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   8530篇
  免费   177篇
  国内免费   6篇
教育   5812篇
科学研究   877篇
各国文化   114篇
体育   876篇
综合类   1篇
文化理论   57篇
信息传播   976篇
  2022年   63篇
  2021年   94篇
  2020年   177篇
  2019年   261篇
  2018年   316篇
  2017年   313篇
  2016年   329篇
  2015年   207篇
  2014年   255篇
  2013年   1565篇
  2012年   216篇
  2011年   221篇
  2010年   184篇
  2009年   180篇
  2008年   218篇
  2007年   196篇
  2006年   155篇
  2005年   134篇
  2004年   120篇
  2003年   130篇
  2002年   111篇
  2001年   144篇
  2000年   157篇
  1999年   148篇
  1998年   77篇
  1997年   64篇
  1996年   79篇
  1995年   76篇
  1994年   79篇
  1993年   66篇
  1992年   126篇
  1991年   117篇
  1990年   99篇
  1989年   128篇
  1988年   93篇
  1987年   82篇
  1986年   86篇
  1985年   107篇
  1984年   84篇
  1983年   79篇
  1982年   82篇
  1981年   75篇
  1980年   69篇
  1979年   84篇
  1978年   87篇
  1977年   64篇
  1976年   63篇
  1974年   54篇
  1973年   44篇
  1969年   46篇
排序方式: 共有8713条查询结果,搜索用时 31 毫秒
981.
Attempts to represent a spherical surface on a plane sheet, so that individual points stand in a proper relation to each other as regards both distance and direction, have occupied cartographers since the time of Ptolemy. Later, as maps were required not only as an aid to travel by land or navigation by sea an increasing amount of detail had to be incorporated in them. By traditional methods this was a difficult and time-consuming process, but very recently the use of the computer has pointed the way to the production of better maps more quickly and more cheaply.  相似文献   
982.
Malabsorption syndromes causing steatorrhoea are quite common in India. Estimation of faecal fat is an important non-invasive investigation, which provides vital information regarding the occurrence of malabsorption. The aim of this study was to estimate the fat excretion per day in stools of apparently healthy adults on an unrestricted diet in random spot stool samples using the Acid Steatocrit Method, which provides an alternate, simpler and yet reliable method of stool fat estimation. Several studies have proved the correlation of the acid steatocrit method with the conventional methods. In India, however, there has been no published data regarding the normal levels of fat in the stools, by the acid steatocrit method. We follow the normal range values, as set by the United States and the European countries, not having a range for the Indian population. Hence, we took up a preliminary study, to estimate stool fat in a section of normal and healthy Indian population. The result obtained after screening 600 healthy and normal adults, showed the mean of stool fat to be 8.72 gms/24 hours, which is much higher than that, defined by Western literature (7 gms/24 hours). This can be accounted for, by the cultural and ethnic variations in dietary and food habits. Further studies are required in the same direction, involving larger population groups, and in different malabsorptive conditions.  相似文献   
983.
The acidification of water leads to disturbances in the water and ion metabolism of fish, including the acid-base balance. Many fish probably possess physiological mechanisms to eliminate these disturbances completely or in part. However successful they may be in the short term, such adaptation mechanisms nevertheless require additional energy, thus causing growth and reproduction to be retarded. Taking into account the high sensitivity of fish eggs and larvae to acidification, these phenomena are probably a major contributory factor to the decline of fish stocks in acidified water.  相似文献   
984.
Humoral immune response against PPD derived A60 antigen was evaluated by quantification of serum A60 antibodies in thrity healthy adults not exposed to tuberculosis (Group 1), in twenty seven healthy adults exposed to tuberculosis patients i.e. staff working in wards of tuberculosis hospital for one to thirty years (group 2), in twenty five pulmonary tuberculosis patients admitted to the Institute for Chest Diseases, Hyderabad (Group 3) and in sixty neurotuberculosis patients admitted to Neurosurgery department of our institute (Group 4). Highly significant elevation of A60 antibodies was observed in pulmonary tuberculosis patients (p<0.01) compared to healthy adult groups. A significant elevation in serum was also observed in case of neurotuberculosis group compared to both healthy groups (p<0.01). A test on A60 antibodies in serum gavv a sensitivity of 100%, specificity of 96.6%, positive predictive value of 81% and negative predictive value of 100% for pulmonary tuberculosis, whereas a sensitivity of 58%, positive predictive value of 79% and negative predictive value of 75% were noted for neurotuberculosis patients. Results of A60 antibodies in ten cerebrospinal fluids (CSF) obtained from non tuberculosis patients and thirty two CSF from patients of neurotuberculosis did not show significant elevation of antibodies. However the ninetyfive percentile value of CSF A60 antibodies was higher in neurotuberculosis (7.4 U/ml) group compared to nontuberculous group (3.8 U/ml) and the test showed a good positive predictive value (83%), very low negative predictive value (25%) and low sensitivity (63%). Serum A60 antibody assay appears to be a good serological marker available today for pulmonary tuberculosis and a supportive marker for neurotuberculosis.  相似文献   
985.
Ovarian cancer is the fifth leading cause of death in women. The incidence of this malignancy increases in women over the age of 40. The overall five years survival is less than 30%, as most women present with advanced stage disease. Until recently, detection of early stage ovarian cancer has been difficult since it is usually nonpalpable and asymptomatic. The definitive diagnosis of an ovarian mass is a common problem in gynecologic patients with adnexal mass. The routine standard evaluation for adnexal masses includes patient's history, physical examination, ultrasound and histopathological examination. These parameters individually or in combination have little predictive value. The accuracy of diagnostic tools are of immense value and great concern to practicsing Gynecologists and Oncologists. The clinical application of serum concentration of CA 125, AFP and hCG is of great help not only as diagnostic aid but also in monitoring efficacy of any treatment modality like chemotherapy, radiotherapy or surgical resection. Additionally, evaluation of tumor marker concentration helps in predicting early biochemical recurrence and in prognostication in different types of ovarian malignancies. The ability to differentiate a malignant mass from a benign pelvic mass pretherapeutically could be enhanced optimally by additional use of tumor markers such as cancer antigen CA-125, alphafetoprotein and human chorionic gonadotrophin in pre-and postmenopausal women.  相似文献   
986.
Online information retrieval systems continued to reach wider audiences. The authors discuss a particular text retrieval system and its techniques for helping the common unsophisticated user through both the search for and understanding of information based on the vocabular file concept. In addition methods for easy construction and maintenance of a suuitable data base organization are described.  相似文献   
987.
988.
Surveillance of drinking water is essentially a health measure intended to protect the public from water borne diseases. Hydride generator accessory coupled with atomic absorption spectrophotometer was used to analyze arsenic level in 49 ground water samples collected from different areas of Delhi. Arsenic level in ground water samples was in the range of 0.0170 to 0.100 ppm (Mean-0.0431, Standard Deviation-0.0136, Std. error of Mean-0.00194) with minimum concentration at Raney Well No. 7 (0.0170 ppm) and maximum at Kotla Mubarak Pur (0.100 ppm). Arsenic containing sediments and percolation of chemicals into soil as the result of dumping of garbage rich in chemicals into open landfills could be the possible source of arsenic in ground water of Delhi. Extensive survey and continuous monitoring is required to be made to assess the magnitude of problem and earlier intervention.  相似文献   
989.
This study examines the relationship between college students' development in maturity and intellectual development with their degree of fiscal responsibility for their expenses during college. Two hundred seventy-six seniors or 64% of a sample of 431 freshmen were retested with the Perceived Self Questionnaire (PSQ) or the Scale of Intellectual Development (SID). Controlling for freshmen's PSQ or SID levels, seniors who financed at least 75% of their college education were less dualistic or rigid in their thinking, were more committed to their life's goals, had a firmer sense of direction and stability, and had a greater ability at expressing their values and thoughts than seniors who did not contribute toward their college expenses.  相似文献   
990.
Educational Psychology Review -  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