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   50821篇
  免费   3204篇
  国内免费   3749篇
化学   22859篇
晶体学   473篇
力学   3754篇
综合类   517篇
数学   10444篇
物理学   19727篇
  2024年   59篇
  2023年   433篇
  2022年   1076篇
  2021年   1057篇
  2020年   1120篇
  2019年   1132篇
  2018年   1008篇
  2017年   1156篇
  2016年   1308篇
  2015年   1023篇
  2014年   1659篇
  2013年   3168篇
  2012年   2023篇
  2011年   2191篇
  2010年   1802篇
  2009年   2891篇
  2008年   3135篇
  2007年   3546篇
  2006年   2991篇
  2005年   2381篇
  2004年   2011篇
  2003年   2283篇
  2002年   2653篇
  2001年   2010篇
  2000年   1909篇
  1999年   1632篇
  1998年   1572篇
  1997年   917篇
  1996年   898篇
  1995年   779篇
  1994年   818篇
  1993年   616篇
  1992年   687篇
  1991年   454篇
  1990年   431篇
  1989年   338篇
  1988年   301篇
  1987年   282篇
  1986年   252篇
  1985年   229篇
  1984年   230篇
  1983年   141篇
  1982年   193篇
  1981年   186篇
  1980年   124篇
  1979年   152篇
  1978年   129篇
  1977年   119篇
  1976年   75篇
  1973年   60篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
内部审核在计量体系中的作用   总被引:1,自引:0,他引:1  
介绍内部审核制度在计量测试工作中的目的和作用,提出了内部审核工作应注意的事项,如内部审核工作计划的完整性,内部审核工作的有效性,管理者工作内容的全面性,以及后续工作的完善性。  相似文献   
132.
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding.  相似文献   
133.
A nonlinear Fokker-Planck equation is derived to describe the cooperative behavior of general stochastic systems interacting via mean-field couplings, in the limit of an infinite number of such systems. Disordered systems are also considered. In the weak-noise limit; a general result yields the possibility of having bifurcations from stationary solutions of the nonlinear Fokker-Planck equation into stable time-dependent solutions. The latter are interpreted as non-equilibrium probability distributions (states), and the bifurcations to them as nonequilibrium phase transitions. In the thermodynamic limit, results for three models are given for illustrative purposes. A model of self-synchronization of nonlinear oscillators presents a Hopf bifurcation to a time-periodic probability density, which can be analyzed for any value of the noise. The effects of disorder are illustrated by a simplified version of the Sompolinsky-Zippelius model of spin-glasses. Finally, results for the Fukuyama-Lee-Fisher model of charge-density waves are given. A singular perturbation analysis shows that the depinning transition is a bifurcation problem modified by the disorder noise due to impurities. Far from the bifurcation point, the CDW is either pinned or free, obeying (to leading order) the Grüner-Zawadowki-Chaikin equation. Near the bifurcation, the disorder noise drastically modifies the pattern, giving a quenched average of the CDW current which is constant. Critical exponents are found to depend on the noise, and they are larger than Fisher's values for the two probability distributions considered.  相似文献   
134.
Based on the discrete-structural theory of thin plates and shells, a calculation model for thin-walled elements consisting of a number of rigid anisotropic layers is put forward. It is assumed that the transverse shear and compression stresses are equal on the interfaces. Elastic slippage is allowed over the interfaces between adjacent layers. The solution to the problem is obtained in a geometrically nonlinear statement with account of the influence of transverse shear and compression strains. The stress-strain state of circular two-layer transversely isotropic plates, both without defects and with a local area of adhesion failure at their center, is investigated numerically and experimentally. It is found that the kinematic and static contact conditions on the interfaces of layered thin-walled structural members greatly affect the magnitude of stresses and strains. With the use of three variants of calculation models, in the cases of perfect and weakened contact conditions between layers, the calculation results for circular plates are compared. It is revealed that the variant suggested in this paper adequately reflects the behavior of layered thin-walled structural elements under large deformations. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 761–772, November–December, 2005.  相似文献   
135.
The effect of 18-crown-6 and kryptofix (2,2,1) on the oxidation of triethylamine byaqueous ferricyanide ion has been studied at pH 4, 7, and 9.The macrocycle retarded the normal oxidation process at all pH values,the effect depending on the macrocyclic ligand concentration Kryptofix (2,2,1) had a greater effect than 18-crown-6 at all pHvalues in this study. For 18-crown-6, retardation decreases in the order pH 9 > 4 > 7 while forkryptofix it follows the order pH 9 > 7 > 4.  相似文献   
136.
本文利用自制云雾室把微观粒子的运动转化为宏观现象,从而供实验观察和研究。  相似文献   
137.
It is shown that the potential perturbation that shifts a chosen standing wave in space is a block of potential barrier and well for every wave bump between neighbouring knots. The algorithms shifting the range of the primary localization of a chosen bound state in a potential well of finite width are as well applicable to the scattering functions if states of the continuous spectrum are considered as bound states normalized to unity but distributed on an infinite interval with vanishing density. The potential perturbations of the same type on the half-axis concentrate the scattering wave at the origin, thus creating a bound state embedded into the continuous spectrum (zero width resonance).  相似文献   
138.
SomeNotesaboutTanaka'sEquationYanZhibin(严质彬)(DepartmentofMathematics,HarbinInstituteofTechnology,Harbin,150001)AbstractLet{Wt...  相似文献   
139.
本文是[1,12]的继续,研究描述架中概念的结构;本文讨论后半部分,内容涉及概念内涵与外延的转换,清晰关系的内投影与内变换,概念的结构*以及有关问题的注记。  相似文献   
140.
本文首先提出逆(反)对策这一新问题,给出了数学模型;探讨了“奇门遁甲”预测理论(术)中的数学问题;通过系统分析“专门遁甲”预测过程,可知它的预测过程隐含着一个特殊的逆(反)对策问题;最后指出逆(反)对策问题的广泛存在并给出案例分析.  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