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   28713篇
  免费   625篇
  国内免费   734篇
教育   16154篇
科学研究   6136篇
各国文化   176篇
体育   1933篇
综合类   1309篇
文化理论   152篇
信息传播   4212篇
  2024年   10篇
  2023年   43篇
  2022年   313篇
  2021年   965篇
  2020年   691篇
  2019年   327篇
  2018年   329篇
  2017年   405篇
  2016年   363篇
  2015年   991篇
  2014年   1425篇
  2013年   1967篇
  2012年   2020篇
  2011年   2322篇
  2010年   2092篇
  2009年   1933篇
  2008年   1898篇
  2007年   2221篇
  2006年   2150篇
  2005年   1702篇
  2004年   855篇
  2003年   873篇
  2002年   820篇
  2001年   720篇
  2000年   480篇
  1999年   485篇
  1998年   340篇
  1997年   292篇
  1996年   219篇
  1995年   151篇
  1994年   133篇
  1993年   98篇
  1992年   96篇
  1991年   47篇
  1990年   51篇
  1989年   48篇
  1988年   32篇
  1987年   13篇
  1986年   16篇
  1985年   15篇
  1984年   19篇
  1983年   13篇
  1982年   6篇
  1981年   6篇
  1980年   11篇
  1979年   12篇
  1978年   6篇
  1977年   7篇
  1974年   12篇
  1957年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
陈少龙 《现代情报》2012,32(4):165-168,177
社会网络分析法能全面透析个体与整体,局部与全部,以及不同网络间的关系。利用CNKI现存数据,使用Pajek分析,是一种很便捷的解析复杂网络的方式。科研人员之间合作发表论文是科研合作最直接的表现形式。通过对合著网络的分析,可以得出该学院的科研合作、资源分配等情况,从而客观的评价、看待发展。  相似文献   
992.
探究式教学法在《有机化学》教学中的应用   总被引:1,自引:0,他引:1  
陈甡  刘平 《中国科技信息》2012,(11):221-222
阐述了有机化学的教学现状及探究式教学的实质,强调了在有机化学教学中应用探究式教学的必要性,并列举实施探究式教学的程序及实施实例。  相似文献   
993.
 Acanthochlamydoideae, a new subfamily of Amaryllidaceae, is proposed in the pre- sent paper, based upon the monotypic genus Acanthochlamys which was detected by the writer in 1979 and named Didymocolpus as a new genus but was preceded by P. C. Kao in 1980 under the former name.  The genus is indeed of great morphological in- terest. It has semicylindric leaves with a deep furrow on the ventral and dorsal sides respectively.  The lower part of the leaf is connate with, or adnate to, the lower mid- rib of a rather large and membranous vagina . Such a feature, as far as we know, is very rare in the monocotyledons.      The flower resembles that of Amaryllidaceae in having inferior ovary, six stamens and corolla-like perianth with a rather long tube.  But it is quite different in other characters, such as head-like cyme, leaf-like bracts and bisulcate leaves, which all are foreign to any taxon known in the Amaryllidaceae.  On the other hand, it bears some resemblance particularly in habit and inflorescence  to  Campynemanthe  of  the Hy- poxidaceae, and also to Borya and Bartlingia of the Liliaceae (in the tribe John- sonieae), but differs in its long perianth-tube and curious leaf structure.  It is highly probable that the resemblance between them is only superficial and not indicative of direct or close relationship.      This is no doubt a very curious plant of which we still know incompletely, and for which an appropriate place in the monocotyledons has not yet been found.  Con- sidering its floral characters, however, it seems safe for the present to place it as a separate subfamily in the Amaryllidaceae and is juxtaposed with the Ixiolirioideae and Amaryllidoideae, the only two subfamilies of Amaryllidaceae according to H. Mel- chior (1964), and, of course, to either of them it is not directly related. Its true affinity remains problematic.      The only species, Acanthochlamys bracteata, is found in Mar-er-kan (102°12'N, 31°47'E), Qian-ning (101°30'N, 30°33'E), Xiang-cheng  (99°39'N, 28°54'E)  and Dau cheng (100°10'N, 29°03'E) in western Sichuan of southwest China, in open bushland or grassland at an altitude between 2700—3500 meters.  Its geographical distribution is mapped and its morphological details are illustrated to facilitate its identification.    相似文献   
994.
995.
996.
This paper deals with the taxa of tribe Arundinarieae Steud. subtribe Pleiobalastinae Keng and Keng f. which comprised three genera (Pseudosasa Makino, Pleioblastus Nakai and Brachystachyum Keng) when it was established in 1957. With the analysis of morphological characters and geographical distribution, a number of revisions connected with the taxon are made as follows:      (1)  Genus Brachystachyum Keng is transferred to the tribe Shibataeeae Nakai ac- cording to its false inflorescence.      (2)  Genus Pseudosasa Makino is transferred to subtribe Sasinae Keng f. according to our study on the numerical taxonomic method.      (3)  Some species of Pleioblastus Nakai established by Keng and Keng f. should be revised. Pleioblastus actinotrichus (Merr. and Chun) Keng f. should be Ampelocalamus actinotrichus (Merr. and Chun) S. L. Chen, T. H. Wen and G. Y. Sheng in subtribe Tham- nocalaminae Keng f.; Pleioblastus dolichanthus (Keng) Keng f. is the synonym of Sinobam- busa tootsik (Sieb.) Makino, belonging to tribe Shibataeeae Nakai. The rest species remain in this genus. Since the genus Pleioblastus is related to genus Arundinaria Michaux., subtribe Pleioblastus Keng and Keng f. does not seem to have a reason to be retained as a subtribe in tribe Arundinarieae Steud., according to the newest Code (1978). A part of it should be a synonym of subtribe Arundinariinae and we may cite it as follows: Subtribe Arundinariinae——Subtribe Pleioblastinae Keng and Keng f. pro parte, syn. nov. The other parts of it should be transferred to other subtribes or tribes.       In addition, one new variety in Branchystachyum, two new species, one new variety in Pseudosasa and six new species, three new varieties in Pleioblastus, are described in this paper.  相似文献   
997.
  It is generally accepted that tea plant (Thea sinensis L.) is originated in China, where has numerous varieties,  According to the literature, the selected work of tea plants may be traced as early as to the 3rd-5th century A.D.  The number of varie- ties discovered in recent years reached more than 300.  Besides, a large number of wild species were discovered. In all tea varieties, the crown canopy, leaf size and the date of sprouting were different.  It was proposed that according to the crown canopy, leaf size and the date of sprouting.   The  principle of the classification  of Chinese tea varieties may be 3 orders.  The first order named “group”, it contains macrophanerophyte group, microphanerophyte group, and frutex group.  The second order named “type”, it contains extreme large leaf size, large leaf size, medium leaf size and small leaf size.  The third order named “species”, it contains the early- sprouting species, medium-sprouting species and late-sprouting species.    相似文献   
998.
本文用矩阵的秩这个工具考察了有限维线性系统具有二次性能指标的最优输出反馈问题,得到了一个必要条件。特殊情形下,这一条件可以演化为最优输出反馈增益与观测矩阵的乘积即为状态反馈增益这个相当清晰的关系。  相似文献   
999.
黑河下游地区土地荒漠化及其治理   总被引:5,自引:1,他引:5  
陈隆亨 《资源科学》1996,18(2):35-43
土地荒漠化的表现有:湖泊干涸;地下水位下降和水质恶化;植被退化;土壤盐渍化;土地风蚀沙化。治理荒漠化的意见:迅速解决水源,加强绿洲的巩固和建设。  相似文献   
1000.
刘枫  陈凯 《科教文汇》2012,(23):203-204
本文论述了监管环境中疏忽与侥幸的原因与表现以及其概念延伸,并探讨了如何克服疏忽与消除侥幸,从而将疏忽与侥幸降至最低,以确保监狱的安全稳定。  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