全文获取类型
收费全文 | 26564篇 |
免费 | 91篇 |
国内免费 | 172篇 |
专业分类
系统科学 | 130篇 |
丛书文集 | 198篇 |
教育与普及 | 83篇 |
理论与方法论 | 85篇 |
现状及发展 | 12123篇 |
研究方法 | 1109篇 |
综合类 | 12795篇 |
自然研究 | 304篇 |
出版年
2012年 | 403篇 |
2011年 | 658篇 |
2009年 | 175篇 |
2008年 | 455篇 |
2007年 | 527篇 |
2006年 | 488篇 |
2005年 | 500篇 |
2004年 | 504篇 |
2003年 | 484篇 |
2002年 | 503篇 |
2001年 | 787篇 |
2000年 | 801篇 |
1999年 | 532篇 |
1994年 | 345篇 |
1992年 | 435篇 |
1991年 | 362篇 |
1990年 | 435篇 |
1989年 | 398篇 |
1988年 | 411篇 |
1987年 | 433篇 |
1986年 | 424篇 |
1985年 | 525篇 |
1984年 | 403篇 |
1983年 | 393篇 |
1982年 | 367篇 |
1981年 | 358篇 |
1980年 | 375篇 |
1979年 | 849篇 |
1978年 | 695篇 |
1977年 | 603篇 |
1976年 | 551篇 |
1975年 | 603篇 |
1974年 | 689篇 |
1973年 | 602篇 |
1972年 | 630篇 |
1971年 | 810篇 |
1970年 | 912篇 |
1969年 | 729篇 |
1968年 | 788篇 |
1967年 | 706篇 |
1966年 | 612篇 |
1965年 | 445篇 |
1964年 | 217篇 |
1959年 | 235篇 |
1958年 | 461篇 |
1957年 | 338篇 |
1956年 | 285篇 |
1955年 | 270篇 |
1954年 | 266篇 |
1948年 | 221篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
1 Results The photosynthetic bacterial reaction center (RC) is a membrane protein complex.The RC is composed of three protein subunits and redox components such as bacteriochlorophylls, bacteriopheophytins,and quinones.The RC performs the photochemical electron transfer from the bacteriochlorophyll dimer through a series of electron donor and acceptor molecules to a secondary quinone,QB.QB accepts electrons from a primary quinone,QA,in two sequential electron transfer reactions.The second electron trans... 相似文献
53.
S. K. MISHRA Shouyang WANG K. K. LAI 《系统科学与复杂性》2007,20(3):344-349
In this paper, we introduce a new class of generalized convex function, namely, a-pseudounivex function, by combining the concepts of pseudo-univex and α-invex functions. Further, we establish some relationships between vector variational-like inequality problems and vector optimization problems under the assumptions of α-pseudo-univex functions. Results obtained in this paper present a refinement and improvement of previously known results. 相似文献
54.
55.
56.
57.
The effects of alcohol consumption, cigarette smoking and age on sister chromatid exchange (SCE) frequency in human lymphocytes were assessed by means of multiple linear regression. An increase in SCE rates was associated with alcohol consumption (p = 0.0001), smoking (p = 0.0231), and, to a small extent (p = 0.057), age. These three confounding factors explain 48% of the inter-personal variation in SCE rates among subjects studied. 相似文献
58.
59.
M. Harada S. Yenbutra K. Tsuchiya S. Takada 《Cellular and molecular life sciences : CMLS》1985,41(12):1610-1611
Summary Karyotypes ofMyotis siligorensis, Myotis mystacinus, Pipistrellus pulveratus, Tylonycteris robustula, Miniopterus schreibersi fuliginosus, Hipposideros fulvus andAselliscus stoliczkanus from Thailand are investigated.Acknowledgment. The authors are very grateful to Dr N. Ratanawarabhan, Mrs S. Sittilert, P. Noonpakdee and S. Kuanchalern of Thailand Institute of Scientific and Technological Research for their valuable advice and assistance during our field survey in Thailand. 相似文献
60.
The way that we perceive and interact with objects depends on our previous experience with them. For example, a bird expert is more likely to recognize a bird as a sparrow, a sandpiper or a cockatiel than a non-expert. Neurons in the inferior temporal cortex have been shown to be important in the representation of visual objects; however, it is unknown which object features are represented and how these representations are affected by categorization training. Here we show that feature selectivity in the macaque inferior temporal cortex is shaped by categorization of objects on the basis of their visual features. Specifically, we recorded from single neurons while monkeys performed a categorization task with two sets of parametric stimuli. Each stimulus set consisted of four varying features, but only two of the four were important for the categorization task (diagnostic features). We found enhanced neuronal representation of the diagnostic features relative to the non-diagnostic ones. These findings demonstrate that stimulus features important for categorization are instantiated in the activity of single units (neurons) in the primate inferior temporal cortex. 相似文献