全文获取类型
收费全文 | 4092篇 |
免费 | 295篇 |
国内免费 | 213篇 |
出版年
2023年 | 62篇 |
2022年 | 76篇 |
2021年 | 95篇 |
2020年 | 102篇 |
2019年 | 107篇 |
2018年 | 102篇 |
2017年 | 112篇 |
2016年 | 111篇 |
2015年 | 101篇 |
2014年 | 156篇 |
2013年 | 335篇 |
2012年 | 132篇 |
2011年 | 139篇 |
2010年 | 106篇 |
2009年 | 185篇 |
2008年 | 239篇 |
2007年 | 239篇 |
2006年 | 177篇 |
2005年 | 174篇 |
2004年 | 172篇 |
2003年 | 146篇 |
2002年 | 117篇 |
2001年 | 105篇 |
2000年 | 66篇 |
1999年 | 71篇 |
1998年 | 78篇 |
1997年 | 60篇 |
1996年 | 65篇 |
1995年 | 73篇 |
1994年 | 61篇 |
1993年 | 59篇 |
1992年 | 60篇 |
1991年 | 49篇 |
1990年 | 40篇 |
1989年 | 56篇 |
1988年 | 54篇 |
1987年 | 43篇 |
1986年 | 38篇 |
1985年 | 59篇 |
1984年 | 74篇 |
1983年 | 39篇 |
1982年 | 53篇 |
1981年 | 37篇 |
1980年 | 36篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 22篇 |
1976年 | 16篇 |
1974年 | 13篇 |
1973年 | 11篇 |
排序方式: 共有4600条查询结果,搜索用时 15 毫秒
1.
2.
R. Mioso F.J. Toledo Marante I. Herrera Bravo de Laguna 《Journal of applied microbiology》2015,118(4):781-791
This is a comprehensive review, with 114 references, of the chemical diversity found in the fungus Penicillium roqueforti. Secondary metabolites of an alkaloidal nature are described, for example, ergot alkaloids such as festuclavine, isofumigaclavines A and B, and diketopiperazine alkaloids such as roquefortines A–D, which are derived from imidazole. Other metabolites are marcfortines A–C, PR‐toxin, eremofortines A–E, mycophenolic and penicillic acids, and some γ‐lactones. Also, recent developments related to the structural characteristics of botryodiplodin and andrastin are studied—the latter has anticancer properties. Finally, we discuss the enzymes of P. roqueforti, which can participate in the biotechnological production of high value‐added molecules, as well as the use of secondary metabolite profiles for taxonomic purposes. 相似文献
3.
Larval cuticle ofHelicoverpa (Heliothis)zea and yeast extract added to a minimal medium (MM) induced germination of conidia ofNomuraea rileyi whereas sterile distilled water or MM alone did not. Yeast extract increased mycelial yield, but when cuticle was added, mycelial yield significantly decreased. Proteases and chitinases ofN. rileyi were only expressed when cuticle was added to the MM.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by US Department of Agriculture. 相似文献
4.
An investigation on the influence of lead toxicity on some of the hepatic enzymes was studied in rats both after a shorter
interval of 15 d and after longer intervals of 60 and 90 d. Three different doses of lead as 5, 10, and 50 mg/kg body wt were
administered orally on every alternate day. Whereas significant inhibition of succinic dehydrogenase was seen following lead
poisoning, the activity acid and alkaline phosphatase increased with lead intoxication. The histoarchitecture of the liver
was grossly intact. Liver accumulated less lead compared to kidney at 60 and 90 d. 相似文献
5.
目的研究复合微生态制剂对幼刺参体壁营养成分、几种消化酶和免疫酶活力的影响。方法在封闭式循环系统中投喂不同的微生态制剂进行30 d刺参养殖实验。结果投喂液态复合微生态制剂组和粉状复合微生态制剂组的刺参体壁的粗脂肪、总糖、粗蛋白含量最高,两组与对照组相比差异有统计学意义(Ps0.05)。添加微生态制剂的3个实验组刺参肠道蛋白酶、淀粉酶活力均比对照组高,且差异有统计学意义(Ps0.05)。实验组刺参的肠道、体壁、体液过氧化氢酶活力均比对照组高,其中投喂液态复合微生态制剂实验组活力最高。实验组刺参组织的酸性磷酸酶和碱性磷酸酶活力也明显高于对照组(与对照组相比差异有统计学意义,Ps0.05)。结论微生态制剂可以有效改善幼刺参体壁营养成分,促进机体消化活力,提高刺参免疫力。 相似文献
6.
为探究自噬抑制剂6-氨基-3-甲基腺嘌呤(3-methyladenine,3-MA)对损伤细胞氧化应激水平的影响,将3-MA作用于H2O2诱导的PC12细胞损伤模型,以自噬增强剂雷帕霉素(rapamycin,Rap)作为对照,探讨自噬与氧化应激的关系。测定线粒体的膜电位和细胞内的活性氧(reactive oxygen species, ROS)与丙二醛(malondialdehyde, MDA)含量,以及超氧化物歧化酶(superoxide dismutase,SOD)和过氧化氢酶(catalase,CAT)活性,评价损伤细胞的氧化应激状态。单丹(磺)酰戊二胺(monodansylcadaverine,MDC)染色,观察损伤细胞的自噬情况。蛋白质印迹分析损伤细胞中的自噬相关蛋白质LC3-II/LC3-I比值变化。实验结果显示:与正常组相比,H2O2损伤细胞的ROS水平上升到正常组的141%,MDA含量增加(P<0.001);CAT与SOD酶活力显著降低(P<0.001),差异均有统计学意义,证明损伤细胞氧化应激水平增加;MDC染色结果表明,H2O2组自噬明显增加。Western印迹结果表明,LC3-II/LC3-I值显著升高(P<0.05);与损伤组相比,3-MA组MDC染色结果表明,自噬水平降低。Western印迹结果表明,LC3-II/LC3-I值下降;细胞内ROS水平升高,增加到正常组的208%。MDA含量增加(P<0.001),CAT、SOD酶活力降低(P<0.001)。综上结果表明,自噬抑制剂可增加H2O2诱导的PC12细胞损伤模型的氧化应激水平,增加细胞凋亡。 相似文献
7.
沼泽、盐化沙丘过渡带和沙丘生境下芦苇的光合及生理生化特性 总被引:1,自引:0,他引:1
对于田地区3种不同生境(沼泽、盐化沙丘过渡带和沙丘顶)芦苇的生长环境特征、光合特性、渗透调节及抗氧化系统的特征进行研究。结果表明:芦苇叶片的Pn日变化在沼泽生境呈单峰曲线,在盐化沙丘过渡带和沙丘顶部均为双峰曲线,光合"午休"现象明显,气孔导度降低是其主要原因。脯氨酸和可溶性糖含量随根区土壤水分减少和盐分加剧增加显著,其中可溶性糖含量变化剧烈,对抵御干旱和盐渍化危害的贡献较大。芦苇叶片超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性随干旱及盐分加剧增加显著,两者对水分亏缺的响应较盐分敏感,且可有效缓解沙丘生境由于缺水所造成的氧化损伤,使丙二醛(MDA)含量维持在相对较低水平。过氧化物酶(POD)活性在沙丘和盐渍化生境内都比较高,对抵抗盐渍化和干旱起着同样重要的作用。 相似文献
8.
Physiological and biochemical parameters for evaluation and clustering of rice cultivars differing in salt tolerance at seedling stage 总被引:1,自引:0,他引:1
《Saudi Journal of Biological Sciences》2016,23(4):467-477
Salinity tolerance levels and physiological changes were evaluated for twelve rice cultivars, including four white rice and eight black glutinous rice cultivars, during their seedling stage in response to salinity stress at 100 mM NaCl. All the rice cultivars evaluated showed an apparent decrease in growth characteristics and chlorophyll accumulation under salinity stress. By contrast an increase in proline, hydrogen peroxide, peroxidase (POX) activity and anthocyanins were observed for all cultivars. The K+/Na+ ratios evaluated for all rice cultivars were noted to be highly correlated with the salinity scores thus indicating that the K+/Na+ ratio serves as a reliable indicator of salt stress tolerance in rice. Principal component analysis (PCA) based on physiological salt tolerance indexes could clearly distinguish rice cultivars into 4 salt tolerance clusters. Noteworthy, in comparison to the salt-sensitive ones, rice cultivars that possessed higher degrees of salt tolerance displayed more enhanced activity of catalase (CAT), a smaller increase in anthocyanin, hydrogen peroxide and proline content but a smaller drop in the K+/Na+ ratio and chlorophyll accumulation. 相似文献
9.
Toshio Sugimoto Tsutomu Kawasaki Tomohiko Kato Robert F. Whittier Daisuke Shibata Yukio Kawamura 《Plant molecular biology》1992,20(4):743-747
A full-length cDNA encoding a subunit of phosphoenolpyruvate carboxylase (PEPC) was isolated from a developing seed expression library of the C3 plant Glycine max. The corresponding mRNA is present at similar levels in leaf, stem, root and developing seed. Two potential start codons exist, and the activity of protein initiated from the first such codon could be subject to regulation by protein kinase. Sequence comparison shows a similar upstream start codon in the case of the Ppc2 gene from Mesembryanthemum crystallinum, previously assumed to lack the sequences necessary for phosphorylation. The soybean encoded protein tends to resemble other C3-type PEPC proteins more closely than those implicated in C4 or crassulacean acid metabolism. 相似文献
10.
Lin Jie Zhang Zhao Li Wu Kuan Fu Wang Qun Liu Hua Mei Zhuang Gang Wu 《Ecology and evolution》2015,5(2):515-530
Fitness costs associated with resistance to insecticides have been well documented, usually at normal temperature conditions, in many insect species. In this study, using chlorpyrifos‐resistant homozygote (RR) and chlorpyrifos‐susceptible homozygote (SS) of resistance ace1 allele of Plutella xylostella (DBM), we confirmed firstly that high temperature experience in pupal stage influenced phenotype of wing venation in insecticide‐resistant and insecticide‐susceptible Plutella xylostella, and SS DBM showed significantly higher thermal tolerance and lower damages of wing veins under heat stress than RR DBM. As compared to SS DBM, RR DBM displayed significantly lower AChE sensitivity to chlorpyrifos, higher basal GSTs activity and P450 production at 25°C, but higher inhibitions on the enzyme activities and P450 production as well as reduced resistance to chlorpyrifos under heat stress. Furthermore, RR DBM displayed significantly higher basal expressions of hsp69s, hsp72s, hsp20, hsp90, Apaf‐1, and caspase‐7 at 25°C, but lower induced expressions of hsps and higher induced expressions of Apaf‐1, caspase‐9, and caspase‐7 under heat stress. These results suggest that fitness costs of chlorpyrifos resistance in DBM may partly attribute to excess consumption of energy caused by over production of detoxification enzymes and hsps when the proteins are less demanded at conducive environments but reduced expressions when they are highly demanded by the insects to combat environmental stresses, or to excess expressions of apoptotic genes under heat stress, which results in higher apoptosis. The evolutionary and ecological implications of these findings at global warming are discussed. 相似文献