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   270398篇
  免费   22356篇
  国内免费   83篇
  292837篇
  2018年   2887篇
  2017年   2730篇
  2016年   3634篇
  2015年   3839篇
  2014年   4900篇
  2013年   6970篇
  2012年   7815篇
  2011年   8352篇
  2010年   5913篇
  2009年   5284篇
  2008年   7594篇
  2007年   7826篇
  2006年   7365篇
  2005年   6939篇
  2004年   7057篇
  2003年   6833篇
  2002年   6744篇
  2001年   12292篇
  2000年   12251篇
  1999年   9200篇
  1998年   2961篇
  1997年   3044篇
  1996年   2707篇
  1995年   2495篇
  1992年   7409篇
  1991年   7547篇
  1990年   7350篇
  1989年   7103篇
  1988年   6614篇
  1987年   6275篇
  1986年   5785篇
  1985年   5947篇
  1984年   4782篇
  1983年   4152篇
  1982年   2863篇
  1981年   2600篇
  1980年   2507篇
  1979年   4590篇
  1978年   3617篇
  1977年   3253篇
  1976年   3040篇
  1975年   3678篇
  1974年   4087篇
  1973年   4070篇
  1972年   3779篇
  1971年   3401篇
  1970年   3018篇
  1969年   2973篇
  1968年   2713篇
  1967年   2550篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Rapid and reproducible method is described here for the purification of the 43 kDa fimbrial protein from P. gingivalis by preferential fractionation in the presence of 1% SDS and 0.2M of a bivalent cation at pH 6.5. Homogeneity of the purified 43 kDa was confirmed by SDS-PAGE and Western blot analysis using monoclonal and polyclonal antibodies raised against this protein. Amino acid composition and the amino acid sequence of the first 30 amino acid residues of the purified fimbriae are consistent with the composition and sequence predicted from the cloned gene of the fimbrial subunit. Circular dichroism spectra shows high levels of beta-sheet structure. The purified 43 kDa polymer shows fimbriae-like morphology under the electron microscope. Ultrastructural localization of the 43 kDa protein by the immunogold technique revealed specific labeling of the fimbriae with a diameter of approximately 3.5 to 5.0 nm. Localization of this protein suggest that the 43 kDa component is a fimbrial subunit.  相似文献   
993.
Species composition and ecological structure of ground beetle population was studied in northern taiga meadows of the Arkhangelsk Region. Meadows in the northern forest zone proved to harbor 91 ground beetle species. Carabid complexes formed in the intrazonal biocenoses of the northern forest zone can be as rich as the family topical groups in the southern forest zone by the number of species and ecological diversity. Ecological properties of the fauna and ground beetle population proved similar in different parts of the forest zone. The proportion of stenobiotic meadow species proved to decrease while that of ecologically plastic ones increased from south to north. The proportion of the genus Harpalus decreased in the ground beetle population while the number of Amara species remained unaltered and their abundance increased. The changes in the species composition caused no transformation of the ecological structure of ground beetle population since they were limited to a single life form or guild.  相似文献   
994.
Summary The gene specifying cytosine deaminase (cod) is shown to be located at approximately 86 minutes on the linkage map of E. coli. The corresponding gene in S. typhimurium has been reported to have a different location.  相似文献   
995.
The influence of spatio-temporal factors (spatial heterogeneity of distribution of the numbers sought for in the matrix of data, processes of learning and development of fatigue, periodic attention oscillations) of the character of solving the task of searching the numbers in a matrix of 176 three-figure numbers (16 lines, 11 columns) was studied in 39 operators. The possibility was shown to use the characteristics obtained for evaluation of professionally important abilities of an operator working at the display.  相似文献   
996.
997.
998.
In two different strains of cholera vibrios two recA-dependent plasmids, pVib I (1.9-2.2 Md) and pVib II (5.2-5.8 Md), have been detected. These plasmids determine the synthesis of vibriocin, coagulase and fibrinolysin, which has been established by the cotransformation of the DNA of plasmids pVib I and pBR322 and by the transfer mobilization with the use of plasmid RP4.  相似文献   
999.
1000.
Ethnobotanical review of wild edible plants in Spain   总被引:5,自引:0,他引:5  
This paper compiles and evaluates the ethnobotanical data currently available on wild plants traditionally used for human consumption in Spain. Forty-six ethnobotanical and ethnographical sources from Spain were reviewed, together with some original unpublished field data from several Spanish provinces. A total of 419 plant species belonging to 67 families was recorded. A list of species, plant parts used, localization and method of consumption, and harvesting time is presented. Of the seven different food categories considered, green vegetables were the largest group, followed by plants used to prepare beverages, wild fruits, and plants used for seasoning, sweets, preservatives, and other uses. Important species according to the number of reports include: Foeniculum vulgare , Rorippa nasturtium-aquaticum , Origanum vulgare , Rubus ulmifolius , Silene vulgaris , Asparagus acutifolius , and Scolymus hispanicus . We studied data on the botanical families to which the plants in the different categories belonged, overlapping between groups and distribution of uses of the different species. Many wild food plants have also been used for medicinal purposes and some are considered to be poisonous. This review highlights the rich traditional knowledge on edible plants that has remained in rural Spain. Until recently, many wild plants were used as dietary supplements. However, most of this knowledge survives only in the memory of the elderly, and will probably disappear in a few decades.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 27–71.  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