全文获取类型
收费全文 | 21873篇 |
免费 | 63篇 |
国内免费 | 107篇 |
专业分类
系统科学 | 95篇 |
丛书文集 | 108篇 |
教育与普及 | 50篇 |
理论与方法论 | 71篇 |
现状及发展 | 9991篇 |
研究方法 | 976篇 |
综合类 | 10484篇 |
自然研究 | 268篇 |
出版年
2013年 | 126篇 |
2012年 | 348篇 |
2011年 | 573篇 |
2010年 | 146篇 |
2008年 | 359篇 |
2007年 | 435篇 |
2006年 | 416篇 |
2005年 | 405篇 |
2004年 | 378篇 |
2003年 | 385篇 |
2002年 | 423篇 |
2001年 | 717篇 |
2000年 | 692篇 |
1999年 | 479篇 |
1992年 | 418篇 |
1991年 | 335篇 |
1990年 | 384篇 |
1989年 | 356篇 |
1988年 | 373篇 |
1987年 | 380篇 |
1986年 | 319篇 |
1985年 | 470篇 |
1984年 | 370篇 |
1983年 | 295篇 |
1982年 | 318篇 |
1981年 | 297篇 |
1980年 | 331篇 |
1979年 | 742篇 |
1978年 | 601篇 |
1977年 | 514篇 |
1976年 | 510篇 |
1975年 | 509篇 |
1974年 | 545篇 |
1973年 | 483篇 |
1972年 | 560篇 |
1971年 | 628篇 |
1970年 | 767篇 |
1969年 | 589篇 |
1968年 | 655篇 |
1967年 | 614篇 |
1966年 | 531篇 |
1965年 | 366篇 |
1964年 | 137篇 |
1959年 | 188篇 |
1958年 | 349篇 |
1957年 | 228篇 |
1956年 | 207篇 |
1955年 | 183篇 |
1954年 | 155篇 |
1948年 | 141篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
71.
72.
73.
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
74.
75.
Maller JB Fagerness JA Reynolds RC Neale BM Daly MJ Seddon JM 《Nature genetics》2007,39(10):1200-1201
The association of variants in complement factors H and B with age-related macular degeneration has led to more intense genetic and functional analysis of the complement pathway. We identify a nonsynonymous coding change in complement factor 3 that is strongly associated with risk of age-related macular degeneration in a large case-control sample. 相似文献
76.
77.
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
78.
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
79.
80.