全文获取类型
收费全文 | 9001篇 |
免费 | 997篇 |
国内免费 | 1篇 |
专业分类
9999篇 |
出版年
2021年 | 105篇 |
2019年 | 71篇 |
2018年 | 117篇 |
2017年 | 111篇 |
2016年 | 150篇 |
2015年 | 277篇 |
2014年 | 300篇 |
2013年 | 400篇 |
2012年 | 450篇 |
2011年 | 452篇 |
2010年 | 295篇 |
2009年 | 238篇 |
2008年 | 395篇 |
2007年 | 442篇 |
2006年 | 382篇 |
2005年 | 392篇 |
2004年 | 344篇 |
2003年 | 328篇 |
2002年 | 312篇 |
2001年 | 187篇 |
2000年 | 196篇 |
1999年 | 165篇 |
1998年 | 134篇 |
1997年 | 134篇 |
1996年 | 120篇 |
1995年 | 103篇 |
1994年 | 124篇 |
1993年 | 107篇 |
1992年 | 176篇 |
1991年 | 137篇 |
1990年 | 124篇 |
1989年 | 128篇 |
1988年 | 119篇 |
1987年 | 135篇 |
1986年 | 107篇 |
1985年 | 148篇 |
1984年 | 155篇 |
1983年 | 111篇 |
1982年 | 132篇 |
1981年 | 119篇 |
1980年 | 109篇 |
1979年 | 102篇 |
1978年 | 75篇 |
1977年 | 75篇 |
1976年 | 85篇 |
1975年 | 66篇 |
1974年 | 84篇 |
1973年 | 74篇 |
1972年 | 63篇 |
1971年 | 61篇 |
排序方式: 共有9999条查询结果,搜索用时 62 毫秒
21.
Caroline van Haaften-Day Peter Russell Susan Carr Lesley Wright 《In vitro cellular & developmental biology. Plant》1988,24(10):965-971
Summary A cell line derived from a human ovarian carcinosarcoma was established in tissue culture and in nude mice. Two sublines,
LDF and HDF, separated by discontinuous density centrifugation were also established from the parent line JoN. The cloning
efficiency of the JoN line was 21%. Morphologic features of adenocarcinoma cells characteristic of the parent JoN cells were
retained in the sublines and clones; all lines showed the same karyotype and DNA content (pseudodiploid and pseudotetraploid).
Keratin, as demonstrated immunohistochemically, was strongly expressed in the parent line JoN and the xenograft tumor, but
not at all in the LDF sublines and only moderately in the HDF sublines. Vimentin, however, was expressed in neither the parent
line JoN nor the xenograft tumor, but was present in both sublines. Transglutaminase and plasminogen activator activity was
high in the parent line JoN. Neither, sublines nor clones showed the same high enzyme activity as the parent line. It is concluded
that this human tumor line JoN is comprised of epithelial cells, capable of multidirectional differentiation. 相似文献
22.
23.
William Russell 《BMJ (Clinical research ed.)》1984,288(6416):580
24.
25.
The prevalence of Salmonella spp. in nestling common barn-owls was investigated in southwestern New Jersey during the summer of 1985. Of 94 owls sampled by swabbing the cloaca, eight (8.5%) were found to harbor Salmonella spp. Three serotypes--S. thompson, S. tuindorp, and S. typhimurium--were identified. Five (20%) of the 25 nest sites examined (all of them in or near farm buildings or dwellings) contained Salmonella-positive owls. 相似文献
26.
Myosin associated with the male germ cells of angiosperms interacts with actin, promoting transport of the non-motile generative
and later sperm cells in the pollen tube. Myosin localizing on the sperm cell plasma membrane seems negligible in Plumbago, as reflected by the absence of: (i) anti-myosin labeling using immunoelectron microscopy, (ii) sperm motility on actin matrices,
and (iii) electrophoretic movement changes after addition of antibody. Sperm cells injected directly into actively streaming
Nitella internodal cells, however, follow actin bundles and their movement is sensitive to ATP and Mg2+. This may be based on simple charge binding since negatively charged latex beads also migrate on actin, whereas neutral or
positively-charged latex beads do not. Sperm cells are negatively charged according to capillary microelectrophoresis, whereas
killed sperm cells, which are positively charged do not migrate. The sperm cell that normally fertilizes the egg has a higher
calculated charge (8.277 × 103 esu/cm2) compared with the sperm cell that fuses with the central cell (6.120 × 103 esu/cm2).
Received: 15 December 1998 / Accepted: 21 January 1999 相似文献
27.
28.
Mouse specific-locus test for the induction of heritable gene mutations by dibromochloropropane (DBCP) 总被引:1,自引:0,他引:1
The nematocide DBCP (1,2-dibromo-3-chloropropane) produced negative results in a specific-locus test for gene-mutation induction in the germline of male (101 X C3H)F1 mice, most of which were treated with 5 daily intraperitoneal injections of 80 mg/kg (total exposure, 400 mg/kg); a few received lower exposures. For treated spermatogonial stem cells, the finding of 2 mutations among 39519 offspring--a rate almost identical to the control rate--rules out (at the 5% significance level) an induced mutation frequency greater than 2.0 times the historical control rate. From treated poststem-cell stages, no mutants were found among 6240 offspring, ruling out (at the 5% significance level) a multiple of 8.0 times the control for these cell types. A multiple rearrangement (7 chromosomes involved in 3 translocations) found in one of the mutants probably arose as a postmeiotic event not associated with the DBCP treatment. The fertility of DBCP-treated males was not disturbed, in keeping with the absence of germ-cell toxicity and dominant lethals found by other investigators in these mice, and in contrast to results in certain other species. While the treated (101 X C3H)F1 mice are Ah-responsive, other findings make it questionable whether biotransformation of DBCP to reactive intermediates is accomplished via the Ah-receptor system. 相似文献
29.
30.