全文获取类型
收费全文 | 4873篇 |
免费 | 184篇 |
国内免费 | 784篇 |
专业分类
5841篇 |
出版年
2024年 | 11篇 |
2023年 | 51篇 |
2022年 | 100篇 |
2021年 | 103篇 |
2020年 | 124篇 |
2019年 | 122篇 |
2018年 | 105篇 |
2017年 | 138篇 |
2016年 | 121篇 |
2015年 | 126篇 |
2014年 | 153篇 |
2013年 | 482篇 |
2012年 | 168篇 |
2011年 | 208篇 |
2010年 | 193篇 |
2009年 | 303篇 |
2008年 | 338篇 |
2007年 | 341篇 |
2006年 | 263篇 |
2005年 | 285篇 |
2004年 | 255篇 |
2003年 | 206篇 |
2002年 | 179篇 |
2001年 | 168篇 |
2000年 | 158篇 |
1999年 | 132篇 |
1998年 | 110篇 |
1997年 | 117篇 |
1996年 | 83篇 |
1995年 | 83篇 |
1994年 | 98篇 |
1993年 | 82篇 |
1992年 | 63篇 |
1991年 | 45篇 |
1990年 | 45篇 |
1989年 | 38篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 35篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1972年 | 1篇 |
排序方式: 共有5841条查询结果,搜索用时 15 毫秒
31.
32.
本研究利用聚合酶链式反应技术,成功地克隆了枯草芽孢杆菌缺陷型原噬菌体PBSX阻遏基因及其温度敏感型等位基因。核苷酸序列分析发现,野生型及其温度敏感型阻遏基因之间的碱基变异较大,但却存在几乎完全相同的开放读框,尤其是开放读框orfⅠ,可能编码着113个氨基酸的阻遏蛋白,并且还推定了开放读框的启动区和核糖体结合位点。通过互补实验,证实了野生型阻遏基因的产物能够抑制温度诱导PBSX原噬菌体,表明克隆的基因有着正常的生物活性。 相似文献
33.
苏芸金杆菌液体深层发酵中用营养体接种二级发酵工艺和用二级发酵初期培养物作种子进行三级发酵工艺是可行的。试验结果表明:二级发酵种子罐营养体最佳移种茵龄为9h左右,此时营养体数量多、整齐、染色均匀,显微镜下菌体有折光点存在,三级接种营养体菌龄约为4h左右,菌体数量多,同步率高,少量染色不均匀。发酵液含菌数和发酵产品毒力均达到芽抱接种相同水平,但生产周期明显缩短4-5h,因此相应提高发酵罐生产能力20%。 相似文献
34.
TwoApium graveolens var.rapaceum (L.) cultivars that differ in their suitability for the survival and growth ofSpodoptera exigua (Hübner) andTrichoplusia ni (Hübner) were used to examine the effect of genetic and seasonal environmental variation in host plant suitability on the
efficacy ofBacillus thuringiensis subsp.kurstaki (Berliner). The effects of host plant genotype andB. thuringiensis were generally independent, so thatB. thuringiensis efficacy was greatest on the resistant host plant cultivar. Host plant suitability varied within growing season for both
insect species but, while host plant suitability decreased with increasing plant age forT. ni, the response ofS. exigua to plant age was not as clear. Within season variation in host plant suitability affectedB. thuringiensis efficacy and the interaction betweenB. thuringiensis and host plant cultivar forS. exigua but not forT. ni. Soluble protein and Folin-Denis phenolic concentrations of host plant tissue were not correlated with changes in host plant
suitability to either insect species. 相似文献
35.
Stabilization of the phosphorylated form of Bacillus subtilis DegU caused by degU9 mutation 总被引:1,自引:0,他引:1
Abstract A Bacillus subtilis response regulator, DegU9, carrying an amino acid alteration caused by the degU9 (Hy) mutation was partially purified, and phosphorylation and dephosphorylation of the protein was studied. The extent of phosphorylation was not as high as the level attained with wild-type DegU, but the DegU9-phosphate once formed was more stable than the wild-type DegU-phosphate. An in vivo study with a degU9 mutant showed that degS was necessary for the overproduction of exoproteases. These results suggest that phosphorylation is necessary for the mutant DegU9 to exert its effect and that the higher stability of phosphorylated DegU9 is responsible for the overproulation phenotype. 相似文献
36.
The oxidative stress response in Bacillus subtilis 总被引:9,自引:0,他引:9
Barbara C.A. Dowds 《FEMS microbiology letters》1994,124(3):255-263
Abstract Bacillus subtilis undergoes a typical bacterial stress response when exposed to low concentrations (0.1 mM) of hydrogen peroxide. Protection is thereby induced against otherwise lethal, challenge concentrations (10 mM) of this oxidant and a number of proteins are induced including the scavenging enzymes, catalase and alkyl hydroperoxide reductase, and a putative DNA binding and protecting protein. Induced protection against higher concentrations (10–30 mM) of hydrogen peroxide is eliminated in a catalase-deficient mutant. Both RecA and Spo0A influence the basal but not the induced resistance to hydrogen peroxide. A regulatory mutation has been characterized that affects the inducible phenotype and is constitutively resistant to high concentrations of hydrogen peroxide. This mutant constitutively overexpresses the proteins induced by hydrogen peroxide in the wild-type. The resistance of spores to hydrogen peroxide is partly attributable to binding of small acid soluble proteins by the spore DNA and partly to a second step which coincides with the depletion of the NADH pool, which may inhibit the generation of hydroxyl radicals from hydrogen peroxide. 相似文献
37.
38.
The long-term effects of biological agents alone and in combination with monoammonium phosphate on tree growth and fruit production
of apple trees planted on apple replant soil was studied for five years. Application of monoammonium phosphate (MAP) in the
year of planting increased shoot growth, cross-sectional trunk area and fruit yield of McIntosh on M.26 rootstock for the
first two years. The application of bacterial agents alone were not effective in increasing young tree growth except BACT-1
in 1987. None of the bacterial agents increased fruit yield when applied alone. The addition of certain bacterial agents to
MAP application increased young tree growth in various years. The combination of bacterial agent B-10 and MAP reduced young
tree growth and yield compared with the MAP treatment alone. These results suggest that the application of MAP alone may be
sufficient to alleviate the replant problem and the addition of BACT-1, EBW-4 or B8 bacterial agents to this treatment may
be beneficial to increase tree growth in some years.
Contribution number 822.
Contribution number 822. 相似文献
39.
40.
以棉铃虫初孵幼虫为供试虫,用合成饲料和天然饲料两种饲毒法,CS3ab-1991(毒力效价Ha 15000IU/mg)为标准品对Bt 8010粉剂进行毒力测定,饲毒后的供试虫在30℃恒温下培育72小时,合成饲料饲毒法测定的CS3ab-1991 LC50=108.6±10.8μg/ml,Bt8010 LC50=197.1±15.6μg/ml,毒力效价8273.1±715.8Ha IU/mg,天然饲料饲毒法测定的CS3ab-1991 LC50=406.3±47.5μg/ml,Bt8010 LC50=705.0±86.8μg/ml,毒力效价8633.2±871.8Ha IU/mg。 相似文献