全文获取类型
收费全文 | 346361篇 |
免费 | 4656篇 |
国内免费 | 1249篇 |
专业分类
化学 | 188481篇 |
晶体学 | 4620篇 |
力学 | 13917篇 |
综合类 | 12篇 |
数学 | 41716篇 |
物理学 | 103520篇 |
出版年
2020年 | 2401篇 |
2019年 | 2284篇 |
2018年 | 2389篇 |
2017年 | 2306篇 |
2016年 | 4730篇 |
2015年 | 3859篇 |
2014年 | 5125篇 |
2013年 | 15475篇 |
2012年 | 12091篇 |
2011年 | 14815篇 |
2010年 | 9265篇 |
2009年 | 9143篇 |
2008年 | 13697篇 |
2007年 | 13830篇 |
2006年 | 13445篇 |
2005年 | 12263篇 |
2004年 | 11002篇 |
2003年 | 9641篇 |
2002年 | 9398篇 |
2001年 | 10719篇 |
2000年 | 8272篇 |
1999年 | 6510篇 |
1998年 | 5264篇 |
1997年 | 5096篇 |
1996年 | 5220篇 |
1995年 | 4794篇 |
1994年 | 4577篇 |
1993年 | 4406篇 |
1992年 | 4960篇 |
1991年 | 4641篇 |
1990年 | 4359篇 |
1989年 | 4153篇 |
1988年 | 4411篇 |
1987年 | 4116篇 |
1986年 | 3956篇 |
1985年 | 5738篇 |
1984年 | 5785篇 |
1983年 | 4716篇 |
1982年 | 5099篇 |
1981年 | 5135篇 |
1980年 | 4898篇 |
1979年 | 5007篇 |
1978年 | 4998篇 |
1977年 | 4973篇 |
1976年 | 4888篇 |
1975年 | 4788篇 |
1974年 | 4643篇 |
1973年 | 4761篇 |
1972年 | 2699篇 |
1971年 | 2031篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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
992.
993.
994.
995.
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
996.
Multistage stochastic programs with continuous underlying distributions involve the obstacle of high-dimensional integrals where the integrands' values again are given by solutions of stochastic programs. A common solution technique consists of discretizing the support of the original distributions leading to scenario trees and corresponding LPs which are – up to a certain size – easy to solve. In order to improve the accuracy of approximation, successive refinements of the support result in rapidly expanding scenario trees and associated LPs. Hence, the solvability of the multistage stochastic program is limited by the numerical solvability of sequences of such expanding LPs. This work describes an algorithmic technique for solving the large-scale LP of refinement ν based on the solutions at the previous ν?1 refinements. Numerical results are presented for practical problem statements within financial applications demonstrating significant speedup (depending on the size of the LP instances). 相似文献
997.
F. Tercero J. A. López Fernández E. García L. de Haro M. C. Carter A. Barcia B. Galocha J. L. Besada 《International Journal of Infrared and Millimeter Waves》2003,24(5):669-681
The Beam Mode Expansion (BME) approach for corrugated conical feed horn plus meniscus lens is presented. This approach is useful for providing the radiation pattern as it propagates through an optical system. A developed theoretical model has been verified measuring near and far field of a built horn and lens. These results have been used for designing the optical system of a Cassegrain antenna at 100GHz using the fundamental Gaussian beam mode (GBM) of the new approach. Multimode analysis has been performed with the pre-designed system in order to test the fundamental GBM results. 相似文献
998.
J. Qing 《Journal of Mathematical Sciences》2004,124(5):5290-5297
In this paper we present our recent work on conformally compact Einstein 4-manifolds. We present our discovery of a conformal compactification by positive eigenfunctions and many interesting consequences of this compactification in the study of topology of conformally compact Einstein 4-manifolds. 相似文献
999.
A method was proposed for the simultaneous determination of trace cadmium and mercury by vapor generation non-dispersive atomic fluorescence spectrometry using an intermittent flow system. The effects of the parameters on the performance were studied systematically. The parameters such as acid concentration of the reaction medium, flow rate of the carrier gas and shield gas, the observation height and the atomizer temperature, etc. which affected the sensitivity, were optimized. Ascorbic acid, cobalt ion and thiourea were used as enhancement reagents or masking agents to enhance the generation efficiency of the volatile species of Cd and Hg. The mechanisms of their effects on vapor generation were investigated. In the presence of thiourea and ascorbic acid, the influences of some coexisting elements on the determination of cadmium and mercury were investigated. The detection limits (3sigma) were 0.010 microg l(-1) for Cd and 0.019 microg l(-1) for Hg, respectively. The relative standard deviations for Cd and Hg at 1.00 microg l(-1) were 2.6% and 0.97% (n = 11), respectively. The proposed method has been satisfactorily applied to the determination of trace cadmium and mercury in Chinese herbal medicine. 相似文献
1000.
The field of medicinal inorganic chemistry is rapidly advancing. In particular organometallic complexes have much potential as therapeutic and diagnostic agents. The carbon‐bound and other ligands allow the thermodynamic and kinetic reactivity of the metal ion to be controlled and also provide a scaffold for functionalization. The establishment of structure–activity relationships and elucidation of the speciation of complexes under conditions relevant to drug testing and formulation are crucial for the further development of promising medicinal applications of organometallic complexes. Specific examples involving the design of ruthenium and osmium arene complexes as anticancer agents are discussed. 相似文献