全文获取类型
收费全文 | 4945篇 |
免费 | 435篇 |
专业分类
5380篇 |
出版年
2022年 | 58篇 |
2021年 | 94篇 |
2020年 | 71篇 |
2019年 | 75篇 |
2018年 | 75篇 |
2017年 | 74篇 |
2016年 | 130篇 |
2015年 | 205篇 |
2014年 | 239篇 |
2013年 | 286篇 |
2012年 | 377篇 |
2011年 | 350篇 |
2010年 | 223篇 |
2009年 | 164篇 |
2008年 | 320篇 |
2007年 | 273篇 |
2006年 | 243篇 |
2005年 | 224篇 |
2004年 | 194篇 |
2003年 | 190篇 |
2002年 | 140篇 |
2001年 | 90篇 |
2000年 | 98篇 |
1999年 | 93篇 |
1998年 | 47篇 |
1997年 | 37篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 32篇 |
1993年 | 27篇 |
1992年 | 61篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 38篇 |
1988年 | 45篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 36篇 |
1984年 | 23篇 |
1983年 | 30篇 |
1981年 | 22篇 |
1980年 | 25篇 |
1979年 | 36篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1974年 | 35篇 |
1970年 | 19篇 |
1968年 | 29篇 |
排序方式: 共有5380条查询结果,搜索用时 10 毫秒
71.
72.
Schwarz RD Spencer CJ Jaen JC Mirzadegan T Moreland D Tecle H Thomas AJ 《Life sciences》1995,56(11-12):923-929
Aspartate 103 (D103) in the third transmembrane domain of the Hm2 receptor was mutated to glutamate (D103E), asparagine (D103N), or alanine (D103A). As measured by [3H]-NMS, no significant binding was observed in D103A, while a 2-fold decrease in ligand affinity was seen in D103E and a 32-fold decrease in affinity was found in the D103N mutant. Examination of reference agonists showed greater loss of affinity in D103N than in D103E with the rank order of change being: L-607,207>carbachol>arecoline>pilocarpine>oxotremorine>McN-A-343. Of the novel 1-azabicyclo[2.2.1]-heptan-3-one oxime agonists examined, arylacetylene oximes showed little alteration in binding in either the D103E or D103N mutants, while the geometric isomers of several bicyclic aryl-ene-yne oximes showed significant changes in affinity, especially in the D103N mutant. Thus, overall size of the agonist and/or spatial orientation of the molecule within the binding pocket contribute to changes measured in binding. 相似文献
73.
74.
Glycosylinositol-phosphoceramide in the free-living protozoan Paramecium primaurelia: modification of core glycans by mannosyl phosphate.
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Glycolipids synthesized in a cell-free system prepared from the free-living protozoan Paramecium primaurelia and labelled with [3H]mannose and [3H]glucosamine using GDP-[3H]mannose and UDP-[3H]N-acetyl glucosamine, respectively, were identified and structurally characterized as glycosylinositol-phosphoceramides (GIP-ceramides). The ceramide-based lipid was also found in the GIP membrane anchor of the G surface antigen of P.primaurelia, strain 156. Using a combination of in vitro labelling with GDP-[3H]mannose and in vivo labelling with 33P, we found that the core glycans of the P.primaurelia GIP-ceramides were substituted with an acid-labile modification identified as mannosyl phosphate. The modification of the glycosylinositol-phospholipid core glycan by mannosyl phosphate has not been described to date in other organisms. The biosynthesis of GIP-ceramide intermediates in P.primaurelia was studied by a pulse-chase analysis. Their structural characterization is reported. We propose the following structure for the putative GIP-ceramide membrane anchor precursor of P.primaurelia surface proteins: ethanolamine phosphate-6Man-alpha 1-2Man-alpha 1-6Man-(mannosyl phosphate)-alpha 1-4glucosamine-inositol-phosphoceramide. 相似文献
75.
Judith Hesselbarth Christiane Werckenthin Babett Liebisch S. Schwarz 《Letters in applied microbiology》1995,20(3):180-183
Staphylococcus intermedius cultures from dogs, pigeons, horses and mink were investigated for the prevalence of the insertion elements IS 256 and IS 257 in relation to their antibiotic resistance. Copies of IS 256 could not be detected in any of the Staph. intermedius isolates tested whereas single copies of IS 257 occurred in the isolates from dogs and horses. The mink strains did not harbour IS 257 elements, whereas Staph. intermedius isolates from pigeons carried multiple copies of IS 257 as predicted from the hybridization patterns obtained with a gene probe derived from the internal part of the IS 257 -encoded transposase gene. Independently of the origin of the Staph. intermedius isolates, all IS 257 copies were found to be located in the chromosomal DNA. The large number of chromosomal IS 257 copies in the pigeon strains might help to explain chromosomal multiresistance in many of those strains. 相似文献
76.
Identification of receptor binding sites by competitive peptide mapping: phages T1, T5, and phi 80 and colicin M bind to the gating loop of FhuA. 总被引:8,自引:6,他引:2
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Previously we proposed a transmembrane model of the FhuA receptor protein in the outer membrane of Escherichia coli. Removal of the largest loop at the cell surface converted the FhuA transport protein into an open channel and rendered cells resistant to the FhuA-specific phages T1, T5, and phi 80 and to colicin M. In the present study we employed acetylated hexapeptide amides covering the entire surface loop to investigate binding of the phages and of colicin M. Competitive peptide mapping proved to be a powerful technique to uncover three ligand binding sites within a region of 34 amino acid residues. Hexapeptides derived from three specific regions of the surface loop inhibited infection of cells by the phages and killing by colicin M. Two of these regions were common among all four FhuA ligands. Electron microscopy of phage T5 revealed that one inhibitory peptide triggered a strong conformational change leading to the release of DNA from the phage head. These results suggest that the FhuA gating loop is the target for specific binding of phages T1, T5, and phi 80 and colicin M. 相似文献
77.
Sorichter Stephan; Mair Johannes; Koller Arnold; Gebert Walter; Rama Daniel; Calzolari Charles; Artner-Dworzak Erika; Puschendorf Bernd 《Journal of applied physiology》1997,83(4):1076-1082
Sorichter, Stephan, Johannes Mair, Arnold Koller, WalterGebert, Daniel Rama, Charles Calzolari, Erika Artner-Dworzak, and BerndPuschendorf. Skeletal troponin I as a marker of exercise-inducedmuscle damage. J. Appl. Physiol.83(4): 1076-1082, 1997.The utility of skeletal troponin I (sTnI)as a plasma marker of skeletal muscle damage after exercise wascompared against creatine kinase (CK), myoglobin (Mb), and myosin heavychain (MHC) fragments. These markers were serially measured in normalphysical education teacher trainees after four different exerciseregimens: 20 min of level or downhill (16% decline) running(intensity: 70% maximal O2uptake), high-force eccentric contractions (70 repetitions), orhigh-force isokinetic concentric contractions of the quadriceps group(40 repetitions). Eccentrically biased exercise (downhill running andeccentric contractions) promoted greater increases in all parameters.The highest plasma concentration were found after downhill running{median peaks: 309 U/l CK concentration ([CK])}, 466 µg/l Mb concentration([Mb]), 1,021 µU/l MHC concentration ([MHC]),and 27.3 µg/l sTnI concentration ([sTnI]). Level running produced a moderate response (median peaks: 178 U/l [CK],98 µg/l [Mb], 501 µU/l [MHC], and 6.6 µg/l [sTnI]), whereas the concentric contraction protocoldid not elicit significant changes in any of the markers assayed. sTnIincreased and peaked in parallel to CK and stayed elevated (>2.2µg/l) for at least 1-2 days after exercise. In contrast to MHC,sTnI is an initial, specific marker of exercise-induced muscle injury,which may be partly explained by their different intracellularcompartmentation with essentially no (MHC <0.1%) or a small solublepool (sTnI: median 3.4%). 相似文献
78.
79.
Abstract A micro method for the isolation and characterization of the penicillin-binding sites in penicillin-binding proteins (PBPs) was developed. Only 10 nmol of a pure PBP are required for the whole procedure which is based on high-pressure liquid chromatography (HPLC). We showed that serine 44 in PBP 5 from Escherichia coli binds penicillin covalently. 相似文献
80.