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   1059篇
  免费   14篇
化学   672篇
晶体学   9篇
力学   12篇
数学   63篇
物理学   317篇
  2021年   9篇
  2020年   12篇
  2019年   19篇
  2018年   9篇
  2017年   11篇
  2016年   21篇
  2015年   22篇
  2014年   16篇
  2013年   31篇
  2012年   45篇
  2011年   56篇
  2010年   39篇
  2009年   32篇
  2008年   56篇
  2007年   59篇
  2006年   37篇
  2005年   46篇
  2004年   38篇
  2003年   48篇
  2002年   57篇
  2001年   31篇
  2000年   35篇
  1999年   13篇
  1998年   22篇
  1997年   17篇
  1996年   18篇
  1995年   22篇
  1994年   14篇
  1993年   10篇
  1992年   15篇
  1991年   18篇
  1990年   16篇
  1989年   8篇
  1988年   12篇
  1987年   9篇
  1986年   12篇
  1985年   12篇
  1984年   12篇
  1982年   11篇
  1981年   5篇
  1980年   8篇
  1979年   6篇
  1978年   9篇
  1977年   9篇
  1974年   7篇
  1973年   6篇
  1969年   5篇
  1968年   5篇
  1967年   6篇
  1966年   5篇
排序方式: 共有1073条查询结果,搜索用时 15 毫秒
71.
Global features of potential-energy curves are drawn using minimal basis SCF –CI method. Potential-energy surfaces are drawn at points of interest. The mechanism of the chemiluminescence is discussed along with the measurement of a rate constant exploiting the phenomena.  相似文献   
72.
The α-decay properties of very short-lived N = 128 isotones, 216Ra, 217Ac and 218Th, were investigated by the pulsed-beam method. Alpha emitters of interest were produced in the bombardment of 208Pb or 209Bi with 65–96 MeV 12C or 14N ions and α-decays were measured between natural beam bursts of the cyclotron. The results obtained are = 9.349±0.008 MeVand t12 = 182±10 ns for216Ra, 9.650±0.010 MeV and 111±7 ns for217Ac, 9.665±0.010 MeV and 96±7 ns for218Th. The experimental reduced α-widths of N = 128 isotones from 212Po to 218Th are shown to agree well with the simple shell model calculation.  相似文献   
73.
74.
The aim of this study was to investigate the effect of temporal resolution on the estimation of left ventricular (LV) function by cardiac magnetic resonance (MR) imaging using a steady-state free precession (SSFP) sequence. Left ventricular function was assessed by cine MR imaging using a segmented SSFP sequence in 10 healthy volunteers. Views per segment (VPS) were set at 8 and 20, resulting in high and low true temporal resolution, respectively. Irrespective of VPS, images were reconstructed at 40 cardiac phases, providing high apparent temporal resolution. Data were analyzed using 40, 20 and 10 phases to simulate different apparent temporal resolutions. Increasing the cardiac phases used for analysis slightly decreased mean end-systolic volume (ESV) and slightly increased mean ejection fraction (EF). No substantial difference in estimates of end-diastolic volume (EDV) was found between VPSs of 8 and 20. Imaging with a VPS of 20 yielded a larger ESV and smaller EF than imaging with a VPS of 8 when 40 phases were used. In conclusion, low true temporal resolution causes overestimation of ESV and underestimation of EF. Improvement of apparent temporal resolution mildly reduces but does not eliminate the errors caused by low true temporal resolution.  相似文献   
75.
In order to predict non-coding RNA genes and functions on the basis of genome sequences, accurate secondary structure prediction is useful. Although single-sequence folding programs such as mfold have been successful, it is of great importance to develop a novel approach for further improvement of the prediction performance. In the present paper, a secondary structure prediction method based on genetic algorithm, Cofolga, is proposed. The program developed performs folding and alignment of two homologous RNAs simultaneously. Cofolga was tested with a dataset composed of 13 tRNAs, seven 5S rRNAs, five RNase P RNAs, and five SRP RNAs; as a result, it turned out that the average prediction accuracies for the tRNAs, 5S rRNAs, RNase P RNAs, and SRP RNAs obtained by Cofolga with an optimal weight factor and default parameters were 83.6, 81.8, 73.5, and 67.7%, respectively. These results were superior to those obtained by a single-sequence folding based on free-energy minimization in which corresponding average prediction accuracies were 52.4, 47.4, 57.7, and 52.3%, respectively. Cofolga has a post-processing in which a single-sequence folding is performed after fixation of a predicted common structure; this post-processing enables Cofolga to predict a structure that is present in one of two RNAs alone. The executable files of Cofolga (for Windows/Unix/Mac) can be obtained by an e-mail request.  相似文献   
76.
77.
A spin model is a square matrix that encodes the basic data for a statistical mechanical construction of link invariants due to V.F.R. Jones. Every spin model W is contained in a canonical Bose-Mesner algebra (W). In this paper we study the distance-regular graphs whose Bose-Mesner algebra satisfies W (W). Suppose W has at least three distinct entries. We show that is 1-homogeneous and that the first and the last subconstituents of are strongly regular and distance-regular, respectively.  相似文献   
78.
We propose an optical method for the investigation of the quantum dot edge channels by utilizing circularly polarized photoluminescence in the integer-quantum-Hall-effect regime. One of the advantages of our method is that the degree of the spin-polarization of the electrons in the inner- and outer-compressible liquids can be probed separately. The observed polarized photoluminescence spectra can be explained by the calculated electron spin-dependent optical transition probabilities based on the local-spin density approximation.  相似文献   
79.
The nanocrystalline BiVO4 film electrode on conducting glass showed an excellent efficiency (IPCE = 29% at 420 nm) for the decomposition of water under visible light.  相似文献   
80.
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