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   152977篇
  免费   1593篇
  国内免费   386篇
化学   82251篇
晶体学   2034篇
力学   6674篇
综合类   7篇
数学   15376篇
物理学   48614篇
  2020年   1116篇
  2019年   1182篇
  2018年   1481篇
  2017年   1458篇
  2016年   2484篇
  2015年   1560篇
  2014年   2448篇
  2013年   6347篇
  2012年   4951篇
  2011年   6285篇
  2010年   4291篇
  2009年   4312篇
  2008年   5716篇
  2007年   5785篇
  2006年   5430篇
  2005年   5015篇
  2004年   4424篇
  2003年   3875篇
  2002年   3908篇
  2001年   4346篇
  2000年   3331篇
  1999年   2573篇
  1998年   2251篇
  1997年   2188篇
  1996年   1985篇
  1995年   1903篇
  1994年   1893篇
  1993年   1735篇
  1992年   1998篇
  1991年   2123篇
  1990年   1923篇
  1989年   1921篇
  1988年   1860篇
  1987年   1760篇
  1986年   1698篇
  1985年   2198篇
  1984年   2337篇
  1983年   1899篇
  1982年   2081篇
  1981年   1970篇
  1980年   1888篇
  1979年   2030篇
  1978年   2199篇
  1977年   2069篇
  1976年   2112篇
  1975年   2020篇
  1974年   2072篇
  1973年   2062篇
  1972年   1355篇
  1971年   1210篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
971.
We report studies of examples of reflection-asymmetric nuclei which are difficult to access using compound nucleus reactions. The octupole radium isotopes withN>132 and radon isotopes are not accessible by reactions employing stable targets and beams; we have shown that multinucleon transfer reactions can populate these nuclei with sufficient yield for their structure to be determined. We report high-spin studies in218, 220, 222Rn and222, 224, 226, 228, 230Ra: these show that the Ra isotopes withA<228 have the characteristics of octupole deformed nuclei whereas the Rn isotopes behave like octupole vibrators. Measurements of theB(E1)/B(E2) ratios indicate that the electric dipole moment in these nuclei is constant with spin. The most octupole deformed nuclei are predicted to be uranium isotopes withN≈132; measurements of the very fissile nucleus226U suggest that it is octupole deformed and has a large intrinsic electric dipole moment. Finally, we speculate that the best examples of pear shapes are the hyperdeformed minima predicted to lie low in uranium isotopes withN≈140; their signature of high-multiplicity low-energyE1 photon cascades should be detectable using present-day high-efficiency germanium arrays.  相似文献   
972.
Iron uptake of the 57Fe-siderophores ferricrocin, rhizoferrin and citrate in M. smegmatis was analyzed by in situ Mössbauer spectroscopy. Siderophore dependent uptake and metabolic utilization patterns of 57Fe were found. Rhizoferrin is accumulated in the organism and, therefore, represents a suitable candidate for the synthesis of novel siderophore-antibiotics conjugates.  相似文献   
973.
The excitation spectrum in an [Fe/Cr]n multilayer structure with non-collinear magnetic ordering was studied by the ferromagnetic resonance (FMR) method in the frequency interval 9.5–37 GHz at room temperature. Besides an acoustic branch, several additional modes were observed under parallel excitation of resonance. The FMR spectrum was calculated analytically in a biquadratic exchange model, neglecting in-plane anisotropy, for an infinite number of layers in the structure and numerically for a finite number of layers contained in real samples. It was shown that the observed modes correspond to excitation of standing spin waves with wave vectors perpendicular to the film plane. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 690–695 (10 May 1998)  相似文献   
974.
We estimate the concentration functions of n-fold convolutions of one-dimensional probability measures. The Kolmogorov–Rogozin inequality implies that for nondegenerate distributions these functions decrease at least as O(n –1/2). On the other hand, Esseen(3) has shown that this rate is o(n –1/2) iff the distribution has an infinite second moment. This statement was sharpened by Morozova.(9) Theorem 1 of this paper provides an improvement of Morozova's result. Moreover, we present more general estimates which imply the rates o(n –1/2).  相似文献   
975.
The reactions of IO radicals with CH3SCH3, CH3SH, C2H4, and C3H6 have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH3SCH3 → products (1): k1 = (1.5 ± 0.2) × 10?14; IO + CH3SH → products (2): k2 = (6.6 ± 1.3) × 10?16; IO + C2H4 →products (3): k3 < 2 × 10?16; IO + C3H6 → products (4): k4 < 2 × 10?16 (units are cm3 molecule?1 s?1). CH3S(O)CH3 and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k1 compared to our previous determination is discussed.  相似文献   
976.
Y2BaCuO5 (211) inclusions are prominent microstructural features found in melt-textured YBa2Cu3Ox (123) superconductors. These particles are of interest because the 123/211 interfaces and the interface-associated defects have been proposed to be flux pinning centers. In addition, the 211 particles are believed to be heterogeneous nucleation centers of dislocation which can increase the critical current density of 123. Unfortunately, only limited studies have been performed on these particles to ascertain their roles in flux pinning. In this investigation, 211 particles, the interfacial structure and defects in undeformed and mechanically deformed melt-textured 123 have been studied by transmission electron microscopy. It was found that there appears to be a preferred orientation between large oblong 211 particles and the 123 matrix. In addition, while the 123/211 interfaces in undeformed 123 are sharp and relatively undistorted, the interfaces in deformed 123 samples are much thicker. Also, the distribution of strained regions and dislocations around oblong 211 particles in undeformed 123 is nonuniform; the interfaces of low surface curvature are relatively free of defects while the surfaces of high curvature are abundant in dislocations. In contrast, the 123/211 interfaces in deformed 123 samples contain high density of dislocations regardless of interface curvature.  相似文献   
977.
This article treats mixed finite-element methods for second-order quasilinear parabolic equations. A fully discrete scheme is presented and L2-error estimates are established. The convergence of both the function value and the flux is demonstrated. In a previous paper, Part I the author introduced powerful numerical methods for dealing with parabolic problems. The technique used here is an extension of the continuous-time results for the discrete-time case. © 1994 John Wiley & Sons, Inc.  相似文献   
978.
979.
A computer program for the optimization of relation for correction of matrix effects in Energy Dispersive X-Ray Fluorescence (EDXRF) analysis is described Program functioning and correction efficiency is studied experimentally in the case of silicate geological samples.  相似文献   
980.
Two organic scintillators — NE104 and a liquid solution of 2,5 diphenyloxazole (PPO) — were investigated through positron annihilation spectroscopy to study the influence of the structural order on the magnetic quenching effect on positron bound systems in solids.Preliminary note in [11]  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