全文获取类型
收费全文 | 8869篇 |
免费 | 1422篇 |
国内免费 | 3667篇 |
出版年
2024年 | 55篇 |
2023年 | 242篇 |
2022年 | 359篇 |
2021年 | 439篇 |
2020年 | 413篇 |
2019年 | 444篇 |
2018年 | 288篇 |
2017年 | 311篇 |
2016年 | 323篇 |
2015年 | 462篇 |
2014年 | 689篇 |
2013年 | 581篇 |
2012年 | 823篇 |
2011年 | 759篇 |
2010年 | 653篇 |
2009年 | 617篇 |
2008年 | 723篇 |
2007年 | 685篇 |
2006年 | 614篇 |
2005年 | 543篇 |
2004年 | 417篇 |
2003年 | 376篇 |
2002年 | 294篇 |
2001年 | 316篇 |
2000年 | 299篇 |
1999年 | 235篇 |
1998年 | 132篇 |
1997年 | 103篇 |
1996年 | 68篇 |
1995年 | 69篇 |
1994年 | 40篇 |
1993年 | 49篇 |
1992年 | 76篇 |
1991年 | 90篇 |
1990年 | 85篇 |
1989年 | 100篇 |
1988年 | 69篇 |
1987年 | 80篇 |
1986年 | 77篇 |
1985年 | 76篇 |
1984年 | 45篇 |
1983年 | 66篇 |
1982年 | 53篇 |
1981年 | 52篇 |
1979年 | 41篇 |
1978年 | 43篇 |
1976年 | 52篇 |
1973年 | 37篇 |
1972年 | 46篇 |
1971年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
973.
利用触角电位和嗅觉测定技术,比较分析松墨天牛Monochamus alternatus Hope对马尾松(Pinus massoniana Lamb)健康和松材线虫危害的枝条挥发物的触角电位和行为反应特点。实验结果表明:未交配松墨天牛对健康枝条挥发物的EAG反应值大于被害枝条的,交配后天牛对被害枝条的EAG反应值明显大于健康枝条的。在“Y”型嗅觉仪中,未交配天牛对健康枝条挥发物表现为正趋性,对被害枝条挥发物表现为负趋性,而交配后天牛对被害枝条挥发物表现为正趋性,对健康枝条挥发物表现为负趋性。说明不同发育时期的松墨天牛成虫对不同生理状态的寄主具有不同的敏感性和选择性。 相似文献
974.
975.
1植物名称红肉苹果[Malus pumila var.niedzwet- zkyana(Dieck)Schneid]。2材料类别春梢幼嫩茎段。3培养条件MS为基本培养基,(1)芽诱导培养基:MS 6-BA 0.2mg·L~(-1)(单位下同) NAA 0.2;(2)芽增殖培养基:MS 6-BA 0.5 NAA 0.5:(3)生根培养基:1/2MS IBA 0.1 NAA 0.1。以上培养基中均加入5.5 g·L~(-1)琼脂粉和30g·L~(-1)蔗糖,pH 5.8; 相似文献
976.
977.
978.
The green tea compound, (-)-epigallocatechin-3-gallate downregulates N-cadherin and suppresses migration of bladder carcinoma cells 总被引:1,自引:0,他引:1
Rieger-Christ KM Hanley R Lodowsky C Bernier T Vemulapalli P Roth M Kim J Yee AS Le SM Marie PJ Libertino JA Summerhayes IC 《Journal of cellular biochemistry》2007,102(2):377-388
Green tea has been reported as potential dietary protection against numerous cancers and has been shown to have activity in bladder tumor inhibition in different animal models. The goal of this study was to examine the effects of (-)-epigallocatechin gallate (EGCG-the major phytochemical in green tea) on growth inhibition and behavior of human bladder carcinoma cells and to identify the altered signaling pathway(s) underlying the response to EGCG exposure. EGCG inhibited the in vitro growth of invasive bladder carcinoma cells with an IC(50) range of 70-87 microM. At a concentration of 20 microM, EGCG decreased the migratory potential of bladder carcinoma cells with concomitant activation of p42/44 MAPK and STAT3 and inactivation of Akt. Using biochemical inhibitors of MAPK/ERK, and siRNA to knockdown STAT3 and Akt, inhibition of migration was recorded associated with Akt but not MAPK/ERK or STAT3 signaling in bladder cells. In addition, EGCG downregulated N-cadherin in a dose-dependent manner where reduction in N-cadherin expression paralleled declining migratory potential. Continuous feeding of EGCG to mice prior to and during the establishment of bladder carcinoma xenografts in vivo revealed >50% reduction in mean final tumor volume (P = 0.05) with no detectable toxicity. EGCG inhibited bladder carcinoma cell growth and suppressed the in vitro migration capacity of cells via downregulation of N-cadherin and inactivation of Akt signaling. Continuous administration of EGCG to mice revealed significant inhibition of tumor growth in vivo indicating a possible preventative role for green tea in bladder cancer. 相似文献
979.
Pimentel-Schmitt EF Thomae AW Amon J Klieber MA Roth HM Muller YA Jahreis K Burkovski A Titgemeyer F 《Journal of molecular microbiology and biotechnology》2007,12(1-2):75-81
Carbon metabolism and regulation is poorly understood in mycobacteria, a genus that includes some major pathogenic species like Mycobacterium tuberculosis and Mycobacterium leprae. Here, we report the identification of a glucose kinase from Mycobacterium smegmatis. This enzyme serves in glucose metabolism and global carbon catabolite repression in the related actinomycete Streptomyces coelicolor. The gene, msmeg1356 (glkA), was found by means of in silico screening. It was shown that it occurs in the same genetic context in all so far sequenced mycobacterial species, where it is located in a putative tricistronic operon together with a glycosyl hydrolase and a putative malonyl-CoA transacylase. Heterologous expression of glkA in an Escherichia coli glucose kinase mutant led to the restoration of glucose growth, which provided in vivo evidence for glucose kinase function. GlkA(Msm) was subsequently overproduced in order to study its enzymatic features. We found that it can form a dimer and that it efficiently phosphorylates glucose at the expense of ATP. The affinity constant for glucose was with 9 mM about eight times higher and the velocity was about tenfold slower when compared to the parallel measured glucose kinase of S. coelicolor. Both enzymes showed similar substrate specificity, which consists in an ATP-dependent phosphorylation of glucose and no, or very inefficient, phosphorylation of the glucose analogues 2-deoxyglucose and methyl alpha-glucoside. Hence, our data provide a basis for studying the role of mycobacterial glucose kinase in vivo to unravel possible catalytic and regulatory functions. 相似文献