全文获取类型
收费全文 | 1461篇 |
免费 | 124篇 |
国内免费 | 1篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 23篇 |
2020年 | 12篇 |
2019年 | 27篇 |
2018年 | 23篇 |
2017年 | 19篇 |
2016年 | 38篇 |
2015年 | 59篇 |
2014年 | 66篇 |
2013年 | 81篇 |
2012年 | 116篇 |
2011年 | 130篇 |
2010年 | 61篇 |
2009年 | 53篇 |
2008年 | 94篇 |
2007年 | 98篇 |
2006年 | 90篇 |
2005年 | 101篇 |
2004年 | 83篇 |
2003年 | 76篇 |
2002年 | 81篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 23篇 |
1997年 | 14篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 16篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 7篇 |
排序方式: 共有1586条查询结果,搜索用时 15 毫秒
1.
Cynthia L. Deitrick Richard E. Katholi David J. Huddleston Kathy Hardiek Lucienne Burrus 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,751(2)
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation. 相似文献
2.
We characterized a mutant T -cell lymphoma line selected for the inability to express the Thy-1 glycoprotein. This cell line is a member of the D complementation class of Thy-1– somatic cell mutants, and it lacks detectable cell-surface Thy-1.1 glycoprotein and detectable cytoplasmic Thy-1 mRNA. Southern blot analysis using a number of probes isolated from the clonedThy-1.2 gene demonstrated that, in the mutant, one copy of theThy-1 gene is absent from the genome and the other has undergone rearrangement. This rearrangement results from a deletion of the 5 portion of the gene removing the first two alternate exons and promoters and a portion of the second intron. The deletion breakpoint within the mutantThy-1 gene was localized to within 400 nucleotides by Southern blot analysis. The breakpoint is near two classes of mouse repetitive elements-a mouse B1-family repetitive element and a simple repetitive sequence-suggesting a mechanism of rearrangement leading to the mutation. Southern blot analysis demonstrated that two closely linked molecular markers on chromosome 9 are unaltered, demonstrating that the deletion in this mutant cell line is subchromosomal. 相似文献
3.
Abstract: A series of l-phenyl-1 H -3-benzazepine analogues were assessed for enantiomeric and structure-affinity relationships at human putamen D-1 dopamine receptors labelled with [3 H]SCH 23390. Substitution at the 7-position of both 3-H and 3-methyl benzazepine molecules critically affected affinity for these receptors over a 500-fold range. The general rank order of potency of 7-substituents was Cl = Br ≫ CH3 > OH ≥ H. 3-Methyl substituents increased the affinity of 7-H and 7-OH compounds two- to fivefold compared to desmethyl counterparts. The displacement of [3 H]SCH 23390 binding showed substantial enantioselec-tivity; the R-enantiomer of SKF 83566 was 500-fold more potent that its S-antipode. However, the displacement of [3 H]spiperone binding from D-2 sites in the same tissue showed negligible enantioselectivity. Through such structure-affinity relationships, these studies may help to define the topography of the human brain D-1 dopamine receptor and guide the design of more selecive agents for functional studies. 相似文献
4.
Renee H. Martin Leona Barclay Kathy Hildebrand Evelyn Ko S. Bea Fowlow 《Human genetics》1990,86(1):33-39
Summary Sperm chromosome complements were studied in three men who carried reciprocal translocations. A total of 400 sperm were karyotyped after in vitro penetration of hamster eggs: 217 sperm from t(2;9) (q21;p22), 164 from t(4;6) (q28;p23) and 19 from t(7;14) (q21;q13). All possible 22 and 31 meiotic segregations were observed for t(2;9) and t(4;6); for t(7;14) only 22 segregations were observed. For alternate segregations, the number of normal sperm was not significantly different from the number of sperm carrying a balanced form of the translocation in any of the translocations, as theoretically expected. The percentage of sperm with an unbalanced form of the translocation was 57% for t(2;9), 54% for t(4;6) and 47% for t(7;14). There was no evidence for an interchromosomal effect in any of the translocations since the frequencies of numerical abnormalities (unrelated to the translocation) were within the normal range of control donors. The frequencies of X- and Y-bearing sperm did not differ significantly from 50%. Results from a total of 17 reciprocal translocations studied by sperm chromosomal analysis were reviewed. 相似文献
5.
Catharina Larsson Günther Weber Eva Kvanta Kathy Lewis Marie Janson Carol Jones Tom Glaser Glen Evans Magnus Nordenskjöld 《Human genetics》1992,89(2):187-193
Summary Multiple endocrine neoplasia type 1 (MEN1) is characterized by neoplasia of the parathyroids, the pancreas, and the pituitary. Tumorigenesis involves unmasking of a recessive mutation at the MEN1 locus, which has been mapped to the centromeric part of chromosomal region 11q. In order to localize the MEN1 gene further and to make its isolation possible, a number of new markers were isolated. Two radiation-reduced somatic cell hybrids were identified that only contained markers close to and flanking the MEN1 region. DNA from these hybrids was used for the construction of a cosmid library, and clones containing human inserts were isolated. In addition, cosmid clones were isolated for locus expansion of 7 other markers that were mapped to the 11q12–13.2 region. The 33 newly isolated clones together with 25 previously published markers from this region were analyzed in a panel of radiation-reduced somatic cell hybrids. From the hybridization pattern, the region was divided into 11 parts. New restriction fragment length polymorphisms were identified in 7 of the newly isolated cosmid clones and in one plasmid. These were then used to sublocalize meiotic cross-overs more precisely in two MEN1 families, thus refining the mapping of the disease gene. 相似文献
6.
Michael Younga Adrian P. Gee Michael D. P. Boyleb Michael J. P. Lawman Kathy L. Mungera 《Molecular and cellular biochemistry》1985,66(1):65-69
Summary High molecular weight mouse nerve growth factor(H M W-NGF), in addition to its effects on certain neural elements, is also chemotactic for human polymorphonuclear leukocytes. One of the subunits of H M W-NGF is a protease of the serine family and its active site contains a serine residue and a closely-neighboring histidine residue that are both essential for proteolysis. Elimination of enzyme activity by irreversibly blocking the single serine has no effect on leukotaxis, but blocking the histidine abolishes leukotaxis. These results suggest the possibility that part of the proteolytic active site of this enzyme may have evolved to perform more than one, completely different, biologic function — proteolysis as well as nonproteolytically mediated chemotaxis.Abbreviations HMW-NGF
mouse submandibular gland nerve growth factor, purified as in Ref. 1
- DFP
diisopropyl-phosphofluoridate
- DIP-NGF
diisopropyl-phosphoryl-NGF; phe-pro-arg-CH2C1, D-phenylalanyl-L-propyl-L-argininyl chloromethyl ketone; TLCK, N-p-tosyl-L-lysine chloromethyl ketone
- TAME
N-p-tosyl L-arginine methyl ester
- EDTA
ethylenediamine tetraacetic acid 相似文献
7.
Summary Quantification of specific allergens in household dust samples may provide important information for selecting appropriate allergen control methods, and monitoring efficacy and compliance. The purpose of this study was to investigate the source of variation in mite and cat allergen measurements associated with dust sample collection. Discrete and composite dust samples were collected on a filter using a special vacuum sampling device. Aqueous extracts of the dust samples were prepared thenDer p I,Der f I, andFel d I were quantitated by enzyme immunoassays (EIA). Mite and cat allergens were frequently detected in dust samples from human dwellings, and the amounts of these allergens varied significantly (p<0.01) among dwellings. The differences of allergen measurements among duplicate samples taken immediately and up to three weeks later appear to be much smaller than differences among houses and between rooms. Variation among dust samples taken from living rooms and bedrooms of the same dwelling suggest differences in allergen reservoirs. Composite samples formed by sampling specific objects within a room may provide a reliable estimate of allergen exposure in that room. Dust samples from discrete objects are useful to find and monitor specific reservoirs of mite and cat allergens. 相似文献
8.
9.
Alison Moore Kathy M. Ensrud Thomas W. White Chris D. Frethem David W. Hamilton 《Molecular reproduction and development》1994,37(2):181-194
Monoclonal antibody 4E9, which was raised against a partially purified detergent extract of rat caudal epididymal sperm, recognizes the tail of sperm from the cauda, but not from caput epididymidis, as well as epithelial cells in a restricted region of the distal caput/corpus epididymidis and proteins in epididymal fluid from corpus and cauda epididymidis. The antigen is apparently a glycoprotein, since it is retained on a Ricinus communis agglutinin l lectin column. Epididymal fluid antigens have apparent MrS of 38–26 kD, whereas the memrane-associated form of the molecule has an Mr of 26 kD. Immunocytochemical data and Western immunoblot data suggest that the membrane antigen is derived from the fluid antigen, which, in turn, is secrteted by the epididymal epithelium. Characterization of the membrane antigen indicates that it is tightly associated with the sperm surface, behaving as though it is an integral membrane protein. The antigen persists on ejaculated sperm. © 1994 Wiley-Liss, Inc. 相似文献
10.
Previous studies with rainbow trout (Oncorhynchus mykiss) have shown that allozymic heterozygotes have increased developmental stability, as measured by reduced fluctuating bilateral
asymmetry. In this paper, we examine the phenotypic effects of null alleles at two lactate dehydrogenase (LDH) loci. If the
association between allozymic heterozygosity and developmental stability is due largely to linked chromosomal segments, then
we would expect null allele heterozygotes to have increased developmental stability. In contrast, heterozygotes for LDH null
alleles in three populations have reduced developmental stability. This suggests that the reduction in enzyme activity at
these loci is having a deleterious effect on development that is strong enough to mask any beneficial effects that may be
associated with heterozygosity for these chromosomal segments. The LDH loci examined in this study are members of two different
paralogous pairs of duplicate genes produced by the polyploidization of the ancestral salmonid genome. The apparent deleterious
effects of these null alleles in heterozygotes could retard the possible loss of duplicate gene expression. 相似文献