全文获取类型
收费全文 | 41600篇 |
免费 | 513篇 |
国内免费 | 53篇 |
专业分类
教育 | 30527篇 |
科学研究 | 3639篇 |
各国文化 | 342篇 |
体育 | 2824篇 |
综合类 | 33篇 |
文化理论 | 667篇 |
信息传播 | 4134篇 |
出版年
2022年 | 218篇 |
2021年 | 338篇 |
2020年 | 526篇 |
2019年 | 801篇 |
2018年 | 3052篇 |
2017年 | 2977篇 |
2016年 | 2425篇 |
2015年 | 741篇 |
2014年 | 1001篇 |
2013年 | 6211篇 |
2012年 | 1077篇 |
2011年 | 1515篇 |
2010年 | 1465篇 |
2009年 | 1068篇 |
2008年 | 1394篇 |
2007年 | 1769篇 |
2006年 | 711篇 |
2005年 | 980篇 |
2004年 | 942篇 |
2003年 | 882篇 |
2002年 | 628篇 |
2001年 | 611篇 |
2000年 | 541篇 |
1999年 | 469篇 |
1998年 | 305篇 |
1997年 | 324篇 |
1996年 | 355篇 |
1995年 | 350篇 |
1994年 | 286篇 |
1993年 | 285篇 |
1992年 | 425篇 |
1991年 | 405篇 |
1990年 | 396篇 |
1989年 | 387篇 |
1988年 | 334篇 |
1987年 | 367篇 |
1986年 | 331篇 |
1985年 | 374篇 |
1984年 | 305篇 |
1983年 | 282篇 |
1982年 | 256篇 |
1981年 | 237篇 |
1980年 | 227篇 |
1979年 | 326篇 |
1978年 | 231篇 |
1977年 | 211篇 |
1976年 | 204篇 |
1975年 | 182篇 |
1974年 | 185篇 |
1971年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
A number of numerical codes have been written for the problem of finding the circle of smallest radius in the Euclidean plane that encloses a finite set P of points, but these do not give much insight into the geometry of this circle. We investigate geometric properties of the minimal circle that may be useful in the theoretical analysis of applications. We show that a circle C enclosing P is minimal if and only if it is rigid in the sense that it cannot be translated while still enclosing P. We show that the center of the minimal circle is in the convex hull of P. We use this rigidity result and an analysis of the case of three points to find sharp estimates on the diameter of the minimal circle in terms of the diameter of P. 相似文献
993.
994.
995.
996.
K. A. Faseehuddin Shakir Basavaraj Madhusudhan 《Indian journal of clinical biochemistry : IJCB》2007,22(1):117-121
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
997.
Maintaining the reversibility of foldings: Making the ethics (politics) of information technology visible 总被引:1,自引:0,他引:1
Lucas D. Introna 《Ethics and Information Technology》2007,9(1):11-25
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
998.
K. Pratibha Usha Anand Rajni Agarwal 《Indian journal of clinical biochemistry : IJCB》2004,19(2):128-131
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
999.
1000.
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