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   1483646篇
  免费   25784篇
  国内免费   6968篇
电工技术   34245篇
综合类   6345篇
化学工业   269735篇
金属工艺   63900篇
机械仪表   41798篇
建筑科学   45599篇
矿业工程   11417篇
能源动力   50165篇
轻工业   108909篇
水利工程   14984篇
石油天然气   37505篇
武器工业   140篇
无线电   195853篇
一般工业技术   280398篇
冶金工业   153531篇
原子能技术   33922篇
自动化技术   167952篇
  2021年   15506篇
  2020年   11784篇
  2019年   14566篇
  2018年   15398篇
  2017年   14780篇
  2016年   21193篇
  2015年   17288篇
  2014年   28575篇
  2013年   87659篇
  2012年   34736篇
  2011年   46801篇
  2010年   41952篇
  2009年   50625篇
  2008年   43862篇
  2007年   41036篇
  2006年   43980篇
  2005年   38716篇
  2004年   40988篇
  2003年   40902篇
  2002年   40043篇
  2001年   36734篇
  2000年   35323篇
  1999年   34077篇
  1998年   41776篇
  1997年   37327篇
  1996年   34100篇
  1995年   30075篇
  1994年   28272篇
  1993年   28135篇
  1992年   25986篇
  1991年   23042篇
  1990年   23378篇
  1989年   22515篇
  1988年   20919篇
  1987年   19233篇
  1986年   18621篇
  1985年   21979篇
  1984年   22197篇
  1983年   20163篇
  1982年   19185篇
  1981年   19274篇
  1980年   17917篇
  1979年   18444篇
  1978年   17657篇
  1977年   17370篇
  1976年   18052篇
  1975年   15934篇
  1974年   15439篇
  1973年   15527篇
  1972年   13000篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel.  相似文献   
994.
We report a 20 month old female patient with diploid-triploid mixoploidy (46,XX/69,XXX) syndrome with hypothyroidism and precocious puberty. The triploid cell line was only expressed in the fibroblast culture and comprised the majority (95%) of the cells. Chromosome analysis of the fetal blood sample and peripheral blood sample were normal. The patient shows typical features of full triploidy (growth and severe mental retardation, cranial and facial dysmorphism, complete syndactyly of fingers 3/4, partial syndactyly of toes 2/3) and facial but no body asymmetry. At the age of 5 months central hypothyroidism and precocious puberty were diagnosed. Thin pigmented streaks were visible on the wrists and legs of the patient at the age of 16 months. This is the first patient reported so far with 46,XX/69,XXX mixoploidy suffering from hypothyroidism and precocious puberty.  相似文献   
995.
996.
36%渗乐乳油     
陈洪超  简锡贤 《农药》1995,34(9):13-14
36%渗乐乳油田HP-1增效剂与乐果及其他助剂调配而成。五年田间小区和大田药效试验证明:36%渗乐乳油高效,安全,用量少,对各类蚜虫防效优异。  相似文献   
997.
Protective immunity against infection with Mycobacterium tuberculosis is imparted by T cells rather than antibodies, but B cells can play a role as antigen-presenting cells and in granuloma formation. We re-evaluated the role of B cells in the course of tuberculous infection in mu-chain knock-out (Ig-) mice. Surprisingly, the organs of M. tuberculosis-infected Ig- mice were found to have three- to eight-fold elevated counts of viable bacilli compared with normal littermates at 3-6 weeks post-infection. Splenic interferon-gamma responses to whole antigen were unimpaired, whilst proliferation to certain mycobacterial peptides was found to be diminished. However, bacille Calmette-Guérin (BCG) vaccination significantly reduced the infection in Ig- mice. The mechanisms by which B cells can influence primary tuberculous infection need further study.  相似文献   
998.
Results of the drift hole mobility in strained and unstrained SiGe alloys are reported for Ge fractions varying from 0 to 30% and doping levels of 1015-1019 cm-3. The mobilities are calculated taking into account acoustic, optical, alloy, and ionized-impurity scattering. The mobilities are then compared with experimental results for a boron doping concentration of 2×1019 cm-3. Good agreement between experimental and theoretical values is obtained. The results show an increase in the mobility relative to that of silicon  相似文献   
999.
We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er3+:Yb3+ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz  相似文献   
1000.
PURPOSE: To assess the role postoperative mydriatics play after extracapsular cataract extraction (ECCE) and posterior chamber intraocular lens (IOL) implantation in causing iris modifications and in controlling inflammation. SETTING: Outpatients Department, Ninewells Hospital, Dundee, Scotland. METHODS: The prospective study comprised 136 patients who had standardized ECCE. Half the patients used a mydriatic for 2 weeks postoperatively. Anterior chamber activity, pain, and eye redness were evaluated at 2 weeks postoperatively; pupil shape, peripheral anterior synechias, IOL position, and iris adhesions, at 6 weeks. RESULTS: Iris-lens adhesions were significantly more common in the group using a mydriatic. There was no difference between the two groups in postoperative inflammation. CONCLUSION: Mydriatics should not be used routinely after ECCE with posterior chamber IOL implantation.  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