全文获取类型
收费全文 | 4845篇 |
免费 | 310篇 |
国内免费 | 305篇 |
出版年
2024年 | 8篇 |
2023年 | 60篇 |
2022年 | 146篇 |
2021年 | 277篇 |
2020年 | 196篇 |
2019年 | 210篇 |
2018年 | 167篇 |
2017年 | 134篇 |
2016年 | 217篇 |
2015年 | 318篇 |
2014年 | 343篇 |
2013年 | 362篇 |
2012年 | 499篇 |
2011年 | 407篇 |
2010年 | 234篇 |
2009年 | 231篇 |
2008年 | 234篇 |
2007年 | 192篇 |
2006年 | 178篇 |
2005年 | 137篇 |
2004年 | 110篇 |
2003年 | 98篇 |
2002年 | 103篇 |
2001年 | 85篇 |
2000年 | 75篇 |
1999年 | 69篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 35篇 |
1995年 | 42篇 |
1994年 | 39篇 |
1993年 | 24篇 |
1992年 | 30篇 |
1991年 | 33篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有5460条查询结果,搜索用时 187 毫秒
11.
云南10个民族红细胞酸性磷酸酶型分布调查 总被引:1,自引:0,他引:1
用淀粉凝胶电泳法对云南省汉族及9个少数民族的红细胞酸性磷酸酶(ACP_1)的表型分布进行了调查,检出A、BA和B3种表型,计算得云南汉、彝、白、傣、瑶、佤、哈尼、布朗、基诺和拉祜族ACP_1~A、ACP_1~B的基因频率依次为0.2067、0.7933;0.2406、0.7594;0.2341、0.7659;0.3750、0.6250;0.2300、0.7700;0.2727、0.7273;0.3594、0.6406;0.3036、0.6964;0.2381、0.76119和0.4474、0.5526。未发现ACP_1~C基因及其它稀有基因。研究表明,ACP_1表型的分布存在着一定的种族与民族差异。 相似文献
12.
Acid sphingomyelinase was purified to homogeneity from human placenta in the presence of a dialyzable detergent, n-octyl-beta-D-glucopyranoside. The major steps in the procedure included column chromatographies with Con A-Sepharose, sphingosylphosphorylcholine-Sepharose 4B, hexyl-agarose, and Mono P. The purified enzyme with pI 7.4 had a specific activity of approx 170,000 units/mg protein with a yield of 3.6%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a single protein band of Mr 62,000. Gel filtration with a Superose 12 column gave a single peak, and the enzyme in the presence 50 mM n-octyl-beta-D-glucopyranoside was of Mr 123,000, indicating that the native enzyme occurs in a dimeric form. The optimal pH was 5.5 with both sphingomyelin and an artificial substrate, 2-N-hexadecanoylamino-4-nitrophenylphosphorylcholine. The Km values were 55 microM with sphingomyelin and 340 microM with the artificial substrate. The enzyme activity was not affected by Mg2+ (1-5 mM), confirming that the enzyme is acid sphingomyelinase. The enzyme was stable at -80 degrees C for more than 4 months. In addition to the enzyme with pI 7.4, the Mono P chromatofocusing gave two peaks (pI 7.0 and 6.7) possessing the enzymatic activity. 相似文献
13.
本文共记述盲蝽科叶盲蝽亚科(Phylinae)新种两个,计为:宽束盲蝽 Pilophorus latus sp.nov.和黄平盲蝽 Zanchius vitellinus sp.nov.。两新种的模式产地均为云南。并记录了6个中国新纪录种,计为:棕二带束盲蝽 Pilophorus alstoni Schuh、长黑束盲蝽 Pilophorus dailahn Schuh、细毛束盲蝽 Pilophorus setulosus Horvath、朝束盲蝽 Pilophorus koreanus Josifov、褐束盲蝽 Pilophorusgallicus Remane、亮束盲椿 Pilophorus lucidus Linnavuori。 相似文献
14.
钐在小鼠肝脏细胞中的动态观察 总被引:8,自引:0,他引:8
It is generally considered that the rare earth compounds are plasma membrane-impermeable, thus affecting the cells only on their surface. Recently, we found that after repeated injections to mice of large dose of samarium trichloride, a soluble compound of rare earth, samarium aggregates appeared in Kupffer cells and hepatocytes of liver. In this study, we aimed at observing the route by which samarium enters the liver cells and the process of the formation of samarium aggregates. Samarium trichloride was given to Swiss mice at one dose of 70 mg/kg intravenously. Thereafter, at different intervals from 15 min to 48 h after the injection, the samarium in liver was traced dynamically by electron microscopy and X ray microanalysis. From 15 min to 2 h both Kupffer cells and hepatocytes endocytosed samarium-containing particles and formed phagosomes, in which the ingested particles were progressively concentrated. Besides, the small phagosomes fused with each other. Phagocytosis was especially active in Kupffer cells. During the 4 h to 24 h many Kupffer cells were degenerated and broken. In hepatocytes the phagosomes gathered mostly around the bile canaliculi. Groups of highly electron-dense particles were found in the lumen of bile canaliculi, implying the excretion of samarium by bile. At the 48 h, the samarium-containing phagosomies were found still in both kinds of cells in the liver. 相似文献
15.
铃兰族rbcL基因的PCR—RFLP分析 总被引:4,自引:1,他引:3
本文用7属9种铃兰族Tribe convallarieae植物的叶绿体DNA中rbcL基因片段的PCR产物的RFLP结果进行聚类分析。结果表明:开口箭属与蜘蛛抱蛋属关系密切,夏须草属与族内其余各属亲缘关系稍远,与外部器官形态、核型和孢粉学资料所得出的结论基本一致。此外,本文对铃兰属的系统位置也进行了讨论。 相似文献
16.
17.
Gene conversion plays the major role in controlling the stability of large tandem repeats in yeast. 总被引:15,自引:0,他引:15
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The genomic stability of the rDNA tandem array in yeast is tightly controlled to allow sequence homogenization and at the same time prevent deleterious rearrangements. In our study, we show that gene conversion, and not unequal sister chromatid exchange, is the predominant recombination mechanism regulating the expansion and contraction of the rDNA array. Furthermore, we found that RAD52, which is essential for gene conversion, is required for marker duplication stimulated in the absence of the two yeast type I topoisomerases. Our results have implications for the mechanisms regulating genomic stability of repetitive sequence families found in all eukaryotes. 相似文献
18.
AlateratioofMyzuspersicaeSulzerwasgreatlycloserinrelationshiptocertaininclusionintherapecrop-QingyouⅡ,suchastryptophan,ratioofcontentsofsolublesugartoproteinandmeancrowdingnessunderconditionsofvariedmateproportionoffertilizers-N,P,K.Thefollowinginclusionintherapecropwerealsorelatedtotheratioofalatate:asperticacid,troeoninie,serine,glutancicacid,phenylalanine,lysine,histidine,valine,methionine,isoleucine,leucine,solublesugarandwater-solubleprotein. 相似文献
19.
造礁石珊瑚群落结构研究的概况,问题和前景 总被引:6,自引:0,他引:6
造礁石珊瑚作为珊瑚礁生态系统中的关键生物类群,其群落结构是珊瑚礁系统研究中的一个重 要方面。本文回顾了20余年以来世界各国对造礁石珊瑚群落结构研究所取得的主要进展和认识,指出了目前研究中存在的问题并分析了不同空间范围研究结论之间的缺乏一致性和中等干扰假说的不足。 最后,结合珊瑚礁生态系统基础理论和应用发展的需求,本文探讨了造礁石珊瑚群落结构研究的前景。 相似文献
20.
通过DNA体外重组技术,以pET-3b为表达载体,构建了重组表达质粒pET-6R(B)和PET-6R(B)4,分别编码28kD的hIL-6R配基结合区片段及其53kD的二联体蛋白,并为酶切分析和DNA序列分析所证实。SDS-PAGE分析表明,含有重组表达质粒的菌株可分别表达出28kD的蛋白rIL6R-28和53kD的rIL6R-53。重组蛋白分别占菌体总蛋白的45%和29%左右。重组蛋白主要以包涵体形式存在,Western印迹表明重组蛋白具有IL-6R的抗原性。 相似文献