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   236篇
  免费   4篇
  国内免费   3篇
化学   171篇
力学   5篇
数学   20篇
物理学   47篇
  2019年   3篇
  2018年   2篇
  2016年   3篇
  2015年   4篇
  2014年   6篇
  2013年   13篇
  2012年   3篇
  2011年   10篇
  2010年   5篇
  2009年   2篇
  2008年   16篇
  2007年   9篇
  2006年   11篇
  2005年   9篇
  2004年   4篇
  2003年   9篇
  2002年   9篇
  2001年   4篇
  1998年   2篇
  1997年   2篇
  1996年   4篇
  1995年   5篇
  1992年   2篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1986年   2篇
  1985年   10篇
  1984年   5篇
  1983年   3篇
  1982年   6篇
  1981年   7篇
  1980年   8篇
  1979年   2篇
  1977年   3篇
  1975年   5篇
  1974年   6篇
  1973年   8篇
  1971年   2篇
  1970年   5篇
  1968年   3篇
  1961年   3篇
  1957年   1篇
  1944年   1篇
  1933年   2篇
  1932年   1篇
  1930年   1篇
  1927年   2篇
  1914年   1篇
  1907年   1篇
排序方式: 共有243条查询结果,搜索用时 0 毫秒
61.
Often it is important to consider the expansion of a quantum state ) in terms of physically meaningful basis states. For example, molecular orbitals can be expressed as linear combinations of atomic orbitals, or vibrational states can be expressed as super positions of local or normal mode eigenstates. In such expansions, it then becomes desirable to determine how much character a quantum state has in one of these basis states. One way of accimplishing this task is to calculate the projected probability of |) on basis state |j). In this paper, we consider this general quantum mechanical problem. If the basis states are orthonormal, then the projected probability of|) on |j) is of course |<|j>|2. However, if the basis states are not orthogonal, then this result is no longer valid and one must develop a more general theory to calculate these projected probabilities. An earlier paper used one-dimensional projection operators to initiate this theory and gave closed form results for the case of two non-orthogonal basis states [1]. One- and many-dimensional projection operators, together with linear algebraic techniques, are used to extend this theory to the n non-orthogonal basis state case. Explicit closed form results are given for the two- and three-state cases, and a general algorithm is developed for the case of four or more basis states. Application of the theory is made to atomic populations in three- to six-atom molecules, and comparisons are made to the related work of Mulliken.  相似文献   
62.
The Ugi reaction with formylphenylboronic acid derivatives as the carbonyl component proceeds to give the corresponding boron-containing dipeptide derivatives (Ugi products) in good yields.   相似文献   
63.
64.
65.
Magnetic resonance in the era of molecular imaging of cancer   总被引:1,自引:0,他引:1  
Magnetic resonance imaging (MRI) has played an important role in the diagnosis and management of cancer since it was first developed, but other modalities also continue to advance and provide complementary information on the status of tumors. In the future, there will be a major continuing role for noninvasive imaging in order to obtain information on the location and extent of cancer, as well as assessments of tissue characteristics that can monitor and predict treatment response and guide patient management. Developments are currently being undertaken that aim to provide improved imaging methods for the detection and evaluation of tumors, for identifying important characteristics of tumors such as the expression levels of cell surface receptors that may dictate what types of therapy will be effective and for evaluating their response to treatments. Molecular imaging techniques based mainly on radionuclide imaging can depict numerous, specific, cellular and molecular markers of disease and have unique potential to address important clinical and research challenges. In this review, we consider what continuing and evolving roles will be played by MRI in this era of molecular imaging. We discuss some of the challenges for MRI of detecting imaging agents that report on molecular events, but highlight also the ability of MRI to assess other features such as cell density, blood flow and metabolism which are not specific hallmarks of cancer but which reflect molecular changes. We discuss the future role of MRI in cancer and describe the use of selected quantitative imaging techniques for characterizing tumors that can be translated to clinical applications, particularly in the context of evaluating novel treatments.  相似文献   
66.
The regioselectivity in the Diels-Alder reactions of styrene with certain substituted 1,4-naphthoquinones was explored. The results were consistent with predictions based upon analysis of dione polarization.  相似文献   
67.
Synthesis of pyridazino[1,2-a][1,2,4]benzotriazin-6-one derivatives involving reaction of either 1,2,3,6-tetra-hydropyridazine ( 9 ) or hexahydropyridazine 14 with 2-fluoro-5-nitrophenylisocyanate ( 5 ) to give, via intramolecular cyclization, 3a and 16 respectively is described. Compound 3a was converted to 18 via methylation and hydroxylation to give 20 followed by conversion to the acetonide derivative 18 . Both 16 and 18 were reduced to the amino derivatives 17 and 19 respectively.  相似文献   
68.
We describe a simple implementation of a slit scanning confocal microscope to obtain an axial resolution better than that of a point-scanning confocal microscope. Under slit illumination, images of a fluorescent object are captured using an array detector instead of a line detector so that out-of-focus light is recorded and then subtracted from the adjacent images. Axial resolution after background subtraction is 2.2 times better than the slit confocal resolution, and out-of-focus image suppression is calculated to attenuate with defocus faster by 1 order of magnitude than in the point confocal case.  相似文献   
69.
The goal of this paper is to provide data that can be used in a variety of exercises ranging from kinetics in general chemistry to advanced problems in physical chemistry. The data provided relates to ozone-decay kinetics in various atmospheres (O2, N2, Ar) as measured by ultraviolet/visible absorbance spectroscopy (UV/vis) at 254 nm. The absorbance of ozone is monitored over a 75-min time period, and by using Beers law the concentration is calculated. Nine data sets, each repeated three times, of absorbance measurements are provided for student exercises, and prelaboratory and postlaboratory questions are suggested.  相似文献   
70.
Pyridinecarboxaldimines (N–N′) derived from pyridin-2-ylcarboxaldehydes and unsaturated amines add to [PdCl2(coe)]2 (coe = cis-cyclooctene) to give complexes of the type PdCl2(N–N′) in moderate yields. The palladium complexes have been investigated as substrates for hydroboration reactions and as antifungal agents against Aspergillus niger, A. flavus, Candida albicans, and Saccharomyces cerevisiae.  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