全文获取类型
收费全文 | 12797篇 |
免费 | 48篇 |
国内免费 | 82篇 |
专业分类
系统科学 | 85篇 |
丛书文集 | 29篇 |
教育与普及 | 28篇 |
理论与方法论 | 47篇 |
现状及发展 | 5608篇 |
研究方法 | 742篇 |
综合类 | 6083篇 |
自然研究 | 305篇 |
出版年
2012年 | 286篇 |
2011年 | 556篇 |
2010年 | 106篇 |
2009年 | 78篇 |
2008年 | 280篇 |
2007年 | 331篇 |
2006年 | 302篇 |
2005年 | 298篇 |
2004年 | 276篇 |
2003年 | 267篇 |
2002年 | 319篇 |
2001年 | 442篇 |
2000年 | 442篇 |
1999年 | 301篇 |
1992年 | 246篇 |
1991年 | 198篇 |
1990年 | 219篇 |
1989年 | 196篇 |
1988年 | 205篇 |
1987年 | 221篇 |
1986年 | 199篇 |
1985年 | 261篇 |
1984年 | 229篇 |
1983年 | 178篇 |
1982年 | 179篇 |
1981年 | 182篇 |
1980年 | 173篇 |
1979年 | 413篇 |
1978年 | 349篇 |
1977年 | 252篇 |
1976年 | 300篇 |
1975年 | 266篇 |
1974年 | 274篇 |
1973年 | 231篇 |
1972年 | 248篇 |
1971年 | 317篇 |
1970年 | 384篇 |
1969年 | 267篇 |
1968年 | 312篇 |
1967年 | 306篇 |
1966年 | 257篇 |
1965年 | 180篇 |
1964年 | 99篇 |
1959年 | 88篇 |
1958年 | 162篇 |
1957年 | 101篇 |
1956年 | 91篇 |
1955年 | 85篇 |
1954年 | 77篇 |
1948年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
41.
1 Results Classic oxidants require rigorous control of the experimental conditions added with the problem of lack of selectivity. Catalysis by transition metals with environmentally safe oxidants provides synthetic routes to minimize pollution by giving environmental benign by-products. Fe (Ⅵ) is a powerful and a selective oxidant with Fe(Ⅲ) as a by-product, while hydrogen peroxide is clean with water as the only by-product. Separation of sodium or potassium ferrates requires tedious processes. Associat... 相似文献
42.
43.
44.
Beyond their role in replication and chromosome end capping, telomeres are also thought to function in meiotic chromosome pairing, meiotic and mitotic chromosome segregation as well as in nuclear organization. Observations in both somatic and meiotic cells suggest that the positioning of telomeres within the nucleus is highly specific and believed to be dependent mainly on telomere interactions with the nuclear envelope either directly or through chromatin interacting proteins. Although little is known about the mechanism of telomere clustering, some studies show that it is an active process. Recent data have suggested a regulatory role for telomere chromatin structure in telomere movement. This review will summarize recent studies on telomere interactions with the nuclear matrix, telomere chromatin structure and factors that modify telomere chromatin structure as related to regulation of telomere movement. 相似文献
45.
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
46.
47.
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
48.
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
49.
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
50.
Yeo S H K Ramesh 《厦门大学学报(自然科学版)》2002,(Z1)
On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5~7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is an ardent task due to its warpage, induced by the high specific grinding energy (2~10 J/mm 3). Therefore, coolant is often used to avoid thermal damage, obtai n better surface integrity and to prolong wheel life. However coolant, the incomp ressibility media introduce high forces at the gri... 相似文献