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   1031篇
  免费   95篇
  2021年   21篇
  2020年   7篇
  2019年   10篇
  2018年   27篇
  2017年   30篇
  2016年   20篇
  2015年   45篇
  2014年   45篇
  2013年   62篇
  2012年   66篇
  2011年   62篇
  2010年   44篇
  2009年   30篇
  2008年   49篇
  2007年   50篇
  2006年   59篇
  2005年   36篇
  2004年   48篇
  2003年   44篇
  2002年   38篇
  2001年   26篇
  2000年   42篇
  1999年   16篇
  1998年   11篇
  1997年   13篇
  1996年   11篇
  1995年   9篇
  1994年   8篇
  1993年   9篇
  1992年   15篇
  1991年   16篇
  1990年   7篇
  1989年   10篇
  1988年   13篇
  1987年   13篇
  1986年   13篇
  1985年   14篇
  1984年   10篇
  1983年   8篇
  1982年   7篇
  1981年   3篇
  1980年   7篇
  1979年   4篇
  1978年   6篇
  1977年   7篇
  1976年   3篇
  1974年   5篇
  1973年   6篇
  1967年   5篇
  1965年   3篇
排序方式: 共有1126条查询结果,搜索用时 15 毫秒
1.
The present study sought to determine which of the common Poaceae species in the study area contribute most to the Poaceae pollen season curve, and to determine the phenological behaviour of the species studied. The different floral phenophases in thirty-three Poaceae species common in and around the city of Córdoba (SW Iberian Peninsula) were checked periodically over the period 2004–2006. Results showed that longer phenological ranges were recorded in the coolest and wettest year, and shorter ranges in the warmest and driest year. Moreover, ranges varied as a function of altitude: populations in lower-lying areas flowered earlier than those at higher altitudes. The results, taken in conjunction with the findings of preliminary research into potential pollen production, showed that probably only four of the Poaceae species studied—Dactylis glomerata, Lolium rigidum, Trisetaria panicea and Vulpia geniculata—were major contributors to the Poaceae airborne pollen curve.  相似文献   
2.
A 45,X male with Y-specific DNA translocated onto chromosome 15.   总被引:6,自引:1,他引:5       下载免费PDF全文
A 20-year-old male patient with chromosomal constitution 45,X, testes and normal external genitalia was examined. Neither mosaicism nor a structurally aberrant Y chromosome was observed when routine cytogenetic analysis was performed on both lymphocytes and skin fibroblasts. Y chromosome-specific single-copy and repeated DNA sequences were detected in the patient's genome by means of 11 different recombinant-DNA probes of known regional assignment on the human Y chromosome. Data indicated that the short arm, the centromere, and part of the long-arm euchromatin of the Y chromosome have been retained and that the patient lacks deletion intervals 6 and 7 of Yq. High-resolution analysis of prometaphase chromosomes revealed additional euchromatic material on the short arm of one of the patient's chromosomes 15. After in situ hybridization with the Y chromosome-specific probe pDP105, a significant grain accumulation was observed distal to 15p11.2, suggesting a Y/15 chromosomal translocation. We conclude that some 45,X males originate from Y-chromosome/autosome translocations following a break in the proximal long arm of the Y chromosome.  相似文献   
3.
Cathepsin L is a major lysosomal cysteine proteinase in mouse and human cells. Despite similar predicted molecular masses, procathepsin L in these two species migrates on SDS/polyacrylamide gels with apparent molecular masses of 39 kDa and 42 kDa respectively. To determine if glycosylation differences account for this discrepancy, and to ascertain whether glycosylation is essential for enzymic activity, mouse and human procathepsins L were expressed at high concentrations in mouse NIH 3T3 cells or in human A431 cells after DNA-mediated transfection of cloned DNAs for these enzymes. In pulse-chase studies, human procathepsin L transfectants synthesized and secreted large amounts of enzymically active 42 kDa proenzyme and processed it into 34 kDa and 26 kDa intracellular peptides, a pattern of secretion and processing similar to that seen with endogenous or transfected mouse procathepsin L. Both translation of cloned procathepsin L cDNAs in vitro and Endoglycosidase H treatment of 39 kDa mouse and 42 kDa human procathepsin L resulted in non-glycosylated proteins 2 kDa lower in molecular mass than the untreated proteins for both species. This suggests that glycosylation differences are not responsible for the molecular-mass disparity between the two species. Moreover, Endoglycosidase H-treated mouse enzyme retained full proteolytic activity, indicating that glycosylation of cathepsin L is not essential for enzymic function.  相似文献   
4.
5.
Summary The genes that encode the alpha 1 (VI) and alpha 2 (VI) collagen chains, designated COL6A1 and COL6A2, map to human chromosomal band 21q22.3. Using pulsed-field gel electrophoresis and somatic cell hybrids, we found that COL6A1 and COL6A2 form a gene cluster on the most distal part of chromosome 21. Furthermore, we detected several DNA polymorphisms (both restriction site and VNTRs) associated with these loci. These polymorphisms make the COL6A1 and COL6A2 genes among the most informative markers on human chromosome 21.  相似文献   
6.
R Gal 《Acta cytologica》1988,32(6):838-839
In cases of breast carcinoma in which only lumpectomy is performed, it is necessary to ascertain that the surgical margins were adequate, i.e., free of tumor. Since the histologic methods used for this purpose are either unreliable or very cumbersome, scrape cytology was evaluated as a method for the examination of lumpectomy margins. In 30 cases examined both cytologically and histologically, a very good correlation was found between the two methods. The scrape cytology method has the advantage of being much easier and quicker and is thus recommended for routine use.  相似文献   
7.
8.
Summary The nuclear DNA content of cotyledonary cells of two lupin seeds (L1 and L2) with markedly different total protein content, were investigated by scanning cytophotometry. Both seeds had polyloid nuclei with DNA levels varying between 8 C and 64 C, the majority being either 16 C or 32 C. The highest DNA levels were found in the abaxial and central cotyledonary zones of both seeds; seed L2 had a higher ploidy level than L1. It is shown that the volume of condensed chromatin (chromocenters) increased proportionally with the DNA content of the nucleus. A comparison was made between the distribution of protein, previously determined byLe Gal andRey (1986) and the DNA throughout the cotyledon. The L2 seed, which has the highest total protein and the highest protein content per cell, also exhibited the greatest DNA content per cell. For both seeds, the r-value for association of DNA and protein content per cell was highly significant (0.98).  相似文献   
9.
The reaction between 2-(benzylamino)-2-deoxy-d-glycero-l-gluco-heptose and 5,5-dimethyl-1,3-cyclohexanedione yields 1-benzyl-4,5,6,7-tetrahydro-6,6-dimethyl-2-(d-galacto-pentitol-1-yl)-indol-4-one (2). Acid-catalyzed, intramolecular dehydration of 2 under kinetically controlled conditions gives 1-benzyl-4,5,6,7-tetrahydro-2-α-d-lyxofuranosyl-6,6-dimethylindol-4-one; the anomeric configuration of this compound is only suggested. When the dehydration reaction is conducted under thermodynamically controlled conditions, it produces a 1:1 mixture of the α- and β-d-lyxopyranosyl compounds. The structures of the new compounds were elucidated by chemical and physical methods.  相似文献   
10.
In Vivo Expression of Inducible Nitric Oxide Synthase in Cerebellar Neurons   总被引:7,自引:2,他引:5  
Abstract: In the CNS, nitric oxide (NO) functions as both neuromodulator and neurotoxic agent. In vivo neuronal expression of NO synthase (NOS) has been attributed to constitutive NOS—both the neuronal and the endothelial types. The other class of NOS—the inducible NOS (iNOS)—is known to mediate toxic effects of NO in various tissues. In this study, we show for the first time that direct intracerebellar injection of endotoxin and cytokine (lipopolysaccharide and interferon-γ) induced in vivo neuronal expression of the iNOS gene, as demonstrated by fluorescent in situ hybridization and immunohistochemical staining analyzed by confocal laser-scanning microscopy. This raises the possibility that neuronal iNOS might contribute significantly to the vulnerability of the brain to various insults.  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