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   2093篇
  免费   76篇
  国内免费   8篇
电工技术   13篇
综合类   1篇
化学工业   288篇
金属工艺   12篇
机械仪表   33篇
建筑科学   19篇
矿业工程   2篇
能源动力   27篇
轻工业   125篇
水利工程   2篇
石油天然气   1篇
无线电   208篇
一般工业技术   247篇
冶金工业   1094篇
原子能技术   6篇
自动化技术   99篇
  2023年   10篇
  2022年   14篇
  2021年   31篇
  2020年   15篇
  2019年   25篇
  2018年   34篇
  2017年   30篇
  2016年   32篇
  2015年   21篇
  2014年   41篇
  2013年   62篇
  2012年   56篇
  2011年   97篇
  2010年   55篇
  2009年   49篇
  2008年   66篇
  2007年   58篇
  2006年   49篇
  2005年   31篇
  2004年   29篇
  2003年   39篇
  2002年   38篇
  2001年   26篇
  2000年   36篇
  1999年   61篇
  1998年   332篇
  1997年   217篇
  1996年   152篇
  1995年   73篇
  1994年   51篇
  1993年   68篇
  1992年   20篇
  1991年   14篇
  1990年   13篇
  1989年   16篇
  1988年   21篇
  1987年   20篇
  1986年   12篇
  1985年   20篇
  1984年   6篇
  1983年   2篇
  1982年   4篇
  1981年   4篇
  1980年   16篇
  1978年   5篇
  1977年   22篇
  1976年   68篇
  1974年   8篇
  1973年   3篇
  1955年   2篇
排序方式: 共有2177条查询结果,搜索用时 15 毫秒
1.
2.
3.
Ten groups of 14 immunosuppressed NMRI-mice (nu/nu) were raised and kept under germ-reduced conditions. The control animals were fed a germ-reduced diet, nine other groups received the same diet with selegiline (CAS 14611-51-9, Deprenyl) or lipoic acid (thioctic acid, CAS 62-46-4) admixed at various amounts. The 50% survival rate, the total life span of each group and the areas under the curves were determined to evaluate life expectancy as compared to the controls. The racemate of lipoic acid at high dosage (350 mg/kg body weight) reduced the life span significantly. The S(-)-enantiomer of lipoic acid (75 mg/kg body weight) increased the 50% survival rate, whereas the physiologic R(+)-enantiomer (9 mg/kg body weight) expanded the total life span of its group. Alteration of only one out of three parameters was not considered significant. All other groups except for one did not differ from controls: only animals which obtained 75 micrograms selegiline per kg of body weight and per day exerted increased life expectancies by all three parameters. This group exhibited also in statistical evaluation a significantly (p < 0.05) prolongated survival time up to about 200% as compared to the control animals.  相似文献   
4.
Based on generalization and analysis of instructions and guidelines for therapeutical and prophylactic diets of workers, ways of its optimization were proposed, by using bifide-containing acid dairy products as a preventive agent against possible occupational diseases caused by occupational factors.  相似文献   
5.
Cancer statistics, 1993   总被引:1,自引:0,他引:1  
  相似文献   
6.
We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH3 is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH3 pre-exposure helps form a Zn3N2 layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar.  相似文献   
7.
8.
A mica-based machinable glass-ceramic has been converted to a glass-ceramic containing cordiertie and body-centered cubic chondrodite through heat treatment at temperatures higher than that used for the crystallization of mica. The machinability is lost, microhardness increases, and the thermal expansion coefficient decreases with the change of the crystalline phase from mica to cordierite and chondrodite.  相似文献   
9.
1. alpha-toxin of Staphylococcus aureus readily permeabilized rat uterine smooth muscle after incubation for a short time. 2. The permeabilized muscle responded to Ca2+ dose-dependently and repeatedly in the same manner. 3. The threshold concentration of Ca2+ for contraction was 0.1-0.3 microM and the maximal contraction was achieved with 1 or 3 microM Ca2+. 4. GTP gamma S or GTP augmented the contractile response to Ca2+. 5. GDP beta S or GDP suppressed the contraction. 6. The role of GTP-binding protein in sensitization of Ca(2+)-induced contractile response of smooth muscle is discussed.  相似文献   
10.
To evaluate an association between Helicobacter pylori (H. pylori) infection and chronic atrophic gastritis (CAG), an established precursor of gastric cancer, we performed a cross-sectional study using IgG antibody against H. pylori and pepsinogens of blood donors in four prefectures in Japan. Although a geographic correlation between the age-adjusted prevalence rates for H. pylori infection and those for CAG was not seen, the age-adjusted odds ratios (OR) of H. pylori infection for CAG were high in each area (around five for men and from four to 12.6 for women). The association between them weakened with advancing age; the ORs in the youngest age group (16-29 yrs) and in the oldest age group (50-64 yrs) were 12.5 and 2.8 for men, and 11.5 and 5.2 for women, respectively. These findings suggest that H. pylori infection is strongly associated with CAG, while there are some other factors interacting in the development of CAG. A prospective cohort study in which CAG and H. pylori infection are taken into account will be necessary to assess the risks of gastric cancer.  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