全文获取类型
收费全文 | 1022篇 |
免费 | 107篇 |
专业分类
1129篇 |
出版年
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 25篇 |
2017年 | 19篇 |
2016年 | 44篇 |
2015年 | 56篇 |
2014年 | 67篇 |
2013年 | 88篇 |
2012年 | 91篇 |
2011年 | 84篇 |
2010年 | 59篇 |
2009年 | 37篇 |
2008年 | 71篇 |
2007年 | 51篇 |
2006年 | 38篇 |
2005年 | 47篇 |
2004年 | 48篇 |
2003年 | 49篇 |
2002年 | 48篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1947年 | 1篇 |
1936年 | 1篇 |
1932年 | 3篇 |
1931年 | 2篇 |
1929年 | 3篇 |
1926年 | 1篇 |
1925年 | 1篇 |
1924年 | 1篇 |
1920年 | 2篇 |
排序方式: 共有1129条查询结果,搜索用时 15 毫秒
1.
Genetic and demographic studies of urban sample of Turkmen-teke (Ashkhabad city) were performed among probands-36 patients with diagnosis of "schizophrenia" and their 840 relatives. Clinical analysis revealed 27.8% of phenocopies. In other 26 families the genealogical analysis showed autosomal-dominant (12 families), probably, autosomal-dominant (9 families) as well as autosomal-recessive (3 families) types of inheritance of pathology, in two families the type being not established. The empiric risk of affection was determined to be 24.2% for parents, 75.5% for sibs and 33.3% for children. Mean number of children per one woman is 3.53, which is significantly lower than mean populational number (6.17). High level of endogamy of the urban sample tested is established, the total coefficient of inbreeding being 0.009856; grandparents of the probands appeared to be exclusively of rural origin. The negative action of selection (decreased fitness), preferentially monogenic type of heredity and high level of endogamy are discussed as factors providing broad hereditary heterogeneity of schizophrenia. 相似文献
2.
Johnson Kristine; Thornhill Randy; Ligon J. David; Zuk Marlene 《Behavioral ecology》1993,4(3):254-259
We used a breeding design involving 18 sires and 108 dams tostudy the heritabilities of male ornaments in red jungle fowl(Gallus gallus). Ornaments used by females to choose mates showedlow heritabilities, with the exception of comb and wattle measures.The general absence of heritability suggests that a geneticcovariance did not exist at the time of this study between mostmale ornaments and female preferences for those ornaments. Thisresult is contrary to a key prediction of the arbitrary or Fisherianhypothesis of sexual selection. Comb size and color are condition-dependenttraits that reflect short-term changes in health, and comb sizeof males was positively correlated with offspring weight. Ourresults are consistent with the expectation of good-genes hypothesesthat male ornaments reflect the ability of males to withstandenvironmental stresses. 相似文献
3.
The immunohistochemical occurrence of sarafotoxin (SRTX), a snake venom peptide under strong evolutionary control, was investigated in the pulmonary diffuse neuroendocrine system (PDNES) of newborn cats and rats. By applying the avidin-biotin-peroxidase complex method on serial lung sections, we have demonstrated its distribution and colocalization with different endothelin (ET) isoforms. A light microscopic study revealed apparent immunostaining for SRTX in neuronal components and smooth muscle tissue and in neuroepithelial bodies (NEB), while isolated neuroendocrine cells (NEC) remain unlabelled. Comparison of the SRTX reactivity pattern with that of different ET peptides on adjacent lung sections showed colocalization of SRTX-b with ET-3 in NEB, intrapulmonary ganglion cells and nerve fibres, on the one hand, and with ET-1 in airway and vascular smooth muscle cells, on the other. These findings, in addition to the remarkable functional and structural similarities between SRTX and ET peptides, suggest a common evolutionary origin and biological significance of sarafotoxin and endothelins. Moreover, this is the first time that a toxic peptide has been demonstrated in the PDNES. 相似文献
4.
Brown Arthur V. Aguila Yolanda Brown Kristine B. Fowler William P. 《Hydrobiologia》1997,347(1-3):119-125
We examined macroinvertebrate communities in small(0.1-1.0 m2) pools of intermittent streams (alwayscontainingsome water but without perennial flow) with small watersheds(2-6 ha) subjected to five types of forest harvest to assesspotential impacts of the different harvest methods. Bufferstrips10 m wide were left on each side of the streams. Each harvesttreatment was coupled with a similar unharvested referencestand.An incomplete block design included three 0.05 m2 vacuumsamples from each treatment paired with three from theadjacentreferences. There was a high degree of similarity amongreferencesfor parameters other than taxonomic composition (e.g.macroinvertebrate density, number of species, Shannondiversity,functional groups, etc.). Statistically significantdifferenceswere found between references and treatments and among harvestmethods but the responses varied among response variables(density,Shannon-Weiner diversity, species composition), differentspeciesassemblages (all invertebrates, chironomids,Ephemeroptera-Plecoptera-Trichoptera [EPT], isopods), andfunctional group categories (shredders, collector-gatherers).Wecollected 56 taxa, 7–16 per site, with low communitysimilarity(mean Jaccards=0.18, mean Bray-Curtis percentdissimilarity=81). The most severe harvest treatmentsresultedin the highest diversities of total invertebrates in thesesmallspring pool communities. 相似文献
5.
Expression of HLA-B27 in transgenic mice is controlled by gene(s) mapping between H-2D and H-2L loci 总被引:2,自引:0,他引:2
The level of HLA-B27 transgene expression on the cell surface is dependent on the host H-2 haplotype. Mice homozygous for the H-2
b
, H-2
f
, H-2
f
, H-2
p
, H-2
r
, and H-2
k
haplotypes express B27 at high levels. An intermediate level of B27 expression is observed in H-2
v
mice whereas low levels of B27 are expressed in H-2
q
and H-2
d
mice. The decreased expression of B27 maps to the D region of the major histocompatibility complex. Recombinant strain B10.RKDB (DdLb) mapped the low expression gene centromeric to H-2L. In order to determine the low expression within the H-2D region, the B27 transgene was introduced into B10.D2-H-2
dm1
and BALB/c-H-2
dm2
mice. Expression of B27 in both of these strains was high indicating that neither H-2D
d
nor H-2L
d
is responsible for the low expression. This maps the effect between the H-2D and H-2L loci. In addition, introduction of human 2-microglobulin (2m) into B10.D2-B27 transgenic mice caused a marked enhancement of B27 expression on the cell surface suggesting that the defect in B27 expression in certain haplotypes is due to an inability of B27 to associate with endogenous mouse 2m. We propose that gene(s) mapping between D and L (either D2, D3, D4, or some as yet unidentified gene) may be involved in class I assembly by helping association of 2m with class I. This putative molecule, designated Assembly Enhancer (AE) might have a negative influence in the association between human class II and mouse 2m. 相似文献
6.
D. James Morr V. Schirrmacher Peter Robinson Kristine Hess Werner W. Franke 《Experimental cell research》1979,119(2):265-275
Purified fractions of plasma membrane, Golgi apparatus, rough endoplasmic reticulum vesicles, nuclear envelope, and mitochondria were isolated from mouse liver and the distribution of H-2 histocompatibility antigens determined by indirect radioimmunoassay before and after membrane disruptive treatments. Fractions enriched in plasma membrane (surface membrane) revealed H-2 antigens in highest concentration; disruptive treatments were not necessary to reveal H-2 antigens with surface membranes. In contrast, internal membranes did not possess H-2 antigens which were accessible to antibody. Golgi apparatus fractions or some component of these fractions (e.g. secretory vesicles) possessed the antigens but in a latent form where accessibility was provided by simple rupture of the membrane vesicles. With endoplasmic reticulum, detergent solubilization of the membranes was required before H-2 antigen could be detected. Nuclear envelope preparations contained little or no demonstrable H-2 activity. These results were confirmed by several techniques including immunoprecipitation of labelled solubilized membrane components with anti-H-2 serum and subsequent analysis in SDS-PAGE. 相似文献
7.
Impacts of Saltwater Incursion on Plant Communities,Anaerobic Microbial Metabolism,and Resulting Relationships in a Restored Freshwater Wetland 总被引:1,自引:0,他引:1
Kristine N. Hopfensperger Amy J. Burgin Valerie A. Schoepfer Ashley M. Helton 《Ecosystems》2014,17(5):792-807
Saltwater incursion carries high concentrations of sea salts, including sulfate, which can alter anaerobic microbial processes and plant community composition of coastal freshwater marshes. We studied these phenomena in a recently restored wetland on the coastal plain of North Carolina. We measured water inundation patterns, porewater chemistry, microbial process rates, plant tissue chemistry and iron plaque on plant roots, and quantified plant community composition across a hydrologic and salinity gradient to understand the potential interactions between saltwater incursion and changes in microbial processes and plant communities. Plant communities showed no obvious response to incursion, but were structured by inundation patterns and plant growth form (for example, graminoid versus forb). Saltwater incursion increased chloride and sulfate concentrations in surface and porewater, and drove resulting spatial patterns in anaerobic microbial metabolism rates. Plots experiencing saltwater incursion had higher sulfate reduction rates and were dominated by graminoid plant species (for example, sedges, rushes, and grasses). Graminoid plant species’ roots had greater iron plaque formation than forb and submerged species, indicative that graminoid plant species are supplying more oxygen to the rhizosphere, potentially influencing microbial metabolism. Future studies should focus on how plant and microbial communities may respond to saltwater incursion at different time scales, and on parsing out the influence that plants and microbes have on each other as freshwater wetlands experience sea level rise. 相似文献
8.
He WQ Qiao YN Zhang CH Peng YJ Chen C Wang P Gao YQ Chen C Chen X Tao T Su XH Li CJ Kamm KE Stull JT Zhu MS 《American journal of physiology. Heart and circulatory physiology》2011,301(2):H584-H591
Vascular tone, an important determinant of systemic vascular resistance and thus blood pressure, is affected by vascular smooth muscle (VSM) contraction. Key signaling pathways for VSM contraction converge on phosphorylation of the regulatory light chain (RLC) of smooth muscle myosin. This phosphorylation is mediated by Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) but Ca(2+)-independent kinases may also contribute, particularly in sustained contractions. Signaling through MLCK has been indirectly implicated in maintenance of basal blood pressure, whereas signaling through RhoA has been implicated in salt-induced hypertension. In this report, we analyzed mice with smooth muscle-specific knockout of MLCK. Mesenteric artery segments isolated from smooth muscle-specific MLCK knockout mice (MLCK(SMKO)) had a significantly reduced contractile response to KCl and vasoconstrictors. The kinase knockout also markedly reduced RLC phosphorylation and developed force. We suggest that MLCK and its phosphorylation of RLC are required for tonic VSM contraction. MLCK(SMKO) mice exhibit significantly lower basal blood pressure and weaker responses to vasopressors. The elevated blood pressure in salt-induced hypertension is reduced below normotensive levels after MLCK attenuation. These results suggest that MLCK is necessary for both physiological and pathological blood pressure. MLCK(SMKO) mice may be a useful model of vascular failure and hypotension. 相似文献
9.
10.
Rømer Thomsen K Lou HC Joensson M Hyam JA Holland P Parsons CE Young KS Møller A Stein A Green AL Kringelbach ML Aziz TZ 《PloS one》2011,6(4):e18686
Emotion and reward have been proposed to be closely linked to conscious experience, but empirical data are lacking. The anterior cingulate cortex (ACC) plays a central role in the hedonic dimension of conscious experience; thus potentially a key region in interactions between emotion and consciousness. Here we tested the impact of emotion on conscious experience, and directly investigated the role of the ACC. We used a masked paradigm that measures conscious reportability in terms of subjective confidence and objective accuracy in identifying the briefly presented stimulus in a forced-choice test. By manipulating the emotional valence (positive, neutral, negative) and the presentation time (16 ms, 32 ms, 80 ms) we measured the impact of these variables on conscious and subliminal (i.e. below threshold) processing. First, we tested normal participants using face and word stimuli. Results showed that participants were more confident and accurate when consciously seeing happy versus sad/neutral faces and words. When stimuli were presented subliminally, we found no effect of emotion. To investigate the neural basis of this impact of emotion, we recorded local field potentials (LFPs) directly in the ACC in a chronic pain patient. Behavioural findings were replicated: the patient was more confident and accurate when (consciously) seeing happy versus sad faces, while no effect was seen in subliminal trials. Mirroring behavioural findings, we found significant differences in the LFPs after around 500 ms (lasting 30 ms) in conscious trials between happy and sad faces, while no effect was found in subliminal trials. We thus demonstrate a striking impact of emotion on conscious experience, with positive emotional stimuli enhancing conscious reportability. In line with previous studies, the data indicate a key role of the ACC, but goes beyond earlier work by providing the first direct evidence of interaction between emotion and conscious experience in the human ACC. 相似文献