全文获取类型
收费全文 | 177708篇 |
免费 | 2277篇 |
国内免费 | 859篇 |
出版年
2018年 | 12764篇 |
2017年 | 11759篇 |
2016年 | 10275篇 |
2015年 | 6776篇 |
2014年 | 6091篇 |
2013年 | 5855篇 |
2012年 | 8943篇 |
2011年 | 14813篇 |
2010年 | 14056篇 |
2009年 | 10252篇 |
2008年 | 10407篇 |
2007年 | 11922篇 |
2006年 | 887篇 |
2005年 | 7208篇 |
2004年 | 6337篇 |
2003年 | 4606篇 |
2002年 | 1942篇 |
2001年 | 1348篇 |
2000年 | 482篇 |
1999年 | 1499篇 |
1998年 | 338篇 |
1997年 | 197篇 |
1992年 | 1946篇 |
1991年 | 2053篇 |
1990年 | 2082篇 |
1989年 | 2011篇 |
1988年 | 1977篇 |
1987年 | 1832篇 |
1986年 | 1634篇 |
1985年 | 1659篇 |
1984年 | 1102篇 |
1983年 | 856篇 |
1982年 | 468篇 |
1981年 | 428篇 |
1980年 | 371篇 |
1979年 | 1082篇 |
1978年 | 770篇 |
1977年 | 609篇 |
1976年 | 633篇 |
1975年 | 888篇 |
1974年 | 1000篇 |
1973年 | 1012篇 |
1972年 | 1203篇 |
1971年 | 1205篇 |
1970年 | 828篇 |
1969年 | 832篇 |
1968年 | 735篇 |
1967年 | 752篇 |
1966年 | 586篇 |
1965年 | 446篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
The number of orientation, feeding and social calls emitted by pipistrelle batsPipistrellus pipistrellus Schreber, 1774 andP. pygmaeus Leach, 1825 was recorded throughout the night at eight different sites. Social calls were unaffected by weather variables,
whereas orientation calls and feeding buzzes were both significantly affected by cloud and temperature conditions. The number
of emissions of each call type was significantly different between sites, indicating that the bats used different sites for
different activities. Significant positive correlations between all three combinations of call types occurred only during
the middle of the night, corresponding with the nadir of flying insects. This suggests that bats were engaged in activities
other than feeding at this time, such as territory protection or mate attraction. 相似文献
223.
224.
225.
226.
B?rbel Maus Camille Jung Jestinah M. Mahachie John Jean-Pierre Hugot Emmanuelle Génin Kristel Van Steen 《PloS one》2013,8(10)
Complex human diseases commonly differ in their phenotypic characteristics, e.g., Crohn’s disease (CD) patients are heterogeneous with regard to disease location and disease extent. The genetic susceptibility to Crohn’s disease is widely acknowledged and has been demonstrated by identification of over 100 CD associated genetic loci. However, relating CD subphenotypes to disease susceptible loci has proven to be a difficult task. In this paper we discuss the use of cluster analysis on genetic markers to identify genetic-based subgroups while taking into account possible confounding by population stratification. We show that it is highly relevant to consider the confounding nature of population stratification in order to avoid that detected clusters are strongly related to population groups instead of disease-specific groups. Therefore, we explain the use of principal components to correct for population stratification while clustering affected individuals into genetic-based subgroups. The principal components are obtained using 30 ancestry informative markers (AIM), and the first two PCs are determined to discriminate between continental origins of the affected individuals. Genotypes on 51 CD associated single nucleotide polymorphisms (SNPs) are used to perform latent class analysis, hierarchical and Partitioning Around Medoids (PAM) cluster analysis within a sample of affected individuals with and without the use of principal components to adjust for population stratification. It is seen that without correction for population stratification clusters seem to be influenced by population stratification while with correction clusters are unrelated to continental origin of individuals. 相似文献
227.
Background
NOL7 is a candidate tumor suppressor that localizes to a chromosomal region 6p23. This locus is frequently lost in a number of malignancies, and consistent loss of NOL7 through loss of heterozygosity and decreased mRNA and protein expression has been observed in tumors and cell lines. Reintroduction of NOL7 into cells resulted in significant suppression of in vivo tumor growth and modulation of the angiogenic phenotype. Further, NOL7 was observed to localize to the nucleus and nucleolus of cells. However, the mechanisms regulating its subcellular localization have not been elucidated. 相似文献228.
Alexander V. Kirdyanov Eugene A. Vaganov Malcolm K. Hughes 《Trees - Structure and Function》2007,21(1):37-44
We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology.
The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed
for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern
timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies
and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance
of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of
four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard
technique is correlated with temperature over a much longer period. For maximum density series from which the relationship
between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing
season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring
formation. 相似文献
229.
A E Sukhov G M Cha?chenko 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1989,39(5):828-835
In experiments on 56 healthy subjects (18-20 years old) the quality of their activity was determined during compensatory watching the mark at complicating regimes of work. Depending on the difficulty of the task five groups of subjects were singled out with optimum working capacity in one of four working conditions: normal, ordinary and strenuous work, model of stress situation. It is established that the change of the number of significant correlative connections between main parameters of psychophysiological state of man-operator reflects the condition of his functional systems. On the basis of computation of total range of organization values of both R-R intervals of the ECG and duration of expiration, the success of the man-operator work in complex conditions of activity is predicted. 相似文献
230.