全文获取类型
收费全文 | 2849篇 |
免费 | 116篇 |
国内免费 | 3篇 |
专业分类
化学 | 2167篇 |
晶体学 | 24篇 |
力学 | 35篇 |
数学 | 174篇 |
物理学 | 568篇 |
出版年
2024年 | 5篇 |
2023年 | 25篇 |
2022年 | 90篇 |
2021年 | 116篇 |
2020年 | 96篇 |
2019年 | 109篇 |
2018年 | 80篇 |
2017年 | 76篇 |
2016年 | 124篇 |
2015年 | 81篇 |
2014年 | 92篇 |
2013年 | 143篇 |
2012年 | 202篇 |
2011年 | 193篇 |
2010年 | 130篇 |
2009年 | 110篇 |
2008年 | 168篇 |
2007年 | 135篇 |
2006年 | 132篇 |
2005年 | 149篇 |
2004年 | 110篇 |
2003年 | 119篇 |
2002年 | 71篇 |
2001年 | 44篇 |
2000年 | 44篇 |
1999年 | 28篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 31篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1975年 | 3篇 |
1971年 | 3篇 |
1969年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有2968条查询结果,搜索用时 542 毫秒
11.
Robert Andreu Gerard Lligadas Joan Carles Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4965-4973
A new oxazolidine derivative was obtained from phenol, 2‐amino‐2‐methylpropane‐1,3‐diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (Mw ~ 400) with 4,4′‐methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965–4973, 2007 相似文献
12.
In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl-N-carbazolyl)-6-(N-carbazolyl)-2,4-hexadyine] (polya-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings. 相似文献
13.
E. N. Abdullin N. G. Ivanov B. M. Kovalchuk I. N. Konovalov V. F. Losev A. N. Panchenko Yu. N. Panchenko V. S. Skakun V. F. Tarasenko A. G. Yastremsky 《Laser Physics》2006,16(1):104-115
Two-high power excimer laser systems with square (25 × 25 cm) and circular (with a diameter of 40 cm) cross sections of the
output laser beam are described. The first (second) system consists of four (five) excimer lasers. The experimental results
on the generation of the high-quality high-power laser pulses are presented. Laser beams with a pulse duration of 1–250 ns,
a divergence of 0.01 mrad, a spectral line width of 0.01 cm−1, and a pulse energy of up to 330 J are obtained.
Original Text ? Astro, Ltd., 2006. 相似文献
14.
Marina DellaGreca 《Tetrahedron》2006,62(12):2877-2882
Examination of the hydroalcoholic extract of the leaves of Aptenia cordifolia has afforded three cinnamic acid amides and two lignanamides. Structures were established on the basis of spectroscopic data, including 2D-NMR analyses. 相似文献
15.
Demetrio Pitea Laura Bonati Elena Collina Ugo Cosentino Marina Lasagni Giorgio Moro Roberto Todeschini 《Fresenius' Journal of Analytical Chemistry》1994,348(1-2):111-120
Summary The role of multivariate analysis methods in evaluating, rationalizing, and working out complex environmental problems is discussed. The discussion is organized in two sections; a literature analysis of the application of chemometric methods to PCDD/PCDF data interpretation and source correlation and a review of the role of chemometric methods in analysing the results obtained by the Authors studying PCDD/PCDF formation and destruction mechanisms in MSW combustion processes. 相似文献
16.
Marina Gorunescu Florin Gorunescu Augustin Prodan 《Journal of Applied Mathematics and Computing》2002,9(1):185-195
Previous research has shown that the flow of patients around departments of geriatric medicine and ex-patients in the community may be modelled by the application of a mixed-exponential distribution. In this paper we considered a five-compartment model using a continuous-time Markov process to describe the flow of patients. Using a M/Ph/c queuing model, we present a way of optimizing the number of beds in order to maintain an acceptable delay probability at a sufficiently low level. Finally, we constructed a Java computer simulation, using data from St George’s Hospital, London. 相似文献
17.
18.
V. F. Tarasenko S. B. Alekseev V. M. Orlovskii V. G. Shpak S. A. Shunailov 《Technical Physics》2004,49(8):982-986
Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse
are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front
of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage
across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with
an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam
is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between
the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific
power input of ≥400 MW/cm3, a density of the discharge current at the anode of up to 3 kA/cm2, and specific energy deposition of ∼1 J/cm3 over 3 to 5 ns is created. 相似文献
19.
Diana C. Skigin Miriam L. Gigli Marina E. Inchaussandague Néstor E. Bonomo Claudio I. Valencia 《International Journal of Infrared and Millimeter Waves》1993,14(6):1323-1339
Theoriginal and theenhanced Maxwell-Garnett estimates for the permittivity of a particulate medium are applied to the reflection of light by a composite dielectric slab. The reflection coefficients for incident s and p polarizations are calculated and some curves are plotted and discussed. 相似文献
20.