全文获取类型
收费全文 | 7265篇 |
免费 | 787篇 |
国内免费 | 935篇 |
出版年
2024年 | 30篇 |
2023年 | 126篇 |
2022年 | 302篇 |
2021年 | 448篇 |
2020年 | 337篇 |
2019年 | 406篇 |
2018年 | 367篇 |
2017年 | 296篇 |
2016年 | 397篇 |
2015年 | 558篇 |
2014年 | 648篇 |
2013年 | 619篇 |
2012年 | 708篇 |
2011年 | 585篇 |
2010年 | 392篇 |
2009年 | 337篇 |
2008年 | 329篇 |
2007年 | 244篇 |
2006年 | 225篇 |
2005年 | 204篇 |
2004年 | 197篇 |
2003年 | 170篇 |
2002年 | 164篇 |
2001年 | 90篇 |
2000年 | 78篇 |
1999年 | 76篇 |
1998年 | 36篇 |
1997年 | 40篇 |
1996年 | 23篇 |
1995年 | 31篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 57篇 |
1991年 | 43篇 |
1990年 | 45篇 |
1989年 | 43篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 27篇 |
1985年 | 24篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 10篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1977年 | 9篇 |
1972年 | 11篇 |
1971年 | 9篇 |
1970年 | 9篇 |
1969年 | 9篇 |
排序方式: 共有8987条查询结果,搜索用时 266 毫秒
21.
The isolation,characterization and application in the Triticeae of a set of wheat RFLP probes identifying each homoeologous chromosome arm 总被引:8,自引:0,他引:8
P. J. Sharp S. Chao S. Desai M. D. Gale 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,78(3):342-348
Summary To investigate the use of RFLP analysis in the Triticeae, a set of low copy number probes has been isolated from a wheat cDNA library. The probes identify each of the 14 homoeologous chromosome arms of wheat as determined by analysis of DNA fragments hybridizing to the probes in aneuploid lines of Chinese Spring. These probes can be used in RFLP analyses both for the assignment of homoeology of alien chromosomes or arms added to wheat, and for the determination of chromosome dosage in wheat aneuploids. Different chromosomes from various Triticeae species can therefore be followed in a wheat genetic background using a single technique. The potential uses of the set in facilitating the transfer of alien segments into wheat are outlined. 相似文献
22.
RFLP-based genetic maps of wheat homoeologous group 7 chromosomes 总被引:23,自引:0,他引:23
S. Chao P. J. Sharp A. J. Worland E. J. Warham R. M. D. Koebner M. D. Gale 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,78(4):495-504
Summary Restriction fragment length polymorphism (RFLP) mapping was attempted using 18 cDNA clones, 14 anonymous and 4 of known function, which had been shown to have homologous DNA sequences on the group 7 chromosomes of wheat. The loci identified by these probes have been mapped on one or more chromosomes in this homoeologous group using linkage data derived from various F2, random inbred, doubled haploid and single chromosome recombinant populations. The maps also include three isozyme loci, five disease resistance loci, two anthocyanin pigment loci and a vernalisation response locus. The mapping data have been used to determine the extent of map co-linearity over the A, B and D genomes, the degree of RFLP variability in the three genomes and the relative efficiency of various restriction enzymes in detecting RFLPs in wheat. The strategy for future mapping in wheat, particularly the use of alien genomes or segments, such as that from Aegilops ventricosa used here, is discussed. 相似文献
23.
T C Madhok C C Chao S G Matta A Hong B M Sharp 《Biochemical and biophysical research communications》1989,165(1):151-157
Polyclonal antibodies were raised against a synthetic decapeptide (designated S3) predicted from a segment of the alpha-3 subunit cDNA (amino acid residues 130-139) encoding the rat brain nicotinic cholinergic receptor. This segment was selected because it may be proximate to the nicotine/acetylcholine-binding site of the receptor (1). By radioligand binding assays and sucrose density gradient centrifugation, these monospecific antibodies were shown to inhibit the binding of [3H]nicotine to both the large molecular weight rat brain receptor (240 kDa) and to an SDS-disaggregated nicotine-binding subunit species (80 kDa), in a dose-dependent manner. The neutralizing effect of the anti-S3 antibodies supports the view that this region of the protein is closely related to the agonist binding site. 相似文献
24.
Acquired immunity against Angiostrongylus cantonensis was induced by immunizing rats with somatic antigens from fifth-stage larvae and adult worms and live third-stage larvae. Rats immunized twice had significantly fewer worms than rats immunized three times. Fewer worms were recovered from rats immunized with 200 live third-stage larvae than from any other groups. Rats immunized with somatic antigens had higher enzyme-linked immunosorbent assay (ELISA) antibody levels than rats immunized with live larvae. Rats immunized with live third-stage larvae of Angiostrongylus cantonensis were more strongly protected against challenge infections (62-92%) than rats immunized with antigens extracted from fifth-stage larvae (0-30%) and adult worms (11-24%). 相似文献
25.
Nine low copy number genomic DNA clones, a ribosomal sequence, and seven cDNA clones were found to identify polymorphisms in cultivated barley (Hordeum vulgare L.). An F2 population consisting of 100 plants was produced from a cross between a high-yielding two-rowed feed barley cultivar and a genetic marker stock homozygous for nine recessive and one dominant morphological marker genes. Through the use of these 10 well-distributed marker genes, five previously mapped isozyme loci, and two storage-protein loci, the approximate recombinational location for each of 17 restriction fragment length polymorphism loci was estimated. One clone, pMSU21, identified variation that appeared to be the result of a small insertion-deletion event that differentiated two-rowed and six-rowed genotypes. This difference was characterized, and one allele was sequenced. Oligonucleotide primers that flanked the insertion-deletion event were synthesized, and DNA samples from the F2 population were subjected to polymerase chain reaction sequence amplification. The variation identified by this technique was determined to be allelic to the variation identified using pMSU21 in Southern blot analysis. Maps of previously undescribed informative clones are included. 相似文献
26.
Dietary copper deficiency has been shown to reduce copper-dependent superoxide dismutase (SOD) activity and to increase lipid peroxidation in rats. Circulating reduced glutathione (GSH) concentrations are elevated in copper-deficient (CuD) rats, which suggests an increased GSH synthesis or decreased degradation, perhaps as an adaptation to the oxidative stress of copper deficiency. GSH synthesis was examined in isolated hepatocytes from CuD rats. Isolated hepatocytes were prepared by collagenase perfusion and incubated in Krebs-Henseleit bicarbonate buffer, pH 7.4, 10 mM glucose, 2.5 mM Ca2+ in the presence and absence of 1.0 mM buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis. Cell viability was assessed by trypan blue exclusion. GSH and oxidized glutathione (GSSG) were measured by the glutathione reductase recycling assay. Copper deficiency depressed hepatocyte Cu by greater than 90% and increased intracellular GSH by 41-117% over the 3-h incubation, with a two- to threefold increase in the rate of intracellular GSH synthesis. Intracellular GSSG values were minimally influenced by CuD, with a constant mol% GSSG. Extracellular total glutathione (GSH + 2GSSG) synthesis was increased by approximately 33%. Both intracellular GSH and extracellular total glutathione synthesis were inhibited by BSO. The pattern of food consumption in CuD rats, meal fed versus ad libitum fed, had no effect on glutathione synthesis. The results indicate an increased hepatic GSH synthesis as a response to dietary copper deficiency and suggest an interrelationship between the essential nutrients involved in oxyradical metabolism. 相似文献
27.
The antigen of hepatitis delta virus: examination of in vitro RNA-binding specificity. 总被引:22,自引:15,他引:7
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The only known protein of hepatitis delta virus (HDV), the delta antigen, is found both within virus particles and within the nucleus of the infected cell, where it has one or more roles essential for RNA genome replication. Others have demonstrated that the antigen has the ability, in vitro, to specifically bind HDV RNA species. We report a further examination of this phenomenon, using partially purified recombinant protein, expressed as a fusion with the staphylococcal protein A. From Northwestern (RNA-immunoblot) analyses with both complete and various subdomains of HDV genomic and antigenomic RNAs, we found that a necessary feature for specific binding was that the RNA be able to fold to some extent into the so-called rodlike structure; this structure is a predicted intramolecular partial base-pairing of the circular RNA, with about 70% of all bases involved, so as to produce an unbranched rodlike structure. Six different subregions of the HDV rodlike structure, three on the genomic RNA and three on its complement, the antigenomic RNA, were tested and found to be sufficient for antigen binding. However, features in addition to the rodlike structure may also be necessary for specific binding, because we found that a similar structure present in the RNA of the potato spindle tuber viroid did not allow binding. 相似文献
28.
Summary A general observer-based estimator method is developed and applied for process modelling and monitoring. This parameter estimation
technique was successfully applied to a L-lysine fermentation process. It was a useful tool to detect the effect of major
culture conditions on cell growth and product synthesis. It can also be used for the development of adaptive optimal control
schemes. 相似文献
29.
1 前言 从外地引进寄蝇或人工助长当地寄蝇种类防治农林害虫,是有效的生防手段之一,国外已有很多成功的报道。King等(1981)在路易斯安娜州蔗田中人工大量释放螟利索寄蝇(Lixophaga diatraeae)成虫防治第1代小蔗杆草螟(Diatraea saccharalis),不同地区的寄生率分别达到4.1、8.7和35.7%;由于降低了农药的使用量,奇痣窄径茧蜂(Agathis stigmatera)的自然寄生率也相应提高,很好地控制了蔗田害虫的发生。在寄蝇的田间释放技术方面,国外还没有详细的报道。在我国,利用寄蝇防治害虫的工作也是刚刚起步,很多具体问题有待于进一步研究。 相似文献
30.
Uniformly fatty livers from orotic acid-fed rats secreted almost no very low density lipoproteins (VLDL) but normal amounts of nascent high density lipoproteins (HDL) accumulated in perfusates. When lecithin:cholesterol acyltransferase (LCAT) was inhibited, nascent HDL were uniformly discoidal and lacked cholesteryl esters. Lipid and apoprotein compositions of nascent HDL from normal and fatty livers were similar whether LCAT was inhibited or not. Apolipoprotein B-100 was not detected in perfusates of uniformly fatty livers, but small amounts of apolipoprotein B-48 were present in HDL2 fractions. Nascent lipoproteins were not seen in Golgi compartments, but lipid-rich particles were clearly evident in endoplasmic reticulum cisternae adjacent to the cis face of the Golgi complex, suggesting that orotic acid blocks VLDL secretion by preventing translocation of nascent particles from the endoplasmic reticulum to the cis Golgi compartment. The accumulation of normal amounts of discoidal HDL in liver perfusates despite virtual absence of triglyceride-rich lipoproteins in Golgi secretory compartments, the space of Disse, and the perfusate is inconsistent with the concept that nascent HDL are exclusively a product of surface remnants cast off during lipolysis of chylomicrons and VLDL. 相似文献