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   4857篇
  免费   303篇
  国内免费   3篇
  2023年   13篇
  2022年   9篇
  2021年   74篇
  2020年   52篇
  2019年   72篇
  2018年   100篇
  2017年   86篇
  2016年   159篇
  2015年   265篇
  2014年   316篇
  2013年   338篇
  2012年   484篇
  2011年   427篇
  2010年   269篇
  2009年   244篇
  2008年   337篇
  2007年   263篇
  2006年   259篇
  2005年   221篇
  2004年   190篇
  2003年   171篇
  2002年   148篇
  2001年   127篇
  2000年   124篇
  1999年   112篇
  1998年   37篇
  1997年   27篇
  1996年   19篇
  1995年   21篇
  1994年   20篇
  1993年   17篇
  1992年   26篇
  1991年   23篇
  1990年   14篇
  1989年   11篇
  1988年   8篇
  1987年   4篇
  1986年   9篇
  1984年   4篇
  1983年   3篇
  1982年   4篇
  1981年   3篇
  1977年   4篇
  1976年   4篇
  1974年   7篇
  1973年   3篇
  1972年   3篇
  1969年   4篇
  1967年   5篇
  1966年   5篇
排序方式: 共有5163条查询结果,搜索用时 15 毫秒
51.
We investigated the role of soluble factors in natural killer (NK) cell-mediated lysis of herpes simplex virus (HSV)-infected cells. Supernatants generated by incubating human peripheral blood mononuclear cells with HSV-infected human fibroblasts contained tumor necrosis factor (TNF) and lysed uninfected U937 cells, but not HSV-infected fibroblasts. U937 cells, but not HSV-infected fibroblasts, were lysed when exposed to recombinant TNF (rTNF) for 18 hr. NK cell-mediated lysis of HSV-infected fibroblasts was not inhibited by addition of anti-TNF or anti-lymphotoxin (LT) antibodies to cytotoxicity assays. Thus, a role for soluble factors, and in particular TNF and LT, in NK cell-mediated lysis of HSV-infected cells could not be demonstrated.  相似文献   
52.
Sciatin Is a Transferrin-Like Polypeptide   总被引:4,自引:0,他引:4  
Abstract: Sciatin, an acidic glycoprotein from chicken sciatic nerve, has myotrophic effects on avian skeletal muscle cells in culture. As sciatin was found to have certain structural similarities to transferrin, we further investigated the physicochemical characteristics of sciatin in order to determine the relationship between these two proteins. Sciatin was found to be strikingly similar to ovotransferrin in amino acid composition. In addition, amino acid sequence analysis revealed that sciatin and ovotransferrin had identical amino-terminal sequences for at least the first 20 amino acid residues. Chicken ovotransferrin, but not human serum transferrin, cross-reacted with rabbit antisciatin antibodies upon rocket immunoelectrophoresis and double immunodiffusion in agar. In addition, in the presence of bicarbonate, sciatin bound approximately 2 mol ferrous iron/mol protein. Using the purification procedure developed for sciatin, we purified a protein from chicken serum that cross-reacted with antisciatin serum, migrated at a position identical to that of sciatin or ovotransferrin on two-dimensional gel electrophoresis, had an amino composition very similar to ovotransferrin and sciatin, and had myotrophic effects on cultured muscle cells. From these data, we conclude that sciatin is a growth-promoting polypeptide closely related in structure to transferrin.  相似文献   
53.
Summary Commercially available maltodextrins were subjected to high pressure size exclusion chromatography (HPSEC) on Toyo Soda G 2000 PW columns with water as the mobile phase. The elution profiles of these samples will allow researchers to select the correct maltodextrin for growth studies requiring specific dextrin oligomers. Characterization of the chromatography system with standards of known molecular weight allows estimation of the weight average molecular weight of polydisperse dextrins. The enzymatic hydrolysis of dextrin by bacterial-amylase and fungal glucoamylase was also monitored by HPSEC.  相似文献   
54.
The finding that animal synthetases are complexes consisting of two polypeptide chains (Stoops, J.K., Arslanian, M.J., Oh, Y.H., Vanaman, T.C., and Wakil, S.J. (1975) Proc. Natl. Acad. Sci. U. S. A. 72, 1940-1944) led us to investigate their 4'-phosphopantetheine content. We have found that the chicken and rat synthetases contain 1.6 to 2.2 mol of 4'-phosphopantetheine per mol of the complex. The implications of this finding concerning the structure of the complex and the biosynthetic pathway of fatty acid synthesis are discussed.  相似文献   
55.
Regeneration of enzymic activity from reduced hen egg lysozyme peptide 1-127 was effected with a glutathione oxidation-reduction buffer. The rate of regeneration was nearly as great for peptide 1-127 as for reduced lysozyme itself, and the yields were the same (greater than 80%). The regenerated fragment 1-127 was shown to be indistinguishable from fragment 1-127 before reduction by ion exchange chromatography, amino acid analysis, polyacrylamide gel electrophoresis, and disulfide analysis. These results show that the COOH-terminal dipeptide Arg-Leu is not essential for the acquisition of the native three-dimensional structure of lysozyme.  相似文献   
56.
The human health risk of soils contaminated with As, Pb, Cu, and Zn was evaluated based on pseudo-total concentrations of metal(loid)s, the physiologically based extraction test (PBET), and diffusive gradients in thin films (DGT). Non-carcinogenic (NCR) and carcinogenic (CR) risks exceeded the U.S. Environmental Protection Agency criteria under both the residential and non-residential scenarios. Human bioavailable concentrations (PBET) were much lower than pseudo-total concentrations. The Hazardous Index of NCR (HI (NCR)) for the PBET in the studied soils was 67% and 94% less than that for pseudo-total concentration, respectively, under the non-residential and residential scenarios. Similarly, CR for the PBET was also 65% and 93% less for the two soils. The concentration of metal(loid)s accumulated in the DGT resin was highly correlated with the PBET-extractable concentration (R2 > 0.649). Therefore, for both the CR and HI (NCR), the DGT-calculated risk was linearly related to the PBET-calculated risk for the studied soils under both scenarios. The results suggest that DGT uptake and PBET-extracted concentrations are good surrogates for risk estimation and that both J1 and J2 soils require remediation before their use for residential or non-residential purposes.  相似文献   
57.
The objective of this study was to evaluate the effects of several different commercial disinfectants on the embryogenic development of Ascaris suum eggs. A 1-ml aliquot of each disinfectant was mixed with approximately 40,000 decorticated or intact A. suum eggs in sterile tubes. After each treatment time (at 0.5, 1, 5, 10, 30, and 60 min), disinfectants were washed away, and egg suspensions were incubated at 25˚C in distilled water for development of larvae inside. At 3 weeks of incubation after exposure, ethanol, methanol, and chlorohexidin treatments did not affect the larval development of A. suum eggs, regardless of their concentration and treatment time. Among disinfectants tested in this study, 3% cresol, 0.2% sodium hypochlorite and 0.02% sodium hypochlorite delayed but not inactivated the embryonation of decorticated eggs at 3 weeks of incubation, because at 6 weeks of incubation, undeveloped eggs completed embryonation regardless of exposure time, except for 10% povidone iodine. When the albumin layer of A. suum eggs remained intact, however, even the 10% povidone iodine solution took at least 5 min to reasonably inactivate most eggs, but never completely kill them with even 60 min of exposure. This study demonstrated that the treatment of A. suum eggs with many commercially available disinfectants does not affect the embryonation. Although some disinfectants may delay or stop the embryonation of A. suum eggs, they can hardly kill them completely.  相似文献   
58.
59.
Many potential applications of genetically engineered microorganisms in environmental and agricultural biotechnology involve introducing genetic capabilities into nonsterile competitive environments in which they provide no advantage to the host. Field application vectors have been designed for the purpose of creating a temporary niche for the host in such environments. This technique involves the addition to the target environment of a selective substrate readily utilizable by the host microorganism but unavailable to most indigenous species. Thirteen nonionic and anionic detergents, representing a wide range of structural complexities and molecular weights, were screened as potential selective substrates. Competition experiments in soil, using Warburg respirometry, indicated that isolates from six different detergent enrichment cultures were more active on their corresponding detergents than the indigenous microorganisms. Detergents of intermediate structural complexities and molecular weights were most effective for use as selective substrates. A field application vector that utilizes 1.0% Igepal CO-720 (detergent) as the selective substrate and Pseudomonas paucimobilis 1IGP4 as the host was tested for its ability to increase the presence of nonadaptive tetracycline resistance marker genes in soil. In soil amended with the selective substrate, strain 1IGP4 plate counts increased by three orders of magnitude and tetracycline-resistant transformant (pRK293) counts increased from 1.8 × 106/g of soil to 4.3 × 108/g in 2 days. Inoculation in the absence of substrate amendment or amendment with a nonselective substrate did not result in growth of strain 1IGP4. These results demonstrate the effectiveness of field application vectors for increasing the concentration of nonadaptive genes in competitive environments.  相似文献   
60.
The digital twin technique has been broadly utilized to efficiently and effectively predict the performance and problems associated with real objects via a virtual replica. However, the digitalization of twin electrochemical systems has not been achieved thus far, owing to the large amount of required calculations of numerous and complex differential equations in multiple dimensions. Nevertheless, with the help of continuous progress in hardware and software technologies, the fabrication of a digital twin‐driven electrochemical system and its effective utilization have become a possibility. Herein, a digital twin‐driven all‐solid‐state battery with a solid sulfide electrolyte is built based on a voxel‐based microstructure. Its validity is verified using experimental data, such as effective electronic/ionic conductivities and electrochemical performance, for LiNi0.70Co0.15Mn0.15O2 composite electrodes employing Li6PS5Cl. The fundamental performance of the all‐solid‐state battery is scrutinized by analyzing simulated physical and electrochemical behaviors in terms of mass transport and interfacial electrochemical reaction kinetics. The digital twin model herein reveals valuable but experimentally inaccessible time‐ and space‐resolved information including dead particles, specific contact area, and charge distribution in the 3D domain. Thus, this new computational model is bound to rapidly improve the all‐solid‐state battery technology by saving the research resources and providing valuable insights.  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