全文获取类型
收费全文 | 2505篇 |
免费 | 217篇 |
出版年
2021年 | 21篇 |
2020年 | 19篇 |
2019年 | 22篇 |
2018年 | 30篇 |
2017年 | 29篇 |
2016年 | 35篇 |
2015年 | 66篇 |
2014年 | 66篇 |
2013年 | 91篇 |
2012年 | 95篇 |
2011年 | 91篇 |
2010年 | 77篇 |
2009年 | 64篇 |
2008年 | 96篇 |
2007年 | 110篇 |
2006年 | 90篇 |
2005年 | 86篇 |
2004年 | 88篇 |
2003年 | 78篇 |
2002年 | 84篇 |
2001年 | 31篇 |
2000年 | 31篇 |
1999年 | 27篇 |
1998年 | 25篇 |
1997年 | 29篇 |
1995年 | 22篇 |
1993年 | 25篇 |
1992年 | 21篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 19篇 |
1984年 | 38篇 |
1983年 | 26篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 25篇 |
1978年 | 23篇 |
1977年 | 29篇 |
1975年 | 28篇 |
1974年 | 34篇 |
1973年 | 32篇 |
1972年 | 22篇 |
1969年 | 19篇 |
1965年 | 18篇 |
1889年 | 17篇 |
排序方式: 共有2722条查询结果,搜索用时 46 毫秒
11.
12.
13.
Peter J. Syapin Terry Ritchie Lorna Noble Ernest P. Noble 《Journal of neurochemistry》1987,48(4):1285-1290
The relationship between the stability of potential neurochemical markers and autolysis time was studied at 4 degrees C and 25 degrees C using postmortem brain samples from two rat strains. In general, qualitatively similar results were obtained with either N/Nih or Sprague-Dawley rats; however, quantitative differences were often observed, particularly in regard to benzodiazepine receptor changes. For every enzyme activity or binding property examined, no significant change was found when brains were kept at 4 degrees C for up to 72 h prior to freezing at -70 degrees C. Na,K-ATPase and low-affinity Ca-ATPase activities were also stable in brains kept at 25 degrees C for up to 72 h. Mg-ATPase activity was reduced in brains kept at 25 degrees C for 24 and 48 h. [3H]Guanidinoethylmercaptosuccinic acid [( 3H]GEMSA) binding to enkephalin convertase in the cytosol was not significantly changed in brains kept at 25 degrees C; however, a small increase was seen for [3H]GEMSA binding to the membrane fraction at 24, but not 48 and 72 h postmortem. [3H]Quinuclidinyl benzilate [( 3H]QNB) binding to muscarinic cholinergic receptors decreased in brains kept at 25 degrees C for 72 h. Opioid receptor binding also decreased in brains kept at 25 degrees C. Using [3H]2-D-alanine-5-D-leucine enkephalin to label delta opioid receptors, a statistically significant decrease in binding was observed as early as 6 h postmortem, and was completely abolished after 72 h at 25 degrees C. In contrast, [3H]naloxone binding was unchanged after 24 h at 25 degrees C, but was decreased after 48 and 72 h.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
14.
Stimulation by Hyphopichia burtonii and Bacillus amyloliquefaciens of aflatoxin production by Aspergillus flavus in irradiated maize and rice grains. 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Aspergillus flavus was grown on maize and rice extract agars and on irradiated viable cracked maize and rice grains, either in pure culture or in dual culture with wild strains of either Hyphopichia burtonii or Bacillus amyloliquefaciens. Aflatoxin production by A. flavus and its growth and interactions with the other microorganisms were studied at three water activities (aw) (0.98, 0.95, and 0.90) and two temperatures (25 and 16 degrees C). Both H. burtonii and B. amyloliquefaciens markedly stimulated growth and aflatoxin production by A. flavus on cracked maize, especially at 25 degrees C and 0.95 and 0.98 aw. No aflatoxin was detected in pure cultures of A. flavus on cracked rice after 12 days of incubation at 25 degrees C, but some was produced by mixed cultures at 16 degrees C and 0.98 aw. The morphological interactions among A. flavus, H. burtonii, and B. amyloliquefaciens were also examined on maize and rice extract agars under similar controlled conditions. 相似文献
15.
E. Lacey K. L. Snowdon G. K. Eagleson E. F. Smith 《International journal for parasitology》1987,17(8):1421-1429
The binding of the [3H] benzimidazole carbamates (BZCs)—albendazole (ABZ), oxibendazole (OBZ), parbendazole (PBZ), mebendazole (MBZ), fenbendazole (FBZ) and oxfendazole (OFZ)—to tubulin from three ecologically-related isolates of adult Haemonchus contortus has been examined. The extent of binding of each BZC was inversely proportional to the known resistance status of the isolate. Biochemically, the change in the formation of the BZC-tubulin complex was due to a reduction in the amount of drug bound to resistant tubulin, with no significant change in the association constant of the complex. The resistance factors derived from the binding data support the hypothesis that the complex is ligand-dependent, with the aryl-substituted BZCs—MBZ, OFZ and FBZ—demonstrating lower resistance factors than those of the alkyl-substituted BZCs—ABZ, OBZ and PBZ. Examination of the slope derived from plots of binding against protein concentration demonstrated that the failure of resistant or partially resistant isolates to bind was due to either a decrease in the number of binding sites or, more likely, to reduced stability of the BZC-tubulin complex rendering it unstable to charcoal extraction. 相似文献
16.
Ernest B. Hook 《Human genetics》1987,77(4):303-306
Summary Data and analyses on paternal age and 47,+21 are reviewed. It is concluded that there are few, if any, grounds to justify the inference of a paternal age effect independent of maternal age for those paternal age-maternal age combinations on which there are prenatal diagnostic data. It is suggested that genetic counseling as to increased (or decreased) risk of Down syndrome associated with various paternal ages is not justified at present. 相似文献
17.
18.
Complete amino acid sequence of human cartilage link protein (CRTL1) deduced from cDNA clones and chromosomal assignment of the gene 总被引:4,自引:0,他引:4
S L Osborne-Lawrence A K Sinclair R C Hicks S W Lacey R L Eddy M G Byers T B Shows A D Duby 《Genomics》1990,8(3):562-567
Little is known about the primary amino acid structure of human cartilage link protein (CRTL1). We screened a human genomic library with a cDNA encoding the 3' untranslated region and the adjoining B1 domain of chicken link protein. One clone was isolated and characterized. A 3.5-kb EcoRI-KpnI fragment from this genomic clone that contains the human B1 exon was used to map the gene to chromosome 5q13----q14.1. The same fragment was used to screen a cDNA library prepared from mRNA of Caco-2, a human colon tumor cell line. Two overlapping clones were isolated and shown to encode all of CRTL1. The deduced amino acid sequence is 354 residues long. The amino acid sequence shows a striking degree of identity to the porcine (96%), rat (96%), and chicken (85%) link protein sequences. Furthermore, there is greater than 86% homology between the 3' untranslated region of the genes encoding human and porcine link proteins. These results indicate that there has been strong evolutionary pressure against changes in the coding and 3' untranslated regions of the gene encoding cartilage link protein. 相似文献
19.
Mark P. Staves David P. Bloch James C. Lacey Jr. 《Origins of life and evolution of the biosphere》1988,18(1-2):97-105
Earlier studies (1) have shown there are direct correlations between the hydrophobicity ranking of most amino acids and their anticodonic nucleotides. However, four anticodonic assignments, i.e. those for Trp, Tyr, Ile and the XGA anticodons for Ser, did not correlate. It was our proposal that this failure to correlate was due to the fact that these assignments were made late, relative to the bulk of the assignments, in evolution through the mutation of existing tRNAs. We have shown (2) thatE. coli tRNAIle 1 and tRNAIle 2 were likely derived from tRNAVal 1 and tRNALys respectively andE. coli tRNATyr was possibly derived fromE. coli 5s rRNA or a common precursor with 5s rRNA (3). The fact that quite high homologies were observed in these comparisons is consistent with the late evolution of the tRNAs in question. We now examine the evolution ofE. coli tRNATrp by comparing its homology with otherE. coli tRNAs. The data suggest a possible evolutionary relationship withE. coli tRNAGly or tRNAArg. The data support the idea of the late assignment of anticodons to Trp.Deceased. 相似文献
20.
Adenosine-triphosphatase activity on the plasmalemma and tonoplast of isolated mesophyll protoplasts, isolated vacuoles and tonoplast-derived microsomes of the Crassulacean-acid-metabolism plant Kalanchoe daigremontiana Hamet et Perr., was localized by a cytochemical procedure using lead citrate. Enzyme activity was detected on the cytoplasmic surfaces of the plasmalemma and tonoplast. The identity of the enzymes was confirmed by various treatments differentiating the enzymes by their sensitivity to inhibitors of plasmalemma and tonoplast H+-ATPase. Isolated vacuoles and microsomes prepared from isolated vacuoles clearly exhibited single-sided deposition on membrane surfaces.Abbveviations CAM
Crassulacean acid metabolism
- H+-ATPase
proton-translocating ATPase 相似文献