全文获取类型
收费全文 | 2323篇 |
免费 | 193篇 |
专业分类
2516篇 |
出版年
2022年 | 15篇 |
2021年 | 27篇 |
2019年 | 23篇 |
2018年 | 34篇 |
2017年 | 26篇 |
2016年 | 47篇 |
2015年 | 75篇 |
2014年 | 76篇 |
2013年 | 107篇 |
2012年 | 169篇 |
2011年 | 144篇 |
2010年 | 113篇 |
2009年 | 82篇 |
2008年 | 142篇 |
2007年 | 125篇 |
2006年 | 125篇 |
2005年 | 121篇 |
2004年 | 124篇 |
2003年 | 119篇 |
2002年 | 106篇 |
2001年 | 32篇 |
2000年 | 11篇 |
1999年 | 30篇 |
1998年 | 33篇 |
1997年 | 28篇 |
1996年 | 26篇 |
1995年 | 35篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 34篇 |
1991年 | 24篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 22篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 19篇 |
1977年 | 22篇 |
1975年 | 17篇 |
1974年 | 15篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1968年 | 13篇 |
排序方式: 共有2516条查询结果,搜索用时 15 毫秒
71.
Summary Differentiating cells ofMicrasterias denticulata have been treated with aqueous solutions of the antibiotic gougerotin. Strong and characteristic cytomorphogenetic aberrations, resembling those of the anuclear type of development could be observed. It has been speculated that the aberrant growth of the growing half cell is the result of inhibition of protein synthesis by gougerotin.In addition to the morphogenetic influence, nuclear migration has been strongly inhibited by the drug. Therefore, it might be suggested that gougerotin is an active anti-microtubule agent. 相似文献
72.
Christine Dreyer Helen Singer Peter Hausen Ursula Müller Elisabeth Siegel 《Development genes and evolution》1981,190(4):197-207
Summary A library of hybridoma cell lines has been established which produce monoclonal antibodies against antigens from the germinal vesicle ofXenopus laevis oocytes. Many of the antigens are also found in the nuclei ofXenopus embryonic cells in culture. The fate of two of these antigens during embryogenesis was traced by immunofluorescence on embryo and tadpole sections. Early in development these antigens appear to be evenly distributed in the nuclei of all cells. In later stages they gradually disappear from most embryonic structures but are strongly accumulated in the nuclei of some specific cell types and organs. 相似文献
73.
A severe and a mild potato spindle tuber viroid isolate differ in three nucleotide exchanges only 总被引:5,自引:0,他引:5
Hans J. Gross Ursula Liebl Heidemarie Alberty Guido Krupp Horst Domdey Karla Ramm Heinz L. Sänger 《Bioscience reports》1981,1(3):235-241
Fingerprint analyses of two potato spindle tuber viroid (PSTV) isolates causing severe and mild symptoms~ respectively, in tomato exhibited defined differences in the RNase T1 and RNase A fingerprints. The complete sequencing of the mild isolate and the comparison of its primary structure with the previously established one of the pathogenic type strain revealed that oligonucleotides CAAAAAAG, CUUUUUCUCUAUCUUACUUG, and AAAAAAGGAC in the severe strain are replaced by CAAUAAG, CUUUUUCUCUAUCUUUCUUUG, AAU, and AAGGAC in the 'mild' strain. Thus, three nucleotide exchanges at different sites of the molecule may change a pathogenic viroid to a practically non-pathogenic isolate. The possible correlation between the secondary structure in a defined region of the PSTV molecule and its pathogenicity for tomato is discussed. 相似文献
74.
Thylakoids of Oscillatoria chalybea are able to split water. The Hill reaction of these thylakoids is sensitive to DCMU. Diphenylcarbazide can substitute for water as the electron donor to photosystem II with these fully functioning thylakoids. However, the diphenylcarbazide photooxidation is completely insensitive to 3-(3,4-dichlorophenyl)-N-N-dimethyl urea (DCMU) at high diphenylcarbazide concentrations. In with Tris-treated Oscillatoria thylakoids the water splitting capacity is lost and diphenylcarbazide restores electron transport through photosystem II as occurs with higher plant chloroplasts. However, also these photoreactions are insensitive to DCMU. If diphenylcarbazide acts in Oscillatoria as an electron donor to photosystem II the result suggests that diphenylcarbazide feeds in its electrons behind the DCMU inhibition site. This in turn indicates that in Oscillatoria the site of inhibition of DCMU is on the donor side of photosystem II.Abbreviations Used DCMU
3-(3,4-dichlorophenyl)-N-N-dimethyl urea
- DPC
diphenylcarbazide
- DCPiP
2,6-dichlorophenol indophenol
- TMB
tetramethyl benzidine
- A-2-sulf
anthraquinone-2-sulfonate 相似文献
75.
Isolated melanophores of the angelfish, Pterophyllum scalare, have been used in a morphometric analysis and a quantitative study of their microtubule system. Using transverse sections spaced at regular intervals, the changes associated with the process of pigment aggregation have been determined. Upon the concentration of pigment granules in the central cell region, almost half of the cytoplasmic portion is also withdrawn from the peripheral cell regions. Counts of microtubules within a cell sector in cells with pigment aggregated and dispersed, respectively, reveal (a) a constancy of the number of microtubules in this sector regardless of the distance from the cell center, and (b) a reduction of microtubule number in cells with pigment aggregated by about 58%. On the basis of these counts, the total number of microtubules has been calculated. In the dispersed state, about 2,400 microtubules extend between the center and the periphery of the cell, while their number is about 1,000 in the aggregated state. Using a 13-protofilament model of a microtubule and relevant data on size and molecular weight of microtubule subunits, the amount of tubulin present as microtubules is calculated. In the average, the cells contain 1.95·108 monomers corresponding to 1.78·10?8 mg tubulin. A tentative estimation of the concentration of tubulin inside a melanophore yields values of 6.1 mg/ml for the whole cell and 16.5 mg/ml for the cytoplasm alone (excluding membrane-bound organelles). Based on this estimation, a comparison, with microtubule assembly in vitro is made. 相似文献
76.
77.
Noemi Luknar-Gabor Ursula Fenger Christoph Wagener Heinz Breuer 《Biochemical and biophysical research communications》1982,109(4):1270-1275
A variant of the carcinoembryonic antigen (CEA) with lower molecular weight than a CEA reference preparation has been separated from CEA. Using a polyclonal, spleen absorbed anti-CEA antiserum, the variant crossreacts with reference CEA in immunodiffusion. The CEA-activity of the variant has been demonstrated using an enzyme-immunoassay with monoclonal CEA specific antibodies. There is sufficient immunological evidence that this variant is a distinct antigen different from the crossreactive antigens described so far. The reactivity of the polyclonal anti-CEA antiserum with the CEA variant was abolished by absorption against the immobilized variant. 相似文献
78.
Jürgen Bachmann Monika Feldmer Ursula Ganten Günter Stock Detlev Ganten 《The Journal of steroid biochemistry and molecular biology》1991,40(4-6):511-515
The prevalence of hypertension in men is higher than in women and the onset of this disease is earlier in male than in female subjects. In spontaneously hypertensive rats, males also have higher blood pressures than females. Evidence from epidemiological, physiological, molecular biological and morphological studies concerning this sexual dimorphism is reviewed. We demonstrate that the gonadal steroids testosterone and estrogen have important effects on the gene regulation of the renin-angiotensin system. This may in part contribute to the sexual dimorphism in blood pressure control. The direct effect of steroid hormones on genes related to hypertension provides a suitable paradigm to improve our understanding of molecular and cellular mechanisms of cardiovascular control. 相似文献
79.
Daniel V. Santi Ursula Edman Svetlana Minkin Patricia J. Greene 《Protein expression and purification》1991,2(5-6)
Gatalytically active Pneumocystis carinii thymidylate synthase is expressed to the extent of about 4% of the soluble protein in Escherichia coli χ2913 harboring plasmid pUETS-1.8 (U. Edman, J. C. Edman, B. Lundgren, and D. V. Santi, Proc. Natl. Acad. Sci. USA 86, 6503–6507, 1989). Ion-exchange, affinity, hydrophobic, and reactive dye agarose chromatography steps were explored to devise a large-scale purification protocol for P. carinii thymidylate synthase. Sequential DE52, Q-Sepharose, phenyl-Sepharose, and Cibacron Blue F3GA chromatography yielded enzyme that was homogeneous by SDS-PAGE in a yield of over 50%. The sequence of the first 10 amino acid residues of the purified protein was in accord with that predicted from the DNA sequence. Isoelectric focusing gave a pI of 6.2. Kinetic analysis of the purified enzyme revealed that the the Km values were 4.7 ± 1.3 μM for dUMP and 15.7 ± 4.3 μM for 5,10-methylenetetrahydrofolate, similar to those of many other thymidylate synthases; the κcat of the most active preparation was 0.8 s−1. The enzyme is stable for at least 2 months when stored at −80°C in the presence of 40% glycerol, Tris-HCl, and thiol. 相似文献
80.
Mathias Schwanstecher Ursula Schaupp Stefan Löser Uwe Panten 《Journal of neurochemistry》1992,59(4):1325-1335
Glibenclamide closes an ATP-sensitive K+ channel (K-ATP channel) by interaction with the sulfonylurea receptor in the plasma membrane of pancreatic B cells and thereby initiates insulin release. Previous studies demonstrated that the Mg2+ complex of ATP decreases glibenclamide binding to the sulfonylurea receptor from pancreatic islets. The aim of the present study was to examine the effect of adenine and guanine nucleotides on binding of sulfonyl-ureas to the cerebral sulfonylurea receptor. For this purpose, binding properties of the particulate and solubilized site from rat or pig cerebral cortex were analyzed. Maximum recovery of receptors in detergent extracts amounted to 40-50%. Specific binding of [3H]glibenclamide to the solubilized receptors corresponded well to specific binding to microsomes. In microsomes and detergent extracts, the Mg2+ complexes of ATP, ADP, GTP, and GDP inhibited binding of [3H]glibenclamide. These effects were not observed in the absence of Mg2+. In detergent extracts, Mg-ATP (300 microM) reduced the number of high-affinity sites for [3H]-glibenclamide by 52% and increased the dissociation constant for [3H]glibenclamide by eightfold; Mg-ATP was half-maximally effective at 41 microM. Alkaline phosphatase accelerated the reversal of Mg-ATP-induced inhibition of [3H]glibenclamide binding. The data suggest similar control of the sulfonylurea receptor from brain and pancreatic islets by protein phosphorylation. 相似文献