全文获取类型
收费全文 | 629篇 |
免费 | 42篇 |
专业分类
671篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 14篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 5篇 |
2016年 | 16篇 |
2015年 | 30篇 |
2014年 | 31篇 |
2013年 | 34篇 |
2012年 | 40篇 |
2011年 | 39篇 |
2010年 | 30篇 |
2009年 | 22篇 |
2008年 | 41篇 |
2007年 | 41篇 |
2006年 | 29篇 |
2005年 | 29篇 |
2004年 | 34篇 |
2003年 | 32篇 |
2002年 | 34篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1942年 | 2篇 |
1941年 | 3篇 |
1940年 | 3篇 |
1932年 | 2篇 |
1929年 | 1篇 |
1924年 | 1篇 |
排序方式: 共有671条查询结果,搜索用时 15 毫秒
1.
Jeroen M. G. Stevens Hilde Vervaecke Han de Vries Linda van Elsacker 《International journal of primatology》2007,28(6):1417-1430
Bonobos have a reputation as a female-dominated and egalitarian species. We examined the 2 aspects of dominance in 6 captive
bonobo groups. Females do not consistently evoke submission from all males in all contexts. Though females occupy the highest-ranking
positions in the dominance hierarchy, there are in each group males that obtain rather high ranks and are able to dominate
≥1 female. Thus female dominance is not complete and hierarchies can be better described as nonexclusive female dominance.
We studied egalitarianism by measuring linearity and steepness of dominance hierarchies. The hierarchies of all groups are
highly linear. Hierarchies among males are steeper than among females. On average, male bonobos are more despotic than females,
but females too can have despotic relations, both with other females and with males. Hence one can call bonobos in captivity
semidespotic rather than egalitarian. 相似文献
2.
Hilde Nybom 《Nordic Journal of Botany》1987,7(4):373-381
Five stands of an apomictic blackberry, Rubus nessensis , were studied. Biennial shoots flower and fruit in their second year on lateral branches developed from axillary buds. Most premature death of reproductive units occurs by withering of entire laterals, presumably due to damage by frost during the preceeding autumn or winter. Health status of the floricane, assessed as percentage live axillary buds in the spring, was positively correlated with the reproduction parameters. Shoot height as well, is positively correlated with number of flower buds and flowers produced on each lateral but, however, negatively correlated with number of berries, probably because tall shoots tend to suffer more damage by frost which seriously afflicts the vascular tissues of the laterals.
The position of the axillary buds on the shoot affects survival and degree of fertility, those situated medially greatly surpassing apical and basal ones. 相似文献
The position of the axillary buds on the shoot affects survival and degree of fertility, those situated medially greatly surpassing apical and basal ones. 相似文献
3.
4.
Jan Van Parijs Hilde M. Joosen Willy J. Peumans Jan M. Geuns André J. Van Laere 《Archives of microbiology》1992,158(1):19-25
The lectin from stinging nettle rhizomes, Urtica dioica agglutinin (UDA), did not affect the evolution of wet and dry weight, protein, nucleic acid, ATP, cAMP and glycerol content during early germination of Phycomyces blakesleeanus spores. However, earlier investigations established a strongly reduced mycelial growth of several phytopathogenic fungi by this small plant lectin. Total uptake and incorporation of radioactive precursors showed no differences between UDA or control hyphae, but UDA significantly altered the distribution patterns of [14C]-glucose incorporated into the walls of Phycomyces blakesleeanus (more label was recovered in the chitin fraction). Moreover, a small but significant stimulation of chitin synthase and a similar inhibition of chitin deacetylase was found in cell wall preparations. These observations could lead to a better understanding of plant-pathogen interrelationships and to a further elucidation of cell wall structure in fungi.Abbreviations GlcNAc
N-Acetylglucosamine
- PDB
potato dextrose broth
- PMM
Phycomyces minimal medium
- UDA
Urtica dioica agglutinin
- TEA
tri-ethyl-amine
- DAB
1,4-diaminobutanone 相似文献
5.
Signal peptidase I overproduction results in increased efficiencies of export and maturation of hybrid secretory proteins in Escherichia coli 总被引:4,自引:0,他引:4
Jan Maarten van Dijl Anne de Jong Hilde Smith Sierd Bron Gerard Venema 《Molecular & general genetics : MGG》1991,227(1):40-48
Summary The effects of 25-fold overproduction ofEscherichia coli signal peptidase I (SPase I) on the processing kinetics of various (hybrid) secretory proteins, comprising fusions between
signal sequence functions selected from theBacillus subtilis chromosome and the mature part of TEM-β-lactamase, were studied inE. coli. One precursor (pre[A2d]-β-lactamase) showed an enhanced processing rate, and consequently, a highly improved release of
the mature enzyme into the periplasm. A minor fraction of a second hybrid precursor (pre[Al3i]-β-lactamase), which was not
processed under standard conditions of SPase I synthesis, was shown to be processed under conditions of SPase I overproduction.
However, this did not result in efficient release of the mature β-lactamase into the periplasm. In contrast, the processing
rates of wild-type pre-β-lactamase and pre(A2)-β-lactamase, already high under standard conditions, were not detectably altered
by SPase I overproduction. These results demonstrate that the availability of SPase I can be a limiting factor in protein
export inE. coli, in particular with respect to (hybrid) precursor proteins showing low (SPase I) processing efficiencies. 相似文献
6.
This contribution illustrates the advantages of some chromophoric and fluorophoric carbohydrate derivatives such asp-nitrophenyl (pNO2Phe) or 4-methylumbelliferyl (MeUmb) glycosides andN-dansylgalactosamine in studies of the binding equilibrium and kinetics with some plant lectins. The methods used involve
continuous titrations of changes in ligand or protein absorption and ligand fluorescence, including substitution titrations
as well as stopped-flow, temperature-jump or pressure-jump relaxation kinetics.
When monitored by temperature-jump relaxation, binding of MeUmbαGal to the bloodgroup A specific lectin GSAI-A4 fromGriffonia simplicifolia is a simple bimolecular association with parametersk
+
= 9.4 × 104 M-1 s-1 andk
-1 = 5.3 s-1 at 23°C, but binding to the GSAI-B4 lectin is biphasic.
The complementarity of the peanut agglutinin binding site with Galβ1 → 3GalNAc that occurs in manyO-glycoproteins follows from enthalpic considerations and also from the value of the dissociation-rate parameterk
-1 = 0.24 s-1 of the MeUmbβGalβl → 3GalNAc.lectin complex. This value, obtained by stopped-flow kinetics is 100 times smaller than for other mono-and disaccharides
investigated. The binding mechanism is simple and the derivatisation of Galβ1 → 3GalNAc does not affect the affinity to a considerable degree.
The binding preference of tetravalentsoybean agglutinin for MeαGalNAc over MeαGal by a factor of 25 is mainly of enthalpic origin with an additional 7 kJ mol-1; the NAc group causes perturbation of a tryptophanyl residue, evidenced by protein difference absorption spectrometry. In
the glycosides, a large aglycon likeβpNO2 Phe orβMeUmb hardly affects the affinity of SBA but a largeN-dansyl group increases the affinity by a factor 20 as compared to GalNAc. The 10-fold increase in carbohydrate-specificN-dansylgalactosamine fluorescence, together with a very favourable entropic contribution point at the presence of a hydrophobic
region in the vicinity of the carbohydrate-binding site. The dissociation-rate parameter of the MeUmbβGalNAc SBA complex is slower than for any reported monosaccharide-lectin complex: 0.4 s-1.
The divalent lectin fromErythrina cristagalli preferentially binds the Galβ1 → 4GlcNAc structure that occurs in manyN-glycoproteins. The combining site was mapped thermodynamically with carbohydrates ranging from mono-to pentasaccharides as
derived fromN-glycoproteins. Here, N-dansylgalactosamine was used as a fluorescent indicator ligand in substitution titrations. When Galβ1 → 4GlcNAc was linkedα1 → 2 orα1 → 6 to Man, the binding enthalpy and entropy remained practically constant. Application of stopped flow kinetics and pressure-jump
relaxation withN-dansylgalactosamine gave mono-exponential signal changes with a concentration dependence corresponding tok
+ = 4.8 x 104 M-1 s-1
k
- = 0.4 to 0.66 s-1 and a change in reaction volume of+7ml/mol. 相似文献
7.
Hilde Beele Hubert Thierens Leo de Ridder 《In vitro cellular & developmental biology. Plant》1989,25(10):923-933
Summary Different organotypical culture methods are used to test the direct effects of serotonin and ketanserin, a S2, α1, and H1 receptor antagonist in vascular tissue, on fibroblasts and epidermal cells of embryonic chick skin in vitro. From light microscopic
and electron microscopic analyses, we learn that serotonin enhances keratinization and differentiation, whereas ketanserin
reduces differentiation in comparison to the control cultures. Incorporation data of fragments cultured with [3H]thymidine show that ketanserin, within a dose range from 0.05 to 5 μg/ml, stimulates proliferation. Serotonin at a concentration
of 10 μg/ml slightly slows down proliferation, whereas lower doses of 0.1 and 1 μg/ml result in tritium activities that do
not differ from control cultures.
This investigation was financially supported by the National Fund of Scientific Research, Belgium, 3.0022.87. 相似文献
8.
Georges Vauquelin Hilde De Vos Jean-Paul De Backer Guy Ebinger 《Neurochemistry international》1990,17(4)
The antagonist [3H]idazoxan binds with comparable affinity to α2 adrenergic receptors and to phentolamine-displaceable non-stereoselective sites in human frontal cortex membranes. In contrast, idazoxan analogs possessing alkyl and alkoxy substituents at the 2-position of the benzodioxan moiety (i.e. RX 821002: 2-methoxy-1,4-[6,7-3H]benzodioxan-2-yl-2-imidazolin HCl, 43.8 Ci/mmol) possess 300–1200 times lower affinity for the non-stereoselective sites. Their affinity for the α2 receptors is increased as well, resulting in more than a 1000-fold selectivity towards the receptors as compared to the non-stereoselective sites. [3H]RX 821002, the 2-methoxy analog of idazoxan possesses an approx. 10-fold higher affinity for the α2 receptors (KD = 2.8 nM than [3H]idazoxan (KD = 24 nM) and about equal affinity as [3H]rauwolscine (KD = 3.6 nM).[3H]Rauwolscine binds with comparable affinity to α2 receptors and to 5-HT1A receptors, and competition studies indicate that the Ki value of unlabelled RX 821002 for the 5-HT1A receptors (30 nM) is about one order in magnitude above its Ki value for the α2 receptors (4.1 nM). Labelling of the 5-HT1A receptors by [3H]RX 821002 and by [3H]rauwolscine can be prevented by selective masking with 8-OH-DPAT (30 nM) or 5-HT (0.3 μM). Under these conditions, specific binding of [3H]RX 821002 to the α2 receptors represents 84% of total binding (at its KD), as compared to 77% for [3H]rauwolscine and 20% for [3H]idazoxan.[3H]RX 821002 labels the α2 receptors as a single class of non-cooperative sites. Association and dissociation kinetics are very fast at 37°C. Antagonist competition curves are steep with Hill coefficients close to one and the agonist curves can be analysed in terms of two affinity sites, confirming the antagonistic properties of [3H]RX821002. About 60% of the α2 receptors possess high agonist affinity. 相似文献
9.
Gerardo H. Vázquez Nin Ernestina Flores Olga M. Echeverría Hilde Merkert Rodolfo Wettstein Ricardo Benavente 《Chromosoma》1993,102(7):457-463
The distribution of DNA in synaptonemal complexes of rat and mouse spermatocytes, and of chick oocytes was investigated by immunogold electron microscopy. Except for a few specific sites, DNA was not immunolocalized in the space between lateral elements of the complex. Some labeled fibrils connecting the lateral elements with the central element were observed associated with recombination nodules or near them. However, other labeled fibrils in the space between lateral elements did not appear to present any relationship to recombination nodules. The immunocytochemical approaches used here confirmed the presence of significant amounts of DNA in the lateral elements as previously indicated by preferential DNA staining methods. Furthermore, our findings support the view that recombination nodules are the site of chiasma formation. 相似文献
10.
Bjørn-Yngvar Nordvåg Ida Ranløv Hilde Monica Frostad Riise Gunnar Husby M. Raafat El-Gewely 《Human genetics》1993,92(3):265-268
Severe familial amyloid cardiomyopathy (FAC) in a Danish kindred is associated with a specific mutation (Met for Leu 111) in the transthyretin (TTR) gene. The mutation causes the loss of a DdeI restriction site in the gene, allowing molecular diagnostic studies. We studied formalin-fixed, paraffin-embedded tissues, up to 39 years old, from 29 family members of this kindred. DNA was partially purified from deparaffinized tissue sections and a DNA sequence of the TTR gene flanking the mutation site was amplified by the polymerase chain reaction (PCR), followed by restriction enzyme analysis. Amplified DNA was obtained from tissues representing 23 of the 29 persons. Ten out of the 23 family members were found to carry the TTR Met 111 mutation, whereas 13 were not affected. The results were consistent with known clinical data and with corresponding serum TTR examinations. This retrospective study shows that archival tissues can be used to confirm the diagnosis and disease pattern in members of families affected by hereditary diseases. 相似文献