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   242篇
  免费   1篇
  国内免费   3篇
化学   115篇
力学   24篇
数学   25篇
物理学   82篇
  2023年   1篇
  2022年   1篇
  2020年   3篇
  2018年   1篇
  2017年   2篇
  2015年   2篇
  2014年   2篇
  2013年   30篇
  2012年   12篇
  2011年   9篇
  2010年   7篇
  2009年   5篇
  2008年   7篇
  2007年   9篇
  2006年   9篇
  2005年   4篇
  2004年   5篇
  2003年   6篇
  2002年   3篇
  2001年   2篇
  2000年   1篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1996年   5篇
  1993年   1篇
  1992年   4篇
  1991年   1篇
  1990年   5篇
  1989年   1篇
  1988年   2篇
  1987年   3篇
  1986年   1篇
  1985年   7篇
  1984年   4篇
  1983年   7篇
  1982年   9篇
  1981年   8篇
  1980年   12篇
  1979年   3篇
  1978年   10篇
  1977年   4篇
  1976年   7篇
  1975年   10篇
  1974年   2篇
  1973年   6篇
  1972年   1篇
  1971年   1篇
  1969年   1篇
  1956年   1篇
排序方式: 共有246条查询结果,搜索用时 375 毫秒
71.
The He I photoelectron spectrum of ethylene sulphide is reported. There are six ionization potentials below 21 eV, the first, corresponding to ionization from a predominantly sulphur 3p orbital, occurring at 9.05 eV. The orbital types and symmetries have been assigned on the basis of semi-empirical calculations. The results indicate that in this highly strained cyclic compound sulphur d-orbital participation may be important.  相似文献   
72.
Summary A cyclic instrumental neutron activation analysis method has been used to calculate sampling constants and to evaluate homogeneity for Se in five biological reference and certified reference materials, namely NRC lobster hepatopancreas (RM TORT-1), IAEA horse kidney (RM-H8), and NIST bovine liver (SRM-1577a), oyster tissue (SRM-1566) and mixed diet (RM-8431). The between-weight-range heterogeneity has been observed to be no greater than the within-weight-range heterogeneity. The subsampling standard deviation (S s) has been found to be less than the measurement standard deviation (S m) for H-8 (>5 mg sample) and TORT-1 (>50 mg). For 1577a, S s is almost equal to S m; while S s is 2–3 times higher than S m for the other two materials. The sampling constants varied between 0.04 and 3.0 g for four materials while the mixed diet had a value of 31 g.  相似文献   
73.
The theory of unconstrained optimization has led to the development of a large class of iterative methods that reduce to conjugate direction methods when they are applied to quadratic functions. The purpose of this paper is to give a generalization of conjugate directions to nonquadratic functions.  相似文献   
74.
Evidence is presented for an I = 1 enhancement observed in the reactions K?p→Λ(Σ)K01K±π? at 4.2 GeVc inciden momentum. The mass and width of the proposed new Y1 are, respectively, (1553 ± 7) MeV) and (80 ± 30) MeV. A decay branching ratio Σπ(Σπ + Λπ) = (35 ± 12)% is also obtained.  相似文献   
75.
From a high-resolution diode laser spectrum of cooled 12CF4, line assignments in ν2 + ν4 at 1066.4 cm?1 have been made for tetrahedral subspecies to J = 20, and in many cases to higher J. Spectroscopic constants have been obtained from a least-squares fit of the Hamiltonian, and the relative intensities of the assigned lines have been calculated. The ground- and excited-state rotational constants, Coriolis constant, and splitting of the F1 and F2 vibrational substates have the values a.The CF bond length in the ground vibrational state is thus r0 = 1.31752 ± 0.00007 A?. The analysis of a combination band such as this provides a method of obtaining ground-state spectroscopic constants of spherical-top molecules directly from the infrared spectrum, without the necessity of measuring weak “forbidden” transitions. The assignments allow accurate predictions of the frequencies emitted by the CO2-pumped CF4 laser.  相似文献   
76.
Experimental data for the scattering of electrons by selected light atoms at intermediate energies have been collected and compared with the predictions of the theoretical models discussed in part I. The data discussed include elastic scattering and discrete excitation but ionization is not covered. The target atoms include H, He; the alkali metals; the alkaline earths; C, N, O and the rare gases from Ne to Xe, together with certain positive ions isoelectronic with these neutral atoms.  相似文献   
77.
We have examined the HeI photoelectron spectra of the oxalyl halides (COX)2, (X = F, Cl, and Br). We assume the presence of the trans-isomer onWe have used semi-empirical calculations (SCF MO), and Koopmans' Theorem, as aids in assigning the spectral bands.  相似文献   
78.
A spin-parity 1+?π enhancement is observed for the 3π mass spectrum in the reaction K?p → Σ?π+π+π? where events with a small (K?Σ?) momentum transfer are selected. The mass (1040 MeV) and width (230 MeV) of this enhancement are reminiscent of the A1 bump which has mainly been observed in the diffractive-like processes. The cross section for this enhancement at 4.15 GeV/c incident K? momentum is (3.6 ± 0.5) μb.  相似文献   
79.
The X-ray photoelectron spectra of some forty-six copper compounds and complexes have been measured. The chemical shifts obtained from accurate determinations of the binding energies have been qualitatively explained on the basis of the Pauling electronegativity concept using the group electronegatives of Huheey for the polyatomic counter anions. The chemical shifts of the copper atoms as well as the atoms in the ligands were found to be dependent not only on the oxidation state but also on the kind and number of ligand atoms.

Intense satellite lines were found in the 2p and 2s bands of the cupric compounds; the number and splitting of the satellites were found to be sensitive to the chemical environment. A correlation was found between the satellite splitting and the binding energies and this is explained by a 3d→4s, 4p ‘shake-up’ mechanism.  相似文献   
80.
Compliance and enforcement in fisheries are important issues from an economic point of view since management measures are useless without a certain level of enforcement. These conclusions come from the well‐established theoretical literature on compliance and enforcement problems within fisheries and a common result is that, it is efficient to set fines as high as possible and monitoring as low as possible, when fines are costless and offenders are risk neutral. However, this result is sensitive to the assumption that fishermen cannot engage in avoidance activities, e.g., activities to reduce the likelihood of being detected when noncomplying. The paper presents a model of fisheries that allows the fishermen to engage in avoidance activities. The conclusions from the model are that, under certain circumstances, fines are costly transfers to society since they not only have a direct positive effect on the level of deterrence, but also an indirect negative effect in the form of increased avoidance activities to reduce the probability of detection. The paper contributes to the literature on avoidance activities by introducing the externality from the illegal behavior as an endogenous effect on other offenders. For an externality, that has an exogenous effect on other actors, Malik shows that fines are only costly transfers for conditional deterrence (when one actor is deterred while another actor is not). For fisheries, we show that fines are also costly transfers under no deterrence (when no agents are deterred).  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