全文获取类型
收费全文 | 889576篇 |
免费 | 57006篇 |
国内免费 | 20737篇 |
出版年
2023年 | 13921篇 |
2022年 | 17681篇 |
2021年 | 29751篇 |
2020年 | 25601篇 |
2019年 | 23763篇 |
2018年 | 38956篇 |
2017年 | 37341篇 |
2016年 | 39244篇 |
2015年 | 50857篇 |
2014年 | 68931篇 |
2013年 | 88002篇 |
2012年 | 42396篇 |
2011年 | 38103篇 |
2010年 | 52524篇 |
2009年 | 44402篇 |
2008年 | 26279篇 |
2007年 | 25621篇 |
2006年 | 22528篇 |
2005年 | 19556篇 |
2004年 | 16264篇 |
2003年 | 15423篇 |
2002年 | 14116篇 |
2001年 | 14329篇 |
2000年 | 11929篇 |
1999年 | 11633篇 |
1998年 | 10659篇 |
1997年 | 9689篇 |
1996年 | 10558篇 |
1995年 | 9825篇 |
1994年 | 8850篇 |
1993年 | 9000篇 |
1992年 | 8068篇 |
1991年 | 7678篇 |
1990年 | 7226篇 |
1989年 | 7007篇 |
1988年 | 6940篇 |
1987年 | 5245篇 |
1986年 | 4766篇 |
1985年 | 5959篇 |
1984年 | 7246篇 |
1983年 | 5127篇 |
1982年 | 5836篇 |
1981年 | 5708篇 |
1980年 | 4927篇 |
1979年 | 4962篇 |
1978年 | 4404篇 |
1977年 | 3939篇 |
1976年 | 3668篇 |
1975年 | 2573篇 |
1973年 | 2605篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
L. N. GILLMAN D. J. KEELING R. C. GARDNER S. D. WRIGHT 《Journal of evolutionary biology》2010,23(6):1327-1330
A faster rate of nuclear DNA evolution has recently been found for plants occupying warmer low latitudes relative to those in cooler high latitudes. That earlier study by our research group compared substitution rates within the variable internal transcribed spacer (ITS) region of the ribosomal gene complex amongst 45 congeneric species pairs, each member of which differed in their latitudinal distributions. To determine whether this rate differential might also occur within highly conserved DNA, we sequenced the 18S ribosomal gene in the same 45 pairs of plants. We found that the rate of evolution in 18S was 51% faster in the tropical plant species relative to their temperate sisters and that the substitution rate in 18S correlated positively with that in the more variable ITS. This result, with a gene coding for ribosomal structure, suggests that climatic influences on evolution extend to functionally important regions of the genome. 相似文献
32.
Identifying common prognostic factors in genomic cancer studies: A novel index for censored outcomes
Background
With the growing number of public repositories for high-throughput genomic data, it is of great interest to combine the results produced by independent research groups. Such a combination allows the identification of common genomic factors across multiple cancer types and provides new insights into the disease process. In the framework of the proportional hazards model, classical procedures, which consist of ranking genes according to the estimated hazard ratio or the p-value obtained from a test statistic of no association between survival and gene expression level, are not suitable for gene selection across multiple genomic datasets with different sample sizes. We propose a novel index for identifying genes with a common effect across heterogeneous genomic studies designed to remain stable whatever the sample size and which has a straightforward interpretation in terms of the percentage of separability between patients according to their survival times and gene expression measurements. 相似文献33.
34.
Claudia Raedig Carsten F. Dormann Anke Hildebrandt Sven Lautenbach 《Biodiversity and Conservation》2010,19(6):1523-1546
Monographic data rely on specimens deposited in herbaria and museums, which have been thoroughly revised by experts. However,
monographic data have been rarely used to map species richness at large scale, mainly because of the difficulties caused by
spatially heterogeneous sampling effort. In this paper we estimate patterns of species richness and narrow endemism, based
on monographic data of 4,055 Neotropical angiosperm species. We propose a geometric interpolation method to derive species
ranges at a 1° grid resolution. To this we apply an inverse distance-weighted summation scheme to derive maps of species richness
and endemism. In the latter we also adjust for heterogeneous sampling effort. Finally, we test the robustness of the interpolated
species ranges and derived species richness by applying the same method but using a leave-one-out-cross-validation (LOOCV).
The derived map shows four distinct regions of elevated species richness: (1) Central America, (2) the Northern Andes, (3)
Amazonia and (4) the Brazilian Atlantic coast (216;Mata Atlantica217;). The region with the highest estimated species richness is
Amazonia, with Central America following closely behind. Centers of narrow endemism are located over the entire Neotropics,
several of them coinciding with regions of elevated species richness. Sampling effort has a minor influence on the interpolation
of overall species richness, but it substantially influences the estimation of regions of narrow endemism. Thus, in order
to improve maps of narrow endemism and resulting conservation efforts, more collection and identification activity is required. 相似文献
35.
This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982). 相似文献
36.
37.
38.
Evangelia Jockers-Wretou Valya Russanova Christo Venkov 《Molecular biology reports》1988,13(3):123-131
In a recent publication the isolation and some characteristics of an anti-histone 3 monoclonal antibody, 1GB3 were described (Muller et al. FEBS Lett. 182: 4592013;464, 1985). We now report that the epitope recognized is phylogenetically conserved and located in the N-terminal part of H3, most likely between residues 40 and 50. Using the ELISA technique we found this region to be accessible in chromatin to the monoclonal antibody. The effect of non-ionic detergents on the adsorbtion of chromatin on microtiter plates was studied in this context.Immunological analysis of the reaction of the monoclonal antibody with chromatin by immunoinhibition and immunosedimentation shows that the H3 epitope is accessible in both folded and unfolded chromatin fibre as well as in high- and low-molecular weight oligonucleosomes.Abbreviations BSA
Bovine srum albumin
- mab
Monoclonal antibody
- PBS
Phosphate buffered saline
- PMSF
Phenylmethyl sulfonyl fluoride 相似文献
39.
I.D. Algranati 《Biochemical and biophysical research communications》1980,96(1):54-60
Polypeptide synthesis programmed by poly(U) and globin mRNA has been studied in cell-free extracts from wheat germ. A two-step reaction with a preincubation at high Mg++ levels followed by a second step carried out after a shift to a low Mg++ concentration and the addition of labeled amino acids is described. Under these conditions the initiation of polyphenylalanine synthesis can be blocked without affecting the elongation of polypeptide chains. This procedure allows the selective inhibition of polypeptide synthesis initiation without using any drug or antibiotic. 相似文献
40.
Cristian A. Acevedo Elizabeth Y. Sanchez Juan G. Reyes Manuel E. Young 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(3-4):449-455
It is known that skin releases volatile organic compounds to the environment, and also that its emission pattern changes with aging of the skin. It could be considered, that these compounds are intermediaries in cell metabolism, since many intermediaries of metabolic pathways have a volatile potential. In this work, a simple and non-destructive method consisting of SPME sampling and GC/MS analysis was developed to identify volatile organic emanations from cell cultures. This technique, applied to skin cells culture, indicates that the cells or cell metabolism produce several skin emissions. Chemometric analysis was performed in order to explore the relationship between a volatile profile and the senescence of cell cultures. Volatile profiles were different for cell cultures in different degrees of senescence, indicating that volatile compound patterns could be used to provide information about the age of skin cells. 相似文献