全文获取类型
收费全文 | 10371篇 |
免费 | 991篇 |
国内免费 | 1363篇 |
专业分类
12725篇 |
出版年
2024年 | 61篇 |
2023年 | 240篇 |
2022年 | 500篇 |
2021年 | 748篇 |
2020年 | 556篇 |
2019年 | 593篇 |
2018年 | 549篇 |
2017年 | 421篇 |
2016年 | 568篇 |
2015年 | 730篇 |
2014年 | 922篇 |
2013年 | 888篇 |
2012年 | 1058篇 |
2011年 | 915篇 |
2010年 | 499篇 |
2009年 | 504篇 |
2008年 | 515篇 |
2007年 | 454篇 |
2006年 | 350篇 |
2005年 | 307篇 |
2004年 | 260篇 |
2003年 | 171篇 |
2002年 | 192篇 |
2001年 | 81篇 |
2000年 | 89篇 |
1999年 | 69篇 |
1998年 | 54篇 |
1997年 | 50篇 |
1996年 | 35篇 |
1995年 | 41篇 |
1994年 | 40篇 |
1993年 | 25篇 |
1992年 | 31篇 |
1991年 | 33篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1977年 | 5篇 |
1973年 | 3篇 |
1966年 | 2篇 |
1962年 | 2篇 |
1950年 | 2篇 |
1940年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Many animals exhibit different behaviors in different seasons. The photoperiod can have effects on migration, breeding, fur growth, and other processes. The cyclic growth of the fur and feathers of some species of mammals and birds, respectively, is stimulated by the photoperiod as a result of hormone-dependent regulation of the nervous system. To further examine this phenomenon, we evaluated the Arbas Cashmere goat (Capra hircus), a species that is often used in this type of research. The goats were exposed to an experimentally controlled short photoperiod to study the regulation of cyclic cashmere growth. Exposure to a short photoperiod extended the anagen phase of the Cashmere goat hair follicle to increase cashmere production. Assessments of tissue sections indicated that the short photoperiod significantly induced cashmere growth. This conclusion was supported by a comparison of the differences in gene expression between the short photoperiod and natural conditions using gene chip technology. Using the gene chip data, we identified genes that showed altered expression under the short photoperiod compared to natural conditions, and these genes were found to be involved in the biological processes of hair follicle growth, structural composition of the hair follicle, and the morphogenesis of the surrounding skin appendages. Knowledge about differences in the expression of these genes as well as their functions and periodic regulation patterns increases our understanding of Cashmere goat hair follicle growth. This study also provides preliminary data that may be useful for the development of an artificial method to improve cashmere production by controlling the light cycle, which has practical significance for livestock breeding. 相似文献
4.
5.
6.
7.
Xian-Hui Dong Dong-Xue Ma Tian-Ci Zhang Xiao-Ping He Li-Jun Xu Ya-Lei Liu Hao Li Wei-Juan Gao 《Neurochemical research》2021,46(5):1068-1080
Neurochemical Research - Alzheimer’s disease (AD) process is characterized classically by two hallmark pathologies: β-amyloid (Aβ) plaque deposition and neurofibrillary tangles of... 相似文献
8.
Mengnan Wang Dongjie Li Mingyue Zhang Wenzhi Yang Yali Cui Shijie Li 《Animal genetics》2015,46(4):354-360
The CDKN1C gene encodes a cyclin‐dependent kinase inhibitor and is one of the key genes involved in the development of Beckwith–Wiedemann syndrome and cancer. In this study, using a direct sequencing approach based on a single nucleotide polymorphism (SNP) at genomic DNA and cDNA levels, we show that CDKN1C exhibits monoallelic expression in all seven studied organs (heart, liver, spleen, lung, kidney, muscle and subcutaneous fat) in cattle. To investigate how methylation regulates imprinting of CDKN1C in cattle, allele‐specific methylation patterns in two putative differential methylation regions (DMRs), the CDKN1C DMR and KvDMR1, were analyzed in three tissues (liver, spleen and lung) using bisulfite sequencing PCR. Our results show that in the CDKN1C DMR both parental alleles were unmethylated in all three analyzed tissues. In contrast, KvDMR1 was differentially methylated between the two parental alleles in the same tissues. Statistical analysis showed that there is a significant difference in the methylation level between the two parental alleles (P < 0.01), confirming that this region is the DMR of KvDMR1 and that it may be correlated with CDKN1C imprinting. 相似文献
9.
10.
A study of the component synthesis method (CSM) for analyzing the normal mode dynamics of macromolecules is reported. The procedure involves a reduction of the dimensions of the normal mode problems for large molecular systems and the accurate extraction of the low-frequency modes. A macromolecule is divided into small components based on a hierarchical clustering of the residues in the structure. Interactions between coupled components are treated by the method of static correlation. The normal modes of the components are obtained first, and a fraction of the low-frequency normal modes of the components under mutual correlations are then used as a reduced basis for solving for the normal modes of the whole molecule. Multiple components are introduced for large macromolecules so that the dimensions of the eigenvalue problems at the component level are small. The method is applied to the protein crambin. In test calculations in which the dimensions of the eigenvalue equations are reduced to 1/6 of their natural size, the errors in the normal mode frequencies calculated by the CSM procedure are only about 1–2% when compared with the exact values. The rms fluctuations of all atoms in crambin calculated by the CSM procedure are basically identical to the exact results. The CSM procedure is shown to be accurate for calculating the normal modes of large macromolecules with a significant reduction of the size of the problem. © 1994 John Wiley & Sons, Inc. 相似文献