首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   34311篇
  免费   399篇
  国内免费   15篇
教育   25074篇
科学研究   3195篇
各国文化   218篇
体育   2236篇
综合类   13篇
文化理论   559篇
信息传播   3430篇
  2022年   181篇
  2021年   261篇
  2020年   385篇
  2019年   608篇
  2018年   2909篇
  2017年   2813篇
  2016年   2250篇
  2015年   552篇
  2014年   774篇
  2013年   4509篇
  2012年   867篇
  2011年   1369篇
  2010年   1313篇
  2009年   900篇
  2008年   1171篇
  2007年   1627篇
  2006年   487篇
  2005年   794篇
  2004年   818篇
  2003年   718篇
  2002年   475篇
  2001年   479篇
  2000年   417篇
  1999年   360篇
  1998年   204篇
  1997年   225篇
  1996年   240篇
  1995年   236篇
  1994年   181篇
  1993年   201篇
  1992年   324篇
  1991年   304篇
  1990年   299篇
  1989年   300篇
  1988年   255篇
  1987年   301篇
  1986年   265篇
  1985年   304篇
  1984年   248篇
  1983年   211篇
  1982年   191篇
  1981年   163篇
  1980年   153篇
  1979年   258篇
  1978年   182篇
  1977年   168篇
  1976年   154篇
  1975年   141篇
  1974年   147篇
  1971年   140篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
871.
Rats fed with hypercholesterolemic diet showed a significant increase in serum total—cholesterol, liver homogenate total-cholesterol, HDL-cholesterol and changed LDL-cholesterol, and HDL/LDL ratio in comparison to control. Flaxseedchutney (FC) supplemented diet (15%, w/w) was found to be more effective in restoring lipid profile changes in rats fed with cholesterol, (1.0%). The activities of serum marker enzymes glutamate oxaloacetate transminase (GOT), glutamate pyruvate transaminase (GPT) and alkaline phosphatase (ALP) were elevated significantly in carbon tetrachloride induced rats. Administration of flaxseedchutney (15%, w/w) resulted in depletion of serum marker enzymes and exhibited recoupment thus showing significant hepatoprotective effect. It was observed that flaxseedchutney supplemented diet could lower the serum cholesterol and as a potential source of antioxidants it could exert protection against hepatotoxic damage induced by carbon tetrachloride (CCl4) in rats.  相似文献   
872.
This paper will address the question of the morality of technology. I believe this is an important question for our contemporary society in which technology, especially information technology, is increasingly becoming the default mode of social ordering. I want to suggest that the conventional manner of conceptualising the morality of technology is inadequate – even dangerous. The conventional view of technology is that technology represents technical means to achieve social ends. Thus, the moral problem of technology, from this perspective, is the way in which the given technical means are applied to particular (good or bad) social ends. In opposition to this I want to suggest that the assumed separation, of this approach, between technical means and social ends are inappropriate. It only serves to hide the most important political and ethical dimensions of technology. I want to suggest that the morality of technology is much more embedded and implicit than such a view would suggest. In order to critique this approach I will draw on phenomenology and the more recent work of Bruno Latour. With these intellectual resources in mind I will propose disclosive ethics as a way to make the morality of technology visible. I will give a brief account of this approach and show how it might guide our␣understanding of the ethics and politics of technology by considering two examples of contemporary information technology: search engines and plagiarism detection systems.  相似文献   
873.
Alkaptonuria, a metabolic disorder characterized by a triad of homogentisic aciduria, arthritis and ochronosis is one of the first conditions in the charter of group of inborn errors of metabolism proposed to have Mendelian recessive inheritance. It is due to the deficiency of the enzyme homogentisic acid oxidase which catalyzes the conversion of homogentisic acid to maleylacetoacetic acid in the catabolism of tyrosine. Homogentisic acid thus accumulates in cells and body fluids and its oxidized polymers bind to collagen, leading to progressive deposition of grey to bluish black pigment resulting in degenerative changes in cartilage, intervertebral disc and other connective tissues, leading to arthritis which is the only disabling effect in an affected older individual. However the diagnosis can be made in neonates when blackish stain is noticed in an unwashed diaper. Alkaptonuria is treated symptomatically, surgical intervention necessitates in advanced stages, treatment with ascorbic acid (Vitamin C) and dietary restrictions of food containing phenylalanine and tyrosine have proved to be successful in alleviating the symptoms.  相似文献   
874.
Serum adenosine deaminase (ADA), 5′ nucleotidase (5′NT) and malondialdehyde (MDA) were estimated in patients with acute infective hepatitis (AIH) along with the routine parameters of liver disease. Present study is done to evaluate these special parameters in patients with clinical history of AIH and to assess the utility of these parameters as diagnostic/ prognostic indices of liver function and to correlate special parameters with routine live function tests (LFT). ADA, 5′NT and MDA along with routine LFT was estimated in 25 patients with AIH and 25 samples from healthy voluntary blood donars served as the control group. Routine LFT was estimated by standard clinical chemistry procedures on dade behring analyser and ADA, 5′NT and MDA were estimated by berthlot reaction, fiske and subbarao method and thiobarbituric acid method respectively. Statistical analysis showed that serum ADA, 5′NT and MDA were significantly higher in patients as compared with the controls. There was a significant positive correlation between ADA and total bilirubin and MDA and total bilirubin. Hence we can conclude that these tests would be more sensitive to diagnose the patients with AIH and that the raised bilirubin levels could be looked upon, as a protective mechanism which the liver has evolved in order to combat oxidative stress.  相似文献   
875.
876.
The objective of this study was to evaluate acrosin activity in spermatozoa of infertile Nigerian men and to compare with those of the fertile men. The acrosin activity was evaluated using the Acroscreen reagent kit. The acrosin activity of the fertile men was 40.7±5.2 mIU/106 sperm (range 30.1–51.3) and those of the infertile men was 22.4±8.33 mIU/106 sperm (range 5.7–39.1). The difference in the mean was statistically significant (P<0.001). There was a subpopulation of the infertile men who had their acrosin activity within normal range of the fertile men, 32.9±1.57 mIU/106 sperm. But the difference in the mean was statistically significant (P<0.001). Acrosin activity decreased with increased morphological changes in the spermatozoa. It is concluded that acrosin activity in the infertile Nigerian men is significantly lower than that in the fertile men. Acrosin activity may also be affected by morphological changes in the spermatozoa.  相似文献   
877.
878.
Aprototype kit for the detection of occurrence of ovulation based on urinary pregnanediol glucuronide estimations by ELISA was developed in our laboratory. This kit was sent for evaluation at 4 centres in Bombay and Pune, India. The diagnosis of ovulation/anovulation based on the results of the kit is comparable with that based on reference parameters commonly used (ultrasonography of ovarian follicles and serum progesterone estimations). The accuracy of the test was 93.5%, specificity was 87.5% and sensitivity was 95.7%. This rapid indigenous test can be very useful in assessing ovulatory status of the woman by the clinicians in their offices.  相似文献   
879.
In this paper a method for the realization of RC transfer immittance functions with an unsymmetrical lattice is presented. The method yields minimal capacitor realizations for Z12(s) with no pole at s = 0 and ?y12(s) having no pole at s = ∞. The number of resistors needed are only two more than the minimum needed.  相似文献   
880.
Induction of diabetes by Streptozotocin in rats   总被引:1,自引:0,他引:1  
The objective of this study is to induce experimental diabetes mellitus by Streptozotocin in normal adult Wistar rats via comparison of changes in body weight, consumption of food and water, volume of urine and levels of glucose, insulin and C-peptide in serum, between normal and diabetic rats. Intra-venous injection of 60mg/kg dose of Streptozotocin in adult wistar rats, makes pancreas swell and at last causes degeneration in Langerhans islet beta cells and induces experimental diabetes mellitus in the 2–4 days. Induction of experimental diabetes mellitus is indeed the first step in the plan of purification of pancreatic Langerhans islet cells of normal rats for transplanting under the testis subcutaneous of experimentally induced diabetic rats. Streptozotocin induces one type of diabetes which is similar to diabetes mellitus with non-ketosis hyperglycemia in some animal species. For induction of experimental diabetes in male adult rats weighted 250–300 grams (75–90 days), 60mg/kg of Streptozotocin was injected intravenously. Three days after degeneration of beta cells, diabetes was induced in all animals. The diabetic and normal animals were kept in the metabolic cages separately and their body weight, consumption of food and water, urine volume, the levels of serum glucose, insulin and C-peptide quantities in all animals were measured and then these quantities were compared. For a microscopic study of degeneration of Langerhans islet beta cells of diabetic rats, sampling from pancreas tissue of diabetic and normal rats, staining and comparison between them, were done. Induction of diabetes with Streptozotocin decreases Nicotinamide-adenine dinucleotide (NAD) in pancreas islet beta cells and causes histopathological effects in beta cells which probably intermediates induction of diabetes. In this study, we used Streptozotocin for our experiments in induction of experimental diabetes mellitus. After Induction of diabetes, consumption of food and water, volume of urine and glucose increased in the diabetic animals in comparison with normal animals, but the weight of body and the volume of insulin and C-peptide decreased in the diabetic animals. Sampling and staining of pancreas tissue of diabetic and normal rats showed that the Langerhans islet beta cells of diabetic rats have been clearly degenerated. In three days, Streptozotocin makes pancreas swell and at last causes degeneration in Langerhans islet beta cells and induces experimental diabetes. It also changes normal metabolism in diabetic rats in comparison with normal rats. Consumption of water and food, volume of urine, serum glucose increases in diabetic animals in comparison with normal rats but the levels of serum insulin, C-peptide and body weight decreases.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号