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   29492篇
  免费   65篇
  国内免费   113篇
系统科学   115篇
丛书文集   352篇
教育与普及   100篇
理论与方法论   108篇
现状及发展   12994篇
研究方法   1217篇
综合类   14363篇
自然研究   421篇
  2013年   186篇
  2012年   422篇
  2011年   812篇
  2008年   534篇
  2007年   548篇
  2006年   544篇
  2005年   572篇
  2004年   593篇
  2003年   522篇
  2002年   495篇
  2001年   796篇
  2000年   806篇
  1999年   559篇
  1994年   347篇
  1992年   462篇
  1991年   376篇
  1990年   451篇
  1989年   433篇
  1988年   436篇
  1987年   448篇
  1986年   454篇
  1985年   578篇
  1984年   412篇
  1983年   383篇
  1982年   353篇
  1981年   331篇
  1980年   393篇
  1979年   857篇
  1978年   690篇
  1977年   638篇
  1976年   553篇
  1975年   659篇
  1974年   802篇
  1973年   722篇
  1972年   747篇
  1971年   917篇
  1970年   1071篇
  1969年   919篇
  1968年   928篇
  1967年   828篇
  1966年   733篇
  1965年   543篇
  1964年   206篇
  1959年   317篇
  1958年   588篇
  1957年   422篇
  1956年   365篇
  1955年   329篇
  1954年   352篇
  1948年   287篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Summary A random distribution of the Y-chromosome at somatic metaphase was found in 50 patients with Ph' positive chronic myelogenous leukemia (CML). Thus, it is concluded that the positive of the Y-chromosome at somatic metaphase does not appear to influence the loss from bone marrow cells.  相似文献   
62.
Summary By comparing steroid sulphatase levels per se, and also ratios to -galactosidase, in 6 sets of mice — normal females, entire and castrated males both with and without exogenous testosterone administration — we obtained support for the contention that induction of this enzyme is in part controlled by male hormones.  相似文献   
63.
Summary Glycosidases like sialidase,-galactosidase, -L-fucosidase, N-acetyl hexosaminidase and proteases were detected in toad testis. Neuraminic acid aldolase activity was also detected. The enzyme activities were found to vary as production of spermatozoa varied. All enzymes, except N-acetyl glucosaminidase, were shown to decrease after injection of toad pituitary extract and they were also found to be absent from testis containing no spermatozoa. The glycosidases were found to act on toad oviduct jelly and they may therefore be involved in the degradation of the jelly after fertilization, into smaller bits, which may be utilized as nutrients by the fertilized zygote.Acknowledgment. We thank Prof. T.R. Ramaiah, Head of the Department of Biochemistry, University of Mysore, for his help. We also acknowledge the financial assistance of University Grants Commission to one of us (MS) and CSIR through a grant No. 9 (165)83/EMR-II to HSS. Please address all correspondence to H.S. Seshadri.  相似文献   
64.
Summary Follow-up investigation of the blood sera from preparturient women and women with habitual, abortions showed the presence of a factor which has an activating effect on smooth muscle preparations because it causes the release of prostaglandins. Gel-chromatographic counter flow separation and microelectrophoresis of the blood sera have shown that the isolated serum factor is a water soluble glycopeptide with a molecular weight of about 2000.  相似文献   
65.
On some significance tests in cluster analysis   总被引:1,自引:1,他引:0  
We investigate the properties of several significance tests for distinguishing between the hypothesisH of a homogeneous population and an alternativeA involving clustering or heterogeneity, with emphasis on the case of multidimensional observationsx 1, ...,x n p . Four types of test statistics are considered: the (s-th) largest gap between observations, their mean distance (or similarity), the minimum within-cluster sum of squares resulting from a k-means algorithm, and the resulting maximum F statistic. The asymptotic distributions underH are given forn and the asymptotic power of the tests is derived for neighboring alternatives.  相似文献   
66.
Summary The organophosphate neurotoxin soman produced impairments in adrenocortical RNA and protein metabolism. Fasciculate and reticular cell RNA and protein contents were supporessed with sublethal to acutely lethal dosages (20, 30 and 40 g/kg, s.c.) during the acute excitatory phase of intoxication and at 6–8 h post injection. All three dosages produced ca 90% inactivation of plasma cholinesterase. A transient elevation of plasma corticosterone occurred with 20 g/kg soman whereas there was a protracted increase with 30 g/kg. Corticosterone was not significantly elevated with 40 g/kg, but death occurred at 13±4 min. Thus, the magnitude and/or nature of soman-induced metabolic impairments does not appear to prevent adrenal activation.Supported by US Army Medical Research and Development Command Contract DAMD 17-81-C-1202.  相似文献   
67.
Summary We report the synthesis, stereochemistry and preliminary pharmacological evaluation of DCN 203-922, a novel ergot alkaloid of the cyclol type, which contains in its peptide moiety the uncommon amino acid L-allo-isoleucine.Part of this paper was reported by this author at the Herbstversammlung der Schweizerischen Chemischen Gesellschaft, Bern, in October 1986.  相似文献   
68.
Chromosomal localization of human haemoglobin structural genes   总被引:15,自引:0,他引:15  
P M Price  J H Conover  K Hirschhorn 《Nature》1972,237(5354):340-342
  相似文献   
69.
Androgen effect on genetic and goldthioglucose-induced obesity   总被引:1,自引:0,他引:1  
  相似文献   
70.
Differential loss of cellular constituents in cytocentrifuge preparations   总被引:1,自引:0,他引:1  
  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