全文获取类型
收费全文 | 101507篇 |
免费 | 3370篇 |
国内免费 | 1116篇 |
出版年
2022年 | 583篇 |
2021年 | 910篇 |
2020年 | 648篇 |
2019年 | 749篇 |
2018年 | 1703篇 |
2017年 | 1600篇 |
2016年 | 3609篇 |
2015年 | 7242篇 |
2014年 | 6984篇 |
2013年 | 6857篇 |
2012年 | 6350篇 |
2011年 | 3400篇 |
2010年 | 2951篇 |
2009年 | 2799篇 |
2008年 | 1524篇 |
2007年 | 1345篇 |
2006年 | 1279篇 |
2005年 | 7263篇 |
2004年 | 5826篇 |
2003年 | 4010篇 |
2002年 | 1512篇 |
2001年 | 1424篇 |
2000年 | 599篇 |
1999年 | 1741篇 |
1998年 | 496篇 |
1992年 | 2012篇 |
1991年 | 2103篇 |
1990年 | 2156篇 |
1989年 | 2064篇 |
1988年 | 2005篇 |
1987年 | 1863篇 |
1986年 | 1661篇 |
1985年 | 1695篇 |
1984年 | 1109篇 |
1983年 | 855篇 |
1982年 | 478篇 |
1979年 | 1093篇 |
1978年 | 775篇 |
1977年 | 625篇 |
1976年 | 644篇 |
1975年 | 886篇 |
1974年 | 1004篇 |
1973年 | 1011篇 |
1972年 | 968篇 |
1971年 | 934篇 |
1970年 | 828篇 |
1969年 | 840篇 |
1968年 | 738篇 |
1967年 | 755篇 |
1966年 | 589篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Bacteriophage receptors of Lactococcus lactis subsp. 'diacetylactis' F7/2 and Lactococcus lactis subsp. cremoris Wg2-1 总被引:2,自引:0,他引:2
Bacteriophage P008 revealed irreversible and uniform adsorption to cell walls of L. lactis subsp. 'diacetylactis' F7/2, whereas phage P127 adsorbed reversibly to a limited number of receptor sites on cell walls of L. lactis subsp. cremoris Wg2-1. Neither extraction of lipids, cell wall- and membrane-teichoic acids nor enzymatic degradation of proteins altered the binding efficiencies of both cell wall fractions. However, phage binding was inhibited, when cell walls were subjected to lysozyme, metaperiodate, or acid treatments. This reflects that a carbohydrate component embedded in the peptidoglycan matrix is part of the phage receptors of strains F7/2 and Wg2-1. 相似文献
992.
The plasminogen activator family from the salivary gland of the vampire bat Desmodus rotundus: cloning and expression 总被引:4,自引:0,他引:4
J Kr?tzschmar B Haendler G Langer W Boidol P Bringmann A Alagon P Donner W D Schleuning 《Gene》1991,105(2):229-237
Complementary DNAs coding for four Desmodus rotundus salivary plasminogen activators (DSPAs) were isolated and characterized. The predicted amino acid sequences display structural features also found in tissue-type plasminogen activator. The largest forms (DSPA alpha 1 and -alpha 2) contain a signal peptide, a finger (F), an epidermal growth factor (EGF), a kringle, and a serine protease domain, whereas DSPA beta and -gamma lack the F and F-EGF domains, respectively. Additional differences between the four forms suggest that distinct genes code for the members of the DSPA family. Transfection of DSPA-encoding cDNAs, placed under the control of the simian virus 40 late promoter, into COS-1 cells resulted in the secretion of highly fibrin-dependent PAs. 相似文献
993.
994.
995.
Polymorphic restriction sites of type II collagen gene: their location and frequencies in the Finnish population 总被引:3,自引:0,他引:3
Restriction fragment length polymorphism (RFLP) of the cartilage-specific type II collagen gene has been studied in the Finnish population. Two high-frequency alleles, also reported in other populations, were detected. The HindIII allele had a frequency of 0.33, and that detected with PvuII a frequency of 0.46. Both of these frequencies resembled the ones reported for other populations. Also one BamHI allele, not earlier reported, was found at a low frequency. Two other previously reported polymorphisms for BamHI and EcoRI were not detected in the Finnish population. The RFLPs showed a fair agreement with the Hardy-Weinberg equilibrium. A linkage disequilibrium was found between PvuII and HindIII markers. The alpha 1(II) collagen gene seems to be more conserved in populations of various origins than the alpha 2(I) collagen gene. These polymorphic collagen markers would be useful in linkage studies of various inherited cartilage disorders. 相似文献
996.
The distribution of the phenotypes of alpha-1-antitrypsin (Pi) was investigated in a Swiss population sample of 1,148 unrelated individuals using isoelectric focusing with a immobilized pH gradient. A short focusing period of only 2 h using high-voltage is an additional asset of this modified method. All common as well as the rarer phenotypes were reliably detected. However, detection of Pi M4 required a narrower pH range as chosen for routine work. The allele frequencies found were: PiM1:0.7121; PiM2:0.1381; PiM3:0.0976; PiS:0.0383; PiZ:0.0113; PiVar(I, N, V.Vdon):0.0026. 相似文献
997.
In a Portuguese family, a null allele was found in the Pi system. An apparent 'exclusion' of the mother was found to be due to the presence of null alleles in mother and child. A transferrin (Tf) null allele was found in a case of disputed paternity. The mother and putative father were heterozygous for Tf null alleles and the child was homozygous (TfQ0) and presented hypotransferrinemia. 相似文献
998.
999.
A highly sensitive and simple method to enhance detection of glycoproteins resolved by either one- or two-dimensional polyacrylamide gel electrophoresis is described. The method is a modification of the procedure described by D. Fargeaud et al. (D. Fargeaud, J. C. Benoit, F. Kato, and G. Chappuis (1984) Arch. Virol. 80, 69-82) that uses concanavalin A conjugated with fluorescein isothyocyanate to detect the carbohydrate moiety of glycoproteins. Briefly, the electrophoresed gel is exposed to the fluorescent lectin, thoroughly washed, and sequentially transferred to 50% methanol in deionized water and to absolute methanol. The result is an abrupt dehydration of the gel which turns evenly white and stiff. At least a twofold enhancement of fluorescence is obtained as detected by exposing the treated gel to an appropriate uv source. The sensitivity of the procedure allows us to detect purified immunoglobulin molecules by their carbohydrate content in the range of 0.2 microgram of total protein. The specificity of the detection is demonstrated by a comparison with the corresponding polypeptide profile obtained by silver nitrate staining of the gel. 相似文献
1000.
Effect of amino acid substitutions and deletions on the thermal stability, the pH stability and unfolding by urea of bovine calbindin D9k 总被引:3,自引:0,他引:3
B Wendt T Hofmann S R Martin P Bayley P Brodin T Grundstr?m E Thulin S Linse S Forsén 《European journal of biochemistry》1988,175(3):439-445
The influence of amino acid substitutions and deletions on the stability of bovine calbindin D9k, the smallest protein known with a pair of EF-hand calcium-binding sites, has been studied using circular dichroism and ultraviolet absorption spectroscopy. The five modifications are confined to one of the two Ca2+ -binding sites. The Ca2+-loaded forms of the wild-type and mutant calbindins are too stable to be significantly denatured by heating at 90 degrees C or by adding 8 M urea. For the Ca2+-free (apo) forms thermal unfolding appears to be only half complete at 90 degrees C, while denaturation is complete in 7-8 M urea. Four of the mutant proteins show reduced resistance towards unfolding by urea, but one of the modified proteins (Glu-17----Gln) shows an increased stability, presumably because of a reduced electrostatic repulsion in the native state. According to X-ray crystallographic data the OH group of the single tyrosine of calbindin (Tyr-13) is hydrogen-bonded to the carboxyl group of Glu-35, thus linking the two alpha helices flanking the N-terminal Ca2+ site. The pK of ionization of the Tyr-13 hydroxyl group was over 13 for calcium forms of the wild-type protein, between 12.3 and 12.8 for the calcium form of three mutants and between 11.5 and 11.7 for the apoproteins. Significant differences in pH stability between wild type and mutants were observed in the calcium forms, but were not apparent in the apo forms. 相似文献