全文获取类型
收费全文 | 3529篇 |
免费 | 123篇 |
国内免费 | 13篇 |
专业分类
化学 | 2767篇 |
晶体学 | 28篇 |
力学 | 47篇 |
数学 | 334篇 |
物理学 | 489篇 |
出版年
2023年 | 21篇 |
2022年 | 42篇 |
2021年 | 40篇 |
2020年 | 60篇 |
2019年 | 55篇 |
2018年 | 37篇 |
2017年 | 37篇 |
2016年 | 90篇 |
2015年 | 96篇 |
2014年 | 106篇 |
2013年 | 155篇 |
2012年 | 236篇 |
2011年 | 279篇 |
2010年 | 140篇 |
2009年 | 114篇 |
2008年 | 241篇 |
2007年 | 236篇 |
2006年 | 231篇 |
2005年 | 232篇 |
2004年 | 195篇 |
2003年 | 151篇 |
2002年 | 143篇 |
2001年 | 57篇 |
2000年 | 53篇 |
1999年 | 39篇 |
1998年 | 22篇 |
1997年 | 22篇 |
1996年 | 40篇 |
1995年 | 26篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 38篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1975年 | 14篇 |
1973年 | 11篇 |
1972年 | 14篇 |
1969年 | 9篇 |
排序方式: 共有3665条查询结果,搜索用时 0 毫秒
1.
2.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
3.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
4.
5.
The detection of serial changes in magnetic resonance (MR) signal intensity of the heart following acute myocardial infarction may provide a useful method of characterizing tissue healing. Fourteen patients with acute Q-wave infarction underwent T2-weighted, spin-echo cardiac imaging during hospitalization, followed by one or more additional MR studies (total 31) over a 6- to 27-wk period (mean: 3 mo). Visual assessment of the images demonstrated a gradual reduction in signal intensity and localization of the bright signal to the subendocardium of the infarction region over the three-mo study period. A quantitative measurement of signal intensity (infarction/normal myocardium) fell from 1.81 +/- 0.42 on the initial study to 1.34 +/- 0.37 (p less than 0.05) at a mean of 14 wk. Two patients had an increase in signal intensity on the follow-up study and both patients had been readmitted with acute coronary syndromes. In summary, characterization of changes in signal intensity may provide a useful method of assessing myocardial healing following acute myocardial infarction. Further studies are indicated to determine the prognostic significance of these parameters. 相似文献
6.
Benjamin M. NugentAmie L. Williams E.N. PrabhakaranJeffrey N. Johnston 《Tetrahedron》2003,59(45):8877-8888
The complete scope of free radical-mediated vinyl amination is described, using 5-exo-trig cyclizations of vinyl radicals to the nitrogen of azomethines. The focus is primarily on N,N-dialkyl enamines since their nucleophilicity renders them the most challenging enamines to synthesize using redox conditions. These studies establish several encouraging precedents for the broader application of this strategy. 相似文献
7.
Johnston CG Vestal JR 《Antarctic journal of the United States / National Science Foundation》1988,21(5):225-226
Photosynthetic activity of three cryptoendolithic microbial communities was studied under controlled conditions in the laboratory. In two of these communities, the dominant organisms were lichens, collected from Linnaeus Terrace and from Battleship Promontory. The third community, dominated by cyanobacteria, was collected from Battleship Promontory. Both sites are in the ice-free valleys of southern Victoria Land. Previous efforts have shown how physical conditions can influence metabolic activity in endolithic communities (Kappen and Friedmann 1983; Kappen, Friedmann, and Garty 1981; Vestal, Federle, and Friedmann 1984). Biological activity can also be strongly influenced by the chemical environment. Inorganic nutrients such as nitrate, ammonia, and phosphate are often limiting factors, so their effects on photosynthetic carbon-14 bicarbonate incorporation were investigated. Iron and manganese are two metals present in Linnaeus Terrace and Battleship Promontory sandstones, and their effects on photosynthesis were also studied. The results may add to our understanding of biogeochemical interactions within this unique microbial community. 相似文献
8.
9.
10.
Primus TM Kohler DJ Goodall MA Yoder C Mathies T Miller L Johnston JJ Vercauteren K 《Journal of AOAC International》2003,86(6):1144-1148
4,4'-Dinitrocarbanilide (DNC) was extracted from chicken, duck, goose, and snake eggs and isolated by reversed-phase liquid chromatography. DNC was detected by ultraviolet absorbance at 347 nm and quantitated by comparison with a calibration standard. Recoveries of DNC from fortified control chicken, duck, goose, and snake egg samples were determined for DNC levels of 0.16, 10, and 16 microg/g. The mean recoveries from chicken, duck, goose, and snake eggs were 92 +/- 4, 88 +/- 9, 87 +/- 7, and 95 +/- 6%, respectively. The method limits of detection for DNC in chicken, duck, goose, and snake eggs ranged from 0.015 to 0.035 microg/g. The reported method is much simpler than and equally efficient as previous methods developed for the determination of DNC residues in egg contents. 相似文献