全文获取类型
收费全文 | 2055篇 |
免费 | 139篇 |
国内免费 | 9篇 |
专业分类
化学 | 1470篇 |
晶体学 | 25篇 |
力学 | 63篇 |
数学 | 256篇 |
物理学 | 389篇 |
出版年
2023年 | 17篇 |
2022年 | 92篇 |
2021年 | 60篇 |
2020年 | 49篇 |
2019年 | 86篇 |
2018年 | 62篇 |
2017年 | 46篇 |
2016年 | 108篇 |
2015年 | 74篇 |
2014年 | 82篇 |
2013年 | 146篇 |
2012年 | 121篇 |
2011年 | 113篇 |
2010年 | 89篇 |
2009年 | 89篇 |
2008年 | 107篇 |
2007年 | 117篇 |
2006年 | 95篇 |
2005年 | 69篇 |
2004年 | 66篇 |
2003年 | 56篇 |
2002年 | 51篇 |
2001年 | 48篇 |
2000年 | 35篇 |
1999年 | 28篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1973年 | 10篇 |
1971年 | 6篇 |
1862年 | 8篇 |
排序方式: 共有2203条查询结果,搜索用时 0 毫秒
91.
S. A. Karamian N. V. Aksenov Yu. A. Al’bin A. G. Belov G. A. Bozhikov S. N. Dmitriev G. Ya. Starodub 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(5):367-372
Among nuclides, 195m Pt isomer is characterized by a number of properties that make it suitable for use in nuclear medicine. Effective ways of optimizing the Pt isomer yield at low impurity contents must be sought. The method based on double neutron capture by the 193Ir target nucleus with subsequent populating of 195m Pt through β decay allows chemical isolation of the isomer. In this work, the problem is analyzed, test experiments on Ir activation with neutrons are conducted, and theoretical estimates of the 195m Pt yield are presented. Full-scale model experiments on the IBR-2 reactor in Dubna should confirm the effectiveness of the method. 相似文献
92.
93.
94.
Rosenani A. Haque Abbas Washeel Salman Srinivasa Budagumpi Amirul Al‐Ashraf Abdullah Zena A. Abdul Hameed Al‐Mudaris Amin M. S. Abdul Majid 《应用有机金属化学》2013,27(8):465-473
A series of Ag(I) complexes ( 6 , 7 , 8 , 9 ) derived from imidazol‐2‐ylidenes was synthesized by reacting Ag2O with an o‐, m‐, p‐xylyl or 1,3,5‐triazine‐linked imidazolium salts ( 1 , 2 , 3 , 4 ) and then characterizing these using various spectro‐analytical techniques. Additionally, triazine‐linked bis‐imidazolium salt 5 was characterized using the single‐crystal X‐ray diffraction method. Complexes 6–9 were formed from the N‐heterocyclic carbene ligand precursors 1–3 as PF6‐ salts in good yields. Conversely, salt 5 does not form Ag(I) complex even under various reaction conditions. Using ampicillin as a standard, complexes 6–9 were tested against bacteria strains Escherichia coli and Staphylococcus aureus as Gram‐negative and Gram‐positive bacteria, respectively, showing potent antimicrobial activities against the tested bacteria even at minimum inhibition concentration and bacterial concentration levels. Furthermore, the potential anticancer activities of the reported complexes were evaluated against the human colorectal cancer (HCT 116) cell lines, using 5‐fluorouracil as a standard drug. The highest anticancer activities were observed for complex 8 with an IC50 value of 3.4 μm , whereas the lowest was observed for complex 9 with an IC50 value of 18.1 μm . Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
95.
There has been a considerable interest in recent years in developing polymer gel matrices for many important applications such as 2DE for quantization and separation of a variety of proteins and drug delivery system to control the release of active agents. However, a well‐defined knowledge of the ultrastructures of the gels has been elusive. In this study, we report the characterization of two different polymers used in 2DE: Gelatin, a naturally occurring polymer derived from collagen (protein) and agar, a polymer of polysaccharide (sugar) origin. Low‐temperature SEM is used to examine the internal structure of these gels in their frozen natural hydrated states. Results of this study show that both polymers have an array of hollow cells that resembles honeycomb structures. While agar pores are almost circular, the corresponding Gaussian curve is very broad exhibiting a range of radii from nearly 370 to 700 nm. Gelatin pores are smaller and more homogeneous reflecting a narrower distribution from nearly 320 to 650 nm. Overall, these ultrastructural findings could be used to correlate with functions of the polymers. 相似文献
96.
97.
98.
Mahmoud Al‐Ktaifani Mwaffak Rukiah 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(9):m246-m250
In order to explore the potential propensity of the 1,1′‐methylenedipyridinium dication to form organic–inorganic hybrid ionic compounds by reaction with the appropriate halide metal salt, the organic–inorganic hybrid salts 1,1′‐methylenedipyridinium tetrachloridocuprate(II), (C11H12N2)[CuCl4], (I), and 1,1′‐methylenedipyridinium bis[tetrachloridoaurate(III)], (C11H12N2)[AuCl4]2, (II), were obtained by treatment of 1,1′‐methylenedipyridinium dichloride with CuCl2 and Na[AuCl4], respectively. Both hybrid salts were isolated as pure compounds, fully characterized by multinuclear NMR spectroscopy and their molecular structures confirmed by powder X‐ray diffraction studies. The crystal structures consist of discrete 1,1′‐methylenedipyridinium dications and [CuCl4]2− and [AuCl4]− anions for (I) and (II), respectively. As expected, the dications form a butterfly shape; the CuII centre of [CuCl4]2− has a distorted tetrahedral configuration and the AuIII centre of [AuCl4]− shows a square‐planar coordination. The ionic species of (I) and the dication of (II) each have twofold axial symmetry, while the two [AuCl4]− anions are located on a mirror‐plane site. Both crystal structures are stabilized by intermolecular C—H...Cl hydrogen bonds and also by Cl...π interactions. It is noteworthy that, while the average intermolecular centroid–centroid pyridinium ring distance in (I) is 3.643 (8) Å, giving strong evidence for noncovalent π–π ring interactions, for (II), the shortest centroid–centroid distance between pyridinium rings of 5.502 (9) Å is too long for any significant π–π ring interactions, which might be due to the bulk of the two [AuCl4]− anions. 相似文献
99.
100.
For the first time, we report the successful application of inhouse synthesized CdS quantum dots (QDs) with particle sizes between 1 and 7 nm exhibiting excellent fungicidal activity based on the interactions with Saccharomyces cerevisiae and Candida utilis. The growth curves and the growth rates of both fungi were established in the presence of three varying concentrations of CdS QDs. It was observed that the CdS QDs were highly inhibitory even at the lowest concentration of 10 mg/L used in this study, while the untreated control cells followed a normal growth pattern in the cases of both Saccharomyces and Candida. MALDI-MS was applied to substantiate the observations obtained by direct cell count method. It was observed that the trend observed in the case of Saccharomyces and Candida was well-represented in the MALDI-MS spectra. This study proposes a mechanism for the first time based on MALDI-MS results, that the CdS QDs interact with the extracellular polymeric substances (EPS) and remove small molecules from EPS layer; on the other hand, it was observed that CdS QDs at all concentrations lead to enrichment of protein signals in MALDI-MS. We have substantiated these results by quantifying the EPS in the control and treated cells and also using TEM to further confirm the results. 相似文献