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   1922篇
  免费   19篇
电工技术   16篇
综合类   1篇
化学工业   147篇
金属工艺   13篇
机械仪表   38篇
建筑科学   61篇
矿业工程   13篇
能源动力   45篇
轻工业   109篇
水利工程   7篇
无线电   81篇
一般工业技术   132篇
冶金工业   1149篇
原子能技术   6篇
自动化技术   123篇
  2022年   8篇
  2021年   8篇
  2019年   10篇
  2018年   15篇
  2017年   13篇
  2016年   13篇
  2014年   17篇
  2013年   41篇
  2012年   24篇
  2011年   33篇
  2010年   15篇
  2009年   24篇
  2008年   23篇
  2007年   38篇
  2006年   28篇
  2005年   32篇
  2004年   24篇
  2003年   22篇
  2002年   17篇
  2001年   19篇
  2000年   14篇
  1999年   54篇
  1998年   345篇
  1997年   214篇
  1996年   116篇
  1995年   80篇
  1994年   67篇
  1993年   79篇
  1992年   26篇
  1991年   27篇
  1990年   32篇
  1989年   19篇
  1988年   25篇
  1987年   25篇
  1986年   28篇
  1985年   28篇
  1984年   19篇
  1983年   22篇
  1982年   19篇
  1981年   17篇
  1980年   29篇
  1979年   11篇
  1978年   12篇
  1977年   30篇
  1976年   61篇
  1975年   12篇
  1974年   12篇
  1973年   13篇
  1972年   7篇
  1968年   6篇
排序方式: 共有1941条查询结果,搜索用时 15 毫秒
1.
The Trichuris muris-mouse model of intestinal helminth infection provides a convenient system to examine the immune mechanisms operating during acute and chronic infection. Particular subsets of helper T lymphocytes (CD4+Th cells) play an important role in regulating infection via the secretion of distinct groups of cytokines. Reciprocal activation of Th cell subsets is associated with either expulsion of the parasites from the intestine (Th2 cells) or chronic infection (Th1 cells). In vivo neutralization experiments using anti-cytokine monoclonal antibodies show that critical cytokines are involved, with interferon-gamma playing an important role in the establishment of chronic trichuriasis and interleukin-4 in expulsion of the parasite from the gut. This model has provided clear evidence of a crucial role for distinct cytokines in mediating host protection against intestinal helminth infection and that manipulation of the immune response through the Th cell-cytokine axis can benefit either the host or the parasite. As such, the T. muris model is poised to generate important new data relevant not only to intestinal helminthiasis but to the wider field of parasite immunity and infection in general.  相似文献   
2.
Composition and microbiological contamination was measured in samples of pre-packed dates purchased from a number of stores and retail outlets in Greater Glasgow. The sugar content of dried pitted dates was c . 74%, about 10% more than reported on those packs where nutritional information was given. Potentially pathogenic bacteria like Escherichia coli, Staphylococcus aureus and Bacillus cereus were identified in some of the samples together with lactic acid bacteria, yeasts and moulds, Aspergillus flavus and A. parasiticus . Fresh dates were the most heavily contaminated of all samples, probably owing to the high moisture content.  相似文献   
3.
The compositions of the fatty acids in the 1, 2 and 3 positions of the principal glycerolipids and their various stereoisomers were determined. Fatty acids in the 1 and 3 positions of triglycerides were similar in composition and less unsaturated than those in the 2 position. Fatty acids in the 1,2-, 1,3- and 2,3-diglycerides were distributed in a pattern which indicated isomerization ofsn-1,2-diacylglycerol. Lysophosphatidyl choline (the principal monoacyl lipid) consisted of about 80% 1-acyl and 20% 2-acyl isomers. The fatty acid compositions indicated that most of the 2-lysophosphatidyl choline was formed by isomerization of 1-lysophosphatidyl choline. Most of the digly cerides and lysophosphatidyl choline were synthesized in the ripening wheat grain. However a small proportion of these partial glycerides and all of the other minor partial glycerides (monoglycerides, digalactosyl monoglycerides) appeared to be the result of limited lipolysis of the corresponding diacyl lipids in the wheat or in the freshly-milled flour. Fatty acids in the 2 position of all the fully acylated glycerides were very similar in composition, but there were considerable differences in the 1 position fatty acids.  相似文献   
4.
A novel stylus based profiling instrument has been developed for rapid measurement of small surface areas. Outlined in the following paper are some of the key features of the prototype system including the wideband stylus pick-up and the dedicated scanning traverse mechanism. In addition, some preliminary results obtained by scanning the instrument over several different surfaces are presented.  相似文献   
5.
The metaphor of plasma is taken up to present and discuss movement and engagement by participants in mixed reality installation arts. Two works involving full body video portraits exhibited through large plasma screens in a variety of public settings are covered. Machinic mediations of video realism are considered in terms of embodied interaction in which viewer-participants contribute to the ‘disquiet’ of gendered figuring. Processural, proximal and personal aspects of responsive engagement are discussed. This is extended to performativity that may lead us to critical reflection of our own actions and responses in mixed reality arts.  相似文献   
6.
Oxidative stress involves the adverse effects of oxygen and other free radicals on living tissue. An overview of the various types of free radicals generated in the body, the basic chemistry of free radicals, and how they arise is presented. The importance of understanding the action of free radicals on specific target tissues in the skin and how this affects the physiology of the skin in relation to treatment is covered.  相似文献   
7.
8.
Photocurrent spectroscopy is used to characterize band edges in quantum-well intermixed InGaAsP material lattice matched to InP. The band edge absorption data is used as a design tool to predict the dc performance of electroabsorption modulators, and is shown to agree well with data obtained from actual devices. In addition, we demonstrate the presence of an exciton peak in InGaAsP quantum wells, and present its evolution as a function of quantum-well intermixing and reverse bias voltage.  相似文献   
9.
In this paper, the discrete wavelet transform (DWT) was applied to analyze the fluctuations in RR interval and systolic arterial pressure (SAP) recorded from eight alpha-chloralose anesthetized pigs. Our aim was to characterize the autonomic modulation before and after cardiac autonomic blockade and during baroreflex function tests. The instantaneous power of decomposed low-frequency (LF) and high-frequency (HF) components was used for a time-variant spectral analysis. Our results suggested that transient events and changes in autonomic modulation were detected with high temporal resolution. A nonlinear relationship between RR interval and SAP during pharmacologically induced changes in blood pressure was found, when the superimposed effect of respiratory sinus arrhythmia was removed. In addition, the baroslopes were nearly linear when both the LF and HF components were removed using DWT decomposition.  相似文献   
10.
The Soxtec System and the AOCS method were compared for oil determination in soybeans, and no significant difference was found between the two methods. The Root Mean Square Error (RMSE) and standard deviation for individual samples were higher for the Soxtec, but this was attributable to the regrinding step used. The study suggests that the Soxtec System is faster and just as accurate as the AOCS method.  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