全文获取类型
收费全文 | 41885篇 |
免费 | 3350篇 |
国内免费 | 2436篇 |
出版年
2024年 | 62篇 |
2023年 | 495篇 |
2022年 | 1141篇 |
2021年 | 1985篇 |
2020年 | 1234篇 |
2019年 | 1523篇 |
2018年 | 1416篇 |
2017年 | 1087篇 |
2016年 | 1630篇 |
2015年 | 2430篇 |
2014年 | 2852篇 |
2013年 | 3094篇 |
2012年 | 3590篇 |
2011年 | 3404篇 |
2010年 | 1947篇 |
2009年 | 1797篇 |
2008年 | 2086篇 |
2007年 | 1871篇 |
2006年 | 1608篇 |
2005年 | 1427篇 |
2004年 | 1199篇 |
2003年 | 1057篇 |
2002年 | 905篇 |
2001年 | 851篇 |
2000年 | 740篇 |
1999年 | 718篇 |
1998年 | 435篇 |
1997年 | 465篇 |
1996年 | 441篇 |
1995年 | 390篇 |
1994年 | 379篇 |
1993年 | 308篇 |
1992年 | 441篇 |
1991年 | 386篇 |
1990年 | 331篇 |
1989年 | 246篇 |
1988年 | 236篇 |
1987年 | 198篇 |
1986年 | 141篇 |
1985年 | 185篇 |
1984年 | 121篇 |
1983年 | 104篇 |
1982年 | 80篇 |
1981年 | 60篇 |
1980年 | 55篇 |
1979年 | 72篇 |
1978年 | 66篇 |
1977年 | 46篇 |
1976年 | 48篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
根瘤细胞早期发育阶段,以宿主细胞器和根瘤菌转化类菌体的数量增多为特征。随后类菌体增殖到填满宿主细胞内的大部分区域。各个类菌体周膜内含有1至几个类菌体。晚期共生发育阶段,类菌体细胞结构和宿主细胞器数量发生了变化。文中还讨论了根瘤的共生固氮作用。 相似文献
992.
993.
994.
995.
Han Wang Qian Zhang BinBin Wang WangJun Wu Julong Wei Pinghua Li Ruihua Huang 《European journal of cell biology》2018,97(4):257-268
Recently, miR-22 was found to be differentially expressed in different skeletal muscle growth period, indicated that it might have function in skeletal muscle myogenesis. In this study, we found that the expression of miR-22 was the most in skeletal muscle and was gradually up-regulated during mouse myoblast cell (C2C12 myoblast cell line) differentiation. Overexpression of miR-22 repressed C2C12 myoblast proliferation and promoted myoblast differentiation into myotubes, whereas inhibition of miR-22 showed the opposite results. During myogenesis, we predicted and verified transforming growth factor beta receptor 1 (TGFBR1), a key receptor of the TGF-β/Smad signaling pathway, was a target gene of miR-22. Then, we found miR-22 could regulate the expression of TGFBR1 and down-regulate the Smad3 signaling pathway. Knockdown of TGFBR1 by siRNA suppressed the proliferation of C2C12 cells but induced its differentiation. Conversely, overexpression of TGFBR1 significantly promoted proliferation but inhibited differentiation of the myoblast. Additionally, when C2C12 cells were treated with different concentrations of transforming growth factor beta 1 (TGF-β1), the level of miR-22 in C2C12 cells was reduced. The TGFBR1 protein level was significantly elevated in C2C12 cells treated with TGF-β1. Moreover, miR-22 was able to inhibit TGF-β1-induced TGFBR1 expression in C2C12 cells. Altogether, we demonstrated that TGF-β1 inhibited miR-22 expression in C2C12 cells and miR-22 regulated C2C12 cell myogenesis by targeting TGFBR1. 相似文献
996.
Zhong L Guo XN Zhang XH Wu ZX Luo XM Jiang HL Lin LP Zhang XW Ding J 《Biochimica et biophysica acta》2005,1722(3):254-261
Vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen, can act in tumor-induced angiogenesis by binding to specific receptors on the surface of endothelial cells. One such receptor, VEGFR-2/KDR, plays a key role in VEGF-induced angiogenesis. Here, we expressed the catalytic domain of VEGFR-2 as a soluble active kinase using Bac-to-Bac expression system, and investigated correlations between VEGFR-2 activity and enzyme concentration, ATP concentration, substrate concentration and divalent cation type. We used these data to establish a convenient, effective and non-radioactive ELISA screening technique for the identification and evaluation of potential inhibitors for VEGFR-2 kinase. We screened 200 RTK target-based compounds and identified one (TKI-31) that potently inhibited VEGFR-2 kinase activity (IC50=0.596 microM). Treatment of NIH3T3/KDR cells with TKI-31 blocked VEGF-induced phosphorylation of KDR in a dose-dependent manner. Moreover, TKI-31 dose-dependently suppressed HUVEC tube formation. Thus, we herein report a novel, efficient method for identifying VEGFR-2 kinase inhibitors and introduce one, TKI-31, that may prove to be a useful new angiogenesis inhibitor. 相似文献
997.
ochotonidaeThomas,l897AlloptoxDaw8on,l96lAlloptoxsihongensis8p.nov.(Figs.lAi6)HolotypeArightp3,V884o.7.Paratypesldp3,V884o.l;3p3,V884o.3,5,6;1p4,V884O.9;2ml/m2,V884o.l2,16;Afragmentof1eftmandiblewithp4,V884O.l8;thefrontpartofrightman-diblewithi2,p3-p4,V884o.24;2I2,V884O.21,23;4P3,V884O-31-33,56;P4,V884o.27;AfragmentofleftupperjawwithP3-M1,V884o-57;2M2,V884o.5o,53.TypelocalityS0nglinzhuang,Sih0ngC0unty,Jiangsu.StratumtypicumandageXiaca0wanFormation,.EarIyMi0cene(Shan-wangian),eq… 相似文献
998.
淀粉分支酶基因sbe是影响玉米直链淀粉含量的主要因素,淀粉分支酶分为3种即sbeI、sbeIIa和sbeIIb,其中sbeIIb对直链淀粉含量影响效应最大,抑制玉米淀粉分支酶sbeIIb基因的表达可减少支链淀粉的含量,从而达到提高直链淀粉的目的;ADP-葡萄糖焦磷酸化酶(AGPase)是直链淀粉合成的关键酶,通过提高AGP表达量同样可提高玉米直链淀粉含量。以此为目的分别克隆了sbeIIb一段375bp高度保守区,玉米SBE基因一段175bp内含子,AGP完整开放阅读框,大麦胚乳特异启动子和ADPG基因终止子。构建了sbeIIb基因正、反义的hpRNA发夹结构,将该发夹结构与上述基因分别连接到pCAM-BIA3301上;构建得到包含sbeIIb基因干扰结构与AGP基因过表达的pCAMB-RSA多基因胚乳特异表达载体。为此,pCAMB-RSA载体的成功构建将为高直链淀粉玉米的培育奠定基础。 相似文献
999.
Xinyi Wu Ruiru Cheng Shulin Xue Zhongxin Kong Hongshen Wan Guoqiang Li Yulong Huang Haiyan Jia Jizeng Jia Lixia Zhang Zhengqiang Ma 《Molecular breeding : new strategies in plant improvement》2014,33(1):129-138
The spike characteristics length, spikelet density and fertile floret number are related yield components and are important in cereal improvement. QSpl.nau-2D is a major quantitative trait locus controlling spike length (SPL) detected in the recombinant inbred line population developed by crossing wheat (Triticum aestivum) cultivars Nanda2419 with Wangshuibai. In this study, to validate its genetic effect and determine its precise location, QSpl.nau-2D’s near-isogenic line (NIL) was developed using Mianyang99-323 as the recurrent parent through marker-assisted selection. Field trials showed that the NIL not only had significantly longer spikes on average than the recurrent parent but also had significantly higher grain weight, but did not differ in spikelet number and kernel number per spike. In the F2 population derived from a cross of the NIL with Mianyang99-323, QSpl.nau-2D functioned like a single gene and conditioned the SPL in a partially dominant manner, and was thus designated as HL1 (for head length). To precisely map HL1, 89 recombinants, consisting of 11 genotypes, were identified in the NIL-derived F2 population of 674 plants by using markers in the Xwmc25–Xgpw4080 interval. Phenotyping these lines showed that the introduction of a 0.9-cM interval flanked by Xcfd53 and DG371 in Nanda2419 resulted in longer spikes and a higher grain weight in the NIL. The availability of markers closely linked to HL1 could facilitate its use in breeding programs. 相似文献
1000.
Klokouzas A Tiffert T van Schalkwyk D Wu CP van Veen HW Barrand MA Hladky SB 《Biochemical and biophysical research communications》2004,321(1):197-201
Plasmodium falciparum proteins that efflux toxic metabolic products such as oxidised glutathione (GSSG) are possible targets for anti-malarial drug development. Proteins capable of transporting GSSG and glutathione conjugates include the multidrug resistance-associated transporters (MRPs). A gene, PFA0590w, encoding a MRP homologue, has been identified in P. falciparum. Here we show the presence of full-length mRNA (5.5 kb) of this PfMRP in trophozoites by RT-PCR and Northern blotting. A polyclonal anti-PfMRP antibody generated against two unique, hydrophilic peptides in the predicted sequence produced a strong immunoreactive protein band of 210-215 kDa on Western blots of schizonts of chloroquine-sensitive and chloroquine-resistant strains, confirming expression of PfMRP protein. Using confocal microscopy the protein was seen to be localised at the edge of the schizonts with no obvious staining of the food vacuole. We suggest that PfMRP may act as the GSSG transporter in the parasite plasma membrane. 相似文献