全文获取类型
收费全文 | 7973篇 |
免费 | 1360篇 |
国内免费 | 617篇 |
专业分类
化学 | 3105篇 |
晶体学 | 102篇 |
力学 | 1592篇 |
综合类 | 114篇 |
数学 | 625篇 |
物理学 | 4412篇 |
出版年
2024年 | 14篇 |
2023年 | 55篇 |
2022年 | 168篇 |
2021年 | 213篇 |
2020年 | 224篇 |
2019年 | 231篇 |
2018年 | 189篇 |
2017年 | 253篇 |
2016年 | 304篇 |
2015年 | 355篇 |
2014年 | 370篇 |
2013年 | 1122篇 |
2012年 | 470篇 |
2011年 | 543篇 |
2010年 | 389篇 |
2009年 | 446篇 |
2008年 | 429篇 |
2007年 | 452篇 |
2006年 | 402篇 |
2005年 | 401篇 |
2004年 | 363篇 |
2003年 | 301篇 |
2002年 | 258篇 |
2001年 | 236篇 |
2000年 | 196篇 |
1999年 | 163篇 |
1998年 | 186篇 |
1997年 | 158篇 |
1996年 | 124篇 |
1995年 | 140篇 |
1994年 | 116篇 |
1993年 | 120篇 |
1992年 | 99篇 |
1991年 | 75篇 |
1990年 | 51篇 |
1989年 | 51篇 |
1988年 | 68篇 |
1987年 | 32篇 |
1986年 | 34篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 7篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1972年 | 5篇 |
排序方式: 共有9950条查询结果,搜索用时 562 毫秒
101.
La-Fe-M(M=Al, Si)化合物磁热性能研究进展 总被引:5,自引:1,他引:5
介绍了La-Fe-M(M=AI,Si)化合物在磁热性能研究方面的最新进展。具有NaZn13型晶体结构,含高浓度Fe的La-Fe—M(M=AI,Si)化合物为良好的软磁材料;用少量的Co替代化合物中Si,Al元素可以将化合物的居里温度提高至室温;对La(Fe1-yCoy)xSi13-x化合物,适量的Si,Co组合可使化合物在室温产生可与Gd5Si2Ge2比拟的磁热效应;加入适量的间隙原子H,也可使La(FexSi1-x)13在室温的磁热性能远远大于金属Gd;对含Si量低及含Si量高的La(FexSi1-x)13化合物在相转变点附近由温度和磁场诱导相变的本质做了详细阐述。 相似文献
102.
A. Hazra K. Alexander D. Dollimore A. Riga 《Journal of Thermal Analysis and Calorimetry》2004,75(1):317-330
The present study was aimed at determining the kinetics of evaporation and establishing vapor pressure curves for both single and multi-component systems by thermogravimetry (TG) and differential scanning calorimetry (DSC). Essential oils (e.g. lavender oil, orange oil, clove oil and eucalyptus oil, etc.) are typically multi-component systems consisting of various volatile pure components (e.g. linalyl acetate, limonene, cinnamaldehyde, etc.) which resemble single component systems. In this study linalyl acetate was taken as the calibration compound for TG. The vapor pressure curves for the pure substances were plotted using TG and vapor pressure plots for clove oil and eucalyptus oil were constructed using DSC. The thermodynamic and kinetic parameters of the pure compounds were compared to that of the multi-component systems to quantitatively and qualitatively measure the influence of different compounds on each other. The k-value from the vapor pressure data for linalyl acetate was calculated as 112006 Pa kg0.5mol0.5s-1 m-2 K-0.5. The vapor pressure values were used to determine the Antoine constants using the SPSS 10.0 software.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
103.
采用分子量500万的聚氧化乙烯和无水溴化铜,通过混溶蒸发法制备成高聚物固体电解质P(EO)n-CuBr2薄膜,并在0.1~300MPa范围不同的流体静水压下详细测量其复平面阻抗谱,分别得到在不同压力下离子电导率和介电常数与测量频率的关系.进一步解谱准确地求出P(EO)n-CuBr2(n=12、16)薄膜离子电导率和介电常数的静水压效应,并结合X-光物相分析,根据离子迁移通道的物理图象和高聚物的极化机构进行了初步的讨论.添加20%的增塑剂碳酸丙烯酯,较大改进了压力下的导电性.120~300MPa的离子电导率提高一个数量级 相似文献
104.
A wide variety of liquid streams are generated as
part of the process research and development effort. Frequently these streams
are drummed off, either as intermediates that must be held for processing
or as wastes that must be sent off-site for disposal. Because of the long
times and low concentrations often involved, current thermoanalytical techniques
were inadequate to detect the potential of streams to generate gas. A custom-made
apparatus, the gas evolution test cell (GETC), was developed in the Merck
Research Laboratories to measure the gas generation potential of various streams
under precisely defined conditions, is the key innovation for the development
of a quantitative gas-generation test method. 相似文献
105.
Lingjun Chou Yingchun Cai Bing Zhang Jianzhong Niu Shengfu Ji Shuben Li 《Reaction Kinetics and Catalysis Letters》2002,76(2):311-315
Na-Mn-W/SiO2 catalysts were prepared and their catalytic performance for oxidative coupling of methane (OCM) was evaluated in a stainless-steel microreactor at elevated pressure. The results show that a CH4 conversion of 15.1% with a C2+ selectivity of 71.8% was obtained under 750oC, 1.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa. Moreover, 17.3% CH4 conversion with 51.6% C2 selectivity and 23.6% C3-C4 selectivity was obtained under 750oC, 2.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa. 相似文献
106.
Suzdalev I. P. Buravtsev V. N. Maksimov Yu. V. Zharov A. A. Imshennik V. K. Novichikhin S. V. Matveev V. V. 《Russian Chemical Bulletin》2003,52(9):1950-1958
Magnetic phase transitions of the first and second order were revealed by Mössbauer spectroscopy in nanosystems of - and -ferric oxides and metallic europium subjected to shear stress (240°) under high pressure (20 kbar). For - and -ferric oxide nanoclusters, the Curie (Neel) points decreased to 300 K, whereas for nanostructured europium the Neel point increased from 90 to 100 K. The thermodynamic model of magnetic phase transitions predicting a change in the character of magnetic phase transitions and a decrease (increase) in the critical Neel (Curie) points in nanoclusters was developed. The type of magnetic phase transitions and the change in the critical points were caused by defects in nanoclusters, whose maximum concentration was observed for the clusters with the 20—50 nm size range. 相似文献
107.
The spherical cell model of colloidal solutions is applied in calculations of the osmotic pressure of micellar systems. The predictions of the nonlinear Poisson-Boltzmann equation (MPB) and of the Modified Poisson-Boltzmann equation (MPB) containing the leading terms of the fluctuation potential and the exclusion volume corrections to the mean potential acting on simple ions are compared with the results of recent computer simulations. Both PB and MPB seem satisfactory for solutions with monovalent counterions while the MPB is preferable for studies of the solutions containing divalent countenons.On leave from the University of Ljubljana, Ljubljana, Yugoslavia 相似文献
108.
Vapor pressure,speciation, and chemical activities in highly concentrated sodium borate solutions at 277 and 317°C 总被引:2,自引:0,他引:2
Oleh Weres 《Journal of solution chemistry》1995,24(5):409-438
The system H2O-B2O3-Na2O has been studied experimentally at 277 and 317°C. The activities of water and boric acid have been determined at mole ratios Na/B from 0 to 1.5, and total dissolved solids 3 to 80 weight percent. The activity of boric acid has been fitted to within experimental error using a speciation model with eight complex species. This model is consistent with the model previously published by Mesmer et al. The electrolyte properties of the liquid are modeled using the Pitzer-Simonson model of very concentrated electrolyte solutions. The calculated values of water activity agree with experiment, and the activity of NaOH and pOH have also been calculated. The potassium borate system also was briefly studied at 317°C, and is adequately described by a model with five complex species. The potassium borate liquid is more alkaline at K/B= 1 than a sodium borate liquid at the same mole ratio, but pOH in the two systems is the same at lower mole ratios. 相似文献
109.
Chiral α,ω-diesters react under high-pressure conditions (10 kbar) with α,ω-diamines to give chiral cyclic tetraamides of C2-symmetry. The complexation properties of tetraamides towards alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) were estimated on the basis of ESI-MS spectra. 相似文献
110.