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   3387篇
  免费   146篇
  国内免费   172篇
系统科学   127篇
丛书文集   95篇
教育与普及   69篇
理论与方法论   14篇
现状及发展   12篇
研究方法   13篇
综合类   3375篇
  2024年   16篇
  2023年   45篇
  2022年   59篇
  2021年   57篇
  2020年   42篇
  2019年   23篇
  2018年   34篇
  2017年   23篇
  2016年   26篇
  2015年   69篇
  2014年   100篇
  2013年   80篇
  2012年   104篇
  2011年   90篇
  2010年   135篇
  2009年   117篇
  2008年   147篇
  2007年   151篇
  2006年   118篇
  2005年   112篇
  2004年   109篇
  2003年   112篇
  2002年   122篇
  2001年   130篇
  2000年   113篇
  1999年   177篇
  1998年   183篇
  1997年   184篇
  1996年   172篇
  1995年   156篇
  1994年   134篇
  1993年   97篇
  1992年   87篇
  1991年   115篇
  1990年   71篇
  1989年   70篇
  1988年   49篇
  1987年   41篇
  1986年   19篇
  1985年   11篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
排序方式: 共有3705条查询结果,搜索用时 31 毫秒
961.
曾昭华 《江西科学》1998,16(1):26-30
根据国家科技攻关研究的结果,论证了长江中下游地区地下水中Ni,Ti,Mo元素的形成、含量及其分布规律与地下水的含水介质成分、氧化还原环境以及地下水酸碱度的关系。  相似文献   
962.
螺旋藻水溶性多糖的分离纯化   总被引:2,自引:0,他引:2  
螺旋藻干粉经乙醇脱脂后用水提取,乙醇沉淀,并经凝胶Sephadex-G柱层析精制,获得4种螺旋藻制多糖SPA-1,SPA-2,SPA-3,SPA-4,研究表明均为均一多糖组分。  相似文献   
963.
The mass recognizing property of DLC film for formic acid vapors   总被引:2,自引:0,他引:2  
The carbon films are prepared by r. f. plasma method with n-butylamine as carbon source. The analysis of Raman spectrosewpy shows that this kind of carbon film has diamond-like structure, and IR spectroscopy measurement indicats that there are SP2 bonding, SP3 bonding and amino-group in the film. It is the existence of amino-group and hydrogen atom that cause the amorphous structure and the deformation of bonding to increase, thus leading the Raman spectrum to form a broad absorption band. The quartz crystal microbalance (QCM) deposited with this kind of carbon film as recognizing coating is very sensitive to formic acid vapors. This QCM sensor has good reproducibility, high stability, rapid response and long lifetime.  相似文献   
964.
The DNA of human factor IX (hF IX) gene vector pMC IX m, which had been proven to be able to express inin vitro and living cells, was introduced into 586 zygotes of Kunming Whlte Mice by positive pressure microinjection technique with manual operation. The 499 survival embryos after microinjection were then transferred into pseudopregnant recipient mice and 216 F, pups were born. The analysis of PCR and Southern blot hybridization showed that, of the 216, 6 (2 females and 4 males) were integrated with foreign DNA in their genornes, giving an integration frequency of 3% (6/216). Two F0 female transgenic mice could express hF IX protein in their milk and the content was over 100 ng/mL as measured with ELISA. The biological activities of hF IV in the milk of two F0 mike were 44.67 % and 79.43 %, respectively.  相似文献   
965.
The method of determining grid sizes of finite element method of water quality models is presented on the basis of characteristics of pollutant distributed in the just downstream grid of discharge. A given length of the grid is applied to calculate the minimum distance for the pollutant to complete mixing in the lateral direction n the just downstream grid of the discharge, and the minimum distance is regarded as the maximum width of the grid. Application of the maximum width of the grid and flow rate per unit width of the river results in the number of flow zones in the lateral direction of the river. Consequently division of grids and numerical calculation of water quality with finite clement method can be carried out on the basis of available method and topographic map of the river course. Analysis of scnsitivity shows that the effect of the width of the river and the effect of the length of the grids on the minimum number of flow zones in the lateral direction is relatively small, and that the effect of the given lateral mixing degree of the pollutants on the minimum number of flow zones is acceptable, which indicates that the method presented is relatively stable. The method can avoid thc blindness and randomness in determining the number of flow zones, and can decrease the amount of computation under the condition that the accuracy requirement is mct. The problem that determining the sizes of the grids must rely on empirical knowledge has bcen solved.  相似文献   
966.
The mega-thick oil-bearing sandstone has been discovered in the Jurassic System in the Tula Basin, among which there are asphalt veins in fractures. The crude oil from oil-bearing sandstone and asphalt in the basin is mature, and similar to that of the Jurassic crude oil in the Qaidam Basin in geochemistry. The discovery not only shows that the Tula Basin can generate hydrocarbon and take on great exploration prospects but also has great implications for the oil and gas exploration in the Qaidam Basin.  相似文献   
967.
对向靶反应溅射制备AlN薄膜的结构及物性   总被引:1,自引:0,他引:1  
用对向靶反应溅射制备的AlN薄膜,高气压为取向,低气压下为取向,精确测量XRD衍射峰位可看出AlN薄膜有较大应力。对硬度的测量发现AlN薄膜硬度较大,取向对硬度没有影响。  相似文献   
968.
提出求解群组AHP的排序向量加权最小几何距离平方法,对不同的专家给出的判断矩阵得出的排序向量提出向量加权最小几何距离平方和概念,以最优化原理求得最优解。从而形成一种新的方便有效的群组排序方法。  相似文献   
969.
综合有关资料及临床实践对白色念珠菌病的发病机理,病因及诊断作一概述  相似文献   
970.
为寻找一种更好的方法,提高股骨颈骨折内固定的治疗效果,笔者应用Hansson钉系统,将2枚带钩的钉以上下平行方式经股骨颈置入股骨头,随机治疗股骨颈骨折患者30例,并进行3~21个月的临床随访观察。结果表明:患肢骨折愈合快、关节功能恢复好,优良率达93%。与其它内固定相比,Hansson钉具有创伤小、操作简便、内固定牢固,符合髋关节生物力学特点,便于推广。  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