全文获取类型
收费全文 | 9204篇 |
免费 | 675篇 |
国内免费 | 2篇 |
出版年
2024年 | 4篇 |
2023年 | 46篇 |
2022年 | 49篇 |
2021年 | 218篇 |
2020年 | 132篇 |
2019年 | 173篇 |
2018年 | 227篇 |
2017年 | 188篇 |
2016年 | 313篇 |
2015年 | 501篇 |
2014年 | 583篇 |
2013年 | 685篇 |
2012年 | 822篇 |
2011年 | 842篇 |
2010年 | 550篇 |
2009年 | 429篇 |
2008年 | 556篇 |
2007年 | 561篇 |
2006年 | 485篇 |
2005年 | 502篇 |
2004年 | 423篇 |
2003年 | 400篇 |
2002年 | 346篇 |
2001年 | 81篇 |
2000年 | 57篇 |
1999年 | 81篇 |
1998年 | 90篇 |
1997年 | 64篇 |
1996年 | 55篇 |
1995年 | 56篇 |
1994年 | 45篇 |
1993年 | 42篇 |
1992年 | 27篇 |
1991年 | 27篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
排序方式: 共有9881条查询结果,搜索用时 140 毫秒
71.
Claudia M. Caillaud J. S. Pierre B. Chaubet J. P. Di Pietro 《Entomologia Experimentalis et Applicata》1995,75(1):9-18
The behaviour ofSitobion avenae (F.), was compared on resistant wheat lines ofTriticum monococcum (L.) and a susceptible variety ofTriticum aestivum (L.). Firstly, stylet penetration activities were monitored with the Electrical Penetration Graph (EPG) technique and subsequently
analysed using flow charts combined with correspondence analysis. Plant resistance was shown to be associated with repeated
penetrations without access to either the xylem or the phloem, and with numerous failures in starting a sustained sap ingestion
(as represented by pattern E2). Access to sieve elements of the phloem did not seem to be much affected on resistant plants
but it took the aphid three times as long to produce a sap ingestion pattern when maintained on the resistant lineT. monococcum no 44 (Tm44) as compared with aphids maintained on susceptible plants. As a result the total time spent in ingesting from sieve
elements was reduced by 72% on Tm44. Secondly, direct observations of freely-moving apterous adults were performed. Aphids
did not discriminate between resistant and susceptible wheat during the first 30 min of access to test leaves, but only 4
out of 25 aphids were still probing after eight hours on resistant Tm44.
The relevance of these results to possible location of the resistance factor(s) are discussed. Although detection of plant
resistance before sieve elements are reached can not be rigorously excluded, the factors involved inT. monococcum resistance toS. avenae undoubtedly occur within the phloem vessels. 相似文献
72.
Contactinhibin was found to be involved in contact-dependent inhibition of growth. The growth inhibitory activity of contactinhibin is mediated by N-linked oligosaccharides with desialylated -glycosidically linked, terminal galactose residues. Here we show that in sparse human fibroblasts contactinhibin was expressed in a biologically inactive, highly sialylated form both on the plasma membrane and intracellularily, while in confluent cells plasma membrane localized contactinhibin was present in a biologically active, low sialylated form. Plasma membranes were shown to contain a glycoprotein sialidase which is suggested to be engaged in the activation of contactinhibin in a cell contact-dependent manner. 相似文献
73.
Isolation and characterization of the mycobacterial phagosome: segregation from the endosomal/lysosomal pathway 总被引:5,自引:0,他引:5
Zahra Hasan Claudia Schlax Lotte Kuhn Ivan Lefkovits Douglas Young Jelle Thole & Jean Pieters 《Molecular microbiology》1997,24(3):545-553
Mycobacteria have the ability to persist within host phagocytes, and their success as intracellular pathogens is thought to be related to the ability to modify their intracellular environment. After entry into phagocytes, mycobacteria-containing phagosomes acquire markers for the endosomal pathway, but do not fuse with lysosomes. The molecular machinery that is involved in the entry and survival of mycobacteria in host cells is poorly characterized. Here we describe the use of organelle electrophoresis to study the uptake of Mycobacterium bovis bacille Calmette Guerin (BCG) into murine macrophages. We demonstrate that live, but not dead, mycobacteria occupy a phagosome that can be physically separated from endosomal/lysosomal compartments. Biochemical analysis of purified mycobacterial phagosomes revealed the absence of endosomal/lysosomal markers LAMP-1 and β-hexosaminidase. Combining subcellular fractionation with two-dimensional gel electrophoresis, we found that a set of host proteins was present in phagosomes that were absent from endosomal/lysosomal compartments. The residence of mycobacteria in compartments outside the endosomal/lysosomal system may explain their persistence inside host cells and their sequestration from immune recognition. Furthermore, the approach described here may contribute to an improved understanding of the molecular mechanisms that determine the intracellular fate of mycobacteria during infection. 相似文献
74.
75.
76.
Maurizio Meta Marco Ponte Marina Guastella Claudia Semino Gabriella Pietra Giovanni Battista Ratto Giovanni Melioli 《Cancer immunology, immunotherapy : CII》1995,40(4):235-240
Despite the combined use of surgery and chemoradiotherapy, the poor prognosis of advanced non-smallcell lung cancer (NSCLC) requires the definition of new therapeutic approaches. The presence of T lymphocytes, with peculiar phenotypic, functional and molecular characteristics within the tumour, suggested the possible use of these cells, expanded in vitro, in protocols of adoptive immunotherapy. We have described how a population of oligoclonal T lymphocytes, derived from advanced NSCLC, can be expanded in vitro and has the capability of lysing autologous cancer cells. What is more important, we observed that patients with advanced NSCLC, treated with TIL expanded in vitro and recombinant interleukin-2, seemed to have a disease-free period longer than that of patients treated with conventional chemoradiotherapy. in an attempt to find new sources of specific lymphocytes for immunotherapy, we describe the analysis of the phenotypic, functional and molecular characteristics of T lymphocytes, derived from lymph nodes draining advanced NSCLC. In this paper we show that these cells, have restriction patterns of T cell receptor chain similar to those detectable in the population of infiltrating T lymphocytes. This finding suggests that T cells derived from draining lymph nodes of advanced NSCLC have peculiar characteristics and can be a suitable source of effector cells for protocols of adoptive immunotherapy in lung cancer treatment. 相似文献
77.
Claudia B. Caputo James H. Kimura Vincent C. Hascall 《Archives of biochemistry and biophysics》1984,230(2):594-604
Rat chondrosarcoma chondrocytes were cultured in the presence of puromycin to induce premature termination of core protein precursor. The structure and function of intracellular and extracellular proteoglycans were assessed by molecular sieve chromatography and polyacrylamide gel electrophoresis. [3H]Serine incorporation was maximally inhibited by 3 × 10?4m puromycin but unaffected by 10 ?5m puromycin. Proteoglycans synthesized in the presence of puromycin exhibited increased monomer size due to increased chondroitin sulfate chain size, typical of proteoglycans synthesized in the presence of protein synthesis inhibitors, but no loss in ability to bind to hyaluronic acid; and no loss in core protein size was observed after treatment with chondroitinase. These data suggest that chondrocytes select only completed or nearly completed core protein molecules to process into proteoglycans. 相似文献
78.
The etioplast»chloroplast transition in the cotyledons of mustard seedlings (Sinapis alba L.) has been studied by electron microscopy. It was found that the active form of phytochrome, established by a red light pulse pretreatment, increases the initial rate and eliminates the lag of grana and stroma thylakoid formation after the onset of white light 60 h after sowing. The effect of a pretreatment with 15 s red light pulses is fully reversible by 756 nm light pulses. This reversibility is lost within 5 min. Evidence is presented which suggests that the time course of grana and stroma thylakoid formation is not correlated with the time course of the dispersal of the prolamellar body. The different functions of phytochrome and chlorophyll in controlling thylakoid formation are discussed. 相似文献
79.
Enhanced Rate of Expression and Biosynthesis of Neuropeptide Y After Kainic Acid-Induced Seizures 总被引:2,自引:0,他引:2
Romuald Bellmann Rudolf Widmann Claudia Olenik Dieter K. Meyer Dagmar Maas Josef Marksteiner Günther Sperk 《Journal of neurochemistry》1991,56(2):525-530
Recent studies have shown marked increases in brain content of neuropeptide Y (NPY) after seizures induced by intraperitoneal injection of kainic acid and after pentylenetetrazole kindling in the rat. We have now investigated possible changes in the rate of biosynthesis of NPY after kainic acid treatment, by using pulse-labeling of the peptide and by determining prepro-NPY mRNA concentrations. For pulse labeling experiments, [3H]tyrosine was injected into the frontal cortex, and the incorporation of the amino acid into NPY was determined after purifying the peptide by gel filtration chromatography, antibody affinity chromatography, and reversed-phase HPLC. At 2 and 30 days after kainic acid treatment, the rate of tyrosine incorporation was enhanced by approximately 380% in the cortex. In addition, concentrations of pre-pro-NPY mRNA were determined in four different brain areas by hybridization of Northern blots with a complementary 32P-labeled RNA probe 2, 10, 30, and 60 days after kainic acid treatment. Marked increases were observed in the frontal cortex (by up to 350% of controls), in the dorsal hippocampus (by 750%), and in the amygdala/pyriform cortex (by 280%) at all intervals investigated. In the striatum only a small, transient increase was observed. The data demonstrate increased expression of prepro-NPY mRNA and an enhanced rate of in vivo synthesis of NPY as a result of seizures induced by the neurotoxin kainic acid. 相似文献
80.