全文获取类型
收费全文 | 594篇 |
免费 | 39篇 |
国内免费 | 194篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 18篇 |
2015年 | 25篇 |
2014年 | 35篇 |
2013年 | 55篇 |
2012年 | 70篇 |
2011年 | 78篇 |
2010年 | 46篇 |
2009年 | 49篇 |
2008年 | 62篇 |
2007年 | 53篇 |
2006年 | 44篇 |
2005年 | 42篇 |
2004年 | 34篇 |
2003年 | 27篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有827条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
以栽培的2年生细叶百合(Lilium pumilum)为材料,于2000年的生长季从蕾期至种子成熟期进行6次取样,对其各器官生物量和氮、磷元素的配置进行了动态研究。结果表明,细叶百合虽然以种子繁殖为主,但在整个生长季用于生殖器官的生物量投资的比例并不很大,大量干物质分配到地下器官鳞茎中(平均为60.17%);茎、叶的生物量分配比例仅次于鳞茎;雄蕊生物量分配比例明显高于雌蕊。在叶萌动及展叶初期植株全氮百分含量最高;从春季萌动至秋季果实成熟,叶中的氮呈逐渐递减的趋势;茎和生殖器官的全氮含量在蕾期最大;生殖器官与叶、鳞茎的全氮含量相关显著。磷在生殖器官的含量较高,这与磷在植物有性生殖过程中的重要作用相一致;生殖器官与茎的全磷含量相关显著。地下器官全氮、全磷随季节变化有增多的趋势;地上各器官全氮、全磷相关显著,随季节变化有明显减少的趋势。 相似文献
85.
Jian-Zhong Liu Qian-Ling Zhang Weng Li-Ping Ji Liang-Nian 《Applied Biochemistry and Microbiology》2003,39(5):493-496
The Aspergillus niger strain ZBY-7 was selected as the original strain of glucose-6-phosphate dehydrogenase production. After mutagenesis of the strain by means of UV irradiation and nitrosoguanidine, mutants of Aspergillus niger resistant to a certain metabolic inhibitor were obtained. Five of the mutants showed increased glucose-6-phosphate dehydrogenase production. The mutant resistant to antimycin A (Aspergillus niger AM-23) produced the highest level of glucose-6-phosphate dehydrogenase (695.9% of that produced by the original strain). 相似文献
86.
Increased thermostability and phenol removal efficiency by chemical modified horseradish peroxidase 总被引:3,自引:0,他引:3
Jian-Zhong Liu Hai-Yan Song Li-Ping Weng Liang-Nian Ji 《Journal of Molecular Catalysis .B, Enzymatic》2002,18(4-6):225-232
Horseradish peroxidase was modified by phthalic anhydride and glucosamine hydrochloride. The thermostabilities and removal efficiencies of phenolics by native and modified HRP were assayed. The chemical modification of horseradish peroxidase increased their thermostability (about 10- and 9-fold, respectively) and in turn also increased the removal efficiency of phenolics. The quantitative relationships between removal efficiency of phenol and reaction conditions were also investigated using modified enzyme. The optimum pH for phenol removal is 9.0 for both native and modified forms of the enzyme. Both modified enzyme could suffer from higher temperature than native enzyme in phenol removal reaction. The optimum molar ratio of hydrogen peroxide to phenol was 2.0. The phthalic anhydride modified enzyme required lower dose of enzyme than native horseradish peroxidase to obtain the same removal efficiency. Both modified horseradish peroxidase show greater affinity and specificity of phenol. 相似文献
87.
稻纵卷叶螟CnaphalocrocismodinalisGuen e ,二化螟Chilosuppressalis (Walker)是缙云县水稻生产上的主要害虫 ,近年来发生危害上升 ,产量损失大。目前防治农药以沙蚕毒素类和有机磷农药为主。沙蚕毒素类农药由于使用多年 ,在部分地区治螟效果明显下降 ,而有机磷农药对水生动物和天敌杀伤大 ,会引起稻飞虱再猖獗 ,其副作用较大。为了筛选防治稻纵卷叶螟、二化螟的理想药剂 ,指导当前的治螟工作 ,1 998~ 1 999年 ,作者对新型复配杀虫剂特杀螟进行了应用技术的试验研究 ,现将结果报道如… 相似文献
88.
广西百色和永乐盆地的始新世猪类化石──兼论早期猪类的分类和演化(英文) 总被引:1,自引:0,他引:1
描述了广西百色及永乐盆地发现的中始新世最晚期一晚始新世的猪类化石。这批已知最早的猪超科化石,大大丰富了亚洲地区的早期猪类,对了解全球猪类的早期演化有着重要价值。广西的材料被确定为两个新属新种:萨氏始新猪Eocenchoerus savagei和广西华夏猪Huaxiachoerus guangxiensis,一个新种:粗壮暹罗猪Siamochoerus viriosus和一个未定属种:Tayassuidae gen.et sp.indet。加上已发表的单尖旅猪Odiochoerus uniconus,百色、永乐盆地共计发现了5种始新世猪类化石。新属Eocenchoerus虽然臼齿结构简单,与原始的古猪类(paiaeochoerid)接近,但因其M3具有一个明显的跟座而被归入猪科。早期猪科动物非常原始的臼齿形式证明,猪科动物的起源并不晚于古猪科(Palaeochoeridae)和西科(Tayassuidae)。旧大陆的古猪类长期以来被认为与新大陆的西类(tayassuid)更为接近,多数学者将其归入西科。笔者认为两者共有的近祖特征,并不能支持它们更近的亲缘关系,而且古猪类缺乏典型西类的近裔特征,因而支持将Pala? 相似文献
89.
Shoot-tips of Rabdosia rubescens, excised from in vitro-grown proliferating shoots that were cold-hardened at 5°C for 3 weeks, were encapsulated in alginate
beads. Subsequently, these were precultured in a mixture of 0.4 M sucrose and 2 M glycerol for 1 h and then desiccated with
silica-gel to about 21% water content prior to freezing in liquid nitrogen. After thawing, about 85% of cryopreserved shoot-tips
grew into true-to-type shoots and with enhanced rooting capacity. Eight single-bud sibling lines were used to assess genetic
stability of these encapsulated shoot-tips. When the relative DNA content was measured by flow cytometry (FCM), no changes
were observed between controls and cryopreserved shoots. Using a sequence-related amplified polymorphism (SRAP) assay, it
was observed that seven out of eight cryopreserved lines showed identical banding patterns; while the eighth line displayed
an absent band, amounting to a low variance rate of 0.01%. These findings suggested that it was necessary to monitor the genetic
stability of recovered cryopreserved R. rubescens shoots. 相似文献
90.
Establishment of the active catalytic domain of human PDGFRbeta tyrosine kinase-based ELISA assay for inhibitor screening 总被引:1,自引:0,他引:1
Zhang XH Guo XN Zhong L Luo XM Jiang HL Lin LP Ding J 《Biochimica et biophysica acta》2007,1770(10):1490-1497
Tyrosine kinases are emerging as frequent targets of primary oncogenic events and therefore represent an optimal focus of therapeutic intervention. In an effort towards therapeutic PDGFR inactivation, we expressed the catalytic domain of PDGFRbeta as a soluble active kinase using Bac-to-Bac expression system, and studied the correlations between PDGFRbeta activity and enzyme concentration, ATP concentration, substrate concentration and divalent cation type. And a convenient, effective and non-radioactive ELISA screening model is then established for identification of the potential inhibitors targeting PDGFRbeta kinase. Of 500 RTK target-based compounds, TKI-30 was identified as a small molecule potential inhibitor of PDGFRbeta (IC(50)=0.34 microM). Further studies indicated that TKI-30 blocked PDGF-BB-induced autophosphorylation of PDGFRbeta in a dose-dependent manner in Swiss 3T3 cells and human umbilical vein smooth muscle cells (HUVSMCs). Moreover, it dose-dependently suppressed the PDGF-BB-induced proliferation in HUVSMCs and tube formation of HUVEC. Our data collectively indicated that PDGFRbeta-based ELISA assay is a new method available for screening inhibitors targeting PDGFRbeta kinase and TKI-30 is a potential novel anti-cancer agent worthy of being further investigated. 相似文献