全文获取类型
收费全文 | 16062篇 |
免费 | 237篇 |
国内免费 | 120篇 |
专业分类
教育 | 11090篇 |
科学研究 | 2063篇 |
各国文化 | 119篇 |
体育 | 1378篇 |
综合类 | 11篇 |
文化理论 | 126篇 |
信息传播 | 1632篇 |
出版年
2021年 | 125篇 |
2020年 | 247篇 |
2019年 | 363篇 |
2018年 | 489篇 |
2017年 | 441篇 |
2016年 | 439篇 |
2015年 | 270篇 |
2014年 | 354篇 |
2013年 | 2725篇 |
2012年 | 318篇 |
2011年 | 359篇 |
2010年 | 258篇 |
2009年 | 254篇 |
2008年 | 274篇 |
2007年 | 294篇 |
2006年 | 280篇 |
2005年 | 276篇 |
2004年 | 260篇 |
2003年 | 256篇 |
2002年 | 241篇 |
2001年 | 256篇 |
2000年 | 273篇 |
1999年 | 277篇 |
1998年 | 143篇 |
1997年 | 150篇 |
1996年 | 185篇 |
1995年 | 170篇 |
1994年 | 131篇 |
1993年 | 143篇 |
1992年 | 217篇 |
1991年 | 223篇 |
1990年 | 231篇 |
1989年 | 258篇 |
1988年 | 209篇 |
1987年 | 225篇 |
1986年 | 219篇 |
1985年 | 250篇 |
1984年 | 222篇 |
1983年 | 211篇 |
1982年 | 176篇 |
1981年 | 170篇 |
1980年 | 159篇 |
1979年 | 245篇 |
1978年 | 193篇 |
1977年 | 180篇 |
1976年 | 150篇 |
1975年 | 133篇 |
1974年 | 152篇 |
1973年 | 132篇 |
1971年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
R. Chawla Navendu Goyal Rajneesh Calton Shweta Goyal 《Indian journal of clinical biochemistry : IJCB》2006,21(1):77-82
Early identification of patients with acute myocardial infarction is of prime importance due to the associated very high mortality.
Only 22% of the patients presenting at emergency cardiology care with chest pain have coronary disease. A number of biochemical
tests like CKMB and Troponin-T/I have been introduced for early detection of the coronary syndrome (ACS). Ischemia modified
albumin (IMA) has been recently introduced as a marker of myocardial ischemia. We estimated serum IMA in four sequential samples
from 25 patients admitted to ICCU. Twenty five healthy volunteers formed the control group from which the normal range was
derived. IMA was significantly raised in ischemia patients than in controls as well as compared to the patients who did not
have cardiac ischemia. IMA demonstrated good discrimination between the ischemic and the non-ischemic patients with an Odds
Ratio of 16.9 (6.29–46.87) than CKMB which showed an Odds Ratio of 2.07 (1.18–6.08). Sensitivity and specificity of IMA for
the detection of ACS was 78.0% and 82.7% compared to 58.0% and 60.0%, respectively for the CK-MB assay. The area under the
ROC curve of IMA for ischemic v/s non-ischemic patients was 0.834. IMA appears to be developing into a new and very potent
marker, of cardiac ischemia. 相似文献
992.
993.
The enzyme theory and the origin of biochemistry 总被引:3,自引:0,他引:3
994.
Technological agglomeration and the emergence of clusters and networks in nanotechnology 总被引:3,自引:0,他引:3
Research and development at the nanoscale requires a large degree of integration, from convergence of research disciplines in new fields of enquiry to new linkages between start-ups, regional actors and research facilities. Based on the analysis of two clusters in nanotechnologies (MESA+ (Twente) and other centres in The Netherlands and Minatec in Grenoble in France), the paper discusses the phenomenon of technological agglomeration: co-located scientific and technological fields associated to coordinated technology platforms to some extent actively shaped by institutional entrepreneurs. Such co-location and coordination are probably a pre-requisite for the emergence of strong nanoclusters. 相似文献
995.
M. V. R. Reddy R. Alli B. C. Harinath 《Indian journal of clinical biochemistry : IJCB》2000,15(1):127-135
Lymphatic filariasis caused mainly by infection fromWuchereria bancrofti andBrugia malayi remains as the major cause of clinical morbidity in tropical and subtropical countries. Development of vaccine against filarial infection can act as additional measure to the existing therapeutic and vector control methods in the control of this disease. The main hurdles in the development of anti-filarial vaccine are the strict primate specificity ofWuchereria bancrofti, the paucity of parasite material, the diversity of clinical manifestations and their associated complex immune responses, lack of clear understanding on host-parasite interactions and the mechanisms involved in protective immunity. However in the past few years, the information generated in immuno-epidemiological studies, correlated with observations in experimental animals suggests that a filarial vaccine is feasible. Initially live irradiated infective larvae have been successfully used to induce high level of protective immunity in several animal models. Applying diverse strategies, variety of purified or recombinant filarial antigens have been explored for their ability to induce protection in different host-parasite systems. Some of these targeted filarial antigens induced high level of resistance in experimental animals against challenge infections. More focussed studies on thorough characterization of parasitological and immunological changes associated with resistance induced by such candidate protective antigens and on delivery mechanisms and safety aspects will be crucial in their selection for possible use in humans. 相似文献
996.
In the United States, Congress has had a long-standing interest in consumer privacy and the extent to which company practices are based on fair information practices. Previously, public policy was largely informed by anecdotal evidence about the effectiveness of industry self-regulatory programs. However, the Internet has made it possible to unobtrusively sample web sites and their privacy disclosures in a way that is not feasible in the offline world. Beginning in 1998, the Federal Trade Commission relied upon a series of three surveys of web sites to assess whether organizations post online privacy disclosures and whether these disclosures represent the U.S. definition of fair information practices. While each year's survey has provided an important snapshot of U.S. web-site practices, there has been no longitudinal analysis of the multiyear trends. This study compares a subset of equivalent individual-level web-site data for the 1998, 1999, 2000, and 2001 web surveys. Implications for using this type of research to inform public policy are discussed. 相似文献
997.
This paper investigates the role of government R&D subsidy programs in stimulating knowledge spillovers. R&D subsidies are an effective public policy instrument when knowledge spillovers exist yet ex ante it is difficult to identify projects that have the greatest potential to increase innovation and economic growth. This paper derives a set of project and firm attributes that the literature finds generate knowledge spillovers and uses data on project proposals to estimate the degree to which a government R&D program conforms. We find that projects that were awarded R&D subsidies were more likely to have attributes such as participation in new research joint ventures and connections to universities and other firms. Following the post-award activities of firm, we find that receipt of a government R&D subsidy increased the funding from other sources when compared to firms that were not awarded funding. 相似文献
998.
R. Kumar S. B. Pachori G. K. Senger Satyanand L. D. Joshi 《Indian journal of clinical biochemistry : IJCB》1994,9(2):72-74
Aim of present study was to compare the adenosine deaminase (ADA) activity in various types of arthritis conditions with synovial
effusion. No. significant difference was observed in ADA activity in serum of control and study groups but results have shown
a definite pattern of ADA activity in synovial fluid in various arthritic conditions. The highest value of ADA activity was
observed in synovial fluid of patients with tubercular arthritis followed by rheumatoid, septic, osteo and post traumatic
arthritis. Thus measurement of ADA activity in synovial fluid can be used as a parameter of differential diagnosis of arthritis
specially tubercular in initial stages. 相似文献
999.
From a number of ML estimators (typically unbiased) of practical interest which include the variance for a Gaussian distribution, the standard deviation for a Laplace distribution, the variance for a Rayleigh distribution and a “spread parameter” for a Cauchy distribution, we design robust estimators according to an emphasis balance between normalized performance and normalized robustness. We measure performance with inverted MSE and robustness with a differential geometric approach. 相似文献
1000.
A. K. Pradhan A. K. Shukla M. V. R. Reddy N. Garg 《Indian journal of clinical biochemistry : IJCB》2004,19(1):83-87
Oxidative stress was assesed by estimating lipid peroxidation product (LPO) in the form of thiobarbituric acid reactive substances
(TBARS), enzymatic antioxidants in the form of superoxide dismutase (SOD), catalase and nonenzymatic antioxidant vitamins
e.g. vitamin C, β carotene and vitamin E in either serum or plasma or erythrocytes in 190 cases of age related cataract in
the age group of 50–80 years. 190 cases were grouped into three morphological types namely, 73 cases of cortical, 77 cases
of posterior subcapsular and 40 cases of nuclear cataract and values of LPO and antioxidants were compared with 78 cases of
age matched healthy control groups. Plasma TBARS levels were cataract cases when compared with control groups. There were
no significant differences in the erythrocyte levels of catalase and plasma levels of Vit E between cataract cases and control
groups. No significant changes of parameters were seen among three different morphological types of age related cataract.
The present study shows that the oxidative stress may play an important role in the age related cataract. 相似文献