全文获取类型
收费全文 | 49506篇 |
免费 | 8245篇 |
国内免费 | 6639篇 |
专业分类
化学 | 25297篇 |
晶体学 | 580篇 |
力学 | 2171篇 |
综合类 | 507篇 |
数学 | 4219篇 |
物理学 | 13053篇 |
无线电 | 18563篇 |
出版年
2024年 | 93篇 |
2023年 | 892篇 |
2022年 | 1343篇 |
2021年 | 1666篇 |
2020年 | 1722篇 |
2019年 | 1719篇 |
2018年 | 1544篇 |
2017年 | 1632篇 |
2016年 | 2015篇 |
2015年 | 2374篇 |
2014年 | 2906篇 |
2013年 | 3519篇 |
2012年 | 4262篇 |
2011年 | 4356篇 |
2010年 | 3405篇 |
2009年 | 3550篇 |
2008年 | 3754篇 |
2007年 | 3373篇 |
2006年 | 3163篇 |
2005年 | 2694篇 |
2004年 | 2239篇 |
2003年 | 1844篇 |
2002年 | 1913篇 |
2001年 | 1698篇 |
2000年 | 1205篇 |
1999年 | 1022篇 |
1998年 | 746篇 |
1997年 | 642篇 |
1996年 | 579篇 |
1995年 | 452篇 |
1994年 | 413篇 |
1993年 | 319篇 |
1992年 | 225篇 |
1991年 | 231篇 |
1990年 | 190篇 |
1989年 | 141篇 |
1988年 | 115篇 |
1987年 | 95篇 |
1986年 | 72篇 |
1985年 | 55篇 |
1984年 | 42篇 |
1983年 | 37篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1959年 | 5篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Nonisothermal kinetics of the solid‐solid phase transition in (n‐C10H21NH3)2ZnCl4(C10Zn), (n‐C16H33NH3)2ZnCl4(C16Zn) and their binary system were determined by Kissinger and Ozawa methods from DSC measurements. The activation energy Ea of the binary system shows a waving dependence on WC10Zn%, which is caused by not only an intermediate (C10H21NH3)(n‐C16H33NH3)ZnCl4 but also three solid solution ranges (α, β, γ) in the phase diagram of C10Zn‐C16Zn. The variations of the layer d‐spacing are also convenient for the above result. 相似文献
993.
Speciation analysis of inorganic arsenic by microchip capillary electrophoresis coupled with hydride generation atomic fluorescence spectrometry 总被引:5,自引:0,他引:5
A novel method for speciation analysis of inorganic arsenic was developed by on-line hyphenating microchip capillary electrophoresis (chip-CE) with hydride generation atomic fluorescence spectrometry (HG-AFS). Baseline separation of As(III) and As(V) was achieved within 54 s by the chip-CE in a 90 mm long channel at 2500 V using a mixture of 25 mmol l(-1) H3BO3 and 0.4 mmol l(-1) CTAB (pH 8.9) as electrolyte buffer. The precisions (RSD, n=5) ranged from 1.9 to 1.4% for migration time, 2.1 to 2.7% for peak area, and 1.8 to 2.3% for peak height for the two arsenic species at 3.0 mg l(-1) (as As) level. The detection limits (3sigma) for As(III) and As(V) based on peak height measurement were 76 and 112 microg l(-1) (as As), respectively. The recoveries of the spikes (1 mg l(-1) (as As) of As(III) and As(V)) in four locally collected water samples ranged from 93.7 to 106%. 相似文献
994.
用ICP研究鹿科动物骨质疏松症的微量元素特征 总被引:1,自引:0,他引:1
鹿科动物的骨质疏松症是近几年出现的一种疾病,它影响鹿的生长发育和繁殖,病重者死亡。我们采集梅花鹿和白唇鹿的毛,血样,用低温灰化方法和温法消解处理样品,用ICP分析了毛,血清中微量元素的含量。病梅花鹿毛样中Mg,Al,Ca,Ti,Fe,Cu,Zn的含量比正常组高,Ti,Cu,Zn的偏差率大于15%,而Si,Mn,P,P,Ag,Ba,La,Ce,Pb比正常组低,V,Ag,Ba,La,Ce,Pb存在... 相似文献
995.
我们发现芳香叔胺是丙烯腈聚合极有效的光引发剂。芳香叔胺苯环上氢被正性基取代时,引发能力增加,被负性基取代时,引发能力下降。下列胺的活性次序是:N,N-二甲基对甲苯胺(DMT)>N,N-二羟乙基对甲苯胺(DHET)>N,N-二甲基苯胺(DMA)>N,N-二甲胺基苯甲醛(DMB)>N,N-二甲基对硝基苯胺(DNA)。芳香叔胺引发丙烯腈光聚合属自由基机构,聚合速度与叔胺浓度的0.66次方成正比。在叔胺浓度为10~(-2)—10~(-4)M范围内,聚合物平均聚合度的倒数与叔胺浓度的0.5次方成正比。初步认为在紫外光激发下,芳香叔胺与丙烯腈分子生成激发态电子转移络合物,再分解产生自由基,引发丙烯腈聚合。 相似文献
996.
997.
本文研究了铀-2-(3,5-二溴-2-吡啶偶氨)-5-二乙氨基苯酚(3,5-diBr-PADAP)-Triton X-100析相光度体系,建立了矿石中微量铀的测定方法,在pH 7.5三乙醇胺-盐酸介质中,将胶束溶液在 95±1℃加热 1h.络合物即被Triton X-100相完全富集.络合物最大吸收峰位于565nm.摩尔吸光系数为1.02×10~5L·mol~(-1)·cm~(-1),铀含量在0~12μg/5mL服从比耳定律.采用TBP萃淋树脂分离干扰离子,测定矿石中微量铀,结果满意. 相似文献
998.
Chen C Huang D Zhang X Chen F Zhu H Liu Q Zhang C Liao D Li L Sun L 《Inorganic chemistry》2003,42(11):3540-3548
A reaction system consisting of terephthalic acid, NaOH, inorganic Mn(II) or Mn(III) salt, and salicylidene alkylimine resulted in dinuclear manganese complexes (salpn)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (1, salpn = N,N'-1,3-propylene-bis(salicylideneiminato); phth = terephthalate dianion), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (2, salen = N,N'-ethylene-bis(salicylideneiminato)), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(H(2)O) (3), and (salen)(2)Mn(2)(mu-phth) (4), while the absence of NaOH in the reaction led to a mononuclear Mn complex (salph)Mn(CH(3)OH)(NO(3)) (5, salph = N,N'-1,2-phenylene-bis(salicylideneiminato)). In addition, a trinuclear mixed metal complex H[Mn(2)Na(salpn)(2)(mu-OAc)(2)(H(2)O)(2)](OAc)(2) (6) was obtained from the reaction system by using maleic acid instead of terephthalic acid. Five-coordinate Mn ions were found in 4 giving rise to an intermolecular interaction and constructing a one-dimensional linear structure. Antiferromagnetic exchange interactions were observed for 1-3, and a total ferromagnetic exchange of 4 was considered to stem from intermolecular magnetic coupling. (1)H NMR signals of phenolate ring and alkylene (or phenylene) backbone of the diamine are similar to those reported in the literature, and the phth protons are at -2.3 to -10.1 ppm. Studies on structure, bond valence sum analysis, and magnetic properties indicate the oxidation states of the Mn ions in 6 to be +3, which are also indicated by ESR spectra in dual mode. Ferromagnetic exchange interaction between the Mn(III) sites was observed with J = 1.74 cm(-1). A quasireversible redox pair at -0.29V/-0.12V has been assigned to the redox of Mn(2)(III)/Mn(III)Mn(II), implying the intactness of the complex backbone in solution. 相似文献
999.
反相高效液相色谱检测丹参药材中4种丹参酮的含量 总被引:6,自引:0,他引:6
建立了测定丹参药材中4种丹参酮含量的反相高效液相色谱法,色谱条件:流动相为水(含0.5%三乙胺)-甲醇-四氢呋喃(45/55/5,V/V/V),流速为1mL/min;PDA检测波长254m;4种成分丹参酮Ⅰ、丹参酮ⅡA、隐丹参酮和二氢丹参酮的加样回收率在95.1%-101.2%之间,线性范围为0.08-2μg。该方法准确,稳定,重现性好。根据该色谱条件,测定了不同产地的丹参药材,结果表明:该色谱方法准确检测了生药中4种丹参酮的含量,适合于丹参药材的质量控制。 相似文献
1000.
ChangLuSHAO HongYuGUAN ShangBinWEN BinCHEN XingHuaYANG JianGONG YiChunLIU 《中国化学快报》2004,15(4):492-494
Thin PVA/cobalt acetate composite fibers were prepared by using sol-gel processing and electrospinning technique.After calcination of the above precursor fibers,Co3O4 nanofibers with a diameter of 50-150 nm could be successfully obtained.The fibers were characterized by SEM,FT-IR,WAXD,respectively. 相似文献