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931.
Claudio Tennie Kathrin Greve Heinz Gretscher Josep Call 《Primates; journal of primatology》2010,51(4):337-351
Individuals observing a proficient model can potentially benefit by copying at least one of the following three elements:
motor movements (i.e., actions), goals, and results. Although several studies have investigated this issue in human infants,
there are still very few studies that have systematically examined great apes’ ability to spontaneously copy each of these
three elements (particularly in comparison with human infants). We tested great apes and human children with eight two-target
puzzle boxes—with varying levels of difficulty—to isolate the aspects that the various species may be more prone to copying.
We found first trial evidence for observational learning of actions, goals, and results in children. Some copying was found
for apes as well, but only if their performance was averaged across trials. 相似文献
932.
933.
Aim During the last ice age large parts of the north boreal and subarctic zones were covered by ice, while the climate in ice‐free regions of northern Asia was extremely cold and dry. The extensive peatlands of these zones with their characteristic vegetation developed at the beginning of the Holocene. We combine a phylogeographical approach with maps of pollen records to identify regions where Rubus chamaemorus, a plant of moist, peaty soils, was likely to grow during this period. Location Circumarctic/circumboreal. Methods Samples were collected from 45 locations throughout much of the range of R. chamaemorus and 398 plants were analysed with amplified fragment length polymorphism (AFLP). Estimates of diversity and differentiation, principal coordinates analysis and Bayesian clustering methods were used for the analysis of genetic data. Dated pollen records were retrieved from the European and the Global Pollen Databases. Results The plants from Sakhalin are highly divergent from the rest of the material and represent the previously described var. pseudochamaemorus. The main genetic division in R. chamaemorus sensu stricto is found in the Taymyr region in central Eurasia. Genetic diversity and the relative number of rare markers are highest in central Siberia and eastern Asia and decrease towards Europe and to a lesser extent eastwards through North America. Pollen dating back to the last ice age is found in central and eastern Siberia and Alaska. The maximum observed clone size is about 250 m, and more than one clone is found in nearly every local population. Main conclusions The genetic data are consistent with the pollen records and indicate that R. chamaemorus was growing in several areas of northern central Siberia and Beringia during the last glaciation. This finding suggests that sufficient humidity for this and other species of peaty soils was present locally in different parts of the generally dry ice‐free areas of northern Asia, as had been previously documented for Beringia. The AFLP data show that var. pseudochamaemorus, which is also morphologically quite divergent, clearly represents a distinct genetic entity. 相似文献
934.
P.C. Hopman G. Koopmans A.P.M. van de Fliert J. Greve 《International journal of biological macromolecules》1980,2(3):143-148
Using dynamic light scattering, the translational diffusion coefficient (DT) and the distance between the hydrodynamic centre and the centre of the head (r0) of the bacteriophage T4B have been determined. For a particle with retracted tail fibres we found DT20.w =2.88 (2.88 ± 0.02) × 10?8cm2s?1 and r0 = 52 ± 1 nm. For a phage with fully extended tail fibres DT20w = (.210 ± 0.02) × 10?8cm2s?1 and r0 = 112 ± nm. These data were obtained by interpreting the correlation function using a theory which takes into account the influence of the lollipop shape of the phage. In the literature this influence has not been taken into account, which has led to erroneous values of diffusion coefficients for T4B and other phages. The sedimentation coefficient of T4B phage is 1040 ± 5 S (fibres retracted) or 829 ± 4 S (fibres extended). With the above mentioned diffusion coefficients, these values correspond to a molecular weight of 236 × 106 ± 3 × 106. Finally, the theory used in this study is applied to other bacterial viruses, to correct reported values of the translational diffusion coefficients and of the corresponding molecular weights of these viruses. 相似文献
935.
936.
BACKGROUND:Flow cytometry has been applied successfully to the sizing of medium to large-sized DNA molecules, thanks to the excellent staining properties of cyanine chromophores such as TOTO (homodimer of thiazole orange) (Petty et al.: Anal Chem 67:1755-1761, 1995). The hydrodynamic flow, used to focus the sample molecules in a small laser-illuminated volume, is also responsible for their alignment, thereby allowing the determination of the TOTO-dipole orientation with respect to the DNA axis (Agronskaia et al.: Appl Opt 38:714-719, 1999). METHODS:We present model calculations of the fluorescence yield of TOTO-stained DNA measured in a flow-cytometric setup with high numerical aperture. The models consider different orientations of the chromophore dipoles. RESULTS:Comparison of measurement and calculation suggests that the absorption dipoles of the TOTO molecule make a mean angle of 61 degrees with the helix axis of the DNA molecule. This mean angle can be the consequence of two binding modes. CONCLUSIONS: Our results indicate that any model with a significant contribution of perpendicularly-oriented chromophores fails to reproduce the experimental results. 相似文献
937.
Paenibacillus larvae is the causative agent of American Foulbrood (AFB), the most severe bacterial disease that affects honeybee larvae. AFB causes a significant decrease in the honeybee population affecting the beekeeping industry and agricultural production. After infection of larvae, P. larvae secretes proteases that could be involved in the pathogenicity. In the present article, we present the secretion of different proteases by P. larvae. Inhibition assays confirmed the presence of metalloproteases. Two different proteases patterns (PP1 and PP2) were identified in a collection of P. larvae isolates from different geographic origin. Forty nine percent of P. larvae isolates showed pattern PP1 while 51% exhibited pattern PP2. Most isolates belonging to genotype ERIC I - BOX A presented PP2, most isolates belonging to ERIC I - BOX C presented PP1 although relations were not significant. Isolates belonging to genotypes ERIC II and ERIC III presented PP2. No correlation was observed between the secreted proteases patterns and geographic distribution, since both patterns are widely distributed in Uruguay. According to exposure bioassays, isolates showing PP2 are more virulent than those showing PP1, suggesting that difference in pathogenicity could be related to the secretion of proteases. 相似文献
938.
Tomasi Matilde Artoni Alessio Mattei Lorenza Di Puccio Francesca 《Biomechanics and modeling in mechanobiology》2023,22(2):379-400
Biomechanics and Modeling in Mechanobiology - Noninvasive estimation of joint loads is still an open challenge in biomechanics. Although musculoskeletal modeling represents a solid resource,... 相似文献
939.
940.
The hCG induced ovulation in sows was studied by use of ultrasonography, and an investigation of the development and diversity of the zygotes/embryos was performed at 24 h after ovulation. Crossbred sows (N=48) were weaned (day 0) and checked for heat twice daily from day 3 onwards. From day 4, the ovaries were transrectally scanned twice daily On day 4, the sows were given an injection of 750 iu hCG im and inseminated 27 ± 2 h (X ± SD) and 38 ± 1 h later. From 38 to 48 h after the hCG injection, the ovaries were scanned at 60 to 90 min intervals. At 24 h after ovulation the oviducts were surgically flushed in 18 sows. Out of the 48 sows, 34 showed heat at 12–36 h after the hCG-treatment and 14 showed heat before the hCG treatment. In the former group of sows, 20 (59%) ovulated within the interval of 38 to 48 h after the hCG treatment, and the follicular size immediately before ovulation was 7.8 ± 0.6 mm. Among the sows which showed heat before hCG treatment only 7 (50%) ovulated within the above interval and the preovulatory follicle size was larger (8.3 ± 0.5, p<0.05) than in the former group of sows, which showed heat after the hCG treatment. The flushing of 18 sows yielded a total of 243 ova, 70 (29 %) 1-cell stages, 160 (66 %) 2-cell stages and 13 (5%) 4-cell stages. A pronounced difference in the degree of variation in embryonic development was seen between sows: 4 animals yielded 1- to 4-cell stages, one exclusively 2-cell stage. In conclusion, the control of ovulation in sows by hCG treatment will affect the follicular growth and the exact timing of ovulation can not always be relied on. It is strongly recommended to use ultrasonography to monitor the time of ovulation if this parameter is important. Ova recovered at 24±1 h after the median time of ovulation revealed a pronounced diversity (1- to 4- cell stage) within sows. No obvious relation with this embryonic diversity and the follicular size at ovulation was seen in these data. 相似文献