全文获取类型
收费全文 | 8695篇 |
免费 | 736篇 |
国内免费 | 809篇 |
出版年
2024年 | 17篇 |
2023年 | 98篇 |
2022年 | 120篇 |
2021年 | 218篇 |
2020年 | 253篇 |
2019年 | 357篇 |
2018年 | 328篇 |
2017年 | 301篇 |
2016年 | 341篇 |
2015年 | 304篇 |
2014年 | 503篇 |
2013年 | 677篇 |
2012年 | 401篇 |
2011年 | 432篇 |
2010年 | 371篇 |
2009年 | 404篇 |
2008年 | 473篇 |
2007年 | 497篇 |
2006年 | 443篇 |
2005年 | 418篇 |
2004年 | 321篇 |
2003年 | 291篇 |
2002年 | 234篇 |
2001年 | 227篇 |
2000年 | 209篇 |
1999年 | 186篇 |
1998年 | 164篇 |
1997年 | 146篇 |
1996年 | 144篇 |
1995年 | 112篇 |
1994年 | 112篇 |
1993年 | 118篇 |
1992年 | 99篇 |
1991年 | 91篇 |
1990年 | 71篇 |
1989年 | 65篇 |
1988年 | 62篇 |
1987年 | 74篇 |
1986年 | 61篇 |
1985年 | 69篇 |
1984年 | 91篇 |
1983年 | 42篇 |
1982年 | 63篇 |
1981年 | 49篇 |
1980年 | 57篇 |
1979年 | 41篇 |
1978年 | 34篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
181.
David Cowburn 《Current opinion in structural biology》1997,7(6):835-838
Protein tyrosine binding (PTB) and ‘post synaptic density disc-large zo-1’ (PDZ) domains bind to short peptidic ligands by augmentation of one of the domain's β sheets and other recognition mechanisms. The two domain classes have a superficial resemblance to each other, even though no sequential homology exists. The structural bases of the interactions are well understood for the domains now experimentally determined, and ligand—target pairs can probably be identified in favorable cases by analogy with the known domains. For both PTB and PDZ classes, functional activities are still not fully defined: it is possible that these domain classes, along with pleckstrin homology domains, have multiple roles. 相似文献
182.
Population density, fecundity andreproduction period of Artemia sp. in TuzLake, Turkey, beside environmental factors, such as oxygen,temperature, salinity, pH and electrical conductivity werestudied during 1993 and 1994.Artemia sp. occurred at two stations at the coast.Overwintering cysts hatched in early May, when the population was composed of 90% metanauplii (93%at Y4 and 99% at Y5) and few adult females. Peak abundanceoccurred in late May, at 106to 114 ind.m–3. 相似文献
183.
Two field experiments were carried out totest whether effects of intraspecific competition ina Littorina littorea population can be detectedin a short-term investigation. Different size classesof L. littorea showed no significant differencein preferences when offered four kinds of eitherpossible food or substrata (Fucus vesiculosus,Ulva lactuca, Carcinus maenas, brick).Large and medium winkles preferred Fucusvesiculosus, followed by Ulva lactuca. Deadshore crabs (Carcinus maenas) were the leastpreferred objects for all size classes. On the firstday of the experiment bricks were more attractive tosmall littorines than to larger ones. Considering allfour days, the same ranking occurred for all sizeclasses: Fucus vesiculosus > Ulvalactuca > brick > Carcinus maenas. The reactionofjuveniles to increased densities was examined using anin situ caging experiment on a mussel bed. Meshsize of the cages allowed adult densities to beincreased while juveniles could escape by passingthrough the meshes. However, there was no significantemigration of small winkles even from cages with 10 to20 times natural density of large individuals. Ofgreater importance was the original number of winklesat the site. The available resources on the musselbeds appear to be sufficient to maintain a highpopulation density. Intraspecific competition does notseem to play a major role in this L. littorea-population. 相似文献
184.
Maria Manuela M. Caniça Chang Y. Lu Rajagopal Krishnamoorthy Gérard C. Paul 《Journal of molecular evolution》1997,44(1):57-65
The molecular diversity of inhibitor-resistant TEM (IRT) enzymes was explored using a strategy which involved DNA amplification
by polymerase chain reaction (PCR), analysis of restriction fragment length polymorphism (RFLP), and direct nucleotide sequencing.
The study of plasmid-borne genes from 27 strains, resistant to amoxicillin and β-lactamase-inhibitor combinations, identified
mutations resulting in amino acid change at positions 69, 244, 275, and 276 known to be associated with the IRT phenotype
and a mutation at nucleotide position 162 in the promoter region. These mutations were found to lie on two different gene
sequences, described here as ``TEM-1B like' and ``TEM-2 like' restriction linkage groups. Further analysis, of nucleotide
sequences of promoter and coding regions of the β-lactamases, confirmed that a given mutation causing IRT phenotype could
be associated with two different gene sequence frameworks and two different causal mutations could lie on identical gene sequence
framework. These data argue in favor of convergent phenotypic evolution of IRT enzymes under the selective pressure imposed
by the intensive clinical use of β-lactam–β-lactamase inhibitor combinations.
Received: 18 March 1996 / Accepted: 15 July 1996 相似文献
185.
Louis Prusse Yvon C. Chagnon France T. Dionne Claude Bouchard 《Obesity (Silver Spring, Md.)》1997,5(1):49-61
An update of the human obesity gene map up to October 1996 is presented. Evidence from Mendelian disorders exhibiting obesity as a clinical feature, single-gene mutation rodent models, quantitative trait loci uncovered in crossbreeding experiments with mouse, rat, and pig models, association and case-control studies with candidate genes, and linkage studies with genes and other markers is reviewed. All chromosomal locations of the animal loci are converted into human genome locations based on syntenic relationships between the genomes. A complete listing of all these loci reveals that only 4 of the 24 human chromosomes are not yet represented, i.e., 9, 18, 21, and Y. Several chromosome arms are characterized by the presence of several putative loci. The following arms include at least three such loci: 1p, 1q, 3p, 4q, 6p, 7q, 8p, 8q, 11p, 11q, 15q, 20q, and Xq. Studies with negative association and linkage results are also reviewed. 相似文献
186.
The effects of different seed sizes, planting densities and planting patterns on the transmission of silver scurf (Helminthosporium solani) and black scurf (Rhizoctonia solani) diseases of potatoes were examined in five field experiments with cv. Estima in 1991–93.
In all experiments, silver scurf was more severe with increase in seed size and planting density. At high planting density, silver scurf was less severe from a square planting pattern than from planting in wide rows. The incidence of black scurf also tended to increase with increase in seed size and was increased markedly high planting density. 相似文献
In all experiments, silver scurf was more severe with increase in seed size and planting density. At high planting density, silver scurf was less severe from a square planting pattern than from planting in wide rows. The incidence of black scurf also tended to increase with increase in seed size and was increased markedly high planting density. 相似文献
187.
Lemaster DM 《Journal of biomolecular NMR》1995,6(4):366-374
Summary The Lipari-Szabo dynamical formalism is extended by setting the time constants of the Lorentzian terms to
and
. This analysis is compared to the earlier proposed three-parameter
extended model free formalism with regard to the range of equivalence and the advantages of the simplified two-parameter (S
inff
sup2
,S
infH
sup2
) and (S
inff
sup2
,S
infN
sup2
) representations. Spectral density components are calculated and compared to those obtained from the spectral density analysis formalism. Protein relaxation data, commonly analyzed in terms of the two-parameter
representation, may correspond to a dynamically heterogeneous behaviour that is more appropriately represented in terms of a fast limit order parameter and a second, lower frequency order parameter. 相似文献
188.
Peter Allard Jüri Jarvet Anders Ehrenberg Astrid Gräslund 《Journal of biomolecular NMR》1995,5(2):133-146
Summary The peptide hormone motilin was synthesised with a 13C-enriched -carbon in the leucine at position 10. In aqueous solution, six different relaxation rates were measured for the 13C–H fragment as a function of temperature and with and without the addition of 30% (v/v) of the cosolvent d
2-1,1,1,3,3,3-hexafluoro-2-propanol (HFP). The relaxation rates were analysed employing the spectral density mapping technique introduced by Peng and Wagner [(1992) J. Magn. Reson., 98, 308–322] and using the model-free approach by Lipari and Szabo [(1982) J. Am. Chem. Soc., 104, 4546–4570]. The fit to various models of dynamics was also considered. Different procedures to evaluate the overall rotational correlation time were compared. A single exponential time correlation function was found to give a good fit to the measured spectral densities only for motilin in 30% (v/v) HFP at low temperatures, whereas at high temperatures in this solvent, and in D2O at all temperatures, none of the considered models gave an acceptable fit. A new empirical spectral density function was tested and found to accurately fit the experimental spectral density mapping points. The application of spectral density mapping based on NMR relaxation data for specific 13C–1H vector is shown to be a highly useful method to study biomolecular dynamics. Advantages are high sensitivity, high precision and uniform sampling of the spectral density function over the frequency range.Abbreviations CD
circular dichroism
- NOE
nuclear Overhauser enhancement
- NOESY
two-dimensional NOE spectroscopy
- INEPT
insensitive nuclei enhanced by polarisation transfer
- DANTE
delays alternating with nutations for tailored excitation
- WALTZ-16
wideband, alternating phase, low-power technique for zero residual splitting
- FID
Free induction decay
- ppm
parts per million
- TSPA
3-trimethylsilyl-(3,3,2,2-d)-propionic acid
- HFP
d
2-1,1,1,3,3,3-hexafluoro-2-propanol
- CPMG
Carr-Purcell-Meiboom-Gill
- TFD
time-resolved fluorescence depolarisation
- CSA
chemical shift anisotropy
Partly presented at the symposium Dynamics and Function of Biomolecules, Szeged, Hungary, July 31–August 2, 1993. 相似文献
189.
Resolving genetic relationships with microsatellite markers: a parentage testing system for the swallow Hirundo rustica 总被引:1,自引:0,他引:1
Eight polymorphic microsatellite markers from the swallow were isolated and characterized. Extraordinary variability was revealed at the HrU6 locus with 45 different alleles scored among 46 unrelated individuals. The probability that the same genotype combination would occur in two random and unrelated individuals at six selected loci was as low as 1.3 × 10-8 and the combined exclusion probability was 0.9996. Stable Mendelian inheritance was observed in about 1000 meioses. No significant linkage was revealed and for almost all combinations of marker-pairs, linkage closer than 5 cM could be excluded. At two loci, null (nonamplifying) alleles were encountered. Thirteen (30%) extra-pair offspring were identified in 5 (56%) broods when applying the marker set on a nearly complete swallow colony. We were able to identify a single male from the other families in the colony as the most likely father for nine of the 13 extra-pair offspring. 相似文献
190.
Shu’a Yagev Michael Heller Arié Pinson 《In vitro cellular & developmental biology. Plant》1984,20(12):893-898
Summary Postnatal rat heart cells in culture enriched with respect to muscle cells were obtained by either high density seeding or
by the replating technique. [3H]Thymidine incorporation to DNA and the enzymatic pattern of cytoplasmic and lysosomal enzymes have been studied as a function
of the culture’s age, of seeding density, and replating. It was shown that (a) replating maintains predominance of myocyte
population for at least 2 wk in culture; (b) heavy seeding density allows homogeneous myocyte population for the 1st wk in
culture; and (c) the enzyme profile of the culture may serve as an indicator for the type of cell population in culture and
its state of differentiation.
This study was done as partial fulfilment of the M.Sc. thesis in Biochemistry (SY). Supported by grants from The Chief Scientist,
Ministry of Health, State of Israel; The Ministry of Education and Sciences, State of Niedersachssen (FRG); and The Foundation
for Heart Research from Mr. and Mrs. D. Vidal-Madjar, Paris, France. 相似文献