全文获取类型
收费全文 | 988篇 |
免费 | 35篇 |
国内免费 | 27篇 |
专业分类
化学 | 536篇 |
晶体学 | 10篇 |
力学 | 23篇 |
数学 | 107篇 |
物理学 | 374篇 |
出版年
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 74篇 |
2012年 | 42篇 |
2011年 | 49篇 |
2010年 | 27篇 |
2009年 | 18篇 |
2008年 | 51篇 |
2007年 | 35篇 |
2006年 | 46篇 |
2005年 | 41篇 |
2004年 | 45篇 |
2003年 | 41篇 |
2002年 | 51篇 |
2001年 | 34篇 |
2000年 | 35篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 24篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1973年 | 9篇 |
1972年 | 6篇 |
排序方式: 共有1050条查询结果,搜索用时 15 毫秒
981.
J. Carter A. A. Cowley H. Diesener R. W. Fearick S. V. Frtsch M. N. Harakeh J. J. Lawrie S. J. Mills P. von Neumann-Cosel R. T. Newman J. V. Pilcher A. Richter K. Schweda F. D. Smit G. F. Steyn S. Strauch D. M. Whittal 《Nuclear Physics A》1998,630(3-4)
The 40Ca(p,p′ α) reaction has been studied at an incident proton energy Ep = 99.5 MeV for proton laboratory scattering angles Θplab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θα 0° − 180° relative to the recoil axis. A multipole decomposition for the α0-decay channel to the 36Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range Ex = 11–21 MeV agrees reasonably well with the results from electron and α-induced α0-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α0) reaction. However, this value is twice what is found in the (e,e′ α0) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved. 相似文献
982.
983.
Phase shift solutions are presented at pion kinetic energies from 88 to 292 MeV where new measurements of the differential elastic cross section are available, and at 310 MeV. The resulting phase shifts are fitted to effective-range formulae. The resonant P33 phase shift is allowed to take different values for π+p and π?p scattering. There are differences in mass and width between these charge states of the resonance of M0 ? M++ = 1.4 ± 0.4 MeV/c2 and Γ0 ? Γ++ = 10.3 ± 1.3 MeV/c2. The difference in width can be accounted for largely but not entirely by the Coulomb barrier, the channel π?p → γn, and the difference in phase space between π?p → π0n and π+p → π+p. 相似文献
984.
A vanadium-catalyzed method for the oxidation of prochiral aryl, allylic selenides with tandem [2,3] sigmatropic rearrangement has been developed. This protocol has been screened on a series of substrates to test for its generality and effectiveness. The applicability of this methodology to the synthesis of enantiomerically enriched allylic alcohols has been studied on a series of chiral oxazole-containing systems with a diastereomeric ratio (d.r.) of up to 85 : 15. The chiral transfer observed in the allyl alcohol products is the result of a net 1,9- and/or 1,10-induction. Finally, the first example of a selenium-oxygen nonbonding interaction in oxazole-containing selenide appears to have been observed via X-ray crystal analysis. 相似文献
985.
Haiyin He Ting-Zhong Wang Xidong Feng Joseph S Ashcroft Guy T Carter 《Tetrahedron letters》2004,45(30):5889-5893
In structure-activity relationship (SAR) studies on mannopeptimycin antibiotics, mannopeptimycin α(1) was acetalized by reacting with certain dialkyl acetals under acidic conditions. The major products of these reactions were determined to be cyclic acetals at the 4,6-positions of the terminal mannose (Man-B), by exemplary spectroscopic analyses of two typical acetalization products 2 and 3. 相似文献
986.
S. J. S. Lister F. M. Grosche F. V. Carter R. K. W. Haselwimmer S. S. Saxena N. D. Mathur S. R. Julian G. G. Lonzarich 《Zeitschrift für Physik B Condensed Matter》1996,103(2):263-265
We have explored the vicinity of the antiferromagnetic quantum critical point in the related heavy fermion metals CePd2Si2 and CeNi2Ge2 as a function of hydrostatic pressure. The normal state resistivity of the antiferromagnet CePd2Si2 near the critical pressure, at which magnetic order disappears, varies as ρ ~ Tχ(1:1 < χ < 1:4) over nearly two orders of magnitude in temperature up to about 30 K. This anomalous form for the resistivity appears to defy not only Fermi-liquid theory, but also simple phenomenological models for the effect of spin fluctuations close to a quantum critical point. An analogous unconventional behaviour is observed in the ambient pressure resistivity of the electronically and structurally equivalent, non-magnetic metal CeNi2Ge2. At pressures above 15 kbar, a new and unexpected superconducting transition appears in CeNi2Ge2 below 220 mK, which rises to higher temperatures with increasing pressure, reaching 400 mK at 26 kbar. 相似文献
987.
J. Scott Carter Daniel Jelsovsky Seiichi Kamada Laurel Langford Masahico Saito 《Transactions of the American Mathematical Society》2003,355(10):3947-3989
The 2-twist spun trefoil is an example of a sphere that is knotted in 4-dimensional space. A proof is given in this paper that this sphere is distinct from the same sphere with its orientation reversed. Our proof is based on a state-sum invariant for knotted surfaces developed via a cohomology theory of racks and quandles (also known as distributive groupoids).
A quandle is a set with a binary operation -- the axioms of which model the Reidemeister moves in classical knot theory. Colorings of diagrams of knotted curves and surfaces by quandle elements, together with cocycles of quandles, are used to define state-sum invariants for knotted circles in -space and knotted surfaces in -space.
Cohomology groups of various quandles are computed herein and applied to the study of the state-sum invariants. Non-triviality of the invariants is proved for a variety of knots and links, and conversely, knot invariants are used to prove non-triviality of cohomology for a variety of quandles.
988.
Aitala EM Amato S Anjos JC Appel JA Ashery D Banerjee S Bediaga I Blaylock G Bracker SB Burchat PR Burnstein RA Carter T Carvalho HS Copty NK Cremaldi LM Darling C Denisenko K Devmal S Fernandez A Fox GF Gagnon P Gobel C Gounder K Halling AM Herrera G Hurvits G James C Kasper PA Kwan S Langs DC Leslie J Lundberg B Magnin J Massafferri A MayTal-Beck S Meadows B de Mello Neto JR Mihalcea D Milburn RH de Miranda JM Napier A Nguyen A d'Oliveira AB O'Shaughnessy K Peng KC Perera LP Purohit MV 《Physical review letters》2001,86(5):765-769
From a sample of 848+/-44 D(+)(s)-->pi(-)pi(+)pi(+) decays, we find gamma(D(+)(s)-->pi(-)pi(+)pi(+))/gamma(D(+)(s)-->straight phipi(+)) = 0.245+/-0.028(+0.019)(-0.012). Using a Dalitz plot analysis of this three body decay, we find significant contributions from the channels rho(0)(770)pi(+), rho(0)(1450)pi(+), f(0)(980)pi(+), f(2)(1270)pi(+), and f(0)(1370)pi(+). We also present the values obtained for masses and widths of the resonances f(0)(980) and f(0)(1370). 相似文献
989.
We report a polarization-maintaining double-clad Yb-doped fiber amplifier employing bow-tie fiber. Borosilicate stress elements were incorporated into the inner cladding of the fiber, yielding a beat length of 5.1 mm at 633 nm. When the fiber was pumped at 975 nm and seeded with linearly polarized light, the polarization extinction ratio was >15 dB , independent of pump power, and the output power was as high as 3.5 W. 相似文献
990.
An electron detector system with a 3 mm × 100 mm2 Si(Li) detector with a cooled FET and vacuum air lock for changing sources was constructed. The absolute efficiency was measured as a function of energy for use in the measurement ofK conversion coefficients. With the Si(Li) and a Ge(Li) detector, theK conversion coefficient of the 320 keV transition in51V was measured to be 0.00156 ± 0.00008 where theK conversion coefficients of the 661 and 279 keV transitions in137Ba and203Tl were used as standards. From absolute detection efficiency measurements, theK conversion coefficients of the 388 and 483 keV transitions in87Sr were measured to be 0.16 ± 0.02 and 0.0024 ± 0.0003, respectively. 相似文献