全文获取类型
收费全文 | 675856篇 |
免费 | 6773篇 |
国内免费 | 2520篇 |
专业分类
化学 | 350621篇 |
晶体学 | 9542篇 |
力学 | 32321篇 |
综合类 | 78篇 |
数学 | 89561篇 |
物理学 | 203026篇 |
出版年
2021年 | 6003篇 |
2020年 | 6664篇 |
2019年 | 7401篇 |
2018年 | 9881篇 |
2017年 | 9961篇 |
2016年 | 14106篇 |
2015年 | 8100篇 |
2014年 | 12871篇 |
2013年 | 29968篇 |
2012年 | 23911篇 |
2011年 | 28436篇 |
2010年 | 20900篇 |
2009年 | 20596篇 |
2008年 | 26752篇 |
2007年 | 26623篇 |
2006年 | 24441篇 |
2005年 | 21958篇 |
2004年 | 20117篇 |
2003年 | 17921篇 |
2002年 | 17781篇 |
2001年 | 18773篇 |
2000年 | 14548篇 |
1999年 | 11166篇 |
1998年 | 9596篇 |
1997年 | 9426篇 |
1996年 | 8965篇 |
1995年 | 8040篇 |
1994年 | 8113篇 |
1993年 | 7777篇 |
1992年 | 8316篇 |
1991年 | 8704篇 |
1990年 | 8276篇 |
1989年 | 8138篇 |
1988年 | 7923篇 |
1987年 | 7633篇 |
1986年 | 7397篇 |
1985年 | 9600篇 |
1984年 | 9968篇 |
1983年 | 8360篇 |
1982年 | 8771篇 |
1981年 | 8217篇 |
1980年 | 7788篇 |
1979年 | 8301篇 |
1978年 | 8675篇 |
1977年 | 8580篇 |
1976年 | 8569篇 |
1975年 | 8115篇 |
1974年 | 8019篇 |
1973年 | 8347篇 |
1972年 | 6177篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
By optimizing pump power ratio between 1st order backward pump and 2nd order forward pump on discrete Raman amplifier, we demonstrated over 2dB noise figure improvement without excessive non-linearity degradation. 相似文献
992.
L. G. Lumbreras R. Gebhard W. Häusler F. Kauffmann-Doig J. Riederer G. Sieben U. Wagner 《Hyperfine Interactions》2003,150(1-4):51-72
Ceramic finds from the Galería de las Ofrendas at Chavín de Huántar and surface finds from the settlement of Chavín were characterised by combining the results of archaeological typology with archaeometric studies using neutron activation analysis, Mössbauer spectroscopy, X-ray diffraction and thin-section microscopy. Sherds from the pyramid Tello are included in the study as representative of local material. The analyses show that the vessels were made from different raw materials and that different firing procedures were used in their production. Sherds of certain styles largely exhibit similar types of Mössbauer patterns and in many instances also have similar element compositions. This supports the archaeological notion that the vessels were brought to Chavín from the provinces, perhaps on the occasion of a festivity. 相似文献
993.
In a Young–Michelson tandem interferometer a Michelson interferometer is illuminated through a pair of Young slits. The pattern produced by this set-up is analyzed theoretically. The consequences of small misalignments and uncompensated arms in the Michelson interferometer are studied. The effects of the spatial and temporal partial coherence of the source are also explored. Experimental results using a laser source are shown to be in good agreement with the predicted theoretical calculations. 相似文献
994.
Glezer A.M. Blinova E.N. Pozdnyakov V.A. Shelyakov A.V. 《Journal of nanoparticle research》2003,5(5-6):551-560
Journal of Nanoparticle Research - It was shown that the thermoelastic martensite transformation B2 ? B19 inside nanoparticles surrounded by amorphous matrix in Ni–Ti–Cu alloys as... 相似文献
995.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献
996.
The ALEPH Collaboration A. Heister et al. 《The European Physical Journal C - Particles and Fields》2003,29(2):143-170
An improved search for B
s
0 oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three
analyses based on complementary event selections are presented. First, decays of B
s
0 mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with
excellent decay length and momentum resolution and hi gh average B
s
0 purity. Semileptonic decays with a reconstructed
D
s
- meson provide a second sample with larger statistics, high average
B
s
0 purity, but a poorer momentum and decay length resolution due to the partial decay reconstruction. Finally, semileptonic
b-hadron decays are inclusively selected and yield the data sample with the highest sensitivity to B
s
0 oscillations, as the much higher statistics compensate for the low average B
s
0 purity and poorer time resolution. A lower limit is set atps-1 at 95% C.L., significantly lower than the expected limit of 15.2 ps-1.
Received: 21 February 2003 / Published online: 11 June 2003 相似文献
997.
Some previous works show that symmetric fixed- and variable-stepsize linear multistep methods for second-order systems which do not have any parasitic root in their first characteristic polynomial give rise to a slow error growth with time when integrating reversible systems. In this paper, we give a technique to construct variable-stepsize symmetric methods from their fixed-stepsize counterparts, in such a way that the former have the same order as the latter. The order and symmetry of the integrators obtained is proved independently of the order of the underlying fixed-stepsize integrators. As this technique looks for efficiency, we concentrate on explicit linear multistep methods, which just make one function evaluation per step, and we offer some numerical comparisons with other one-step adaptive methods which also show a good long-term behaviour.
998.
In the paper the asymptotics for Dirichlet polynomials associated to certain cusp forms are obtained.
Partially supported by Lithuanian Foundation of Studies and Science 相似文献
999.
1000.
A. V. Pukhlikov 《Computational Mathematics and Modeling》2004,15(3):223-256
The article develops the principles of optimal control theory for probability distributions on the configuration space of a controlled dynamical system. Necessary conditions of optimality are derived in the form of the Pontryagin principle for various classes of problems. Analytical representations in the space of distributions and observables are considered. Special modes are examined. The relationship between distribution control theory and nonlocal optimization problems is demonstrated. 相似文献