全文获取类型
收费全文 | 6229篇 |
免费 | 697篇 |
国内免费 | 3篇 |
专业分类
6929篇 |
出版年
2021年 | 75篇 |
2019年 | 62篇 |
2018年 | 52篇 |
2017年 | 77篇 |
2016年 | 116篇 |
2015年 | 174篇 |
2014年 | 203篇 |
2013年 | 236篇 |
2012年 | 313篇 |
2011年 | 282篇 |
2010年 | 180篇 |
2009年 | 175篇 |
2008年 | 249篇 |
2007年 | 233篇 |
2006年 | 217篇 |
2005年 | 227篇 |
2004年 | 193篇 |
2003年 | 199篇 |
2002年 | 218篇 |
2001年 | 216篇 |
2000年 | 183篇 |
1999年 | 186篇 |
1998年 | 99篇 |
1997年 | 78篇 |
1996年 | 64篇 |
1995年 | 71篇 |
1994年 | 55篇 |
1993年 | 66篇 |
1992年 | 136篇 |
1991年 | 113篇 |
1990年 | 101篇 |
1989年 | 116篇 |
1988年 | 106篇 |
1987年 | 94篇 |
1986年 | 103篇 |
1985年 | 91篇 |
1984年 | 63篇 |
1983年 | 74篇 |
1982年 | 65篇 |
1981年 | 52篇 |
1980年 | 64篇 |
1979年 | 62篇 |
1975年 | 63篇 |
1974年 | 67篇 |
1973年 | 64篇 |
1972年 | 72篇 |
1970年 | 63篇 |
1969年 | 57篇 |
1968年 | 55篇 |
1967年 | 58篇 |
排序方式: 共有6929条查询结果,搜索用时 15 毫秒
71.
Ronald J. Hill Margaret R. Mott Fujiko Watt Theodora Fifis P. Anne Underwood 《Chromosoma》1986,94(6):441-448
An antigen making a major contribution to the immune response to Drosophila melanogaster chromatin resides primarily on a nonhistone charge-class family of proteins of Mr 74,000. Immunofluorescence detects this antigen at interbands, puffs and diffuse bands of D. melanogaster salivary chromosomes isolated without exposure to acid fixatives, and on nucleoplasmic ribonucleoprotein droplets. In the electron microscope, gold labelling reveals the binding of monoclonal antibodies specific for the antigen at chromosomal loci generally bearing putative ribonucleoprotein (RNP) particles. However, the locus 3C 11–12 is remarkable in that it bears putative RNP particles but is virtually unlabelled, suggesting protein specificity at different active loci. 相似文献
72.
73.
Enumeration by DNA colony hybridization of virulent Yersinia enterocolitica colonies in artificially contaminated food. 总被引:8,自引:5,他引:3 下载免费PDF全文
A genetic probe was used to identify and enumerate virulent Yersinia enterocolitica colonies in 11 artificially contaminated foods. Efficiency of enumeration, determined by autoradiography after DNA colony hybridization, ranged from 66 to 100% (average, 86%) and was influenced by the number of indigenous bacteria. The use of nitrocellulose filters and agar medium had little effect on efficiency of enumeration. 相似文献
74.
The intrinsic fluorescence of lauryl maltoside solubilized bovine heart cytochrome c oxidase has been determined to arise from tryptophan residues of the oxidase complex. The magnitude of the fluorescence is approximately 34% of that from n-acetyltryptophanamide (NATA). This level of fluorescence is consistent with an average heme to tryptophan distance of 30 A. The majority of the fluorescent tryptophan residues are in a hydrophobic environment as indicated by the fluorescence emission maximum at 328 nm and the differing effectiveness of the quenching agents: Cs+, I-, and acrylamide. Cesium was ineffective up to a concentration of 0.7 M, whereas quenching by the other surface quenching agent, iodide, was complex. Below 0.2 M, KI was ineffective whereas between 0.2 and 0.7 M 15% of the tryptophan fluorescence was found to be accessible to iodide. This pattern indicates that protein structural changes were induced by iodide and may be related to the chaotropic character of KI. Acrylamide was moderately effective as a quenching agent of the oxidase fluorescence with a Stern-Volmer constant of 2 M-1 compared with acrylamide quenching of NATA and the water-soluble enzyme aldolase having Stern-Volmer constants of 12 M-1 and 0.3 M-1, respectively. There was no effect of cytochrome c on the tryptophan emission intensity from cytochrome c oxidase under conditions where the two proteins form a tight, 1:1 complex, implying that the tryptophan residues near the cytochrome c binding site are already quenched by energy transfer to the homes of the oxidase. The lauryl maltoside concentration used to solubilize the enzyme did not affect the fluorescence of NATA.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
75.
The ligand binding specificity and tissue localization of a rat alveolar macrophage lectin 总被引:2,自引:0,他引:2
The parameters of the reaction between a rat alveolar macrophage lectin (Mr = 180,000) and its ligands have been examined. The reaction is dependent on Ca2+ over the optimal pH range for binding. The apparent dissociation constant for fucosyl bovine serum albumin, the standard ligand used in these studies, is 1.4 X 10(-10) M. The ligand binding specificity was determined by measurement of the inhibition of binding of fucosyl bovine serum albumin by various glycoproteins and saccharides. D-Mannose, L-fucose, and N-acetyl-D-glucosamine were the most effective inhibitors, and D-galactose was much poorer. The equatorial hydroxyl groups on the C-3 and C-4 of the mannose ring are important in the lectin-ligand interaction, and the axial hydroxyl group on the C-2 contributes to a lesser extent. Immunocytological studies revealed that the lectin isolated from alveolar macrophages is widely distributed in other rat tissues. Hepatocytes are devoid of the lectin, but hepatic Kupffer cells and endothelial cells contain significant amounts. This was confirmed by isolation of the lectin from liver. Spleen and skeletal muscle also contain lectin, but much smaller amounts were found in brain, kidney, and heart muscle. 相似文献
76.
Regulation of major acute-phase plasma proteins by hepatocyte- stimulating factors of human squamous carcinoma cells 总被引:19,自引:0,他引:19 下载免费PDF全文
Human squamous carcinoma (COLO-16) cells release factors which specifically stimulate the synthesis of major acute-phase plasma proteins in human and rodent hepatic cells. Anion exchange, hydroxyapatite, lectin, and gel chromatography of conditioned medium of COLO-16 cells result in separation into three distinct forms of hepatocyte-stimulating factors (designated HSF-I, HSF-II, and HSF-III) with apparent molecular weights of 30,000, 50,000 and 70,000, respectively. None of the preparations contains detectable amounts of thymocyte-stimulating activity. Each of the three HSF forms stimulates the accumulation of mRNA for alpha 1-antichymotrypsin in the human hepatoma cell line, HepG2. When the same factors were added to primary cultures of adult rat hepatocytes, the expression of the same set of plasma proteins was modulated as by nonfractionated medium. The hormonally induced accumulation of mRNA for acute phase proteins is qualitatively comparable to that occurring in the liver of inflamed rats. Unlike in human cells, in rat liver cells dexamethasone acts additively and synergistically with HSFs. The only functional difference between the three HSF forms lies in the level of maximal stimulation. HSF-I represents the predominant form produced by normal human keratinocytes and closely resembles in molecular size and isoelectric point the activity produced by activated peripheral blood monocytes while the larger molecular weight forms are more prevalent in human as well as mouse squamous carcinoma cells. The observation that HSFs from different sources elicit essentially the same pleiotropic response in hepatic cells led to the hypothesis that the species-specific reaction of adult liver cells to inflammatory stimuli is pre-programmed and that the function of any HSF is to trigger and tune the execution of this fixed cellular process. 相似文献
77.
Carbonic anhydrase (CA) activity was measured by the Bowes-Davis technique in diluted hemolysates of dog erythrocytes, rabbit erythrocytes, and dog lung tissue homogenates. Plasma (from the same animal) inhibited the CA activity in each case. For 1:16,700 dilution of dog erythrocytes, the CA catalyzed the CO2 hydration reaction by 5.3 +/- 0.4-fold above the uncatalyzed rate, and half that activity was inhibited by plasma concentrations of 0.44 +/- 0.05%. Similar rabbit CA concentrations were inhibited by plasma concentrations of 1.02 +/- 0.24%. CA from dog lung tissue homogenate is only partially inhibited by plasma even at high plasma concentrations, suggesting different isozymes, at least one of which is not inhibited by plasma. The results suggest that extrapolating from artificially perfused lungs or histological observations to in vivo conditions may not be valid, and the possibility of inhibition by plasma in at least some species should be considered. 相似文献
78.
The equipment used for the first sampling of arterial blood at depth on free-diving Weddell seals Leptonychotes weddelli is described. Blood was withdrawn through an aortic catheter by a submersible, peristaltic roller pump and stored in a single- or multiple-sample collection device. The multiple sampler allowed up to eight individual blood samples to be collected during a single dive. The blood pump was controlled by a dedicated microcomputer that allowed initiation of blood sampling at flexible combinations of depth and/or time during either the descending or ascending phase of the dive. The dedicated microcomputer also recorded swimming depth, velocity, heart rate, and body temperature at selectable time intervals. These data were transmitted to a laboratory computer, and blood samples were retrieved, when the seal surfaced to breathe. 相似文献
79.
M Ogasawara K Granfors D H Kono J L Hill D T Yu 《Journal of immunology (Baltimore, Md. : 1950)》1985,135(1):553-559
It has been suggested that the O-side chains of the lipopolysaccharide (LPS) of serotype 0:3 strains of Yersinia enterocolitica vary quantitatively and qualitatively depending on whether they are cultured at 37 degrees C or 25 degrees C. It is uncertain whether this affects the expression of the serotype-specific antigens that are probably carried on the LPS. We studied this question with a serotype 0:3-specific monoclonal antibody, 2C1. This monoclonal antibody immunoprecipitated a 39K major protein from detergent-solubilized 125I-labeled Yersinia preparation. However, results of Western blot experiments demonstrated that the antigens reactive with 2C1 were not actually the 39K protein but the O-side chains of the LPS. Significantly, reactivity could be detected whether the bacteria were cultured at room temperature or at 37 degrees C. However, absorption experiments confirmed that there were less accessible antigenic determinants on the 37 degrees C-LPS. The LPS preparations were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining. These SDS-PAGE profiles showed that less O-side chains were present in the 37 degrees C-LPS. Hence, the most likely explanation for our observation is that the 37 degrees C incubation condition induced a partial smooth to rough transition of the Yersinia LPS with a decrease in the amount of 2C1-reactive antigen. 相似文献
80.