全文获取类型
收费全文 | 3240篇 |
免费 | 144篇 |
国内免费 | 13篇 |
专业分类
化学 | 2466篇 |
晶体学 | 39篇 |
力学 | 50篇 |
数学 | 362篇 |
物理学 | 480篇 |
出版年
2023年 | 16篇 |
2022年 | 17篇 |
2021年 | 61篇 |
2020年 | 65篇 |
2019年 | 72篇 |
2018年 | 44篇 |
2017年 | 37篇 |
2016年 | 108篇 |
2015年 | 85篇 |
2014年 | 104篇 |
2013年 | 176篇 |
2012年 | 226篇 |
2011年 | 234篇 |
2010年 | 165篇 |
2009年 | 172篇 |
2008年 | 206篇 |
2007年 | 219篇 |
2006年 | 197篇 |
2005年 | 172篇 |
2004年 | 147篇 |
2003年 | 125篇 |
2002年 | 116篇 |
2001年 | 109篇 |
2000年 | 90篇 |
1999年 | 66篇 |
1998年 | 48篇 |
1997年 | 32篇 |
1996年 | 47篇 |
1995年 | 29篇 |
1994年 | 31篇 |
1993年 | 24篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有3397条查询结果,搜索用时 15 毫秒
991.
The oxidation of heroin on a carbon paste electrode has been studied by using voltammetric techniques under both semi-infinite linear diffusion and hydrodynamic conditions. By employing a simple and rapid in situ pre-treatment of the electrode, excellent reproducibility of the current signal was obtained. Subsequently, the current was measured and the concentration of total heroin present could be determined. The method compared favourably with instrumental methods that are more commonly used for the quantification of heroin in clinical laboratories such as chromatographic, spectrophotometric or radiometric techniques. Moreover, the proposed method showed good selectivity and was superior with respect to cost and time of analysis, permitting the determination of heroin in seized drug samples over a wide concentration range. 相似文献
992.
Evidence from the coupling constants and solvent shifts of the protons in cedranone rules out the boat and chair conformations of the cyclohexanone ring. Linear correlation of the solvent shifts of the C-15 methyl protons of cedranone with those of the α-methyl groups of fenchone indicates a nearly planar conformation of the cedranone ring. Site factor analysis of the ASIS effect of the methyl protons of cedranone provides conclusive evidence of a quasi-chair conformation of the 6-membered ring. 相似文献
993.
In this work we present several Mössbauer emission spectra of the spinels 57CoMn2O4, 57CoY2O4 and 57CoV2O4 prepared under well determined conditions. The consequences of electronic capture in 57Co in spinels are studied. It is found that the appearance of anomalous charge states is connected with the macroscopic properties of the spinel. 相似文献
994.
Molina E Díaz HG González MP Rodríguez E Uriarte E 《Journal of chemical information and computer sciences》2004,44(2):515-521
A novel application of TOPological Substructural MOlecular DEsign (TOPS-MODE) was carried out in antibacterial drugs using computer-aided molecular design. Two series of compounds, one containing antibacterial and the other containing non-antibacterial compounds, were processed by a k-means cluster analysis in order to design training and predicting series. All clusters had a p-level < 0.005. Afterward, a linear classification function has been derived toward discrimination between antibacterial and non-antibacterial compounds. The model correctly classifies 94% of active and 86% of inactive compounds in the training series. More specifically, the model showed a global good classification of 91%, i.e., 263 cases out of 289. In predicting series, the model has shown overall predictabilities of 91 and 83% for active and inactive compounds, respectively. Thereby, the model has a global percentage of good classification of 89%. The TOPS-MODE approach, also, similarly compares with respect to one of the most useful models for antimicrobials selection reported to date. 相似文献
995.
There is currently urgent interest in identifying the species of origin of the components of different animal by-products. In Europe, this interest is expected to increase with authorization of the re-introduction of these proteins into animal feed formulations. The number of validated methods to differentiate the species of origin for most of these products is limited. An easy, inexpensive, and accurate test was developed to determine the cross-contamination of bovine blood or plasma in porcine whole blood and plasma, both before and after spray drying. Agar gel immunodiffusion (AGID), the studied technique, detected the presence of bovine immunoglobulin G (IgG) in porcine plasma and in whole blood at inclusion levels >0.5% (v/v) in all cases. However, detectability was lower in liquid plasma (0.3%, v/v) and in liquid whole blood (0.5%, v/v). No differences were found when cross-contamination was simulated before or after whole blood centrifugation. The method described is reliable and inexpensive, and the samples are easy to prepare. Both minimal laboratory equipment and expertise are required for detection of bovine IgG in porcine blood products at inclusion levels of >0.5% (v/v). 相似文献
996.
997.
998.
999.
Fragoso A Baratto MC Díaz A Rodríguez Y Pogni R Basosi R Cao R 《Dalton transactions (Cambridge, England : 2003)》2004,(9):1456-1460
Three copper(II) complexes containing beta-cyclodextrin (betaCD) derivatives as ligands [mono-6-methylamino-6-deoxy-betaCD dithiocarbamate (CDTC), mono-6-histamino-6-deoxy-betaCD (CDHM) and mono-6-Nalpha-arginyl-6-deoxy-betaCD (CDARG)] have been studied by electron paramagnetic resonance. The spectra have been recorded at X- and S-bands and different temperatures and simulated to obtain the best set of magnetic parameters. In particular, the 300 K spectra are typical of the slow motion regime, as expected considering the high molecular weight of the ligands. Some structural characteristics of the complexes are proposed on the basis of dynamic and covalency parameters obtained from simulation. 相似文献
1000.
Sens C Romero I Rodríguez M Llobet A Parella T Benet-Buchholz J 《Journal of the American Chemical Society》2004,126(25):7798-7799
We have prepared three new dinuclear ruthenium complexes having the formulas [Ru2II(bpp)(trpy)2(mu-L)]2+ (L = Cl, 1; L = AcO, 2) and [Ru2II(bpp)(trpy)2(H2O)2]3+ (3). The three complexes have been characterized through the usual spectroscopic and electrochemical techniques and, in the cases of 1 and 2, the X-ray crystal structures have been solved. In aqueous acidic solution, the acetato bridge of 2 is replaced by aqua ligands, generating the bis(aqua) complex 3 which, upon oxidation to its RuIVRuIV state, has been shown to catalytically oxidize water to molecular oxygen. The measured pseudo-first-order rate constant for the O2-evolving process is 1.4 x 10-2 s-1, more than 3 times larger than the higher one previously reported for Ru-O-Ru type catalysts. This new water-splitting catalyst also has improved stability with regard to any previously described, achieving a total of 18.6 metal cycles. 相似文献