全文获取类型
收费全文 | 950篇 |
免费 | 88篇 |
专业分类
1038篇 |
出版年
2022年 | 10篇 |
2021年 | 22篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 17篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 41篇 |
2014年 | 44篇 |
2013年 | 46篇 |
2012年 | 65篇 |
2011年 | 73篇 |
2010年 | 35篇 |
2009年 | 31篇 |
2008年 | 39篇 |
2007年 | 34篇 |
2006年 | 36篇 |
2005年 | 39篇 |
2004年 | 46篇 |
2003年 | 45篇 |
2002年 | 50篇 |
2001年 | 33篇 |
2000年 | 31篇 |
1999年 | 26篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 11篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1968年 | 3篇 |
1967年 | 5篇 |
排序方式: 共有1038条查询结果,搜索用时 15 毫秒
991.
992.
Eric A. VanderWerf Lindsay C. Young Norine W. Yeung David B. Carlon 《Conservation Genetics》2010,11(4):1283-1298
The elepaio (Chasiempis sandwichensis) is a monarch flycatcher endemic to the Hawaiian Islands of Kauai, Oahu, and Hawaii. Elepaio vary in morphology among and
within islands, and five subspecies are currently recognized. We investigated phylogeography of elepaio using mitochondrial
(ND2) and nuclear (LDH) markers and population structure within Hawaii using ND2 and microsatellites. Phylogenetic analyses
revealed elepaio on each island formed reciprocally monophyletic groups, with Kauai ancestral to other elepaio. Sequence divergence
in ND2 among islands (3.02–2.21%) was similar to that in other avian sibling species. Estimation of divergence times using
relaxed molecular clock models indicated elepaio colonized Kauai 2.33 million years ago (95% CI 0.92–3.87 myr), Oahu 0.69
(0.29–1.19) myr ago, and Hawaii 0.49 (0.21–0.84) myr ago. LDH showed less variation than ND2 and was not phylogenetically
informative. Analysis of molecular variance within Hawaii showed structure at ND2 (fixation index = 0.31), but microsatellites
showed no population structure. Genetic, morphological, and behavioral evidence supports splitting elepaio into three species,
one on each island, but does not support recognition of subspecies within Hawaii or other islands. Morphological variation
in elepaio has evolved at small geographic scales within islands due to short dispersal distances and steep climatic gradients.
Divergence has been limited by lack of dispersal barriers in the extensive forest that once covered each island, but anthropogenic
habitat fragmentation and declines in elepaio population size are likely to decrease gene flow and accelerate differentiation,
especially on Oahu. 相似文献
993.
Summary The glutathione-glutathione disulfide redox pair was utilized to improve white spurce somatic embryo development. Mature cotyledonary-stage
somatic embryos were divided into two groups (A and B) based on morphological normality and the ability of the mature somatic
embryos to convert into plantlets. Group A embryos had four or more cotyledons and converted readily upon germination after
a partial drying treatment. Group B embryos had three or fewer cotyledons with a low conversion frequency. The addition of
reduced glutathione (GSH) at a concentration of 0.1 mM resulted in an increase in embryo production (total population) with a mean total number of 64 embryos per 100 mg embryogenic
tissue as well as an increase in post-embryonic root growth. However, at a higher concentration (1 mM), GSH inhibited embryo formation. The manipulation of the tissue culture environment via the inclusion of glutathione disulfide
(GSSG), at concentrations of 0.1 and 1.0 mM, enhanced the development of better-quality embryos. This quality was best exemplified when embryos forming four or more
cotyledons increased by at least twofold to 73.9% when treated with 1.0 mM GSSG, compared to 38% in control. Furthermore, this improved quality was reflected by an increased conversion frequency.
A 20% increase in the ability of the somatic embryo to produce both root and shoot structures during post-embryonic development
was noted when embryos were matured on maturation medium supplemented with 1.0 mM GSSG over the control. 相似文献
994.
Joyce Chai Vivian Chi-Yan Lee Tracy Wing-Yee Yeung Raymond Wun-Hang Li Pak-Chung Ho Ernest Hung-Yu Ng 《PloS one》2015,10(3)
ObjectiveTo determine the live birth and cumulative live birth rates of expected poor ovarian responders according to the Bologna criteria and to compare their outcomes with those of expected normal respondersDesignRetrospective analysisSettingUniversity infertility clinicPatientsA total of 1,152 subfertile women undergoing their first in vitro fertilization (IVF) cycleInterventionsWomen were classified into 4 groups according to the Bologna criteria for comparisonResultsWomen with expected poor response (POR) had the lowest live birth rate than the other 3 groups (23.8%, p = 0.031). Cumulative live birth rates were significantly lower in those with expected POR than those with expected normal ovarian response (NOR) (35.8% vs 62.8%, p<0.0001). In the subgroup analysis, the cumulative live birth rates in expected PORs were significantly lower in those who had ≤3 oocytes retrieved (18.6% for ≤3 oocytes vs 44.0% for >3 oocytes, p = 0.006) whereas the live birth rates in fresh cycle did not differ (17.8% vs 30.9%, p = 0.108).ConclusionWomen who were expected POR according to the Bologna criteria had lower live birth and cumulative live birth than expected NOR but they still can achieve reasonable treatment outcomes and IVF treatment should not be precluded. 相似文献
995.
A technique for perfusing the lumen of rat epididymal tubules maintained in vitro showed that [3H]inulin was largely excluded from the lumen of unravelled tubules from the cauda and tubules from the corpus if the connective tissue capsule was removed. The preparation transported [3H]inositol from the bath fluid for 3 h against a concentration gradient in both regions with activity rising (16-29% of bath fluid values) in the cauda and reaching a plateau (18%) in the corpus epididymidis. HPLC showed that radioactivity was solely associated with inositol and its movement to the lumen was reduced by raising inositol in the bath fluid from 50 microM (plasma levels) to 10 mM, but not affected by reducing the glucose concentration in the bath fluid or introducing physiological concentrations of inositol (30 mM) into the lumen. Secretion into the caudal lumen of unlabelled inositol measured by g.l.c. was maintained for 3 h at concentrations (300 microM) greater than those in the bath fluid and was not reduced when glucose or inositol were removed from the bath. In contrast, glucose was only detectable in the lumen when it was present in the bathing medium, reaching 1% of this concentration. Radioactivity appeared in the epididymal lumen reaching a plateau (19% of bath fluid values) in the corpus and cauda when [3H]glucose was added to the bath fluid, but no radiolabelled inositol was found in the lumen. We conclude that epididymal tissue is a major source of secreted inositol. 相似文献
996.
997.
J. C. Kuo Edward S. Yeung 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1981,223(2):321-329
Improvements in a detector for liquid chromatography based on optical activity of the components have led to a detectability of 100 ng. This allows the simultaneous determination of six naturally occurring carbohydrates in 100-μl samples of human urine, which is injected directly except for a simple deionization step. The reproducibility and reliability of this method should allow better insight into the relation between urinary sugars and physiological conditions. 相似文献
998.
Total protein or high-abundance protein: Which offers the best loading control for Western blotting?
Jonathan S. Thacker Derrick H. Yeung W. Richard Staines John G. Mielke 《Analytical biochemistry》2016
Western blotting routinely involves a control for variability in the amount of protein across immunoblot lanes. Normalizing a target signal to one found for an abundantly expressed protein is widely regarded as a reliable loading control; however, this approach is being increasingly questioned. As a result, we compared blotting for two high-abundance proteins (actin and glyceraldehyde 3-phosphate dehydrogenase [GAPDH]) and two total protein membrane staining methods (Ponceau and Coomassie Brilliant Blue) to determine the best control for loading variability. We found that Ponceau staining optimally balanced accuracy and precision, and we suggest that this approach be considered as an alternative to normalizing with a high-abundance protein. 相似文献
999.
C W Yeung 《International journal of peptide and protein research》1984,24(6):636-644
125I[D-Ala2, Met5] enkephalin with high specific activity (122-185 Ci/mmol) was prepared and purified by Sep-Pak C18 reverse phase cartridge followed by high performance liquid chromatography (HPLC). HPLC at pH 3.0 resolved 125I[D-Ala2, Met5] enkephalin into two fractions, which ran as a single spot in thin-layer chromatography with the same Rf values. Alkaline hydrolysates of the HPLC-purified fractions showed a single spot corresponding to monoiodotyrosine standard when analysed by thin-layer chromatography. Binding kinetics of the tracer was found to approach equilibrium after 30 min at 24 degrees. Scatchard analysis of the saturation equilibrium binding studies gave an equilibrium dissociation constant of 3.58 nM and the number of binding site of 30 fmol/mg protein. Enkephalin analogs were capable of displacing 125I[D-Ala2, Met5] enkephalin binding from the rat brain plasma membrane. The effective concentration of [D-Ala2, Met5] enkephalin and [D-Ala2, Leu5] enkephalin for 50% inhibition of 125I[D-Ala2, Met5] enkephalin binding was estimated to be 79 nM and 23 nM, respectively. Both substance P and gastrin tetrapeptide failed to displace the 125I[D-Ala2, Met5] enkephalin binding to any significant extent. The 125I[D-Ala2, Met5] enkephalin prepared by the present procedure is therefore a useful tracer. This method of preparing radioiodinated peptide may be applicable to other enkephalin analogs or neuropeptides in general. 相似文献
1000.