全文获取类型
收费全文 | 202448篇 |
免费 | 2216篇 |
国内免费 | 505篇 |
专业分类
化学 | 110794篇 |
晶体学 | 3657篇 |
力学 | 8006篇 |
综合类 | 11篇 |
数学 | 19271篇 |
物理学 | 63430篇 |
出版年
2020年 | 1728篇 |
2019年 | 1926篇 |
2018年 | 2244篇 |
2017年 | 2359篇 |
2016年 | 3520篇 |
2015年 | 2196篇 |
2014年 | 3560篇 |
2013年 | 9092篇 |
2012年 | 6531篇 |
2011年 | 8038篇 |
2010年 | 5705篇 |
2009年 | 5671篇 |
2008年 | 7169篇 |
2007年 | 7093篇 |
2006年 | 6731篇 |
2005年 | 6076篇 |
2004年 | 5527篇 |
2003年 | 5109篇 |
2002年 | 4885篇 |
2001年 | 6150篇 |
2000年 | 4636篇 |
1999年 | 3525篇 |
1998年 | 2747篇 |
1997年 | 2704篇 |
1996年 | 2598篇 |
1995年 | 2447篇 |
1994年 | 2334篇 |
1993年 | 2166篇 |
1992年 | 2831篇 |
1991年 | 2732篇 |
1990年 | 2674篇 |
1989年 | 2691篇 |
1988年 | 2713篇 |
1987年 | 2724篇 |
1986年 | 2593篇 |
1985年 | 3306篇 |
1984年 | 3317篇 |
1983年 | 2604篇 |
1982年 | 2713篇 |
1981年 | 2767篇 |
1980年 | 2541篇 |
1979年 | 2882篇 |
1978年 | 2863篇 |
1977年 | 2984篇 |
1976年 | 2817篇 |
1975年 | 2559篇 |
1974年 | 2512篇 |
1973年 | 2467篇 |
1972年 | 1703篇 |
1968年 | 1703篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Ivanova N. I. Gusarova N. K. Reutskaya A. M. Shaikhutdinova S. I. Arbuzova S. N. Trofimov B. A. 《Russian Journal of General Chemistry》2003,73(6):877-879
Symmetrical and unsymmetrical tertiary phosphine oxides containing benzyl and 5-chloro-2-thienyl radicals stereoselectively react with benzaldehyde in the sodium amide-THF system to form the E isomers of 1-organyl-2-phenylethene and diorganylphosphinic acids in high yields. Triethyl, tris(2-phenyl- ethyl)-, and tris[(4-methoxyphenyl)methyl]phosphine oxides under the above-mentioned conditions do not react with benzaldehyde. 相似文献
902.
Delauré B. Beck M. Golovko V. V. Kozlov V. Phalet T. Schuurmans P. Severijns N. Vereecke B. Versyck S. Beck D. Quint W. Ames F. Reisinger K. Forstner O. Deutsch J. Bollen G. Schwarz S. 《Hyperfine Interactions》2003,150(1-4):91-105
We present data from three seasons of experimental field work designed to recreate ancient Andean coastal ceramic firing techniques. Based on the recent discovery of two different archaeological ceramic production sites in the La Leche river valley of northern coastal Peru, the opportunity arose to apply Mössbauer spectroscopy and other analytical methods to reconstruct ancient firing procedures. Two sets of firings took place in 1993 and 1997 in Batán Grande using a partially restored Formative kiln from about 800 BC, local hardwood and cow dung as fuel. A third experiment followed in 2000 after the discovery of a Middle Sicán ceramics workshop in use between ca. AD 950 and 1050 at Huaca Sialupe, where an exact replica of an ancient kiln was built from local clay, and fired with local wood and cow dung. Additionally, inverted urns found at Huaca Sialupe were tested for their potential use as furnaces for metal working. Mössbauer spectroscopy was used to compare the physical and chemical state of specimens produced in the field experiments with ancient ceramics and with specimens produced in controlled laboratory experiments. 相似文献
903.
Synthesis of 1,3-Bis(trialkylammonio)-2-propanol Dihalides Exhibiting Retardant Activity toward Rape
Merkis A. I. Novickiene L. L. Daukšas V. K. Šaltite Z. A. Miliuviene L. I. Gaveliene V. A. 《Russian Journal of Applied Chemistry》2003,76(1):160-161
1,3-Bis(trialkylammonio)-2-propanol dihalides were prepared, and their retardant activity was studied in relation to the chemical structure. 相似文献
904.
V. V. Kuznetsov Yu. V. Ermolenko A. Ya. Zheltov K. A. Kornev S. V. Sheremet'ev 《Journal of Analytical Chemistry》2004,59(1):17-22
The coprecipitation of azo compounds based on 4-nitrophenyl- and 4-sulfophenyldiazonium naphthol sulfonates as their diphenylguanidinium ion-pair complexes with analogous compounds of naphthalene-2-sulfonic acid and 4-phenylsulfodiazonium is investigated. The optimization of the coprecipitation is considered based on the notions of the driving force of the cocrystallization of impurities. The optical characteristics of colored ion-pair complexes are measured. It is found that the water solubility is decreased most substantially for azosulfonates with hydrophobic nitro groups and with no more than two sulfo groups in different aromatic nuclei, which can lead to a decrease in the detection limit due to preconcentration by coprecipitation, which stimulates the thermodynamic flux of concentrate elution. Coprecipitation is combined with flow-injection analysis in the on-line mode, and new procedures are developed for determining naphthol sulfonates and related azo compounds with the detection limit equal to 0.003–0.006 mg/50 mL. 相似文献
905.
The processes occurring in expanding laser-produced antimony plasma are investigated by the emission spectroscopy method.
The plasma expansion velocity, the recombination time of SbII, and the electron temperature and density are determined from
the dynamics of SbI line emission. Based on the results obtained, the processes occurring during the formation and expansion
of laser-produced antimony plasma are qualitatively analyzed. 相似文献
906.
Classical electrodynamics based on the Maxwell–Born–Infeld field equations coupled with a Hamilton–Jacobi law of point charge motion is partially quantized. The Hamilton–Jacobi phase function is supplemented by a dynamical amplitude field on configuration space. Both together combine into a single complex wave function satisfying a relativistic Klein–Gordon equation that is self-consistently coupled to the evolution equations for the point charges and the electromagnetic fields. Radiation-free stationary states exist. The hydrogen spectrum is discussed in some detail. Upper bounds for Born's “aether constant” are obtained. In the limit of small velocities of and negligible radiation from the point charges, the model reduces to Schrödinger's equation with Coulomb Hamiltonian, coupled with the de Broglie–Bohm guiding equation. 相似文献
907.
A. M. Elaiw K. Kiss M. A. L. Caetano 《Journal of Applied Mathematics and Computing》2005,18(1-2):95-112
This work concerns the stabilization of uninfected steady state of an ordinary differential equation system modeling the interaction of the HIV virus and the immune system of the human body. The control variable is the drug dose, which, in turn, affects the rate of infection of CD4+ T cells by HIV virus. The feedback controller is constructed by a variant of the receding horizon control (RHC) method. Simulation results are discussed. 相似文献
908.
K. Vinay Kumar Reddy B. Sreenivasa Reddy M. Sreenath Reddy Ch. Gopal Reddy P. Yadagiri Reddy K. Rama Reddy 《Radiation measurements》2003,36(1-6):419-423
Studies conducted by Atomic Minerals Directorate of Exploration and Research (AMD) of Hyderabad, India had established the presence of higher concentrations of uranium in Lambapur and Peddagattu areas of Nalgonda district, AP, India and it was estimated that it could be a viable source for commercial extraction. The envisaged extraction process involves dispersion of radioactive particulate matter into atmosphere. Environmental radioactive studies in and around proposed mining areas at this point of time will be extremely useful for establishing base line data before a large scale uranium extraction process comes into existence. To this end, Solid State Nuclear Track Detectors were installed to evaluate indoor radon and thoron concentration levels in the dwellings of the area. The geometric means of radon and thoron concentration levels were found to be (7.1±0.2)×101 and (6.7±0.3)×101 Bq/m3, respectively. Simultaneously, natural background radiation measurements were also made and these levels are found to vary from 770 to 3995 μGy/y in the spatial distribution. 相似文献
909.
Annihilation of positrons in hydrogen-saturated titanium 总被引:1,自引:0,他引:1
K. P. Aref’ev O. V. Boev O. N. Imas A. M. Lider A. S. Surkov I. P. Chernov 《Physics of the Solid State》2003,45(1):1-5
The effect of atomic hydrogen on the electronic structure of α-titanium samples is studied using the electron-positron annihilation methods. It is shown that different states of hydrogen atoms are manifested in different ways in the positron lifetime distribution spectrum. The results of theoretical calculations of the first component of the positron lifetime are in accord with the obtained experimental data. 相似文献
910.
Vladimir B. Arion Alexey A. Nazarov Christian G. Hartinger Gerald Giester Bernhard K. Keppler 《应用有机金属化学》2003,17(9):723-724
For the unsymmetrical title compound, 1‐bromo‐1′‐[(2S)‐N‐(1‐hydroxy‐3‐methylbutane‐2‐yl)]‐ferroceneamide, two independent molecules were found in the asymmetric unit. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献