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   2484篇
  免费   209篇
  国内免费   2篇
  2022年   16篇
  2021年   25篇
  2020年   36篇
  2019年   34篇
  2018年   55篇
  2017年   40篇
  2016年   57篇
  2015年   83篇
  2014年   108篇
  2013年   113篇
  2012年   136篇
  2011年   137篇
  2010年   63篇
  2009年   67篇
  2008年   112篇
  2007年   100篇
  2006年   104篇
  2005年   88篇
  2004年   116篇
  2003年   97篇
  2002年   104篇
  2001年   29篇
  2000年   18篇
  1999年   25篇
  1998年   34篇
  1997年   20篇
  1996年   32篇
  1995年   29篇
  1994年   30篇
  1993年   25篇
  1992年   15篇
  1991年   17篇
  1990年   18篇
  1989年   20篇
  1988年   26篇
  1987年   16篇
  1986年   13篇
  1985年   15篇
  1984年   15篇
  1983年   29篇
  1982年   24篇
  1981年   20篇
  1980年   21篇
  1978年   19篇
  1977年   15篇
  1974年   15篇
  1973年   17篇
  1970年   13篇
  1954年   14篇
  1953年   16篇
排序方式: 共有2695条查询结果,搜索用时 296 毫秒
61.
A variant of the baculovirus, Autographa californica nuclear polyhedrosis virus, has been isolated in Idaho during an epizootic disease in a field population of A. californica. Genotypic characterization indicates that the virus is distinct from variants previously characterized. Analysis of five clones, derived by plaque purification in cell culture, indicates relative homogeneity of the original virus isolate. Further exploration of the factors involved in natural genetic variability of baculoviruses is appropriate.  相似文献   
62.
Synopsis Ages determined by counts of apparent annuli on scales, sagittae, vertebrae, pectoral fin ray and dorsal fin spine cross sections of largemouth bass from northern populations, which are older and slower growing fish than in the southern parts of its native range, were compared to establish the accuracy of each method. Linear regression techniques indicated strong agreement (r> 0.9) among ages assigned from the examination of scales, sagittae, and vertebrae. The pattern of growth zones on pectoral fin ray and dorsal fm spine cross sections proved too variable for accurate age determination. Limited data suggest that ages greater than 7+ assigned from scales were more likely to underestimate true ages than the other body parts used, although none of these methods gave satisfactory results. Examination of scales from recovered tagged fish, and the similarity between back-calculated lengths of fish through age 7+ to annulus I and observed lengths of juvenile largemouth bass near the end of their first growing season, support the validity of ages determined from scales. Despite a very limited amount of habitat suitable for largemouth bass and severe climatic conditions, growth of this species in Tadenac Lake was similar to growth in other waters north of the Great Lakes. Differences in physical characteristics among these waters does not appear to influence growth rates of largemouth bass, but probably affects production and biomass.  相似文献   
63.
64.
65.
The iron-containing violet acid phosphatases from beef spleen and pig allantoic fluid have been purified to homogeneity. Molecular weight determinations by zonal gel filtration, SDS-gel electrophoresis, and ultracentrifugation support values close to 40,000 for both enzymes, necessitating reappraisal of literature values. Similarly, the equivalent weight for iron is close to 20,000 for both enzymes, indicating the presence of two iron atoms per molecule of enzyme. The enzymes also have very similar ultraviolet and visible spectra, with λmax values close to 550 nm, and ?550 values(in terms of iron) of 2.04 × 103 and 2.00 × 103 for the beef spleen and pig allantoic fluid enzymes respectively.  相似文献   
66.
The protective capacities of different sources of immune lymphocytes against Nippostrongylus brasiliensis infection were examined. Thoracic duct lymphocytes (TDL) drained from donors on the tenth day of a primary infection (Day 10 TDL) conferred greater protection against adult worms established by larval infection than either mesenteric lymph node cells (MLNC) or TDL drained from hyperimmune donors. Day 10 TDL also conferred a high degree of protection against intraduodenally implanted “normal” and “damaged” worms. These results suggest that the different susceptibilities of “normal” and “damaged” worms to adoptive protection is a quantitative rather than a qualitative phenomenon. The results also emphasise that kinetic and dose-response experiments are important in evaluating the protective capacities of transferred cells.  相似文献   
67.
Summary The surface topography of the intact 70S ribosome and free 30S and 50S subunits from Bacillus stearothermophilus strain 2184 was investigated by lactoperoxidase-catalyzed iodination. Two-dimensional polyacrylamide gel electrophoresis was employed to separate ribosomal proteins for analysis of their reactivity. Free 50S subunits incorporated about 18% more 125I than did 50S subunits derived from 70S ribosomes, whereas free 30S subunits and 30S subunits derived from 70S ribosomes incorporated similar amounts of 125I. Iodinated 70S ribosomes and subunits retained 62–78% of the protein synthesis activity of untreated particles and sedimentation profiles showed no gross conformational changes due to iodination. The proteins most reactive to enzymatic iodination were S4, S7, S10 and Sa of the small subunit and L2, L4, L5/9, L6 and L36 of the large subunit. Proteins S2, S3, S7, S13, Sa, L5/9, L10, L11 and L24/25 were labeled substantially more in the free subunits than in the 70S ribosome. Other proteins, including S5, S9, S12, S15/16, S18 and L36 were more extensively iodinated in the 70S ribosome than in the free subunits. The locations of tyrosine residues in some homologus ribosomal proteins from B. stearothermophilus and E. coli are compared.  相似文献   
68.
Anionic peroxidase isoenzymes, separated on acrylamide gels, were examined in two flax genotrophs and in their reciprocal F2 hybrids. Isoenzyme 1 exhibited a significant difference in Rm between stem base and apex and there was a gradient of decreasing Rm and activity between base and apex. Isoenzyme 2 displayed only the activity gradient. The parents differed significantly in the Rm's and activities of isoenzymes 1 and 2, and the F2's showed complete dominance of the L parent for Rm, with activities being approximately intermediate.  相似文献   
69.
70.
Ten glycosides of kaempferol and quercetin, including the hitherto unknown kaempferol and quercetin 3-rutinoside-7-rhamnosides, have been isolated from Equisetum silvaticum L.  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