全文获取类型
收费全文 | 5145篇 |
免费 | 428篇 |
国内免费 | 279篇 |
出版年
2024年 | 11篇 |
2023年 | 47篇 |
2022年 | 122篇 |
2021年 | 206篇 |
2020年 | 129篇 |
2019年 | 182篇 |
2018年 | 209篇 |
2017年 | 139篇 |
2016年 | 234篇 |
2015年 | 323篇 |
2014年 | 373篇 |
2013年 | 329篇 |
2012年 | 459篇 |
2011年 | 428篇 |
2010年 | 260篇 |
2009年 | 252篇 |
2008年 | 270篇 |
2007年 | 256篇 |
2006年 | 217篇 |
2005年 | 201篇 |
2004年 | 187篇 |
2003年 | 165篇 |
2002年 | 171篇 |
2001年 | 100篇 |
2000年 | 68篇 |
1999年 | 72篇 |
1998年 | 60篇 |
1997年 | 42篇 |
1996年 | 40篇 |
1995年 | 35篇 |
1994年 | 30篇 |
1993年 | 23篇 |
1992年 | 21篇 |
1991年 | 28篇 |
1990年 | 24篇 |
1989年 | 25篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有5852条查询结果,搜索用时 265 毫秒
1.
Fang Chang An Yan Li-Na Zhao Wei-Hua Wu Zhenbiao Yang 《植物学报(英文版)》2007,49(8):1261-1270
A tip-focused Ca^2+ gradient is tightly coupled to polarized pollen tube growth, and tip-localized influxes of extracellular Ca^2+ are required for this process. However the molecular identity and regulation of the potential Ca^2+ channels remains elusive. The present study has implicated CNGC18 (cyclic nucleotide-gated channel 18) in polarized pollen tube growth, because its overexpression induced wider and shorter pollen tubes. Moreover, CNGC18 overexpression induced depolarization of pollen tube growth was suppressed by lower extracellular calcium ([Ca^2+]ex). CNGC18-yellow fluorescence protein (YFP) was preferentially localized to the apparent post-Golgi vesicles and the plasma membrane (PM) in the apex of pollen tubes. The PM localization was affected by tip-localized ROP1 signaling. Expression of wild type ROP1 or an active form of ROP1 enhanced CNGC18-YFP localization to the apical region of the PM, whereas expression of RopGAP1 (a ROP1 deactivator) blocked the PM localization. These results support a role for PM-Iocalized CNGC18 in the regulation of polarized pollen tube growth through its potential function in the modulation of calcium influxes. 相似文献
2.
J C Lambert G Vallette G E Seralini R Vranckx E Nunez C Stora 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1986,302(9):353-358
Data are presented which indicate a possible action of alpha-fetoprotein (AFP) on female germinal cells. The in vitro maturation of mature mice oocytes was significantly inhibited when mouse AFP replaced albumin in the culture medium. In addition, the degenerative aspect of oocytes cultured with AFP seemed to indicate that this me?otic inhibition was caused by a premature degeneration of oocytes rather than by a blockage at a specific stage of maturation. Thus AFP, perhaps through its ligands, may play a role in the reduction of germinal cells during fetal and immediate post-natal life rather than in the arrest of me?osis at the diplotene stage. 相似文献
3.
4.
5.
Gynheung An 《Molecular & general genetics : MGG》1987,207(2-3):210-216
Summary Expression of the three chlorophyll a/b binding protein (cab) genes of Arabidopsis thaliana was studied in transformed tobacco tissues. For each cab gene, approximately 1000 bp of the promoter region plus a portion of the structural gene was inserted into a promoter-expression vector such that a translational fusion between the cab gene and the promoter-less chloramphenicol acetyltransferase (cat) gene was formed. The constructed molecules were introduced into either cultured tobacco cells or tobacco leaves and the promoter activity was monitored as chloramphenicol acetyltransferase activity. The light-grown tissues exhibited 1.5- to 60-fold greater promoter activity than did dark-grown tissues. Expression of the cab promoters was tissue specific: activities were much stronger in green leaves than other tissues. The cab promoters were almost equally active in transformed calli or shoots derived from leaves. However, in cultured tobacco cells, one promoter was two to three times stronger than the other two. The chimeric gene fusion, cab-cat, segregated in the F1 generation as a dominant Mendelian trait. 相似文献
6.
L Savu R Vranckx M Maya E A Nunez 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1987,305(17):627-632
It has been reported evidence based on equilibrium binding, electrophoretic, immunoelectrophoretic studies, that the rat possesses a major high affinity thyroid hormone binding protein, with an electrophoretic mobility and binding properties similar to those of the human thyroxine binding globulin (TBG). It is shown that in the sera of postnatal developing animals, between 3 and 21 days, the thyroxine (T4) and the triiodothyronine (T3) binding activities increase up to 10 times over adult or foetal levels, due to a high transient post-natal surge of the rat TBG. In the adult serum, the TBG persists in decreased amounts: it then yields the predominant role as T4 carrier to the thyroid binding prealbumin (TBPA), but retains the major role as binder of T3, i.e. of the biologically active thyroid hormone. 相似文献
7.
Three distinct regulatory elements comprise the upstream promoter region of the nopaline synthase gene 总被引:5,自引:0,他引:5
Summary Fine deletion mutants were generated in the upstream control region of the nopaline synthase (nos) promoter to define the position and role of upstream regulatory elements. The results indicated that the 8 bp sequence (CAGAAACC) at -106/-113 and its inverted repeat (GGTTTCTG) at -140/-147 are important for promoter function. The downstream element appears more important than the upstream element since deletion of the former reduced promoter activity more significantly than deletion of the latter. Deletion of the element alone, however, did not abolish promoter function, whereas, deletion of the 10 bp potential Z-DNA-forming (Z) element located between the repeat elements nullified promoter activity. Therefore, it appears that the Z element is an essential upstream regulator and the repeated elements are upstream modulators of the nos promoter. These elements are functionally distinct since alteration of stereospecificity or insertion of short oligonucleotides between the elements did not significantly influence promoter activity. These regulatory elements were unable to function from 200 bp upstream of the CCAAT-TATA box region. 相似文献
8.
L Savu R Vranckx M Maya E A Nunez 《Biochemical and biophysical research communications》1989,159(3):919-926
We use gel equilibration and electrophoretic techniques to compare the binding properties of thyroxine binding globulin and thyroxine binding prealbumin in rat sera. The evidence indicates that TBG bears the serum lowest capacity highest affinity sites for thyroxine (T4) and triiodothyronine (T3) (Ka1 greater than or equal to 10(9) M-1) as well as weaker saturable T3 sites (Ka2 approximately 10(8) M-1). TBPA bears for T4 only Ka2 approximately 10(8) M-1 sites and for T3 only Ka approximately 10(6) M-1 sites. Consistent with these parameters are the specific responses of TBG and TBPA binding activities to varying serum concentrations of T4, T3, oleic acid, the drugs diphenylhydantoin or salicylate. The primary attack of these compounds is aimed at TBG. Small T4, oleate or DPH doses chase the TBG-bound T4 to TBPA, high doses of T4 or oleate but not of DPH inhibiting the T4 binding to both proteins. In the T3-serum interactions, all tested compounds displace the TBG-bound hormone without chasing it to TBPA. The high reactivity of TBG sites designates the protein as crucially involved in modulating the free vs bound serum levels of T4 and T3 against physiological or pathological variations of binding competitors. 相似文献
9.
10.