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   1201篇
  免费   119篇
  国内免费   2篇
  2022年   13篇
  2021年   27篇
  2020年   9篇
  2019年   10篇
  2018年   10篇
  2017年   16篇
  2016年   28篇
  2015年   42篇
  2014年   50篇
  2013年   58篇
  2012年   75篇
  2011年   61篇
  2010年   39篇
  2009年   31篇
  2008年   43篇
  2007年   53篇
  2006年   31篇
  2005年   47篇
  2004年   25篇
  2003年   39篇
  2002年   23篇
  2001年   33篇
  2000年   48篇
  1999年   51篇
  1998年   29篇
  1997年   35篇
  1996年   21篇
  1995年   23篇
  1994年   22篇
  1993年   13篇
  1992年   17篇
  1991年   16篇
  1990年   24篇
  1989年   21篇
  1988年   16篇
  1987年   17篇
  1986年   8篇
  1985年   6篇
  1984年   10篇
  1983年   16篇
  1982年   12篇
  1981年   7篇
  1980年   7篇
  1979年   11篇
  1976年   13篇
  1975年   9篇
  1974年   14篇
  1973年   8篇
  1972年   7篇
  1971年   7篇
排序方式: 共有1322条查询结果,搜索用时 812 毫秒
31.
Two cases are reviewed in which the presence of intranuclear cytoplasmic inclusions in fine needle aspiration biopsy specimens of the thyroid suggested a diagnosis of papillary carcinoma. Subsequent surgical specimens were consistent with diagnoses of microfollicular adenoma and follicular carcinoma. These cases suggest that the presence of intranuclear inclusions in epithelial thyroid cells is not limited to papillary and medullary carcinoma, as some authors have suggested.  相似文献   
32.
Human serum was fractionated by high resolution agarose isoelectricfocusing and the galactosyltransferase activity profile was determined using the ovalbumin, mucin, glucose and N-acetylglucosamine acceptor assays. The four acceptors gave very similar activity profiles. There were minor quantitative differences in some of the 12 or more peaks of activity detected and the only qualitative difference between them was a minor peak at pH 3.90 (2% of the total activity) which reacted only with the mucin acceptor. This suggests that most of the isoenzymes of human serum galactosyltransferase have broad and similar acceptor specificities and that the heterogeneity seen in serum cannot be accounted for by acceptor-specific forms of the enzyme.  相似文献   
33.
Summary Laboratory prescreening ofRhizobium trifolii for acid tolerance, based upon the ability of rhizobia to grow in acid media (pH 4.2) containing Al (15 M), was successful for the selection of strains capable of survival in acid soil.Both sterile and non-sterile soils of varying acidity were inoculated with several strains ofR. trifolii.Acid tolerant strains generally had significantly higher populations at every sample period than an acid sensitive strain. Amelioration of soil acidity by liming improved persistence of all strains. Soil sterilization by autoclaving adversely affected survival of all strains at each soil acidity level.Paper Number 8766 of the Journal Series, North Carolina Agricultural Research Service, Raleigh, NC 27650, USA.  相似文献   
34.
35.
Davey K. G., Sommerville R. I. and Rogers W. P. 1982. The effect of ethoxyzolamide, an analogue of insect juvenile hormone, nor-adrenaline and iodine on changes in the optical path difference in the excretory cells and oesophagus during exsheathment in Haemonchus contortus. International Journal for Parasitology12: 509–513. Ethoxyzolamide, an inhibitor of carbonic anhydrase, markedly inhibits exsheathment of Haemonchus when the larvae are subsequently exposed to an exsheathing stimulus of CO2 at 38.5°C. Ethoxyzolamide at 2 × 10?5M does not prevent the increase in optical path difference in the oesophageal region which normally accompanies exsheathment, but markedly inhibits the increase in optical path difference in the excretory cells. An analogue of juvenile hormone (JHA; the methyl ester of 3,7,11 trimethyl-7,11-dichloro-2-dodecenic acid) does not affect the optical path difference in either the oesophagus or the excretory cells of ensheathed worms. When worms are artificially desheathed by exposure to NaOCl, a procedure which mimics the effect of CO2 upon the oesophagus, but which does not affect the excretory cells, subsequent exposure to JHA at room temperature increases the optical path difference in the excretory cells. This increase is enhanced by subsequent incubation of the worms at 38.5°C at 30–60 min and further enhanced when CO2 is present during the incubation at 38.5°C. The stimulation of the excretory cells by JHA is inhibited by ethoxyzolamide at 2 × 10?5M. Noradrenaline at 10?3M has no effect on ensheathed larvae, but causes an increase in optical path difference in the excretory cells of larvae desheathed with NaOCl. This increase is inhibited by ethoxyzolamide. A brief exposure to I2 blocks the response of the excretory cells of both CO2 and JHA, but does not significantly reduce the effect of nor-adrenaline. On the basis of these and previous results, it is proposed that both CO2 and JHA stimulate a hypothetical CO2 receptor which leads to the release of nor-adrenaline. The noradrenaline in turn stimulates, either directly or indirectly, the excretory cells.  相似文献   
36.
In juvenile wild rats, bronchus-associated lymphoid tissue (BALT) development was similar to that seen in adult specified-pathogen-free rats. In adult wild rats the BALT was widespread. In one animal infected with a mycoplasma-like organism, a region of bronchoepithelium overlying a large BALT nodule was seen, through which lymphocytes appeared able to pass to make direct contact with the bronchial lumen: the significance of this observation is discussed. There was no evidence of infection in lungs from any of the specified-pathogen-free animals, where small foci of BALT were seen.  相似文献   
37.
38.
A total of 203 samples of faeces from 124 cows was examined for the presence of Yersinia enterocolitica and related species by a variety of isolation procedures. Cold enrichment at 5°C for three weeks, followed by plating on cefsulodin-irgasannovobiocin agar yielded Yersinia species most frequently. Yersinia enterocolitica or related species were isolated from 50% of the cows.  相似文献   
39.
Glycine argyrea accession G1420 was evaluated for its response to inoculation with Agrobacterium rhizogenes strains LBA9402 and A4T, carrying wild type Ri plasmids, and by strains R1601 and A4TIII with engineered plasmids. Hypocotyls from young seedlings were the most responsive in producing roots at inoculation sites. Root production was also dependent on bacterial concentration. Excised, cultured roots produced green nodular callus which regenerated shoots on SC2 medium containing 1.1 mg l–1 6-benzylaminopurine and 0.005 mg l–1 indole-3-butyric acid. The transformed nature of the roots and of callus regenerating shoots was confirmed by the presence of opines and by dot blot analysis for Ri TL-DNA. Tissues regenerated from roots transformed by A. rhizogenes strains R1601 and A4TIII exhibited NPTII enzyme activity, confirming the stable integration and expression of the chimaeric kanamycin resistance gene in transgenic tissues.Abbreviations BAP 6-benzylaminopurine - IBA indole-3-butyric acid - NPTII neomycin phosphotransferase II - SDS sodium dodecyl sulphate  相似文献   
40.
A theoretical model was developed and used to estimate quantitatively the "worst case", i.e., the longest, time to reach equilibrium temperature in the center of a clump of bacteria heated in fluid. For clumps with 10 to 10(6) cells heated in vapor, such as dry and moist air, and liquid fluids such as purees and juices, predictions show that temperature equilibrium will occur with sterilization temperatures up to 130 degrees C in under 0.02 s. Model development highlighted that the controlling influence on time for heating up the clump is the surface convection thermal resistance and that the internal conduction resistance of the clump mass is negligible by comparison. The time for a clump to reach equilibrium sterilization temperature was therefore decreased with relative turbulence (velocity) of the heating fluid, such as occurs in many process operations. These results confirm widely held suppositions that the heat-up time of bacteria in vapor or liquid is not significant with usual sterilization times.  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