全文获取类型
收费全文 | 2858篇 |
免费 | 203篇 |
国内免费 | 242篇 |
出版年
2023年 | 35篇 |
2022年 | 39篇 |
2021年 | 79篇 |
2020年 | 76篇 |
2019年 | 86篇 |
2018年 | 74篇 |
2017年 | 70篇 |
2016年 | 96篇 |
2015年 | 86篇 |
2014年 | 180篇 |
2013年 | 224篇 |
2012年 | 138篇 |
2011年 | 130篇 |
2010年 | 113篇 |
2009年 | 148篇 |
2008年 | 144篇 |
2007年 | 145篇 |
2006年 | 133篇 |
2005年 | 131篇 |
2004年 | 104篇 |
2003年 | 97篇 |
2002年 | 79篇 |
2001年 | 75篇 |
2000年 | 59篇 |
1999年 | 68篇 |
1998年 | 54篇 |
1997年 | 45篇 |
1996年 | 36篇 |
1995年 | 64篇 |
1994年 | 39篇 |
1993年 | 38篇 |
1992年 | 37篇 |
1991年 | 27篇 |
1990年 | 36篇 |
1989年 | 32篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 28篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有3303条查询结果,搜索用时 109 毫秒
1.
以半矮秆育种为代表的“绿色革命”极大地提高了作物产量,但也带来氮营养利用效率降低的严重问题。“绿色革命”主要基于调控赤霉素的代谢和信号转导而实现。前期的研究发现,赤霉素信号转导关键因子DELLA蛋白通过调控GRF4而负调控氮素的吸收利用,为半矮秆品系氮利用效率低的问题提供了解决方案。最近的一项研究进一步揭示了GA信号途径与氮响应交叉互作的新机制。该研究发现水稻(Oryza sativa)NGR5是氮素调控分蘖数目的一个关键基因,其表达受氮诱导。通过招募PRC2,NGR5对D14和OsSPL14等分蘖抑制基因所在位点进行H3K27me3甲基化修饰,从而抑制其表达。而在半矮秆背景下超表达NGR5可以提高低氮水平下的水稻产量。NGR5同时也被发现为赤霉素受体GID1的一个新靶标,受到其负调控。该研究发现了调控赤霉素信号通路的新机制,并对高产高效的新一代“绿色革命”育种实践具有重要启示。 相似文献
2.
Elena C. Guzman Alfonso Jimenez-Sanchez Elisha Orr Robert H. Pritchard 《Molecular & general genetics : MGG》1988,212(2):203-206
Summary A temperature shift-up accompanied by a reduction in RNA polymerase activity in Escherichia coli causes an increased rate of initiation leading to a 1.7- to 2.2-fold increase in chromosome copy number. A temperature shift-up without a reduction in polymerase activity induces only a transient non-scheduled initiation of chromosome replication caused by heat shock with no detectable effect on chromosome copy number. 相似文献
3.
We isolated a Zea mays cDNA encoding the 40S subunit cytoplasmic ribosomal protein S11. The nucleotide sequence was determined and the derived amino acid sequence compared to the corresponding Arabidopsis thaliana protein showing an homology of 90%. This ribosomal protein is encoded by a small multigene family of at least two members. The mRNA steady-state level is about one order of magnitude higher in rapidly growing parts of the plant such as the roots and shoots of seedlings compared to fully expanded leaf tissue. 相似文献
4.
Current patterns of floral design in Pedicularis must have undergone an evolutionary process of interacting among components of floral traits, and then formed internal relationships among these traits. To detect such correlations, which may provide insight to understand flower evolution, 40 Pedicularis species representing all corolla types of the genus were studied. Results show that, interspecifically, pollen size correlates negatively with pollen number, but positively with pistil length. This suggests that plants evolve an optimal pollen size, which balances the advantages of large pollen size for gametophytic competition against the fecundity disadvantages of fewer pollen grains. In contrast to sex allocation theory, this study does not find a trade-off, but an interspecific positive correlation between pollen and ovule number. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the lack of negative correlation between male and female function.This work was supported by the State Key Basic Research and Development Plan, China (Grant No. G2000046804) to YHG. The authors would like to thank Peter K. Endress and two anonymous reviewers for providing critical comments and helpful suggestions, Qing-Feng Wang, Jing-Yuan Wang and Jin-Ming Chen for their helpful suggestions. Shi-Guo Sun, Jing Xia, and Qian Yu are thanked for their assistance in both the field work and laboratory phases of the project. 相似文献
5.
6.
Xiaoqing Wu Xiaorui Xie Linjuan Su Na Lin Bin Liang Nan Guo Qingquan Chen Liangpu Xu Hailong Huang 《Journal of cellular and molecular medicine》2021,25(18):8929-8935
Pallister-Killian syndrome (PKS) is a rare sporadic genetic disorder usually caused by mosaicism of an extra isochromosome of 12p (i(12p)). This retrospective study analysed the prenatal ultrasound manifestations and molecular and cytogenetic results of five PKS foetuses. Samples of amniotic fluid and/or cord blood, skin biopsy and placenta were collected. Conventional karyotyping and single nucleotide polymorphism array (SNP array) were performed on all the amniotic fluid or cord blood samples. Copy number variants sequencing (CNV-seq) and fluorescence in situ hybridization (FISH) were also used for the validation for one foetus. All the five foetuses were from pregnancies with advanced parental age. Two foetuses involved structural abnormalities and one foetus had only soft markers, all of which included increased nuchal translucency. The rest two foetuses had normal ultrasounds in the second trimester, which has rarely been reported before. The karyotype revealed typical i(12p) in four cases and a small supernumerary marker chromosome consisting of 12p and 20p in the remaining one case. The proportion of cells with i(12p) ranged from 0 to 100% in cultural cells, while SNP array results suggested 2−4 copies of 12p. For one foetus, metaphase FISH showed normal results, but the interphase FISH suggested cell lines with two, three and four copies of 12p in the amniotic fluid. Advanced parental age may be an important risk factor for PKS, and there were no typical ultrasound manifestations related to PKS. A combination of karyotype analysis and molecular diagnosis is an effective method for the diagnosis of PKS. 相似文献
7.
8.
L. M. McMurphy A. L. Rayburn 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,84(7-8):798-802
Summary C-band number, guard cell length, and chloroplast number per guard cell were determined for eight maize populations. These populations consisted of maize selected for cold tolerance at the University of Nebraska as well as the original unselected populations. The genome size of these populations had previously been determined. C-band number fluctuated concertedly with the changes in genome size indicating that deletions and additions of constitutive heterochromatin occurred during selection, resulting in altered genome sizes. Guard cell size of all the cold tolerant populations was greater than the cell size of the respective nonselected populations. Chloroplast number per guard cell was also higher in all the cold tolerant populations than in their parental populations, but the increases were not statistically significant. The results indicate that changes in genome size that occurred during selection for cold tolerance are the result of changes in amounts of C-band heterochromatin and that the selection process results in an increase in cell size in the cold tolerant populations. 相似文献
9.
10.