全文获取类型
收费全文 | 2788篇 |
免费 | 115篇 |
国内免费 | 9篇 |
专业分类
化学 | 2154篇 |
晶体学 | 33篇 |
力学 | 75篇 |
数学 | 135篇 |
物理学 | 515篇 |
出版年
2024年 | 3篇 |
2023年 | 20篇 |
2022年 | 52篇 |
2021年 | 54篇 |
2020年 | 56篇 |
2019年 | 49篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 91篇 |
2015年 | 81篇 |
2014年 | 88篇 |
2013年 | 155篇 |
2012年 | 218篇 |
2011年 | 249篇 |
2010年 | 161篇 |
2009年 | 133篇 |
2008年 | 219篇 |
2007年 | 194篇 |
2006年 | 170篇 |
2005年 | 168篇 |
2004年 | 113篇 |
2003年 | 93篇 |
2002年 | 99篇 |
2001年 | 57篇 |
2000年 | 42篇 |
1999年 | 48篇 |
1998年 | 22篇 |
1997年 | 19篇 |
1996年 | 28篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 22篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2912条查询结果,搜索用时 0 毫秒
31.
Polypyrrole (PPy) nanotubes were readily fabricated through chemical oxidation polymerization in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse (water-in-oil) emulsions. The reverse cylindrical micelle phase was characterized, and the key factors affecting the formation of PPy nanotubes were systematically inspected. AOT reverse cylindrical micelles were prepared via a cooperative interaction between an aqueous FeCl3 solution and AOT in an apolar solvent. In the H2O/FeCl3/AOT/apolar solvent system, the aqueous FeCl3 solution played a role in increasing the ionic strength and decreasing the second critical micelle concentration of AOT. As a result, AOT reverse cylindrical micelles could be spontaneously formed in an apolar solvent. In addition, iron cations were adsorbed to the anionic AOT headgroups that were capable of extracting metal cations from the aqueous core. Under these conditions, the addition of pyrrole monomer resulted in the chemical oxidation polymerization of the corresponding monomer at the surface of AOT reverse cylindrical micelles, followed by the formation of tubular PPy nanostructures. In a typical composition (74.0 wt % hexane, 22.4 wt % AOT, and 3.6 wt % aqueous FeCl3 solution at 15 degrees C), the average diameter of PPy nanotubes was approximately 94 nm and their length was more than 2 mum. The PPy nanotube dimensions were affected by synthetic variables such as the weight ratio of aqueous FeCl3 solution/AOT, type of apolar solvent, and reaction temperature. Moreover, the relationship between the diameter and the conductivity of the nanotubes was investigated. 相似文献
32.
33.
Y. E. Kim M. Rabinowitz J. -H. Yoon 《International Journal of Theoretical Physics》1993,32(7):1197-1223
Previously overlooked condensed matter effects (CME) can significantly influence nuclear fusion rates in both laboratory and astrophysical environments. In dense plasmas, the ensemble of fusing particles has a significant exchange of kinetic and potential energies. Thus, there are diminished effective flux velocities resulting in a significant selective reduction of fusion rates. Our CME predictions are testable in laboratory experiments and have broad-ranging implications on the fusion rates for stellar media in general. By calculating reaction rates forp(p, e
+
v
e
) D and7Be(p, )8B in the sun, we show that CME help to solve the solar neutrino problem. 相似文献
34.
Yong‐Min Lee Yoon‐Bo Shim Seung Jae Lee Sung Kwon Kang Sung‐Nak Choi 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(12):o733-o734
The structure of the title compound, C15H27N2+·ClO4?, consists of a monoprotonated sparteinium cation and a perchlorate anion. The two tertiary N atoms of the cation, one perchlorate O atom and a H atom form a bifurcated hydrogen bond, the four hydrogen‐bonding atoms being nearly in the same plane. 相似文献
35.
You WK So SH Lee H Park SY Yoon MR Chang SI Kim HK Joe YA Hong YK Chung SI 《Experimental & molecular medicine》1999,31(4):197-202
Endostatin, a carboxyl-terminal fragment of collagen XVIII is known as an anti-angiogenic agent, that specifically inhibits the proliferation of endothelial cell and the growth of several primary tumor. We report here the purification and characterization of the recombinant murine endostatin (rmEndostatin) which was expressed in a prokaryotic expression system. This rmEndostatin has similar physiochemical properties of yeast-produced recombinant endostatin, and it also specifically inhibits the proliferation and migration of bovine capillary endothelial cells stimulated by basic fibroblast growth factor. The biological activity of rmEndostatin was also shown by its anti-angiogenic ability on the chorioallantoic membrane of chick embryo in vivo. In this article, we demonstrate the refolding and purification of rmEndostatin, expressed using E. coli system, to a biologically active and soluble form. In addition, these results confirm the activity of endostatin as a potent anti-angiogenic agent. 相似文献
36.
37.
A new calix[4]crown chemosensor based on dual sensing probes reveals Pb2+ ion selectivity over other metal ions, which arises from a hypsochromic shift of azo units in UV spectrum as well as a fluorescence enhancement of pyrenyl parts in fluorescence spectrum via a suppressed FRET. 相似文献
38.
Styrene was polymerized in the presence of benzoyl peroxide (BPO) and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to yield polystyrene-TEMPO (PS-TEMPO) macroinitiator. The PS-TEMPO macroinitiator with different molecular weight was reacted with 4-vinyl pyridine (4-VP) to synthesize polystyrene-block-poly(4-vinyl pyridine) (PS-b-PVP), which was then quaternized with n-octyl iodide. Antibacterial activity of the quaternized copolymers was assessed against a gram negative bacterium (Pseudomonas aeruginosa) and a gram positive one (Staphylococcus aureus) by using the shake flask test method, and the results were compared with those of poly(styrene-random-4-vinyl pyridine) (P(ST-r--VP)). The quaternized copolymers inhibited greatly the growth of the bacteria, and PS-b-PVP was more active than P(ST-r-VP), which was ascribed to the fact that the content of quaternized 4-VP units on the surface of the particles of the former copolymer was higher than that corresponding to the latter one. 相似文献
39.
J. Jung J. H. Yoon H. H. Chung M. J. Lee 《Journal of Radioanalytical and Nuclear Chemistry》2002,252(3):451-454
Gamma-ray treatment in the presence of ozone (O3) and titanium dioxide (TiO2) showed an efficient removal of trichloroethylene (TCE) and perchloroethylene (PCE). Without gamma-irradiation, TCE and PCE were not sufficiently decomposed to comply with the water quality limit of groundwater. However, near 100% of TCE and PCE were removed at a dose of 300 Gy in the presence of O3 and TiO2, where TiO2 showed an explicit enhancement of decomposition. Cytotoxicity test using Chinese hamster V79 cells showed no toxicity of the TCE and PCE decomposition products. 相似文献
40.
[reaction: see text] A new recyclable supported catalyst system for orthoalkylation was devised using a self-assembly consisting of the barbiturate and 2,4,6-triaminopyrimidine H-bonding motifs. At high temperature, the system is completely homogeneous so as to give an efficient catalytic activity, while it is heterogenized at room temperature to form an insoluble solid phase for the easy recovery of the catalyst after the reaction. 相似文献