全文获取类型
收费全文 | 3837篇 |
免费 | 325篇 |
国内免费 | 4篇 |
出版年
2021年 | 42篇 |
2020年 | 28篇 |
2019年 | 43篇 |
2018年 | 48篇 |
2017年 | 57篇 |
2016年 | 56篇 |
2015年 | 112篇 |
2014年 | 120篇 |
2013年 | 135篇 |
2012年 | 198篇 |
2011年 | 225篇 |
2010年 | 144篇 |
2009年 | 151篇 |
2008年 | 225篇 |
2007年 | 196篇 |
2006年 | 190篇 |
2005年 | 221篇 |
2004年 | 220篇 |
2003年 | 214篇 |
2002年 | 202篇 |
2001年 | 77篇 |
2000年 | 52篇 |
1999年 | 74篇 |
1998年 | 67篇 |
1997年 | 62篇 |
1996年 | 43篇 |
1995年 | 48篇 |
1994年 | 30篇 |
1993年 | 41篇 |
1992年 | 47篇 |
1991年 | 39篇 |
1990年 | 43篇 |
1989年 | 48篇 |
1988年 | 46篇 |
1987年 | 42篇 |
1986年 | 45篇 |
1985年 | 35篇 |
1984年 | 36篇 |
1983年 | 38篇 |
1982年 | 39篇 |
1981年 | 39篇 |
1980年 | 23篇 |
1979年 | 25篇 |
1978年 | 19篇 |
1977年 | 25篇 |
1976年 | 19篇 |
1975年 | 16篇 |
1974年 | 17篇 |
1973年 | 14篇 |
1971年 | 15篇 |
排序方式: 共有4166条查询结果,搜索用时 15 毫秒
1.
A simple new procedure was described for producing a sequential series of overlapping clones for use in DNA sequencing. The technique used single-stranded M13 DNA and complementary DNA oligomers to form specific cleavage and ligation substrates. It was, therefore, independent of the sequence of the DNA cloned into the vector. Deletions of varying sizes were generated from one end of the insert through the 3' to 5' exonuclease activity of T4 DNA polymerase. The approximate size of the deletion and therefore the starting point for DNA sequencing could be estimated by electrophoresis of the subcloned phage DNA on a agarose gel. This greatly reduced the number of templates that must be sequenced to obtain a complete sequence. The entire procedure could be carried out in one tube in less than a day. The procedure was used to subclone and sequence the maize mitochondrial 18 S rDNA and 5' flanking region (2622 bases) in less than a week. Other applications of oligomers and single-stranded DNA in the construction of insertions, deletions, and cDNAs are discussed. 相似文献
2.
3.
Ana Isabell Paulino Aud Larsen Gunnar Bratbak Dale Evens Svein Rune Erga Einar Bye-Ingebrigtsen 《Marine Biology Research》2018,14(5):421-435
Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by Skeletonema marinoi and Chaetoceros socialis, and other Chaetoceros and Thalassiosira spp. Blooms of the haptophytes Phaeocystis pouchetii and Emiliania huxleyi were irregular and in some years totally absent. Although E. huxleyi was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes. 相似文献
4.
We have analysed the lineage of olfactory receptor neurons usinga replication-incompetent retrovirus injected beneath the olfactoryepithelium of young rats. There are two major types of clustersof infected cells seen at 540 days after infection: (i)horizontal basal cells (HBCs); (ii) variable numbers of globosebasal cells (GBCs), and immature and mature sensory neurons.Olfactory nerve lesion increased the frequency of the globose/sensoryneuron clusters, as well as the number of cells/cluster, butdid not change the number of HBC clusters or cells/cluster.No clusters contained sustentacular cells. These data indicatethat, at least in young rats: (i) HBCs are not precursors ofolfactory neurons; (ii) there is a lineage path from GBCs tomature neurons; and (iii) sustentacular cells arise from a separatelineage. 相似文献
5.
6.
Silvia Penuela Alexander W Lohman Wesley Lai Laszlo Gyenis David W Litchfield Brant E Isakson Dale W Laird 《Channels (Austin, Tex.)》2014,8(2):124-130
The pannexin family of channel-forming proteins is composed of 3 distinct but related members called Panx1, Panx2, and Panx3. Pannexins have been implicated in many physiological processes as well as pathological conditions, primarily through their function as ATP release channels. However, it is currently unclear if all pannexins are subject to similar or different post-translational modifications as most studies have focused primarily on Panx1. Using in vitro biochemical assays performed on ectopically expressed pannexins in HEK-293T cells, we confirmed that all 3 pannexins are N-glycosylated to different degrees, but they are not modified by sialylation or O-linked glycosylation in a manner that changes their apparent molecular weight. Using cell-free caspase assays, we also discovered that similar to Panx1, the C-terminus of Panx2 is a substrate for caspase cleavage. Panx3, on the other hand, is not subject to caspase digestion but an in vitro biotin switch assay revealed that it was S-nitrosylated by nitric oxide donors. Taken together, our findings uncover novel and diverse pannexin post-translational modifications suggesting that they may be differentially regulated for distinct or overlapping cellular and physiological functions. 相似文献
7.
8.
The development of a population of spinal cord neurons and their axonal projections revealed by GABA immunocytochemistry in frog embryos 总被引:2,自引:0,他引:2
N Dale A Roberts O P Ottersen J Storm-Mathisen 《Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)》1987,232(1267):205-215
The development of a population of cerebrospinal-fluid-contacting neurons in the spinal cord of the Xenopus embryo ('Kolmer-Agduhr' cells) has been followed by using an immunocytochemical procedure that identifies GABA in fixed nervous tissue. Stained Kolmer-Agduhr cells containing GABA first appeared at stage 25 and their numbers increased steadily with the developmental age of the embryo. The Kolmer-Agduhr neurons had ascending ipsilateral axons that often terminated in growth cones. These axons and growth cones could be stained by the GABA antiserum from the earliest stages of outgrowth from the Kolmer-Agduhr cell body. We measured the angle of the earliest axons' outgrowth relative to the rostrocaudal axis of the spinal cord. The initial outgrowth of axons was always rostral over a narrow range of angles. This observation is inconsistent with the hypothesis of random initial outgrowth followed by later selection of the correct orientation, which would predict that axons would initially grow out over a wide range of angles. Instead, it suggests that, even from the earliest moments, axon outgrowth from the Kolmer-Agduhr cells is directed rostrally in a specific stereotyped manner. 相似文献
9.
R. E. Dale 《European biophysics journal : EBJ》1987,14(3):179-193
The effects of the fact that the laser sources typically used in fluorescence photobleaching recovery (FPR) experiments in the most commonly employed in-line microscope imaging geometries, are highly linearly polarized, are examined in some detail. The implications of the results, in particular for the interpretation of FPR data in complex cell membrane systems in terms of laterally mobile and immobile sub-populations of the labelled molecular species of concern, are discussed. Methods of experimentally eliminating the potentially major rotational diffusion-based artifacts, different from those appropriate to three-dimensional (solution or suspension) systems which require other than in-line geometries, are delineated.Abbreviations FPR
fluorescence photobleaching recovery
- FRAP
fluorescence recovery after photobleaching
- 2- and 3-D
two- and three-dimensional 相似文献
10.
Svein Valla Dag Hugo Coucheron Johs. Kjosbakken 《Molecular & general genetics : MGG》1987,208(1-2):76-83
Summary
Acetobacter xylinum contains a complex system of plasmid DNA molecules. Plasmids of molecular weights or copy numbers different from the original wild-type, are found in different types of mutants. Restriction endonuclease digestion and DNA/DNA hybridization analysis, showed that the plasmids often contained partly, but not completely the same DNA sequences. Two of these plasmid classes were analysed in more detail, and could be shown to differ in size by about 5 kb. Hybridization analysis using cloned DNA fragments as probes, showed that sequences lacking in the smallest plasmid were still present in a DNA fraction co-migrating with linearized chromosomal DNA. In addition, at least part of the DNA in the smallest plasmid was present both in the plasmid and chromosomal DNA fraction. Analysis of a particular strain containing an insertion of transposon Tn1, also indicated the existence of complex interactions between plasmids and chromosomal DNA. Together with experiments on conjugative transfer and curing of the plasmids, the results indicate that at least part of the genetic system of A. xylinum is unusual when compared to that of other genetically characterized bacteria. 相似文献