首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   928篇
  免费   44篇
  国内免费   1篇
  2023年   8篇
  2022年   18篇
  2021年   29篇
  2020年   12篇
  2019年   25篇
  2018年   31篇
  2017年   30篇
  2016年   36篇
  2015年   45篇
  2014年   67篇
  2013年   71篇
  2012年   82篇
  2011年   88篇
  2010年   59篇
  2009年   41篇
  2008年   34篇
  2007年   50篇
  2006年   30篇
  2005年   27篇
  2004年   29篇
  2003年   25篇
  2002年   23篇
  2001年   8篇
  2000年   10篇
  1999年   3篇
  1997年   4篇
  1996年   5篇
  1994年   5篇
  1992年   8篇
  1991年   8篇
  1990年   4篇
  1989年   3篇
  1988年   4篇
  1987年   2篇
  1986年   3篇
  1985年   8篇
  1984年   10篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1979年   2篇
  1978年   1篇
  1976年   2篇
  1974年   1篇
  1973年   1篇
  1972年   4篇
  1970年   1篇
  1969年   3篇
  1967年   2篇
  1950年   1篇
排序方式: 共有973条查询结果,搜索用时 15 毫秒
181.
Reactive oxygen or nitrogen species are generated in the plant cell during the extreme stress condition, which produces toxic compounds after reacting with the organic molecules. The glutathione-S-transferase (GST) enzymes play a significant role to detoxify these toxins and help in excretion or sequestration of them. In the present study, we have cloned 1023 bp long promoter region of tau class GST from an extreme halophyte Salicornia brachiata and functionally characterized using the transgenic approach in tobacco. Computational analysis revealed the presence of abiotic stress responsive cis-elements like ABRE, MYB, MYC, GATA, GT1 etc., phytohormones, pathogen and wound responsive motifs. Three 5’-deletion constructs of 730 (GP2), 509 (GP3) and 348 bp (GP4) were made from 1023 (GP1) promoter fragment and used for tobacco transformation. The single event transgenic plants showed notable GUS reporter protein expression in the leaf tissues of control as well as treated plants. The expression level of the GUS gradually decreases from GP1 to GP4 in leaf tissues, whereas the highest level of expression was detected with the GP2 construct in root and stem under control condition. The GUS expression was found higher in leaves and stems of salinity or osmotic stress treated transgenic plants than that of the control plants, but, lower in roots. An efficient expression level of GUS in transgenic plants suggests that this promoter can be used for both constitutive as well as stress inducible expression of gene(s). And this property, make it as a potential candidate to be used as an alternative promoter for crop genetic engineering.  相似文献   
182.
183.
S. Jha  S. Sen 《Genetica》1990,80(1):9-15
Bulb scale and inflorescence explants of Urginea indica Kunth. (2n=20) were cultured in vitro on modified Murashige & Skoog's medium with different hormonal composition. Media containing 2,4-dichlorophenoxy-acetic acid (2,4-D) (2 and 4 mgl–1) and -naphthalene-acetic acid (NAA) (2 mgl–1) could induce callus in inflorescence explants. Combination of 2,4-D (4 mgl–1) + NAA (2 mgl–1) + Kinetin (2 mgl–1) only could induce callus formation in scale explants. The bulb scale explants contained mostly diploid cells while the inflorescence explants contained cells with nuclear DNA content ranging from 2C to 64C. The lowest karyological heterogeneity was recorded in callus derived from bulb scale and in callus derived from inflorescence induced with NAA. The highest variability was recorded on media with 2,4-D alone. Induction of division, probably of the pre-existing polytenic nuclei in the inflorescence explant, has been suggested to be the cause of origin of polyploid cells in such cases.  相似文献   
184.
Trichoplusia ni and Spodoptera littoralis larvae were infected with a recombinant AcNPV, having the viral polyhedrin gene replaced with the cDNA encoding firefly luciferase. Both S. littoralis and T. ni synthesized very high levels of luciferase representing greater than or equal to 25% and greater than or equal to 15%, respectively of the total Coomassie blue stainable protein. Luciferase was apparently not secreted into the hemolymph but was contained within the body tissue. Expression in S. littoralis larvae suggests that luciferase can be an excellent reporter enzyme to study virus infection, dissemination and expression in different tissues, host range determination, insect physiology and also to monitor the release of recombinant virus in the environment when used as a biocide.  相似文献   
185.
Human diploid fibroblasts have a limited life span in vitro, and spontaneous immortalization is an extremely rare event. We have used transformation of human diploid fibroblasts by an origin-defective simian virus 40 genome to develop series of genetically matched immortal cell lines to analyze immortalization. Comparison of a preimmortal transformant (SVtsA/HF-A) with its uncloned and cloned immortalized derivatives (AR5 and HAL) has failed to reveal any major alteration involving the simian virus 40 genome. Karyotypic analysis, however, demonstrated that all of the immortal cell lines in this series have alterations of chromosome 6 involving loss of the portion distal to 6q21. The karyotypic analysis was corroborated by DNA analyses. Southern analysis demonstrated that only one copy of three proto-oncogene loci (ros1, c-myb, and mas1) on 6q was retained in immortal cells. Polymerase chain reaction analysis of the microsatellite polymorphism at 6q22 (D6S87) showed loss of heterozygosity. In addition, elevated expression of c-myb (6q22-23) was observed. We hypothesize that the region at and/or distal to 6q21 plays a role in immortalization, consistent with the presence of a growth suppressor gene.  相似文献   
186.
Allogeneic stem cell transplantation is currently the only curative therapy for primary myelofibrosis (MF), while the JAK2 inhibitor, ruxolitinib. Has been approved only for palliation. Other therapies are desperately needed to reverse life‐threatening MF. However, the cell(s) and cytokine(s) that promote MF remain unclear. Several reports have demonstrated that captopril, an inhibitor of angiotensin‐converting enzyme that blocks the production of angiotensin II (Ang II), mitigates fibrosis in heart, lung, skin and kidney. Here, we show that captopril can mitigate the development of MF in the Gata1low mouse model of primary MF. Gata1low mice were treated with 79 mg/kg/d captopril in the drinking water from 10 to 12 months of age. At 13 months of age, bone marrows were examined for fibrosis, megakaryocytosis and collagen expression; spleens were examined for megakaryocytosis, splenomegaly and collagen expression. Treatment of Gata1low mice with captopril in the drinking water was associated with normalization of the bone marrow cellularity; reduced reticulin fibres, splenomegaly and megakaryocytosis; and decreased collagen expression. Our findings suggest that treating with the ACE inhibitors captopril has a significant benefit in overcoming pathological changes associated with MF.  相似文献   
187.
Cisplatin (cis-diamminedichloroplatinum) is a common chemotherapeutic drug that reacts with the N7 atoms of adjacent guanines in DNA to form the Pt-1,2-d(GpG) intrastrand cross-link (Pt-GG), a major product to block DNA replication. Translesion DNA synthesis has been implicated in chemoresistance during cisplatin treatment of cancer due to Pt-GG lesion bypass. Gene knockdown studies in human cells have indicated a role for polκ during translesion synthesis of the Pt-GG lesion. However, the bypass activity of polκ with cisplatin lesions has not been well characterized. In this study, we investigated polκ's ability to bypass Pt-GG lesion in vitro and determined two crystal structures of polκ in complex with Pt-GG DNA. The ternary complex structures represent two consecutive stages of lesion bypass: nucleotide insertion opposite the 5′G (Pt-GG2) and primer extension immediately after the lesion (Pt-GG3). Our biochemical data showed that polκ is very efficient and accurate in extending DNA primers after the first G of the Pt-GG lesion. The structures demonstrate that the efficiency and accuracy is achieved by stably accommodating the bases with the cisplatin adduct in the active site for proper Watson–Crick base pairing with the incoming nucleotide in both the second insertion and post-insertion complexes. Our studies suggest that polκ works as an extender for efficient replication of the Pt-GG lesion in cells. This work holds promise for considering polκ, along with polη, as potential targets for drug design, which together could improve the efficacy of cisplatin treatment for cancer therapy.  相似文献   
188.
189.
190.
The metal(II) complexes [M(4-Me-5-NH2-1-iqtsc- H)Cl2] (M = Co(II), Ni(II) or Cu(II) and 4-Me-5- NH2-1-iqtsc-H = 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone), [Zn(4-Me-5-NH2-1-iqtsc-H)- (OAc)2]· H2O and [Pt(4-Me-5-NH2-1-iqtsc)Cl)] were isolated and characterized by elemental analysis, conductance measurement, magnetic moments (300- 78 K)and spectral studies. On the basis of these studies distorted trigonal-bipyramidal structures for the Co(II), Ni(II), Cu(II) and Zn(II) complexes and a square-planar structure for the Pt(II) complex are proposed. All these complexes were screened for their antitumour activity in the P388 lymphocytic leukaemia test system in mice. With the exception of the Pt(II) and Zn(II) complexes, the complexes showed no significant activity; the Zn(II) and Pt(II) complexes showed T/C (%) values of 150 and 144 at a much lesser extent [2].  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号