全文获取类型
收费全文 | 4090篇 |
免费 | 283篇 |
国内免费 | 2篇 |
专业分类
4375篇 |
出版年
2023年 | 13篇 |
2022年 | 21篇 |
2021年 | 39篇 |
2020年 | 31篇 |
2019年 | 43篇 |
2018年 | 64篇 |
2017年 | 55篇 |
2016年 | 88篇 |
2015年 | 197篇 |
2014年 | 168篇 |
2013年 | 224篇 |
2012年 | 295篇 |
2011年 | 284篇 |
2010年 | 215篇 |
2009年 | 163篇 |
2008年 | 232篇 |
2007年 | 273篇 |
2006年 | 255篇 |
2005年 | 242篇 |
2004年 | 225篇 |
2003年 | 238篇 |
2002年 | 214篇 |
2001年 | 41篇 |
2000年 | 35篇 |
1999年 | 57篇 |
1998年 | 62篇 |
1997年 | 49篇 |
1996年 | 52篇 |
1995年 | 45篇 |
1994年 | 37篇 |
1993年 | 50篇 |
1992年 | 38篇 |
1991年 | 27篇 |
1990年 | 17篇 |
1989年 | 32篇 |
1988年 | 13篇 |
1987年 | 27篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 22篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有4375条查询结果,搜索用时 15 毫秒
61.
Silvia Köchling Johan T. den Dunnen Bernd Dworniczak Jürgen Horst 《Human genetics》1995,95(4):475-477
Duchenne muscular dystrophy (DMD) is one of the most common and severe X-linked disorders with an incidence of approximately 1 in 3500 newborn males. In more than 60% of DMD patients, deletions of part or all of the dystrophin gene have been shown. Despite this, carrier detection still poses a problem in some cases, because of the enormous size of the gene and the lack of sufficient numbers of informative markers. Here, we report the isolation and characterization of two additional microsatellite markers (IVS44SK12 and IVS44SK21) in intron 44 of the dystrophin gene. Both markers are useful for carrier detection either by indirect DNA analysis or by direct proof of loss of heterozygosity. 相似文献
62.
HPLC-analysis of algal pigments: comparison of columns,column properties and eluents 总被引:1,自引:0,他引:1
The effects of columns (Nucleosil C18ODS, MZ-PAH, YMC-PACK C30), column properties (inner diameters of 4 mm, 3 mm and 2 mm, pore-width 10 nm and 30 nm) and eluents (methanol, acetonitrile,
acetone, water) were tested on the separation of algal pigments. The length of columns was 250 mm and particle size was 5
μm. Flow rates and gradients were adjusted to optimize peak separation; remaining chromatographic conditions were kept constant.
The resolution of chromatographic systems was tested with pigment standards and various algal cultures. Total flow rate and
retention times decreased with decreasing inner diameter, whereas pressure, sensitivity and peak-width increased. Pore width
had negligible effects on the chromatographic separation of pigments under the test conditions. Only with acetonitrile as
eluent were all the taxonomically important pigments resolved adequately: zeaxanthin (Cyanophyceae), lutein (Chlorophyceae),
fucoxanthin (Bacillariopyceae), alloxanthin (Cryptophyceae), peridinin (Dinophyceae). 相似文献
63.
Ouabain-blocked toad urinary bladders were maintained in Na+-free mucosal solutions, and a depolarizing solution of high K+ activity containing only 5 mM Na+ on the serosal side. Exposure to mucosal sodium (20 mM activity) evoked a transient amiloride-blockable inward current, which decayed to near zero within one hour. The apical sodium conductance increased in the initial phase of the current decay and decreased in the second phase. The conductance decrease required Ca2+ to be present on the serosal side and was more rapid when the mucosal Na+ activity was higher. At 20 mM mucosal Na+ and 3 mM serosal Ca2+ the initial (maximal) rate of inhibition amounted to 20% in 10 min. The conductance decrease could be accelerated by raising the serosal Ca2+ activity to 10 mM. The inhibition reversed on lowering the serosal Ca2+ to 3 μM and, in addition, the mucosal Na+ to zero. Exposure of the mucosal surface to the ionophore nystatin abolished the Ca2+ sensitivity of the transcellular conductance, showing that the Ca2+-sensitive conductance resides in the apical membrane. The data imply that in the K+-depolarized epithelia, cellular Ca2+, taken up from the serosal medium by means of a Na+-Ca2+ antiport, cause feedback inhibition by blockage of apical Na+ channels. However, the rate of inhibition is small, such that this regulatory mechanism will have little effect at 1 mM serosal Ca2+ and less than 20 mM cellular Na+. 相似文献
64.
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
65.
Four strains of obligately thermophilic Bacilli capable of growing with carbon monoxide as a sole carbon and energy source were isolated from settling ponds of a sugar factory. Most of them could be identified as strains of Bacillus schlegelii on the basis of cell wall composition, DNA homology menaquinone and DNA base content. Growth with CO was very fast (t
d
=3 h) and was optimal at 65°C. No growth occurred below 50°C. As with the mesophilic carboxydotrophs, hydrogen plus carbon dioxide could also serve as autotrophic substrates. Growth of the isolates with CO depended on the presence of molybdenum in the growth medium. This suggested CO oxidase in the newly isolated Bacilli being a molybdenum hydroxylase similar to the enzymes from the mesophilic carboxydotrophs. Some data characterizing the CO-oxidizing activity in extracts of the thermophilic isolates are also provided.This paper is respectively dedicated to Professor Dr. H. G. Schlegel on the occasion of his 60th birthday 相似文献
66.
The role of sodium-channel density in the natriferic response of the toad urinary bladder to an antidiuretic hormone 总被引:5,自引:0,他引:5
Jack H. Y. Li Lawrence G. Palmer Isidore S. Edelman Bernd Lindemann 《The Journal of membrane biology》1982,64(1-2):77-89
Summary Urinary bladders ofBufo marinus were depolarized, by raising the serosal K concentration, to facilitate voltage-clamping of the apical membrane. Passive Na transport across the apical membrane was then studied with near-instantaneous current-voltage curves obtained before and after eliciting a natriferic response with oxytocin. Fitting with the constant-field equation showed that the natriferic effect is accounted for by an increase in the apical Na permeability. It is accompanied by a small increase in cellular Na activity. Furthermore, fluctuation analysis of the amiloride-induced shot-noise component of the short-circuit current indicated that the permeability increase is not due to increased Na translocation through those Na channels which were already conducting prior to hormonal stimulation. Rather, the natriferic effects is found to be based on an increase in the population of transporting channels. It appears that, in response to the hormone, Na channels are rapidly recruited from a pool of electrically silent channels. 相似文献
67.
Analysis of a drosophila tRNA gene cluster 总被引:23,自引:0,他引:23
68.
ADENOSINE REGULATES VIA TWO DIFFERENT TYPES OF RECEPTORS, THE ACCUMULATION OF CYCLIC AMP IN CULTURED BRAIN CELLS 总被引:24,自引:2,他引:22
Abstract— In cell cultures of glial character derived from perinatal mouse brain adenosine elicits two effects. (a) At submicromolar concentrations It inhibits the increase in the intracellular level of cyclic AMP caused by β-adrenoceptor agonists. (b) At concentrations above micromolar it increases the level of cyclic AMP in the cultures. These two effects are mediated by two different adenosine receptors present on the outer surface of the cells. This is concluded from the following evidence. (a) Both effects are antagonized by methylxanthines but not by blockage of adenosine uptake or inhibition of phosphodiesterase activity. (b) In both cases activity depends on the integrity of the ribose moiety of the nucleotide. Substituents of the purine system are tolerated comparatively well. (c) The order of potency of adenosine analogues is different for the two effects. We suggest the name A1 receptors for those that mediate the inhibition and A2 for those that mediate the stimulation of cyclic AMP accumulation. 相似文献
69.
Heterogeneity of high affinity LSD-binding sites was confirmed by displacement studies with 2-bromo (+)—LSD and with apamin, a peptide neurotoxin. In line with the concept of multiple binding sites, a number of fractions of putative endogenous ligands could be separated from rat brain extract. The LSD-displacing β-fraction was not detectable in tissues lacking high affinity LSD-binding sites. High affinity dopamine- and serotonin-binding was differentially affected by the β-fraction. 相似文献
70.
Uptake, transport and metabolism of cytokinin in the protonemaof Funaria hygrometrica were studied using labelled kinetin(6-furfurylamino [8-14C]-purine). All cells of the protonema,chloronema and caulonema, were able to take up kinetin, whichwas carried in the symplastic transport system from cell tocell. Radioactivity was especially accumulated in growing cellsof the protonema. Kinetin was metabolized immediately afteruptake. While only very little kinetin (less than 1%) remainedas free kinetin and one part was immobilized in chromatographicseparation [e.g. attached to proteins and incorporated intonucleic acids (17)], most of the remaining kinetin was metabolizedto adenine derivatives. Exogenously supplied adenosine changedthe metabolism of kinetin. In the caulonema, adenosine reducedthe turnover of kinetin to other adenine derivatives and enhancedthe content of labelling in the start fraction. Thus adenosinecan stimulate cytokinin-dependent bud formation in moss protonema. (Received November 24, 1977; ) 相似文献