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   1508篇
  免费   28篇
  国内免费   17篇
化学   945篇
晶体学   10篇
力学   52篇
数学   205篇
物理学   341篇
  2022年   11篇
  2021年   16篇
  2020年   15篇
  2019年   11篇
  2018年   11篇
  2016年   23篇
  2015年   20篇
  2014年   17篇
  2013年   79篇
  2012年   42篇
  2011年   78篇
  2010年   50篇
  2009年   35篇
  2008年   52篇
  2007年   75篇
  2006年   57篇
  2005年   63篇
  2004年   52篇
  2003年   42篇
  2002年   47篇
  2001年   33篇
  2000年   38篇
  1999年   39篇
  1998年   15篇
  1997年   22篇
  1996年   32篇
  1995年   19篇
  1994年   19篇
  1993年   35篇
  1992年   13篇
  1991年   21篇
  1990年   28篇
  1989年   21篇
  1988年   19篇
  1987年   25篇
  1986年   17篇
  1985年   32篇
  1984年   33篇
  1983年   18篇
  1982年   17篇
  1981年   21篇
  1980年   25篇
  1979年   20篇
  1978年   13篇
  1977年   13篇
  1976年   16篇
  1975年   15篇
  1974年   12篇
  1973年   14篇
  1972年   12篇
排序方式: 共有1553条查询结果,搜索用时 15 毫秒
101.
Nested-wire array experiments have been conducted at the 7 MA level with 150 ns implosion times from an outer diameter of 40 mm. Analysis of spectral data indicates that material from the outer array preferentially occupies the high temperature core of the stagnated pinch independent of the interwire gap in the range of 1.1 to 4.5 mm.  相似文献   
102.
We say that a subset of Cn is hypoconvex if its complement is the union of complex hyperplanes. We say it is strictly hypoconvex if it is smoothly bounded hypoconvex and at every point of the boundary the real Hessian of its defining function is positive definite on the complex tangent space at that point. Let Bn be the open unit ball in Cn.Suppose K is a C compact manifold in ∂B1 × Cn, n > 1, diffeomorphic to ∂B1 × ∂Bn, each of whose fibers Kz over ∂B1 bounds a strictly hypoconvex connected open set. Let K be the polynomialhull of K. Then we show that K∖K is the union of graphs of analytic vector valued functions on B1. This result shows that an unnatural assumption regarding the deformability of K in an earlier version of this result is unnecessary. Next, we study an H optimization problem. If pis a C real-valued function on ∂B1× Cn, we show that the infimum γρ = infƒ∈H (B1)n ‖ρ(z, ƒ (z))‖ is attained by a unique bounded ƒ provided that the set (z, w) ∈ ∂B1 × C n|ρ(z, w) ≤ γρ has bounded connected strictly hypoconvex fibers over the circle.  相似文献   
103.
This review consolidates biological activity data reported for pyridoacridine 1 molecules in the literature from 1983-2003 into several tables with brief discussions of assays used and results obtained. This review summarizes recent progress in structure activity relationships for analogues of amphimedine 2 and ascididemin 3 classes of pyridoacridines and correlates reported molecular mechanisms of action with biological activities.  相似文献   
104.
Towards quantum superpositions of a mirror   总被引:1,自引:0,他引:1  
We propose an experiment for creating quantum superposition states involving of the order of 10(14) atoms via the interaction of a single photon with a tiny mirror. This mirror, mounted on a high-quality mechanical oscillator, is part of a high-finesse optical cavity which forms one arm of a Michelson interferometer. By observing the interference of the photon only, one can study the creation and decoherence of superpositions involving the mirror. A detailed analysis of the requirements shows that the experiment is within reach using a combination of state-of-the-art technologies.  相似文献   
105.
We report electron capture dissociation (ECD) and infrared multiphoton dissociation (IRMPD) of doubly protonated and protonated/alkali metal ionized oligodeoxynucleotides. Mass spectra following ECD of the homodeoxynucleotides polydC, polydG, and polydA contain w or d "sequence" ions. For polydC and polydA, the observed fragments are even-electron ions, whereas radical w/d ions are observed for polydG. Base loss is seen for polydG and polydA but is a minor fragmentation pathway in ECD of polydC. We also observe fragment ions corresponding to w/d plus water in the spectra of polydC and d(GCATGC). Although the structure of these ions is not clear, they are suggested to proceed through a pentavalent phosphorane intermediate. The major fragment in ECD of d(GCATGC) is a d ion. Radical a- or z-type fragment ions are observed in most cases. IRMPD primarily results in base loss, but backbone fragmentation is also observed. IRMPD provides more sequence information than ECD, but the spectra are more complex due to extensive base and water losses. It is proposed that the smaller degree of sequence coverage in ECD, with fragmentation mostly occurring close to the ends of the molecules, is a consequence of a mechanism in which the electron is captured at a P=O bond, resulting in a negatively charged phosphate group. Consequently, at least two protons (or alkali metal cations) must be present to observe a w or d fragment ion, a requirement that is less likely for small fragments.  相似文献   
106.
Hyperuricosuria has long been documented as a predisposing factor to calcium oxalate (CaOx) stone pathogenesis. However, its mechanism is still without sound scientific foundation. Previously, we showed that hyperuricosuria, simulated by the addition of dissolved sodium urate, promotes the crystallization of CaOx. In the present study, we demonstrate that the urate's effect on the crystallization is attributable to its salting out CaOx from solution. Furthermore, analysis of urines revealed that their metastable limit decreased with increases in the product of the prevailing concentrations of calcium and urate: this has implications for CaOx stone genesis. We also outline anti-salting out strategies for future research for the prevention and/or treatment of CaOx calculi.  相似文献   
107.
[reaction: see text] Treatment of 1-iodomethyl-1,5-bis-epoxides with zinc in refluxing ethanol affords cis or trans 2-vinyl-5-(1-hydroxyethy)-substituted tetrahydrofurans stereospecifically in high yield.  相似文献   
108.
[reaction: see text] An analytical construct resin, designed to aid the analysis of solid-phase chemistry, has been mixed in a small proportion with a conventional resin. The analytical construct ("reporter resin") contains two orthogonal linkers that allow cleavage of either the synthetic intermediates (at linker 2) or their analytically enhanced derivatives (at linker 1). The convenient and rapid monitoring of each step in the syntheses of representative library compounds was possible using small resin aliquots.  相似文献   
109.
Measurements of muon-catalyzed dt fusion ( d(mu)t-->4He + n + mu(-)) in solid HD have been performed. The theory describing the energy dependent resonant molecular formation rate for the reaction (mu)t + HD-->[(d(mu)t)pee](*) is compared to experimental results in a pure solid HD target. Constraints on the rates are inferred through the use of a Monte Carlo model developed specifically for the experiment. From the time-of-flight analysis of fusion events in 16 and 37 microg x cm(-2) targets, an average formation rate consistent with 0.897+/-(0.046)(stat)+/-(0.166)(syst) times the theoretical prediction was obtained.  相似文献   
110.

A uniqueness theorem is proved for trigonometric series and another one is proved for multiple trigonometric series. A corollary of the second theorem asserts that there are two subsets of the -dimensional torus, the first having a countable number of points and the second having points such that whenever a multiple trigonometric series ``converges' to zero at each point of the former set and also converges absolutely at each point of the latter set, then that series must have every coefficient equal to zero. This result remains true if ``converges' is interpreted as any of the usual modes of convergence, for example as ``square converges' or as ``spherically converges.'

  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