全文获取类型
收费全文 | 21121篇 |
免费 | 52篇 |
国内免费 | 95篇 |
专业分类
系统科学 | 80篇 |
丛书文集 | 190篇 |
教育与普及 | 70篇 |
理论与方法论 | 51篇 |
现状及发展 | 9593篇 |
研究方法 | 835篇 |
综合类 | 10255篇 |
自然研究 | 194篇 |
出版年
2013年 | 130篇 |
2012年 | 277篇 |
2011年 | 432篇 |
2008年 | 329篇 |
2007年 | 367篇 |
2006年 | 352篇 |
2005年 | 359篇 |
2004年 | 419篇 |
2003年 | 360篇 |
2002年 | 351篇 |
2001年 | 605篇 |
2000年 | 591篇 |
1999年 | 410篇 |
1994年 | 324篇 |
1992年 | 351篇 |
1991年 | 283篇 |
1990年 | 343篇 |
1989年 | 307篇 |
1988年 | 324篇 |
1987年 | 348篇 |
1986年 | 335篇 |
1985年 | 420篇 |
1984年 | 304篇 |
1983年 | 320篇 |
1982年 | 264篇 |
1981年 | 248篇 |
1980年 | 300篇 |
1979年 | 649篇 |
1978年 | 557篇 |
1977年 | 485篇 |
1976年 | 410篇 |
1975年 | 489篇 |
1974年 | 607篇 |
1973年 | 527篇 |
1972年 | 538篇 |
1971年 | 684篇 |
1970年 | 795篇 |
1969年 | 658篇 |
1968年 | 672篇 |
1967年 | 573篇 |
1966年 | 532篇 |
1965年 | 382篇 |
1964年 | 166篇 |
1959年 | 199篇 |
1958年 | 381篇 |
1957年 | 287篇 |
1956年 | 239篇 |
1955年 | 232篇 |
1954年 | 236篇 |
1948年 | 194篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
I. Grattan-Guinness 《Archive for History of Exact Sciences》1970,6(5):372-400
Summary In this paper I discuss the development of mathematical analysis during the second and third decades of the nineteenth century; and in particular I assert that the well-known correspondence of new ideas to be found in the writings of Bolzano and Cauchy is not a coincidence, but that Cauchy had read one particular paper of Bolzano and drew on its results without acknowledgement. The reasons for this conjecture involve not only the texts in question but also the state of development of mathematical analysis itself, Cauchy both as personality and as mathematician, and the rivalries which were prevalent in Paris at that time. 相似文献
53.
54.
Genetics of the alkaline phosphatase polymorphism of the human placenta 总被引:27,自引:0,他引:27
55.
Hypothalamic histamine modulates adaptive behavior of rats at high environmental temperature 总被引:1,自引:0,他引:1
K. Fujimoto T. Sakata K. Ookuma M. Kurokawa A. Yamatodani H. Wada 《Cellular and molecular life sciences : CMLS》1990,46(3):283-285
Summary Histamine content in the rat hypothalamus was lower at 4°C and higher at 31°C compared to that at 21°C. Pretreatment with -fluoromethylhistidine, a suicide inhibitor of histidine decarboxylase, attenuated both the increased level of hypothalamic histamine and rat adaptive behavior at 31°C. Increase of histamine content in the hypothalamus appears to be an important factor contributing to rat adaptive behavior to high environmental temperature. 相似文献
56.
MDMethodinSolvingMultipleCriteriaDecisionProblemsArisingfromInvestmentSystemsDUWenzhong;CIJianhua(EconomicInformationCenterof... 相似文献
57.
H. Tsuchiya M. Sato M. Iinuma J. Yokoyama M. Ohyama T. Tanaka I. Takase I. Namikawa 《Cellular and molecular life sciences : CMLS》1994,50(9):846-849
Phytoalexins, defensive compounds produced by plants against microbial infections, were purified fromSophora exigua (Leguminosae) and their growth inhibitory effects on oral cariogenic bacteria were determined in vitro. Among three isolated compounds, 5,7,2,4-tetrahydroxy-8-lavandulylflavanone completely inhibited the growth of oral bacteria including primary cariogenic mutans streptococci, other oral streptococci, actinomycetes, and lactobacilli, at concentrations of 1.56 to 6.25 g/ml. 相似文献
58.
The in vivo expression of the globin genes of theβ cistron in γ-,δ-, andδβ-thalassemia heterozygotes
A. J. Dimovski A. D. Adekile T. H. J. Huisman 《Cellular and molecular life sciences : CMLS》1994,50(2):167-170
There is considerable evidence suggesting that the switch from to and chain production after birth is due, in part, to silencing of the genes by stage-specific factors which bind to their promoters and to the competition from the adult ( and ) genes for a common enhancer element located in the locus control region. As a consequence one can expect that the increased Hb F production in adults with hereditary persistence of fetal hemoglobin or -thalassemia is directed mainly by -globin genes in cis to the deletion(s) responsible for these conditions. Here we review data on heterozygotes with -, -, or -thalassemia, who also had anAT mutation, in cis or in trans, which was used as a marker of gene expression. The results show that a deletion affecting adult genes favors the expression of genes in cis, while the deletion of a single gene does not affect the expression of the gene in cis but leads to a faster switch postnatally. 相似文献
59.
Highly active metabolites have been detected in the hemolymph of the lepidopteranSpodoptera exigua infected with the mycopathogen,Beauveria bassiana. A combination of phenyl sepharose and CM ion exchange chromatography was utilized to extract the active metabolites from infected hemolymph samples. The active in vivo metabolites, having a molecular mass greater than 10 KDa, were thermolabile and were inactivated by proteinase K. These metabolites were characterized by their ability to disrupt metamorphosis, killing treated larvae at the wandering or pupal stage. Additionally, injection ofS. exigua larvae with active samples caused a reduction in the number of filopodial-producing hemocytes. The biological activities and biochemical properties suggest that novel compounds are produced duringB. bassiana mycosis. 相似文献
60.