全文获取类型
收费全文 | 3291篇 |
免费 | 345篇 |
国内免费 | 2篇 |
出版年
2022年 | 19篇 |
2021年 | 44篇 |
2020年 | 48篇 |
2019年 | 40篇 |
2018年 | 62篇 |
2017年 | 50篇 |
2016年 | 75篇 |
2015年 | 121篇 |
2014年 | 137篇 |
2013年 | 153篇 |
2012年 | 179篇 |
2011年 | 182篇 |
2010年 | 89篇 |
2009年 | 97篇 |
2008年 | 135篇 |
2007年 | 127篇 |
2006年 | 144篇 |
2005年 | 115篇 |
2004年 | 140篇 |
2003年 | 133篇 |
2002年 | 136篇 |
2001年 | 48篇 |
2000年 | 38篇 |
1999年 | 55篇 |
1998年 | 44篇 |
1997年 | 29篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 40篇 |
1993年 | 32篇 |
1992年 | 46篇 |
1991年 | 41篇 |
1990年 | 29篇 |
1989年 | 40篇 |
1988年 | 42篇 |
1987年 | 33篇 |
1986年 | 25篇 |
1985年 | 25篇 |
1984年 | 25篇 |
1983年 | 33篇 |
1982年 | 28篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 18篇 |
1978年 | 23篇 |
1977年 | 17篇 |
1973年 | 18篇 |
1971年 | 17篇 |
1970年 | 17篇 |
1953年 | 17篇 |
排序方式: 共有3638条查询结果,搜索用时 15 毫秒
101.
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
102.
103.
104.
Hugh D. Campbell David A. Dionysius Dianne T. Keough Bruce E. Wilson John de Jersey Burt Zerner 《Biochemical and biophysical research communications》1978,85(2):615-622
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
105.
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
106.
Hugh M. Miller S. Marvin Friedman David J. Litman Charles R. Cantor 《Molecular & general genetics : MGG》1976,144(3):273-280
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
107.
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
108.
109.
Hassan-Fahmi Aly Hans Geiger Ursula Schücker Hugh Waldrum George Vander Velde Tom J. Mabry 《Phytochemistry》1975,14(7):1613-1615
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
110.
Hugh McAllister 《Curtis's Botanical Magazine》2019,36(4):365-374
The very rare Japanese birch, Betula chichibuensis Hara, is described and illustrated. It has become widely available since its 1986 introduction from seed, from a breeding population derived from the then single known wild stand. In 2015 it was reintroduced from further, recently discovered, wild populations. 相似文献