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排序方式: 共有727条查询结果,搜索用时 15 毫秒
1.
Peter Hechtman Bernard Boulay Marc De Braekeleer Eve Andermann Serge Melançon Jean Larochelle Claude Prevost Feige Kaplan 《Human genetics》1992,90(4):402-406
Mutations at the hexosaminidase A (HEXA) gene which cause Tay-Sachs disease (TSD) have elevated frequency in the Ashkenazi Jewish and French-Canadian populations. We report a novel TSD allele in the French-Canadian population associated with the infantile form of the disease. The mutation, a GA transition at the +1 position of intron 7, abolishes the donor splice site. Cultured human fibroblasts from a compound heterozygote for this transition (and for a deletion mutation) produce no detectable HEXA mRNA. The intron 7+1 mutation occurs in the base adjacent to the site of the adult-onset TSD mutation (G805A). In both mutations a restriction site for the endonuclease EcoRII is abolished. Unambiguous diagnosis, therefore, requires allele-specific oligonucleotide hybridization to distinguish between these two mutant alleles. The intron 7+1 mutation has been detected in three unrelated families. Obligate heterozygotes for the intron 7+1 mutation were born in the Saguenay-Lac-St-Jean region of Quebec. The most recent ancestors common to obligate carriers of this mutation were from the Charlevoix region of the province of Quebec. This mutation thus has a different geographic centre of diffusion and is probably less common than the exon 1 deletion TSD mutation in French Canadians. Neither mutation has been detected in France, the ancestral homeland of French Canada. 相似文献
2.
Scott L. Hooper Michael B. O'Neil Robert Wagner John Ewer Jorge Golowasch Eve Marder 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1986,159(2):227-240
Summary The muscles of the pyloric region of the stomach of the crab,Cancer borealis, are innervated by motorneurons found in the stomatogastric ganglion (STG). Electrophysiological recording and stimulating techniques were used to study the detailed pattern of innervation of the pyloric region muscles. Although there are two Pyloric Dilator (PD) motorneurons in lobsters, previous work reported four PD motorneurons in the crab STG (Dando et al. 1974; Hermann 1979a, b). We now find that only two of the crab PD neurons innervate muscles homologous to those innervated by the PD neurons in the lobster,Panulirus interrruptus. The remaining two PD neurons innervate muscles that are innervated by pyloric (PY) neurons inP. interruptus. The innervation patterns of the Lateral Pyloric (LP), Ventricular Dilator (VD), Inferior Cardiac (IC), and PY neurons were also determined and compared with those previously reported in lobsters. Responses of the muscles of the pyloric region to the neurotransmitters, acetylcholine (ACh) and glutamate, were determined by application of exogenous cholinergic agonists and glutamate. The effect of the cholinergic antagonist, curare, on the amplitude of the excitatory junctional potentials (EJPs) evoked by stimulation of the pyloric motor nerves was measured. These experiments suggest that the differences in innervation pattern of the pyloric muscles seen in crab and lobsters are also associated with a change in the neurotransmitter active on these muscles. Possible implications of these findings for phylogenetic relations of decapod crustaceans and for the evolution of neural circuits are discussed.Abbreviations
ACh
acetylcholine
-
Carb
carbamylcholine
-
cpv
muscles of the cardio-pyloric valve
-
cpv7n
nerve innervating muscle cpv7
-
cv
muscles of the ventral cardiac ossicles
-
cv1n
nerve innervating muscle cvl
-
cv2n
nerve innervating muscle cv2
-
EJP
excitatory junctional potential
-
IC
inferior cardiac neuron
-
IV
inferior ventricular neuron
-
IVN
inferior ventricular nerve
-
LP
lateral pyloric neuron
-
LPG
lateral posterior gastric neuron
-
lvn
lateral ventricular nerve
-
mvn
medial ventricular nerve
-
p
muscles of the pylorus
-
PD
pyloric dilator neuron
-
PD
in
intrinsic PD neuron
-
PD
ex
extrinsic PD neuron
-
pdn
pyloric dilator nerve
-
PY
pyloric neuron
-
pyn
pyloric nerve
-
STG
stomatogastric ganglion
-
VD
ventricular dilator neuron 相似文献
3.
Further Studies on the Phage Sensitivity and the Determination of Phytopathogenic Pseudomonas spp. 总被引:1,自引:1,他引:0
Eve Billing 《Journal of applied microbiology》1970,33(3):478-491
4.
Ülo Niinemets 《Ecological Research》1996,11(3):269-281
Dependencies of foliage arrangement and structure on relative irradiance and total height (TH) were studied in saplings ofAcer platanoides andQuercus robur. The distribution of relative foliar area and dry weight (leaf area and weight in a crown layer per total tree leaf area
and weight, respectively) were examined with respect to relative height (RH, height in the crown per TH) and characterized
by the Weibull function. The distributions of relative area and weight were nearly identical, and the differences between
them were attributable to a systematic decline in leaf dry weight per area with increasing crown depth. Foliage distribution
was similarly altered by tree size in both species; RH at foliage maximum was lower and relative canopy size (RCS, length
of live crown per TH) greater in taller trees. However, the distribution was more uniform inA. platanoides than inQ. robur. Apart from the size effects, relative irradiance also influenced canopy structure; RCS increased inQ. platanoides and decreased inQ. robur with increasing irradiance. As crown architecture was modified by irradiance, foliage distribution was shifted upwards with
decreasing irradiance inA. platanoides, but it was independent of irradiance inQ. robur. Higher foliage maximum at lower irradiance in more shade-tolerantA. platanoides is likely to contribute towards more efficient foliar display for light interception and increase the competitive ability
of this species in light-limited environments. Consequently, these differences in crown architecture and foliage distribution
may partly explain the superior behavior ofA. platanoides in understory. 相似文献
5.
Mechanisms for oscillation and frequency control in reciprocally inhibitory model neural networks 总被引:5,自引:0,他引:5
We describe four different mechanisms that lead to oscillations in a network of two reciprocally inhibitory cells. In two cases (intrinsic release and intrinsic escape) the frequency of the network oscillation is insensitive to the threshold voltage of the synaptic potentials. In the other two cases (synaptic release and synaptic escape) the network frequency is strongly determined by the threshold voltage of the synaptic connections. The distinction between the different mechanisms blurs as the function describing synaptic activation becomes less steep and as the model neurons are removed from the relaxation regime. These mechanisms provide insight into the parameters that control network frequency in motor systems that depend on reciprocal inhibition. 相似文献
6.
We investigate spike initiation and propagation in a model axon that has a slow regenerative conductance as well as the usual Hodgkin-Huxley type sodium and potassium conductances. We study the role of slow conductance in producing repetitive firing, compute the dispersion relation for an axon with an additional slow conductance, and show that under appropriate conditions such an axon can produce a traveling zone of secondary spike initiation. This study illustrates some of the complex dynamics shown by excitable membranes with fast and slow conductances. 相似文献
7.
8.
Ülo Niinemets 《Trees - Structure and Function》1997,11(7):420-431
The relationship between stand biomass production, and tree age and size is generally a curve with a maximum. To understand
why wood production decreases in the final stages of stand development, the influence of increasing tree size on foliage chemical
composition and substrate requirement for foliage construction in terms of glucose [CC, g glucose (g dry mass) –
1] was investigated in the evergreen conifer Picea abies (L.) Karst. Because it was already known that irradiance affects both foliage morphology and chemistry in this species, and
it was expected that the foliage in large overstory trees would intercept on average more light than that in saplings in understory,
irradiance was measured in the sampling locations and included in the statistical models. CC of needles increased with increasing
total tree height (TH) and was independent of relative irradiance. A major reason for increasing CC with increasing TH was
a greater proportion of carbon-rich lignin in the needles in large trees. However, lignin did not fully account for the observed
changes in CC, and it was necessary to assume that certain other carbon-rich secondary metabolites such as terpenes also accumulate
in the foliage of large trees. Enhanced requirements for needle mechanical strength as evidenced by greater lignin concentrations
in large trees were attributed to increased water limitations with increasing tree height. Because water relations may also
control the sink capacities for assimilate usage, apart from the mechanical requirements, they may provide an explanation
for the accumulation of other energetically expensive compounds in the needles as well. Biomass partitioning within the shoot
was another foliar parameter modified in response to increasing tree size. The proportion of shoot axes, which serve to provide
needles with mechanical support and to supply them with water, decreased with increasing TH. This may limit water availability
in the needles, and/or manifest a lower water requirement of the needles containing proportionally more supporting and storage
substances, and consequently, less physiologically active compounds such as proteins. Probably the same factors which caused
CC of the needles to depend on TH, were also responsible for greater CC of the shoot axes in larger trees. These results collectively
suggest that increasingly more adverse water relations with increasing tree size may provide a mechanistic explanation for
the decline in foliar biomass and its functional activity during stand ageing.
Received: 9 April 1996 / Accepted: 14 January 1997 相似文献
9.
Ming Li Wang Lu Huang Deverie K. Bongard-Pierce Stephen Belmonte Eve Ann Zachgo John W. Morris Maureen Dolan Howard M. Goodman 《The Plant journal : for cell and molecular biology》1997,12(3):711-730
A method for construction of bacterial artificial chromosome (BAC) contigs from a yeast artifical chromosome (YAC) physical map is described. An ∼2 Mb contig, consisting of two large BAC contigs linked by a small YAC, has been assembled in the region around 80 cM of Arabidopsis thaliana chromosome 2. Clones from this contig will facilitate gene isolation in the region and can be used directly as substrates for DNA sequencing. 相似文献
10.
Martin Poe Joseph K. Wu Tsau-Yen Lin Karst Hoogsteen Herbert G. Bull Eve E. Slater 《Analytical biochemistry》1984,140(2):459-467
A synthetic tetradecapeptide, H-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His-Ser-OH, which corresponds to the 13 amino terminal residues of human angiotensinogen plus a carboxy terminal serine to replace a suggested site of carbohydrate attachment, has been shown to be a good substrate for human kidney renin. At pH 7.2 and 37 degrees C the KM or Michaelis constant was 8.4 +/- 2.9 microM, and the VM or velocity at infinite tetradecapeptide concentration was 11.3 +/- 2.4 mumol angiotensin I made per hour per milligram renin. The tetradecapeptide was highly resistant to cleavage by mouse submaxillary renin. The tetradecapeptide was also slowly cleaved by human liver cathepsin D, by rabbit lung angiotensin-converting enzyme, and by reconstituted human serum, but did not yield angiotensin I. Thus, this synthetic renin substrate should permit more specific measurement of human kidney renin activity. 相似文献