全文获取类型
收费全文 | 615篇 |
免费 | 111篇 |
出版年
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 7篇 |
2019年 | 19篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 27篇 |
2015年 | 27篇 |
2014年 | 29篇 |
2013年 | 33篇 |
2012年 | 31篇 |
2011年 | 35篇 |
2010年 | 32篇 |
2009年 | 16篇 |
2008年 | 24篇 |
2007年 | 24篇 |
2006年 | 33篇 |
2005年 | 25篇 |
2004年 | 21篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 17篇 |
1998年 | 5篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有726条查询结果,搜索用时 31 毫秒
1.
2.
Ly1+ PRO-B lymphocyte clones. Phenotype, growth requirements and differentiation in vitro and in vivo. 总被引:27,自引:4,他引:23 下载免费PDF全文
Several clones obtained from the bone marrow of a BALB/c mouse were found to contain the heavy and light chain Ig genes in the germline configuration, to express Ly1 and to carry the B cell lineage markers B-220, Lyb8 and BP-1; these clones are Pgp-1+, LFA-1+, J11d+, Mac-1+ and Thy1-, Lyt2-, L3T4-, GM1.2- and Ia-. Three clones analyzed in detail (Lyd9, LyH7 and Lyb9) have receptors for interleukin (IL) 2 and IL3 as assessed with the 7D4 and CC11 monoclonal antibodies respectively. They grow in rIL3 but not in rIL2 or rIL1; both rIL4 and rIL5 also promote their proliferation, albeit to a much lesser extent than rIL3. None of the interleukins tested alone or in various combinations promoted the clones to differentiate in vitro along the B cell pathway. Treatment with 5-Azacytidine (5-Aza) induced cell surface Ia expression but not rearrangement or expression of Ig genes. However, 5-Aza-treated Lyd9, LyH7 and Lyb9 cells co-cultured with X-ray irradiated accessory cells and LPS gave rise to Ly1+, IgM+ B lymphocytes (range 14-51%) including mu + kappa + (78-93%), and mu + lambda + (9-25%) B lymphocytes. In vivo, the Lyd9, LyH7 and Lyb9 clones gave rise to IgM+ B lymphocytes (8.5-17%) including mu + kappa +, and mu + lambda +, but not to Lyt2+ or L3T4+ T lymphocytes after 4-6 weeks of transfer into Scid mice. Our results indicate that Ly1+ IgM+ cells comprise a subpopulation of B lymphocytes that is derived from IL3-responsive Ly1+ PRO-B lymphocytes. 相似文献
3.
Nitric oxide from L-arginine stimulates the soluble guanylate cyclase in adrenal glands 总被引:23,自引:0,他引:23
M Palacios R G Knowles R M Palmer S Moncada 《Biochemical and biophysical research communications》1989,165(2):802-809
The formation of nitric oxide (NO) by an L-arginine:NO synthase and its stimulation of the soluble guanylate cyclase was studied in rat whole adrenal and bovine cortex and medulla cytosol. In the presence of L-arginine, the stimulation of soluble guanylate cyclase was accompanied by the formation of citrulline and NO2-, formed from NO. The NO synthase was NADPH- and Ca(2+)-dependent and was inhibited by several L-arginine analogues. These results indicate that rat and bovine adrenal cytosol contains an L-arginine:NO synthase. 相似文献
4.
H. Nquyen H.H. Le R.Y. Lee M. Staufenbiel J.M. Palacios G. Mengod H. Lübbert 《Neurochemistry international》1991,19(4):433-436
We have previously isolated serotonin 5-HT1C receptor cDNA clones. In contrast to most other receptors coupled to GTP binding proteins, the 5-HT1C receptor gene contains several introns in its coding region. A similar exon-intron distribution is found in the 5-HT2 receptor gene. The presence of large introns tempted us to test whether exchange of exons contributes to serotonin receptor heterogeneity. Therefore, blots with RNAs from different regions of the brain and brain slices were hybridized in situ with probes representing individual exons. We did not find any evidence for the exchange of exons which should result in an unequal distribution of hybridization signals found with the exon-specific probes. With the methodology used we should be able to see differential splicing in the form where individual exons are used alternatively resulting in mRNAs coding for different serotonin receptor types. We would not, however, see if a given exon can be modified by the alternative use of several splice-junctions. 相似文献
5.
Effect of Naturally Occurring nif Reiterations on Symbiotic Effectiveness in Rhizobium phaseoli 总被引:2,自引:0,他引:2 下载免费PDF全文
David Romero Paul W. Singleton Lorenzo Segovia Enrique Morett B. Ben Bohlool Rafael Palacios Guillermo Dvila 《Applied microbiology》1988,54(3):848-850
Most naturally occurring strains of Rhizobium phaseoli possess reiteration of the nif genes. Three regions contain nitrogenase structural genes in strain CFN42. Two of these regions (a and b) have copies of nifH, nifD, and nifK, whereas the third region (c) contains only nifH. Strains containing mutations in either nif region a or nif region b had significantly diminished symbiotic effectiveness compared with the wild-type strain on the basis of nodule mass, total nitrogenase activity per plant, nitrogenase specific activity, total nitrogen in the shoot, and percentage of nitrogen. A strain containing mutations in both nif region a and nif region b was totally ineffective. These data indicate that both nif region a and nif region b are needed for full symbiotic effectiveness in R. phaseoli. 相似文献
6.
Narrow- and Broad-Host-Range Symbiotic Plasmids of Rhizobium spp. Strains That Nodulate Phaseolus vulgaris 总被引:11,自引:4,他引:7 下载免费PDF全文
Susana Brom Esperanza Martinez Guillermo Dvila Rafael Palacios 《Applied microbiology》1988,54(5):1280-1283
Agrobacterium transconjugants containing symbiotic plasmids from different Rhizobium spp. strains that nodulate Phaseolus vulgaris were obtained. All transconjugants conserved the parental nodulation host range. Symbiotic (Sym) plasmids of Rhizobium strains isolated originally from P. vulgaris nodules, which had a broad nodulation host range, and single-copy nitrogenase genes conferred a Fix+ phenotype to the Agrobacterium transconjugants. A Fix− phenotype was obtained with Sym plasmids of strains isolated from P. vulgaris nodules that had a narrow host range and reiterated nif genes, as well as with Sym plasmids of strains isolated from other legumes that presented single nif genes and a broad nodulation host range. This indicates that different types of Sym plasmids can confer the ability to establish an effective symbiosis with P. vulgaris. 相似文献
7.
Nitrogen Source Regulates Glutamate Dehydrogenase NADP Synthesis in Neurospora crassa 总被引:8,自引:4,他引:4 下载免费PDF全文
Georgina Hernndez Ray Snchez-Pescador Rafael Palacios Jaime Mora 《Journal of bacteriology》1983,154(1):524-528
Neurospora crassa glutamate dehydrogenase-NADP (EC 1.3.1.3) has a higher activity when mycelium is grown on ammonium or nitrate as nitrogen source than when grown on glutamate or glutamine. Quantitative immunoelectrophoresis established that, under all conditions, enzyme activity corresponded to enzyme concentration. Isotope incorporation studies demonstrated that the nitrogen source exerts its regulation at the level of de novo enzyme synthesis. 相似文献
8.
J C Reubi G Mengod J M Palacios U Horisberger W H Hackeng S W Lamberts 《Cell growth & differentiation》1990,1(6):299-303
The somatostatin (SS), the SS mRNA, and the SS receptor contents were measured and compared in 25 human meningiomas. The SS tissue content, measured with radioimmunoassay, amounted to 2.89 +/- 0.82 pg/mg tissue (mean +/- SEM). The SS mRNA levels visualized by in situ hybridization using a 32P-labeled synthetic oligonucleotide probe were undetectable in all cases. SS receptors were measured with autoradiography using the octapeptide SS analogue 125I-204-090 as radioligand and were found to be present in high density in all meningiomas. For comparison, three SS-producing tumors, i.e., two human medullary thyroid carcinomas and one neuroendocrine gut tumor, were shown to have a high level of immunoreactive tissue SS, reaching, respectively, 2807, 401, and 22 pg/mg tissue, as well as moderate to high levels of SS mRNA detected with in situ hybridization. It can be concluded that meningioma tissue is not synthesizing significant amounts of SS in situ and that the low amount of tissue SS found in these tumors is likely to be due to SS transported there from a distant source, via blood, cerebrospinal fluid, or axons from nerve fibers terminating in this tissue. The high number of SS receptors found in meningiomas is therefore unlikely to be regulated by an autocrine SS production from the meningioma tissue itself but rather from another, unknown distant SS source. 相似文献
9.
Mutational analysis identifies functional domains in the influenza A virus PB2 polymerase subunit. 总被引:4,自引:3,他引:1 下载免费PDF全文
A collection of influenza virus PB2 mutant genes was prepared, including N-terminal deletions, C-terminal deletions, and single-amino-acid insertions. These mutant genes, driven by a T7 promoter, were expressed by transfection into COS-1 cells infected with a vaccinia virus encoding T7 RNA polymerase. Mutant proteins accumulated to levels similar to that of wild-type PB2. Immunofluorescence analyses showed that the C-terminal region of the protein is essential for nuclear transport and that internal sequences affect nuclear localization, confirming previous results (J. Mukaijawa and D. P. Nayak, J. Virol. 65:245-253, 1991). The biological activity of these mutants was tested by determining their capacity to (i) reconstitute RNA polymerase activity in vivo by cotransfection with proteins NP, PB1, and PA and a virion-like RNA encoding the cat gene into vaccinia virus T7-infected COS-1 cells and (ii) complete with the wild-type PB2 activity. In addition, when tested at different temperatures in vivo, two mutant PB2 proteins showed a temperature-sensitive phenotype. The lack of interference shown by some N-terminal deletion mutants and the complete interference obtained with a C-terminal deletion mutant encoding only 124 amino acids indicated that this protein domain is responsible for interaction with another component of the polymerase, probably PB1. To further characterize the mutants, their ability to induce in vitro synthesis of viral cRNA or mRNA was tested by using ApG or beta-globin mRNA as a primer. One of the mutants, 1299, containing an isoleucine insertion at position 299, was able to induce cRNA and mRNA synthesis in ApG-primed reactions but required a higher beta-globin mRNA concentration than wild-type PB2 for detection of in vitro synthesis. This result suggested that mutant I299 has diminished cap-binding activity. 相似文献
10.
In the present study we investigated if administration of vitamin A could protect rat liver microsomes and mitochondria from in vitro peroxidation. Appreciable decrease of chemiluminescence and lipid peroxidation was measured in microsomal membranes from rats receiving vitamin A, with respect to control animals. In membranes derived from control animals, the fatty acid composition was profoundly modified when subjected to in vitro peroxidation mediated by ascorbate-Fe++, with a considerable decrease of 20:4 n6 and 22:6 n3 in mitochondria and 18:2 n6 and 20:4 n6 in microsomes. As a consequence the peroxidizability index, a parameter based on the maximal rate of oxidation of specific fatty acids was higher in supplemented animals than in control group when both kind of membranes were analyzed. These changes were less pronounced in membranes derived from rats receiving vitamin A. These results are in agreement with previous results that indicated that vitamin A may act as an antioxidant protecting membranes from deleterious effects.Abbreviations BHT
butylated hydroxytoluene
- BSA
bovine serum albumin
- CL
chemiluminescence
- PI
peroxidizability index
Member of Carrera del Investigador Científico, Consejo Nacional de Investigaciones Cientificas y Técnicas de la Republica Argentina 相似文献