfering ions and desorption conditions were investigated. Trace Bi3+, In3+, Sn4+, Ga3+ and Ti4+ were enriched and separated from real sample solutions and detected using inductively coupled plasma optical emission spectrometry (ICP-OES) with satisfactory results. The experiments show that the method is rapid, precise, simple and convenient to use. 相似文献
999.
利用Sc^3+与SO^2-4形成络阴离子后强烈吸附在强碱性阴离子交换树脂上的性质,分离掉大部分基体钪后,留下一小部分钪作基体。定量加入内标,利用火花源介谱单曝光法测定杂质元素。 相似文献
1000.
[reaction: see text] An asymmetric intermolecular aza variant of the Mannich reaction is reported utilizing chiral sulfinimine anions as the nucleophile and N-sulfonyl aldimines as the electrophilic component. A wide range of nucleophiles and electrophiles are tolerated by the reaction conditions, delivering the condensation products in good to excellent yield with a high degree of stereocontrol. Application of this methodology to the total synthesis of a natural product is reported. 相似文献