全文获取类型
收费全文 | 9264篇 |
免费 | 878篇 |
国内免费 | 999篇 |
专业分类
11141篇 |
出版年
2024年 | 21篇 |
2023年 | 70篇 |
2022年 | 190篇 |
2021年 | 344篇 |
2020年 | 275篇 |
2019年 | 373篇 |
2018年 | 380篇 |
2017年 | 307篇 |
2016年 | 399篇 |
2015年 | 581篇 |
2014年 | 669篇 |
2013年 | 731篇 |
2012年 | 849篇 |
2011年 | 814篇 |
2010年 | 587篇 |
2009年 | 568篇 |
2008年 | 596篇 |
2007年 | 537篇 |
2006年 | 445篇 |
2005年 | 412篇 |
2004年 | 338篇 |
2003年 | 339篇 |
2002年 | 305篇 |
2001年 | 208篇 |
2000年 | 134篇 |
1999年 | 113篇 |
1998年 | 87篇 |
1997年 | 74篇 |
1996年 | 47篇 |
1995年 | 44篇 |
1994年 | 46篇 |
1993年 | 35篇 |
1992年 | 49篇 |
1991年 | 31篇 |
1990年 | 22篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
卵泡抑素相关蛋白的病理生理功能 总被引:1,自引:0,他引:1
卵泡抑素相关蛋白(follistatin related protein,FRP)是一种细胞外基质糖蛋白,该蛋白参与细胞增殖、迁移、组织重塑、胚胎发育、细胞间相互作用及多种病理生理过程.近年研究显示,该蛋白同时具有抑制细胞凋亡和抑制细胞增殖的双重功能:在心肌缺血的动物模型中,FRP被证实有保护心肌细胞、抗凋亡、促进内皮细胞增殖等功能;FRP也可由血管平滑肌细胞合成分泌,并具有反馈调节平滑肌细胞功能的作用,该蛋白还可抑制多种肿瘤细胞增殖. 相似文献
73.
Rui Cheng Xiaoman Zheng Yingmei Wang Xing Ma Xin Liu Wenjun Xu Mengyun Wang Yuanpeng Gao Xupeng Xing Chuan Zhou Hongzheng Sun Zekun Guo Fusheng Quan Jun Liu Song Hua Yongsheng Wang Yong Zhang Xu Liu 《中国科学:生命科学英文版》2022,65(11):2257-2268
Animal cloning can be achieved by somatic cell nuclear transfer(SCNT), but the resulting live birth rate is relatively low. We previously improved the efficiency of bovine SCNT by exogenous melatonin treatment or by overexpression of lysine-specific demethylase 4D(KDM4D) and 4E(KDM4E). In this study, we revealed abundant alternative splicing(AS) transitions during fertilization and embryonic genome activation, and demonstrated abnormal AS in bovine SCNT embryos compared with in vitro fertilized ... 相似文献
74.
Guanjun Shen Xianzhu Wu Qian Wang Hua Tu Yue-xing Feng Jian-xin Zhao 《Journal of human evolution》2013
Most researchers believe that anatomically modern humans (AMH) first appeared in Africa 160-190 ka ago, and would not have reached eastern Asia until ∼50 ka ago. However, the credibility of these scenarios might have been compromised by a largely inaccurate and compressed chronological framework previously established for hominin fossils found in China. Recently there has been a growing body of evidence indicating the possible presence of AMH in eastern Asia ca. 100 ka ago or even earlier. Here we report high-precision mass spectrometric U-series dating of intercalated flowstone samples from Huanglong Cave, a recently discovered Late Pleistocene hominin site in northern Hubei Province, central China. Systematic excavations there have led to the in situ discovery of seven hominin teeth and dozens of stone and bone artifacts. The U-series dates on localized thin flowstone formations bracket the hominin specimens between 81 and 101 ka, currently the most narrow time span for all AMH beyond 45 ka in China, if the assignment of the hominin teeth to modern Homo sapiens holds. Alternatively this study provides further evidence for the early presence of an AMH morphology in China, through either independent evolution of local archaic populations or their assimilation with incoming AMH. Along with recent dating results for hominin samples from Homo erectus to AMH, a new extended and continuous timeline for Chinese hominin fossils is taking shape, which warrants a reconstruction of human evolution, especially the origins of modern humans in eastern Asia. 相似文献
75.
Zhang LX Tong XJ Sun XH Tong L Gao J Jia H Li ZH 《Cellular and molecular neurobiology》2008,28(4):501-509
Objectives To observe the effect of ultrashortwave (USW) therapy on nerve regeneration after acellular nerve allografts(ANA) repairing
the sciatic nerve gap of rats and discuss its acting mechanisms. Methods Sixteen Wistar rats weighing 180–220 g were randomly divided into four groups with four rats in each group: normal control
group; acellular group (ANA, treated by hypotonic-chemical detergent, was applied for bridging a 10 mm-long sciatic nerve
defect); USW group (After 24 h of ANA repairing the sciatic nerve gap, low dose USW was administrated for 7 min, once a day,
20 times a course of treatment, three courses of treatment in all); and autografts group. 12 weeks after operation, a series
of examinations was performed, including electrophysiological methods, the restoring rate of tibialis anterior muscle wet
weight, histopathological observation (myelinated nerve number, myelin sheath thickness, and axon diameter), vascular endothelial
growth factor (VEGF) mRNA expression of spinal cord, and muscle at injury site, and analyzed statistically. Results Compared to acellular nerve allografts alone, USW therapy can increase nerve conductive velocity, the restoring rate of tibialis
anterior muscle wet weight, myelinated nerve number, axon diameter, VEGF mRNA expression of spinal cord, and muscle at injury
site, the difference is significant. There were no differences between USW group and autografts group except myelin sheath
thickness. Conclusions USW therapy can promote nerve axon regeneration and Schwann cells proliferation after ANA repairing the sciatic nerve gap
of rats, the upregulation of VEGF mRNA expression of spinal cord and muscle may play an important role. 相似文献
76.
The insect neuropeptide, [Arg7]-corazonin was injected into larvae of the silkworm, Bombyx mori to investigate its influence on development and behavior. A single injection of 50 pmol of corazonin into the fourth and fifth instar larvae induced prolongation of the spinning period in all experimental groups except for those injected on day 10 of the fifth instar. The injection also caused a prolongation of the pupal period in some experimental groups, while it had no effect on the timing of larval ecdysis and the length of feeding period of the fifth instar. The spinning period was significantly prolonged even at a low dose of 1 pmol. Both the spinning rate and the rate of increase in hemolymph ecdysteroid level during the spinning stage were reduced by injection of corazonin. However, corazonin injection during days 5-7 of the fifth instar reduced the spinning rate without influencing the ecdysteroid level until the end of day 8, thereafter the rate of increase in hemolymph ecdysteroid level was slower in the corazonin-injected larvae than in the control larvae. Therefore, the suppressed ecdysteroid level observed in the corazonin-injected larvae appears to be a result rather than a cause of the reduced spinning rate. This study is the first published report for the corazonin effect on the behavior in insects. 相似文献
77.
在实验条件下比较了四个(龙州、九宫山、监利、新会)褐飞虱Nilaparvata lugens(Stal)地理种群的发育、繁殖、内禀增长能力等参数的异同。结果表明:1.北迁的迁入当代九宫山种群雌虫降落取食3.6d开始产卵,产卵量平均为522粒,低于其第二代居留型种群的714粒;2.四个种群在若虫l龄、5龄历期上有显著差异(a=0.05).但决定翅型分化的2、3、4龄历期上无显著差异;成虫寿命、产卵历期无显著差异;新会种群产卵量高于其它三个种群;同龄期若虫的世代存活率,九宫山种群低于其它三个种群;综合反映发育、存活、繁殖等生命信息的内禀增长能力rm差异较小,在0.1874~0.1982间变化。本文还分析了产生上述异同的原因。 相似文献
78.
Repression of microRNA‐382 inhibits glomerular mesangial cell proliferation and extracellular matrix accumulation via FoxO1 in mice with diabetic nephropathy 下载免费PDF全文
79.
Becky Xu Hua Fu Loren L. Hansen Karen L. Artiles Michael L. Nonet Andrew Z. Fire 《Nucleic acids research》2014,42(22):13778-13787
To study target sequence specificity, selectivity, and reaction kinetics of Streptococcus pyogenes Cas9 activity, we challenged libraries of random variant targets with purified Cas9::guide RNA complexes in vitro. Cleavage kinetics were nonlinear, with a burst of initial activity followed by slower sustained cleavage. Consistent with other recent analyses of Cas9 sequence specificity, we observe considerable (albeit incomplete) impairment of cleavage for targets mutated in the PAM sequence or in ‘seed’ sequences matching the proximal 8 bp of the guide. A second target region requiring close homology was located at the other end of the guide::target duplex (positions 13–18 relative to the PAM). Sequences flanking the guide+PAM region had measurable (albeit modest) effects on cleavage. In addition, the first-base Guanine constraint commonly imposed by gRNA expression systems has little effect on overall cleavage efficiency. Taken together, these studies provide an in vitro understanding of the complexities of Cas9–gRNA interaction and cleavage beyond the general paradigm of site determination based on the ‘seed’ sequence and PAM. 相似文献
80.
Tian X Wang LY Xia S Li ZB Liu XH Yuan Y Fang L Zuo H 《Bioorganic & medicinal chemistry letters》2012,22(1):204-206
Novel 2H-benzo[b][1,4]oxazin-3(4H)-ones have been synthesized by condensation, reduction, O-alkylation and Smiles rearrangement using 3-bromo-4-hydroxy benzaldehyde, anilines, and chloroacetyl chloride as starting materials. All the synthesized compounds have been characterized by (1)H NMR, (13)C NMR, and HRMS, and tested for the inhibitory ability on platelet aggregation. The results have shown that the ADP (adenosine 5'-diphosphate)-induced platelet aggregation was inhibited by 7a-g with the IC(50) value at 10.14-18.83 μmol/L. Compound 7a exhibited the most potent inhibitory effect (IC(50)=10.14 μmol/L) among all the compounds, but less potent than the control drug ticlopidine (3.18 μmol/L) and aspirin (6.07 μmol/L). The preliminary structure-activity relationship (SAR) was initially investigated in the study. 相似文献