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   2564篇
  免费   80篇
  国内免费   3篇
电工技术   156篇
综合类   6篇
化学工业   636篇
金属工艺   99篇
机械仪表   49篇
建筑科学   59篇
能源动力   113篇
轻工业   126篇
水利工程   29篇
无线电   233篇
一般工业技术   453篇
冶金工业   398篇
原子能技术   86篇
自动化技术   204篇
  2023年   10篇
  2022年   25篇
  2021年   65篇
  2020年   22篇
  2019年   37篇
  2018年   51篇
  2017年   27篇
  2016年   51篇
  2015年   48篇
  2014年   63篇
  2013年   141篇
  2012年   85篇
  2011年   140篇
  2010年   89篇
  2009年   150篇
  2008年   103篇
  2007年   99篇
  2006年   93篇
  2005年   87篇
  2004年   76篇
  2003年   76篇
  2002年   54篇
  2001年   59篇
  2000年   57篇
  1999年   54篇
  1998年   149篇
  1997年   117篇
  1996年   65篇
  1995年   60篇
  1994年   47篇
  1993年   44篇
  1992年   27篇
  1991年   35篇
  1990年   15篇
  1989年   32篇
  1988年   25篇
  1987年   28篇
  1986年   17篇
  1985年   22篇
  1984年   24篇
  1983年   20篇
  1982年   14篇
  1981年   19篇
  1980年   14篇
  1979年   10篇
  1978年   13篇
  1977年   13篇
  1976年   21篇
  1973年   9篇
  1972年   12篇
排序方式: 共有2647条查询结果,搜索用时 15 毫秒
1.
Xanthohumol (XH) is an important prenylated flavonoid that is found within the inflorescence of Humulus lupulus L. (Hop plant). XH is an important ingredient in beer and is considered a significant bioactive agent due to its diverse medicinal applications, which include anti-inflammatory, antimicrobial, antioxidant, immunomodulatory, antiviral, antifungal, antigenotoxic, antiangiogenic, and antimalarial effects as well as strong anticancer activity towards various types of cancer cells. XH acts as a wide ranging chemopreventive and anticancer agent, and its isomer, 8-prenylnaringenin, is a phytoestrogen with strong estrogenic activity. The present review focuses on the bioactivity of XH on various types of cancers and its pharmacokinetics. In this paper, we first highlight, in brief, the history and use of hops and then the chemistry and structure–activity relationship of XH. Lastly, we focus on its prominent effects and mechanisms of action on various cancers and its possible use in cancer prevention and treatment. Considering the limited number of available reviews on this subject, our goal is to provide a complete and detailed understanding of the anticancer effects of XH against different cancers.  相似文献   
2.
3.
4.
Niobium- or vanadium-doped anatase sols were prepared by hydrothermal treatment of 0.1 mol/dm3 peroxotitanium complex aqueous solutions dissolving 0–10 mol% niobium or vanadium at 100°C for 8 h. Niobium-doping caused the increase of lattice constants of anatase and the shape change of anatase crystal from spindle-like to cubic-like structure, but no change of the optical absorbance. Vanadium-doping caused the decrease of lattice constant of c -axis, the miniaturization of anatase crystal and the increase of optical absorbance at the wavelength from 350–700 nm.  相似文献   
5.
This paper discusses environmental conservation in reservoir watersheds, an important aspect relating to dam construction. The discussion of the subject describes how, in response to today's growing awareness of environmental issues, measures to absolutely minimize the effects on the environment of a dam project that will submerge the natural environment should be included in initial project plans, and how special concern for the environment ought to be shown throughout project implementation. Details are explained by introducing examples encountered in Japan.  相似文献   
6.
With the growing size and complexity of power systems, system analysis—such as transients calculation—takes much time. Hence, fast calculation methods are required. Although parallel processing is a hopeful method, there have been difficulties in the parallel solution of linear equations which appear in power-flow calculations by the Newton-Raphson method. This paper aims at the fast calculation of the power-flow problem by means of parallel processing. In order to improve the suitability to the parallel solution of the differential equation in transients calculation, we assume the use of a direct-mapping parallel processing machine to map directly the network of a power system onto a network of processors. Under this assumption, we propose a new parallel-processing-oriented method in which the linear equation is solved by linear iterations between nodes with Aitken acceleration. We simulate the method on three model power systems and compare this Parallel Iterative Method (PIN) with a Parallel Direct Method (PDM) which uses the banded matrix according to the number of operations required. As a result, we can expect that PIM may solve linear equations faster than PDM with m processors, although the PIM might be inferior to the PDM with m × m processors, where m denotes the half-band width of the banded matrix.  相似文献   
7.
The initial stage of iron silicide formation is investigated by high-resolution Rutherford backscattering spectroscopy. During the Fe deposition on Si(001) at 470 °C, the formation of FeSi2 is confirmed by the surface peak analysis. Initially, FeSi2 grows epitaxially so that one of the major crystallographic axes is parallel to the <111> axis of the Si substrate. With increasing Fe deposition, the deviation between the major crystallographic axis of the silicide region and Si<111> increases although the electron diffraction pattern is independent of the amount of Fe deposition. Therefore, the subsurface crystallographic structure of iron silicide is transformed from a cubic-like to a low-symmetry structure.  相似文献   
8.
Data fitting with a spline using a real-coded genetic algorithm   总被引:2,自引:0,他引:2  
To obtain a good approximation for data fitting with a spline, frequently we have to deal with knots as variables. The problem to be solved then becomes a continuous nonlinear and multivariate optimization problem with many local optima. Therefore, it is difficult to obtain the global optimum. In this paper, we propose a method for solving this problem by using a real-coded genetic algorithm. Our method can treat not only data with a smooth underlying function, but also data with an underlying function having discontinuous points and/or cusps. We search for the best model among candidate models by using the Bayes Information Criterion (BIC). With this, we can appropriately determine the number and locations of knots automatically and simultaneously. Five examples of data fitting are given to show the performance of our method.  相似文献   
9.
10.
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