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81.
J. C. Oosterwijk Gabriela Richard Michiel J. R. van der Wielen E. van de Vosse Wolfgang Harth Lodewijk A. Sandkuijl Egbert Bakker Gert-Jan B. van Ommen 《Human genetics》1997,100(5-6):520-524
X-linked keratosis follicularis spinulosa decalvans (KFSD) is a rare disorder affecting both skin and eyes. In the two extended
KFSD families analysed to date, the gene was mapped to Xp22.13–p22.2. By analyzing several new markers in this region, we
were able to narrow the candidate region to a 1-Mb interval between DXS7161 and (DXS7593, DXS7105) in the large Dutch pedigree.
In addition, we analyzed 23 markers in Xp21.2– p22.2 in a German family with KFSD. Haplotype and recombination analysis positioned
the KFSD gene in this family most likely outside the candidate region on Xp22.13–p22.2. This finding is suggestive for genetic
heterogeneity: in this pedigree there is either another locus on the X-chromosome, or KFSD is transmitted here as an autosomal
dominant trait with variable expression.
Received: 28 May 1996 / Accepted: 28 May 1997 相似文献
82.
Some shallow lakes switch repeatedly back and forth between a vegetation dominated clear-water state and a contrasting turbid
state. Usually such alternations occur quite irregularly, but in some cases the switches between states are remarkably regular.
Here we use data from a well-studied Dutch lake and a set of simple models to explore possible explanations for such cyclic
behavior. We first demonstrate from a graphical model that cycles may in theory occur if submerged macrophytes promote water
clarity in the short run, but simultaneously cause an increased nutrient retention, implying an accumulation of nutrients
in the long run. Thus, although submerged plants create a positive feedback on their own growth by clearing the water, they
may in the long run undermine their position by creating a slow “internal eutrophication”. We explore the potential role of
two different mechanisms that may play a role in this internal eutrophication process using simulation models: (1) reduction
of the P concentration in the water column by macrophytes, leading to less outflow of P, and hence to a higher phosphorus
accumulation in the lake sediments and (2) a build-up of organic matter over time resulting in an increased sediment oxygen
demand causing anaerobic conditions that boost P release from the sediment. Although the models showed that both mechanisms
can produce cyclic behavior, the period of the cycles caused by the build-up of organic material seemed more realistic compared
to data of the Dutch Lake Botshol in which regular cycles with a period of approximately 7 years have been observed over the
past 17 years. 相似文献
83.
84.
Egbert Giles LeighJr. 《Trends in ecology & evolution》1999,14(12):495
The ‘modern evolutionary synthesis’ convinced most biologists that natural selection was the only directive influence on adaptive evolution. Today, however, dissatisfaction with the synthesis is widespread, and creationists and antidarwinians are multiplying. The central problem with the synthesis is its failure to show (or to provide distinct signs) that natural selection of random mutations could account for observed levels of adaptation. 相似文献
85.
Daniel Eibach Ralf Krumkamp Hassan M. Al-Emran Nimako Sarpong Ralf Matthias Hagen Yaw Adu-Sarkodie Egbert Tannich Jürgen May 《PLoS neglected tropical diseases》2015,9(3)
BackgroundThe relevance of Cryptosporidium infections for the burden of childhood diarrhoea in endemic settings has been shown in recent years. This study describes Cryptosporidium subtypes among symptomatic and asymptomatic children in rural Ghana to analyse subtype-specific demographic, geographical, seasonal and clinical differences in order to inform appropriate control measures in endemic areas.Conclusions/SignificanceCryptosporidiosis is characterized by seasonal anthroponotic transmission of strains typically found in Sub-Saharan Africa. The infection mainly affects young infants, with vomiting and diarrhoea being one of the leading symptoms in C. parvum infection. Combining molecular typing and clinical data provides valuable information for physicians and is able to track sources of infections. 相似文献
86.
Streptomyces reticuli produces a 35-kDa cellulose-binding protein (AbpS) which interacts strongly with crystalline forms of cellulose (Avicel, bacterial microcrystalline cellulose, and tunicin cellulose); other polysaccharides are recognized on weakly (chitin and Valonia cellulose) or not at all (xylan, starch, and agar). The protein could be purified to homogeneity due to its affinity to Avicel. After we sequenced internal peptides, the corresponding gene was identified by reverse genetics. In vivo labelling experiments with fluorescein isothiocyanate (FITC), FITC-labelled secondary antibodies, or proteinase K treatment revealed that the anchored AbpS protrudes from the surfaces of the hyphae. When we investigated the hydrophobicity of the deduced AbpS, one putative transmembrane segment was predicted at the C terminus. By analysis of the secondary structure, a large centrally located α-helix which has weak homology to the tropomyosin protein family was found. Physiological studies showed that AbpS is synthesized during the late logarithmic phase, independently of the carbon source. 相似文献
87.
Arginine is classified as a conditionally essential amino acid required exogenously during catabolic disease states and periods of rapid growth, both characterized by increased arginine utilization. Arginine plays an important role in the intestine, where it is extensively metabolized, and enhances its immune-supportive function and mucosal repair. Cell proliferation is important for the latter process. This study aimed for a better molecular insight in the response to arginine deprivation/supplementation of preconfluent and 5-day-confluent, differentiated Caco-2 intestinal cells. The potential of citrulline to counteract the effects of arginine deprivation was investigated in preconfluent cells. 2-DE combined with MALDI-TOF-MS and the antibody microarray technology were applied. Evidence is provided that arginine deficiency modulates the protein expression profiles of preconfluent Caco-2 cells differently than that of postconfluent differentiated cells. In preconfluent cells, certain proteins changed in direct response to arginine deficiency, whereas other proteins did not, but instead responded during the recovery phase after an arginine/citrulline resupplementation. The protein changes suggest that arginine deprivation decreases cell proliferation and heat shock protein expression, and enhances the cells susceptibility to apoptosis. These processes are critical for proper cell function, and hence a state of arginine deficiency can be detrimental for intestinal cells which proliferate actively in vivo. 相似文献
88.
Positive Feedbacks in Seagrass Ecosystems: Implications for Success in Conservation and Restoration 总被引:1,自引:0,他引:1
Tjisse van der Heide Egbert H. van Nes Gertjan W. Geerling Alfons J. P. Smolders Tjeerd J. Bouma Marieke M. van Katwijk 《Ecosystems》2007,10(8):1311-1322
Abstract
Seagrasses are threatened by human activity in many locations around the world. Their decline is often characterized by sudden
ecosystem collapse from a vegetated to a bare state. In the 1930s, such a dramatic event happened in the Dutch Wadden Sea.
Before the shift, large seagrass beds (Zostera marina) were present in this area. After the construction of a large dam and an incidence of the “wasting disease” in the early
1930s, these meadows became virtually extinct and never recovered despite restoration attempts. We investigated whether this
shift could be explained as a critical transition between alternative stable states, and whether the lack of recovery could
be due to the high resilience of the new turbid state. We analyzed the depth distribution of the historical meadows, a long-term
dataset of key factors determining turbidity and a minimal model based on these data. Results demonstrate that recovery was
impossible because turbidity related to suspended sediment was too high, probably because turbidity was no longer reduced
by seagrass itself. Model simulations on the positive feedback suggest indeed the robust occurrence of alternative stable
states and a high resilience of the current turbid state. As positive feedbacks are common in seagrasses, our findings may
explain both the worldwide observed collapses and the low success rate of restoration attempts of seagrass habitats. Therefore,
appreciation of ecosystem resilience may be crucial in seagrass ecosystem management. 相似文献
89.
90.
Characterization of dimeric ATP synthase and cristae membrane ultrastructure from Saccharomyces and Polytomella mitochondria 总被引:3,自引:0,他引:3
There is increasing evidence now that F(1)F(0) ATP synthase is arranged in dimers in the inner mitochondrial membrane of several organisms. The dimers are also considered to be the building blocks of oligomers. It was recently found that the monomers in beef and the alga Polytomella ATP synthase dimer make an angle of approximately 40 degrees and approximately 70 degrees, respectively. This arrangement is considered to induce a strong local bending of the membrane. To further understand the packing of dimers into oligomers we performed an electron microscopy analysis of ATP synthase dimers purified from Saccharomyces cerevisiae. Two types of dimers were found in which the angle between the monomers is either approximately 90 degrees or approximately 35 degrees. According to our interpretation, the wide-angle dimers (70-90 degrees) are "true-dimers" whereas the small-angle dimers (35-40 degrees) rather are "pseudo-dimers", which represent breakdown products of two adjacent true dimers in the oligomer. Ultrathin sectioning of intact Polytomella mitochondria indicates that the inner mitochondrial or cristae membrane is folded into lamellae and tubuli. Oligomers of ATP synthase can arrange in a helical fashion in tubular-shaped cristae membranes. These results strongly support the hypothesized role of ATP synthase oligomers in structural determination of the mitochondrial inner membrane. 相似文献