全文获取类型
收费全文 | 2074篇 |
免费 | 355篇 |
国内免费 | 248篇 |
专业分类
化学 | 1498篇 |
晶体学 | 17篇 |
力学 | 98篇 |
综合类 | 8篇 |
数学 | 287篇 |
物理学 | 769篇 |
出版年
2024年 | 6篇 |
2023年 | 51篇 |
2022年 | 52篇 |
2021年 | 53篇 |
2020年 | 68篇 |
2019年 | 63篇 |
2018年 | 71篇 |
2017年 | 60篇 |
2016年 | 89篇 |
2015年 | 69篇 |
2014年 | 94篇 |
2013年 | 137篇 |
2012年 | 158篇 |
2011年 | 177篇 |
2010年 | 102篇 |
2009年 | 134篇 |
2008年 | 128篇 |
2007年 | 125篇 |
2006年 | 121篇 |
2005年 | 102篇 |
2004年 | 76篇 |
2003年 | 58篇 |
2002年 | 60篇 |
2001年 | 63篇 |
2000年 | 55篇 |
1999年 | 65篇 |
1998年 | 36篇 |
1997年 | 51篇 |
1996年 | 49篇 |
1995年 | 39篇 |
1994年 | 23篇 |
1993年 | 29篇 |
1992年 | 33篇 |
1991年 | 29篇 |
1990年 | 25篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有2677条查询结果,搜索用时 838 毫秒
991.
Mutation and polymorphism detection is of increasing importance for a variety of medical applications, including identification of cancer biomarkers and genotyping for inherited genetic disorders. Among various mutation-screening technologies, enzyme mismatch cleavage (EMC) represents a great potential as an ideal scanning method for its simplicity and high efficiency, where the heteroduplex DNAs are recognized and cleaved into DNA fragments by mismatch-recognizing nucleases. Thereby, the enzymatic cleavage activities of the resolving nucleases play a critical role for the EMC sensitivity. In this study, we utilized the unique features of microfluidic capillary electrophoresis and de novo gene synthesis to explore the enzymatic properties of T7 endonuclease I and Surveyor nuclease for EMC. Homoduplex and HE DNAs with specific mismatches at desired positions were synthesized using PCR (polymerase chain reaction) gene synthesis. The effects of nonspecific cleavage, preference of mismatches, exonuclease activity, incubation time, and DNA loading capability were systematically examined. In addition, the utilization of a thermostable DNA ligase for real-time ligase mediation was investigated. Analysis of the experimental results has led to new insights into the enzymatic cleavage activities of T7 endonuclease I and Surveyor nuclease, and aided in optimizing EMC conditions, which enhance the sensitivity and efficiency in screening of unknown DNA variations. 相似文献
992.
Mo Y 《The journal of physical chemistry. A》2012,116(21):5240-5246
The block-localized wave function (BLW) method, which is the simplest variant of ab initio valence bond (VB) theory, together with the quantum theory of atoms in molecules (QTAIM) approach, have been used to probe the intramolecular hydrogen bonding interactions in a series of representative systems of resonance-assisted hydrogen bonds (RAHBs). RAHB is characteristic of the cooperativity between the π-electron delocalization and hydrogen bonding interactions and is identified in many biological systems. While the deactivation of the π resonance in these RAHB systems by the use of the BLW method is expected to considerably weaken the hydrogen bonding strength, little change on the topological properties of electron densities at hydrogen bond critical points (HBCPs) is observed. This raises a question of whether the QTAIM topological parameters can be an effective measure of hydrogen bond strength. 相似文献
993.
Dehydrogenative cross-coupling reaction of primary anilines, secondary anilines, carboxamides, and sulfonamides with 1,3-diarylpropenes to form a series of allylic amines promoted by DDQ have been realized. Both monoallylation and diallylation products can be selectively synthesized when primary anilines are used as the starting materials. The method may provide a wide scope of allylamines in scientific research including biologically active compound library construction. 相似文献
994.
Here we present for the very first time a single-crystal investigation of the Cu-poor Zn-rich derivative of Cu(2)ZnSnS(4). Nowadays, this composition is considered as the one that delivers the best photovoltaic performances in the specific domain of Cu(2)ZnSnS(4)-based thin-film solar cells. The existence of this nonstoichiometric phase is definitely demonstrated here in an explicit and unequivocal manner on the basis of powder and single-crystal X-ray diffraction analyses coupled with electron microprobe analyses. Crystals are tetragonal, space group I ?4, Z = 2, with a = 5.43440(15) ? and c = 10.8382(6) ? for Cu(2)ZnSnS(4) and a = 5.43006(5) ? and c = 10.8222(2) ? for Cu(1.71)Zn(1.18)Sn(0.99)S(4). 相似文献
995.
The anti-inflammatory activity and the mechanism of action of Gentiana striata Maxim. has been investigated. The most active phase, the ethyl acetate extract of Gentiana striata Maxim. (EGS), displayed potent inhibitory activity on feet oedema of rheumatoid arthritis (RA) inflicted rats. This anti-inflammatory activity might be partly based on the notable reduction of prostaglandin E2 (PGE?) and nitric oxide (NO) levels. Six further compounds isolated from EGS have previously been reported as having anti-inflammatory activity. 相似文献
996.
Structural analysis of saponins from medicinal herbs using electrospray ionization tandem mass spectrometry 总被引:4,自引:0,他引:4
Liu S Cui M Liu Z Song F Mo W 《Journal of the American Society for Mass Spectrometry》2004,15(2):133-141
The underivatized saponins from Tribulus terrestris and Panax ginseng have been investigated by electrospray ionization multi-stage tandem mass spectrometry (ESI-MS(n)). In ESI-MS spectra, a predominant [M + Na](+) ion in positive mode and [M - H](-) ion in negative mode were observed for molecular mass information. Multi-stage tandem mass spectrometry of the molecular ions was used for detailed structural analysis. Fragment ions from glycoside cleavage can provide information on the mass of aglycone and the primary sequence and branching of oligosaccharide chains in terms of classes of monosaccharides. Fragment ions from cross-ring cleavages of sugar residues can give some information about the linkages between sugar residues. It was found that different alkali metal-cationized adducts with saponins have different degrees of fragmentation, which may originate from the different affinity of a saponin with each alkali metal in the gas phase. ESI-MS(n) has been proven to be an effective tool for rapid determination of native saponins in extract mixtures, thus avoiding tedious derivatization and separation steps. 相似文献
997.
Han Mo Jeong Hyun Soo Kim Young Soo La 《Journal of Macromolecular Science: Physics》2013,52(1):119-130
The hydroxyl group of HEMA was cross‐linked with 1,3‐diethoxy‐1,1,3,3‐tetramethyldisiloxane in order to enhance the actuation force of the ionic polymer‐metal composite (IPMC) made from the acrylic ter‐polymer of fluoroalkyl methacrylate, 2‐acylamido‐2‐methyl‐1‐propanesulfonic acid, and 2‐hydroxyethyl methacrylate (HEMA). The water uptake was reduced and the mechanical strengths of the membrane were improved by the cross‐linkage. The actuation force of the IPMC was generally enhanced, although it was reduced somewhat at high levels of cross‐linking. The current and deformation responses of the IPMC were both decreased by cross‐linking. 相似文献
998.
Hee Baek Lee Anjanapura V. Raghu Koo Sik Yoon Han Mo Jeong 《Journal of Macromolecular Science: Physics》2013,52(4):802-809
The nanocomposite films of a functionalized graphene sheet (FGS) and poly(ethylene oxide) (PEO) were cast from the physical blend of an aqueous FGS dispersion assisted by sodium dodecyl sulfate and an aqueous PEO solution. The thermal properties observed by differential scanning calorimetry suggested that FGS had a nucleating effect on the PEO crystallization. However, we found FGS actually hindered the growth of PEO crystals. The dynamic mechanical properties indicated that FGS effectively reinforced the matrix PEO. The FGS also efficiently improved the electric conductivity of PEO. With the addition of 2 parts of FGS per 100 parts of PEO, the conductivity was increased by more than 103-fold from that of pristine PEO. 相似文献
999.
Our purpose in this paper is to present a new tripartite quantum state sharing using partially quantum resources. The first scheme is to probabilistically split an unknown n-particle state using pre-shared a partially entangled four-particle cluster state as quantum resource by constructing some proper POVM. This scheme is further extended to share an unknown multi-particle cluster state using different states as quantum resources. Our schemes with general quantum channels are useful for various quantum information processing and quantum network tasks. 相似文献
1000.
Xin Mo Chen-Yi Wang Guang Li Jian-Ming Jiang 《Journal of Macromolecular Science: Physics》2013,52(7):1370-1383
A series of novel polyimides (PIs) were polymerized from 4,4′-(cyclohexane-1,4-diylbis (oxy))bis(3-(trifluoromethyl)aniline) (1) and 1,4-bis((4-amino-2-(trifluoromethyl) phenoxy)methyl)cyclohexane (2), with two aromatic tetracarboxylic dianhydrides using the typical one-step method. The inherent viscosity of these resulting PIs were in the range of 0.53–0.91 dl/g in N,N-dimethylacetamide (DMAc) at 30°C. They were readily soluble in numerous solvents, such as N-methyl-2-pyrrolidone (NMP), DMAc, N,N-dimethylformamide (DMF), meta-cresol (m-Cresol), and dimethylsulfoxide (DMSO). The PI films showed high optical transparency and were colorless with an ultraviolet-visible absorption cut-off wavelength around 330 nm, and a low dielectric constants of 2.49–2.93 at 1 MHz. The PIs also showed good thermal properties. Their glass-transition temperatures (T g) were higher than 337°C, and the temperatures of 10% weight loss in air and nitrogen were higher than 412°C and 417°C. Furthermore, the PI films possessed good mechanical properties with tensile strengths of 54–71 MPa, elongations at break of 11.6%–17.3% and low moisture absorption (<1.34%). Due to their properties, these PIs could be considered as materials for photoelectric and micro-electronic applications. 相似文献