全文获取类型
收费全文 | 50266篇 |
免费 | 2831篇 |
国内免费 | 5248篇 |
出版年
2023年 | 783篇 |
2022年 | 1032篇 |
2021年 | 1505篇 |
2020年 | 1430篇 |
2019年 | 1861篇 |
2018年 | 1483篇 |
2017年 | 1234篇 |
2016年 | 1277篇 |
2015年 | 1576篇 |
2014年 | 2483篇 |
2013年 | 3347篇 |
2012年 | 2174篇 |
2011年 | 2541篇 |
2010年 | 2020篇 |
2009年 | 2448篇 |
2008年 | 2637篇 |
2007年 | 2807篇 |
2006年 | 2716篇 |
2005年 | 2480篇 |
2004年 | 2274篇 |
2003年 | 2050篇 |
2002年 | 1844篇 |
2001年 | 1472篇 |
2000年 | 1199篇 |
1999年 | 1147篇 |
1998年 | 1046篇 |
1997年 | 896篇 |
1996年 | 898篇 |
1995年 | 825篇 |
1994年 | 776篇 |
1993年 | 575篇 |
1992年 | 531篇 |
1991年 | 442篇 |
1990年 | 388篇 |
1989年 | 296篇 |
1988年 | 313篇 |
1987年 | 296篇 |
1986年 | 242篇 |
1985年 | 308篇 |
1984年 | 389篇 |
1983年 | 281篇 |
1982年 | 316篇 |
1981年 | 240篇 |
1980年 | 259篇 |
1979年 | 241篇 |
1978年 | 196篇 |
1977年 | 149篇 |
1976年 | 141篇 |
1975年 | 114篇 |
1974年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
5’核苷酸酶碱性磷酸酶双重染色法在毛细淋巴管研究中的应用 总被引:8,自引:0,他引:8
本文应用5’-N-ALP双重染色法观察了裸鼠皮肤及人胃癌组织内淋巴管的形态和细微分布.在光镜下毛细淋巴管、淋巴管呈5’-N强阳性反应,管壁显示明显的棕色或深棕色,而毛细血管、血管的ALP呈强阳性,管壁呈明显的蓝色.据此可用组化方法将毛细淋巴管和毛细血管区别开来.本法能显示呈褐色的毛细淋巴管,特别是呈实性条索状的毛细淋巴管,因而双重染色比HE染色更能客观、准确地显示毛细淋巴管的分布. 相似文献
962.
The majority of clinical trials for gene therapy currently employ retroviral-mediated gene delivery. This is because the life
cycle of the retrovirus is well understood and can be effectively manipulated to generate vectors that can be efficiently
and safely packaged. Here, we review the molecular technology behind the generation of recombinant retroviral vectors. We
also highlight the problems associated with the use of these viruses as gene therapy vehicles and discuss future developments
that will be necessary to maintain retroviral vectors at the forefront of gene transfer technology. 相似文献
963.
本文综述了近年来对链霉菌酪氨酸酶基因的研究。由酪氨酸酶合成黑色素是链霉菌属各个种的共同特性,并受到酪氨酸酶基因的控制。链霉菌几个种的酪氨酸酶基因已克隆到,其产黑色素的特性使之作为重要的标记基因得以广泛应用,同时,该基因在链霉菌的不同种及不同属的微生物中得到了高水平的表达。链霉菌酪氨酸酶基因表达调控的分子机制也得到较深入的研究。 相似文献
964.
利用RT-PCR技术分离低密度脂蛋白受体基因cDNA,将长为2605bp的cDNA插入质粒pJN6,并经全序列测定证实,该序列与已报道序列相比,存在两个变异碱基,即第754位C→T,和1654位的G→A,这两个变异碱基并不改变编码的氨基酸,利用LDL受体基因cDNA中的ClaⅠ片段作为探针,检测到LDL受体基因上外显子8的StuⅠ位点是个限制性片段长度多态性位点。所克隆的cDNA含有可译框架的全部密码,因此可作为基因表达材料。 相似文献
965.
Forskolin(FSK)是一种植物二萜类化合物,为腺苷酸环化酶的特异激活剂,实验发现:FSK和作为参照的诱导分化剂维甲酸(RA)单独或联合应用均可升高胞浆蛋白激酶C(PKC)活性,并降低膜PKC活性,FSK可使表皮生长因子(EGF)诱导的细胞内三磷酸肌醇(IP3-1,4,5)水平降低至对照组的44.4%至67%;FSK与RA合用可显著降低成骨样细胞特征蛋白碱性磷酸酶(AKP)的活性。以上结果表明,FSK对成骨样细胞内磷脂酰肌醇信息传递体系有深刻影响,可能与其调节细胞的增殖分化有关。 相似文献
966.
设计并建立一套适合国内应用的改良PCR-RFLR方法,分5组特异性扩增DNA样品,随后进行酶切定型分析,准确检测了编码DR抗原特异性的HLA-DRB1基因位点的多态性,该法采用分组扩增,不发生与其它DRB位点等位基因的交叉扩增,不仅适合纯合子的区分而且可以清楚准确地检测杂合子样品,已报道过的DRB1位点编码的特异性组合都可以通过这个方法得到准确分析。所使用的Ⅱ类限制性内切酶均价格便宜、易购。 相似文献
967.
Genomic sequencing by ligation-mediated PCR 总被引:8,自引:0,他引:8
Genomic sequencing permits studies of in vivo DNA methylation and protein-DNA interactions, but its use has been limited due
to the complexity of the mammalian genome. Ligation-mediated PCR (LMPCR) is a sensitive genomic sequencing procedure that
generates high quality, reproducible sequence ladders starting with only 1 μg of uncloned mammalian DNA per reaction. This
genomic sequencing procedure can be adapted for various methylation, in vivo footprinting and DNA adduct mapping procedures.
We provide a detailed protocol for genomic sequencing by LMPCR and discuss the principles and applications of the method. 相似文献
968.
Charlotte Helfrich-Förster 《Seminars in cell & developmental biology》1996,7(6):791-802
Theperiod(per) gene and thetimeless(tim) gene are essential components of the circadian clock inDrosophila melanogaster. Both gene products interact in interdependent feedback loops, producing a self-sustained cellular rhythmin situ. Several oscillating cells are combined to discrete pacemaker centers that control rhythmic behavior. This paper reviews the work on localizing the circadian pacemaker neurons controlling activity and eclosion, leading to questions about how these pacemaker cells are synchronized to the external light–dark cycle, and how they impose periodicity on behavior. The circadian system ofDrosophilais also compared with that of other arthropods. 相似文献
969.
Detection of Short Protein Coding Regions within the Cyanobacterium Genome: Application of the Hidden Markov Model 总被引:3,自引:0,他引:3
The gene-finding programs developed so far have not paid muchattention to the detection of short protein coding regions (CDSs).However, the detection of short CDSs is important for the studyof photosynthesis. We utilized GeneHacker, a gene-finding programbased on the hidden Markov model (HMM), to detect short CDSs(from 90 to 300 bases) in a 1.0 mega contiguous sequence ofcyanobacterium Synechocystis sp. strain PCC6803 which carriesa complete set of genes for oxygenic photosynthesis. GeneHackerdiffers from other gene-finding programs based on the HMM inthat it utilizes di-codon statistics as well. GeneHacker successfullydetected seven out of the eight short CDSs annotated in thissequence and was clearly superior to GeneMark in this rangeof length. GeneHacker detected 94 potentially new CDSs, 9 ofwhich have counterparts in the genetic databases. Four of thenine CDSs were less than 150 bases and were photosynthesis-relatedgenes. The results show the effectiveness of GeneHacker in detectingvery short CDSs corresponding to genes. 相似文献
970.
Summary The monoclonal antibody (MAb) JIM5, marking acidic pectins, was used to localize ultrastructurally pectin molecules in the pollen tube wall ofNicotiana tabacum. Longitudinal sections of LR-White embedded pollen tubes were exposed to antibody treatment; accumulations of pectins were identified by counting the density of the gold particles representing the pectin epitopes along the pollen tube wall. Significant accumulations of gold grains were marked and the distances between them were measured. In many pollen tubes a more or less regular distribution of the accumulations was observed along the tube indicating a periodical deposition of pectin. The distances between the accumulations were 4–6 m. Most of the label was found in the inner part of the outer layer of the bilayered cell wall. These findings correspond to and confirm the earlier observation by our group reporting ring-shaped periodical deposits in pollen tubes after immunofluorescence labelling with the MAb JIM5 under the confocal laser scanning microscope.Abbreviations Ab
antibody
- MAb
monoclonal antibody 相似文献