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91.
Characterization of the binding sites for nimodipine and (-)-desmethoxyverapamil in bovine cardiac sarcolemma 总被引:5,自引:0,他引:5
P Ruth V Flockerzi E von Nettelbladt J Oeken F Hofmann 《European journal of biochemistry》1985,150(2):313-322
The bovine cardiac sarcolemmal binding sites for the dihydropyridine nimodipine and the phenylalkylamine (-)-desmethoxyverapamil were studied. The density of the nimodipine and (-)-desmethoxyverapamil binding sites increased 8.3-fold and 3.4-fold with the sarcolemma. The binding sites for both compounds were destroyed by trypsin. Nimodipine bound in the presence of 1 mM free calcium to a high-affinity and a low-affinity site with apparent Kd values of 0.35 +/- 0.09 nM (n = 9) and 33 +/- 6.0 nM (n = 9) and with apparent densities of 0.3 +/- 0.05 pmol/mg (n = 9) and 8.2 +/- 1.0 pmol/mg (n = 9). The binding to the high-affinity site was abolished by 1 mM EGTA. The binding sites were specific for dihydropyridines. The (-)-isomers of several phenylalkylamines inhibited nimodipine binding by an apparent allosteric mechanism. (-)-Desmethoxyverapamil bound in the presence of 5 mM EGTA to a high-affinity and a low-affinity site with apparent Kd values of 1.4 +/- 0.3 nM (n = 6) and 171 +/- 26 nM (n = 6) and with apparent densities of 0.16 +/- 0.02 pmol/mg (n = 6) and 13.6 +/- 2.7 pmol/mg (n = 6). The binding to both sites was inhibited by calcium with a half-maximal concentration of 4.3 mM. The binding sites were specific for the other phenylalkylamines and had a higher affinity for the (-)-isomers than for the (+)-isomers. Nimodipine inhibited the binding of (-)-desmethoxyverapamil by an apparent allosteric mechanism. d-cis-Diltiazem inhibited non-competitively the binding of (-)-[3H]desmethoxyverapamil with a Ki of 3.7 microM. Diltiazem up to concentrations of 10 microM did not affect the amount of nimodipine bound at equilibrium at 20 degrees C. However, but in agreement with this result, diltiazem decreased threefold at 20 degrees C the dissociation and association rates for the high-affinity nimodipine receptor. These rates were only marginally affected at 4 degrees C and 37 degrees C. d-cis-Diltiazem reversed in a competitive manner the inhibition of nimodipine binding elicited by the addition of (-)-desmethoxyverapamil with a Ka value of 1.6 microM. The amount of nimodipine bound was inhibited by 50% by the adenosine uptake inhibitors nitrobenzylthioinosine and hexobendine with apparent median inhibitory concentrations of 1 nM and 3 nM, respectively. Nitrobenzylthioinosine completely abolished binding of nimodipine to the low-affinity site, but did not affect binding to the high-affinity site.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
92.
M I Al-Sheikhly H P Schuchmann C von Sonntag 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1985,47(4):457-462
In the radiolysis of aqueous formate-containing solutions a chain reaction (i, ii) proceeds in the presence of N2O. CO2-. + N2O + H2O----CO2 + N2 + .OH + OH- (i) .OH + HCO2-.----CO2-. + H2O (ii) The chain length depends on the dose rate and the N2O concentration but not on the formate concentration. Typically, G(CO2) approximately 140 molecules (100 eV)-1 is found, with an equivalent amount of N2, at a dose rate of 3 X 10(-3) Gy s-1. The rate constant for the rate-determining step in this chain reaction has been calculated at k(i) = 1600 dm3 mol-1 s-1. The possible relevance of this chain reaction in radiation biological studies is briefly discussed. 相似文献
93.
Peter von Feiten Hans Zürrer Reinhard Bachofen 《Applied microbiology and biotechnology》1985,23(1):15-20
Summary Cells ofRhodospirillum rubrum have been immobilized in various gels and tested for photobiological hydrogen production. Agar proved to be the best immobilizing
agent with respect to production rates as well as stability. Agar immobilized cells were also superior compared to liquid
suspension cultures. Growth conditions of the cells prior to immobilization, e.g. cell age, light intensity or nutrient composition,
were of primary importance for the activity in the later immobilized state. A reactor with agar immobilized cells has been
operated successfully over 3000 h with a loss of the activity of about 60%. Mean rates for hydrogen production for immobilized
cells in this work during the first 60 to 70 hours after immobilization were in the range of 18 to 34 μl H2 mg−1 d.w. h−1 and thus by a factor of up to 2 higher than liquid cultures under the same conditions. Maximal rates of hydrogen production
(57 μl H2 ml−1 immobilized cell suspension) were reached in agar gel beads with cells immobilized after 70 h growth in liquid culture in
the light and a cell density of 1.0 mg ml−1, 70 h after immobilization. 相似文献
94.
Cell surface influenza haemagglutinin can mediate infection by other animal viruses. 总被引:11,自引:0,他引:11 下载免费PDF全文
We have used filter-grown Madin-Darby canine kidney (MDCK) cells to explore the mechanism by which influenza virus facilitates secondary virus infection. Vesicular stomatitis virus (VSV) and Semliki Forest virus (SFV) infect only through the basolateral surface of these polarized epithelial cells and not through the apical surface. Prior infection with influenza virus rendered the cell susceptible to infection by VSV or SFV through either surface. The presence of both a permissive and a restrictive surface for virus entry in the same cell allowed us to determine how the influenza infection enhanced the subsequent infection of a second virus. Biochemical and morphological evidence showed that influenza haemagglutinin on the apical surface serves as a receptor for the superinfecting virus by binding to its sialic acid-bearing envelope proteins. Influenza virus also facilitates secondary virus infection in non-epithelial cells; baby hamster kidney cells (BHK-21), which are normally resistant to infection by the coronavirus (mouse hepatitis virus MHV-A59), could be infected via the haemagglutinin-sialic acid interaction. Facilitation of secondary virus infection requires only the sialic acid-binding properties of the haemagglutinin since the uncleaved haemagglutinin could also mediate virus entry. 相似文献
95.
Swantje Vellguth Priv.-Doz. Dr. Brita von Gaudecker Hans-Konrad Müller-Hermelink 《Cell and tissue research》1985,242(3):579-592
Summary Splenic tissue of human fetuses from the 14th to the 24th week of gestation (menstrual age) were investigated by light- and electron microscopy to describe the development of the red and white pulp in close relationship to the differentiation of the vascular tree. Special interest is focussed on the differentiation of the T-cell- and the B-cell regions and their specific stationary cells.The preliminary stage, here called the primary vascular reticulum, lasts up to the 14th gestational week (gw). Numerous erythrocytes, normoblasts and macrophages are seen among a network of mesenchymal cells and argyrophilic fibers. Hematopoiesis, especially erythropoiesis, can be recognized.The characteristic organ structure becomes established during the subsequent transformation stage of the fetal spleen, beginning with the 15th gw. Splenic lobules begin to form during the 15th to 17th gw. They consist of a central artery, surrounded by a sheath of lightly stained stationary cells which resemble myofibroblasts. At the periphery of these lobules the red pulp forms. Initially mobile cells are distributed throughout the reticulum. Soon they begin to accumulate in the venous sinuses, which develop from lacunae among the reticular network and come into contact with the venous system. The endothelial wall of these sinuses remains discontinuous, confirming the theory of the open vascularization of the spleen. The development of the larger veins is correlated with the differentiation of the splenic trabeculae.The development of the white pulp is correlated with the stage of lymphoid colonization within the spleen, beginning around the 18th gw. An accumulation of lymphocytes around the central arteries can be recognized during the 19th and 20th gw. These lymphoid cells show morphological and immunohistochemical characteristics of T-precursor cells. Within the now assembling periarterial lymphoid sheath (PALS) a few precursors of interdigitating cells (IDC) are recognizable, giving evidence for the differentiation of the T-cell region.Around the 23rd gw the assemblage of primary follicles is discernible at the periphery of the PALS. Precursors of the follicular dendritic reticulum cell (FDRC), the specific stationary cell of the B-cell region, have been recognized. This observation leads to the conclusion that the small primary follicles represent the beginning formation of the B-cell region.The significance of the vascular system for the differentiation of the specific splenic organization is discussed.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 111)The authors appreciate the contribution of human fetal material from Dr. von Hollweg and Dr. Körner from the Hospital Heidberg, Hamburg, and the excellent technical assistance of Mrs. H. Hansen, Mrs. I. Knauer, Mrs. M.v. Kolszynski, Mrs. J. Quitzau, Mrs. H. Siebke and Mrs. H. Waluk 相似文献
96.
Optimum growth conditions for the fermentation of non-concentrated whey permeate by Kluyveromyces fragilis NRRL 665 have been defined. Use of 3.75 g yeast extract l?1, a growth temperature of 38°C and a pH of 4.0 allowed a maximum productivity of 5.23 g ethanol l?1 h?1 in continuous culture with a yield 91% of theoretical. Complete batch fermentation of permeate with 100 g lactose l?1 was possible with a maximum specific growth rate of 0.276 h?1 without any change in ethanol yield. Fermentation of concentrated permeate resulted, however, in a general decrease of specific substrate consumption rate, demonstrated by the inability to completely convert an initial 90 or 150 g lactose l?1 in continuous culture, even at dilution rates as low as 0.05 and 0.08 h?1, respectively. The decrease could be related to substrate inhibition, to an increase in osmotic pressure caused by lactose and salts, and to ethanol inhibition of both alcohol and biomass yield. The decrease in specific productivity could be counterbalanced by use of high cell density cultures, obtained by cell recycle of K. fragilis. Fermentation of a non-concentrated permeáte at a dilution rate of 1 h?1 resulted in a productivity of 22 g l?1 h?1 at 22 g ethanol l?1. Cell recycle using flocculating Kluyveromyces lactis NCYC 571 was also tested. With this strain a productivity of 9.3 g l?1 h?1 at 45 g product l?1 was attained at a dilution rate of 0.2 h?1, with an initial lactose concentration of 95 g l?1. 相似文献
97.
Internalization of blocking antibodies against mannose-6-phosphate specific receptors. 总被引:18,自引:3,他引:15 下载免费PDF全文
Antibodies against mannose-6-phosphate specific receptors inhibit the receptor-dependent endocytosis of exogenous lysosomal enzymes as well as the sorting of endogenous lysosomal enzymes. This inhibition was correlated with an apparent loss of the receptors. We report here that treatment of cells with the antibody results in the formation of receptor-antibody complexes that are not extracted by the procedure used for the solubilization of receptors prior to immunoprecipitation and detection of the receptor. The apparent loss of receptors is observed with both native antibody and the F(ab)2 fragments, but not with Fab fragments. In contrast the transport of lysosomal enzymes is inhibited by all three forms of the antibody. The inhibition is ascribed to masking by the antibody of the enzyme-binding site in the receptor. The inhibition of the sorting of endogenous lysosomal enzymes by antibodies added to the medium indicates that the mannose-6-phosphate specific receptors at the sorting site are in dynamic equilibrium with those at the cell surface. The receptor-antibody complexes formed at the cell surface appear to cycle between the cell surface and intracellular membranes. A fraction of the internalized antibodies dissociates from the receptors and is degraded after transfer into lysosomes. Complexing with Fab increases the concentration of the receptor in the lysosomes and decreases 2- to 3-fold the half-life of the receptor. 相似文献
98.
99.
Primary production data from the south-eastern Weddell Sea 总被引:2,自引:2,他引:0
Klaus von Bröckel 《Polar Biology》1985,4(2):75-80
Summary Phytoplankton production for three size classes (<20 m, 20–100 m, >100 m), total primary production and qualitative composition of phytoplankton populations were recorded from 18 stations in the south-eastern Weddell Sea in February/March 1983. Total primary production ranged between 80 and 1670 mg C m-2 d-1 with an average of 670 mg C m-2 d-1, nearly 70% of which was contributed by the <20 m size fraction (usually pennate and/or centric diatoms). Production of phytoplankton was in the higher range of values reported by other authors for the same region. Variations in primary production could not be attributed to composition of populations, ambient light levels or concentrations of macronutrients (N, P, Si). Phytoplankton populations had a higher diversity in the deeper parts of the Weddell Sea and coincided with different oceanographic situations. Three zones (along the shelf-ice edge from Atka Bay to Halley Bay, west of Halley Bay and off the Filchner/Rønne Ice Shelf) with different communities could be clearly distinguished. 相似文献
100.
Gunnar von Heijne 《Journal of molecular biology》1984,173(2):243-251
The specificity of the signal sequence cleavage reaction has been postulated to reside in a signal peptidase active site that can bind only to particular (i, i + 2) pairs of amino acids. In this paper, we present further patterns of non-random amino acid utilization in a region around in vivo cleavage sites, and show that they can be interpreted in terms of selection acting to reduce the number of potential competing sites in the vicinity of the correct one. 相似文献