全文获取类型
收费全文 | 669278篇 |
免费 | 7514篇 |
国内免费 | 1987篇 |
专业分类
化学 | 344079篇 |
晶体学 | 9875篇 |
力学 | 31096篇 |
综合类 | 14篇 |
数学 | 91035篇 |
物理学 | 202680篇 |
出版年
2021年 | 4735篇 |
2020年 | 5317篇 |
2019年 | 5850篇 |
2018年 | 13235篇 |
2017年 | 13639篇 |
2016年 | 13998篇 |
2015年 | 7884篇 |
2014年 | 11169篇 |
2013年 | 28033篇 |
2012年 | 23895篇 |
2011年 | 34277篇 |
2010年 | 22788篇 |
2009年 | 22595篇 |
2008年 | 30762篇 |
2007年 | 33058篇 |
2006年 | 21833篇 |
2005年 | 24419篇 |
2004年 | 20467篇 |
2003年 | 18406篇 |
2002年 | 16805篇 |
2001年 | 17805篇 |
2000年 | 13655篇 |
1999年 | 10701篇 |
1998年 | 8933篇 |
1997年 | 8679篇 |
1996年 | 8472篇 |
1995年 | 7675篇 |
1994年 | 7482篇 |
1993年 | 7351篇 |
1992年 | 8126篇 |
1991年 | 8232篇 |
1990年 | 7862篇 |
1989年 | 7697篇 |
1988年 | 7780篇 |
1987年 | 7575篇 |
1986年 | 7183篇 |
1985年 | 9496篇 |
1984年 | 9775篇 |
1983年 | 7922篇 |
1982年 | 8288篇 |
1981年 | 8133篇 |
1980年 | 7661篇 |
1979年 | 8105篇 |
1978年 | 8444篇 |
1977年 | 8151篇 |
1976年 | 8294篇 |
1975年 | 7548篇 |
1974年 | 7628篇 |
1973年 | 7907篇 |
1972年 | 5354篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
992.
S. A. Bulgakova A. I. Mashin I. A. Kazantseva D. E. Kashtanov M. M. Jones G. S. Tsepkov A. V. Korobkov A. V. Nezhdanov 《Russian Journal of Applied Chemistry》2008,81(8):1446-1451
Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined. 相似文献
993.
994.
M C Testik J K Cochran G C Runger 《The Journal of the Operational Research Society》2004,55(3):233-239
We study the short-term staffing problem of systems that experience random, non-stationary demand. The typical method to accommodate changes in arrival rate is to use historical data to identify peak periods and associated forecasting for upcoming time windows. In this paper, we develop a method that instead detects change as it happens. Motivated by an automatic call distributor system in a call centre with time-varying arrivals, we propose a change detection algorithm based upon non-homogeneous Poisson processes. The proposed method is general and may be thought of as a feed-forward strategy, in which we detect a change in the arrival process, estimate the new magnitude of the arrival rate, and assign an appropriate number of servers to the tasks. The generalized likelihood ratio statistic is used and a recommendation for its decision limit is developed. Simulation results are used to evaluate the performance of the detector in the context of a telephone call centre. 相似文献
995.
M. R. McEwen J. P. Sephton P. H. G. Sharpe D. R. Shipley 《Radiation Physics and Chemistry》2003,68(6):1017-1022
A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level). 相似文献
996.
The pumiceous products of the large-scale explosive eruptions at Santorini show a high grade of similarity in their optical
appearance as well as in their chemical composition. The demand for a clear classification of these eruption products was
raised from archaeological research, where pumice can be interpreted as a “post-eruption” time marker. The aim of this work
was to find elements that underwent significant changes because of geochemical processes and that could be indicative for
a distinction of pumice produced by the five major explosive eruptions. INAA of 25 elements allows a clear classification
and contributes new information to the chemical evolution of Santorini volcano.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
S. Tavazzi A. Borghesi M. Campione A. Papagni A. Sassella P. Spearman 《Journal of luminescence》2004,110(4):212-216
We examine absorption of light in quaterthiophene crystals for different directions of the ray and wave-normal vector after refraction on the vacuum/crystal interface. Experimental non-normal incidence spectra are reported where different absorption bands show different behaviour as a function of the angle of incidence. This allows to identify those originating from the bu Frenkel exciton state. 相似文献
998.
A method for increasing measurement sensitivity in the visualization of dynamics of changes in wavefront shape with the use of holographic lateral-shearing interferometry is considered. At the first stage of this method, a photograph of a reference shear interferogram obtained with tuning to closely spaced fringes is recorded under linear conditions. After chemical treatment, the photograph of the reference shear interferogram is installed in exactly its initial position. At the second stage, a series of photographs of lateral-shear interferograms of the wavefront under study is recorded under nonlinear conditions using the photograph of the reference interferogram. The photographs of the lateral-shear interferograms are optically processed by two coherent beams with selection of the highest diffraction orders, which makes it possible to visualize the dynamic component of the wavefront deformation with an increase in the measurement sensitivity (the static component is excluded in this case). The effect of the degree of nonlinearity of photograph recording on the range in which the measurement sensitivity can be controlled during the optical processing of a pair of matched photographs or one double-exposure photograph of interferograms recorded at different values of a lateral shift is analyzed. 相似文献
999.
The mechanism of transition of a Bose gas to the superfluid state via thermal fluctuations under the condition of external cooling at a temperature above the transition point is considered. The probability of formation of such critical fluctuations (instantons) is calculated; it is found that this probability increases as the system approaches the transition temperature. It is shown that the evolution of an individual instanton is impossible without the formation of vortices in its superfluid part. 相似文献
1000.
The dynamic structure factors (DSFs) of several strong glasses (SF6, SF10, BK7, SUPRASIL) measured by Brillouin light scattering spectroscopy are reported. Spectra have been collected, at and above room temperature, at two scattering angles, θ=90° and θ=180° corresponding to exchanged wavevector q values ranging from 0.0256 to 0.0448 nm−1. In particular we find that the isotropic spectral lineshapes are in all cases well described by the simple hydrodynamic theory of an amorphous solid. The width of the Brillouin peaks are found to be consistent with the predicted q2 dependence at both investigated temperatures. This damping is however found to account only partially for the strong asymmetry of the Brillouin line clearly visible on a logarithmic intensity scale. As a matter of fact there is an excess intensity in the very low frequency plateau underlying the central component. The height of this plateau and hence the entire lineshape is well reproduced if a relaxation process is taken into account in the hydrodynamic equations. Owing to the intense elastic scattering we are able to determine unambiguously only the ratio between amplitude and characteristic time of this process which quantifies the sound dispersion to be of the order of a few percent in all samples. The temperature dependence of the parameters indicates that this relaxation cannot be attributed to thermally activated relaxation phenomena. These general findings favorably compare with molecular dynamics simulation results on similar systems. 相似文献