全文获取类型
收费全文 | 8533篇 |
免费 | 876篇 |
国内免费 | 303篇 |
专业分类
9712篇 |
出版年
2024年 | 42篇 |
2023年 | 233篇 |
2022年 | 334篇 |
2021年 | 444篇 |
2020年 | 410篇 |
2019年 | 570篇 |
2018年 | 407篇 |
2017年 | 300篇 |
2016年 | 272篇 |
2015年 | 328篇 |
2014年 | 516篇 |
2013年 | 702篇 |
2012年 | 345篇 |
2011年 | 375篇 |
2010年 | 278篇 |
2009年 | 296篇 |
2008年 | 314篇 |
2007年 | 296篇 |
2006年 | 264篇 |
2005年 | 248篇 |
2004年 | 207篇 |
2003年 | 189篇 |
2002年 | 202篇 |
2001年 | 147篇 |
2000年 | 110篇 |
1999年 | 134篇 |
1998年 | 131篇 |
1997年 | 134篇 |
1996年 | 97篇 |
1995年 | 112篇 |
1994年 | 93篇 |
1993年 | 93篇 |
1992年 | 96篇 |
1991年 | 81篇 |
1990年 | 88篇 |
1989年 | 83篇 |
1988年 | 60篇 |
1987年 | 70篇 |
1986年 | 38篇 |
1985年 | 71篇 |
1984年 | 93篇 |
1983年 | 95篇 |
1982年 | 91篇 |
1981年 | 66篇 |
1980年 | 47篇 |
1979年 | 48篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1975年 | 7篇 |
排序方式: 共有9712条查询结果,搜索用时 0 毫秒
81.
The effects of dietary intake of vitamin E and selenium on arginase activity in the liver, kidneys, and heart of rats treated with high doses of prednisolone were investigated. Rats were divided into five groups. Groups 3, 4, and 5 received a daily supplement in their drinking water of vitamin E, Se, and a combination of vitamin E and Se, respectively, for 30 days. For 3 days subsequently, the control group (group 1) was given a placebo, and the remaining four groups were injected intramuscularly with prednisolone. The tissue samples were collected from each group at 4, 8, 12, 24, and 48 h after the last administration of prednisolone. In the group treated with prednisolone alone, arginase activity in the liver was found to have increased at all the time periods, whereas it had decreased significantly in the heart at 48 h. Arginase activity in the kidneys was not affected by prednisolone. Compared to the control and prednisolone groups, arginase activity in the kidneys and heart of the vitamin E- and Se-supplemented groups was found to be significantly increased at all time periods, however, no difference was seen in the combination group. Arginase activity in the liver of the vitamin E-supplemented group was found to have decreased at all time periods, however, in the Se group compared to the prednisolone group it had reduced at 24 and 48 h only. In the combination group compared to the prednisolone group, liver arginase activity increased constantly up to 12 h returning to normal values at 48 h. Vitamin E and Se in combination may prevent the changes in arginase activity in various tissues caused by prednisolone. 相似文献
82.
Aims: To investigate the effect of diet on the survival of Salmonella in the bovine abomasum. Methods and Results: Five fistulated cows were randomly assigned to one of five diets denoted as: (i) 100% grass, (ii) grass + 5·3 kg DM concentrate, (iii) 100% grass silage, (iv) 100% hay and (v) maize/grass silage plus concentrates. Rumen fluid was harvested from each dietary treatment and inoculated with nonacid (NA) and acid‐adapted (AA) 5‐strain Salmonella cocktails. After 24‐h incubation period, Salmonella were acid challenged to synthetic abomasum fluid (SAF, pH 2·5) for 5 h to determine their resistance to low pH. The study found that the volatile fatty acids composition and the pH profile of bovine rumen fluid were significantly altered (P < 0·05) by some of the dietary treatments but not others. Regression analysis found that significantly higher numbers of acid‐adapted Salmonella survived in SAF after incubation in rumen fluid from diets 1, 2 and 4, but fewer significant differences were found between diets for nonacid–adapted Salmonella. The results suggest that the acid‐adapted cells were subjected to a higher level of cell injury than the nonadapted cells. Conclusions: Pre‐incubation in rumen fluid did influence the resistance of nonacid and acid‐adapted Salmonella to SAF but it was dependant on the dietary treatment fed to the cows. Significance and Impact of the Study: This study examined the use of diet, as a modulating factor to limit the bovine excretion of Salmonella with a view to providing a scientific basis for the design of dietary management controls in the future. 相似文献
83.
中药博落回的药理实验研究 总被引:1,自引:0,他引:1
博落回对四氯化碳、半乳糖胺所致急性肝损伤模型,均有显著改善肝脏功能作用;对四氯化碳所致慢性肝损伤大鼠模型,博落回可显著降低血清LDH水平。降低动物死亡率。提高血清A/G比值,有效保护肝细胞胰。抑制肝脏纤维化;博落回还可显著增强T和B淋巴细胞功能。 相似文献
84.
Royal jelly: can it reduce physiological strain of growing rabbits under Egyptian summer conditions? 总被引:1,自引:0,他引:1
Elnagar SA Elghalid OA Abd-Elhady AM 《Animal : an international journal of animal bioscience》2010,4(9):1547-1552
Exposure of growing rabbits to heat stress during summer adversely affects their performance leading to major production losses. A total number of 48 rabbits, unsexed V-line weaned rabbits, were randomly divided into four experimental groups, temperature ranged from high at 32°C to low at 23°C. Animals of the 2nd, 3rd and 4th group were individually orally given 200, 400 or 800 mg royal jelly (RJ)/kg BW once a week, respectively, to evaluate RJ ability to reduce physiological strain resulted from heat stress. Weekly BW gain increased by 10.4, 11.8 and 10.8%, and feed conversion ratio was significantly improved by 20, 24 and 18% with RJ treatments. Serum total protein, albumin and globulin increased, whereas serum total lipids, cholesterol and triglycerides decreased with RJ treatments. Creatinine was reduced by 21, 30 and 18% and uric acid by 14, 25 and 18% compared with the heat stressed control with the three doses of RJ. Glucose level increased significantly to reach 116, 125, and 120% of heat stressed control. Calcium, phosphorus and alkaline phosphatase increased significantly with RJ treatments indicating the occurrence of active bone deposition. Thyroid hormone levels increased significantly to reach 108, 111, and 112% of heat stressed control rabbits with the three doses of RJ, counteracting the hypothyroid state resulted from heat stress. It can be concluded that RJ administration to heat stressed growing rabbits can reduce physiological strain resulted from heat stress. 相似文献
85.
Yuhan Lin Penglin Xia Fangyu Cao Cheng Zhang Yajie Yang Haitao Jiang Haishan Lin Hu Liu Ruling Liu Xiaodong Liu Jianming Cai 《Journal of cellular and molecular medicine》2023,27(2):246
Radiation‐induced intestinal injury (RIII) is a common complication after radiation therapy in patients with pelvic, abdominal, or retroperitoneal tumours. Recently, in the model of DSS (Dextran Sulfate Sodium Salt) ‐induced intestinal inflammatory injury, it has been found in the study that transgenic mice expressing hVDR in IEC (Intestinal Epithelial Cell) manifest highly anti‐injury properties in colitis, suggesting that activated VDR in the epithelial cells of intestine may inhibit colitis by protecting the mucosal epithelial barrier. In this study, we investigated the effect of the expression and regulation of VDR on the protection of RIII, and the radiosensitivity in vitro experiments, and explored the initial mechanism of VDR in regulating radiosensitivity of IEC. As a result, we found that the expression of VDR in intestinal tissues and cells in mice can be induced by ionizing radiation. VDR agonists are able to prolong the average survival time of mice after radiation and reduce the radiation‐induced intestinal injury. For lack of vitamin D, the radiosensitivity of intestinal epithelial cells in mice increased, which can be reduced by VDR activation. Ensuing VDR activation, the radiation‐induced intestinal stem cells damage is decreased, and the regeneration and differentiation of intestinal stem cells is promoted as well. Finally, on the basis of sequencing analysis, we validated and found that VDR may target the HIF/PDK1 pathway to mitigate RIII. We concluded that agonism or upregulation of VDR expression attenuates radiation‐induced intestinal damage in mice and promotes the repair of epithelial damage in intestinal stem cells. 相似文献
86.
Chu-Fang Chou Xiaolin Zhu Yi-Yu Lin Karen L. Gamble W. Timothy Garvey Ching-Yi Chen 《Journal of lipid research》2015,56(2):227-240
Hepatic lipid metabolism is controlled by integrated metabolic pathways. Excess accumulation of hepatic TG is a hallmark of nonalcoholic fatty liver disease, which is associated with obesity and insulin resistance. Here, we show that KH-type splicing regulatory protein (KSRP) ablation reduces hepatic TG levels and diet-induced hepatosteatosis. Expression of period 2 (Per2) is increased during the dark period, and circadian oscillations of several core clock genes are altered with a delayed phase in Ksrp−/− livers. Diurnal expression of some lipid metabolism genes is also disturbed with reduced expression of genes involved in de novo lipogenesis. Using primary hepatocytes, we demonstrate that KSRP promotes decay of Per2 mRNA through an RNA-protein interaction and show that increased Per2 expression is responsible for the phase delay in cycling of several clock genes in the absence of KSRP. Similar to Ksrp−/− livers, both expression of lipogenic genes and intracellular TG levels are also reduced in Ksrp−/− hepatocytes due to increased Per2 expression. Using heterologous mRNA reporters, we show that the AU-rich element-containing 3′ untranslated region of Per2 is responsible for KSRP-dependent mRNA decay. These findings implicate that KSRP is an important regulator of circadian expression of lipid metabolism genes in the liver likely through controlling Per2 mRNA stability. 相似文献
87.
Quinazoline-based compounds such as prazosin and its congeners including doxazosin, bunazosin, and terazosin are widely used
as antihypertensive agents. However, there were many clinical observations showing that using these agents may result in higher
risk of cardiovascular accidents in recent years. In this study, we compared the effects of four α-adrenoceptor antagonists:
prazosin, doxazosin, bunazosin, and terazosin on occlusion–reperfusion injury. Langendorff-perfused rat hearts were pretreated
with these four antagonists, and then the left main coronary artery was occluded. After 30 min occlusion, the hearts were
reperfused for 2 h and the infarct sizes were measured. Two of the compounds studied, prazosin and doxazosin, apparently increased
infarct size, CK-MB, and LDH activities after 2 h reperfusion. In contrast, bunazosin decreased infarct size and those biochemical
indicators of cellular damage compared to control hearts. Although infarct size after reperfusion was differently changed
by these four α-adrenoceptor antagonists, TUNEL-positive nuclei and caspase-3 protein expressions of all the groups were not
significantly different. We supposed that the different effects of these four agents on infarct size came from the difference
in necrosis rather than apoptosis. 相似文献
88.
Ishwar Singh Upendra Kumar S. K. Singh Charu Gupta Madhulika Singh S. R. Kushwaha 《Physiology and Molecular Biology of Plants》2012,18(3):229-236
Germination and early seedling growth are important for establishment of maize because maize is chilling sensitive crop and low temperature during early period of growth can be detrimental to subsequent crop growth and productivity. Therefore, it is important to protect maize seedling from cold stress. A study was conducted on induced cold tolerance by 24-epibrassinoslide (EBR) at the Indian Agricultural Research Institute, New Delhi, India. Maize seedlings were raised in green house condition (25/18 °C day-night temperatures). Ten days old seedlings were treated with EBR (0.0, 0.01, 0.1, 1.0 and 10 μM) and then divided into two sets, one set was kept in greenhouse (25/18 °C day-night temperatures) and another was transferred to net house (cold stress). Data on various morpho-physiological traits was recorded after 7, 14 and 21 days of treatment. Exogenous application of 1.0 μM EBR had significant effect on growth and morpho-physiological traits under both conditions. The maize seedlings treated with EBR were more tolerant to cold stress than the untreated one. Significant increase in plant height, dry matter accumulation, chlorophyll content, total soluble proteins and starch contents was observed under both conditions, however, the results were more pronounced under cold stress. 1.0 μ M concentration being the most effective under both conditions. Maintenance of high tissue water content, reduced membrane injury index, increased total chlorophyll, soluble sugar and protein content were taken as the possible indicators of EBR induced chilling tolerance. 相似文献
89.
PurposeTo compare the noise and accuracy on images of the whole porcine liver acquired with iterative reconstruction (IMR, Philips Healthcare, Cleveland, OH, USA) and filtered back projection (FBP) methods.Materials and methodsWe used non-enhanced porcine liver to simulate the human liver and acquired it 100 times to obtain the average FBP value as the ground-truth. The mean and the standard deviation (“inter-scan SD”) of the pixel values on the 100 image acquisitions were calculated for FBP and for three levels of IMR (L1, L2, and L3). We also calculated the noise power spectrum (NPS) and the normalized NPS for the 100 image acquisitions.ResultsThe spatial SD for the porcine liver parenchyma on these slices was 9.92, 4.37, 3.63, and 2.30 Hounsfield units with FBP, IMR-L1, IMR-L2, and IMR-L3, respectively. The detectability of small faint features was better on single IMR than single FBP images. The inter-scan SD value for IMR-L3 images was 53% larger at the liver edges than at the liver parenchyma; it was only 10% larger on FBP images. Assessment of the normalized NPS showed that the noise on IMR images was comprised primarily of low-frequency components.ConclusionIMR images yield the same structure informations as FBP images and image accuracy is maintained. On level 3 IMR images the image noise is more strongly suppressed than on IMR images of the other levels and on FBP images. 相似文献
90.