全文获取类型
收费全文 | 2505篇 |
免费 | 278篇 |
国内免费 | 1篇 |
专业分类
2784篇 |
出版年
2022年 | 22篇 |
2021年 | 34篇 |
2020年 | 24篇 |
2019年 | 28篇 |
2018年 | 39篇 |
2017年 | 32篇 |
2016年 | 71篇 |
2015年 | 120篇 |
2014年 | 116篇 |
2013年 | 135篇 |
2012年 | 167篇 |
2011年 | 157篇 |
2010年 | 122篇 |
2009年 | 73篇 |
2008年 | 121篇 |
2007年 | 128篇 |
2006年 | 119篇 |
2005年 | 92篇 |
2004年 | 106篇 |
2003年 | 75篇 |
2002年 | 73篇 |
2001年 | 60篇 |
2000年 | 84篇 |
1999年 | 65篇 |
1998年 | 28篇 |
1997年 | 21篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 27篇 |
1992年 | 32篇 |
1991年 | 33篇 |
1990年 | 36篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 21篇 |
1974年 | 16篇 |
1973年 | 21篇 |
1972年 | 17篇 |
1969年 | 25篇 |
1968年 | 12篇 |
排序方式: 共有2784条查询结果,搜索用时 0 毫秒
71.
The 5′ untranslated regions (UTR) of chloroplast mRNAs often contain regulatory sequences that control RNA stability and/or
translation. The petD chloroplast mRNA in Chlamydomonas reinhardtii has three such essential regulatory elements in its 362-nt long 5′ UTR. To further analyze these elements, we compared 5′
UTR sequences from four Chlamydomonas species (C. reinhardtii, C. incerta, C. moewusii and C. eugametos) and five independent strains of C. reinhardtii. Overall, these petD 5′ UTRs have relatively low sequence conservation across these species. In contrast, sequences of the three regulatory elements
and their relative positions appear partially conserved. Functionality of the 5′ UTRs was tested in C. reinhardtii chloroplasts using β-glucuronidase reporter genes, and the nearly identical C. incerta petD functioned for mRNA stability and translation in C. reinhardtii chloroplasts while the more divergent C. eugametos petD did not. This identified what may be key features in these elements. We conclude that these petD regulatory elements, and possibly the corresponding trans-acting factors, function via mechanisms highly specific and surprisingly sensitive to minor sequence changes. This provides
a new and broader perspective of these important regulatory sequences that affect photosynthesis in these algae. 相似文献
72.
Alicia M Ebert Catherine A McAnelly Ashok Srinivasan Rachel Lockridge Mueller David B Garrity Deborah M Garrity 《BMC molecular biology》2008,9(1):38
Background
Cardiomyocyte contraction is initiated by influx of extracellular calcium through voltage-gated calcium channels. These oligomeric channels utilize auxiliary β subunits to chaperone the pore-forming α subunit to the plasma membrane, and to modulate channel electrophysiology [1]. Several β subunit family members are detected by RT-PCR in the embryonic heart. Null mutations in mouse β2, but not in the other three β family members, are embryonic lethal at E10.5 due to defects in cardiac contractility [2]. However, a drawback of the mouse model is that embryonic heart rhythm is difficult to study in live embryos due to their intra-uterine development. Moreover, phenotypes may be obscured by secondary effects of hypoxia. As a first step towards developing a model for contributions of β subunits to the onset of embryonic heart rhythm, we characterized the structure and expression of β2 subunits in zebrafish and other teleosts. 相似文献73.
74.
Wen Fong Ooi Catherine Ong Tannistha Nandi Jason F. Kreisberg Hui Hoon Chua Guangwen Sun Yahua Chen Claudia Mueller Laura Conejero Majid Eshaghi Roy Moh Lik Ang Jianhua Liu Bruno W. Sobral Sunee Korbsrisate Yunn Hwen Gan Richard W. Titball Gregory J. Bancroft Eric Valade Patrick Tan 《PLoS genetics》2013,9(9)
75.
Ledig MM McKinnell IW Mrsic-Flogel T Wang J Alvares C Mason I Bixby JL Mueller BK Stoker AW 《Journal of neurobiology》1999,39(1):81-96
Receptor tyrosine kinases and receptor protein tyrosine phosphatases (RPTPs) appear to coordinate many aspects of neural development, including axon growth and guidance. Here, we focus on the possible roles of RPTPs in the developing avian retinotectal system. Using both in situ hybridization analysis and immunohistochemistry, we show for the first time that five RPTP genes--CRYPalpha, CRYP-2, PTPmu, PTPgamma, and PTPalpha--have different but overlapping expression patterns throughout the retina and the tectum. PTPalpha is restricted to Muller glia cells and radial glia of the tectum, indicating a possible function in controlling neuronal migration. PTPgamma expression is restricted to amacrine neurons. CRYPalpha and CRYP-2 mRNAs in contrast are expressed throughout the retinal ganglion cell layer from where axons grow out to their tectal targets. PTPmu is expressed in a subset of these ganglion cells. CRYPalpha, CRYP-2, and PTPmu proteins are also localized in growth cones of retinal ganglion cell axons and are present in defined laminae of the tectum. Thus, the spatial and temporal expression of three distinct RPTP subtypes--CRYPalpha, CRYP-2, and PTPmu--are consistent with the possibility of their involvement in axon growth and guidance of the retinotectal projection. 相似文献
76.
Daiwen Yang Ronald A. Venters Geoffrey A. Mueller W.Y. Choy Lewis E. Kay 《Journal of biomolecular NMR》1999,14(4):333-343
HNCO-based 3D pulse schemes are presented for measuring 1HN-15N,15N-13CO, 1HN-13CO,13CO-13C and 1HN-13C dipolar couplings in 15N,13C,2-labeled proteins. The experiments are based on recently developed TROSY methodology for improving spectral resolution and sensitivity. Data sets recorded on a complex of Val, Leu, Ile (1 only) methyl protonated 15N,13C,2H-labeled maltose binding protein and -cyclodextrin as well as 15N,13C,2H-labeled human carbonic anhydrase II demonstrate that precise dipolar couplings can be obtained on proteins in the 30–40 kDa molecular weight range. These couplings will serve as powerful restraints for obtaining global folds of highly deuterated proteins. 相似文献
77.
78.
79.
A new flow cytometer with a very small observation volume has been developed to detect individual viruses with good resolution, and has been used to discriminate between two types of viral particles based on differences in their light scattering. Measurements of light scattering and fluorescence made with such an instrument can provide a basis for quantitative analysis and sorting of viruses and other particles in the micron and submicron size range. 相似文献
80.
Many animals change their body pigmentation according to illumination of their environment. In aquatic vertebrates, this reaction is mediated through aggregation or dispersion of melanin-filled vesicles (melanosomes) in dermal pigment cells (melanophores). The adaptive value of this behavior is usually seen in camouflage by allowing the animal to visually blend into the background. When exposed to visible light from below, however, dark-adapted zebrafish embryos at the age of 2 days post fertilization (dpf) surprisingly display dispersal instead of aggregation of melanosomes, i.e. their body coloration becomes dark on a bright background. Melanosomes of older embryos and early larvae (3–5 dpf) on the other hand aggregate as expected under these conditions. Here we provide an explanation to this puzzling finding: Melanosome dispersion in larvae 3 dpf and older is efficiently triggered by ultraviolet (UV) light, irrespective of the visual background, suggesting that the extent of pigmentation is a trade-off between threats from predation and UV irradiation. The UV light-induced dispersion of melanosomes thereby is dependent on input from retinal short wavelength-sensitive (SWS) cone photoreceptors. In young embryos still lacking a functional retina, protection from UV light predominates, and light triggers a dispersal of melanosomes via photoreceptors intrinsic to the melanophores, regardless of the actual UV content. In older embryos and early larvae with functional retinal photoreceptors in contrast, this light-induced dispersion is counteracted by a delayed aggregation in the absence of UV light. These data suggest that the primary function of melanosome dispersal has evolved as a protective adaption to prevent UV damage, which was only later co-opted for camouflage. 相似文献