全文获取类型
收费全文 | 5731篇 |
免费 | 77篇 |
国内免费 | 144篇 |
专业分类
系统科学 | 102篇 |
丛书文集 | 138篇 |
教育与普及 | 100篇 |
理论与方法论 | 9篇 |
现状及发展 | 1977篇 |
研究方法 | 202篇 |
综合类 | 3412篇 |
自然研究 | 12篇 |
出版年
2022年 | 53篇 |
2021年 | 64篇 |
2015年 | 62篇 |
2014年 | 87篇 |
2013年 | 93篇 |
2012年 | 137篇 |
2011年 | 170篇 |
2010年 | 121篇 |
2009年 | 182篇 |
2008年 | 179篇 |
2007年 | 182篇 |
2006年 | 126篇 |
2005年 | 177篇 |
2004年 | 175篇 |
2003年 | 126篇 |
2002年 | 119篇 |
2001年 | 246篇 |
2000年 | 216篇 |
1999年 | 173篇 |
1998年 | 58篇 |
1997年 | 56篇 |
1995年 | 59篇 |
1992年 | 129篇 |
1991年 | 105篇 |
1990年 | 105篇 |
1989年 | 79篇 |
1988年 | 85篇 |
1987年 | 84篇 |
1986年 | 61篇 |
1985年 | 98篇 |
1984年 | 81篇 |
1983年 | 62篇 |
1982年 | 65篇 |
1981年 | 59篇 |
1980年 | 75篇 |
1979年 | 146篇 |
1978年 | 134篇 |
1977年 | 107篇 |
1976年 | 79篇 |
1975年 | 73篇 |
1974年 | 98篇 |
1973年 | 103篇 |
1972年 | 89篇 |
1971年 | 111篇 |
1970年 | 100篇 |
1969年 | 96篇 |
1968年 | 95篇 |
1967年 | 87篇 |
1966年 | 86篇 |
1965年 | 58篇 |
排序方式: 共有5952条查询结果,搜索用时 15 毫秒
11.
混合氯化稀土催化合成DOP,DOM和DOA 总被引:1,自引:0,他引:1
本文报道:价廉的混合氯化稀土,对合成DOP等增塑剂有明显的催化效果。产品精制简单,转化率高,有应用前景。 相似文献
12.
Summary Host cell reactivation capacity for ozone T3 phage was determined for differentE. coli strains deficient in one or more of the DNA repair mechanisms. The results indicate that DNA polymerase I appears to play a key role in the repair of damage produced on the DNA by ozone while thelexA gene product seems to play a minor one.This research was sponsored by the National Sciences and Engineering Council of Canada. One of us (PLH) acknowledges a scholarship from the NSERCof Canada. 相似文献
13.
A topoisomerase II inhibitor, novobiocin, and a deacetylase inhibitor, butyrate, synergistically transformed human liver cells into fibroblast-like cells. This morphological change was associated with an increased production of procollagen type III peptide and a simultaneous assembly of actin, tubulin, vimentin and cytokeratin. Novobiocin and butyrate had no marked effect on the phosphorylation state of cytokeratin proteins, but synergistically enhanced [3H]acetate uptake. From these results, it can be speculated that protein acetylation plays an important role in inducing the assembly of cytoskeletal proteins and the morphological transformation of human liver cells. 相似文献
14.
M. Ishibashi M. Tsuda Y. Ohizumi T. Sasaki J. Kobayashi 《Cellular and molecular life sciences : CMLS》1991,47(3):299-300
Summary A new bromotyrosine-derived alkaloid with antileukemic activity, purealidin A (5), has been isolated from the Okinawan marine spongePsammaplysilla purea and its chemical structure elucidated on the basis of the spectroscopic data. 相似文献
15.
Support vector machine (SVM), as a novel approach in pattern recognition, has demonstrated a success in face detection and face recognition. In this paper, a face recognition approach based on the SVM classifier with the nearest neighbor classifier (NNC) is proposed. The principal component analysis (PCA) is used to reduce the dimension and extract features. Then one-against-all stratedy is used to train the SVM classifiers. At the testing stage, we propose an al- 相似文献
16.
On Mar.23,2006,a project in the Major Program of NSFC-"Evolutionary computation and its application",managed by Prof.Licheng Jiao,Prof.Lishan Kang,Prof.Zhenya He,and Prof.Tao Xie,passed its Final Qualification Process and was evaluated as Excellent. 相似文献
17.
18.
Y. G. Ma 《复旦学报(自然科学版)》2007,46(1):33-40
Progress on nuclear liquid gas phase transition (LGPT) or critical behavior has been simply reviewed and some signals of LGPT in heavy ion collisions, especially in NIMROD data, are focused. These signals include the power-law charge distribution, the largest fluctuation of the fragment observables, the nuclear Zipf law, caloric curve and critical exponent analysis etc. 相似文献
19.
Edwin Y.B.Pun 《复旦学报(自然科学版)》2007,(5)
1 Results Rare earth doped waveguide amplifiers and devices have been demonstrated in silica, crystal and other glass hosts. These rare earth doped optical waveguide devices are based on inorganic materials. Many processing steps are required and can lead to long fabrication time and low yield.Polymer materials offer many distinct properties compared to inorganic materials, such as ease of fabrication, low production costs, simple processing steps, and compatibility with micro-fabrication technologies. ... 相似文献
20.