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   6596篇
  免费   75篇
  国内免费   7篇
电工技术   38篇
综合类   3篇
化学工业   499篇
金属工艺   35篇
机械仪表   45篇
建筑科学   143篇
矿业工程   4篇
能源动力   68篇
轻工业   273篇
水利工程   18篇
石油天然气   10篇
无线电   355篇
一般工业技术   440篇
冶金工业   4419篇
原子能技术   40篇
自动化技术   288篇
  2021年   30篇
  2019年   27篇
  2018年   32篇
  2017年   37篇
  2016年   34篇
  2015年   31篇
  2014年   49篇
  2013年   106篇
  2012年   62篇
  2011年   110篇
  2010年   75篇
  2009年   85篇
  2008年   86篇
  2007年   98篇
  2006年   94篇
  2005年   82篇
  2004年   61篇
  2003年   65篇
  2002年   52篇
  2001年   57篇
  2000年   58篇
  1999年   165篇
  1998年   1344篇
  1997年   742篇
  1996年   556篇
  1995年   313篇
  1994年   289篇
  1993年   289篇
  1992年   67篇
  1991年   81篇
  1990年   97篇
  1989年   97篇
  1988年   93篇
  1987年   87篇
  1986年   81篇
  1985年   73篇
  1984年   44篇
  1983年   50篇
  1982年   40篇
  1981年   43篇
  1980年   64篇
  1979年   32篇
  1978年   35篇
  1977年   122篇
  1976年   242篇
  1975年   35篇
  1974年   35篇
  1973年   28篇
  1971年   32篇
  1970年   24篇
排序方式: 共有6678条查询结果,搜索用时 51 毫秒
51.
52.
53.
Using the data from vendors and open literature, we have constructed a preliminary cost model to predict the cost of liquid hydrogen (LH2) from water electrolysis. The model has been applied to two LH2 plants. Both have a production rate of 10 886 kg day−1. The first plant (Plant 1) consists of a tank-type electrolyzer and a liquefier and runs all day at the base-load (or equivalent base-load) power rate. The second (Plant 2) consists of a tank-type electrolyzer, a liquefier, a compressor, and storage vessels. The electrolyzer and the compressor shall run only during the off-peak hours at the off-peak power rate. However, the liquefier shall run all day at the base-load (or equivalent base-load) power rate. The costs of LH2 from both plants are presented. Unless the base-load power rate is high and the off-peak power rate is substantially low, Plant 1 appears to be economically more feasible than Plant 2.  相似文献   
54.
55.
56.
The active iodide uptake of the thyroid gland in humans is mediated by the human sodium iodide symporter (hNIS). In this report, we show that hNIS expression was detected primarily in thyroid tissue, but also in breast, colon, and ovary tissues. Expression of hNIS is greatly reduced in thyroid tumors compared to normal thyroid tissue. Among tumor tissues, hNIS expression appears to be variable, consistent with the variable response to radioiodide treatment observed for thyroid carcinomas. The coding region of hNIS is interrupted by 14 introns, and the nucleotide sequence of each exon-intron junction is reported. Using this information, an alternatively spliced form of hNIS was identified. Finally, the chromosome location of the hNIS gene was mapped to chromosome 19p.  相似文献   
57.
58.
Parasite-specific antibody responses were detected using an indirect fluorescent antibody (IFA) test in cattle that were naturally or experimentally infected with Neospora parasites. The test was developed using Neospora tachyzoites isolated from an aborted bovine fetus and grown in bovine cell cultures (isolate BPA1). In all cases, infections were confirmed by the identification of Neospora tachyzoites and/or bradyzoite cysts in fetal or calf tissues using an immunoperoxidase test procedure. Fifty-five naturally infected cows that aborted Neospora-infected fetuses had titers of 320-5,120 at the time of abortion. The titer of 6 cows that were serologically monitored over a prolonged period decreased to 160-640 within 150 days after they aborted infected fetuses. Two of the cows showed an increase in their Neospora titers during their subsequent pregnancy, and they gave birth to congenitally infected calves that had precolostral titers of 10,240-20,480. Postcolostral titers of these calves and of 4 other calves with congenital Neospora infections were all > or = 5,120, whereas calves with no detectable parasites had titers < or = 160. Two pregnant heifers that were experimentally infected with the BPA1 isolate at approximately 120 days gestation seroconverted to Neospora antigens within 9 days and developed peak titers of 5,120 and 20,480 within 32 days of infection. The fetus taken by caesarean section 32 days postinfection from 1 heifer and the full-term calf born to the other had Neospora titers of 640 and 10,240, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
59.
60.
This paper treats the steady axisymmetric flow and mass transport in a cylindrical liquid bridge between the melting end of a feed rod and the solidifying end of an alloyed semiconductor crystal. There is a strong, uniform, steady, axial magnetic field. The surface tension depends on the temperature and the concentration of the species, while variations of the concentration occur because one species is rejected into the liquid during solidification. The thermocapillary and solutocapillary convections tend to cancel over part of the liquid bridge. For certain parameter ranges, there are two different stable solutions: one where the concentration gradient along the free surface leads to dominance by the solutocapillary convection and one where the mass transport due to the thermocapillary convection makes the concentration gradient along the free surface small, so that the thermocapillary convection is dominant.  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