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   1730篇
  免费   5篇
电工技术   4篇
综合类   1篇
化学工业   91篇
金属工艺   3篇
机械仪表   41篇
建筑科学   17篇
矿业工程   3篇
能源动力   25篇
轻工业   128篇
水利工程   4篇
石油天然气   9篇
无线电   39篇
一般工业技术   78篇
冶金工业   1217篇
原子能技术   5篇
自动化技术   70篇
  2022年   2篇
  2021年   9篇
  2019年   2篇
  2018年   6篇
  2017年   4篇
  2016年   7篇
  2015年   2篇
  2014年   5篇
  2013年   34篇
  2012年   18篇
  2011年   25篇
  2010年   17篇
  2009年   24篇
  2008年   17篇
  2007年   23篇
  2006年   16篇
  2005年   28篇
  2004年   20篇
  2003年   17篇
  2002年   13篇
  2001年   16篇
  2000年   20篇
  1999年   50篇
  1998年   411篇
  1997年   213篇
  1996年   164篇
  1995年   88篇
  1994年   78篇
  1993年   75篇
  1992年   15篇
  1991年   22篇
  1990年   18篇
  1989年   15篇
  1988年   22篇
  1987年   9篇
  1986年   10篇
  1985年   14篇
  1984年   13篇
  1983年   9篇
  1982年   10篇
  1981年   14篇
  1980年   12篇
  1979年   7篇
  1978年   6篇
  1977年   41篇
  1976年   62篇
  1975年   6篇
  1974年   7篇
  1973年   7篇
  1972年   3篇
排序方式: 共有1735条查询结果,搜索用时 15 毫秒
41.
Ten human volunteers completed a 4-month diet series consisting of 1 month each of a control diet, a meatless diet, a high-beef diet, and the same control diet. Fat and fiber contents were essentially the same in all four diets, but protein content was doubled during the high-beef diet. During the 4th week on each diet, three stool specimens collected from each volunteer were analyzed for chemical composition and content of facultative, aerobic, and anaerobic bacteria. The bacteriological data are presented in this paper. High beef protein consumption had little effect on the composition of the intestinal flora. There were no significant differences in total counts of facultative and aerobic or anaerobic organisms in the feces when volunteers were on meatless or high-beef diets. At the species level, when counts during the two control diets were comparable, in only three instances did the change from the meatless to a high-beef diet significantly influence the bacterial numbers. The ratio of mean counts of anaerobic to facultative and aerobic organisms was approximately 15:1 during the meatless diet and 34:1 during the high-meat diet. The data indicate that animal protein consumption has little effect on the fecal bacterial profile in humans.  相似文献   
42.
Abnormal-delta8-tetrahydrocannabinol (ABN-delta8-THC) failed to elicit central nervous system and cardiovascular effects in laboratory animals. Abnormal-cannabidiol (ABN-CBD) was also devoid of overt behavioral effects but produced marked hypotension with only slight bradycardia in anesthesized dogs.  相似文献   
43.
44.
Concentrations of the potent, HIV(human immunodeficiency virus) inactivating protein, cyanovirin-N (CV-N), which completely inhibit HIV-1 infectivity, do not block the binding of soluble CD4-receptor (sCD4) to HIV-1 lysates nor the attachment of intact HIV-1 virions to several target T-cell lines. Furthermore, in contrast to the known disassociative effects of sCD4 on viral envelope glycoproteins, treatment of HIVRF with high concentrations of CV-N results in complete viral inactivation but without apparent shedding of gp120 or other ultrastructural changes. These results are consistent with the view that the virucidal effects of CV-N result from interference with step(s) in the fusion process subsequent to the initial binding of the virus to target cells.  相似文献   
45.
Cell-cell and cell-extracellular matrix interactions are fundamental processes involved in cell migration and tissue remodeling. Both the cyclic regeneration of the human endometrium during the menstrual cycle as well as the process of embryo implantation involve such dynamic interactions. It has become quite clear that integrin adhesion molecules expressed on the surface of cells play critical roles in the transmission of signals from the extracellular milieu to the cells. It is these signals that presumably regulate the behavior of these cells during major morphogenetic processes. In recent years, work in human endometrium and trophoblasts has uncovered both the regulated and constitutive expression of integrin subunits and their extracellular matrix ligands in these tissues. In addition, attempts have been made to correlate pathological states related to either infertility or abnormal pregnancy to the aberrant expression of several of these integrins. The purpose of the present review is to describe briefly our present state of knowledge of the expression of integrins in human endometrium and trophoblasts and provide the reader with the necessary background needed to understand, at the cellular and molecular levels, processes in reproduction such as embryo implantation.  相似文献   
46.
47.
48.
The two-channel system previously reported has been implemented in hardware using system parameters appropriate to consumer television. The basic system divides the spectrum into lowand high-frequency spatial components. The lows are coarsely sampled and finely quantized and the highs finely sampled and coarsely quantized using a companded, randomized quantizer. The purpose of this experiment was to demonstrate the potential of the system for low-cost practical application, to study the effect of the character of the randomizing noise, and to ascertain that there were no deleterious effects due to interlace, motion, or input noise. Theoretical noise calculations were qualitatively confirmed.  相似文献   
49.
50.
A novel toroidal cross capacitor was used to measure accurately the dielectric polarizability(p) (i.e., the dielectric constant as a function of the pressure) of helium, argon, nitrogen, methane, and carbon dioxide atT=50°C. The data extend up to 7 MPa (5 MPa for CO2) and may be useful for calibrating on-line, capacitance-based systems that are designed to measure the heating value of natural gas. The uncertainties ofandpare 4×10–6and (3.0×10–5 p+84 Pa), respectively. The properties of helium that had been calculatedab initiofrom quantum mechanics were used to verify that the cross capacitor deformed in a predictable manner under hydrostatic (gas) pressure. Thus, a common cause of systematic errors in measuring the dielectric constant of gases was avoided. For helium, the rms deviation of(p) from the calculations was only 2.7×10–7. This suggests that the estimated uncertainty is very conservative.  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