全文获取类型
收费全文 | 398625篇 |
免费 | 5217篇 |
国内免费 | 1775篇 |
专业分类
化学 | 220944篇 |
晶体学 | 5116篇 |
力学 | 16269篇 |
综合类 | 72篇 |
数学 | 43574篇 |
物理学 | 119642篇 |
出版年
2020年 | 3380篇 |
2019年 | 3735篇 |
2018年 | 4600篇 |
2017年 | 4759篇 |
2016年 | 7098篇 |
2015年 | 4623篇 |
2014年 | 7021篇 |
2013年 | 17598篇 |
2012年 | 13682篇 |
2011年 | 16658篇 |
2010年 | 11845篇 |
2009年 | 11646篇 |
2008年 | 15361篇 |
2007年 | 15284篇 |
2006年 | 14308篇 |
2005年 | 12954篇 |
2004年 | 11677篇 |
2003年 | 10499篇 |
2002年 | 10182篇 |
2001年 | 11898篇 |
2000年 | 9102篇 |
1999年 | 6777篇 |
1998年 | 5454篇 |
1997年 | 5025篇 |
1996年 | 4936篇 |
1995年 | 4682篇 |
1994年 | 4674篇 |
1993年 | 4417篇 |
1992年 | 5207篇 |
1991年 | 5189篇 |
1990年 | 4945篇 |
1989年 | 4901篇 |
1988年 | 4886篇 |
1987年 | 4820篇 |
1986年 | 4655篇 |
1985年 | 6191篇 |
1984年 | 6288篇 |
1983年 | 5063篇 |
1982年 | 5349篇 |
1981年 | 5183篇 |
1980年 | 4790篇 |
1979年 | 5279篇 |
1978年 | 5464篇 |
1977年 | 5604篇 |
1976年 | 5452篇 |
1975年 | 5001篇 |
1974年 | 5039篇 |
1973年 | 5069篇 |
1972年 | 3735篇 |
1968年 | 3224篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Scientific-Research Institute of Applied Physics; Tashkent State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 80, No. 3, pp. 391–398, September, 1989. 相似文献
992.
Summary In the present paper we study truncated projections for the fanbeam geometry in computerized tomography. First we derive consistency conditions for the divergent beam transform. Then we study a singular value decomposition for the case where only the interior rays in the fan are provided, as for example in region-of-interest tomography. We show that the high angular frequency components of the searched-for densities are well determined and we present reconstructions from real data where the missing information is approximated based on the singular value decomposition.The work of the authors was supported by the Deutsche Forschungsgemeinschaft under grant Lo 310/2-4 相似文献
993.
Summary We consider a class of infinite delay equations of neutral type which includes Volterrra type integral und integrodifferential equations. Using abstract approximation results (cf. Trotter-Kato-type) for strongly continuous semigroups we develop an approximation scheme which is based on approximation of the system state by Laguerre (and Legendre) polynomials. Numerical examples demonstrate the feasibility of the scheme and show infinite order convergence for smooth data.Supported in part by the Air Force Office of Scientific Research under Contracts AFORS-84-0398 and AFORS-85-0303 and the National Aeronautics and Space Administration under NASA Grant NAG-1-517 and by NSF under Grant UINT-8521208Supported in part by the Air Force Office of Scientific Research under Contract AFORS-84-0398 and in part by the Fonds zur Förderung der wissenschaftlichen Forschung, Austria, under project No. S3206 相似文献
994.
995.
A new singular integral equation is obtained that describes the elastic equilibrium of a strip with both an inner and an edge slit (crack) and has a considerable advantage over existing equations /1–9/, etc.) from the viewpoint of a numerical realization and clarification of the analytical relationship with an analogous equation for a half-plane. Numerical results are given of a computation of the stress intensity coefficients at the tips of the inner and edge cracks that refine data in the literature. 相似文献
996.
997.
We investigated the morphological, structural and electronic properties of Pentacene thin films grown by vacuum thermal evaporation on different inert substrates at room temperature. The results of our AFM and STM analysis give an interplanar spacing of 1.54 nm corresponding to the (0 0 1) distance of the so-called “thin film phase”. The STS measurements show an HOMO-LUMO gap of 2.2 eV. 相似文献
998.
L. Portugal 《Acta Physica Hungarica A》2006,27(2-3):315-318
To investigate uncertainties in air shower simulations caused by the small-x regime, a model including leading-twist hard pQCD plus soft processes was built, which are separated by an energy dependent transverse momentum cut-off. We provide a fit of the cut-off to the total pp cross section for different PDFs using the eikonal formalism and show that for modern PDF sets there is only a small uncertainty in the mini-jet cross section, and hence in the finalstate multiplicity and the number of produced muons. 相似文献
999.
S.N. Abdulmadjid M.M. Suliyanti K.H. Kurniawan T.J. Lie M. Pardede R. Hedwig K. Kagawa M.O. Tjia 《Applied physics. B, Lasers and optics》2006,82(1):161-166
We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium
ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited
state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark
broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation
respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen
analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration
of the conventional LIBS method.
PACS 51-52 相似文献
1000.
Raman scattering studies were performed on hot-wall chemical vapor deposited (heteroepitaxial) silicon carbide (SiC) films grown on Si substrates with orientations of (1 0 0), (1 1 1), (1 1 0) and (2 1 1), respectively. Raman spectra suggested that good quality cubic SiC single crystals could be obtained on the Si substrate, independent of its crystallographic orientation. Average residual stresses in the epitaxially grown 3C-SiC films were measured with the laser waist focused on the epilayer surface. Tensile and compressive residual stresses were found to be stored within the SiC film and in the Si substrate, respectively. The residual stress exhibited a marked dependence on the orientation of the substrate. The measured stresses were comparable to the thermal stress deduced from elastic deformation theory, which demonstrates that the large lattice mismatch between cubic SiC and Si is effectively relieved by initial carbonization. The confocal configuration of the optical probe enabled a stress evaluation along the cross-section of the sample, which showed maximum tensile stress magnitude at the SiC/Si interface from the SiC side, decreasing away from the interface in varied rate for different crystallographic orientations. Defocusing experiments were used to precisely characterize the geometry of the laser probe in 3C-SiC single crystal. Based on this knowledge, a theoretical convolution of the in-depth stress distribution could be obtained, which showed a satisfactory agreement with stress values obtained by experiments performed on the 3C-SiC surface. 相似文献