全文获取类型
收费全文 | 12308篇 |
免费 | 889篇 |
国内免费 | 8篇 |
出版年
2021年 | 121篇 |
2020年 | 94篇 |
2019年 | 124篇 |
2018年 | 151篇 |
2017年 | 158篇 |
2016年 | 216篇 |
2015年 | 372篇 |
2014年 | 372篇 |
2013年 | 556篇 |
2012年 | 685篇 |
2011年 | 599篇 |
2010年 | 461篇 |
2009年 | 373篇 |
2008年 | 547篇 |
2007年 | 546篇 |
2006年 | 545篇 |
2005年 | 553篇 |
2004年 | 543篇 |
2003年 | 560篇 |
2002年 | 537篇 |
2001年 | 132篇 |
2000年 | 100篇 |
1999年 | 138篇 |
1998年 | 170篇 |
1997年 | 158篇 |
1996年 | 150篇 |
1995年 | 157篇 |
1994年 | 127篇 |
1993年 | 162篇 |
1992年 | 113篇 |
1991年 | 138篇 |
1990年 | 120篇 |
1989年 | 104篇 |
1988年 | 123篇 |
1987年 | 107篇 |
1986年 | 91篇 |
1985年 | 113篇 |
1984年 | 168篇 |
1983年 | 141篇 |
1982年 | 140篇 |
1981年 | 151篇 |
1980年 | 128篇 |
1979年 | 112篇 |
1978年 | 135篇 |
1977年 | 101篇 |
1976年 | 88篇 |
1975年 | 94篇 |
1974年 | 80篇 |
1973年 | 67篇 |
1970年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 165 毫秒
121.
122.
Jan Johansson Ella Cederlund Sudhir B. Moodbidri Anil Sheth Hans Jörnvall 《Bioscience reports》1986,6(6):535-541
A protein fraction from human testis was structurally investigated. The main component of the fraction reported to contain inhibin-like activity was purified and analyzed by tryptic digestion. The peptides obtained identified the protein as an enzyme, superoxide dismutase, previously known to be present in seminal plasma. The results show that superoxide dismutase is a major enzyme, also of testicular material. They further demonstrate the importance of using pure fractions, and controls such as checks with structural analysis or synthetic peptides, in the work of elucidating the nature of inhibin and other hormonal peptides. 相似文献
123.
Lineage-specific expression of c-fos and c-fms in human hematopoietic cells: Discrepancies with the in vitro differentiation of leukemia cells 总被引:2,自引:0,他引:2
Hans Kreipe Heinz J. Radzun Klaus Heidorn Mohammad Reza Parwaresch Bernard Verrier Rolf Müller 《Differentiation; research in biological diversity》1986,33(1):56-60
In vitro differentiation studies using the bipotential human leukemia cell line, HL60, have indicated that high levels of expression of two proto-oncogenes, c-fos and c-fms, are restricted to the myelomonocytic lineage. No such expression has been detected in induced granulocytic cells. In striking contrast to these observations, we found that c-fos mRNA levels are very high in purified human granulocytes, but barely detectable in blood monocytes and tissue macrophages. Human granulocytes contain, however, relatively low levels of c-fos protein, indicating that c-fos mRNA is inefficiently translated or that the protein is rapidly degraded in these cells. In closer agreement with the in vitro results, the level of the expression of c-fms is high in purified blood monocytes and undetectable in granulocytes. We found, however, that the evolution of monocytes into tissue macrophages is accompanied by a significant decrease in c-fms expression, suggesting that the function of c-fms is restricted to specific stages of monocytic differentiation. Our observations also show that results obtained using in vitro differentiation systems have to be regarded with caution, since they may not reflect the in vivo situation. 相似文献
124.
4-Trifluoroacetamidoaniline was reacted with reducing oligosaccharides in the presence of sodium cyanoborohydride to give aminoalditol derivatives, useful for linkage to proteins or solid matrices. A mixture of reducing oligosaccharides, difficult to separate by HPLC, was treated in the same way. The resulting derivatives were easily separated by HPLC.Abbreviations TFAN
4-trifluoroacetamidoaniline
- LcOse4
lacto-N-tetraose
- IV2Fuc-LcOse4
lacto-N-fucopentaose l
- III4Fuc-LcOse4
lacto-N-fucopentaose II
- III3Fuc-nLcOse4
lacto-N-fucopentaose III
- IV2Fuc, III4Fuc-LcOse4
lacto-N-difucohexaose I
- II6Galß1-4GlcNAc-LcOse4
lacto-N-hexaose
- II3NeuAc-Lac
3-sialyllactose
- GlcNAcß1-4GlcNAcß1-4GlcNAc
chitotriose
- GalNac1-3|Fuc1-2|Galß1-4Glc
A-tetrasaccharide 相似文献
125.
Chromatophores isolated from the marine phototrophic bacterium Rhodobacter sulfidophilus were found to photoreduce NAD with sulfide as the electron donor. The apparent K
m for sulfide was 370 M and the optimal pH was 7.0. The rate of NAD photoreduction in chromatophore suspensions with sulfide as the electron donor (about 7–12 M/h·mol Bchl) was approximately onetenth the rate of sulfide oxidation in whole cell suspensions. NAD photoreduction was inhibited by rotenone, carbonyl cyanide-m-chlorophenylhydrazone, and antimycin A. Sulfide reduced ubiquinone in the dark when added to anaerobic chromatophore suspensions. These results suggest that electron transport from sulfide to NAD involves an initial dark reduction of ubiquinone followed by reverse electron transport from ubiquinol to NAD mediated by NADH dehydrogenase.Abbreviations Bchl
bacteriochlorophyll
- CCCP
carbonyl cyanide-m-chlorophenylhydrazone
- MOPS
3(N-morpholino)-propane sulfonate
- Uq
ubiquinone 相似文献
126.
Max Kaufmann Jorgen Marqverson Kenneth E. Stanley Christian Mouritzen Hans Hvid-Hansen 《Cancer immunology, immunotherapy : CII》1986,22(1):56-61
Summary The distribution of Corynebacterium parvum labeled with 131iodine or 99mtechnetium was studied in 17 patients with bronchogenic carcinoma. The labeled bacteria were given intravenously or intrapleurally and monitored by whole-body gamma tracking and samples of blood and urine. Even though the rate of physical decay is quite different for 131iodine and 99mtechnetium, the tracking time of labeled bacteria was limited to 24 h after injection for both radioactive isotopes. Technetium labeling was preferred because of greater imaging resolution and less radiation dose to the patient. Following intravenous administration, labeled C. parvum was found predominantly in the liver and spleen, and in a lesser amount in the lung. Radioactivity was confined to the pleural cavity after intrapleural injection. These results suggest the combined intravenous and intrapleural route of adjuvant immunosupportive agents such as C. parvum for operable lung cancer patients. 相似文献
127.
Hans G. Wallraff 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1986,159(2):143-159
Summary 1,324 vanishing bearings of individual pigeons, completely inexperienced in homing, were recorded during 100 releases at 36 sites symmetrically distributed around their home loft near Würzburg at distances ranging from 7 to 180 km. Two directional components could be derived from the data: (a) a weak but significant homeward component pointing to the loft site and (b) a more pronounced compass component pointing to the northwest (Fig. 1). With the latter kind of tendency the pigeons clearly demonstrated what earlier had been described as preferred compass direction (PCD).Homeward directedness at the 36 differently situated release sites is negatively correlated with angular divergence between PCD and homeward direction (Fig. 2). Compass preferences derived from different quartets of symmetrically arranged sites were similar. Over a period of 11 years the PCD varied significantly in time but did not change fundamentally (Figs. 3, 4). Interrelations between various parameters of initial-orientation data were investigated by correlation analyses (Table 3).PCDs have not only been found in the Würzburg area but around many other loft sites as well. They are, however, differently pronounced, and in experienced pigeons they are generally weaker than in first-flight birds. Various reasons (partly evident, partly thought possible) for variability of PCDs, and for their absence in some series of experiments, are discussed.As a PCD persists, and even tends to become clearer, after elimination of homeward orientation by olfactory deprivation, it is concluded that it reflects directional tendencies which are independent of the process of site localization. A great deal of what is called release-site biases, i.e., site-specific deviations from the beeline course towards home, can be understood on a PCD basis. The functional background of the PCD is unknown. Hypothetical advantages for the pigeons homing strategy are considered.Abbreviations
RSB
release-site bias
-
PCD
preferred compass direction 相似文献
128.
Kurt Kraeuchi Anna Wirz-Justice Tadaomi Morimasa Rosi Suetterlin-Willener Hans Feer 《Chronobiology international》1986,3(2):127-133
Specific binding of [3H]-imipramine in the rat suprachiasmatic nuclei, occipital cortex and caudate putamen underwent significant and replicable changes throughout 24 hr under a light-dark cycle or under constant conditions. Daily variations were also found in the medial and dorsal raphe nuclei and the lateral hypothalamus. Methamphetamine, a psychoactive drug with marked effect on circadian rhythms in physiological and hormonal parameters and adrenergic receptors, did not have any significant effect on imipramine binding rhythms in eight discrete brain regions. Thus a drug known to reduce serotoninergic neurotransmission did not change characteristics of the modulatory binding site related to serotonin uptake. 相似文献
129.
The hematological micronucleus test is regarded as an indicator of the clastogenic effect of chemicals and acute cytogenetic damage. The test can be carried out in red blood cells of the bone marrow and of the spleen, as well as in peripheral erythrocytes. We have determined the precise background values of micronucleated red blood cells for the peripheral blood of BALB/c DBA/2, and NMRI mice. Bleeding, phenylhydrazine-induced hemolysis, and splenectomy generated an increase of micronucleated erythrocytes in the peripheral blood of mice. Our data thus demonstrate that such factors should be taken into consideration when the micronucleus test is used for screening the genotoxic potential of chemicals. Furthermore, the micronucleus-inducing effect of cyclophosphamide was studied in normal and splenectomized mice and, in addition, a comparison of the sensitivity of the micronucleus test was carried out in peripheral blood and bone marrow after cyclophosphamide treatment. Our data demonstrate that the kinetics of micronucleus formation were similar in normal and in splenectomized mice in which the micronucleus levels had returned to normal. The comparison of micronucleus formation in bone marrow and peripheral blood after cyclophosphamide treatment revealed the generation of similar quantities of micronucleated red blood cells in both tissues. The physiological mechanisms of micronucleus formation and removal and the potential role of chemically induced spleen damage during this process are discussed; the usefulness of the peripheral micronucleus test as a simple, rapid, and animal-saving modification of the standard bone marrow test is evaluated.Abbreviations CP
cyclophosphamide
- MN
micronuclei
- MNCE
micronucleated normochromatic erythrocytes
- MNPCE
micronucleated polychromatic erythrocytes
- MNRBC
micronucleated red blood cells
- NCE
normochromatic erythrocytes
- PCE
polychromatic erythrocytes 相似文献
130.
Isolated muscle cells from adult rat heart have been used to study the relationship between myocardial glucose transport and the activity of the Na+/K+ pump. 86Rb+-uptake by cardiac cells was found to be linear up to 2 min with a steady-state reached by 40–60 min, and was used to monitor the activity of the Na+/K+ pump. Ouabain (10?3 mol/I) inhibited the steady-state uptake of 86Rb+ by more than 90%. Both, the ouabain-sensitive and ouabain-insensitive 86Rb+-uptake by cardiac cells were found to be unaffected by insulin treatment under conditions where a significant stimulation of 3-O-methylglucose transport occurred. 86Rb+-uptake was markedly reduced by the presence of calcium and/or magnesium, but remained unresponsive towards insulin treatment. Inhibition of the Na+/K+ pump activity by ouabain and a concomitant shift in the intracellular Na+:K+ ratio did not affect basal or insulin stimulated rates of 3-O-methylglucose transport in cardiac myocytes. The data argue against a functional relationship between the myocardial Na+/K+ pump and the glucose transport system. 相似文献