全文获取类型
收费全文 | 203961篇 |
免费 | 1955篇 |
国内免费 | 593篇 |
专业分类
化学 | 102338篇 |
晶体学 | 3340篇 |
力学 | 9289篇 |
综合类 | 5篇 |
数学 | 22510篇 |
物理学 | 69027篇 |
出版年
2021年 | 1658篇 |
2020年 | 1797篇 |
2019年 | 2000篇 |
2018年 | 2702篇 |
2017年 | 2601篇 |
2016年 | 3766篇 |
2015年 | 2307篇 |
2014年 | 3614篇 |
2013年 | 9088篇 |
2012年 | 7246篇 |
2011年 | 8739篇 |
2010年 | 6047篇 |
2009年 | 5913篇 |
2008年 | 7914篇 |
2007年 | 8082篇 |
2006年 | 7724篇 |
2005年 | 6894篇 |
2004年 | 6431篇 |
2003年 | 5651篇 |
2002年 | 5499篇 |
2001年 | 6426篇 |
2000年 | 4933篇 |
1999年 | 3794篇 |
1998年 | 3039篇 |
1997年 | 3047篇 |
1996年 | 2792篇 |
1995年 | 2614篇 |
1994年 | 2463篇 |
1993年 | 2340篇 |
1992年 | 2691篇 |
1991年 | 2673篇 |
1990年 | 2600篇 |
1989年 | 2398篇 |
1988年 | 2451篇 |
1987年 | 2450篇 |
1986年 | 2280篇 |
1985年 | 2961篇 |
1984年 | 3215篇 |
1983年 | 2632篇 |
1982年 | 2802篇 |
1981年 | 2772篇 |
1980年 | 2639篇 |
1979年 | 2727篇 |
1978年 | 2821篇 |
1977年 | 2819篇 |
1976年 | 2887篇 |
1975年 | 2670篇 |
1974年 | 2644篇 |
1973年 | 2776篇 |
1972年 | 1763篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
O. Moze M. Hofmann J. M. Cadogan K. H. J. Buschow D. H. Ryan 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,36(4):511-518
The magnetic structure and ordering temperatures of three intermetallic compounds which crystallize in the tetragonal ThCr2Si2 structure, TbCr2Si2, HoCr2Si2 and ErCr2Si2, have been determined by neutron diffraction, differential scanning calorimetry and magnetization measurements. The Cr-sublattice orders anti-ferromagnetically with Néel temperatures of 758 K for TbCr2Si2, 718 K for HoCr2Si2 and 692 K for ErCr2Si2. Chromium atoms located at 4d crystallographic sites are aligned anti-parallel along the c-axis, with GZCr magnetic modes. In contrast with metallic bcc Cr, the refined room temperature value of the ordered Cr moment is anomalously large for all three compounds. No long range magnetic order of the R sublattice in TbCr2Si2 and HoCr2Si2 is observed, whilst the Er sublattice in ErCr2Si2 orders independently of the Cr sublattice below 2.4 K with moments ferromagnetically aligned in the basal plane.Received: 4 November 2003, Published online: 30 January 2004PACS:
75.25. + z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) - 75.30.Cr Saturation moments and magnetic susceptibilities - 75.50.Ee Antiferromagnetics 相似文献
942.
In this paper an extension of the (r|X
p
)-medianoid on networks introduced by Hakimi (1983) is studied. In this extension the customer considers not only the distance
but some characteristics of the facilities such as store size, quality of service and parking space. A new firm wants to establishr new facilities which have to compete with thep facilities that already exist in the market. The entry firm wants to find their locations and characteristics to maximize
profits. Three different customer choice rules (binary, partially binary and proportional preferences) are considered. Some
discretization results are obtained and a resolution procedure is proposed. The problem is solved combining a global search
algorithm based on a branch and bound procedure with some combinatorial heuristics (greedy, interchange, and tabu search).
Some computational experiences are presented.
Partially supported by Ministerio de Ciencia y Tecnología (Spain) and FEDER, grant BFM2002-04525-C02-01. 相似文献
943.
944.
A. V. Novikov D. N. Lobanov A. N. Yablonsky Yu. N. Drozdov N. V. Vostokov Z. F. Krasilnik 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):467
The dependence of photoluminescence spectra of structures with GeSi/Si(0 0 1) self-assembled nanoislands on growth temperature has been investigated. It was shown that the redshift of the island-related photoluminescence peak with a decrease of the growth temperature is associated with suppression of Si diffusion in the islands and an increase of Ge content in them. For the first time a photoluminescence signal from SiGe islands was observed at energies much lower than the Ge band gap. The energy position of the island-related photoluminescence peak is well described by the model of optical transition, which is indirect in real space. The photoluminescence signal at 1.55 μm from GeSi/Si(0 0 1) self-assembled islands was obtained up to room temperature. 相似文献
945.
In Leitmann (Ref. 1), a coordinate transformation method was introduced to obtain global solutions for free problems in the calculus of variations. This direct method was extended and broadened in Carlson (Ref. 2) and later in Leitmann (Ref. 3). The applicability of the original work of Leitmann (Ref. 1) was further developed in Dockner and Leitmann (Ref. 4) to include the class of open-loop dynamic games. In the present work, we improve the results of Ref. 4 in two directions. First, we enlarge the class of open-loop dynamic games to permit coupling among the dynamic equations via the states of the players; second, we incorporate the modifications given in Refs. 2 and 3. Our results greatly increase the applicability of this method. An example arising from the harvesting of a renewable resource is presented to illustrate the utility of our results. 相似文献
946.
G. Acbas G. B. Kim X. Chen S. Wang M. Cheon C. J. Meining H. Luo B. D. McCombe Y. Sasaki X. Liu J. K. Furdyna 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):382
We have investigated the magnetic and magneto-transport properties of a systematic sequence of five InAs/Mn digital alloys grown by a combination of molecular beam epitaxy and atomic layer epitaxy. The samples consist of 30 periods of Mn fractional monolayers (ML) (0.17–0.5 ML) separated by 14 ML thick InAs spacer layers in a superlattice configuration. Four samples show n-type electrical conduction while the fifth (0.25 ML Mn) is p-type. Squid magnetization measurements performed on these samples show remnant magnetization above room temperature, which is apparently related to a second phase. 相似文献
947.
D. I. T. Fávaro D. Mafra V. A. Maihara L. Cuppari M. B. A. Vasconcellos S. M. F. Cozzolino 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(3):533-536
Having in mind the importance of Fe and Zn content in the diets of nondialyzed patients with chronic renal failure, diets
of 39 patients with ages varying from 18 to 79 years under a conservative treatment were analyzed by INAA. The 24-hour recall
method was used for sample collection. The content of proximate composition was also determined. The average daily dietary
intake was compared to the new recommended values by the Food and Nutrition Board. It was observed that the diets were deficient
for these elements and, therefore, there should be a nutritional follow-up to avoid possible negative effects.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
948.
Adsorption of uranium, as UO2
2+, and thorium, as Th4+, has been studied using a modified fly ash bed. Effects of pH and various ions like La3+, Fe3+, Ce4+, SiO3
2- etc., have been examined. Synthetic mixtures of UO2
2+ and Th4+ in different concentrations were passed through the bed and eluted separately with various selective reagents viz. ammonium carbonate, sodium carbonate and acetic acid-sodium hydroxide buffer. Separations of these elements at ppm level are shown to be very effective. The separation of uranium and thorium in the presence of lanthanides in monazite sand has been studied successfully. In the analysis of monazite sand, the oxalate precipitation has been avoided. The method is simple and of very low cost. The modified fly ash bed can also be used to remove uranium from contaminated water. 相似文献
949.
A. K. Ghosh A. D. Williams J. M. Zucker J. L. Mathews N. Spinhirne 《Experimental Mechanics》2008,48(2):139-152
In nature, shape and structure evolve from the struggle for better performance. Often, biological structures combine multiple
beneficial properties, making research into mimicking them very complex. Presented here is a summary of observations from
a series of experiments performed on a material that closely resembles the human skull bone’s cancellous structure under acoustic
loads. Transmission loss through flat and curved open-cell polyurethane foam samples is observed using air and water as the
two interstitial fluids. Reduction in strength and stiffness caused by porosity can be recovered partially by filling the
interstitial pores with a fluid. The test findings demonstrate the influence of the interstitial fluid on the mechanical characteristics
of a porous structure in a quantitative manner. It is also demonstrated that the transmission loss does not depend only on
the mass per unit area of the structure as predicted by acoustic mass law. Current tests also demonstrate that the transmission
loss is more sensitive to the interstitial fluid than the shape and support conditions of the structures. Test observations
thus support the concepts of “moisture-sensitivity of biological design” and the “law of hierarchy in natural design”. 相似文献
950.
G. N. Kozhemyakin D. V. Lutskiy M. A. Rom P. V. Mateychenko 《Crystallography Reports》2008,53(7):1267-1271
The growth conditions and structural quality of Sb-Bi gradient single crystals with Bi content from 2 to 18 at %, grown by
the Czochralski method with solid phase feed, are investigated. Bi distribution in the crystals along their pulling direction
are studied by electron probe microanalysis and the change in the interplanar spacing is analyzed by double-crystal X-ray
diffraction. It is established that the pulling rate and feed mass affect the Bi distribution in Sb-Bi single crystals. 相似文献