全文获取类型
收费全文 | 248469篇 |
免费 | 22835篇 |
国内免费 | 259篇 |
专业分类
271563篇 |
出版年
2018年 | 2747篇 |
2017年 | 2666篇 |
2016年 | 3610篇 |
2015年 | 3894篇 |
2014年 | 4808篇 |
2013年 | 6799篇 |
2012年 | 7563篇 |
2011年 | 8190篇 |
2010年 | 5560篇 |
2009年 | 4946篇 |
2008年 | 7086篇 |
2007年 | 7288篇 |
2006年 | 6889篇 |
2005年 | 6577篇 |
2004年 | 6489篇 |
2003年 | 6271篇 |
2002年 | 6144篇 |
2001年 | 12024篇 |
2000年 | 11985篇 |
1999年 | 9164篇 |
1998年 | 2698篇 |
1997年 | 2761篇 |
1996年 | 2708篇 |
1995年 | 2489篇 |
1994年 | 2440篇 |
1993年 | 2323篇 |
1992年 | 7185篇 |
1991年 | 6984篇 |
1990年 | 7058篇 |
1989年 | 6844篇 |
1988年 | 6358篇 |
1987年 | 6009篇 |
1986年 | 5360篇 |
1985年 | 5668篇 |
1984年 | 4467篇 |
1983年 | 3863篇 |
1982年 | 2672篇 |
1981年 | 2495篇 |
1980年 | 2305篇 |
1979年 | 4109篇 |
1978年 | 3134篇 |
1977年 | 2881篇 |
1976年 | 2826篇 |
1975年 | 3269篇 |
1974年 | 3500篇 |
1973年 | 3525篇 |
1972年 | 3059篇 |
1971年 | 2844篇 |
1970年 | 2536篇 |
1969年 | 2300篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Binding of the cationic tetra(tributylammoniomethyl)-substituted hydroxoaluminum phthalocyanine (AlPcN4) to bilayer lipid membranes was studied by fluorescence correlation spectroscopy (FCS) and intramembrane field compensation (IFC) methods. With neutral phosphatidylcholine membranes, AlPcN4 appeared to bind more effectively than the negatively charged tetrasulfonated aluminum phthalocyanine (AlPcS4), which was attributed to the enhancement of the coordination interaction of aluminum with the phosphate moiety of phosphatidylcholine by the electric field created by positively charged groups of AlPcN4. The inhibitory effect of fluoride ions on the membrane binding of both AlPcN4 and AlPcS4 supported the essential role of aluminum-phosphate coordination in the interaction of these phthalocyanines with phospholipids. The presence of negative or positive charges on the surface of lipid membranes modulated the binding of AlPcN4 and AlPcS4 in accord with the character (attraction or repulsion) of the electrostatic interaction, thus showing the significant contribution of the latter to the phthalocyanine adsorption on lipid bilayers. The data on the photodynamic activity of AlPcN4 and AlPcS4 as measured by sensitized photoinactivation of gramicidin channels in bilayer lipid membranes correlated well with the binding data obtained by FCS and IFC techniques. The reduced photodynamic activity of AlPcN4 with neutral membranes violating this correlation was attributed to the concentration quenching of singlet excited states as proved by the data on the AlPcN4 fluorescence quenching. 相似文献
22.
I. N. Semenchuk L. A. Taranova A. A. Kalenyuk P. V. Il’yasov A. N. Reshetilov 《Applied Biochemistry and Microbiology》2000,36(1):69-72
The operating and storage stability of a receptor element of an amperometric biosensor based on thePseudomonas rathonis strain T capable of degrading surfactants was tested. Microbial cells were immobilized by incorporation in gels (agar, agarose,
and calcium-alginate), polyvinyl alcohol membrane, adhesion to Chromatographic paper GF/A, or by cross-linking induced by
glutaric aldehyde. Incorporation of microbial cells in agar gel provides long-standing conservation of their activity and
viability during measurements of high concentrations of surfactants and allows the receptor element of the biosensor to be
rapidly recovered after measurements. 相似文献
23.
24.
Sensitization of mice with wild-type and cold-adapted influenza virus variants: immune response to two H1N1 and H3N2 viruses 下载免费PDF全文
Two A strain influenza viruses, A/Hong Kong/123/77 (A/HK/123/77) (H1N1) and A/Queensland/6/72 (A/Qld/6/72) (H3N2), and the two cold-adapted reassortants which possess the surface antigens of these strains (CR35 and CR6, respectively) were tested for their ability both to induce primary cytotoxic T-cell (Tc cell) responses in mice and to sensitize mice for a second Tc cell response when challenged with a distantly related A strain virus, A/Shearwater/72 (H6N5). After intranasal inoculation, A/Qld/6/72 replicated to higher titers in the lung (1 to 2 log10 50% egg infective doses) than did A/HK/123/77 or either of the reassortants. A/Qld/6/72 induced higher Tc cell responses in the lung than did CR6, and both were more effective than either A/HK/123/77 or CR35 in this respect. When similar doses (10 or 10(3) hemagglutinin units) of each virus were injected intravenously into mice and the spleens were tested for Tc cell activity 6 days later, both A/Qld/6/72 and CR6 were ca. 100-fold better at inducing a primary Tc cell response than A/HK/123/77 or CR35. In contrast, the H1N1 and H3N2 viruses gave rather similar anti-hemagglutinin antibody titers (after intravenous injection) and delayed-type hypersensitivity reactions (after subcutaneous injection). If mice were primed with a low dose of these viruses (10(4) 50% egg infective doses intranasally), A/Qld/6/72 and CR6 were more effective than A/HK/123/77 or CR35 at sensitizing for a secondary Tc cell response when challenged with A/Shearwater/72, but if larger doses were given either intranasally (10(6) 50% egg infective doses) or intravenously (10 to 10(3) hemagglutinin units), all viruses sensitized the mice equally well, despite the fact the A/Shearwater/72 gives a poor primary Tc cell response in mice. Thus, the viral glycoprotein antigens can be important in determining the immunogenicity of the virus and, particularly, the class I antigen-restricted Tc cell response of the host. 相似文献
25.
V K Khugaeva E D Klimenko P N Aleksandrov G F Leskova M I Reutov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(7):15-19
Experiments were made on rabbit fed an atherogenic diet (0.5 g/kg cholesterol) singly for 15 and 24 h and repeatedly for 3, 9 and 30 days. At early stages of lipid metabolism distress the interrelationship was established between blood rheological disorders and microcirculatory abnormalities. The dependence of the initial reaction of some rheological characteristics on their initial level was marked. 相似文献
26.
Transport of chloride across cell membranes through exchange, cotransport, or conductive pathways is a subject of great biological importance. Current methods of measurement are restricted in their sensitivity, time resolution, and applicability. A new transport measurement technique has been developed on the basis of the fluorescence quenching by chloride of the dye 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ). SPQ fluorescence quenching by chloride is rapid (less than 1 ms) and sensitive, with a greater than 50% decrease in fluorescence at 10 mM chloride. SPQ fluorescence is not altered by other physiological anions or by pH and can be used to measure both neutral and conductive transport processes. The high water solubility and membrane permeability properties of SPQ make it ideal for use in both membrane vesicles and cells. Chloride transport determined with SPQ was validated by measurement of erythrocyte chloride/anion exchange and membrane vesicle chloride conductance. 相似文献
27.
The absence of centromeric bands in the karyotype of Felis catus is confirmed. It is also confirmed that no satellite band is visible in CsCl density gradients. However, a satellite is observed both by recentrifuging the fraction of the DNA that bands at high density in CsCl and by using netropsin to enhance the resolution of a CsCl gradient containing total F. catus DNA. The satellite, about 0.5% of total DNA, was isolated by repeated centrifugation in CsCl alone and in CsCl with netropsin. Netropsin was removed and a pure satellite DNA obtained. The reassociation kinetics (C0t1/2 less than 10(-3) M . s) show that the satellite is of the simple sequence type and hence a candidate for centromeric heterochromatin. Its cytological localisation awaits in situ hybridisation experiments. 相似文献
28.
K N Iarygin A N Kazimirski? G I Kositski? A Iu Rubina V A Vinogradov 《Biulleten' eksperimental'no? biologii i meditsiny》1986,101(6):680-682
The authors studied the anabolic effect of peptide morphogen of the hydra undecapeptide on normal and regenerating rat liver. Ornithine decarboxylase (EC 4.1.1.17) activity served as a marker. Intraperitoneal injection of the peptide into intact animals stimulated ornithine decarboxylase activity in a dose-dependent manner. In partially hepatectomized rats the peptide stimulated ornithine decarboxylase activity in the dose of 20 micrograms/kg body weight while greater doses inhibited the enzyme activity. 相似文献
29.
Monosomy 21: a new case confirmed by in situ hybridization 总被引:4,自引:0,他引:4
M. C. Pellissier N. Philip M. A. Voelckel-Baeteman M. G. Mattei J. F. Mattei 《Human genetics》1987,75(1):95-96
Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation. 相似文献
30.