全文获取类型
收费全文 | 355860篇 |
免费 | 2391篇 |
国内免费 | 638篇 |
专业分类
化学 | 170189篇 |
晶体学 | 5410篇 |
力学 | 18520篇 |
综合类 | 9篇 |
数学 | 52546篇 |
物理学 | 112215篇 |
出版年
2019年 | 2291篇 |
2018年 | 11088篇 |
2017年 | 11869篇 |
2016年 | 8210篇 |
2015年 | 3411篇 |
2014年 | 4386篇 |
2013年 | 10777篇 |
2012年 | 12034篇 |
2011年 | 21168篇 |
2010年 | 13569篇 |
2009年 | 13464篇 |
2008年 | 18860篇 |
2007年 | 22219篇 |
2006年 | 9055篇 |
2005年 | 13927篇 |
2004年 | 10448篇 |
2003年 | 9878篇 |
2002年 | 7943篇 |
2001年 | 7474篇 |
2000年 | 5963篇 |
1999年 | 4396篇 |
1998年 | 3897篇 |
1997年 | 3861篇 |
1996年 | 3754篇 |
1995年 | 3434篇 |
1994年 | 3580篇 |
1993年 | 3265篇 |
1992年 | 3731篇 |
1991年 | 3735篇 |
1990年 | 3672篇 |
1989年 | 3541篇 |
1988年 | 3654篇 |
1987年 | 3543篇 |
1986年 | 3359篇 |
1985年 | 4444篇 |
1984年 | 4730篇 |
1983年 | 3959篇 |
1982年 | 4092篇 |
1981年 | 4017篇 |
1980年 | 3990篇 |
1979年 | 3975篇 |
1978年 | 4293篇 |
1977年 | 4140篇 |
1976年 | 4229篇 |
1975年 | 3897篇 |
1974年 | 3938篇 |
1973年 | 4127篇 |
1972年 | 2883篇 |
1971年 | 2399篇 |
1970年 | 2205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
M. G. Voronkov E. A. Grebneva O. M. Trofimova A. I. Albanov N. F. Chernov N. N. Chipanina 《Russian Journal of General Chemistry》2006,76(12):1851-1853
Reaction of tetrafluorosilane with tris(2-hydroxyethyl)-and tris(2-trimethylsiloxyethyl)amine results in formation of 1-fluorosilatrane and fluorosilatrane in 75 and 53% yield, respectively. Reaction of tetrafluorosilane with bis(2-trimethylsiloxyethyl)amine and its N-methyl derivative leads to the hitherto unknown 1,1-difluoroquasisilatranes (N → Si) F2Si(OCH2CH2)2NR (R = H, Me) containing donor-acceptor bond N → Si and pentacoordinate silicon atom. The structure of the synthesized compounds was proved by 1H, 13C, 15N, 19F, 29Si NMR and IR spectroscopy. 相似文献
982.
983.
984.
985.
G. McCartor 《Zeitschrift fur Physik C Particles and Fields》1987,36(2):329-336
A method of performing perturbation calculations for infrared divergent problems is formulated for problems in quantum field theory and is illustrated by applying it to the Schwinger Model and to QCD in 1+1 dimensions. 相似文献
986.
E. Mathieu Y. Foucher P. Dellamonica J. P. Daures 《Methodology and Computing in Applied Probability》2007,9(3):389-397
In AIDS control, physicians have a growing need to use pragmatically useful and interpretable tools in their daily medical
taking care of patients. Semi-Markov process seems to be well adapted to model the evolution of HIV-1 infected patients. In
this study, we introduce and define a non homogeneous semi-Markov (NHSM) model in continuous time. Then the problem of finding
the equations that describe the biological evolution of patient is studied and the interval transition probabilities are computed.
A parametric approach is used and the maximum likelihood estimators of the process are given. A Monte Carlo algorithm is presented
for realizing non homogeneous semi-Markov trajectories. As results, interval transition probabilities are computed for distinct
times and follow-up has an impact on the evolution of patients.
相似文献
987.
T. Hansel J. Müller C. Falldorf C. von Kopylow W. Jüptner R. Grunwald G. Steinmeyer U. Griebner 《Applied physics. B, Lasers and optics》2007,89(4):513-516
Digital holographic shape measurements using femtosecond laser pulses are reported. For contouring of very fast moving objects,
the simultaneous generation of at least two spectrally separated ultrashort pulses is required. To deliver this particular
spectral signature at high pulse energies, a chirped-pulse Ti:sapphire laser amplifier was modified to emit two spectrally
separated pulses with energies above 1 μJ each. The wavelength separation of these pulses was adjustable within the 50 nm
gain bandwidth, cutting out two distinct wavelength peaks by a variable double-slit assembly in a prism sequence. A Michelson-type
interferometer was employed to perform the two-wavelength contouring. The phases of the holograms and the phase differences
are calculated numerically, which allow us to deduce the contour lines of the topology of the object. The suitability of the
light source for digital holography is demonstrated with contouring of stationary objects and the potential for high-speed
applications is indicated.
PACS 42.40.-i; 42.60.By 相似文献
988.
A. M. Kharitonov 《Thermophysics and Aeromechanics》2007,14(1):3-11
Sergey Alekseevich Khristianovich is one of the famous Russian mechanical engineers of the 20th century together with N.E.
Zhukovsky, S.A. Chaplygin, N.E. Kochin, and others. He made an immense contribution to some aspects of mechanics, such as
aerogasdynamics, rock mechanics, theory of plasticity, filtration theory, and environmental power engineering. All this was
preceded by a long, hard, and fruitful life full of outstanding events. 相似文献
989.
A. I. Fedoseev S. G. Lushnikov S. N. Gvasaliya S. Kojima 《Physics of the Solid State》2006,48(6):1102-1105
The behavior of acoustic phonons in crystals of a relaxor ferroelectric, namely, the lead scandium tantalate PbSc1/2Ta1/2O3 (PST), is studied in the vicinity of the diffuse phase transition. The behavior of longitudinal and transverse acoustic phonons in a PST single crystal is examined using Brillouin scattering. The phonon subsystem is found to behave anomalously in the vicinity of T = 297 K, which can probably be assigned to the existence of a phase transition. Analysis of the results obtained yields the values of the elastic moduli C11, C12, and C44 for the cubic phase of the crystal over a wide temperature range. 相似文献
990.
The atomic structure and magnetic and electric properties of the Cr0.5TiSe2-Cr0.5TiTe2 system of intercalated phases were studied in detail by gradually replacing selenium by tellurium. It was revealed that this replacement changes the crystalline structure from monoclinic in the initial compounds to hexagonal in the compounds containing various types of chalcogen atoms; this is accompanied by disordering of chromium atoms in the van der Waals gaps. The electrical resistance and magnetic characteristics vary nonmonotonically on replacement of selenium by tellurium, which is associated with a change in the degree of atomic disordering during the transition from Cr0.5TiSe2 to Cr0.5TiTe2. 相似文献