全文获取类型
收费全文 | 19651篇 |
免费 | 1883篇 |
国内免费 | 642篇 |
专业分类
22176篇 |
出版年
2023年 | 132篇 |
2022年 | 315篇 |
2021年 | 474篇 |
2020年 | 321篇 |
2019年 | 413篇 |
2018年 | 473篇 |
2017年 | 350篇 |
2016年 | 593篇 |
2015年 | 965篇 |
2014年 | 1057篇 |
2013年 | 1253篇 |
2012年 | 1452篇 |
2011年 | 1431篇 |
2010年 | 939篇 |
2009年 | 742篇 |
2008年 | 1009篇 |
2007年 | 944篇 |
2006年 | 891篇 |
2005年 | 820篇 |
2004年 | 750篇 |
2003年 | 716篇 |
2002年 | 642篇 |
2001年 | 551篇 |
2000年 | 484篇 |
1999年 | 451篇 |
1998年 | 217篇 |
1997年 | 203篇 |
1996年 | 187篇 |
1995年 | 167篇 |
1994年 | 152篇 |
1993年 | 121篇 |
1992年 | 245篇 |
1991年 | 244篇 |
1990年 | 203篇 |
1989年 | 216篇 |
1988年 | 189篇 |
1987年 | 152篇 |
1986年 | 144篇 |
1985年 | 168篇 |
1984年 | 125篇 |
1983年 | 98篇 |
1982年 | 90篇 |
1981年 | 97篇 |
1979年 | 109篇 |
1978年 | 91篇 |
1977年 | 71篇 |
1976年 | 68篇 |
1975年 | 88篇 |
1974年 | 89篇 |
1973年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
In the adult murine brain, the microtubule-associated protein tau exists as three major isoforms, which have four microtubule-binding repeats (4R), with either no (0N), one (1N) or two (2N) amino-terminal inserts. The human brain expresses three additional isoforms with three microtubule-binding repeats (3R) each. However, little is known about the role of the amino-terminal inserts and how the 0N, 1N and 2N tau species differ. In order to investigate this, we generated a series of isoform-specific antibodies and performed a profiling by Western blotting and immunohistochemical analyses using wild-type mice in three age groups: two months, two weeks and postnatal day 0 (P0). This revealed that the brain is the only organ to express tau at significant levels, with 0N4R being the predominant isoform in the two month-old adult. Subcellular fractionation of the brain showed that the 1N isoform is over-represented in the soluble nuclear fraction. This is in agreement with the immunohistochemical analysis as the 1N isoform strongly localizes to the neuronal nucleus, although it is also found in cell bodies and dendrites, but not axons. The 0N isoform is mainly found in cell bodies and axons, whereas nuclei and dendrites are only slightly stained with the 0N antibody. The 2N isoform is highly expressed in axons and in cell bodies, with a detectable expression in dendrites and a very slight expression in nuclei. The 2N isoform that was undetectable at P0, in adult brain was mainly found localized to cell bodies and dendrites. Together these findings reveal significant differences between the three murine tau isoforms that are likely to reflect different neuronal functions. 相似文献
23.
24.
The detection of sequence variation with restriction fragment length polymorphisms is advancing our knowledge of plant genetics on several fronts. In the past year, there has been progress in genetic map construction, phylogeny studies, and the dissection of multigenic traits. In addition, new methods that are independent of restriction sites are being developed for polymorphism detection. 相似文献
25.
Corinna Richter Ron L. Dy Rebecca E. McKenzie Bridget N.J. Watson Corinda Taylor James T. Chang Matthew B. McNeil Raymond H.J. Staals Peter C. Fineran 《Nucleic acids research》2014,42(13):8516-8526
Clustered regularly interspaced short palindromic repeats (CRISPR), in combination with CRISPR associated (cas) genes, constitute CRISPR-Cas bacterial adaptive immune systems. To generate immunity, these systems acquire short sequences of nucleic acids from foreign invaders and incorporate these into their CRISPR arrays as spacers. This adaptation process is the least characterized step in CRISPR-Cas immunity. Here, we used Pectobacterium atrosepticum to investigate adaptation in Type I-F CRISPR-Cas systems. Pre-existing spacers that matched plasmids stimulated hyperactive primed acquisition and resulted in the incorporation of up to nine new spacers across all three native CRISPR arrays. Endogenous expression of the cas genes was sufficient, yet required, for priming. The new spacers inhibited conjugation and transformation, and interference was enhanced with increasing numbers of new spacers. We analyzed ∼350 new spacers acquired in priming events and identified a 5′-protospacer-GG-3′ protospacer adjacent motif. In contrast to priming in Type I-E systems, new spacers matched either plasmid strand and a biased distribution, including clustering near the primed protospacer, suggested a bi-directional translocation model for the Cas1:Cas2–3 adaptation machinery. Taken together these results indicate priming adaptation occurs in different CRISPR-Cas systems, that it can be highly active in wild-type strains and that the underlying mechanisms vary. 相似文献
26.
27.
28.
29.
30.
Neurofascin: a novel chick cell-surface glycoprotein involved in neurite-neurite interactions 总被引:17,自引:0,他引:17
We have identified neurofascin, a novel chick cell-surface glycoprotein involved in neurite-neurite interactions. Neurofascin is defined by its reactivity with monoclonal antibody (MAb) F6, which detects two polypeptides (160 and 185 kd) in immunotransfers of brain plasma membrane proteins. Immunoaffinity chromatography using immobilized MAb F6 yields major molecular mass bands at 185, 160, 135-110, and 92 kd. Fingerprint analyses show that these polypeptides are related. Neurofascin is expressed primarily in fiber-rich areas of embryonic cerebellum, spinal cord, and retina. Fab fragments of polyclonal antibodies to neurofascin interfere with the outgrowth of retinal and sympathetic axons in two different in vitro bioassays. Neurofascin is immunologically distinct from other known neurite-associated surface glycoproteins. 相似文献