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   309篇
  免费   8篇
  国内免费   4篇
化学   189篇
晶体学   2篇
力学   10篇
数学   29篇
物理学   91篇
  2023年   2篇
  2021年   3篇
  2020年   5篇
  2019年   3篇
  2018年   6篇
  2016年   6篇
  2015年   3篇
  2014年   2篇
  2013年   10篇
  2012年   12篇
  2011年   8篇
  2010年   11篇
  2009年   8篇
  2008年   12篇
  2007年   8篇
  2006年   10篇
  2005年   16篇
  2004年   17篇
  2003年   14篇
  2002年   14篇
  2001年   5篇
  2000年   15篇
  1999年   2篇
  1996年   7篇
  1995年   2篇
  1994年   5篇
  1993年   7篇
  1992年   7篇
  1991年   4篇
  1990年   4篇
  1989年   6篇
  1988年   3篇
  1987年   5篇
  1986年   5篇
  1985年   7篇
  1984年   8篇
  1983年   3篇
  1982年   3篇
  1981年   3篇
  1980年   8篇
  1978年   5篇
  1977年   5篇
  1976年   4篇
  1975年   5篇
  1974年   3篇
  1973年   3篇
  1971年   2篇
  1970年   2篇
  1969年   3篇
  1935年   1篇
排序方式: 共有321条查询结果,搜索用时 78 毫秒
31.
Summary This paper is concerned with the formulation of a plane thermoelastic problem in a multiplyconnected region exhibiting temperature-dependent material properties in terms of a stress function by deriving the integral conditions necessary for the assurance of the single-valuedness of the rotation and displacements, i.e., new Michell's conditions and the finite difference representation of the resulting fundamental equations.The method of solution for the thermoelastic problem in the multiply-connected region is applied to a transient plane-strain thermal stress problem in a hollow circular cylinder having temperature-dependent material properties subjected to an asymmetrical heating by a high-temperature fluid on the inner surface of the cylinder.
Zur Methode der Spannungsfunktion bei thermoelastischen Problemen mit mehrfach zusammenhängendem Gebiet und temperaturabhängigen Materialeigenschaften
Übersicht In dieser Untersuchung wird ein thermoelastisches Problem mit mehrfach zusammenhängendem Gebiet und temperaturabhängigen Materialeigenschaften mit Hilfe einer Spannungsfunktion behandelt. Die Bedingungen für Eindeutigkeit von Rotation und Verschiebung werden hergeleitet. Die Grundgleichungen des Problems werden mit der Methode der finiten Differenzen gelöst.Als Anwendungsbeispiel wird ein hohler Kreiszylinder mit temperaturabhängigen Werkstoffeigenschaften betrachtet. Der Zylinder wird dabei durch eine Flüssigkeit mit hoher Temperatur in seinem Innern einer symmetrischen Erwärmung unterworfen.
  相似文献   
32.
The 13C labels of [13C]carbon dioxide and D-[13C?]glucose were incorporated into cyanamide (NH?CN) when they were administered to Vicia villosa subsp. varia shoots. In contrast, the administration of sodium [2,3-13C?]pyruvate did not affect the relative area of the [M + 1]+ ion of cyanamide in the gas chromatography-mass spectrometry analysis. [2,3-13C?]pyruvate was incorporated into organic acids that are part of the citric acid cycle, such as succinate and fumarate, confirming that the shoots absorbed and metabolised it. These observations demonstrated that the carbon atom of cyanamide is derived from any of the carbohydrates that are present upstream of pyruvate in the metabolic pathway.  相似文献   
33.
Lectin-like oxidized LDL receptor-1 (LOX-1) is an endothelial receptor for oxidized LDL (oxLDL) and plays multiple roles in the development of cardiovascular diseases. We screened more than 400 foodstuff extracts for identifying materials that inhibit oxLDL binding to LOX-1. Results showed that 52 extracts inhibited LOX-1 by more than 70% in cell-free assays. Subsequent cell-based assays revealed that a variety of foodstuffs known to be rich in procyanidins such as grape seed extracts and apple polyphenols, potently inhibited oxLDL uptake in Chinese hamster ovary (CHO) cells expressing LOX-1. Indeed, purified procyanidins significantly inhibited oxLDL binding to LOX-1 while other ingredients of apple polyphenols did not. Moreover, chronic administration of oligomeric procyanidins suppressed lipid accumulation in vascular wall in hypertensive rats fed with high fat diet. These results suggest that procyanidins are LOX-1 inhibitors and LOX-1 inhibition might be a possible underlying mechanism of the well-known vascular protective effects of red wine, the French Paradox.  相似文献   
34.
35.
The E(4) 1Πu←X 1Σ+g band system of the K2 molecule is investigated by the technique of Doppler-free optical–optical double resonance polarization spectroscopy. The observed vibrational levels v=0 to 9 of the E state are subject to numerous rotational perturbations by the neighboring 4 3Πu, 4 1Σ+u, and 5 3Σ+u electronic states. By using deperturbation methods, the potential curves of the 4 1Πu and 4 3Πu states are determined as well as some properties of the 4 1Σ+u and 5 3Σ+u state potentials. The results are compared with predictions of ab initio calculations.  相似文献   
36.
37.
38.
To elucidate the physiological role of poly(ADP-ribose) polymerase (PARP), we studied the levels of PARP mRNA and protein during the developmental stages of Sarcophaga peregrina. PARP mRNA expression changed remarkably throughout the developmental stages. The level of PARP mRNA (the molecular ratio of PARP mRNA to the total RNA) was highest in unfertilized eggs and that of PARP protein (the molecular ratio of PARP protein to the total protein of the crude extract) was high in unfertilized and fertilized eggs and in 1st instar larvae. During the embryogenesis period, the levels of PARP mRNA and protein gradually decreased. The levels of PARP mRNA during larval and pupal periods became less than about 5% of that in unfertilized eggs. After the emergence of adult flies, the levels of PARP mRNA and protein increased both in female and male flies. PARP activity normalized with the total amount of protein in the crude extract changed in parallel to the level of PARP protein throughout the developmental stages. The biological significance of the drastic change of mRNA and protein levels of PARP still remains to be clarified.  相似文献   
39.
A high density mark edge recording method on a phase change rewritable disk is reported. A carrier-to-noise ratio of 55 dB for a mark length of 0.55,μm is obtained by using a 680 nm, NA 0.6 head and a phase change rewritable disk. In mark edge recording, it is necessary to record each mark in correct length. A new laser power modulation pattern is proposed. This pattern consists of a first-pulse, a multi-pulse chain and a last-pulse. Both positions of the first-ptilse and the last-pulse are movable. By adjusting these positions, a jitter, σ/Tw (Tw is window margin), is improved to 6.5% in high density EFM (Eight to Fourteen Modulation) recording of 0.4 μm/bit.  相似文献   
40.
The charged particle multiplicity distributions for two-jet events ine + e ? annihilation at 29 GeV have been measured using the High Resolution Spectrometer at PEP. A Poisson distribution describes the data for both the complete event and for the single jets. In addition, no correlation is observed between the multiplicities in the two jets of an event. For fixed values of the prong number of the complete event, the multiplicity sharing between the two jets is in good agreement with a binomial distribution. The rapidity gap distribution is exponential with a slope equal to the mean rapidity density. These observations, which are consistent with a picture of independent emission of single particles, are contrasted to the results from soft hadronic collisions and conclusions are drawn about the nature of clusters.  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