全文获取类型
收费全文 | 12688篇 |
免费 | 50篇 |
国内免费 | 71篇 |
专业分类
系统科学 | 78篇 |
丛书文集 | 29篇 |
教育与普及 | 21篇 |
理论与方法论 | 41篇 |
现状及发展 | 6023篇 |
研究方法 | 681篇 |
综合类 | 5805篇 |
自然研究 | 131篇 |
出版年
2012年 | 244篇 |
2011年 | 347篇 |
2010年 | 101篇 |
2009年 | 88篇 |
2008年 | 270篇 |
2007年 | 287篇 |
2006年 | 308篇 |
2005年 | 276篇 |
2004年 | 247篇 |
2003年 | 245篇 |
2002年 | 286篇 |
2001年 | 456篇 |
2000年 | 462篇 |
1999年 | 303篇 |
1992年 | 240篇 |
1991年 | 194篇 |
1990年 | 219篇 |
1989年 | 195篇 |
1988年 | 207篇 |
1987年 | 225篇 |
1986年 | 193篇 |
1985年 | 261篇 |
1984年 | 232篇 |
1983年 | 177篇 |
1982年 | 186篇 |
1981年 | 189篇 |
1980年 | 192篇 |
1979年 | 414篇 |
1978年 | 354篇 |
1977年 | 258篇 |
1976年 | 304篇 |
1975年 | 275篇 |
1974年 | 275篇 |
1973年 | 240篇 |
1972年 | 258篇 |
1971年 | 329篇 |
1970年 | 390篇 |
1969年 | 268篇 |
1968年 | 324篇 |
1967年 | 309篇 |
1966年 | 263篇 |
1965年 | 192篇 |
1964年 | 105篇 |
1959年 | 95篇 |
1958年 | 166篇 |
1957年 | 106篇 |
1956年 | 100篇 |
1955年 | 86篇 |
1954年 | 85篇 |
1948年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
We develop in this paper an efficient way to select the best subset threshold autoregressive model. The proposed method uses a stochastic search idea. Differing from most conventional approaches, our method does not require us to fix the delay or the threshold parameters in advance. By adopting the Markov chain Monte Carlo techniques, we can identify the best subset model from a very large of number of possible models, and at the same time estimate the unknown parameters. A simulation experiment shows that the method is very effective. In its application to the US unemployment rate, the stochastic search method successfully selects lag one as the time delay and five best models from more than 4000 choices. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
42.
Dina C Meyre D Gallina S Durand E Körner A Jacobson P Carlsson LM Kiess W Vatin V Lecoeur C Delplanque J Vaillant E Pattou F Ruiz J Weill J Levy-Marchal C Horber F Potoczna N Hercberg S Le Stunff C Bougnères P Kovacs P Marre M Balkau B Cauchi S Chèvre JC Froguel P 《Nature genetics》2007,39(6):724-726
We identified a set of SNPs in the first intron of the FTO (fat mass and obesity associated) gene on chromosome 16q12.2 that is consistently strongly associated with early-onset and severe obesity in both adults and children of European ancestry with an experiment-wise P value of 1.67 x 10(-26) in 2,900 affected individuals and 5,100 controls. The at-risk haplotype yields a proportion of attributable risk of 22% for common obesity. We conclude that FTO contributes to human obesity and hence may be a target for subsequent functional analyses. 相似文献
43.
44.
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
45.
46.
47.
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
48.
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
49.
50.
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