全文获取类型
收费全文 | 6018篇 |
免费 | 227篇 |
国内免费 | 147篇 |
专业分类
化学 | 4333篇 |
晶体学 | 64篇 |
力学 | 146篇 |
综合类 | 23篇 |
数学 | 557篇 |
物理学 | 1269篇 |
出版年
2023年 | 52篇 |
2022年 | 213篇 |
2021年 | 206篇 |
2020年 | 159篇 |
2019年 | 169篇 |
2018年 | 145篇 |
2017年 | 120篇 |
2016年 | 229篇 |
2015年 | 208篇 |
2014年 | 260篇 |
2013年 | 358篇 |
2012年 | 401篇 |
2011年 | 464篇 |
2010年 | 321篇 |
2009年 | 314篇 |
2008年 | 410篇 |
2007年 | 344篇 |
2006年 | 318篇 |
2005年 | 256篇 |
2004年 | 212篇 |
2003年 | 163篇 |
2002年 | 136篇 |
2001年 | 117篇 |
2000年 | 100篇 |
1999年 | 65篇 |
1998年 | 55篇 |
1997年 | 47篇 |
1996年 | 42篇 |
1995年 | 39篇 |
1994年 | 45篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 25篇 |
1990年 | 28篇 |
1989年 | 18篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 24篇 |
1982年 | 10篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有6392条查询结果,搜索用时 0 毫秒
71.
Magno Aparecido G. Trindade Glaucia Maria da Silva Valdir Souza Ferreira 《Microchemical Journal》2005,81(2):209-216
This work presents an electroanalytical methodology developed for square-wave voltammetry based in the electrochemical reduction in hanging mercury drop electrode (HMDE), which is simple, fast, reliable and sensitive for determination of moxifloxacin (MOXI) in tablets and spiked urine human samples. The support electrolyte that provided a more defined and intense peak current for MOXI determination was the phosphate buffer 0.04 mol l− 1 pH 8.0. In the best-optimized conditions the drug presented an only peak of reduction at − 1.38 V vs. Ag/AgCl, using an Eacc. of − 0.30 V. An LOD of 0.44 and 3.20 ng ml− 1 and an LOQ of 1.46 and 10.60 ng ml− 1 were found for the pure standard of moxifloxacin and in the presence of matrix, respectively. A good recovery was obtained for assay spiked urine samples and a good quantification of MOXI was achieved in a commercial formulation. The methodology proposed was more sensitive than the spectrofluorimetric and spectrophotometric method with precision and accuracy equivalent. 相似文献
72.
A preconcentration and determination methodology for vanadium at trace levels in parenteral solutions was developed. Cloud point extraction was successfully employed for the preconcentration of vanadium prior to inductively coupled plasma atomic optical emission spectrometry (ICP-OES) coupled to a flow injection (FI) system. The vanadium was extracted as vanadium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol [V-(5-Br-PADAP)] complex, at pH 3.7 mediated by micelles of the nonionic surfactant polyoxyethylene (5.0) nonylphenol (PONPE 5.0). The extracted surfactant-rich phase (100 mul) was mixed with 100 mul of ethanol and this final volume injected into ICP-OES for the vanadium determination. Under these conditions, the 50 ml sample solution preconcentration allowed raising an enrichment factor of 250-fold; however, it was possible to obtain a theoretical enrichment factor of 500-fold. The lower limit of detection (LOD) obtained under the optimal conditions was 16 ng l(-1). The precision for 10 replicate determinations at the 2.0 mug l(-1) V level was 2.3% relative standard deviation (RSD), calculated with the peak heights. The calibration graph using the preconcentration system for vanadium was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 50 mug l(-1). The method was successfully applied to the determination of vanadium in parenteral solution samples. 相似文献
73.
Silva Julio Cezar Soares de Lima Silva Diogo Ferreira Ferreira Luciano de Almeida-Filho Adiel Teixeira 《4OR: A Quarterly Journal of Operations Research》2022,20(1):139-164
4OR - Even though sovereign bonds represent low-risk alternatives that give investors a healthy income, the risk assessment process for these bonds is still considered subjective because of the... 相似文献
74.
R. D. Sinisterra R. Najjar O. L. Alves P. S. Santos C. A. Alves De Carvalho A. L. Conde Da Silva 《Journal of inclusion phenomena and macrocyclic chemistry》1995,22(2):91-98
The preparation and characterization of the 1:1 inclusion compound of rhodium(II) -methyl cinnamate in -cyclodextrin is reported. Evidence of inclusion was obtained from X-ray powder diffraction results, Raman, IR and UV-Vis spectroscopic studies and thermal analysis. Given the potential antitumor activity of the rhodium(II) carboxylate and its virtual insolubility in water, its inclusion in -cyclodextrin opens the possibility for its transference to the aqueous phase. 相似文献
75.
76.
77.
78.
79.
Nuclear Track Detectors (NTD's) are a useful option forin situ measurements of the distribution of alpha contamination as a function of soil depth. The contamination profile of alpha emitting elements, e.g. Pu, Am and U, can be determined by detecting their alpha emission at varying depths. This paper discusses a stake type device, containing strips of CR-39 (allyl diglycol carbonate) that can be inserted into the soil up to ten centimeters or more, depending on the firmness of the soil. The CR-39 is exposed directly to the contaminated soil for a few hours. The stake is then withdrawn from the soil, the plastic detectors recovered and the alpha tracks developed by chemical etching with KOH. The distribution of tracks can be used to determine the alpha contamination depth profile as well as for detecting hot spots. It has a sensitivity of less than a pCi/g of soil.Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract W-7405-ENG-48. 相似文献
80.