首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2679篇
  免费   99篇
  国内免费   1篇
  2021年   30篇
  2020年   28篇
  2019年   36篇
  2018年   61篇
  2017年   46篇
  2016年   62篇
  2015年   32篇
  2014年   67篇
  2013年   108篇
  2012年   91篇
  2011年   112篇
  2010年   86篇
  2009年   73篇
  2008年   112篇
  2007年   106篇
  2006年   100篇
  2005年   97篇
  2004年   110篇
  2003年   100篇
  2002年   112篇
  2001年   100篇
  2000年   115篇
  1999年   49篇
  1998年   29篇
  1996年   14篇
  1992年   47篇
  1991年   49篇
  1990年   54篇
  1989年   53篇
  1988年   36篇
  1987年   54篇
  1986年   43篇
  1985年   51篇
  1984年   38篇
  1983年   27篇
  1979年   23篇
  1978年   18篇
  1977年   20篇
  1976年   23篇
  1975年   29篇
  1974年   29篇
  1973年   42篇
  1972年   25篇
  1971年   14篇
  1970年   17篇
  1969年   20篇
  1968年   20篇
  1967年   20篇
  1966年   14篇
  1965年   14篇
排序方式: 共有2779条查询结果,搜索用时 31 毫秒
61.
The nanowire (NW) detection is one of the fast-acting and high-sensitive methods, which can recognize potentially relevant protein molecules. A NW-biosensor based on the silicon-on-insulator (SOI)-structures has been used for biospecific label-free real time detection of the NFATc1 (D-NFATc1) oncomarker. For this purpose, SOI-nanowires (NWs) were modified with aptamers against NFATc1 used as molecular probes. It was shown that using this biosensor it is possible to reach sensitivity of 10?15 M. This sensitivity was comparable to that of the NW-biosensor with immobilized antibodies used as macromolecular probes. The results demonstrate that approaches used in this study are promising for development of sensor elements for high-sensitive diagnostics of diseases.  相似文献   
62.
The aim of this study was to evaluate and to compare the long-term kinetics curves of biodegradation of poly(3-hydroxybutyrate) (PHB), its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and a PHB/polylactic acid composite. The total weight loss and the change of average viscosity molecular weight were used as the parameters reflecting the biodegradation degree. The rate of biodegradation was analyzed in vitro in the presence of lipase and in vivo after film implantation in animal tissues. The morphology of the PHB film surface was studied by the atomic force microscopy technique. It was shown that PHB biodegradation involves both polymer hydrolysis and its enzymatic biodegradation. The results obtained in this study can be used for the development of various PHB-based medical devices.  相似文献   
63.
An optical biosensor employing surface plasmon resonance (SPR; SPR-biosensor) is a highly efficient instrument applicable for direct real time registration of molecular interactions without additional use of any labels or coupled processes. As an independent approach it is especially effective in analysis of various ligand receptor interactions. SPR-biosensors are used for validation of studies on intermolecular interactions in complex biological systems (affinity profiling of various groups of proteins, etc.). Recently, potential application of the SPR-biosensor for molecular fishing (direct affinity binding of target molecules from complex biological mixtures on the optical biosensor surface followed by their elution for identification by LCMS/MS) has been demonstrated. Using SPR-biosensors in such studies it is possible to solve the following tasks: (a) SPR-based selection of immobilization conditions required for the most effective affinity separation of a particular biological sample; (b) SPR-based molecular fishing for subsequent protein identification by mass spectrometry; (c) SPR-based validation of the interaction of identified proteins with immobilized ligand. This review considers practical application of the SPR technology in the context of recent studies performed in the Institute of Biomedical Chemistry on molecular fishing of real biological objects.  相似文献   
64.
Invariant natural killer T (iNKT) cells are non-conventional lipid-reactive αβ T lymphocytes that play a key role in host responses during viral infections, in particular through the swift production of cytokines. Their beneficial role during experimental influenza A virus (IAV) infection has recently been proposed, although the mechanisms involved remain elusive. Here we show that during in vivo IAV infection, mouse pulmonary iNKT cells produce IFN-γ and IL-22, a Th17-related cytokine critical in mucosal immunity. Although permissive to viral replication, IL-22 production by iNKT cells is not due to IAV infection per se of these cells but is indirectly mediated by IAV-infected dendritic cells (DCs). We show that activation of the viral RNA sensors TLR7 and RIG-I in DCs is important for triggering IL-22 secretion by iNKT cells, whereas the NOD-like receptors NOD2 and NLRP3 are dispensable. Invariant NKT cells respond to IL-1β and IL-23 provided by infected DCs independently of the CD1d molecule to release IL-22. In vitro, IL-22 protects IAV-infected airway epithelial cells against mortality but has no role on viral replication. Finally, during early IAV infection, IL-22 plays a positive role in the control of lung epithelial damages. Overall, IAV infection of DCs activates iNKT cells, providing a rapid source of IL-22 that might be beneficial to preserve the lung epithelium integrity.  相似文献   
65.
Ivanov A  Zhao H  Modyanov NN 《Biochemistry》2000,39(32):9778-9785
Spatial relationships among the transmembrane (TM) segments of alpha- and beta-subunits of the Na,K-ATPase molecule have been investigated using oxidative induction of disulfide bonds. The catalytic alpha-subunit contains 10 TM alpha-helices (H1-H10) with 9 Cys residues located within or close to the membrane moiety. There is one Cys residue in the single TM segment of beta-subunit (Hbeta). Previously, the cross-linking products containing the beta-subunit and two fragments of alpha-subunit (the N-terminal containing H1-H2 helices and the C-terminal containing H7-H10 helices) have been identified in experiments with membrane-bound or detergent-solubilized preparations of the membrane moiety of trypsin-digested Na,K-ATPase [Sarvazyan, N. A., Modyanov, N. N., and Askari, A. (1995) J. Biol. Chem. 270, 26528-26532 and Sarvazyan, N. A., Ivanov, A., Modyanov, N. N., and Askari, A. (1997) J. Biol. Chem. 272, 7855-7858]. Here, we have shown that Cu(2+)-phenanthroline treatment of digitonin-solubilized preparation provides the most efficient formation of intersubunit cross-linked product that is predominantly a dimer of beta-subunit and a 22-kDa C-terminal alpha-fragment containing H7-H10 helices. This cross-linked product was isolated and subjected to CNBr cleavage. The resulting fragments were electrophoretically separated and sequenced. A 17-kDa peptide composed of Ile853-Met942 alpha-fragment and Ala5-Met56 beta-fragment was identified as a product of intersubunit disulfide cross-link between Cys44 of Hbeta and either Cys911 or Cys930, located in H8. This provides the first direct experimental evidence of the juxtaposition of Hbeta and H8 within the Na,K-ATPase molecule. The second detected cross-linked product was composed of alpha-fragments Lys947-Met963 and Tyr974-Tyr1016 linked by induced disulfide bridge between Cys964 (H9) and Cys983 (H10). The spatial proximity of these Cys residues defines the mutual orientation of H9 and H10 helices of alpha-subunit.  相似文献   
66.
Testing 54 strains of staphylococci (Staphylococcus aureus, S. epidermidis, S. haemolyticus, S. warneri, S. hominis, S. capitis) revealed that S. aureus in contrast to coagulase-negative staphylococci (CNS) is more resistant to bactoriocidal action of human thrombodefensins (resistance index: 60.3 vs 25.6%), less hydrophilicolipophilic balance-HLB: -0.42 vs -0.64) and less charged (x-potential: -32.4 vs -35.6 mV). In groups of staphylococci (S. aureus and CNS) correlation links of bacterial resistance to human thrombodefensins with their HLB and x-potential (r=-0.32...-0.36). By In vitro experiments, it was shown that 5 passages of staphylococci in meat-peptonic broth with human thrombodefensins (50 mkg protein/ml) lead to adaptation of bacteria followed by the formation of resistance to cationic peptides from thrombocytes, a decrease of hydrophobicity and x-potencial. The role of physico-chemical properties in providing thrombodefensin-resistance of staphylococci as a developmental factor of infectious-and-inflammatory process and persistence of bacteria was confirmed with Salmonella infection.  相似文献   
67.
The isotopic composition of particulate organic carbon (POC) from the Black Sea deep-water zone was studied during a Russian-Swiss expedition in May 1998. POC from the upper part of the hydrogen sulfide zone (the C-layer) was found to be considerably enriched with the12C isotope, as compared to the POC of the oxycline and anaerobic zone. In the C-layer waters, the concurrent presence of dissolved oxygen and hydrogen sulfide and an increased rate of dark CO2 fixation were recorded, suggesting that the change in the POC isotopic composition occurs at the expense of newly formed isotopically light organic matter of the biomass of autotrophic bacteria involved in the sulfur cycle. In the anaerobic waters below the C-layer, the organic matter of the biomass of autotrophs is consumed by the community of heterotrophic microorganisms; this results in weighting of the POC isotopic composition. Analysis of the data obtained and data available in the literature allows an inference to be made about the considerable seasonable variability of the POC δ13C value, which depends on the ratio of terrigenic and planktonogenic components in the particulate organic matter.  相似文献   
68.
Microbially induced calcium carbonate precipitation (MICP) is a phenomenon based on urease activity of halotolerant and alkaliphilic microorganisms that can be used for the soil bioclogging and biocementation in geotechnical engineering. However, enrichment cultures produced from indigenous soil bacteria cannot be used for large-scale MICP because their urease activity decreased with the rate about 5 % per one generation. To ensure stability of urease activity in biocement, halotolerant and alkaliphilic strains of urease-producing bacteria for soil biocementation were isolated from either sandy soil or high salinity water in different climate zones. The strain Bacillus sp. VUK5, isolated from soil in Ukraine (continental climate), was phylogenetically close in identity (99 % of 16S rRNA gene sequence) to the strain of Bacillus sp. VS1 isolated from beach sand in Singapore (tropical rainforest climate), as well as to the strains of Bacillus sp. isolated by other researchers in Ghent, Belgium (maritime temperate climate) and Yogyakarta, Indonesia (tropical rainforest climate). Both strains Bacillus sp. VS1 and VUK5 had maximum specific growth rate of 0.09/h and maximum urease activities of 6.2 and 8.8 mM of hydrolysed urea/min, respectively. The halotolerant and alkaliphilic strain of urease-producing bacteria isolated from water of the saline lake Dead Sea in Jordan was presented by Gram-positive cocci close to the species Staphylococcus succinus. However, the strains of this species could be hemolytic and toxigenic, therefore only representatives of alkaliphilic Bacillus sp. were used for the biocementation studies. Unconfined compressive strengths for dry biocemented sand samples after six batch treatments with strains VS1and VUK5 were 765 and 845 kPa, respectively. The content of precipitated calcium and the strength of dry biocemented sand at permeability equals to 1 % of initial value were 12.4 g Ca/kg of dry sand and 454 kPa, respectively, in case of biocementation by the strain VS1. So, halotolerant, alkaliphilic, urease-producing bacteria isolated from different climate zones have similar properties and can be used for biocementation of soil.  相似文献   
69.
The distribution of the two photosystems, PSI and PSII, in grana and stroma lamellae of the chloroplast membranes is not uniform. PSII are mainly concentrated in grana and PSI in stroma thylakoids. The dynamics and factors controlling the spatial segregation of PSI and PSII are generally not well understood, and here we address the segregation of photosystems in thylakoid membranes by means of a molecular dynamics method. The lateral segregation of photosystems was studied assuming a model comprising a two-dimensional (in-plane), two-component, many-body system with periodic boundary conditions and competing interactions between the photosystems in the thylakoid membrane. PSI and PSII are represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and an exponentially decaying attractive part. The modeling results suggest a complicated phase behavior of the system, including quasi-crystalline phase of randomly distributed complexes of PSII and PSI at low ionic screening, well defined clustered state of segregated complexes at high screening, and in addition, an intermediate agglomerate phase where the photosystems tend to aggregate together without segregation. The calculations demonstrated that the ordering of photosystems within the membrane was the result of interplay between electrostatic and lipid-mediated interactions. At some values of the model parameters the segregation can be represented visually as well as by analyzing the correlation functions of the configuration.  相似文献   
70.
This article considers the role of marine mammals in a sea or ocean ecosystem based on the example of the Far Eastern seas with adjacent waters of the North Pacific, which is one of the regions of the World Ocean that is distinguished by its high biological and fish capacity and by a high abundance of cetaceans and pinnipeds. Based on extensive data, which was published mostly by Russian experts, the authors have estimated the quantities of annual consumption of fish and invertebrates by marine mammals in three Far Eastern seas: 14.6–18.2 million tons in the early 20th century; 12.3–15.1 million tons in the late 1970s; 22.7–28.8 million tons in the pre-harvest period; and 24.0–24.7 million tons in the early 21st century (27.0–29.5 million tons, if 3–5 million tons in ocean waters off the Kuril Islands and Kamchatka are taken into account). More than half of this quantity is formed by zooplankton and zoobenthos; the second largest portion consists of fish and squid. At the same time, the values of food consumption by fish and large invertebrates are much higher than these estimates for the 0–1000 m layer: 516 million tons were consumed in the 1980s–1990s; 389 million tons in 1991–1995; and 461 million tons in 1996–2005. In the years of high abundance, large walleye pollock alone consumed nearly 40 million tons of small fish and squid. Based on the data of 35-year-long ecosystem studies that were conducted by the Pacific Research Fisheries Center (TINRO Center), the following biomass estimates have been obtained for the biota of the Far Eastern Economic Zone of Russia: mesoand macroplankton, 1000 million tons; zoobenthos, 500 million tons; nekton, 100 million tons; benthic fish, 5 million tons; and large benthic invertebrates that are not included in the benthos, 2.43 million tons. By using these estimates and by comparing the quantities of food consumption by marine mammals, the conclusion was made that the role of marine mammals in food webs of waters of the Russian Far East is remarkable, but it does not reach a level that is high enough to regulate such a large-scale ecosystem as the macro-ecosystem of a sea or ocean.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号