全文获取类型
收费全文 | 5448篇 |
免费 | 353篇 |
国内免费 | 8篇 |
出版年
2023年 | 32篇 |
2022年 | 108篇 |
2021年 | 205篇 |
2020年 | 83篇 |
2019年 | 105篇 |
2018年 | 147篇 |
2017年 | 118篇 |
2016年 | 174篇 |
2015年 | 259篇 |
2014年 | 290篇 |
2013年 | 379篇 |
2012年 | 446篇 |
2011年 | 476篇 |
2010年 | 264篇 |
2009年 | 186篇 |
2008年 | 279篇 |
2007年 | 227篇 |
2006年 | 213篇 |
2005年 | 185篇 |
2004年 | 178篇 |
2003年 | 147篇 |
2002年 | 121篇 |
2001年 | 98篇 |
2000年 | 81篇 |
1999年 | 85篇 |
1998年 | 34篇 |
1997年 | 27篇 |
1995年 | 31篇 |
1994年 | 23篇 |
1993年 | 31篇 |
1992年 | 48篇 |
1991年 | 57篇 |
1990年 | 41篇 |
1989年 | 43篇 |
1988年 | 32篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 26篇 |
1984年 | 27篇 |
1983年 | 29篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 39篇 |
1978年 | 21篇 |
1977年 | 29篇 |
1975年 | 20篇 |
1974年 | 25篇 |
1973年 | 25篇 |
1972年 | 24篇 |
排序方式: 共有5809条查询结果,搜索用时 15 毫秒
991.
Hassan Imran Afridi Tasneem Gul Kazi Naveed Kazi Ghulam Abbas Kandhro Jameel Ahmed Baig Abdul Qadir Shah Sham Kumar Wadhwa Sumaira Khan Nida Fatima Kolachi Faheem Shah Mohammad Khan Jamali Mohammad Balal Arain Sirajuddin 《Biological trace element research》2011,143(1):20-40
The most common cause of blindness in developing countries is vitamin A deficiency. The World Health Organization estimates 13.8 million children to have some degree of visual loss related to vitamin A deficiency. The causes of night blindness in children are multifactorial, and particular consideration has been given to childhood nutritional deficiency, which is the most common problem found in underdeveloped countries. Such deficiency can result in physiological and pathological processes that in turn influence biological samples composition. Vitamin and mineral deficiency prevents more than two billion people from achieving their full intellectual and physical potential. This study was designed to compare the levels of Zn, Mg, Ca, K, Na, As, Cd, and Pb in scalp hair, blood, and urine of night blindness children age ranged 3–7 and 8–12 years of both genders, comparing them to sex- and age-matched controls. A microwave-assisted wet acid digestion procedure was developed as a sample pretreatment, for the determination of As, Ca, Cd, K, Pb, Mg, Na, and Zn in biological samples of night blindness children. The proposed method was validated by using conventional wet digestion and certified reference samples of hair, blood, and urine. The concentrations of trace and toxic elements were measured by atomic absorption spectrophotometer prior to microwave-assisted acid digestion. The results of this study showed that the mean values of As, Cd, Na, and Pb were significantly higher in scalp hair, blood, and urine samples of male and female night blindness children than in referents (p?<?0.001), whereas the concentrations of Zn, Ca, K, and Mg were lower in the scalp hair and blood but higher in the urine samples of night blindness children. These data present guidance to clinicians and other professional investigating deficiency of essential mineral elements in biological samples (scalp hair and blood) of night blindness children. 相似文献
992.
Hassan Imran Afridi Tasneem Gul Kazi Naveed Kazi Ghulam Abbas Kandhro Abdul Qadir Shah Jameel Ahmed Baig Sham Kumar Wadhwa Sumaira Khan Nida Fatima Kolachi Faheem Shah Mohammad Khan Jamali Mohammad Balal Arain 《Biological trace element research》2011,143(1):103-115
This study was designed to compare the levels of chromium (Cr) and manganese (Mn) in scalp hair, blood, and urine of night blindness in children age ranged (3–7) and (8–12) years of both genders, comparing them to sex- and age-matched controls. A microwave-assisted wet acid digestion procedure, was developed as a sample pretreatment, for the determination of Cr and Mn in biological samples of night blindness children. The proposed method was validated by using conventional wet digestion and certified reference samples of hair, blood and urine. The digests of all biological samples were analyzed for Cr and Mn by electrothermal atomic absorption spectrometry. The results indicated significantly higher levels of Cr, whilst low level of Mn in the biological samples (blood and scalp hair) of male and female night blindness children, compared with control subjects of both genders. These data present guidance to clinicians and other professional investigating deficiency of Mn and excessive level of Cr in biological samples (scalp hair and blood) of night blindness children. 相似文献
993.
Nida Fatima Kolachi Tasneem Gul Kazi Hassan Imran Afridi Naveed Kazi Ghulam Abbas Kandhro Abdul Qadir Shah Jameel Ahmed Baig Sham Kumar Wadhwa Sumaira Khan Faheem Shah Mohammad Khan Jamali Mohammad Balal Arain 《Biological trace element research》2011,143(1):116-130
The aim of the present study was to compare the level of copper (Cu), iron (Fe) and zinc (Zn) in biological samples (serum, blood, urine, and scalp hair) of patients suffering from different viral hepatitis (A, B, C, D, and E; n?=?521) of both gender age ranged 31–45 years. For comparative study, 255 age-matched control subjects, of both genders residing in the same city were selected as referents. The elements in the biological samples were analyzed by flame atomic absorption spectrophotometry, prior to microwave-assisted acid digestion. The validity and accuracy of the methodology was checked by using certified reference materials (CRMs) and with those values obtained by conventional wet acid digestion method on same CRMs. The results of this study showed that the mean values of Cu and Fe were higher in blood, sera, and scalp hair samples of hepatitis patients, while Zn level was found to be lower than age-matched control subjects. The urinary levels of these elements were found to be higher in the hepatitis patients than in the age-matched healthy controls (p?<?0.05). These results are consistent with literature-reported data, confirming that the deficiency of zinc and hepatic iron and copper overload can directly cause lipid peroxidation and eventually hepatic damage. 相似文献
994.
995.
996.
Reactive oxygen species (ROS) are formed as a natural by-product of the normal metabolism of oxygen and have important roles in cell signaling. The aim of this study was to investigate direct effects of ROS on atrial hemodynamics and ANP secretion in isolated perfused beating rat atria with antioxidants. When atria were paced at 1.2 Hz, N-acetyl cystein (antioxidant, NAC), α-lipoic acid (antioxidant), tempol (superoxide dismutase mimic), and apocynin (NADPH oxidase inhibitor; NOX inhibitor) did not affect ANP secretion and atrial contractility. When pacing frequency was increased from 1.2 Hz to 4 Hz, the ANP secretion increased and atrial contractility decreased. H2O2 level was increased in perfusate obtained from atria stimulated by high pacing frequency. NAC, α-lipoic acid and tempol attenuated high pacing frequency-induced ANP secretion but apocynin did not. In contrast, pyrogallol (a superoxide generator) augmented high pacing frequency-induced ANP secretion. NOX-4 protein was increased by high pacing stimulation and in diabetic rat atria. In diabetic rat atria, high pacing frequency caused an increased ANP secretion and a decreased atrial contractility, that were markedly attenuated as compared to control rats. NAC and apocynin reduced high pacing frequency-induced ANP secretion in diabetic rat atria. These results suggest that intracellular ROS formation partly through an increasing NOX activity in response to high pacing frequency is associated with an increased ANP secretion in rat atria. 相似文献
997.
998.
Nakashima H Terabe M Berzofsky JA Husain SR Puri RK 《Journal of immunology (Baltimore, Md. : 1950)》2011,187(10):4935-4946
Optimum efficacy of therapeutic cancer vaccines may require combinations that generate effective antitumor immune responses, as well as overcome immune evasion and tolerance mechanisms mediated by progressing tumor. Previous studies showed that IL-13Rα2, a unique tumor-associated Ag, is a promising target for cancer immunotherapy. A targeted cytotoxin composed of IL-13 and mutated Pseudomonas exotoxin induced specific killing of IL-13Rα2(+) tumor cells. When combined with IL-13Rα2 DNA cancer vaccine, surprisingly, it mediated synergistic antitumor effects on tumor growth and metastasis in established murine breast carcinoma and sarcoma tumor models. The mechanism of synergistic activity involved direct killing of tumor cells and cell-mediated immune responses, as well as elimination of myeloid-derived suppressor cells and, consequently, regulatory T cells. These novel results provide a strong rationale for combining immunotoxins with cancer vaccines for the treatment of patients with advanced cancer. 相似文献
999.
Castro-Perez J Previs SF McLaren DG Shah V Herath K Bhat G Johns DG Wang SP Mitnaul L Jensen K Vreeken R Hankemeier T Roddy TP Hubbard BK 《Journal of lipid research》2011,52(1):159-169
High resolution LC/MS-MS and LC/APPI-MS methods have been established for the quantitation of flux in the turnover of cholesterol and cholesterol ester. Attention was directed toward quantifying the monoisotopic mass (M0) and that of the singly deuterated labeled (M+1) isotope. A good degree of isotopic dynamic range has been achieved by LC/MS-MS ranging from 3-4 orders of magnitude. Correlation between the linearity of GC/MS and LC atmospheric pressure photoionization (APPI)-MS are complimentary (r2 = 0.9409). To prove the viability of this particular approach, male C57Bl/6 mice on either a high carbohydrate (HC) or a high fat (HF) diet were treated with 2H2O for 96 h. Gene expression analysis showed an increase in the activity of stearoyl-CoA desaturase (Scd1) in the HC diet up to 69-fold (P < 0.0008) compared with the HF diet. This result was supported by the quantitative flux measurement of the isotopic incorporation of 2H into the respective cholesterol and cholesterol ester (CE) pools. We concluded that it is possible to readily obtain static and dynamic measurement of cholesterol and CEs in vivo by coupling novel LC/MS methods with stable isotope-based protocols. 相似文献
1000.
Ghosn MG Mashiatulla M Syed SH Mohamed MA Larin KV Morrisett JD 《Journal of lipid research》2011,52(7):1429-1434
Atherosclerosis is an inflammatory process occurring in arterial tissue, involving the subintimal accumulation of LDL. Measurement of the rate at which LDL and other lipoproteins, such as HDL and VLDL, enter and exit the tissue can provide insight into the mechanisms involved in the development of atherosclerotic lesions. Permeation of VLDL, LDL, HDL, and glucose was measured for both normal and atherosclerotic human carotid endarterectomy tissues (CEA) at 20°C and 37°C using optical coherence tomography (OCT). The rates for LDL permeation through normal CEA tissue were (3.16 ± 0.37) × 10(-5) cm/s at 20°C and (4.77 ± 0.48) × 10(-5) cm/s at 37°C, significantly greater (P < 0.05) than the rates for atherosclerotic CEA tissue at these temperatures [(1.97 ± 0.34) × 10(-5) cm/s at 20°C and (2.01 ± 0.23) × 10(-5) cm/s at 37°C]. This study effectively used OCT to measure the rates at which naturally occurring lipoproteins enter both normal and diseased carotid intimal tissue. 相似文献