全文获取类型
收费全文 | 6195篇 |
免费 | 183篇 |
国内免费 | 944篇 |
专业分类
化学 | 6302篇 |
晶体学 | 123篇 |
力学 | 24篇 |
综合类 | 41篇 |
数学 | 7篇 |
物理学 | 825篇 |
出版年
2023年 | 68篇 |
2022年 | 66篇 |
2021年 | 78篇 |
2020年 | 113篇 |
2019年 | 94篇 |
2018年 | 117篇 |
2017年 | 160篇 |
2016年 | 178篇 |
2015年 | 131篇 |
2014年 | 218篇 |
2013年 | 509篇 |
2012年 | 436篇 |
2011年 | 398篇 |
2010年 | 297篇 |
2009年 | 353篇 |
2008年 | 375篇 |
2007年 | 440篇 |
2006年 | 398篇 |
2005年 | 384篇 |
2004年 | 362篇 |
2003年 | 266篇 |
2002年 | 233篇 |
2001年 | 176篇 |
2000年 | 165篇 |
1999年 | 167篇 |
1998年 | 144篇 |
1997年 | 132篇 |
1996年 | 115篇 |
1995年 | 139篇 |
1994年 | 111篇 |
1993年 | 98篇 |
1992年 | 97篇 |
1991年 | 52篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 31篇 |
1987年 | 12篇 |
1986年 | 25篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有7322条查询结果,搜索用时 984 毫秒
141.
作者调查了珠海市568名0~6岁健康儿童的发锌含量,结果表明,集体儿童的低锌发生率为59.1%,门诊儿童为72.04%,在珠海市儿童中低锌有较高的发生率。 相似文献
142.
Sukhendu Mandal 《Journal of solid state chemistry》2004,177(6):2198-2204
A solvothermal reaction of ZnO, HCl, H3PO4, and N,N′(3-bisaminopropyl)-1,2-ethylenediamine (BAPEN) in diethyleneglycol at 160°C yields a new zinc chlorophosphate, [C8N4H26][Zn3Cl(HPO4)3(PO4)], I. The structure comprises ZnO4, ZnO3Cl, HPO4 and PO4 tetrahedral units connected through their vertices giving rise to a layered structure with 10-membered apertures. The position of the Zn and P atoms gives rise to double-four ring like building unit with one Zn missing. The fully protonated amine molecules occupy the inter-lamellar region and interacts with the framework through N-H?O hydrogen bonds. Crystal data: M=792.85, orthorhombic, space group=Pca21 (no. 29), a=9.8410(2), b=15.0912(2), c=16.1220(4) Å, V=2394.32(8) Å3, Z=4, ρcalc=2.199 g cm−3, μ(MoKα)=3.443 mm−1, R1=0.0520, wR2=0.1256 and S=1.054. 相似文献
143.
钾镁氯化物(硫酸盐)与脲、水体系的溶度研究 总被引:7,自引:0,他引:7
报导了KCl-MgCl2-CO(NH2)2-H2O和K2SO4-MgSO4-CO(NH2)2-H2O两个四元体系在25℃时的溶度及其饱和溶液的折光率、密度,相应的溶度图和组成-折光率、组成-密度图.前一体系中形成3个三元化合物:MgCl2·4CO(NH2)2·2H2O、MgCl2·CO(NH2)2·4H2O和KCl·MgCl2·6H2O溶度盐份图由9支共饱线、4个四元无变点组成.四元体系的水量图、性质-组成图有类似的变化.后一体系中有2个异成份溶解化合物MgSO4·CO(NH2)2·2H2O和K2SO4·MgSO4·6H2O形成,溶度等温图由7支双饱溶度线、3个四元无变点组成.对两个体系相图的相似性和差异点进行了讨论. 相似文献
144.
Dagobert Achatz Markus A. Lang Alfons Vlkl Wolf Peter Fehlhammer Wolfgang Beck 《无机化学与普通化学杂志》2005,631(12):2339-2346
Carbonyl Complexes of Chromium, Molybdenum and Tungsten with Isocyano Acetate. Reactions of Coordinated Isocyanoacetate. Stabilization of Isocyanoacetic Acid and Isocyanoacetyl Chloride at the Metal Atom. Isocyanopeptides The reactions of [(OC)5MCNCH2CO2Et] (M = Cr, W) with Na[N(SiMe3)2] or with KOH afford the isocyanoacetate complexes [(OC)5MCNCH2CO2]? ( 1,2 ). Similarly, the complex [(OC)3Mo(CNCH2CO2?Li+)3] ( 4 ) was obtained from [(OC)3Mo(CNCH2CO2Et)3] ( 3 ) and LiOH. Protonation of 1 and 2 affords the sublimable isocyanoacetic acid complexes [(OC)5MCNCH2CO2H] ( 5 , 6 ; M = Cr, W) in which the functional isocyanide is stabilized at the metal atom. Reactions of [(OC)5WCNCH2CO2?K+] and of [(OC)3Mo(CNCH2CO2?Li+)3] with oxalyl dichloride give the isocyanoacetyl chloride compounds [(OC)5WCNCH2COCl] ( 9 ) (sublimable) and [(OC)3Mo(CNCH2COCl)3] ( 10 ); the latter ( 10 ) was not isolated. Complexes 9 and 10 were reacted in situ with β‐alanine, glycine, phenylalanine and methionine esters as well as the peptide esters GlyGlyOEt, PhePheOMe, Phe‐β‐AlaOMe, and GlyGlyGlyOMe to form the isocyanoacetyl amino acid esters ( 11 ‐ 14 ) and the isocyanoacetyl peptide esters ( 15 ‐ 18 ) which are stabilized at the molybdenum atom. 相似文献
145.
Zn—TppS4极谱络合物吸附波的研究:中草药天麻,川芎,当归中锌的测定 总被引:1,自引:0,他引:1
锌是人体必需的微量元素之一。它具有重要的生理功能和营养作用,是合成脱氧核糖核酸(DNA),核糖核酸(RNA)和蛋白质必需的金属离子。锌是DNA,RNA聚合酶等80多种酶的组成成分及激剂,直接影响细胞代谢,免疫过程,细胞分裂和再生。最近美国有人提出缺 相似文献
146.
A polyaluminum chloride (PAC) sample was prepared using a slow alkaline titration method. The Bio-Gel P-100 gel column chromatographic
technique was used to separate and characterize the various forms of aluminum present in the prepared PAC solution. The effluents
from a gel column were monitored using online chemical method: Al-Ferron timed complexation spectrophotometry and by 27Al nuclear magnetic resonance (NMR) spectroscopy. Effects of different experimental conditions such as eluent flow rate, ionic
strength and pH on separation of Al13 were investigated. Experimental results indicated that molecule size exclusion was not the only parameter affecting the column
chromatographic separation efficiency of Al13 but molecule charge as well. Reducing the eluent flow rate, increasing the ionic strength and suitable pH resulted in increase
in the separation efficiency. Experimental results clearly indicated that by varying the experimental conditions, it is possible
to produce pure Al13 species using a gel column chromatographic technique. 相似文献
147.
148.
E. R. T. Bevers P. J. van Ekeren W. G. Haije H. A. J. Oonk 《Journal of Thermal Analysis and Calorimetry》2006,86(3):825-832
Ammonia
absorption by and desorption from lithium chloride at different pressures
has been studied using high-pressure differential scanning calorimetry, for
application in a high-lift high temperature chemical heat pump. The measurements
were performed under isobaric as well as under isothermal circumstances. Clausius–Clapeyron
plots were constructed and used to calculate the thermodynamic parameters
and to determine the stability regions of the different complexes. Controversies
in literature as to the real existing phases are resolved. 相似文献
149.
Zhivka J. Simeonova Kiril B. Gavazov Alexander V. Alexandrov 《Central European Journal of Chemistry》2006,4(2):258-265
The formation of a new ternary ion-associate complex of vanadium(V) with 2,3-dihydroxynaphthalene and iodonitrotetrazolium
chloride with a composition ratio of 1:2:1 is reported. The complex is quantitatively extracted from water into chloroform.
The molar absorptivity (ɛ) of the extract at λ
max=340 nm is 2.5 × 104 dm3/mol cm, and Beer’s law is obeyed for concentrations ranging from 0.1 to 0.9 μg/cm3 V(V). The following constants are determined: the extraction constant, the association constant, the distribution constant,
and the recovery factor. The effects of foreign ions and reagents are studied. A selective and sensitive method is developed
for determination of vanadium in steels. 相似文献
150.
Mohamed El Guendouzi Abderrahim Dinane Abdelfetah Mounir 《Journal of solution chemistry》2002,31(2):119-129
The mixed aqueous electrolyte system of ammonium and lithium chlorides has been studied by the hygrometric method at 25°C. The relative humidities of this system are measured at total molalities from 0.3 to 6 mol-kg– 1 for different ionic-strength fractions y of NH4Cl with y = 0.33, 0.50, and 0.67. The data obtained allow the deduction of new water activities and osmotic coefficients. The experimental results are compared with the predictions of the ECA (extended composed additivity) law proposed in our previous work. The Zdanovskii–Stokes–Robinson (ZSR), the Robinson–Stokes (RS), Reilly–Wood–Robinson (RWR), the Pitzer, and the Lietzke–Stoughton (LS II) models are also compared with our results. Predictions made using these models are, in general, consistent with our results. From these measurements, new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture for different ionic-strength fractions. 相似文献