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   16559篇
  免费   1246篇
  国内免费   1212篇
  19017篇
  2024年   42篇
  2023年   238篇
  2022年   573篇
  2021年   949篇
  2020年   572篇
  2019年   760篇
  2018年   758篇
  2017年   558篇
  2016年   788篇
  2015年   1036篇
  2014年   1292篇
  2013年   1413篇
  2012年   1507篇
  2011年   1366篇
  2010年   830篇
  2009年   745篇
  2008年   845篇
  2007年   703篇
  2006年   562篇
  2005年   504篇
  2004年   419篇
  2003年   362篇
  2002年   268篇
  2001年   250篇
  2000年   222篇
  1999年   231篇
  1998年   163篇
  1997年   137篇
  1996年   123篇
  1995年   111篇
  1994年   106篇
  1993年   87篇
  1992年   102篇
  1991年   100篇
  1990年   54篇
  1989年   55篇
  1988年   42篇
  1987年   34篇
  1986年   23篇
  1985年   28篇
  1984年   23篇
  1983年   16篇
  1982年   9篇
  1981年   4篇
  1980年   3篇
  1979年   3篇
  1977年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
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   
112.
Zhu  Zhu  Zhang  Luoyan  Gao  Lexuan  Tang  Shaoqing  Zhao  Yao  Yang  Ji 《Tree Genetics & Genomes》2016,12(1):1-10
Tree Genetics &; Genomes - To breed a new variety of coffee (Coffea arabica) requires approximately 25&;nbsp;years due to the long generation time (5–6&;nbsp;years) of this perennial...  相似文献   
113.
Sun W  Xing B  Sun Y  Du X  Lu M  Hao C  Lu Z  Mi W  Wu S  Wei H  Gao X  Zhu Y  Jiang Y  Qian X  He F 《Molecular & cellular proteomics : MCP》2007,6(10):1798-1808
Hepatocellular carcinoma (HCC) is a highly malignant tumor, and chronic infection with hepatitis B virus is one of its major risk factors. To identify the proteins involved in HCC carcinogenesis, we used two-dimensional fluorescence DIGE to study the differentially expressed proteins in tumor and adjacent nontumor tissue samples. Samples from 12 hepatitis B virus-associated HCC patients were analyzed. A total of 61 spots were significantly up-regulated (ratio >/= 2, p 相似文献   
114.
Paek  Hyo-Jin  Luo  Zhao-Bo  Choe  Hak-Myong  Quan  Biao-Hu  Gao  Kai  Han  Sheng-Zhong  Li  Zhou-Yan  Kang  Jin-Dan  Yin  Xi-Jun 《Transgenic research》2021,30(5):663-674
Transgenic Research - Herein, we investigate the high incidence of umbilical hernia and tippy-toe standing and their underlying changes in gene expression and proliferation in myostatin knockout...  相似文献   
115.
Isaria fumosorosea is one of important entomopathogenic fungi showed a good potential in controlling Bemisia tabaci. The effects of I. fumosorosea Ifchit1 mutant (Ifchit1 gene deletion mutant) on the mortality, oviposition, and host immunological response of B. tabaci, on Brassica campestris L. plant, were evaluated under laboratory conditions. The wild-type fungal strain infection significantly increased insect mortality and reduced the oviposition effeciency of B. tabaci, whereas the Ifchit1 mutant was much less effective, resulting in higher survival and ovipositing of B. tabaci. The activities of four insect enzymes were examined during a time course of fungal infection. Insect phenoloxidase, perioxidase, and catalase activities were decreased in whiteflies treated with the wild type and mutant I. fumosorosea strain at 12–36?h post treatment. However, these enzyme activities increased in fungal-treated whiteflies as compared to controls between 36 and 60?h post-infection, reaching peak values. Superoxide dismutase activity in fungal-treated whiteflies was higher than that in controls during the entire experimental time course examined. The overall enzyme activity profiles in Ifchit1 mutant-treated whiteflies were significantly different from wild-type strain treatments. Our results showed that loss of the Ifchit1 gene in I. fumosorosea affects whitefly mortality, ovipositioning and various antioxidant enzyme activities, providing new insights into the role of chitinases in I. fumosorosea-insect host–pathogen interactions.  相似文献   
116.
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   
117.
118.
Bocaviruses are associated with many human infectious diseases, such as respiratory tract infections, gastroenteritis, and hepatitis. Rats are known to be reservoirs of bocaviruses, including rodent bocavirus and rat bocavirus. Recently, ungulate bocaparvovirus 4, a known porcine bocavirus, has also been found in rats. Thus, investigating bocaviruses in rats is important for determining the origin of the viruses and preventing and controlling their transmission. To the best of our knowledge, no study to date has investigated bocaviruses in the livers of rats. In this report, a total of 624 rats were trapped in southern China between 2014 and 2017. Liver and serum samples from rats were tested for the prevalence of bocaviruses using PCR. Sequences related to ungulate bocaparvovirus 4 and rodent bocavirus were detected in both liver and serum samples. Interestingly, the prevalence of ungulate bocaparvovirus 4 (reference strain:KJ622366.1) was higher than that of rodent bocavirus (reference strain:KY927868.1) in both liver (2.24% and 0.64%, respectively) and serum samples (2.19% and 0.44%, respectively). The NS1 regions of ungulate bocaparvovirus 4 and rodent bocavirus related sequences displayed over 84% and 88% identity at the nucleic acid and amino acid levels, respectively. Furthermore, these sequences had similar genomic structure, genomic features, and codon usage bias, and shared a common ancestor. These viruses also displayed greater adaptability to rats than pigs. Our results suggested that ungulate bocaparvovirus 4 and rodent bocavirus may originate from rats and may be different genotypes of the same bocavirus species.  相似文献   
119.
120.
Most aerobic granule cultivation has been based on the sequencing batch reactor (SBR) and then the factors that affect aerobic granulations were developed in the SBR. However, little work has been done to cultivate aerobic granules in a continuous-flow bioreactor with simple structure that is realistic for engineering. This work is the first to cultivate aerobic granules in a continuous flow airlift fluidized bed reactor (CAFB) possesses a very simple structure and without settling time and starvation time controlling. The configuration of CAFB was the simplest continuous-flow aerobic granular bioreactor reported by now. The majority of granules could be formatted in the CAFB after 12 days cultivation. The effluent COD concentration maintained at 50 ± 10 mg/L for the variable COD loading rate of 3.5 g COD/L/d and 4.8 g COD/L/d, which confirmed that the CAFB performed good anti-shock abilities. CAFB performed good nitrification ability, however, little denitrification was found under the operating conditions of this study. The shear stress acting on the solid phase were hundreds of times stronger in the CAFB than in the SBR at the same aeration strength. It seems CAFB is very efficient for granulation due to the strong shear-force exertion, which is promising for continuous-flow aerobic granular bioreactor. Protein, positive to the hydrophobicity, was predominant in extracellular polymeric substances in the granules, and favored the granules formation in the CAFB combined with the polysaccharides. However, filamentous bulking always happened in 35 days operation of the CAFB, thus further study on the stability of this bioreactor is urgently necessary.  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