全文获取类型
收费全文 | 5736篇 |
免费 | 218篇 |
国内免费 | 15篇 |
专业分类
化学 | 3790篇 |
晶体学 | 60篇 |
力学 | 123篇 |
数学 | 612篇 |
物理学 | 1384篇 |
出版年
2023年 | 55篇 |
2022年 | 132篇 |
2021年 | 180篇 |
2020年 | 140篇 |
2019年 | 161篇 |
2018年 | 130篇 |
2017年 | 130篇 |
2016年 | 264篇 |
2015年 | 197篇 |
2014年 | 192篇 |
2013年 | 350篇 |
2012年 | 372篇 |
2011年 | 479篇 |
2010年 | 292篇 |
2009年 | 280篇 |
2008年 | 388篇 |
2007年 | 360篇 |
2006年 | 291篇 |
2005年 | 243篇 |
2004年 | 237篇 |
2003年 | 154篇 |
2002年 | 136篇 |
2001年 | 102篇 |
2000年 | 98篇 |
1999年 | 60篇 |
1998年 | 41篇 |
1997年 | 40篇 |
1996年 | 47篇 |
1995年 | 41篇 |
1994年 | 41篇 |
1993年 | 37篇 |
1992年 | 53篇 |
1991年 | 28篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1972年 | 9篇 |
排序方式: 共有5969条查询结果,搜索用时 390 毫秒
21.
Rajesh Pereira 《Journal of Mathematical Analysis and Applications》2003,285(1):336-348
In 1959, Davis introduced the concept of a differentiator of an operator on a finite-dimensional Hilbert space. We prove that every such operator possesses a differentiator. We also use the theory of differentiators to solve several problems in the geometry of polynomials. For instance, we answer in the affirmative a twenty year old unsolved conjecture of Schoenberg, a related conjecture of Katsoprinakis and a fifty year old unsolved conjecture of De Bruijn and Springer. 相似文献
22.
E. Casarejos P. Armbruster L. Audouin J. Benlliure M. Bernas A. Boudard R. Legrain S. Leray B. Mustapha S. Czajkowski T. Enqvist B. Fernandez J. Pereira M. Pravikoff F. Rejmund K. -H. Schmidt C. Stephan J. Taieb L. Tassan-Got C. Villagrasa C. Volant W. Wlazlo 《Physics of Atomic Nuclei》2003,66(8):1413-1420
The isotopic production cross sections of heavy residues in relativistic heavy-ion collisions have been investigated in inverse kinematics. The primary reaction products were fully identified in mass and atomic number prior to beta decay using the fragment separator FRS. The huge collection of data obtained helps in the understanding of the two main reaction mechanisms involved: fragmentation and fission. These data provide basic information for future radioactive ion beam facilities and for technical applications like intense neutron sources by means of spallation targets. 相似文献
23.
结合声表面波和光致发光谱在低温(15K)下对非故意掺杂的GaAs(110)量子阱结构的发光特性进行了研究.实验结果表明,由于声表面波的作用GaAs(110)量子阱的发光强度减弱,并且其对应的重空穴能级出现了分裂的现象,当施加的声波强度Prf达到20dBm时,能级分裂ΔE达到了10meV.进一步讨论了声表面波对GaAs(110)量子阱圆偏振光自旋注入的影响.
关键词:
发光
GaAs量子阱
声表面波
自旋极化 相似文献
24.
J. C. S. Moraes E. M. Telles F. C. Cruz A. Scalabrin D. Pereira C. Garelli N. Ioli A. Moretti F. Strumia 《International Journal of Infrared and Millimeter Waves》1991,12(12):1475-1486
We report the discovery of 57 new fir laser lines from13CD3OH molecule optically pumped by a waveguide CO2 laser of 300 MHz tunability. For all lines, precise frequency offset measurements between the CO2 line center and the center of the absorbing13CD3OH line were performed using the transferred Lamb-Dip technique. We have also measured directly the frequency of seven FIR laser lines by heterodyning with already known laser lines. We present a complete list of all known laser lines (134) and frequency measurements (24) for this molecule.Work supported by CNPq, FAPESP, FAEP-Brasil, and CNR-Italia 相似文献
25.
By incorporating the holographic principle in a time-depending Λ-term cosmology, new physical bounds on the arbitrary parameters of the model can be obtained. Considering then the dark energy as a purely geometric entity, for which no equation of state has to be introduced, it is shown that the resulting range of allowed values for the parameters may explain both the coincidence problem and the universe accelerated expansion, without resorting to any kind of additional structures. 相似文献
26.
Carolina Pereira De Souza Margareth Spangler Andrade Bernardo Ruegger Almeida Neves 《Microscopy and microanalysis》2002,8(6):509-517
In this work, effective, yet simple, recycling mechanisms for used scanning probe microscopy (SPM) tips were implemented. Comprising a tip profile characterization methodology and specific cleaning procedures, which decontaminate SPM tips whether the contamination nature is known or not, such routes were optimized during numerous tests with brand new, previously used, and already discarded categories of SPM tips. The results show that if the used tip suffered contamination only, but no physical damages, during its scanning lifetime, it becomes readily available for reutilization after the cleansing process, characterizing a recycling route. On the other hand, if the tip went through wear and breakages during its utilization, it still can be decontaminated, but may not be directly reutilized due to its inadequate physical profile. Nevertheless, the methodology developed in this work may yet be applied as part of a more complex recycling route. 相似文献
27.
28.
J. L. Souza A. F. Santos L. Polese Marisa S. Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2007,87(3):673-677
Poly(3-hydroxybutyrate), PHB has been structurally
modified through reaction with maleic anhydride, MA. Transesterification reaction
was carried out fixing the PHB and MA and besides time and temperature the
concentration of the triethylamine (used as catalyst) was changed. Glass transition,
melting and crystallization temperature obtained from DSC curves and thermal
degradation temperatures obtained from TG traces were used to evaluate the
influence of the reaction conditions on the modification of PHB according
to factorial design. On the base of the results the optimum conditions are
to perform the PHB modification reaction with MA reaction at 110°C for
1 h with 5% v/v triethylamine. 相似文献
29.
In this work we show that the energy associated to the linear three-dimensional magneto-elastic system decays polynomially to zero as time goes to infinity, provided the initial data is smooth enough. 相似文献
30.
SbPO4, a phosphate with a layered structure, was tested as an electrode material for lithium cells spanning the 3.0-0.0 V range. Two main electrochemical processes were detected as extensive plateaus at ca. 1.6 and 0.7 V in galvanostatic measurements. The first process was found to be irreversible, thus excluding a potential intercalation-like mechanism for the reaction and being better interpreted as a decomposition reaction leading to the formation of elemental Sb. This precludes the use of this compound as a cathodic material for lithium cells. By contrast, the process at 0.7 V is reversible and can be ascribed to the formation of lithium-antimony alloys. The best electrochemical response was obtained by cycling the cell at a C/20 discharge rate over the voltage range 1.25-0.25 V. Under these conditions, the cell delivers an average capacity of 165 Ah/kg—a value greater than those reported for other phosphates—upon successive cycling. 相似文献