首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   222333篇
  免费   1999篇
  国内免费   620篇
化学   109977篇
晶体学   3640篇
力学   10099篇
综合类   16篇
数学   25469篇
物理学   75751篇
  2021年   1920篇
  2020年   2067篇
  2019年   2391篇
  2018年   3457篇
  2017年   3447篇
  2016年   4773篇
  2015年   2702篇
  2014年   4460篇
  2013年   10393篇
  2012年   8394篇
  2011年   9944篇
  2010年   7387篇
  2009年   7266篇
  2008年   9239篇
  2007年   9334篇
  2006年   8850篇
  2005年   7573篇
  2004年   6892篇
  2003年   5906篇
  2002年   5756篇
  2001年   6674篇
  2000年   5428篇
  1999年   4054篇
  1998年   3406篇
  1997年   3400篇
  1996年   2883篇
  1995年   2640篇
  1994年   2485篇
  1993年   2341篇
  1992年   2695篇
  1991年   2677篇
  1990年   2611篇
  1989年   2402篇
  1988年   2454篇
  1987年   2455篇
  1986年   2283篇
  1985年   2965篇
  1984年   3218篇
  1983年   2638篇
  1982年   2805篇
  1981年   2777篇
  1980年   2642篇
  1979年   2728篇
  1978年   2823篇
  1977年   2824篇
  1976年   2887篇
  1975年   2672篇
  1974年   2647篇
  1973年   2776篇
  1972年   1764篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
New results are presented of an experimental investigation of the spectrum of 36P → 37P two-photon microwave transition in Rydberg atoms of sodium in a constant electric field. Depending on the conditions of excitation of the initial 36P state (the constant electric field is switched on either before or after the exciting laser pulse) and polarization of laser radiation, a strong variation is observed of the amplitudes of individual two-photon transitions between the fine-structure Stark components of the 36P and 37P states. This effect is an analog of the Paschen-Back effect in a strong magnetic field and is due to the break of L-S coupling and to the variation of the wave functions of Rydberg electrons in an electric field. It is also found that the break of L-S coupling affects considerably the shape of double Stark resonance arising upon intersection of the virtual intermediate level of two-photon transition with the real intermediate 37S level.  相似文献   
992.
We describe W-geometry of two-dimensional Toda systems associated with the Lie algebra C n . __________ Translated from Fundamental’naya i Prikladnaya Matematika (Fundamental and Applied Mathematics), Vol. 11, No. 1, Geometry, 2005.  相似文献   
993.
The lantadenes fraction from Lantana camara was isolated and transformed to the medicinally important intermediate 22β-hydroxyoleanonic acid. The compound was studied for hepatotoxicity using lantadene A as standard and found to be nontoxic. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 357–358, July–August, 2006.  相似文献   
994.
The statistics of left-and right-handed vortical magnetization states in a system of submicron-sized ferromagnetic disks is studied experimentally. Lattices of elliptic cobalt particles with a planar size of 750 × 450 nm and a thickness of 25 nm were formed using high-resolution electronic lithography. To visualize the magnetization distributions in the disks, magnetic force microscopy was used. The experimental results indicate the conservation of magnetic chiral symmetry in cobalt ferromagnetic particles of the above size and shape.  相似文献   
995.
996.
The organic matter of schungite rock from the Zazhogino Deposit of Karelian Transonega region was extracted in the sequential mode. The extract composition was determined by several modern physicochemical methods.  相似文献   
997.
A new series of RGDF mimetics, derivatives of 4-(isoindolin-5-yl)amino-4-oxobutanoic acid, was synthesized. The compounds obtained inhibit efficiently the thrombocytes aggregation in experiments in vitro; their biological targets are fibrinogen receptors. The antiaggregatory activity and the affinity correlate with the hydrophobicity of the compounds.  相似文献   
998.
Role of readily hydrolyzable polysaccharides of larch wood in production of board materials is studied.  相似文献   
999.
A special model of a rarefied hard-sphere gas is considered. The hard-sphere particles undergo absolutely elastic collisions. It is assumed that particles can collide only if their nonzero velocities are orthogonal to each other. The model makes it possible to proceed from the Boltzmann equation to the Smoluchowski coagulation equation, where coagulation means that the kinetic energies of the colliding particles are added. A Monte Carlo scheme for simulation of the phenomenon is described, and the convergence of the simulation algorithm is proved. The convergence of numerical results to exact solutions of the Smoluchowski equation and to finite-difference solutions is tested.  相似文献   
1000.
A decelerator will be installed at GSI in order to provide and study heavy nuclei without or with only few electrons at very low energies or even at rest. Highly-charged ions will be produced by stripping at relativistic energies. After electron cooling and deceleration in the Experimental Storage Ring (ESR) the ions are ejected out of the storage ring at 4 MeV/u and further decelerated in a combination of linear accelerator structures operated in reverse. Finally, they are injected into a Penning trap where the ions are cooled to 4 K by electron cooling in combination with resistive cooling. From here, the ions can be transferred in a quasi DC or in a pulsed mode to different experimental setups. This article describes the technical concepts of this project focused on the Penning trap.   相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号