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   697篇
  免费   6篇
  国内免费   9篇
化学   394篇
晶体学   1篇
力学   16篇
数学   116篇
物理学   185篇
  2022年   5篇
  2019年   10篇
  2018年   9篇
  2017年   9篇
  2016年   11篇
  2014年   7篇
  2013年   18篇
  2012年   25篇
  2011年   28篇
  2010年   15篇
  2009年   18篇
  2008年   24篇
  2007年   30篇
  2006年   43篇
  2005年   45篇
  2004年   22篇
  2003年   15篇
  2002年   19篇
  2001年   24篇
  2000年   13篇
  1999年   7篇
  1998年   5篇
  1997年   6篇
  1996年   8篇
  1995年   6篇
  1994年   6篇
  1993年   5篇
  1992年   10篇
  1991年   8篇
  1990年   11篇
  1989年   8篇
  1988年   12篇
  1987年   9篇
  1986年   13篇
  1985年   17篇
  1984年   15篇
  1982年   13篇
  1981年   10篇
  1980年   7篇
  1979年   8篇
  1977年   10篇
  1976年   7篇
  1975年   12篇
  1974年   9篇
  1973年   11篇
  1971年   5篇
  1966年   6篇
  1938年   10篇
  1933年   4篇
  1890年   4篇
排序方式: 共有712条查询结果,搜索用时 15 毫秒
41.
Using data recorded with the CLEO II and CLEO II.V detector configurations at the Cornell Electron Storage Rings, we report the first observation and mass measurement of the Sigma(*+)(c) charmed baryon, and an updated measurement of the mass of the Sigma(+)(c) baryon. We find M(Sigma(*+)(c))-M(Lambda(+)(c)) = (231.0+/-1.1+/-2.0) MeV, and M(Sigma(+)(c))-M(Lambda(+)(c)) = (166.4+/-0.2+/-0.3) MeV, where the errors are statistical and systematic, respectively.  相似文献   
42.
Near-infrared Raman spectroscopy, an optical technique that is able to interrogate biological tissues, has been used to study bladder and prostate tissues, with the objective being to provide a first approximation of gross biochemical changes associated with the process of carcinogenesis. Prostate samples for this study were obtained by taking a chip at TURP, and bladder samples from a biopsy taken at TURBT and TURP, following ethical approval. Spectra were taken from purchased biochemical constituents and different pathologies within the bladder and the prostate. We were then able to determine the biochemical basis for these pathologies by utilising an ordinary least-squares fit. We have shown for the first time that we are able to utilise Raman spectroscopy in determining the biochemical basis for the different pathologies within the bladder and prostate gland. In this way we can achieve a better understanding of disease processes such as carcinogenesis. This could have major implications in the future of the diagnosis of disease within the bladder and the prostate gland.  相似文献   
43.
Observations concerning the (CC) isomerization of several vinylic RhIII complexes suggest an intramolecular pathway; isomerization occurs at a rate which is affected by the backbonding ability of the metal and the π-acidity of the vinylic ligand in the complex.  相似文献   
44.
Many studies have implicated cis-urocanic acid (cis-UCA) in UVB-induced immunomodulation. The strongest evidence came from studies in mice whereby a cis-UCA antibody blocked UVB-induced suppression of delayed-type hypersensitivity responses. Furthermore, in several studies, the cis-UCA antibody at least partially reversed UVB suppression of contact hypersensitivity responses. Previous reports suggested that cis-UCA was immunomodulatory through its effects on keratinocytes, Langerhans cells, fibroblasts, T lymphocytes, natural killer cells and monocytes/macrophages. As dermal mast cells were recently demonstrated to be critical to UVB-induced systemic suppression of certain delayed-type and contact hypersensitivity responses, we investigated whether they were involved in the processes by which cis-UCA was immunomodulatory. Not only was there a correlation between dermal mast cell prevalence and the degree of susceptibility of different strains of mice to the immunomodulatory effects of cis-UCA, there was also a functional link. Mast cell-depleted Wf/Wf mice were rendered susceptible to immunomodulation by cis-UCA injected subcutaneously only after their dorsal skin had been reconstituted with bone marrow-derived mast cell precursors. These studies suggest that mast cells are critical to the processes by which cis-UCA suppresses systemic contact hypersensitivity responses to the hapten, trinitrochlorobenzene, in mice.  相似文献   
45.
An inexpensive flow-injection instrument for determining low concentrations of dissolved reactive phosphorus in natural waters is reported. The unique feature is the use of an inexpensive detector consisting of a flow cell and a simple photometer that incorporates a super-bright light-emitting diode as the source and a photodiode as the detector. The tin(II) chloride-molybdate method was optimized using a modified simplex optimization method. Silicate interference up to 5 mg Si l?1 was removed by addition of 0.10% (w/v) tartaric acid. Using the tartaric acid-modified optimized reagents, a detection limit of 0.6 μg P l?1 was achieved. The method was linear over the range 0–100 μg P l?1 with an excellent precision (r.s.d. 2.9% at 2.0 and 0.5% at 50 μg P l?1). An in-line pre-concentration anion-exchange column was used to obtain an even lower detection limit of 0.1 μg P l?1 and applied to the analysis of real samples.  相似文献   
46.
A search for the nonconservation of lepton flavor number in the decay tau(+/-) --> mu(+/-) has been performed using 2.07 x 10(8) e(+ )e(-) tau(+) tau(-) events produced at a center-of-mass energy near 10.58 GeV with the BABAR detector at the PEP-II storage ring. We find no evidence for a signal and set an upper limit on the branching ratio of Beta(tau(+/-) --> mu(+/-) gamma) < 6.8 x 10(-8) at 90% confidence level.  相似文献   
47.
Surfaces coated with nanoscale filaments such as silicon nanowires and carbon nanotubes are potentially compelling for high‐performance battery and capacitor electrodes, photovoltaics, electrical interconnects, substrates for engineered cell growth, dry adhesives, and other smart materials. However, many of these applications require a wet environment or involve wet processing during their synthesis. The capillary forces introduced by these wet environments can lead to undesirable aggregation of nanoscale filaments, but control of capillary forces can enable manipulation of the filaments into discrete aggregates and novel hierarchical structures. Recent studies suggest that the elastocapillary self‐assembly of nanofilaments can be a versatile and scalable means to build complex and robust surface architectures. To enable a wider understanding and use of elastocapillary self‐assembly as a fabrication technology, we give an overview of the underlying fundamentals and classify typical implementations and surface designs for nanowires, nanotubes, and nanopillars made from a wide variety of materials. Finally, we discuss exemplary applications and future opportunities to realize new engineered surfaces by the elastocapillary self‐assembly of nanofilaments.  相似文献   
48.
49.
We prove that when q is any odd prime power, the distance-2 graph on the set of vertices at maximal distance D from any fixed vertex of the Hemmeter graph HemD(q) is isomorphic to the graph QuadD-1(q) of quadratic forms on .  相似文献   
50.
    
Ohne Zusammenfassung  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