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   66882篇
  免费   4501篇
  国内免费   12篇
  71395篇
  2023年   383篇
  2022年   542篇
  2021年   1072篇
  2020年   866篇
  2019年   932篇
  2018年   2156篇
  2017年   1864篇
  2016年   2318篇
  2015年   3098篇
  2014年   3163篇
  2013年   4161篇
  2012年   4883篇
  2011年   4438篇
  2010年   2934篇
  2009年   2400篇
  2008年   3443篇
  2007年   3343篇
  2006年   3309篇
  2005年   2843篇
  2004年   2810篇
  2003年   2522篇
  2002年   2355篇
  2001年   1529篇
  2000年   1394篇
  1999年   1198篇
  1998年   616篇
  1997年   446篇
  1996年   443篇
  1995年   427篇
  1994年   339篇
  1993年   315篇
  1992年   658篇
  1991年   623篇
  1990年   552篇
  1989年   538篇
  1988年   476篇
  1987年   454篇
  1986年   423篇
  1985年   432篇
  1984年   341篇
  1983年   287篇
  1982年   240篇
  1981年   221篇
  1980年   209篇
  1979年   339篇
  1978年   232篇
  1977年   209篇
  1974年   248篇
  1973年   236篇
  1972年   209篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
To date, the effects of long-term growth hormone (GH)-releasing hormone [GHRH(1-29)-NH2] treatment on the plasma concentrations of somatostatin-like immunoreactivity (SLI) remain undefined. In the present study, the effect of GHRH(1-29)-NH2 therapy on plasma SLI levels has been studied in 11 non-GH-deficient children. The pattern of administration was 5 micrograms/kg body weight, given subcutaneously once every day. There was no significant change in plasma SLI levels after bolus injection of GHRH(1-29)-NH2 before and during GHRH(1-29)-NH2 therapy. However, plasma SLI rose in basal plasma and nocturnal sleep after 3 months of GHRH(1-29)-NH2 therapy and remained the same during 6 months of treatment with GHRH(1-29)-NH2. The reason for this finding is uncertain, but an increase in SLI release from the enteroinsular axis is a possible explanation. The association of our findings with the role of the circulating SLI on nutrient homeostasis and the effects of GNRH on growth velocity is discussed.  相似文献   
82.
Several products derived from processed maca hypocotyls (Lepidium peruvianum Chacón, previously known asL. meyenii Walp.) were surveyed for glucosinolate content and quantified by HPLC analysis. These included pills, capsules, flour, liquor, tonic and mayonnaise. Different plant organs such as fresh hypocotyls and leaves, seeds, dry hypocotyls, and sprouts were also included in the survey. The most abundant glucosinolates detected in fresh and dry hypocotyls and leaves were the aromatic glucosinolates, benzylglucosinolate (glucotropaeolin) and p-methoxybenzylglucosinolate. Maca seeds and sprouts differed in profile from hypocotyls and leaves due to the modification of benzylglucosinolate. No glucosinolates were detected in liquor and tonic, while mayonnaise had only trace amounts of those glucosinolates. It had instead allylglucosinolate (sinigrin), which is an aliphatic glucosinolate. The pills, capsules and flour had the same glucosinolates as those observed in hypocotyls, but in variable amounts. The richest sources of glucosinolates were seeds, fresh hypocotyls and sprouts, in that order.  相似文献   
83.
Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described.  相似文献   
84.
Administration of choline chloride i.p. to rats causes a dose-dependent increase in the brain concentration of the neurotransmitter, acetylcholine (ACh). This increase is maximal (22% after a 60-mg/kg dose) 40 minutes after injection. These observations suggest that precursor availability may influence brain ACh synthesis, just as brain tryptophan and tyrosine levels have previously been shown to control the synthesis of brain serotonin and catecholamines.  相似文献   
85.
86.
Changes in quality of blood units containing one and a half or double amounts of glucose, stored at +4 degrees C for three weeks were analysed. An experimental preservative containing glucose and fructose (1 : 1) was also used. No other additives (purine or purine-nucleoside) were applied. A standard CPD preservative of the National Inst. of Haematology and Blood Transfusion was used as control. The pH, plasma free haemoglobin, K+ content, red blood cell (RBC) ATP and 2,3-DPG content, and RBC fragility index were determined in each sample. Increase of glucose concentration, the addition of fructose had a beneficial effect on blood pH, and on plasma free haemoglobin and K+ concentration. 150% glucose improved the 2,3-DPG maintenance in stored blood.  相似文献   
87.
88.
Using reversed-phase high-performance liquid chromatography with electrochemical detection we have demonstrated the occurrence of 5,6,7,8-tetrahydropterin and 5,6,7,8-tetrahydrobiopterin in Drosophila melanogaster. The former is the first time that has been detected in vivo. The identification has been based on the retention times, hydrodinamic voltagrams and the differential concentration in three strains of Drosophila melanogaster. Compared to the wild type, the Punch2 mutant has diminished levels of both pteridines, whereas Henna-recessive3 lacks completely tetrahydropterin and has increased levels of tetrahydrobiopterin, as expected according to their biochemical lesions.  相似文献   
89.
L Pikó 《Cell》1977,12(3):697-707
The expression of murine leukemia virus (MuLV)-related antigens in oocytes and early embryos of Swiss mice was studied by the unlabeled antibody peroxidase-antiperoxidase method using an antiserum to the major core protein, p30, of AKR MuLV. This procedure resulted in an intense staining, at antibody dilutions up to 1:500, of the germinal vesicles of oocytes and the interphase nuclei of early embryos. Nuclear staining was restricted to a specific period of oocyte growth and embryo development. It developed gradually in oocytes having reached one third to one half the full-grown size and persisted until meiotic maturation. In early embryos, nuclear staining was present from the one-cell stage to the morula, but disappeared during transition from morula to blastocyst and was not seen in expanded blastocysts. Nuclear staining was abolished by absorption of the anti-p30 serum with detergent-disrupted virions of Gross(A), AKR, Kirsten and Moloney MuLV, and Kirsten MSV(MuLV), but not with the Friend and Rauscher strains of MuLV, the xenotropic BALB:virus 2, a mouse tropic and an amphotropic clone of wild mouse MuLV, or with FeLV and RSV. On the basis of these results, it is suggested that the nuclear antigen (termed germinal vesicle antigen) reacting with the anti-p30 serum is the product of a cellular gene having a normal function in early embryonic development, and that sequences related to this gene are incorporated into the genome of AKR-type MuLV.  相似文献   
90.
Frequency of infection by Cryptosporidium sp. in 1,039 faecal smears stained by Ziehl-Neelsen, obtained from undernourished patients of a Nutritional Recovery Center and an ambulatory undernourished center from the Fifth Region, Chile, were studied. All underwent a coproparasitological examination by the modified Telemann method. Thirty eight (3.7%) patients infected by the parasite were detected, with an overall frequency of 8.5% among patients of the Nutritional Recovery Center and 1.9% among the ambulatory patients; this difference was statistically significant. The highest percentage of positive results were detected among the younger milk feeding infants. Also the percentage of difference among these and the older milk feeding infants (3.7%) was statistically significant. Association of Cryptosporidium sp. and Giardia lamblia was observed in 6 ambulatory patients (2.3%).  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