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   2739篇
  免费   30篇
  国内免费   13篇
化学   1847篇
晶体学   10篇
力学   27篇
数学   539篇
物理学   359篇
  2016年   23篇
  2015年   17篇
  2014年   36篇
  2013年   82篇
  2012年   67篇
  2011年   67篇
  2010年   48篇
  2009年   43篇
  2008年   65篇
  2007年   67篇
  2006年   78篇
  2005年   72篇
  2004年   60篇
  2003年   52篇
  2002年   51篇
  2001年   21篇
  2000年   37篇
  1999年   42篇
  1998年   27篇
  1997年   37篇
  1996年   58篇
  1995年   42篇
  1994年   39篇
  1993年   51篇
  1992年   45篇
  1991年   42篇
  1990年   31篇
  1989年   32篇
  1988年   23篇
  1987年   31篇
  1986年   37篇
  1985年   58篇
  1984年   33篇
  1983年   36篇
  1982年   47篇
  1981年   38篇
  1980年   59篇
  1979年   55篇
  1978年   53篇
  1977年   48篇
  1976年   51篇
  1975年   33篇
  1974年   35篇
  1973年   40篇
  1972年   26篇
  1971年   24篇
  1970年   27篇
  1967年   17篇
  1930年   18篇
  1929年   15篇
排序方式: 共有2782条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
Summary In the present paper we study truncated projections for the fanbeam geometry in computerized tomography. First we derive consistency conditions for the divergent beam transform. Then we study a singular value decomposition for the case where only the interior rays in the fan are provided, as for example in region-of-interest tomography. We show that the high angular frequency components of the searched-for densities are well determined and we present reconstructions from real data where the missing information is approximated based on the singular value decomposition.The work of the authors was supported by the Deutsche Forschungsgemeinschaft under grant Lo 310/2-4  相似文献   
6.
Utilization of carbohydrates by radiation processing   总被引:2,自引:0,他引:2  
Upgrading and utilization of carbohydrates such as chitosan, sodium alginate, carrageenan, cellulose, pectin have been investigated for recycling these bio-resources and reducing the environmental pollution. These carbohydrates were easily degraded by irradiation and various kinds of biological activities such as anti-microbial activity, promotion of plant growth, suppression of heavy metal stress, phytoalexins induction, etc. were induced. On the other hand, some carbohydrate derivatives, carboxymethylcellulose and carboxymethylstarch, could be crosslinked under certain radiation condition and produce the biodegradable hydrogel for medical and agricultural use.  相似文献   
7.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions.  相似文献   
8.
In solid state fermentation, Pleurotus sajor-caju has been found to be able to degrade at least 30% oil palm empty Fruit Bunch (EFB) fibre leaving 70 % useful materials. Conditions under which fermentation carried out were investigated. It was found that, in the temperature range between 25– 28 °C, relative ph between 6–8, moisture between 60–70 % and medium composition of CaCO3: rice bran 2 %: 5 % were the optimum conditions. The results showed in fermented products that, there were substantial reduction in cellulosic component such as Crude Fiber (CF, 18 %); Acid Detergent Fibre (ADF, 45 %), Neutral Detergent Fibre (NDF, 61 %) and Acid Detergent Lignin (ADL, 14 %). However, Crude Protein (CP, 10%) increased resulted from single cell protein enrichment of mycelial microbial mass. The mass reductions of substrate in fermentation process corresponds to the CO2 released during fermentation. Hence, attributable to the decreased in content of CF, ADF, NDF, and ADL. The digestibility study has also been carried out to determine the useful level of this product to ruminant. Aflatoxin content was detected low in both the initial substrates and products. Based on nutritional value and low content of aflatoxin, the product is useful as a source of roughage to ruminant.  相似文献   
9.
10.
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