全文获取类型
收费全文 | 63657篇 |
免费 | 4757篇 |
国内免费 | 3928篇 |
专业分类
化学 | 25903篇 |
晶体学 | 467篇 |
力学 | 5309篇 |
综合类 | 555篇 |
数学 | 17184篇 |
物理学 | 22924篇 |
出版年
2024年 | 90篇 |
2023年 | 597篇 |
2022年 | 1281篇 |
2021年 | 1357篇 |
2020年 | 1570篇 |
2019年 | 1470篇 |
2018年 | 1293篇 |
2017年 | 1433篇 |
2016年 | 1805篇 |
2015年 | 1536篇 |
2014年 | 2317篇 |
2013年 | 4255篇 |
2012年 | 2668篇 |
2011年 | 2928篇 |
2010年 | 2318篇 |
2009年 | 3731篇 |
2008年 | 3884篇 |
2007年 | 4337篇 |
2006年 | 3633篇 |
2005年 | 2838篇 |
2004年 | 2459篇 |
2003年 | 2719篇 |
2002年 | 3028篇 |
2001年 | 2327篇 |
2000年 | 2253篇 |
1999年 | 1898篇 |
1998年 | 1912篇 |
1997年 | 1154篇 |
1996年 | 1124篇 |
1995年 | 939篇 |
1994年 | 926篇 |
1993年 | 724篇 |
1992年 | 781篇 |
1991年 | 534篇 |
1990年 | 493篇 |
1989年 | 391篇 |
1988年 | 371篇 |
1987年 | 348篇 |
1986年 | 329篇 |
1985年 | 308篇 |
1984年 | 313篇 |
1983年 | 168篇 |
1982年 | 238篇 |
1981年 | 224篇 |
1980年 | 143篇 |
1979年 | 188篇 |
1978年 | 169篇 |
1977年 | 164篇 |
1976年 | 122篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
A tomographic reconstruction method based on Monte Carlo random searching guided by the information contained in the projections
of radiographed objects is presented. In order to solve the optimization problem, a multiscale algorithm is proposed to reduce
computation. The reconstruction is performed in a coarse-to-fine multigrid scale that initializes each resolution level with
the reconstruction of the previous coarser level, which substantially improves the performance. The method was applied to
a real case reconstructing the internal structure of a small metallic object with internal components, showing excellent results. 相似文献
82.
Vinod Kumar Pragya Das R.P. Singh S. Muralithar R.K. Bhowmik 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):153-157
The fusion evaporation reaction 122Sn(14N, 4n)132La was used to populate the high-spin states of 132La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2- and the isomeric state 6-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh
11/2 ⊗ νh
11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies
in the spin assignment of the band head.
Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003 相似文献
83.
本文提出的MMD算法用于提高模型区别错误信息和正确信息的能力.利用该算法在对模型的参数进行重估计时.涉及到复杂的目标函数的梯度运算.击运用矩阵运算使得梯度运算变得简单明了,因此本文给出了MMD算法下的HMM参数重估计的矩阵表示形式并给出了证明. 相似文献
84.
The cocrystal of 1,2-bis(diphenylphosphinoyl)ethane (DPPEO) with phenol (1:1) were studied theoretically with AM1, PM3, MNDO and MINDO/3 semi-empirical methods to elucidate its structure. The bond lengths and angles from theoretical studies of molecule DPPEO/phenol (1:1) were found to be as expected. Theoretical results, concerning with intermolecular van der Waals forces in cocrystal, were compared with the previously obtained experimental data and AM1 results were found to be the best fit for bond lengths and angles of DPPEO/phenol. 相似文献
85.
本文提供了预条件不精确牛顿型方法结合非单调技术解光滑的非线性方程组.在合理的条件下证明了算法的整体收敛性.进一步,基于预条件收敛的性质,获得了算法的局部收敛速率,并指出如何选择势序列保证预条件不精确牛顿型的算法局部超线性收敛速率. 相似文献
86.
在综述光电对抗内涵的基础上,论述光电对抗在现代战争作战平台中的具体应用,并着重从电子战的角度论述了光电对抗在现代防空作战中的最新应用。最后指出光电对抗技术在未来电子战中的作用和发展方向。 相似文献
87.
Most of the methods used in the ARCH literature for selecting the appropriate model are based on evaluating the ability of the models to describe the data. An alternative model selection approach is examined based on the evaluation of the predictability of the models in terms of standardized prediction errors. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
88.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
89.
We derive a test problem for evaluating the ability of time-steppingmethods to preserve the statistical properties of systems inmolecular dynamics. We consider a family of deterministic systemsconsisting of a finite number of particles interacting on acompact interval. The particles are given random initial conditionsand interact through instantaneous energy- and momentum-conservingcollisions. As the number of particles, the particle density,and the mean particle speed go to infinity, the trajectory ofa tracer particle is shown to converge to a stationary Gaussianstochastic process. We approximate this system by one describedby a system of ordinary differential equations and provide numericalevidence that it converges to the same stochastic process. Wesimulate the latter system with a variety of numerical integrators,including the symplectic Euler method, a fourth-order Runge-Kuttamethod, and an energyconserving step-and-project method. Weassess the methods' ability to recapture the system's limitingstatistics and observe that symplectic Euler performs significantlybetter than the others for comparable computational expense. 相似文献
90.
Ab initio calculations showed that the tetrachlorodibenzo-para-dioxin radical cations (TCDD RCs) with a planar structure have two steady states with asymmetric dioxin cycles. The activation barriers between these states are up to 2 kcal/mole, so that the RCs may be regarded as being structurally nonrigid within the dioxin cycle. The 2,3,7,8-TCDD RC is more stable than the 1,4,6,9-TCDD RC, the energy difference being 5.2 kcal/mole. The adiabatic ionization potential of 2,3,7,8-TCDD (7.54 eV) is 0.1 eV smaller than the corresponding potential of 1,4,6,9-TCDD. These factors account for the increased hemoproteide affinity and hence increased biological activity of 2,3,7,8-TCDD. 相似文献