全文获取类型
收费全文 | 2075篇 |
免费 | 60篇 |
国内免费 | 2篇 |
出版年
2013年 | 44篇 |
2012年 | 27篇 |
2011年 | 61篇 |
2010年 | 93篇 |
2009年 | 91篇 |
2008年 | 63篇 |
2007年 | 79篇 |
2006年 | 60篇 |
2005年 | 56篇 |
2004年 | 26篇 |
2003年 | 29篇 |
2001年 | 25篇 |
1999年 | 28篇 |
1998年 | 41篇 |
1997年 | 58篇 |
1996年 | 29篇 |
1995年 | 41篇 |
1994年 | 32篇 |
1993年 | 56篇 |
1992年 | 43篇 |
1991年 | 42篇 |
1990年 | 38篇 |
1989年 | 34篇 |
1988年 | 39篇 |
1987年 | 44篇 |
1986年 | 29篇 |
1985年 | 24篇 |
1983年 | 38篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 35篇 |
1979年 | 26篇 |
1978年 | 40篇 |
1977年 | 21篇 |
1976年 | 20篇 |
1975年 | 32篇 |
1974年 | 29篇 |
1973年 | 27篇 |
1972年 | 44篇 |
1971年 | 33篇 |
1959年 | 20篇 |
1958年 | 23篇 |
1957年 | 45篇 |
1956年 | 23篇 |
1955年 | 33篇 |
1954年 | 21篇 |
1953年 | 33篇 |
1952年 | 26篇 |
1951年 | 23篇 |
1950年 | 25篇 |
排序方式: 共有2137条查询结果,搜索用时 62 毫秒
1.
2.
3.
MUKARATIRWA SAMSON; KRISTENSEN THOMAS K.; SIEGISMUND HANS R.; CHANDIWANA STEPHEN K. 《Journal of Molluscan Studies》1998,64(4):435-446
Aquatic snails from south western Zimbabwe belonging to theBulinus trunscatus/tropicus complex vary widely in shell formsuggesting that more than one taxon could be present. This possibilitywas investigated by making observations on snail samples from13 populations from the Plumtree area, in respect of allozymevariation (5 polymorphic loci), shell morphology (9 variables),copulatory organ and chromosome number. Comparative data wereobtained from snails from north western Zimbabwe identifieddefinitely as B. tropicus. Analysis of the genetic structurerevealed a high degree of polymorphism (P) ranging from 0.290.80among populations from Plumtree and expected heterozygosity(He) from 0.020.22. No enzymatic diagnostic loci werefound which could differentiate the different morphs or populationsand discriminant function analysis on the morphological datashowed an overlap of morphs among populations. Snails analyzedfor chromosome number were all diploid (2n = 36). Snails exposedto Schistosoma haematobium mira-cidia were all refractory. Thisinformation supports the view of a single species, B. tropicus,which is differentiated due to migration barriers and whereenvironmental variables might be implicated in the morphometricdivergence. (Received 31 July 1995; accepted 15 January 1998) 相似文献
4.
5.
During long-term storage in modified gas atmospheres (MGA), some of the biochemical changes occurring in tomato fruit, cv. Sleaford Abundance, were compared with those in fruit of some Israeli cultivars which had been selected for firmness and slow ripening. The MGA used in the experiments did not succeed in completely restricting changes in sugars and acids during storage, although colour change was prevented. This separation of processes is discussed in relation to the practice of long-term storage and its implications for fruit flavour. 相似文献
6.
On blocking rules for the bootstrap with dependent data 总被引:9,自引:0,他引:9
We address the issue of optimal block choice in applicationsof the block bootstrap to dependent data. It is shown that optimalblock size depends significantly on context, being equal ton1/3, n1/4 and n1/5 in the cases of variance or bias estimation,estimation of a onesided distribution function, and estimationof a two-sided distribution function, respectively. A clearintuitive explanation of this phenomenon is given, togetherwith outlines of theoretical arguments in specific cases. Itis shown that these orders of magnitude of block sizes can beused to produce a simple, practical rule for selecting blocksize empirically. That technique is explored numerically. 相似文献
7.
8.
9.
10.
DIURNAL VARIATIONS IN ENDOGENOUS ETHYLENE LEVELS IN PLANTS 总被引:1,自引:0,他引:1