全文获取类型
收费全文 | 395篇 |
免费 | 26篇 |
专业分类
421篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 21篇 |
2014年 | 22篇 |
2013年 | 21篇 |
2012年 | 27篇 |
2011年 | 38篇 |
2010年 | 22篇 |
2009年 | 22篇 |
2008年 | 19篇 |
2007年 | 26篇 |
2006年 | 28篇 |
2005年 | 20篇 |
2004年 | 22篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有421条查询结果,搜索用时 15 毫秒
101.
Martin Ve
ea Jan Divíek Jonathan Lenoir Borja Jimnez‐Alfaro Idoia Biurrun Ilona Knollov Emiliano Agrillo Juan Antonio Campos Andra arni Guillermo Crespo Jimnez Mirjana uk Panayotis Dimopoulos Jrg Ewald Federico Fernndez‐Gonzlez Jean‐Claude Ggout Adrian Indreica Ute Jandt Florian Jansen Zygmunt Kcki Valerijus Raomavi
ius Marcela ezní
kov John S. Rodwell Joop H.J. Schamine Urban ilc Jens‐Christian Svenning Grzegorz Swacha Kiril Vassilev Roberto Venanzoni Wolfgang Willner Thomas Wohlgemuth Milan Chytrý 《Journal of Biogeography》2019,46(9):1919-1935
102.
Mirjana Ruml Ana Vuković Dragan Milatović 《International journal of biometeorology》2010,54(4):411-422
The aim of this study was to examine different methods for determining growing degree-day (GDD) threshold temperatures for two phenological stages (full bloom and harvest) and select the optimal thresholds for a greater number of apricot (Prunus armeniaca L.) cultivars grown in the Belgrade region. A 10-year data series were used to conduct the study. Several commonly used methods to determine the threshold temperatures from field observation were evaluated: (1) the least standard deviation in GDD; (2) the least standard deviation in days; (3) the least coefficient of variation in GDD; (4) regression coefficient; (5) the least standard deviation in days with a mean temperature above the threshold; (6) the least coefficient of variation in days with a mean temperature above the threshold; and (7) the smallest root mean square error between the observed and predicted number of days. In addition, two methods for calculating daily GDD, and two methods for calculating daily mean air temperatures were tested to emphasize the differences that can arise by different interpretations of basic GDD equation. The best agreement with observations was attained by method (7). The lower threshold temperature obtained by this method differed among cultivars from −5.6 to −1.7°C for full bloom, and from −0.5 to 6.6°C for harvest. However, the “Null” method (lower threshold set to 0°C) and “Fixed Value” method (lower threshold set to −2°C for full bloom and to 3°C for harvest) gave very good results. The limitations of the widely used method (1) and methods (5) and (6), which generally performed worst, are discussed in the paper. 相似文献
103.
Plant plasma membranes are known to produce superoxide radicals, while the production of the hydroxyl radical, previously detected in complex plant tissues, is thought to occur in the cell wall. The mechanism of production of superoxide radicals by plant plasma membranes is, however, under dispute. It is shown, using electron paramagnetic resonance spectroscopy with a 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide spin-trap capable of differentiating between radical species, that isolated purified plasma membranes from maize roots produce hydroxyl radicals besides superoxide radicals. The results argue in favour of superoxide production through an oxygen and diphenylene iodonium-sensitive, NADH-dependent superoxide synthase mechanism, as well as through other unidentified mechanism(s). The hydroxyl radical is produced by an oxygen-insensitive, NADH-stimulated mechanism, which is enhanced in membranes in which the superoxide synthase is incapacitated by substrate removal or inhibition. 相似文献
104.
Popović-Suić S Sikić J Vukojević N Cerovski B Nasić M Pokupec R 《Collegium antropologicum》2005,29(Z1):149-151
Achievement of target intraocular pressure is the goal of every efficient antiglaucoma therapy. Target intraocular pressure is the level of intraocular pressure which is associated with minimal likelihood of visual field or optic nerve lesion, or an existing lesion progression due to elevated intraocular pressure. Results of large clinical studies which have offered some new concepts on target intraocular pressure in the management of glaucoma are reviewed. An association between the curve of intraocular pressure decrease and glaucoma progression was demonstrated in these studies. Generally, a lower value of target intraocular pressure implies better protection from the loss of vision and visual field impairment in glaucoma patients. In advanced glaucoma, the greatest possible reduction from the initial intraocular pressure should be attempted. A 20% reduction from the initial intraocular pressure or decrease to < 18 mmHg in advanced glaucoma has been recognized as a favorable strategy to reach target intraocular pressure. In normal tension glaucoma, a lower value of target intraocular pressure is associated with a slower disease progression. In patients with initial glaucoma, 25% reduction from the initial intraocular pressure will slow down the disease progression by 45%. The value of target intraocular pressure depends on the pretreatment level of intraocular pressure, optic nerve condition, glaucoma disease state, rate of glaucoma progression, patient's age, and other risk factors for the development of glaucoma. 相似文献
105.
Padyukov L Hahn-Zoric M Blomqvist SR Ulanova M Welch SG Feeney AJ Lau YL Hanson LA 《Immunogenetics》2001,53(1):22-30
Polymorphism in the IGKV2-29 gene was shown to decrease the recombination frequency in B cells and to be important for immune responses to Haemophilus influenzae type b polysaccharide. By using the combination of PCR and restriction enzyme mapping, the distribution of IGKV2D-29 and IGKV2-29 gene alleles was estimated in two geographically and ethnically different groups. We found that V2D-29*01 homozygous individuals were most common in Swedish Caucasians (82%), but less common in the Chinese population of Hong Kong (28%). The homozygous V2D-29*02 genotype was found in 19% Chinese, but only in one Caucasian (1%). The frequency of the heterozygous V2D-29*01/V2D-29*02 genotype was also higher in the Chinese population (46%) compared with the Caucasians (7%). V2-29*01 homozygosity was more frequent among Caucasians (85%) than among Chinese (19%). In contrast, homozygous V2-29*02 individuals were over-represented in the Chinese population (18%), whereas only one was found among Caucasians (1%). Heterozygous V2-29*01/V2-29*02 individuals were also more common in the Chinese (63%) than the Caucasian (15%) population. Most Caucasians had the combination of V2D-29*01/V2D-29*01+V2-29*01/V2-29*01 (74%), while the most common genotype for Chinese was V2D-29*01/V2D-29*02+ V2-29*01/V2-29*02 (41%). Analysis of the association of V2D-29*02 and V2-29*02 alleles demonstrated a high degree of linkage, as for V2D-29*01 with V2-29*01. These data show a significant difference in the distribution of IGKV2D-29 and IGKV2-29 alleles among Swedish Caucasians and Hong Kong Chinese. This may help to explain differences in the occurrence of H. influenzae type b infection in the two populations. Evaluated methods for IGKV2D-29 and IGKV2-29 allele detection can be used for the screening allele polymorphisms in other particular patient groups. 相似文献
106.
Mirjana Gavella Marina Kveder Vaskresenija Lipovac Darija Jurašin Nada Filipovi-Vinceković 《Free radical research》2013,47(10):1143-1150
Antioxidant activity of gangliosides GM1 and GT1b in the Fenton type of reaction was investigated by EPR spectroscopy using DMPO as a spin trap. Hydroxyl radical spin adduct signal intensity was significantly reduced in the presence of gangliosides at their micellar concentrations. Mean micellar hydrodynamic diameter was not changed, whereas significant changes in negative Zeta potential values were observed as evidenced by Zetasizer Nano ZS. This study showed that the primary mode of ganglioside action was not due to direct scavenging of OH·, but rather to the inhibition of hydroxyl radical formation. This phenomenon is related to the ability of ganglioside micelles to bind oppositely charged ferrous ions, thus reducing their concentration and consequently inhibiting OH· formation. 相似文献
107.
Objective
We assessed the adequacy of randomized controlled trial (RCT) registration, changes to registration data and reporting completeness for articles in ICMJE journals during 2.5 years after registration requirement policy.Methods
For a set of 149 reports of 152 RCTs with ClinicalTrials.gov registration number, published from September 2005 to April 2008, we evaluated the completeness of 9 items from WHO 20-item Minimum Data Set relevant for assessing trial quality. We also assessed changes to the registration elements at the Archive site of ClinicalTrials.gov and compared published and registry data.Results
RCTs were mostly registered before 13 September 2005 deadline (n = 101, 66.4%); 118 (77.6%) started recruitment before and 31 (20.4%) after registration. At the time of registration, 152 RCTs had a total of 224 missing registry fields, most commonly ‘Key secondary outcomes’ (44.1% RCTs) and ‘Primary outcome’ (38.8%). More RCTs with post-registration recruitment had missing Minimum Data Set items than RCTs with pre-registration recruitment: 57/118 (48.3%) vs. 24/31 (77.4%) (χ2 1 = 7.255, P = 0.007). Major changes in the data entries were found for 31 (25.2%) RCTs. The number of RCTs with differences between registered and published data ranged from 21 (13.8%) for Study type to 118 (77.6%) for Target sample size.Conclusions
ICMJE journals published RCTs with proper registration but the registration data were often not adequate, underwent substantial changes in the registry over time and differed in registered and published data. Editors need to establish quality control procedures in the journals so that they continue to contribute to the increased transparency of clinical trials. 相似文献108.
Ivan Jarić Mirjana Lenhardt Jan Pallon Mikael Elfman Aleksandar Kalauzi Radu Suciu Gorčin Cvijanović Torbjörn Ebenhard 《Environmental Biology of Fishes》2011,90(2):171-181
Sturgeon populations in the Danube River have experienced severe decline during the last several decades, mostly due to the
poorly regulated fishery, river fragmentation and water pollution. This study focuses on gaining better understanding of sturgeon
life history primarily by addressing the assessment of microelement accumulation in sturgeon pectoral fin rays, especially
of strontium and calcium, as a method that can reveal migration patterns of anadromous sturgeons. Analysis was performed on
pectoral fin samples of three anadromous Danube sturgeon species (beluga, Russian sturgeon and stellate sturgeon) by the use
of a Nuclear Microprobe technique. The most frequent pattern in analyzed samples was represented by a low Sr:Ca ratio in the
innermost annuli, followed by an increased ratio in the middle annuli segment, and often with a decreased ratio in the outermost
annuli. Probability density estimate has revealed three distinguished maxima of the Sr:Ca ratio, 7.08 × 10−3, 8.98 × 10−3 and 9.90 × 10−3, which might correspond, respectively, to fresh, brackish and saltwater. Although the analysis of the Sr:Ca ratio in sturgeon
pectoral fin rays has revealed changes that might indicate probable migration between habitats with different water salinity,
further studies are needed for improvement of this method. This study represents the first analysis of this kind that was
conducted on sturgeon species from the Black Sea basin. 相似文献
109.
The main objective of this study was to develop feasible, easy to apply models for early prediction of full flowering (FF)
and maturing (MA) in apricot (Prunus armeniaca L.). Phenological data for 20 apricot cultivars grown in the Belgrade region were modeled against averages of daily temperature
records over ten seasons for FF and eight seasons for MA. A much stronger correlation was found between the phenological timing
and temperature at the very beginning than at the end of phenophases. Also, the length of developmental periods were better
correlated to daily maximum than to daily minimum and mean air temperatures. Using prediction models based on daily maximum
temperatures averaged over 30-, 45- and 60-day periods, starting from 1 January for FF prediction and from the date of FF
for MA prediction, the onset of examined phenophases in apricot cultivars could be predicted from a few weeks to up to 2 months
ahead with acceptable accuracy. The mean absolute differences between the observations and cross-validated predictions obtained
by 30-, 45- and 60-day models were 8.6, 6.9 and 5.7 days for FF and 6.1, 3.6 and 2.8 days for MA, respectively. The validity
of the results was confirmed using an independent data set for the year 2009. 相似文献
110.