全文获取类型
收费全文 | 2436篇 |
免费 | 278篇 |
国内免费 | 3篇 |
出版年
2021年 | 28篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 43篇 |
2014年 | 63篇 |
2013年 | 70篇 |
2012年 | 93篇 |
2011年 | 116篇 |
2010年 | 59篇 |
2009年 | 59篇 |
2008年 | 74篇 |
2007年 | 85篇 |
2006年 | 65篇 |
2005年 | 79篇 |
2004年 | 77篇 |
2003年 | 78篇 |
2002年 | 75篇 |
2001年 | 81篇 |
2000年 | 73篇 |
1999年 | 73篇 |
1998年 | 39篇 |
1997年 | 37篇 |
1996年 | 36篇 |
1995年 | 28篇 |
1994年 | 27篇 |
1993年 | 37篇 |
1992年 | 57篇 |
1991年 | 63篇 |
1990年 | 63篇 |
1989年 | 62篇 |
1988年 | 42篇 |
1987年 | 52篇 |
1986年 | 31篇 |
1985年 | 45篇 |
1984年 | 30篇 |
1983年 | 39篇 |
1982年 | 31篇 |
1981年 | 27篇 |
1979年 | 46篇 |
1978年 | 35篇 |
1977年 | 36篇 |
1976年 | 36篇 |
1975年 | 20篇 |
1974年 | 35篇 |
1973年 | 33篇 |
1972年 | 33篇 |
1971年 | 25篇 |
1969年 | 22篇 |
1967年 | 24篇 |
排序方式: 共有2717条查询结果,搜索用时 31 毫秒
121.
M D Armstrong 《Biochimica et biophysica acta》1979,587(4):638-642
N-delta-Acetylornithine and S-methylcysteine have been identified as minor components of deproteinized blood plasma of human and bovine blood. Human blood plasma contains a variable amount of acetylornithine, averaging 1.1 +/- 0.4 mumol/l (range 0.8--0.2 mumol/l). Urine contains a very small amount of acetylornithine, approximately 1 nmol/mg creatinine (1 mumol/day). Human blood plasma contains 3.9 +/- 1.9 mumol/l (range 1.4--6.5 mumol/l) of S-methylcysteine. Urine contains approximately 5 nmol/mg creatinine; after acid hydrolysis the amount is increased to 20 nmol/mg creatinine. 相似文献
122.
Optil rotatory dispersion and circular dichroism of human carbonic anhydrases B and C 总被引:5,自引:0,他引:5
S Beychok J M Armstrong C Lindblow J T Edsall 《The Journal of biological chemistry》1966,241(21):5150-5160
123.
124.
A correlation between BCL-2 modifying factor,p53 and livin gene expressions in cancer colon patients
Eman AE. Badr Mohamed FA. Assar Abdel Monem A. Eltorgoman Azza Zaghlol Labeeb Gehad A. Breaka Enas A. Elkhouly 《Biochemistry and Biophysics Reports》2020
Accumulating evidence has revealed that livin gene and BCL-2 modifying factor (BMF) gene are closely associated with the initiation and progression of colon carcinoma by activating or suppressing multiple malignant processes. Those genes that can detect colon - cancer are a promising approach for cancer screening and diagnosis. This study aimed to evaluate correlation between livin, BMF and p53 genes expression in colon cancer tissues of patients included in the study, and their relationship with clinicopathological features and survival outcome in those patients. In this study, 50 pathologically diagnosed early cancer colon patients included and their tissue biopsy with 50 matched adjacent normal tissue, and 50 adenoma tissue specimens were analyzed for livin gene and BMF gene expressions using real time PCR. The relationship of those genes expressions with clinicopathological features, tumor markers, Time to Progression and overall survival for those patients were correlated in cancer colon group. In this study, there was a significant a reciprocal relationship between over expression of livin gene and down regulation of BMF and p53 genes in colon cancer cells. Livin mRNA was significantly higher, while BMF and p53 mRNA were significantly lower in colorectal cancer tissue compared to benign and normal colon tissue specimens (P < 0.001), however, this finding was absent between colon adenomas and normal mucosa. There was a significant association between up regulation of livin and down regulation of BMF and p53 expressions with more aggressive tumor (advanced TNM stage), rapid progression with metastasis and decreased overall survival in cancer colon patients, hence these genes can serve as significant prognostic markers of poor outcome in colon cancer patients. This work highlights the role of livin, BMF and p53 genes in colorectal tumorigenesis and the applicability of using those genes as a diagnostic and prognostic markers in patients with colon carcinoma and as a good target for cancer colon treatment in the future. 相似文献
125.
In this perspective, we discuss the physiological roles of Na and K channels, emphasizing the importance of the K channel for cellular homeostasis in animal cells and of Na and K channels for cellular signaling. We consider the structural basis of Na and K channel gating in light of recent structural and electrophysiological findings. 相似文献
126.
Anthony J. Petrella Jeffrey R. Armstrong Peter J. Laz Paul J. Rullkoetter 《Computer methods in biomechanics and biomedical engineering》2013,16(11):1223-1232
Wear testing of polyethylene in total joint replacements is common and required for any new device. Computational wear modelling has obvious utility in this context as it can be conducted with much greater economy than physical testing. Archard's law has become the accepted standard for wear simulation in total joints but it does not account for cross-shear, which is known to increase wear significantly relative to unidirectional sliding. The purpose of this study was to develop a robust cross-shear model applicable to any interface geometry under any kinematic conditions. The proposed metric, x *, is distinguished from existing cross-shear models by the fact that it measures cross-path motion incrementally throughout a motion cycle and quantifies cross-shear based on incremental changes in sliding direction. Validation showed strong support for the predictive capability of x * when applied to pin-on-disc test data. 相似文献
127.
128.
The effectiveness of management plans developed for responding to coral disease outbreaks is limited due to the lack of rapid methods of disease diagnosis. In order to fulfill current management guidelines for responding to coral disease outbreaks, alternative methods that significantly reduce response time must be developed. Hyperspectral sensing has been used by various groups to characterize the spectral signatures unique to asymptomatic and bleached corals. The 2010 combined bleaching and Caribbean yellow band disease outbreak in Puerto Rico provided a unique opportunity to investigate the spectral signatures associated with bleached and Caribbean yellow band-diseased colonies of Orbicella faveolata for the first time. Using derivative and cluster analyses of hyperspectral reflectance data, the present study demonstrates the proof of concept that spectral signatures can be used to differentiate between coral disease states. This method enhanced predominant visual methods of diagnosis by distinguishing between different asymptomatic conditions that are identical in field observations and photographic records. The ability to identify disease-affected tissue before lesions become visible could greatly reduce response times to coral disease outbreaks in monitoring efforts. Finally, spectral signatures associated with the poorly understood Caribbean yellow band disease are presented to guide future research on the role of pigments in the etiology. 相似文献
129.
Najealicka Armstrong Malaisamy Ramamoorthy Delina Lyon Kimberly Jones Atanu Duttaroy 《PloS one》2013,8(1)
Silver nanoparticles (AgNPs), like almost all nanoparticles, are potentially toxic beyond a certain concentration because the survival of the organism is compromised due to scores of pathophysiological abnormalities past that concentration. However, the mechanism of AgNP toxicity remains undetermined. Instead of applying a toxic dose, we attempted to monitor the effects of AgNPs at a nonlethal concentration on wild type Drosophila melanogaster by exposing them throughout their development. All adult flies raised in AgNP doped food showed that up to 50 mg/L concentration AgNP has no negative influence on median survival; however, these flies appeared uniformly lighter in body color due to the loss of melanin pigments in their cuticle. Additionally, fertility and vertical movement ability were compromised due to AgNP feeding. Determination of the amount of free ionic silver (Ag+) led us to claim that the observed biological effects have resulted from the AgNPs and not from Ag+. Biochemical analysis suggests that the activity of copper dependent enzymes, namely tyrosinase and Cu-Zn superoxide dismutase, are decreased significantly following the consumption of AgNPs, despite the constant level of copper present in the tissue. Consequently, we propose a mechanism whereby consumption of excess AgNPs in association with membrane bound copper transporter proteins cause sequestration of copper, thus creating a condition that resembles copper starvation. This model also explains the cuticular demelanization effect resulting from AgNP since tyrosinase activity is essential for melanin biosynthesis. Finally, we claim that Drosophila, an established genetic model system, can be well utilized for further understanding of the biological effects of nanoparticles. 相似文献
130.
Benjamin J. Ridenhour Michael A. Campitelli Jeffrey C. Kwong Laura C. Rosella Ben G. Armstrong Punam Mangtani Andrew J. Calzavara David K. Shay 《PloS one》2013,8(10)