全文获取类型
收费全文 | 1148篇 |
免费 | 77篇 |
国内免费 | 54篇 |
专业分类
1279篇 |
出版年
2021年 | 12篇 |
2020年 | 11篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 53篇 |
2012年 | 56篇 |
2011年 | 45篇 |
2010年 | 43篇 |
2009年 | 49篇 |
2008年 | 46篇 |
2007年 | 36篇 |
2006年 | 39篇 |
2005年 | 42篇 |
2004年 | 31篇 |
2003年 | 32篇 |
2002年 | 20篇 |
2001年 | 35篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 32篇 |
1997年 | 20篇 |
1996年 | 14篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1983年 | 13篇 |
1979年 | 22篇 |
1974年 | 13篇 |
1973年 | 15篇 |
1970年 | 11篇 |
1968年 | 11篇 |
1958年 | 16篇 |
1957年 | 15篇 |
1956年 | 25篇 |
1955年 | 15篇 |
1954年 | 11篇 |
1953年 | 21篇 |
1952年 | 14篇 |
1951年 | 15篇 |
1950年 | 15篇 |
排序方式: 共有1279条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Kazuhiro Yamaguchi Klaus D. Jürgens Heinz Bartels Johannes Piiper 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(1):1-9
Summary To estimate the advantage of the small red blood cells (RBC) of high-altitude camelids for O2 transfer, the kinetics of O2 uptake into and release from the RBC obtained from llama, vicuña and alpaca were investigated at 37°C with a stopped-flow technique. O2 transfer conductance of RBC (G) was estimated from the rate of O2 saturation change and the corresponding O2 pressure difference between medium and hemoglobin. For comparison, O2 kinetics for the RBC of a lowaltitude camelid (dromedary camel) and the pygmy goat were determined and previously measured values for human RBC were used. O2 transfer of RBC was found to be strongly influenced by extracellular diffusion, except with O2 release into dithionite solutions of sufficiently high concentration (>30 mM). TheG values measured in these standard conditions,G
st (in mmol · min–1 · Torr–1 · (ml RBC)–1) were: high-altitude camelids, 0.58 (averaged for llama, alpaca and vicuña since there were no significant interspecific differences); camel 0.42; goat, 0.42; man, 0.39. The differences can in part be attributed to expected effects of the size and shape of the RBC (volume, surface area, mean thickness), as well as to the intracellular O2 diffusivity which depends on the concentration of cellular hemoglobin. The highG
st of RBC of highaltitude camelids may be considered to enhance O2 transfer in lungs and tissues. But the O2 transfer conductance of blood, , equal toG
st multiplied by hematocrit (in mmol · min–1 · Torr–1 · (ml blood)–1), was only slightly higher as compared to other species: 0.20 (llama, alpaca, vicuña), 0.14 (camel), 0.18 (goat), 0.17 (man).Abbreviations
DPG
2,3-diphosphoglycerate
-
G
conductance
-
Hb
hemoglobin
-
RBC
red blood cells
-
percent saturation of hemoglobin 相似文献
5.
Karyometry and histometry of renal-cell carcinoma 总被引:1,自引:0,他引:1
M Bibbo H Galera-Davidson H E Dytch J Gonzalez de Chaves J Lopez-Garrido P H Bartels G L Wied 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》1987,9(2):182-187
In an attempt to more objectively predict the outcome of renal cancers, karyometric and histometric studies were performed using an interactive computer-based system for the quantitative analysis of tissue sections. Analysis showed a significant relationship between patient survival and metastases and the histometric parameters of nuclear elongation, nuclear crowding and mitotic density, as well as tumor grade. Patients who died tended to have a high mitotic density, elongated and crowded nuclei and high-grade tumors. Ploidy showed no significant correlation with prognosis while nuclear elongation and crowding did. Differences in histologic grade were significantly associated with several histometric variables, including nuclear area, shape, crowding, elongation and mitotic density. 相似文献
6.
In rat liver parenchyma, expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene was studied by Northern blot analysis with a biotinylated cRNA probe and the zonal localization of PEPCK mRNA was demonstrated by in situ hybridization with a radiolabelled cRNA probe. During the feeding period at night, overall PEPCK mRNA levels were low and PEPCK mRNA was detected only in small areas of the periportal zone. At the beginning of the light period (7 am) the overall PEPCK mRNA level began increasing and the periportal areas containing PEPCK mRNA broadened. The maximum of the total abundance and of the area with high levels of PEPCK mRNA was reached at noon. Fasting for 24-72 h did not cause further significant alterations in the level or localization of PEPCK mRNA. The present data are in line with previous findings of the predominant localization of PEPCK activity and enzyme protein in periportal hepatocytes. They suggest that the heterogeneous expression of the PEPCK gene in rat liver is regulated at the pretranslational level. 相似文献
7.
M Bibbo D H Kim C di Loreto H E Dytch H Galera-Davidson D Thompson D L Richards H G Bartels P H Bartels 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》1990,12(4):229-236
In research for the development of a computer-aided workstation for the objective grading of prostatic carcinoma, tissue architectural (histometric) features were analyzed in ten cases each of well-differentiated, moderately differentiated and poorly differentiated carcinoma (as subjectively graded by the consensus of a panel of experts). Sections were cut at 4 microns, stained by the Feulgen reaction and digitized by two different video-based photometric systems. Some images were interactively segmented, considering the histometric clues to be studied; others were automatically segmented by an expert system-guided technique. The latter procedure produced good results, with over 90% of the nuclei judged to be correctly segmented in 64% of the fields studied and over 80% in another 24% of the fields. While the number of nuclei per field provided some separation of well-differentiated from other lesions, the number of nuclei per gland distinguished between well-differentiated and moderately differentiated lesions. Simplicial decomposition of the images also provided a measure of the degree of differentiation, as did the "texture" of the nuclear placement, based on two run-length statistics. Combination of the run-length features distinguished the three categories of lesions with statistical significance. The results of this study provided insights into the problems (such as the effect of field boundaries) faced in the design of an computer-aided grading system. They also showed the value of expert system-guided scene segmentation and of such histometric features as the field cellularity and the number of nuclei per gland for the discrimination between lesions of different grades of differentiation. 相似文献
8.
H Galera-Davidson P H Bartels A Fernandez-Rodriguez H E Dytch E Lerma-Puertas M Bibbo 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》1990,12(1):35-41
Karyometric measurements were performed on fine needle aspirates of clearly identifiable tumor areas and adjacent normal-appearing areas in the surgical specimens from ten patients with invasive follicular carcinoma of the thyroid. Similar measurements were performed on aspirates from nine patients free of thyroid disease (controls). A total of 95 karyometric features were evaluated for each nucleus. Analysis of variance of optical density values indicated (1) a similarity between tumor and normal-appearing nuclei from carcinoma cases, (2) a significant difference between those nuclei and control nuclei and (3) that most of the differences were due to the differences of tissue origin. Stepwise linear discriminant analysis selected ten features that produced a statistically highly significant separation of tumor nuclei from control nuclei. A similar analysis selected six features that produced a statistically highly significant discrimination of normal-appearing nuclei from control nuclei; the validity of those karyometric features as markers of malignancy in normal-appearing nuclei from tissues adjacent to invasive follicular carcinomas of the thyroid was demonstrated by analysis in further training and control sets of nuclei. This analysis in thyroid aspirates identified more marker features than did a previous similar analysis using tissue sections. 相似文献
9.
The isolated liver from 24 h fasted rats was perfused in a non-recirculating manner in the ortho- and retrograde direction with erythrocyte-containing (20% v/v) media to provide adequate oxygenation of the liver. Glucose and/or gluconeogenic precursors were added as substrates. Glycogen formation was determined biochemically and demonstrated histochemically. With glucose as the sole exogenous substrate glycogen was deposited in the perivenous area, with gluconeogenic precursors it was formed in the periportal zone during ortho- and retrograde flow. When glucose and gluconeogenic compounds were offered together, glycogen was deposited in both zones. The results corroborate the model of metabolic zonation predicting that periportal glycogen is synthesized indirectly from gluconeogenic precursors while perivenous glycogen is formed directly from glucose. 相似文献
10.
S W Jordan J M Brayer P H Bartels R E Anderson 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》1988,10(1):37-46
Obtaining histologic images for computer-based morphometric analysis is associated with a number of standardization problems, which must be solved if reproducible data collection is expected. These problems include tissue processing, sectioning and staining, standardizing and calibrating the video camera and determining the appropriate sampling rate (pixels/micron). Suggested solutions for these problems are presented for a specific image analysis system, but are applicable to other systems with similar capabilities. Biologic variability is not eliminated by computer-assisted analysis, so it is important to minimize data-collection artifacts by parallel processing of experimental and control material, as in other investigative work. 相似文献