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751.
Bovine spermatozoa, maturing in the caudal epididymis, apparently have a low content of mobilizable Ca2+ (6 ± 1 nmoles cells) in situ, but will accumulate added Ca2+ when simply diluted into isotonic media. It is suggested that the low concentrations of Ca2+ (0.5 ± 0.1 mM) and O2 present in epididymal fluids prevent the accumulatin of Ca2+ by sperm prior to ejaculation. Although the seminal plasma that surrounds ejaculated sperm contains 9 ± 1 mM Ca2+, washed ejaculated sperm also have a low Ca2+ content (7 ± 1 nmoles cells). Moreover, in contrast to epididymal sperm, washed ejaculated sperm are incapable of accumulating Ca2+ supplied exogenously. Evidence is presented that bovine seminal fluids contain a component that is added to the surface membranes of the sperm at ejaculation which prevents or delays the active uptake of Ca2+ by these cells. 相似文献
752.
M A Lynes L L Lanier G F Babcock P J Wettstein G Haughton 《Journal of immunology (Baltimore, Md. : 1950)》1978,121(6):2352-2357
Two unusual murine lymphomas, designated CH1 and CH2, were produced in the newly developed double congenic strain of mice, B10 H-2a H-4b p/Wts. Both tumors lack the T cell-specific antigen (thy-1), but express cell surface immunoglobulin and the H-2K, H-2D, and Ia specificities determined by the H-2a haplotype. Further studies have demonstrated that these tumors represent "early" B cells in that they express surface IgM (mu heavy and lambda light chains), but do not bear surface delta, gamma, or alpha heavy chains. CH1 and CH2 lack surface C3 receptors and results from assays for Fc receptors have proven variable. A competition radioimmunoassay directed against the gp71 group-specific antigen of Friend leukemia virus has shown that there is a murine leukemia virus associated with these tumors, however, we have been unable to establish a causal relationship between the virus and this malignancy. A comparison of the surface characteristics of these tumors with other mammalian B cell lymphomas is presented. 相似文献
753.
Isolation and characterization of canine advanced preantral and early antral follicles 总被引:3,自引:0,他引:3
This study was designed to develop preantral follicle isolation and classification protocols for the domestic dog as a model for endangered canids. Ovary donors were grouped by age, size, breed purity, ovary weight and ovary status. Ovaries were randomly assigned to 1 of 3 digestion protocols: A) digestion and follicle isolation on the day of spaying; B) storage at 4 degrees C for 18 to 24 h prior to digestion and follicle isolation; C) digestion on the day of spaying, then incubation at 4 degrees C for 18 h prior to follicle isolation. Minced tissue was placed in a collagenase/DNase solution at 37 degrees C for 1 h. Follicles were classified by oocyte size and opaqueness and by size and appearance of the granulosa cell layers. Preantral follicles contained small, pale oocytes. Preantral follicles containing grown oocytes with dense cytoplasmic lipid were designated as advanced preantral. Only advanced preantral and early antral follicles were examined and classified further. Group 1 follicles had incomplete or absent granulosa layers, Group 2 follicles had several intact granulosa layers, while Group 3 were vesicular (early antral) follicles. Misshapen or pale grown oocytes were classified as degenerated. The percentage of intact germinal vesicles (GV) was recorded for each Group. Digestion Protocol B produced the lowest percentage of degenerated follicles (P < 0.01). Prepubertal donors had fewer (P < 0.01) follicles in each Group and more (P < 0.001) degenerated follicles than older bitches. Larger ovaries yielded the highest total number of follicles (P < 0.05). Ovary status did not affect follicle yield. Oocytes from Group 1 follicles had fewer intact GVs than those from Group 2 or Group 3 (P < 0.0001). These findings provide an opportunity for quantitative studies of the factors regulating folliculogenesis in the domestic dog as a model for endangered canids. 相似文献
754.
755.
This study examined the effect of fishing on the abundance and species richness of families of coral reef fish at two islands
(Sumilon and Apo) in the Philippines from 1983 to 1993. Natural fishing experiments occurred in marine reserves at each island,
where long term estimates of fishing intensity were available. Responses to fishing were interpreted in terms of life histories
of fish. The intensity of fishing and fish life histories were generally good predictors of the differential rates of decline
and recovery of abundance in response to fishing. Large predators had vulnerable life histories (low rates of natural mortality,
growth and recruitment) and were subjected to high intensity fishing. They declined significantly in density when fished and
increased significantly but slowly when protected from fishing. Caesionidae, a family with a life history resilient to fishing
(high rates of natural mortality, growth and recruitment) but fished intensively also declined rapidly in abundance when fished.
Thus, knowledge of life history alone was insufficient to predict response to fishing. Acanthuridae were fished relatively
hard and had a life history of intermediate vulnerability but displayed weak responses to fishing. Thus level of fishing intensity
alone was also not sufficient to predict response to fishing. For Chaetodontidae, effects of fishing conformed to expectations
based on life history and fishing intensity at one island but not the other. Three families with intermediate vulnerability
and subjected to intermediate to light fishing (F. Scaridae, Labridae and Mullidae) displayed predictably weak responses to
fishing, or counter-intuitive responses (e.g., increasing in abundance following fishing). These counter-intuitive responses
were unlikely to be secondary effects of increase in prey in response to declines of predators. Two lightly-fished families
with resilient life histories (F. Pomacentridae, Sub F. Anthiinae) predictably displayed weak numerical responses to fishing
except during a period of use of explosives and drive nets.
Accepted: 30 June 1998 相似文献
756.
This study examined the effect of fishing on the density, biomass, species richness and overall structure of the reef fish
community at two islands (Sumilon and Apo) in the Philippines from 1983 to 1993. A series of natural fishing experiments over
this period involving marine reserves were monitored at each island, where estimates of fishing intensity and selectivity
were available. Fishing intensity (15% and 25% of biomass removed per year at Sumilon and Apo, respectively) was high enough
to affect total community biomass, but not density, significantly. Species richness was not affected significantly by fishing,
except at Sumilon reserve. The fishery was relatively non-selective with most families/trophic groups caught roughly in proportion
to their contribution to community biomass. Thus fishing did not alter the relative abundance of the major families/trophic
groups significantly, except during a period of use of explosives and drive nets in the Sumilon reserve. At the level of family/trophic
group the community displayed strong resilience of structure. There was little evidence of secondary effects e.g. declines
in abundance of large predators resulting in measurable increases in abundance of their prey. This resilience of the community
to the effects of fishing most likely results from three important community attributes (open nature of the component populations,
likely maintenance of upstream recruitment supply and apparent lack of any obvious “keystone” species or families) and one
important characteristic of the fishery (relatively non-selective with respect to the components of the community).
Accepted: 30 June 1998 相似文献
757.
DNA photolyase repairs pyrimidine dimer lesions in DNA through light-induced electron donation to the dimer. During isolation of the enzyme, the flavin cofactor necessary for catalytic activity becomes one-electron-oxidized to a semiquinone radical. In the absence of external reducing agents, the flavin can be cycled through the semiquinone radical to the fully reduced state with light-induced electron transfer from a nearby tryptophan residue. This cycle provides a convenient means of studying the process of electron transfer within the protein by using transient EPR. By studying the excitation wavelength dependence of the time-resolved EPR signals we observe, we show that the spin-polarized EPR signal reported earlier from this laboratory as being initiated by semiquinone photochemistry actually originates from the fully oxidized form of the flavin cofactor. Exciting the semiquinone form of the flavin produces two transient EPR signals: a fast signal that is limited by the time response of the instrument and a slower signal with a lifetime of approximately 6 ms. The fast component appears to correlate with a dismutation reaction occurring with the flavin. The longer lifetime process occurs on a time scale that agrees with transient absorption data published earlier; the magnetic field dependence of the amplitude of this kinetic component is consistent with redox chemistry that involves electron transfer between flavin and tryptophan. We also report a new procedure for the rapid isolation of DNA photolyase. 相似文献
758.
Thomas C. Sparks John R. Skomp Jon Babcock Chaoxian Geng 《Archives of insect biochemistry and physiology》1994,25(1):1-8
Whole body extracts of the two-spotted spider mite (Tetranychus urticae Koch) were analyzed using a 16-channel electrochemical array high performance liquid chromatography (HPLC)-based detection system that allows the simultaneous isolation and identification of a variety of biogenic amines. The spider mite extracts were found to contain the biogenic amines octopamine, dopamine, and 5-hydroxytryptamine (5-HT), as well as several precursors and metabolites including tyrosine, tyramine, tryptophan, and N-acetyl octopamine. Differences in the levels of biogenic amines were observed between eggs and the adult stages and between males and females. This is the first direct determination of biogenic amines in the Tetranychidae and the first demonstration of 5-HT in any mite species. © 1994 Wiley-Liss, Inc. 相似文献
759.
Altman RB Bergman CM Blake J Blaschke C Cohen A Gannon F Grivell L Hahn U Hersh W Hirschman L Jensen LJ Krallinger M Mons B O'Donoghue SI Peitsch MC Rebholz-Schuhmann D Shatkay H Valencia A 《Genome biology》2008,9(Z2):S7
This article collects opinions from leading scientists about how text mining can provide better access to the biological literature, how the scientific community can help with this process, what the next steps are, and what role future BioCreative evaluations can play. The responses identify several broad themes, including the possibility of fusing literature and biological databases through text mining; the need for user interfaces tailored to different classes of users and supporting community-based annotation; the importance of scaling text mining technology and inserting it into larger workflows; and suggestions for additional challenge evaluations, new applications, and additional resources needed to make progress. 相似文献
760.
Francisco Zamudio Russ Wolfinger Brian Stanton Fernando Guerra 《Tree Genetics & Genomes》2008,4(2):299-313
The paper reviews the linear mixed models (LMM) methodology that is suitable for the statistical and genetic analyses of spatially
repeated measures collected from clonal progeny tests. For example, we consider a poplar clonal trial where progenies of different
families are propagated by cuttings, and only one ramet per clone is planted on each block. Modeling covariance structures
following the LMM theory allows improving genetic parameter estimation based on clonal testing. Besides variance components,
we also obtained an estimate of the covariance between residuals (within clonal effects in two different blocks). This covariance
is due to planting more than one ramet from the same genotype in the same trial, which generates correlated residual effects
from different blocks. Its estimation can significantly improve the comparison among clones within a progeny test or between
tests in a clonal testing network. Results indicate that the covariance is also a component of the genetic variance estimator
and plays a significant role in assessing the variance of specific (micro) environmental effects. A positive covariance implies
that ramets show a similar performance in more than one block. Thus, a larger and more positive covariance implies a stronger
genetic effect controlling the expression of the trait in the local environment and a smaller variance of specific environmental
effects. On the contrary, a negative covariance implies that the performance of individual ramets is affected by strong microenvironmental
effects, specific to one or more blocks, which can also directly increase the within-clone variability. 相似文献