全文获取类型
收费全文 | 6379篇 |
免费 | 849篇 |
国内免费 | 627篇 |
专业分类
化学 | 2722篇 |
晶体学 | 111篇 |
力学 | 1495篇 |
综合类 | 53篇 |
数学 | 946篇 |
物理学 | 2528篇 |
出版年
2024年 | 9篇 |
2023年 | 97篇 |
2022年 | 155篇 |
2021年 | 165篇 |
2020年 | 203篇 |
2019年 | 182篇 |
2018年 | 190篇 |
2017年 | 212篇 |
2016年 | 268篇 |
2015年 | 217篇 |
2014年 | 322篇 |
2013年 | 466篇 |
2012年 | 370篇 |
2011年 | 435篇 |
2010年 | 362篇 |
2009年 | 441篇 |
2008年 | 405篇 |
2007年 | 437篇 |
2006年 | 351篇 |
2005年 | 315篇 |
2004年 | 309篇 |
2003年 | 237篇 |
2002年 | 204篇 |
2001年 | 190篇 |
2000年 | 164篇 |
1999年 | 131篇 |
1998年 | 136篇 |
1997年 | 119篇 |
1996年 | 130篇 |
1995年 | 81篇 |
1994年 | 68篇 |
1993年 | 75篇 |
1992年 | 66篇 |
1991年 | 57篇 |
1990年 | 50篇 |
1989年 | 39篇 |
1988年 | 35篇 |
1987年 | 30篇 |
1986年 | 27篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有7855条查询结果,搜索用时 46 毫秒
71.
应用中药材开发微量元素保健品 总被引:3,自引:0,他引:3
介绍了用中药村开发几种微量元素保健品,有补锌,有助小儿生长,补硒抗癌,补铁钴养血,补铬治糖尿病和补锌铅的肝病滋补保健品。 相似文献
72.
73.
采用透射电子显微术(TEM),研究了用磁控溅射技术在柔性金属基体上制备的、钇稳定的ZrO2(YSZ)为过镀层的YBa2Cu3O7-y(YBCO)薄膜的横断面结构。所得YBCO膜的超导临界转变温度Tc为91K,临界电流密度Jc=2×103A/cm2(77K,0T)。基体为Ni基合金(HasteloyC)。YSZ层为致密、均匀的细晶组织,约12μm厚,具有织构取向,并与基体紧密连接。YBCO层的厚度不均匀,约500nm;YBCO/YSZ界面有时连接较差,在该界面上有杂质出现,杂质有可能引发裂纹。 相似文献
74.
《Surface and interface analysis : SIA》2003,35(6):544-547
We have developed multiple short‐period delta layers as a reference material for SIMS ultra‐shallow depth profiling. Boron nitride delta layers and silicon spacer layers were sputter‐deposited alternately, with a silicon spacer thickness of 1–5 nm. These delta‐doped layers were used to measure the sputtering rate change in the initial stage of oxygen ion bombardment. A significant variation of sputtering rate was observed in the initial 3 nm or less. The sputtering rate in the initial 3 nm was estimated to be about four times larger than the steady‐state value for 1000 eV oxygen ions. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
75.
《Electroanalysis》2005,17(11):953-958
An electron transfer reaction between ascorbic acid (H2A) in an aqueous solution and oxidizing agent in an organic solution immiscible with water has been studied by thin‐layer cyclic voltammetry (TLCV) for charge transfer at the interface between two immiscible electrolyte solutions (ITIES). As an antioxidant, H2A provide electrons through the aqueous/organic interface to reduce Fc+ and the procedure has been proved to be a one electron process again. In this work, the first combination of TLCV and scanning electrochemical microscopy (SECM) was achieved and showed a reasonable agreement between the results from the two different approaches. Otherwise, lower concentration ratios Kr of aqueous to organic reactants was adopted, which is given as evidence to the proposed procedure of Barker. 相似文献
76.
V. G. Nefedov O. A. Artyushenko E. V. Kashevarova 《Russian Journal of Electrochemistry》2006,42(6):638-642
Mass transfer to a horizontal electrode during electrolytic evolution of oxygen and hydrogen at current densities of 100 to 10 000 A/m2 is studied. The mass transfer intensity is evaluated from the diffusion layer thickness, which varies from 60 to 5 μm at such current densities. Calculations show that the decrease in the diffusion layer thickness is due to bubbles with a stationary interphase surface crossing the diffusion layer. During the hydrogen evolution, the diffusion layer thickness is nearly the same for vertical and horizontal electrodes. During the oxygen evolution, the diffusion layer is much thinner for a horizontal electrode. Additional decrease of the diffusion layer thickness during the evolution of oxygen is associated with the lesser solution density in the near-electrode layer and with its transport away by means of natural convection. 相似文献
77.
A simple, rapid, cost-effective and accurate high performance thin layer chromatographic method has been developed for quantification
of valerenic acid in Valeriana jatamansi and Valeriana officinalis which is one of the stable compounds of Valeriana officinalis and designated as a key marker compound. Valerenic acid makes substantial contribution to the sedative and spasmolytic activity
of the essential oil and extract of Valeriana officinalis. Separation and quantification was achieved by HPTLC using ternary mobile phase of hexane: ethyl acetate: acetic acid (80:20:0.5
v/v) on precoated silica gel 60F254 aluminium plates and densitometric determination was carried out after derivatization with anisaldehyde-sulphuric acid reagent
at 700 nm, in absorption-reflectance mode. The calibration curves were linear in the range of (500 ng–2.5 μg). This is the
first HPTLC report for the identification and quantification of valerenic acid in Valeriana jatamansi and Valeriana officinalis. 相似文献
78.
C. Christov S. Petrenko C. Balarew V. Valyashko 《Monatshefte für Chemie / Chemical Monthly》1994,125(12):1371-1382
Summary The standard method ofPitzer for predicting the solubility isotherms of systems in which solid phases with a constant composition crystallize is applied to cases when mixed crystals are formed. The four-component carnallite type systems RbCl-CsCl-MgCl2-H2O, RbCl-KCl-MgCl2-H2O, and RbCl-RbBr-MgCl2-MgBr2-H2O and the corresponding subsystems are thermodynamically simulated at 25°C. It is established that the solubility diagrams consist of crystallization regions of the simple saltsMX,MX, MgX
2·6H2O, and MgX2·6H2O and of the corresponding carnallite type double salts with the composition 1:1:6. A method of calculation of the integralGibbs energy of mixingG
mix(s) of crystals formed in water-salt systems has been proposed. The results on the systems RbCl-KCl-H2O, RbCl-RbBr-H2O, and MgCl2-MgBr2-H2O are compared with experimental data from the literature and with values calculated using various models.
Thermodynamische Simulation von Vierkomponentensystemen des Carnallit-Types
Zusammenfassung DiePitzer-Methode zur Voraussage der Löslichkeitsisothermen in Mehrstoffsystemen, in welchen feste Phasen mit konstanter Zusammensetzung auskristallisieren, wurde auch für Fälle angewendet, bei denen sich Mischkristalle bilden. Die Vierstoffsysteme RbCl-CsCl-MgCl2-H2O, RbCl-KCl-MgCl2-H2O und RbCl-RbBr-MgCl2-MgBr2-H2O, aus welchen Carnallit-Typ-Mischkristalle auskristallisieren, und die dazugehörigen Dreistoff-Randsysteme wurden bei 25°C simuliert. Man stellt fest, daß die Löslichkeitsdiagramme sowohl Kristallisationsbereiche der einfachen SalzeMX,M'X, MgX 2·6H2O und MgX 2·6H2O als auch der entsprechenden carnallitartigen Doppelsalze mit der Zuzammensetzung 1:1:6 umfassen. Eine Methode zur Berechnung derGibbs-EnergieG mix(s) für die in Wasser-Salz-Systemen gebildeten Mischkristalle wird vorgeschlagen. Die für die Systeme RbCl-KCl-H2O, RbCl-RbBr-H2O und MgCl2-MgBr2-H2O erhaltenen Ergebnisse werden mit experimentellen Literaturdaten und Resultaten von Berechnungen aufgrund verschiedener Modelle verglichen.相似文献
79.
Ogbonnaya Ofor 《Journal of colloid and interface science》1996,180(2):323
Using “pure” natural hematite selected from a high silica Nigerian hematitic ore, oleate adsorption densities at the hematite–water interface were determined in the presence of various inorganic ions (anions and cations) of different charges and at varying concentrations. Adsorption density was determined using electrical conductivity measurements. The specific surface area of the hematite particles was determined using the method of adsorption of paranitrophenol in aqueous solution. Inorganic ions in solution depressed oleate adsorption at the aqueous hematite surface. The charge of the ion proved to be the dominant factor determining the depression of oleate adsorption. Ionic strength also was an influence, up to a limiting value at which monolayer oleate coverage of the hematite surface occurred. The inorganic ions in solution are considered to function through nonspecific adsorption in the diffuse region of the electric double layer. 相似文献
80.