全文获取类型
收费全文 | 23393篇 |
免费 | 2011篇 |
国内免费 | 2726篇 |
专业分类
28130篇 |
出版年
2024年 | 65篇 |
2023年 | 241篇 |
2022年 | 609篇 |
2021年 | 999篇 |
2020年 | 710篇 |
2019年 | 913篇 |
2018年 | 835篇 |
2017年 | 647篇 |
2016年 | 914篇 |
2015年 | 1452篇 |
2014年 | 1628篇 |
2013年 | 1781篇 |
2012年 | 2213篇 |
2011年 | 1945篇 |
2010年 | 1236篇 |
2009年 | 1108篇 |
2008年 | 1461篇 |
2007年 | 1237篇 |
2006年 | 1211篇 |
2005年 | 1018篇 |
2004年 | 860篇 |
2003年 | 811篇 |
2002年 | 655篇 |
2001年 | 474篇 |
2000年 | 401篇 |
1999年 | 411篇 |
1998年 | 264篇 |
1997年 | 226篇 |
1996年 | 218篇 |
1995年 | 188篇 |
1994年 | 177篇 |
1993年 | 129篇 |
1992年 | 170篇 |
1991年 | 149篇 |
1990年 | 101篇 |
1989年 | 123篇 |
1988年 | 71篇 |
1987年 | 56篇 |
1986年 | 67篇 |
1985年 | 79篇 |
1984年 | 25篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 13篇 |
1980年 | 25篇 |
1979年 | 22篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1974年 | 10篇 |
1972年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
A stable xylan suspension was prepared and characterized. Hydrolysis of the particles converts them into soluble fragments, thereby lowering the turbidity of the suspension. The small volume of the assay mixture, the short incubation time required, and the simplicity of the procedure permit the rapid analysis of many samples. Furthermore, the procedure can be used to assay xylanase activities in the presence of other reducing materials and is also useful for monitoring low-level xylanase activities. 相似文献
32.
借助于5'和3'末端删切后重建的IL-2R a链基因调控区次级克隆,在体外合成有放射性同位素参入的反意义RNA探针与总RNA进行液相杂交,结果表明TPA或PHA分别活化的T细胞在IL-2R a链表达过程中都在不同程度上有选择地利用了调控区内分别为-58(5')和+1(3')位两个转录起始点中3'转录起始点。热休克使PHA活化细胞更明显地利用+1位点。PHA诱导Jurkat细胞表达IL-2RamRNA斑点杂交证实,Jurkat细胞在活化16小时表达IL-2Ra基本达到高峰,至24小时已明显下降。根据这一规律提取PHA诱导活化15小时的Jurkat细胞S100和NE,进行有关结合蛋白的研究,初步结果显示磷酸纤维素柱的KCI洗脱组分中存在着DNA结合蛋白,有关结合蛋白性质的研究正在进行中。 相似文献
33.
九种罕见的人类染色体异常核型报告 总被引:1,自引:1,他引:0
ReportonNineRareSpeciesofHumanChromosomalAbnormalKaryotypesHanWeitian;QuOu;YuPing;JiangMiao(LiaoningResearchInstituteofFamilyPlanning,Shenyang110031)自1983年以来,我们对数千例不育及胚胎丢失等生殖异常患者进行细胞遗传学研究,发现大量异常染色体核型,而且异常种类繁多,已报道世界首报人类异常核型25种[1]。最近,在不良妊娠患者中又发现9种异常核型,经湖南医科大学医学细胞遗传学国家培训中心鉴定,为世界首次报道.现报告如下。1病例摘要及核型例1男,30岁,表型及智力正常,其妻子妊娠两次,均在无任何诱因情… 相似文献
34.
Ping Z. Ding Kunio Kawamura James P. Ferris 《Origins of life and evolution of the biosphere》1996,26(2):151-171
The 5-phosphorimidazolide of uridine reacts on Na+-montmorillonite 22A in aqueous solution to give oligomers as long as 7 mers. The maximum chain length increases to 9 mers and the overall oligomer yield increases when 9:1 ImpU, A5 ppA mixtures react under the same conditions. The oligomer yield and maximum chain length decreases with the structure of the added pyrophosphate in the order A5 ppA>A5 ppU>U5 ppU. Structure analysis of individual oligomer fractions was performed by selective enzymatic hydrolyses followed by HPLC analysis of the products. The regioselectivity for 3,5-bond formation is 80–90% in the 9:1 ImpU, A5 ppA reaction, a percentage comparable to that observed in the 9:1 ImpA, A5 ppA reaction. Oligomerization of ImpU is inhibited by addition of dA5 ppdA, and MeppA. No oligomers containing A5 ppU were products of the 9:1 ImpU, A5 ppA reaction, a finding consistent with the simple addition of the ImpU to the A5 ppA and not the rearrangement of an ImpU-A5 ppA adduct. Concentrations of lysine or arginine which were close to that of the ImpU did not inhibit oligomer formation. Treatment of Na+-montmorillonite with 1 M arginine yielded arginine-montmorillonite, an amino acid-mineral adduct which did not catalyze ImpU oligomerization. Neither the 4–9 mers formed in the 9:1 ImpU, A5 ppA reaction nor the 4–9 mers formed by the base hydrolysis of poly(U) served as templates for the formation of oligo(A)s. 相似文献
35.
36.
APC基因是1991年被发现的一类肿瘤抑制基因,它被定位于人第5号染色体5q21处。APC基因如发生缺失或突变,则易患直肠肿瘤,并伴有部分先天痴呆的病例。本工作在孟帆已获得的APC基因在豚鼠中的同源cDNA的基础上,完成了对它的亚克隆,并利用原位杂交和RNA酶保护分析的方法,对它在脑中的分布进行了研究。发现APCmRNA主要在海马、大脑和小脑中表达;嗅球中杂交信号稍弱,脑干中最弱。海马中阳性细胞主要是锥体细胞,小脑中则主要是内层颗粒细胞。在一个月大的豚鼠胚胎的脑中也观察到相似的表达型式。进一步的研究有助于我们更好地了解神经发育和先天痴呆发生的分子机制。 相似文献
37.
38.
Desulfurization of dibenzothiophene to 2-hydroxybiphenyl by some newly isolated bacterial strains 总被引:7,自引:0,他引:7
Gram-positive, non-spore-forming, non-acid-fast, rod-shaped aerobic bacteria with the ability to desulfurize dibenzothiophene (DBT) or dibenzosulfone (DBTO2) were isolated from soil samples contaminated with fossil fuels. Using a bioavailability method, cells with the desired DbtS+ phenotype were enriched. Modified fluorescence and colorimetric assays were used for the initial detection of 2-hydroxybiphenyl (OH-BP) in microtiter plates; subsequently, isolates were grown in wells of microtiter plates and screened for the production of desulfurization product. Fluorescence under UV light and the production of colored product in the phenol assay were used as presumptive indications of production of OH-BP. Confirmation of the presence of OH-BP was achieved with HPLC, UV-absorbance, and mass spectrometry. Nutrient utilization and fatty acid composition (as discerned with Biolog plates and gas chromatography, respectively) were used to identify presumptively the strains as Rhodococcus erythropolis; colony and cell morphology may not be consistent with the identification achieved by nutrient utilization and fatty acid composition. The desulfurization end product, OH-BP, can not be used as carbon source by the tested strain, N1-36. 相似文献
39.
Summary A novel method of lactic acid fermentation byLactobacillus casei immobilized in Ca—alginate gels is described, in which an ion—exchange resin packed column is attached to a fermentor for
separation of lactic acid from fermentative broth. The technique successfully alleviated the restriction imposed by lactic
acid on bacterial growth and product formation. As compared to the conventional batch fermentation, the new fermentation technique
enhanced the lactic acid productivity and sugar conversion rate from 0.328g/L·h and 88. 2% to 0.482g/L·h and 98.6%, respectively. 相似文献
40.