全文获取类型
收费全文 | 481篇 |
免费 | 69篇 |
出版年
2022年 | 3篇 |
2021年 | 8篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 24篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 22篇 |
2009年 | 16篇 |
2008年 | 25篇 |
2007年 | 27篇 |
2006年 | 12篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 22篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 23篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1969年 | 5篇 |
1967年 | 4篇 |
1966年 | 4篇 |
排序方式: 共有550条查询结果,搜索用时 15 毫秒
101.
Localization of sperm antigen SP-10 during the six stages of the cycle of the seminiferous epithelium in man 总被引:2,自引:0,他引:2
The distribution of the sperm protein SP-10 was investigated in plastic-embedded samples of human testes by light and electron microscopy. An immunogold and silver enhancement technique, in conjunction with a monoclonal antibody (MHS-10) raised against SP-10, was used to localize the protein. SP-10 was detected in spermatids at each of the six stages of the cycle of the seminiferous epithelium. Light microscopy showed immunoreactive material at the circumference of developing acrosomes in the early steps of spermiogenesis. As differentiation proceeded and cell shape changed from round to elongated, immunoreactive material appeared in an arc, which gradually became a V shape bordering the spermatid nucleus. The area of the immunoreactive material and its shape corresponded to that of the developing acrosome. At the electron microscopic level, gold particles indicative of the presence of SP-10 were detected on electron-dense material found within the developing acrosomal vesicle in early steps of spermiogenesis. As the electron density of the acrosome increased, a high concentration of gold particles was seen in the vesicle matrix. The gold particles gradually became associated with the inner and outer acrosomal membranes of the most mature spermatids. 相似文献
102.
Andreas Keller Tobias Fehlmann Nicole Ludwig Mustafa Kahraman Thomas Laufer Christina Backes Claus Vogelmeier Caroline Diener Frank Biertz Christian Herr Rudolf A.Jrres Hans-Peter Lenhof Eckart Meese Robert Bals 《基因组蛋白质组与生物信息学报(英文版)》2018,16(3):162-171
Chronic obstructive pulmonary disease(COPD) significantly increases the risk of developing cancer. Biomarker studies frequently follow a case-control set-up in which patients diagnosed with a disease are compared to controls. Longitudinal cohort studies such as the COPD-centered German COPD and SYstemic consequences-COmorbidities NETwork(COSYCONET) study provide the patient and biomaterial base for discovering predictive molecular markers. We asked whether microRNA(miRNA) profiles in blood collected from COPD patients prior to a tumor diagnosis could support an early diagnosis of tumor development independent of the tumor type. From 2741 participants of COSYCONET diagnosed with COPD, we selected 534 individuals including 33 patients who developed cancer during the follow-up period of 54 months and 501 patients who did not develop cancer, but had similar age, gender and smoking history. Genome-wide miRNA profiles were generated and evaluated using machine learning techniques. For patients developing cancer we identified nine miRNAs with significantly decreased abundance(two-tailed unpaired t-test adjusted for multiple testing P 0.05), including members of the miR-320 family. The identified mi RNAs regulate different cancer-related pathways including the MAPK pathway(P = 2.3 x 10~(-5)). We also observed the impact of confounding factors on the generated miRNA profiles, underlining the value of our matched analysis. For selected miRNAs, qRT-PCR analysis was applied to validate the results. In conclusion, we identified several miRNAs in blood of COPD patients, which could serve as candidates for biomarkers to help identify COPD patients at risk of developing cancer. 相似文献
103.
104.
J. M. Herr Jr. 《American journal of botany》1995,82(4):547-564
Of several theories for the origin of the ovule advanced in this century and based largely on fossil evidence, the telomic concept is widely considered the most plausible. Its principal tenet is the evolution of the integument through fusion of sterile branches or telomes around a terminal megasporangium. The only point of agreement in these theories is that the entire nucellus is a megasporangium that retains a single megaspore and the endosporic female gametophyte. Their differences center on the origin of the integument. A new concept offered here on evidence from ovules of both Paleozoic and extant seed plants significantly alters the telomic theory. It proposes that the nucellus is a sporangiophore of stem origin that bears a terminal megasporangium; that at least some of the fused integumentary telomes were fertile; and that among all features cited to characterize ovules, the unique nature of the retained megaspore alone defines the seed habit. Changes in the seed plant megaspore that extended the period of nutrient absorption over the whole course of female gametophyte development, along with complex physiological changes in the nucellus, were probably achieved along a single phylogenetic line beginning in a Late Devonian population of progymnosperms. For such a combination of events to have occurred more than once is highly unlikely, and, therefore, a monophyletic origin for seed plants is proposed. Several primitive features in ovule structure, some not evidenced since the Lower Carboniferous Period, occur in a mutant form of Arabidopsis thaliana isolated from genetically transformed plants. Their recurrence provides additional support for the proposed concept of ovule origin and also suggests that the genetic mechanisms for expression of primitive features in advanced taxa could be initiated in each case by mutation of a single homeotic gene. 相似文献
105.
Dominik Gruszka Robert Herr Hans Hely Peer Hofmann Daniela Klitscher Alexander Hofmann Pol Maria Rommens 《PloS one》2016,11(1)
Purpose
The use of new headless compression screws (HCSs) for scaphoid fixation is growing, but the nonunion rate has remained constant. The aim of this study was to compare the stability of fixation resulting from four modern HCSs using a simulated fracture model to determine the optimal screw design(s).Methods
We tested 40 fresh-frozen cadaver scaphoids treated with the Acumed Acutrak 2 mini (AA), the KLS Martin HBS2 midi (MH), the Stryker TwinFix (ST) and the Synthes HCS 3.0 with a long thread (SH). The bones with simulated fractures and implanted screws were loaded uniaxially into flexion for 2000 cycles with a constant bending moment of 800 Nmm. The angulation of the fracture fragments was measured continuously. Data were assessed statistically using the univariate ANOVA test and linear regression analysis, and the significance level was set at p < 0.05.Results
The median angulation of bone fragments φ allowed by each screw was 0.89° for AA, 1.12° for ST, 1.44° for SH and 2.36° for MH. With regards to linear regression, the most reliable curve was achieved by MH, with a coefficient of determination of R2 = 0.827. This was followed by AA (R2 = 0.354), SH (R2 = 0.247) and ST (R2 = 0.019). Data assessed using an adapted ANOVA model showed no statistically significant difference (p = 0.291) between the screws.Conclusions
The continuous development of HCSs has resulted in very comparable implants, and thus, at this time, other factors, such as surgeons’ experience, ease of handling and price, should be taken into consideration. 相似文献106.
107.
Summary Living protoplasts were isolated from the interplacental tissue ofLycopersicum esculentum L. var.Manalucie with 5% polygalacturonase in 0.4 M sucrose solution. The protoplasts were treated under standardized conditions with eleven hydrolytic enzymes, and the effects were determined through microscopic examination. Increase in optical density with the cessation of cyclosis, instantaneous collapse, lysis, disruption by cleavage, and the formation of protuberances followed by disruption were considered indicative of impairment in membrane structure. The similarity of response to RNAse, phosphodiesterase and pancreatin strongly suggests the presence of membrane RNA as an important constituent in the maintenance of structural integrity. 相似文献
108.
Constancy of the length of human Y chromosome 总被引:3,自引:0,他引:3
D S Borgaonkar V A McKusick H M Herr L de los Cobos O C Yoder 《Annales de génétique》1969,12(4):262-264
109.
Hydrogen metabolism was studied in three Casuarina species, C, equisetifolia Forst., C. glauca Sieb. ex. Spreng. and C. obesa Miq., either inoculated with the pure Frankia culture HFP CcI3 or inoculated with a crushed nodule inoculum made from C. glauca nodules. Nitrogenase (EC 1.7.99.2) activity and hydrogen evolution was measured on intact plants, while hydrogen uptake was measured on excised nodules and in nodule homogenates.
Nitrogenase activity was highest in C. glauca inoculated with C. glauca nodules, while no hydrogen evolution was detected. Hydrogen evolution was highest in the symbiosis between C. equisetifolia and HFP CcI3, but the nitrogenase activity showed intermediate values compared to the other symbioses. Measured at a concentration of 93 μ M H2 , H2 uptake was highest in C. glauca inoculated with the C. glauca inoculum. H2 uptake activity in homogenates was 83% of the intact nodule rate. With phenazinemethosulfate as the electron acceptor, H2 uptake by nodule homogenates showed typical Michaelis-Menten kinetics with a Km of 21.3 μ M for H2 .
The data presented here indicate a host plant effect on the endobiont which alters the hydrogen metabolism. 相似文献
Nitrogenase activity was highest in C. glauca inoculated with C. glauca nodules, while no hydrogen evolution was detected. Hydrogen evolution was highest in the symbiosis between C. equisetifolia and HFP CcI3, but the nitrogenase activity showed intermediate values compared to the other symbioses. Measured at a concentration of 93 μ M H
The data presented here indicate a host plant effect on the endobiont which alters the hydrogen metabolism. 相似文献
110.
The possibility that respiration limits oxygen access to nitrogenase was tested by artificially upsetting the balance between oxygen consumption (respiration) and oxygen influx (diffusion). Argon treatment of the nodulated root system on intact plants stopped in vivo nitrogenase activity almost completely. Upon return to air, nitrogenase activity was very low and recovered gradually to full activity after about 5 h. In vitro measurements on nodule homogenates indicated that active nitrogenase was lost upon the shift from low (argon) to normal (air) oxygen. Maintenance of nodulated root systems at low temperature (2°C) inhibited both respiration and in vivo nitrogenase activity. Upon return to normal temperature (22°C), oxygen uptake recovered very rapidly, but nitrogenase activity recovered only gradually to full activity after about 5 to 6 h. Again, loss of active nitrogenase could, at least partly, explain the reduced in vivo nitrogenase activity. The effects from a temporarily impaired balance between oxygen consumption and oxygen influx thus point to the importance of respiration for limiting oxygen access to nitrogenase. 相似文献