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   10923篇
  免费   352篇
  国内免费   798篇
系统科学   338篇
丛书文集   384篇
教育与普及   61篇
理论与方法论   19篇
现状及发展   457篇
研究方法   1篇
综合类   10805篇
自然研究   8篇
  2024年   17篇
  2023年   51篇
  2022年   100篇
  2021年   142篇
  2020年   127篇
  2019年   107篇
  2018年   118篇
  2017年   153篇
  2016年   184篇
  2015年   256篇
  2014年   430篇
  2013年   348篇
  2012年   585篇
  2011年   665篇
  2010年   550篇
  2009年   696篇
  2008年   649篇
  2007年   834篇
  2006年   781篇
  2005年   641篇
  2004年   571篇
  2003年   567篇
  2002年   459篇
  2001年   394篇
  2000年   388篇
  1999年   365篇
  1998年   230篇
  1997年   246篇
  1996年   211篇
  1995年   180篇
  1994年   177篇
  1993年   162篇
  1992年   155篇
  1991年   144篇
  1990年   108篇
  1989年   107篇
  1988年   75篇
  1987年   42篇
  1986年   19篇
  1985年   26篇
  1984年   8篇
  1981年   3篇
  1980年   1篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
神经网络在成组技术方面的应用   总被引:3,自引:0,他引:3  
阐述了成组技术及其在高级制造技术中的作用,在此基础上描述了神经网络在零件编码分类系统中的应用以及用神经网络设计制造单元的方法。  相似文献   
72.
KF or K2CO3 was added into the 1-butanol-water system and two phases were formed: water-rich phase (water phase) and 1-butanol-rich phase (1-butanol phase). The liquid liquid equilibrium (LLE) data for 1-butanol-water-KF and 1-butanol-water-K2CO3 systems were measured at 25℃ and showed that 1-butanol phase contained negligible salt and water phase contained negligible 1-butanol when the concentrations of KF and K2CO3 in the water phase were equal to or higher than 27.11% and 31.68% , respectively. Thus water could be separated efficiently from 1-butanol-water by adding KF or K2CO3 into the system. A theoretical calculation of LLE data was calculated by using the Pitzer theory to get water activity in the water phase, and by the models, such as the Wilson, NRTL or the UNIQUAC for the 1-butanol phase. For 1-hutanol-water-KF system, the experimental data were found in good agreement with the calculated results by using Pitzer theory and Wilson equa tion, while for 1-butanol-water-K2CO3 system, the experimental data were found in good agreement with the calculated results by using Pitzer theory and UNIQUAC eauation.  相似文献   
73.
设计并实现了以Nexperia PNX1300 Series媒体处理器为核心,集视频、音频、通信、图象和控制为一体的数字多媒体平台,它具有高性能的实时数字信号处理能力,是数字多媒体编解码标准的算法研究与实现的理想平台,实验证明,数字多媒体平台是一个性能卓越、功能强大的实时信号采集与处理系统,完全满足数字多媒体实时处理的需要,它将MPEG-4的视频压缩技术与流媒体技术结合,具有广泛的应用前景。  相似文献   
74.
为寻求简便、合理的合成超细粉体的方法,利用NH4HCO3 作沉淀剂,通过考察料液配比、加料速度、升温速度等实验因素,得到了简单的合成超细 Ce Zr O粉末的工艺,并利用比表面积测定仪、激光粒度仪、XRD、Raman等仪器对相关产物进行了表征.结果表明:利用简单工艺合成的超细 Ce Zr O粉末具有中位粒径为0.30μm、比表面积为21.2 m2/g、悬浮性大于30 min、松装密度小于 1 g/cm3等性能,产物具有 CaF2 型的空间结构.  相似文献   
75.
该文介绍了在Windowe3.1环境下.利用MicrosoftC(++)及其基本类库(MFC)开发光伏水泵报价系统的方法。该方法采用了面向对象技术,使软件具备可重用性。同时,MFC类库的使用使复杂的Win-dows应用程序的编程接口变得更容易。该方法对其它工程报价问题也具借鉴意义。  相似文献   
76.
Summary Intraperitoneal injection of allogeneic liver cells from 43-day-old male fetuses into normal 60-day female goat fetuses resulted in persistent hemopoietic chimerism in surviving recipients without clinical evidence of graft-versus-host disease. Transplantation of normal fetal liver cells into preimmunocompetent goat fetuses affected with -D-mannosidosis may provide an alternative strategy for evaluating hemopoietic stem cell transplantation in the treatment of human lysosomal storage diseases.  相似文献   
77.
Summary The profile of action in animals of CQP 201-403, a novel 8-amino-ergoline, is in most aspects that of a very potent dopaminomimetic, both as a prolactin secretion inhibitor, and at the levels of the CNS and the cardiovascular system. Qualitatively CQP 201-403 differs slightly from bromocriptine and apomorphine in its effects on the CNS (no influence on serotonin metabolism in the rat cortex; induction of masculine mounting behavior in rats) and the cardiovascular system of the dog (reflex tachycardia in response to a blood-pressure fall). In man the new compound proved to be highly active in lowering prolactin serum levels and to be more potent than bromocriptine (Parlodel®).In memory of Dr Annemarie Closse, who died 14 June 1987.  相似文献   
78.
We demonstrate for the first time a hair cycle-dependent gene and protein expression of proopiomelanocortin in mouse skin in vivo. Northern blot detected POMC mRNA with an apparent size of 0.9 kb in anagen but not telogen skin. Western blot emphasized a specific protein of 30–33 kDa recognized by anti -endorphin in late but not early anagen or telogen skin. By immunocytochemistry, -endorphin antigen was localized in the sebaceous gland in a hair cycle dependent manner.  相似文献   
79.
In 1986, Brown and Clemmons (Proc. natl Acad. Sci. USA83 (1986) 3321) showed that platelets contain a substance, platelet-derived growth inhibitor (PDGI), that inhibits in vitro endothelial cell replication. Although platelets are rich in transforming grwoth factor (TGF-), PDGI was considered not to be related to TGF-, on the basis of its reported properties (extraction from platelets at neutral pH, binding to heparin-Sepharose). However, we purified PDGI to near homogeneity and showed that on the basis of HPLC retention behavior, in vitro growth inhibitory activities with several cell types, receptor binding, and immunoneutralization of growth inhibitory activity with specific anti-TGF- type 1 antibodies, PDGI is most probably identical with TGF- type 1.  相似文献   
80.
Both in vivo and in vitro models have certain disadvantages for the study of the chronic hepatotoxicity of drugs. The aim of this work was to evaluate a new approach based on an in vivo/in vitro model. After chronic in vivo treatment of rats with Vincamine and Vindeburnol (an eburnamenine derivative which exhibits hepatotoxic properties in man) liver cells were isolated, and functional and metabolic disorders (metabolic utilization of fructose and protein biosynthesis) were studied to determine injury. The results showed no modification of blood parameters, but a direct relationship between the dose of Vindeburnol administered in vivo and the metabolic disorders observed in vitro, evidencing the high sensitivity and reliability of this model.  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