全文获取类型
收费全文 | 8530篇 |
免费 | 177篇 |
国内免费 | 6篇 |
专业分类
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 |
出版年
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.
T. A. Margerison Ph.D. 《Endeavour》1977,1(3-4)
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.
Anita R. Bijoor S. Geetha T. Venkatesh 《Indian journal of clinical biochemistry : IJCB》2004,19(2):20-22
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.
T. Malati G. Rajani Kumari I. Dinakar 《Indian journal of clinical biochemistry : IJCB》1995,10(2):72-76
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.
T. Malati G. Rajani Kumari B. Yadagiri 《Indian journal of clinical biochemistry : IJCB》2001,16(2):224-233
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.
T. G. Burket 《Information processing & management》1979,15(6):281-289
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.
Study on arsenic level in ground water of Delhi using hydride generator accessory coupled with atomic absorption spectrophotometer 总被引:1,自引:0,他引:1
Sanjeev Lalwani T. D. Dogra D. N. Bhardwaj R. K. Sharma O. P. Murty Aarti Vij 《Indian journal of clinical biochemistry : IJCB》2004,19(2):135-140
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.
T. Dary Erwin 《Research in higher education》1986,25(2):194-203
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