全文获取类型
收费全文 | 365980篇 |
免费 | 4177篇 |
国内免费 | 1067篇 |
专业分类
化学 | 202663篇 |
晶体学 | 6420篇 |
力学 | 15032篇 |
综合类 | 15篇 |
数学 | 36339篇 |
物理学 | 110755篇 |
出版年
2019年 | 2951篇 |
2018年 | 3361篇 |
2017年 | 3426篇 |
2016年 | 5517篇 |
2015年 | 3706篇 |
2014年 | 5704篇 |
2013年 | 15836篇 |
2012年 | 11130篇 |
2011年 | 13745篇 |
2010年 | 9489篇 |
2009年 | 9396篇 |
2008年 | 12283篇 |
2007年 | 12280篇 |
2006年 | 11662篇 |
2005年 | 10560篇 |
2004年 | 9620篇 |
2003年 | 8746篇 |
2002年 | 8412篇 |
2001年 | 10477篇 |
2000年 | 8026篇 |
1999年 | 6282篇 |
1998年 | 5037篇 |
1997年 | 4980篇 |
1996年 | 4859篇 |
1995年 | 4536篇 |
1994年 | 4335篇 |
1993年 | 4103篇 |
1992年 | 5090篇 |
1991年 | 4906篇 |
1990年 | 4771篇 |
1989年 | 4804篇 |
1988年 | 4774篇 |
1987年 | 4807篇 |
1986年 | 4532篇 |
1985年 | 5983篇 |
1984年 | 6010篇 |
1983年 | 4861篇 |
1982年 | 5136篇 |
1981年 | 5167篇 |
1980年 | 4864篇 |
1979年 | 5260篇 |
1978年 | 5500篇 |
1977年 | 5454篇 |
1976年 | 5240篇 |
1975年 | 4880篇 |
1974年 | 4811篇 |
1973年 | 4793篇 |
1972年 | 3228篇 |
1968年 | 3383篇 |
1967年 | 3460篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
831.
832.
Keka Chakraborty S K Paranjpe V Siruguri O D Jayakumar S K Kulshreshtha 《Pramana》1997,48(6):1115-1122
Neutron diffraction and M?ssbauer measurements have been carried out on the cubic Laves phase intermetallic TbMnFe. The magnetic
moment on the transition metal atom is found to be low, 0.2μ
B, at room temperature. This moment is temperature independent down to 10 K. Magnetic moment on the rare earth atom varies
from 2.5μ
B at 296 K to 7.27μ
B at 10 K. M?ssbauer spectra recorded at 298 K and 78 K have magnetic character but there is a large distribution of hyperfine
field values. Both these features arise due to magnetic frustration created in the sample due to the competing ferro and antiferromagnetic
interactions between the transition metal atoms. 相似文献
833.
This study was undertaken to investigate the sorption behavior of chromium hydroxide sol on silica type adsorbent in aqueous solution. Radioisotopic tracer method was used to assess data. This technique allowed sensitive kinetic and equilibrium measurements in both direction: sorption and desorption, which are strongly dependent on solution conditions, such as pH, ionic strength or the presence of complexing species. Total removal of sol particles could not be achieved, even under the most favorable experimental conditions (acidification). 相似文献
834.
835.
B. Pümpin H. Keller W. Kündig I. M. Savić J. W. Schneider H. Simmler P. Zimmermann E. Kaldis S. Rusiecki C. Rossel 《Hyperfine Interactions》1991,63(1-4):25-31
A systematic μSR study of the local magnetic field distribution in a series of oxygen deficient YBa2Cu3O
x
samples with 6.5⩽x⩽7.0 is reported. Special attention was given to perform the experiments under the same conditions, so that the oxygen content
of the measured samples was the only parameter varied. The behavior of the depolarization rate σ as a function of the oxygen
contentx was found to have strong similarities with the behavior of the critical temperatureT
c
as a function ofx. In particular, two step-like increases of σ were observed abovex=6.7 and 6.9. The temperature dependence of the normalized depolarization rate σ(T)/σ(0) is well described by the two-fluid model forx⩾6.781(1) and clearly deviates from this behavior forx⩽6.704(1). Our results are compared to those obtained by other groups. 相似文献
836.
H. M. Phillips D. L. Callahan R. Sauerbrey G. Szabo Z. Bor 《Applied Physics A: Materials Science & Processing》1992,54(2):158-165
Periodic line structures with a period of 167 nm and linewidths varying from 30 to 100 nm have been produced in polyimide by direct ablation with a KrF laser using an interferometric technique. The characteristics of this interferometer as it applies to the ablation of these line structures, including linewidth and alignment sensitivity, are analyzed. The ability to control the linewidth by varying the average incident fluence is described theoretically and demonstrated experimentally. This externally generated period of 167 nm also prevents the spontaneous growth of laser induced periodic surface structures (LIPSS). 相似文献
837.
The equations describing the behaviour of temperature/flow microsensorsemploy-ing polysilicon thermistors form a degenerate nonlinearparabolic system. One special feature is that different equationsof this system are to be satisfied on different domains. Bymeans of supersolutions and subsolutions, the maximum principle,and fixed point arguments, the authors show the existence ofsolutions to the equations. 相似文献
838.
R. P. Spielmann Jin Zhen H. J. Triebel V. Nicolas M. Heller E. Bü cheler 《Magnetic resonance imaging》1992,10(6):893-901
To correlate the appearance of poststenotic jets on gradient echo images with features of localized Doppler spectra of the jets, we studied an in vitro model of steady flow-through stenoses of 86, 96, and 99% area reduction. As fluids, water and a 40% glycerol solution in water were used. MRI was performed with a 1.5 T whole body imager and gradient echo images were obtained in planes parallel to the direction of flow. Doppler spectra were acquired separately from the MR measurements at 1 cm intervals for a distance of 10 cm downstream from the stenosis. Poststenotic signal void was observed for water and for the 40% glycerol solution only if the mean velocity within the stenosis exceeded a limit of 50–60 cm/sec. On the MR images, the jets could be divided into two segments: A proximal jet segment of uniform width equal to the diameter of the stenosis, followed by a distal jet segment which was characterized by broadening and then dissipating signal void. Except for the 99% stenosis, a high signal intensity core was present within the proximal jet segment. In the proximal jet segment, the Doppler measurements showed a low temporal fluctuation of the maximal flow velocity and only little flow opposite to the main flow direction. In the distal jet segment, the velocity fluctuation and the intensity of reverse flow increased sharply. The high signal intensity core of the jet was associated with a poststenotic zone of constant maximal flow velocity. The results demonstrate a close relationship between characteristic features of poststenotic jets in MRI and pulsed Doppler sonography. 相似文献
839.
840.