全文获取类型
收费全文 | 6429篇 |
免费 | 785篇 |
国内免费 | 483篇 |
出版年
2023年 | 74篇 |
2022年 | 97篇 |
2021年 | 282篇 |
2020年 | 206篇 |
2019年 | 311篇 |
2018年 | 259篇 |
2017年 | 230篇 |
2016年 | 267篇 |
2015年 | 362篇 |
2014年 | 428篇 |
2013年 | 490篇 |
2012年 | 555篇 |
2011年 | 506篇 |
2010年 | 307篇 |
2009年 | 261篇 |
2008年 | 329篇 |
2007年 | 271篇 |
2006年 | 266篇 |
2005年 | 213篇 |
2004年 | 176篇 |
2003年 | 190篇 |
2002年 | 154篇 |
2001年 | 133篇 |
2000年 | 130篇 |
1999年 | 109篇 |
1998年 | 66篇 |
1997年 | 40篇 |
1996年 | 47篇 |
1995年 | 42篇 |
1994年 | 43篇 |
1993年 | 30篇 |
1992年 | 43篇 |
1991年 | 59篇 |
1990年 | 43篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 33篇 |
1984年 | 40篇 |
1983年 | 38篇 |
1982年 | 25篇 |
1979年 | 26篇 |
1977年 | 18篇 |
1976年 | 23篇 |
1975年 | 19篇 |
1974年 | 26篇 |
1973年 | 29篇 |
1972年 | 20篇 |
1971年 | 19篇 |
排序方式: 共有7697条查询结果,搜索用时 16 毫秒
51.
52.
超干处理对几种芸苔属植物种子生理生化和细胞超微结构的效应 总被引:1,自引:0,他引:1
几种芸苔属植物种子经过超干处理后,发芽力和活力不受影响,耐藏性大为提高。超干及老化后种子的脱氢酶、超氧物歧化酶、过氧化物酶、过氧化氢酶等酶系统保持完好;丙二醛和挥发性醛类物质等劣变产物相应减少;电导率测定表明,细胞膜系统的完整性良好;透射电镜(TEM)和扫描电镜(SEM)观察表明,细胞超微结构及功能保持完好。不同干燥方法和不同干燥剂的系列实验证实,生石灰的脱水效果并不亚于冰冻真空干燥法,且经济实用。 相似文献
53.
聚乙二醇处理大豆种子子叶中几种酶活性和可溶性蛋白含量的变化 总被引:5,自引:0,他引:5
聚乙二醇处理的大豆种子的异柠檬酸裂解酶、苹果酸脱氢酶、过氧化氢酶、超氧物歧化酶、酸性磷酸酶、碱性磷酸酶的活性明显高于受低温吸胀冷害的种子子叶的活性,相关的酶活性协同地增长,而蛋白质的含量没有明显的变化。这些酶活性的提高可能是渗透调控处理对细胞膜系统修补的结果。 相似文献
54.
Susceptibility of insecticide-susceptible and wild house flies (Diptera: Muscidae) to abamectin on whitewashed and unpainted wood 总被引:2,自引:0,他引:2
C J Geden D C Steinkraus S J Long D A Rutz W L Shoop 《Journal of economic entomology》1990,83(5):1935-1939
Unpainted plywood panels treated with 0.1% abamectin (avermectin B1) provided greater than 90% control of house flies, Musca domestica L., susceptible to insecticides for 4 wk and greater than 70% control for 7 wk compared with 46-92% control observed with permethrin at the same time and rate of application. Efficacy of abamectin on whitewashed panels was similar to that observed on unpainted panels, whereas permethrin was ineffective on whitewashed panels at all rates tested (range, 0.001-0.1%) at all intervals after treatment. Bioassays of newly colonized house flies resistant to permethrin indicated that wild populations may be cross-resistant to abamectin. 相似文献
55.
Two clones have been isolated from a genomic library of the moss Physcomitrella patens and a cDNA library of the halotolerant green alga Dunaliella salina. The isolates contain genes coding for the major light-harvesting chlorophyll-a/b-binding protein (CAB) in the photosystem II (PSII) light-harvesting complex (LHCII). The 2544-bp insert of the moss genomic clone contains the complete CAB-coding region and 5' and 3' flanking sequences. The coding region contains an intron of 359 bp which is spanned by a pair of 9-bp perfect direct repeats. There are two CCAAT boxes and five enhancer-like elements related to (G)TGGTTTAAA(G) (Weiher et al., 1983) residing in the intron. Comparisons of the moss cab gene with sequences of light-inducible genes of higher plants reveal homologous and repeated sequences similar to the enhancer element in the 5' region upstream from the TATA and CCAAT boxes thought to be responsive to light inducibility. The 1256-bp algal cDNA contains the complete CAB-coding sequence, a 170-bp 5'-nontranslated region, and a 264-bp 3'-nontranslated region. While the overall homology in the nontranslated regions is low between the cab gene of the moss and that of the alga, the 3'-nontranslated regions of the two contain some sequences that are conserved among the cab genes in higher plants. The deduced amino acid sequences of these two clones are highly conserved except for the N-terminal region. Their hydropathic plots are very similar and both possess three hydrophobic segments that are likely alpha-helical transmembrane segments. The proposed CAB transit peptide sequence of the alga is divergent from that of the moss or higher plants, suggesting that they may have evolved from different origins. Southern blot analysis shows that the cab genes in the moss and the alga, as in higher plants, are encoded by a number of homologous genes constituting a multigene family. 相似文献
56.
Prostaglandin E2, when infused into the renal artery of the dog, is a vasodilator and increases both renal interstitial hydrostatic pressure and sodium excretion. Similar studies in the rat, however, have been inconclusive. The present study examined the effect of prostaglandin E2 infusion into the renal interstitium, by means of a chronically implanted matrix, on renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat. Prostaglandin E2 was continuously infused directly into the kidney interstitium to mimic endogenous prostaglandin E2 production by renal cells. The maximum change in each of these parameters occurred when 10(-5) M PGE2 was infused. Renal blood flow increased from 4.70 +/- 0.91 to 5.45 +/- 0.35 ml/min (p less than 0.05) while renal interstitial hydrostatic pressure decreased from 3.9 +/- 0.4 to 2.6 +/- 0.5 mmHg (p less than 0.05) and fractional excretion of sodium decreased from 1.02 +/- 0.20 to 0.61 +/- 0.12% (p less than 0.05). Thus, the present study demonstrates that renal interstitial infusion of prostaglandin E2 increases total renal blood flow but decreases both renal interstitial hydrostatic pressure and urinary sodium excretion in the rat. 相似文献
57.
What is the relationship between the endothelium derived relaxant factor and nitric oxide? 总被引:4,自引:0,他引:4
Nitric oxide gas in solution (NO) relaxes blood vessels with similar actions and pharmacodynamics as the endothelium derived relaxant factor (EDRF) and has been proposed to be a component of the materials released from stimulated endothelial cells. Certain data however suggest that EDRF and NO may not be identical. In some non-vascular smooth muscles, NO and EDRF exhibit markedly different pharmacologic profiles. Furthermore the interaction of EDRF and NO with anion exchange resins differ. The hypothesis that EDRF is identical to nitric oxide gas in solution or a nitrogen oxide containing compound is discussed. 相似文献
58.
粉纹夜蛾(Trichoplusia ni)核型多角体病毒(TnNPV)感染草地贪夜蛾(Spodop-tera frugiperda)细胞后能诱导提高胸苷激酶的活性。不论是正常或感染细胞中的胸苷激酶都可将脱氧胞苷磷酸化,酶活最适pH及Mg~( )离子浓度值基本相同,DEAE-纤维素和Cibacron blue-sepharose柱层析所得酶活性图谱亦相似。TnNPV在胸苷激酶缺陷型的草地贪夜蛾细胞中能正常复制,但被感染细胞不具有胸苷激酶活性。由此可以确定,经TnNPV感染诱导后,活性有所提高的胸苷激酶不是病毒基因编码的。 相似文献
59.
60.
Use of green fluorescent protein to visualize the early events of symbiosis between Rhizobium meliloti and alfalfa (Medicago sativa). 总被引:10,自引:0,他引:10 下载免费PDF全文
A gene encoding a variant of green fluorescent protein (GFP) of Aequorea victoria was put under the control of a promoter which is constitutive in Rhizobium meliloti. The heterologous GFP gene was expressed at high levels during all stages of symbiosis, allowing R. meliloti cells to be visualized as they grew in the rhizosphere, on the root surface, and inside infection threads. In addition, nodules that were infected with bacteria which were synthesizing GFP fluoresced when illuminated with blue light. GFP-tagged bacteria could be seen inside infection threads, providing the opportunity to measure the growth rate and determine the patterns of growth of R. meliloti residing inside its host plant. 相似文献