全文获取类型
收费全文 | 11723篇 |
免费 | 2181篇 |
国内免费 | 1408篇 |
专业分类
化学 | 8112篇 |
晶体学 | 195篇 |
力学 | 716篇 |
综合类 | 118篇 |
数学 | 1274篇 |
物理学 | 4897篇 |
出版年
2024年 | 31篇 |
2023年 | 283篇 |
2022年 | 390篇 |
2021年 | 533篇 |
2020年 | 581篇 |
2019年 | 547篇 |
2018年 | 458篇 |
2017年 | 416篇 |
2016年 | 551篇 |
2015年 | 662篇 |
2014年 | 715篇 |
2013年 | 907篇 |
2012年 | 1020篇 |
2011年 | 1014篇 |
2010年 | 691篇 |
2009年 | 742篇 |
2008年 | 788篇 |
2007年 | 656篇 |
2006年 | 591篇 |
2005年 | 473篇 |
2004年 | 382篇 |
2003年 | 292篇 |
2002年 | 298篇 |
2001年 | 210篇 |
2000年 | 205篇 |
1999年 | 166篇 |
1998年 | 136篇 |
1997年 | 107篇 |
1996年 | 96篇 |
1995年 | 80篇 |
1994年 | 70篇 |
1993年 | 75篇 |
1992年 | 62篇 |
1991年 | 47篇 |
1990年 | 54篇 |
1989年 | 51篇 |
1988年 | 43篇 |
1987年 | 69篇 |
1986年 | 54篇 |
1985年 | 63篇 |
1984年 | 55篇 |
1983年 | 38篇 |
1982年 | 47篇 |
1981年 | 40篇 |
1980年 | 38篇 |
1979年 | 37篇 |
1978年 | 30篇 |
1977年 | 30篇 |
1976年 | 27篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We classify smooth subvarieties of codimension twoX⊂P
n
, 4≤n≤5, which are arithmetically Cohen-Macaulay and of non general type. By the way we exhibit some classes of non extendable
subvarieties. Then we give new proofs of the classification of scrolls inP
4; finally we consider smooth surfaces of non general type inP
4 arising from rank three vector bundles.
Sunto Classifichiamo le sottovarietà lisce di codimensione dueX⊂P n , 4≤n≤5, aritmeticamente Cohen-Macaulay e non di tipo generale. Nel contempo descriviamo alcune classi di sottovarietà non estendibili. Diamo poi due nuove dimostrazioni della classificazione degli scrolls inP 4; infine consideriamo superfici lisce inP 4, non di tipo generale, associate a fibrati di rango tre.相似文献
102.
Zusammenfassung Mittels des Einsatzes einer Hochdrucksichtzelle wurden Eigenschaften der Kontaktbereiche in Trennverfahren mit unterschiedlichen wäßrigen Lösungen und CO2 unter hohen Drücken untersucht. Die Methode des hängenden Tropfens wurde zur Messung der Grenzflächenspannung bis zu Drücken von 280 bar angewandt. Der mit dem Druck abnehmende Verlauf weist nach der Gibbs'schen Theorie auf die Anreicherung von CO2 in der Phasengrenze. Weiterhin wurde die für Packungskolonnen bedeutsame Feststoffbenetzung in Abhängigkeit von Druck und Oberflächenbeschaffenheit des Feststoffes untersucht. Der die Feststoffbenetzung charakterisierende Kontaktwinkel wurde mittels der Methode der gekippten Platte vermessen und ergab eine schlechtere Benetzung bei höheren Drücken und glatten Stahloberflächen.
相似文献
The effect of interfacial phenomena on mass transport and performance of separations in countercurrent columns with supercritical CO2
Interfacial phenomena affecting countercurrent separation processes have been studied in systems containing aqueous solutions and CO2 at elevated pressures by means of a high pressure optical cell. The pendant drop method was applied in order to measure the interfacial tension up to 280 bar. The decreasing course as a function of the pressure is due to the adsorption of CO2 at the interface according to Gibbs' law. Further, wetting characteristics have been investigated as they are of considerable importance to packed columns. Therefore, the contact angle was determined by the method of the tilting plate and came out to increase with pressure and smoothness of the solid surface, indicating the loss of wettability.
相似文献
103.
104.
In [2], Chen et al. showed that the average genus for a graph of maximum degree at most 3 is at least 1/2 its maximum genus. In this paper, the structure for a graph of maximum degree at most 3 with average genus equal to 1/2 its maximum genus is described. Furthermore, LetH be a subgraph ofG and γavg(G) = γavg(H). It’s shown thatG can be obtained by a series operations of type I and II onH. 相似文献
105.
106.
Chun‐Hao Huang Sheng‐Hsiung Yang Kuei‐Bai Chen Chain‐Shu Hsu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):519-531
Five novel fluorene‐containing polymers, poly[(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA1 ), poly[(1‐pentyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene) ( PFA2 ), poly[1‐decyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA3 ), poly[1‐phenyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA4 ), and poly[1‐(3,4‐difluorophenyl)‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA5 ) were synthesized by the polymerization of the corresponding fluorene‐substituted acetylenic monomers ( M1–M5), using WCl6, MoCl5, and TaCl5 as catalysts and n‐Bu4Sn as a cocatalyst. The synthesized polymers were thermally stable and readily soluble in common organic solvents. The degradation temperatures for a 5% weight loss of the polymers were ∼352–503 °C under nitrogen. PFA1–PFA5 show emission peaks from 402 to 590 nm. Besides, their electroluminescent properties were studied in heterostructure light‐emitting diodes (LEDs), using PFA2–PFA5 as an emitting layer. The PFA5 device revealed an orange‐red emission peak at 602 nm with a maximum luminescence of 923 cd/m2 at 8 V. A device with the ITO/PEDOT/ a mixture of PFA2 (98 wt %) and PFA5 (2 wt %)/Ca/Al showed near white emission. Its maximum luminance and current efficiency are 450 cd/m2 at 15 V and 1.3 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 519–531, 2006 相似文献
107.
Lagrangian relaxation is commonly used in combinatorial optimization to generate lower bounds for a minimization problem.
We study a modified Lagrangian relaxation which generates an optimal integer solution. We call it semi-Lagrangian relaxation
and illustrate its practical value by solving large-scale instances of the p-median problem.
This work was partially supported by the Fonds National Suisse de la Recherche Scientifique, grant 12-57093.99 and the Spanish
government, MCYT subsidy dpi2002-03330. 相似文献
108.
109.
D. Bisello G. Busetto A. Castro M. Nigro M. Penzo L. Pescara M. Posocco P. Sartori L. Stanco Z. Ajaltouni A. Falvard J. Jousset B. Michel J. C. Montret A. Antonelli R. Baldini A. Calcaterra G. Capon M. Schioppa J. -E. Augustin G. Cosme F. Couchot B. Dudelzak F. Fulda G. Grosdidier B. Jean-Marie S. Jullian D. Lalanne V. Lepeltier F. Manè C. Paulot R. Riskalla Ph. Roy G. Szklarz DM Collaboration 《Zeitschrift fur Physik C Particles and Fields》1988,39(1):13-19
Thee + e ?→K + K ? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ± form factor |F F ±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment. 相似文献
110.
E. Ph. Horwitz M. L. Dietz R. Chiarizia 《Journal of Radioanalytical and Nuclear Chemistry》1992,161(2):575-583
A simple method for the separation and preconcentration of radiostrontium from acidic nuclear waste solutions for subsequent determination is described. The method involves passage of the waste solution, acidified to at least 2M with nitric acid, through an extraction chromatographic column consisting of a 1M solution of bis-4,4(5)[(t-butyl)cyclohexano]-18-crown-6 in 1-octanol sorbed on an inert polymeric substrate, which preferentially retains strontium. The strontium may then be stripped from the column with a small volume of either dilute (0.05M) nitric acid or water. Actinides present are removed quantitatively prior to strontium separation by passage of the sample through an actinide-specific extraction chromatographic column.Work performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, U. S. Department of Energy, under contract number W-31-109-ENG-38. 相似文献