全文获取类型
收费全文 | 5389篇 |
免费 | 259篇 |
国内免费 | 518篇 |
专业分类
化学 | 4426篇 |
晶体学 | 11篇 |
力学 | 387篇 |
综合类 | 99篇 |
数学 | 383篇 |
物理学 | 860篇 |
出版年
2024年 | 7篇 |
2023年 | 57篇 |
2022年 | 396篇 |
2021年 | 348篇 |
2020年 | 215篇 |
2019年 | 193篇 |
2018年 | 176篇 |
2017年 | 193篇 |
2016年 | 302篇 |
2015年 | 254篇 |
2014年 | 232篇 |
2013年 | 412篇 |
2012年 | 268篇 |
2011年 | 233篇 |
2010年 | 192篇 |
2009年 | 232篇 |
2008年 | 213篇 |
2007年 | 278篇 |
2006年 | 246篇 |
2005年 | 199篇 |
2004年 | 206篇 |
2003年 | 174篇 |
2002年 | 148篇 |
2001年 | 148篇 |
2000年 | 92篇 |
1999年 | 97篇 |
1998年 | 76篇 |
1997年 | 79篇 |
1996年 | 73篇 |
1995年 | 56篇 |
1994年 | 65篇 |
1993年 | 40篇 |
1992年 | 51篇 |
1991年 | 33篇 |
1990年 | 36篇 |
1989年 | 32篇 |
1988年 | 27篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有6166条查询结果,搜索用时 46 毫秒
51.
两组份互穿网络聚合物的合成研究 总被引:1,自引:0,他引:1
以蓖麻油聚氨酯和聚醚聚氨酯的不同重量比与光敏剂、催化剂、稀释剂、促进剂所组成的多相体系为反应物,分别在紫外光照射和加热的条件下合成网络Ⅰ和网络Ⅱ的互穿网络聚合物(IPN)。改变网络Ⅱ聚醚聚氨酯中各组份的摩尔比制得系列样品。红外光谱,应力-应变曲线和动态力学性能测定发现,样品的力学性能与两组份重量比和网络Ⅱ中不同组成都存在着一定关系。这些结果,为该体系IPN的合成和应用提供了一定依据。 相似文献
52.
Xuan-Ming Zhang Long-Long Guo Ning-Hui Yang Hua Zhang 《Natural product research》2019,33(17):2549-2553
This study investigated the flavonoid constituents of a traditional Chinese medical plant Ziziphora clinopodioides Lam. by using ultra-performance liquid chromatography coupled with quadruple time-of-flight mass spectrometry and screened the active components in regulating autophagy.Normal rat kidney (NRK) cells transfected with green fluorescent protein- microtubule-associated protein 1 light Chain 3(GFP-LC3) were treated with Z. clinopodioides flavonoids and its chemical compositions. After 4 h of treatment, the auto-phagy spot aggregation in NRK cells was photographed and observed by laser scanning confocal microscopy. The following 10 flavonoid components of Z. clinopodioides were identified: baicalein(1), quercetin(2), hyperoside(3), quercetin3-O-β-d-glucopyranoside(4), apigenin(5), kaempferol(6), chrysin(7), diosimin(8), linarin(9) and rutin(10). Among these flavonoids, chrysin, apigenin and quercetin were identified as the active principles in activating autophagy. This research may provide a reference for further developing and utilizing Z. clinopodioides. 相似文献
53.
原油三维荧光分析中猝灭现象辨析 总被引:5,自引:0,他引:5
研究了原油的三维荧光猝灭现象,指出浓度过高是原油产生荧光猝灭的主要原因,将会造成三维荧光等值线图畸变,致使定量分析数据失真,谱图特征变异,难以获取原油特征三维指纹图。提出了避免荧光猝灭的预试方法,并列出了不同类型原油的最佳测试浓度。 相似文献
54.
The chemical composition of the essential oils of the flowers and leaves of Anthemis hyalina were analyzed by GC and GC-MS for the first time. The oils were found to contain seventy-two components. cis-Chrysanthenyl acetate (14.9% and 17.8%), camphor (11.6% and 1.7%), terpinen-4-ol (8.3% and 1.2%), germacrene-D (5.1% and
2.1%), β-caryophyllene (4.1% and 5.4%), myrcene (3.6% and 16.9%), bicyclogermacrene (3.5% and 0.9%), α-pinene (2.3% and 4.1%), cis-β-ocimene (2.1% and 4.3%) and isospathulenol (0.4% and 4.3%) were found to be the major constituents of the oils of flowers
and leaves respectively.
Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 428–429, September–October, 2006. 相似文献
55.
Barkia H. Belkbir L. Jayaweera S. A. A. 《Journal of Thermal Analysis and Calorimetry》2003,71(1):97-106
Organic matter evolution and kinetics of combustion of Tarfaya and Timahdit oil shales have been examined by thermogravimetry (TG) and by differential thermal analysis (DTA). An agreement is observed between both techniques where it was found that combustion of organic matter occurs in two steps. Kissinger's method applied on experimental results gives an activation energy of the same magnitude for the first step of both oil shales (103 kJ mol–1) whereas the second is 148 kJ mol–1 for Timahdit and 118 kJ mol–1 for Tarfaya.The changes in specific surface area during thermal combustion of Timahdit and Tarfaya oil shales have been studied by thermogravimetric gas sorption balance and correlated with experimental results obtained on TG/DTA in air. For Timahdit oil shale oxidation products, specific surface areas calculated from nitrogen adsorption data shows a slight increase during the temperature domain of 280 to 430°C and after this temperature, they increase sharply. However, data obtained with Tarfaya oil shales shows a significant increase at the temperature of maximum oxidation of the first stage of combustion of organic matter.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
56.
H. Saglam T. Gozler B. Kivcak B. Demirci K. H. C. Baser 《Chemistry of Natural Compounds》2001,37(5):439-441
The chemical composition of the essential oil ofHaplophyllum myrtifoliumBoiss., endemic to Turkey, was examined by GC/MS. Ninety-seven compounds were characterized with linalool (12.8%), -caryophyllene (10.3 %), and methyleugenol (5.9 %) as the main constituents. 相似文献
57.
采用阳离子表面活性剂十六烷基三甲基溴化铵为模板剂,以正硅酸乙酯为硅源,以硫酸铝为铝源,水热合成了以催化油浆窄馏分为添加剂的高比表面积Al-MCM-41介孔分子筛,并利用XRD,HREM,TG-DTA及N2吸附-脱附等测试手段对合成样品进行了表征.合成的Al-MCM-41分子筛的比表面积和孔体积分别达到1295m2/g和1.5cm3/g,其平均孔径为4.3nm.重点研究了Al-MCM-41分子筛结晶度、晶胞参数、比表面积、孔体积及平均孔径等结构性质随催化油浆窄馏分添加量及其组成的变化规律,并从合成机理上进行了解释. 相似文献
58.
淫羊藿根与叶活性成分的分析和比较 总被引:8,自引:0,他引:8
采用细胞膜色谱法(CMC)筛选,并结合离体药理实验确定主要活性成分,利用高效液相色谱法分析比较了淫羊藿根与叶中的活性成分及其差异性.色谱条件为Kromasil ODS 柱(150 mm× 4.6 mm.I.D )流动相甲醇-水(70:30,V:V);检测波长270nm。筛选发现淫羊藿根中的两个有效成分YYH-214和YYH-216对血管有较强的舒张作用,表明活性成分在CMC模型体系中的保留特性与药理作用之间存在良好的相关性。在此色谱条件下淫羊藿叶未检测到这两种活性成分. 相似文献
59.
The root of Carlina acanthifolia All. (Asteraceae) contained 1.0% of essential oil (expressed in g per 100 g of dried plant material). Using GC and GC/MS,
nine components were identified (100% of total oil). The structure of benzyl 2-furylacetylene (carlina oxide), which is the
principal component of the oil (91.5%), was spectrometrically identified.
__________
Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 331–332, July–August, 2005. 相似文献
60.
Regenerated cellulose films with water-resistance were obtained by an improved method ofpreparing cellulose cuoxam solution from pulps of agricultural wastes (linters, wheat straw, reedand Bamao). Experimental results showed that the mechanical properties of both the dry. and wetfilms were excellent. Data from IR, SEM and tensile strength measurements implied that thesignificant improvement of water-resistance of the films was due to the cohesion between the thinTung oil covers with hydrophobicity and the regenerated cellulose films. The films werecompletely biodegraded after being buried in soil for 100 days. The transmittance of the filmsderived from linter and reed in visible band range were 80-90%. 相似文献