全文获取类型
收费全文 | 79046篇 |
免费 | 6310篇 |
国内免费 | 6977篇 |
专业分类
化学 | 31133篇 |
晶体学 | 311篇 |
力学 | 7471篇 |
综合类 | 1254篇 |
数学 | 29392篇 |
物理学 | 22772篇 |
出版年
2023年 | 716篇 |
2022年 | 1290篇 |
2021年 | 1471篇 |
2020年 | 1706篇 |
2019年 | 1883篇 |
2018年 | 1543篇 |
2017年 | 1731篇 |
2016年 | 2166篇 |
2015年 | 2029篇 |
2014年 | 2846篇 |
2013年 | 5248篇 |
2012年 | 3235篇 |
2011年 | 3615篇 |
2010年 | 3016篇 |
2009年 | 4340篇 |
2008年 | 4731篇 |
2007年 | 4992篇 |
2006年 | 4641篇 |
2005年 | 3904篇 |
2004年 | 3596篇 |
2003年 | 3624篇 |
2002年 | 3286篇 |
2001年 | 2832篇 |
2000年 | 2752篇 |
1999年 | 2451篇 |
1998年 | 2319篇 |
1997年 | 1903篇 |
1996年 | 1720篇 |
1995年 | 1513篇 |
1994年 | 1381篇 |
1993年 | 1191篇 |
1992年 | 1132篇 |
1991年 | 889篇 |
1990年 | 731篇 |
1989年 | 640篇 |
1988年 | 589篇 |
1987年 | 460篇 |
1986年 | 406篇 |
1985年 | 458篇 |
1984年 | 461篇 |
1983年 | 220篇 |
1982年 | 360篇 |
1981年 | 422篇 |
1980年 | 316篇 |
1979年 | 311篇 |
1978年 | 256篇 |
1977年 | 245篇 |
1976年 | 188篇 |
1975年 | 115篇 |
1974年 | 122篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Kayll Lake 《General Relativity and Gravitation》2004,36(5):1159-1169
The norms associated with the gradients of the two non-differential invariants of the Kerr vacuum are examined. Whereas both locally single out the horizons, their global behavior is more interesting. Both reflect the background angular momentum as the volume of space allowing a timelike gradient decreases with increasing angular momentum becoming zero in the degenerate and naked cases. These results extend directly to the Kerr-Newman geometry. 相似文献
92.
Semra Harmandar 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):395-407
A radiation code based on method of lines solution of discrete ordinates method for radiative heat transfer in axisymmetric cylindrical enclosures containing absorbing-emitting medium was developed and tested for predictive accuracy by applying it to (i) test problems with black and grey walls (ii) a gas turbine combustor simulator enclosing a non-homogeneous absorbing-emitting medium and benchmarking its steady-state predictions against exact solutions and measurements. Comparisons show that it provides accurate solutions for radiative heat fluxes and can be used with confidence in conjunction with CFD codes based on the same approach. 相似文献
93.
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
94.
95.
通过用毛细管测量纯水表面张力系数实验,得到管内径d与接触角θ的相对误差之间的关系曲线,由此说明实验测得的表面张力系数α和理论公式相比呈现一定的偏差,并简单地讨论了实验的理想状态与实际情况的差别. 相似文献
96.
97.
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
98.
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
99.
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
100.
Grishin D. F. Semyonycheva L. L. Telegina E. V. Smirnov A. S. Nevodchikov V. I. 《Russian Chemical Bulletin》2003,52(2):505-507
Organometallic compounds Cp2TiCl2, (EtC5H4)2NbCl2, and (PriC5H4)2WCl2 were assessed as additives that control polymer chain growth in the polymerization of methyl methacrylate. In the presence of compounds mentioned in amounts comparable with that of the initiator, a uniform process with no gel-effect occured and respective linear increase in the molecular weight of the polymer up to high degrees of the monomer conversion was observed. 相似文献