全文获取类型
收费全文 | 18068篇 |
免费 | 2031篇 |
国内免费 | 18篇 |
专业分类
20117篇 |
出版年
2021年 | 197篇 |
2020年 | 118篇 |
2019年 | 164篇 |
2018年 | 192篇 |
2017年 | 207篇 |
2016年 | 333篇 |
2015年 | 536篇 |
2014年 | 623篇 |
2013年 | 773篇 |
2012年 | 1039篇 |
2011年 | 1035篇 |
2010年 | 733篇 |
2009年 | 614篇 |
2008年 | 975篇 |
2007年 | 952篇 |
2006年 | 894篇 |
2005年 | 876篇 |
2004年 | 899篇 |
2003年 | 892篇 |
2002年 | 868篇 |
2001年 | 337篇 |
2000年 | 294篇 |
1999年 | 292篇 |
1998年 | 310篇 |
1997年 | 233篇 |
1996年 | 216篇 |
1995年 | 215篇 |
1994年 | 208篇 |
1993年 | 197篇 |
1992年 | 229篇 |
1991年 | 269篇 |
1990年 | 267篇 |
1989年 | 224篇 |
1988年 | 228篇 |
1987年 | 224篇 |
1986年 | 221篇 |
1985年 | 207篇 |
1984年 | 208篇 |
1983年 | 191篇 |
1982年 | 197篇 |
1981年 | 214篇 |
1980年 | 201篇 |
1979年 | 172篇 |
1978年 | 160篇 |
1977年 | 130篇 |
1976年 | 129篇 |
1975年 | 104篇 |
1974年 | 144篇 |
1973年 | 140篇 |
1972年 | 125篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We have partially purified the yeast spliceosome by differential sedimentation in glycerol gradients. By electron microscopy we have identified a particle in these fractions that is the spliceosome. In 100 mM KCl buffer, the yeast spliceosome is an ovoid disc with the dimensions of 20 x 23.5 nm with a central indentation. To verify that these ovoid particles were spliceosomes, specific labels were used to tag them. These tagged spliceosomes were then identified in the electron microscope. The salt dependent shift of sedimentation rate for the spliceosome can be explained by a change in size of the particle. 相似文献
102.
Identification of the glucose transporter in mammalian cell membranes with a 125I-forskolin photoaffinity label. 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The glucose transporter has been identified in a variety of mammalian cell membranes using a photoactivatable carrier-free radioiodinated derivative of forskolin, 3-[125I]iodo-4-azidophenethylamido-7-O-succinyldeacetylforskoli n ([125I]IAPS-forskolin) at 1-3 nM. The membranes that were photolabelled with [125I]IAPS-forskolin were human placental membranes, rat cortical and cerebellar synaptic membranes, rat cardiac sarcolemmal membranes, rat adipocyte plasma membranes, smooth-muscle membranes, and S49 wild-type (WT) lymphoma-cell membranes. The glucose transporter in plasma membranes prepared from the insulin-responsive rat cardiac sarcolemmal cells, rat adipocytes and smooth-muscle cells were determined to be approx. 45 kDa by SDS/polyacrylamide-gel electrophoresis (PAGE). Photolysis of human placental membranes, rat cortical and cerebellar synaptic membranes, and WT lymphoma membranes with [125I]-IAPS-forskolin, followed by SDS/PAGE, indicated specific derivatization of a broad band (43-55 kDa) in placental membranes and a narrower band (approx. 45 kDa) in synaptic membranes and WT lymphoma membranes. Digestion of the [125I]IAPS-forskolin-labelled placental and WT lymphoma membranes with endo-beta-galactosidase showed a reduction in the apparent molecular mass of the radiolabelled band to approx. 40 kDa. The membranes that were photolabelled with [125I]IAPS-forskolin and trypsin-treated produced a radiolabelled proteolytic fragment with an apparent molecular mass of 18 kDa. [125I]IAPS-forskolin is a highly effective probe for identifying low levels of glucose transporters in mammalian tissues. 相似文献
103.
RNA11 protein is associated with the yeast spliceosome and is localized in the periphery of the cell nucleus. 总被引:37,自引:14,他引:23
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
T H Chang M W Clark A J Lustig M E Cusick J Abelson 《Molecular and cellular biology》1988,8(6):2379-2393
The yeast rna mutations (rna2 through rna10/11) are a set of temperature-sensitive mutations that result in the accumulation of pre-mRNAs at the nonpermissive temperature. Most of the yeast RNA gene products are involved in and essential for mRNA splicing in vitro, suggesting that they code for components of the splicing machinery. We tested this proposal by using an in vitro-synthesized RNA11 protein to complement the temperature-sensitive defect of the rna11 extract. During the in vitro complementation, the input RNA11 protein was associated with the 40S spliceosome and a 30S complex, suggesting that the RNA11 protein is indeed a component of the spliceosome. The formation of the RNA11-associated 30S complex did not require any exogenous RNA substrate, suggesting that this 30S particle is likely to be a preassembled complex involved in splicing. The RNA11-specific antibody inhibited the mRNA splicing in vitro, confirming the essential role of the RNA11 protein in mRNA splicing. Finally, using the anti-RNA11 antibody, we localized the RNA11 protein to the periphery of the yeast nucleus. 相似文献
104.
Role of cell-cycle in regulating neuroepithelial cell shape during bending of the chick neural plate
Summary Neuroepithelial cells transform from spindle-shaped to wedge-shaped within the median and paired dorsolateral hinge points of the bending neural plate, but the mechanisms underlying these localized changes are unclear. This study was designed to evaluate further the hypothesis that localized wedging of neuroepithelial cells during bending involves basal cellular expansion resulting from alteration of the cell-cycle. Neurulating chick embryos were treated with tritiated thymidine, and transverse sections through the midbrain were examined autoradiographically. Parameters of the cell-cycle as well as nuclear position and size were assessed in the median hinge point, which contains predominantly wedge-shaped cells, and in adjacent lateral areas of the neural plate, which contain predominantly spindle-shaped cells. Both the DNA-synthetic phase and non-DNA synthetic portion of the cell-cycle were significantly longer in the median hinge point than in lateral neuroepithelial areas, some nuclei in both regions were located basally during these phases, and virtually all basal nuclei in the median hinge point were large. Additionally, the mitotic phase was significantly shorter in the median hinge point than in lateral areas. We present a model to explain how alteration of the cell-cycle in the median hinge point could generate wedging of cells in this region. 相似文献
105.
106.
107.
H. Barton Grossman Gary Wedemeyer Judith Stein 《Cancer immunology, immunotherapy : CII》1988,26(3):269-272
Summary The autologous serologic reactivity of 13 patients with bladder cancer was evaluated using cell lines derived from each individual's own tumor as targets. Protein A and immune adherence assays were employed to determine antibody binding to the tumor targets at varying passage numbers. Autologous reactivity was found in 6 of the 13 cell lines tested. However, the titer was usually low regardless of the passage number. Seven autologous serum/cell line combinations were tested using both low and high passage cells as targets. In six of these combinations, the degree of antibody binding was similar with both low and high passage target cells. The incidence of autologous reactivity in the 12 patients with urothelial tumors was 50%.This investigation was supported by PHS Grant number CA36933, awarded by the National Cancer Institute, DHHS. 相似文献
108.
Dori R. Germolec Robert R. Maronpot Michael F. Ackermann Stephen J. Vore Kathleen Dittrich Gary J. Rosenthal Michael I. Luster 《Cancer immunology, immunotherapy : CII》1988,27(2):121-127
Summary The relationship between immune function and chemically induced hepatocarcinogenesis was studied employing an in vivo murine model. Neonatal B6C3F1 mice were given a single carcinogenic dose of diethylnitrosamine (DEN) and the time-response kinetics for the early (foci of alteration) and late (adenomas/carcinomas) phases of hepatocellular carcinogenesis were compared to changes in hematopoiesis and immune functions associated with immune surveillance and natural resistance. Increases in hematopoiesis occurred just prior to or concurrent with the appearance of hepatocellular carcinomas, while increased macrophage and natural killer cell cytotoxicity and suppression of cell-mediated immunity occurred following tumor appearance and progressed with increasing tumor burden. Neither immunological nor hematopoietic changes were associated with early phases of hepatocarcinogenesis, as monitored by the appearance of altered hepatocellular foci. Although changes in hematopoiesis may represent an early indicator for hepatocarcinogenesis in the mouse tumor model, the data suggest that altered immune surveillance and natural resistance are not factors in the development of chemically induced hepatocellular tumors, and the changes in immune function are probably secondary to tumor development. 相似文献
109.
Mandip Singh Gary Faulkner Tarun I. Ghose Michael Mezei 《Cancer immunology, immunotherapy : CII》1988,27(1):17-25
Summary The potential of antibody-linked SUVs containing MTX in anticancer therapy was investigated. The SUVs, mean diameter 50±20 nm, were prepared by probe sonication of MTX-containing MLVs and were covalently linked either to a RAMG or NRG. After incubation with M21 melanoma cells for 2 h, RAMG-linked SUVs showed 2 and 4 times more binding than NRG-linked MTX-containing SUVs or MTX-containing SUVs unlinked to any Ig. Furthermore, on incubating M21 melanoma cells with RAMG-linked 3H MTX-containing SUVs for 2, 4, and 8 h at 4° C or 37° C, a higher radioactivity was associated with cells at 37° C than at 4° C. Membrane immunofluorescence revealed aggregation of and cap formation by RAMG-linked SUVs after 2 h (37° C) and endocytosis at 4 and 8 h at 37° C. Electron microscopic and autoradiographic studies confirmed aggregation of 3H MTX-containing SUVs around and on the surface of M21 cells. Electron microscopy also revealed these SUVs inside invaginations of and under the plasma membrane of melanoma cells. A colony inhibition assay showed that RAMG-linked, MTX-containing SUVs were 60 times, 8 times, and 4.5 times more growth inhibitory than free MTX, NRG-linked MTX-containing SUV, and MTX-containing SUVs unlinked to any Ig, but not toxic to a human kidney cancer line (that did not react with RAMG).
Abbreviations used: DPPC, DL- -dipalmitoyl phosphatidylcholine; DTT, dithiothreitol; MTX, methotrexate; (MTX)SUV or MLV, MTX-containing SUV or MLV; MLV, multilamellar vesicle; NRG, normal rabbit immunoglobulin G; RAMG, rabbit antimelanoma IgG; SA, stearylamine; SPDP, N-succinimidy1-3-(2-pyridyldithio)propionate; SUV, small unilamellar vesicle; CHOL, cholesterol; LUV, large unilamellar vesicle; Ig, immunoglobulin; PDP-SA, N-[3-(2-pyridyldithio)-propinyl]stearylamine 相似文献
110.
In past attempts, the experimental germination of the seeds of Euonymus americanus L. in vitro has had little success. However, treatment of seeds with ruminal fluid containing viable microflora has been successful in stimulating germination. In the presence of the cellulolytic ruminal bacterium, Clostridium cellobioparum ATCC 15832, seeds of E. americanus were stimulated to germinate. Subsequent studies were designed to determine whether the bacterium synthesized a cellulolytic enzyme responsible for initiating germination. The cell-free endocellulase from C. cellobioparum induced germination of the seeds. To support the hypothesis that the endocellulase from C. cellobioparum was responsible for triggering germination, a 1,4-beta-d-glucan glucanohydrolase (EC 3.2.1.4) from Penicillum funiculosum was used to treat the seeds. In addition, no germination was obtained from seeds treated with a commercial exocellulase enzyme. Also, Ruminococcus flavefaciens FD-1 was found to initiate germination of E. americanus seeds. Thus, cellulase activity is indicated in the degradation of the testa of the seed, allowing imbibition and germination. 相似文献