全文获取类型
收费全文 | 782篇 |
免费 | 17篇 |
专业分类
化学 | 389篇 |
晶体学 | 6篇 |
力学 | 6篇 |
数学 | 51篇 |
物理学 | 347篇 |
出版年
2021年 | 9篇 |
2019年 | 6篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 6篇 |
2013年 | 38篇 |
2012年 | 27篇 |
2011年 | 39篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 24篇 |
2007年 | 25篇 |
2006年 | 20篇 |
2005年 | 38篇 |
2004年 | 32篇 |
2003年 | 36篇 |
2002年 | 16篇 |
2001年 | 19篇 |
2000年 | 25篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 22篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 19篇 |
1984年 | 6篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 18篇 |
1973年 | 9篇 |
1972年 | 13篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1969年 | 11篇 |
1968年 | 7篇 |
1966年 | 8篇 |
排序方式: 共有799条查询结果,搜索用时 15 毫秒
61.
A.A. Gorbunov R. Friedlein O. Jost M.S. Golden J. Fink W. Pompe 《Applied Physics A: Materials Science & Processing》1999,69(7):S593-S596
The abundance of carbon single-wall nanotubes (SWNTs) in soot synthesized by pulsed laser evaporation of graphite is studied over a wide range of synthesis conditions. The derived SWNT growth time-scale appears to be much longer than any characteristic time-scale in a simplified model of the relaxation of a high-pressure hot condensing gas bubble in a background atmosphere. It is concluded that SWNT nucleation and growth take place in relaxed, condensed, thermalized evaporation products at an optimal temperature between 850-1250 °C at a rate of few 7m length per second, which is consistent with a condensed state "precipitation" mechanism for the SWNT formation. 相似文献
62.
63.
64.
65.
With calibrated Ge(Li) detectors, γ-γ coincidences have been observed in the decay of249Cf. The total conversion coefficient of the 54.7 and 66.7 keV transitions in the first rotational band have been determined to be 237±30 and 69±15, respectively. The branching ratio of the 121.5keV crossover transition is (22±7)%. The errors are the 2σ statistical uncertainties, linearily added to the errors in the detector efficiencies. 相似文献
66.
67.
Sinkus R Tanter M Xydeas T Catheline S Bercoff J Fink M 《Magnetic resonance imaging》2005,23(2):159-165
Elastography is a technique to assess the viscoelastic properties of tissue by measuring an acoustic wave propagating though the object. Here, the technique is applied in the course of standard MR mammography to 15 patients with different pathologies (six breast cancer cases, six fibroadenoma cases and three mastopathy cases). Low-frequency mechanical waves are coupled longitudinally into the tissue in order to obtain sufficient wave amplitude throughout the entire breast. This leads to the presence of a substantial fraction of compressional waves, which contribute to the total displacement field. It is shown theoretically that the correct evaluation of these contributions from the compressional wave is rather difficult due to the almost incompressible nature of tissue. To overcome this problem, it is proposed to apply the curl-operator to the measured displacement field in order to completely remove contributions from the compressional wave. Results from simulations and a breast phantom demonstrate the feasibility of the technique. The in vivo results show a good separation between breast cancer and benign fibroadenoma utilizing the shear modulus. Breast cancer appears on average 2.2 (P<.001) times stiffer. All breast cancer cases showed a good delineation to the surrounding breast tissue with an average elevation of a factor of 3.3 (P< 1.4 x 10(-6)). The results as obtained for the shear viscosity do not indicate to be useful for separating benign from malignant lesions. 相似文献
68.
Amoureux JP Delevoye L Fink G Taulelle F Flambard A Montagne L 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,175(2):285-299
Gan and Kwak recently introduced two new tools for high-resolution 2D NMR methods applied to quadrupolar nuclei: double-quantum filtering in STMAS (DQF-STMAS) and the soft-pulse added mixing (SPAM) idea. Double-quantum filtering suppresses all undesired signals in the STMAS method with limited loss in sensitivity. With SPAM, all pathways are added constructively after the second hard-pulse instead of using a single pathway as previously. Here, the sensitivity, advantages and drawbacks of DQF-STMAS are compared to 3QMAS. Additionally, SPAM can be included into DQF-STMAS method, resulting in a net sensitivity gain with respect to 3QMAS of ca. 10-15. 相似文献
69.
Virtually all electromagnetic waveguiding structures support a multiplicity of modes. Nevertheless, to date, an experimental method for unique decomposition of the fields in terms of the component eigenmodes has not been realized. The fundamental problem is that all current attempts of modal decomposition do not yield phase information. Here we introduce a noninterferometric approach to achieve modal decomposition of the fields at the output of a general waveguiding structure. The technique utilizes a mapping of the two-dimensional field distribution onto the one-dimensional space of waveguide eigenmodes, together with a phase-retrieval algorithm to extract the amplitudes and phases of all the guided vectorial modes. Experimental validation is provided by using this approach to examine the interactions of 16 modes in a hollow-core photonic-band gap fiber. 相似文献
70.
Folegot T de Rosny J Prada C Fink M 《The Journal of the Acoustical Society of America》2005,117(6):3757-3765
Time reversal arrays are becoming common tools whether for detection or tomography. These applications require the measurement of the response from the array to one or several receivers. The most natural way to record the impulse responses for several sources is to generate pulses successively from each emitting point and record simultaneously the signals from the receivers. However, this method is very time consuming or inefficient in terms of signal-to-noise ratio. To overcome this limitation quasi-orthogonal pseudonoise signals like Kasami sequences can be used. For guided wave propagation, a very high degree of orthogonality between the signal is necessary to allow an accurate measure of the whole multipath structure of the transfer function. Hence, in this work, we propose a new family of pseudo-orthogonal signals that is adapted to the environment and more specifically, to highly dispersive media. These adaptive instant records signals are used experimentally to detect targets using the time reversal operator decomposition method. The accuracy of the 15 x 15 transfer functions acquired simultaneously, and therefore the detection capability, are demonstrated in an experimental ultrasonic waveguide as a small-scale model of shallow water propagation including bottom absorption and reverberation. 相似文献