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The maturation of IgM-expressing B cells to IgM-secreting plasma cells is
associated with both an increase in mu mRNA and the ratio of secreted to
membrane forms of mu mRNA. In contrast, previous studies demonstrated that
in vitro the secreted form of alpha mRNA (alpha s mRNA) predominates
regardless of the stage of B cell differentiation. The present study
demonstrates that alpha s mRNA predominates in both B cells derived from
the germinal centers of murine Peyer's patches and in the functional IgA
memory population, suggesting that in vitro events accurately represent the
generation of a secretory IgA response in vivo. Although the predominant
usage of the alpha s poly(A) site is due to RNA processing, it does not
depend on either the alpha s poly(A) site, the 3' splice site associated
with the exon encoding the membrane exon of IgA (alphaM) or the alphaM
poly(A) sites. Analysis of the sequence of the intron between the alpha s
terminus and alphaM (alpha s- alphaM intron) demonstrates the existence of
several potential regulatory elements. Furthermore, the effects of
deletions within the alpha s-alphaM intron on 3' terminus usage demonstrate
that the predominant usage of the proximal terminus is not strictly
dependent on the length of the intron. Together with previous work, these
observations support the idea that choice of 3' terminus for all Ig heavy
chain genes is regulated by a similar mechanism, but specific sequences
within a heavy chain gene can impinge upon that mechanism.
相似文献
995.
A new catheter-needle combination is described for use in translumbar aortography using a T-12 approach. The catheter has a 90 degree angle 1.5 cm from the tip that allows ready antegrade or retrograde catheterization of the abdominal and thoracic aorta. Injections of contrast material are performed with a tip occluder in place. 相似文献
996.
997.
Based on statistical approach, a novel dose uncertainty model was introduced considering both nonspatial and spatial dose deviations. Non-space-oriented uncertainty is mainly caused by dosimetric uncertainties, and space-oriented dose uncertainty is the uncertainty caused by all spatial displacements. Assuming these two parts are independent, dose difference between measurement and calculation is a linear combination of nonspatial and spatial dose uncertainties. Two assumptions were made: (1) the relative standard deviation of nonspatial dose uncertainty is inversely proportional to the dose standard deviation sigma, and (2) the spatial dose uncertainty is proportional to the gradient of dose. The total dose uncertainty is a quadratic sum of the nonspatial and spatial uncertainties. The uncertainty model provides the tolerance dose bound for comparison between calculation and measurement. In the statistical uncertainty model based on a Gaussian distribution, a confidence level of 3sigma theoretically confines 99.74% of measurements within the bound. By setting the confidence limit, the tolerance bound for dose comparison can be made analogous to that of existing dose comparison methods (e.g., a composite distribution analysis, a gamma test, a chi evaluation, and a normalized agreement test method). However, the model considers the inherent dose uncertainty characteristics of the test points by taking into account the space-specific history of dose accumulation, while the previous methods apply a single tolerance criterion to the points, although dose uncertainty at each point is significantly different from others. Three types of one-dimensional test dose distributions (a single large field, a composite flat field made by two identical beams, and three-beam intensity-modulated fields) were made to verify the robustness of the model. For each test distribution, the dose bound predicted by the uncertainty model was compared with simulated measurements. The simulated measurements were within the tolerance bound as expected by a statistical prediction of the model. Using the dose uncertainty distributions, an uncertainty length (uncertainty area and uncertainty volume for two-dimensional and three-dimensional, respectively) histogram (a plot of the dose uncertainty of 1sigma received by a length of field) was made. The histogram provides additional information on superiority of a treatment plan in terms of uncertainty. In summary, the uncertainty model provides the dose comparison tool as well as the evaluation tool of a treatment planning system. 相似文献
998.
Adipose tissue engineering using mesenchymal stem cells attached to injectable PLGA spheres 总被引:22,自引:0,他引:22
The reconstruction of soft tissue defects remains a challenge in plastic and reconstructive surgery, and a real clinical need exists for an adequate solution. This study was undertaken in order to differentiate mesenchymal stem cells (MSCs) into adipocytes, and to then assess the possibility of constructing adipose tissue via the attachment of MSCs to injectable PLGA spheres. We also designed injectable PLGA spheres for scar-free transplantation. In this study, MSCs and adipo-MSCs (MSCs cultured in adipogenic medium for 7 days) were attached to PLGA spheres and cultured for 7 days, followed by injection into nude mice for 2 weeks. As a result, the difference between lipid accumulation in adipo-MSCs at 1 and 7 days was much higher in vitro than in the MSCs. Two weeks after injection, a massive amount of new tissue was formed in the APLGA group, whereas only a small amount was formed in the MPLGA group. We verified that the newly formed tissue originated from the injected MSCs via GFP testing, and confirmed that the created tissue was actual adipose tissue by oil red O staining and Western blot (PPAR(gamma) and C/EBP(alpha) were expressed only in APLGA groups). Therefore, this study presents an efficient model of adipose tissue engineering using MSCs and injectable PLGA spheres. 相似文献
999.
Randomized trial of short- versus long-course radiotherapy for palliation of painful bone metastases
1000.
Asimitrin and 4-hydroxytrilobin, new bioactive annonaceous acetogenins from the seeds of Asimina triloba possessing a bis-tetrahydrofuran ring 总被引:1,自引:0,他引:1
Kim EJ Suh KM Kim DH Jung EJ Seo CS Son JK Woo MH McLaughlin JL 《Journal of natural products》2005,68(2):194-197
Bioactivity-directed fractionation of the seeds of Asimina triloba resulted in the isolation of asimitrin (1) and 4-hydroxytrilobin (2). Compound 1 represents an adjacent ring-hydroxylated bis-tetrahydrofuran (THF) acetogenin. Compound 2 has an adjacent bis-THF ring with two flanking hydroxyl groups and a alpha,beta-unsaturated gamma-lactone with a 4-hydroxyl group. Compounds 1 and 2 showed cytotoxic selectivity, with 100-10 000 times the potency of adriamycin against prostate adenocarcinoma (PC-3) and colon adenocarcinoma (HT-29) cell lines. 相似文献