全文获取类型
收费全文 | 4153篇 |
免费 | 267篇 |
国内免费 | 5篇 |
专业分类
4425篇 |
出版年
2023年 | 14篇 |
2022年 | 24篇 |
2021年 | 59篇 |
2020年 | 22篇 |
2019年 | 51篇 |
2018年 | 50篇 |
2017年 | 58篇 |
2016年 | 92篇 |
2015年 | 131篇 |
2014年 | 157篇 |
2013年 | 268篇 |
2012年 | 262篇 |
2011年 | 277篇 |
2010年 | 151篇 |
2009年 | 149篇 |
2008年 | 285篇 |
2007年 | 263篇 |
2006年 | 261篇 |
2005年 | 274篇 |
2004年 | 274篇 |
2003年 | 235篇 |
2002年 | 208篇 |
2001年 | 47篇 |
2000年 | 35篇 |
1999年 | 57篇 |
1998年 | 60篇 |
1997年 | 40篇 |
1996年 | 41篇 |
1995年 | 40篇 |
1994年 | 44篇 |
1993年 | 36篇 |
1992年 | 34篇 |
1991年 | 27篇 |
1990年 | 35篇 |
1989年 | 46篇 |
1988年 | 16篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 37篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1973年 | 9篇 |
1967年 | 8篇 |
排序方式: 共有4425条查询结果,搜索用时 15 毫秒
11.
Intensely pigmented and spherical vesicles (anthocyanoplasts) were found in anthocyanin-containing cells of sweet potato (Ipomoea batatas) suspension cultures. Anthocyanin synthesis began to first occur 24–48 h after exposure to light, and then numerous small red vesicles were detected under a microscope. The frequency of anthocyanoplast-containing cells rapidly increased to finally about 80% of the total cultured cells after 5 days of irradiation. Fully developed anthocyanoplasts reached 10–15 m in diameter. On the other hand, neither anthocyanin synthesis nor development of anthocyanoplasts was induced in the dark-cultured cells. 2,4-D also inhibited anthocyanin synthesis and development of these vesicles. The results suggest that anthocyanoplasts might be a site of anthocyanin synthesis and/or accumulation.Abbreviation 2,4-D
2,4-dichlorophenoxyacetic acid 相似文献
12.
13.
To evaluate the influence of overwintering individuals of zooplankton on spring zooplankton communities, the dynamics of zooplankton
communities with or without overwintering individuals were observed in experimental ponds from fall to spring. An insecticide,
carbaryl, was used to regulate the overwintering individuals. In ponds which received insecticide applications in November
or January, all cladoceran and rotiferan species were eliminated by the treatments and did not reappear until late March or
early April, even when the chemical disappeared rapidly. The low water temperature may delayed the establishment of the populations
from resting eggs. In these ponds, populations of various cladoceran and rotiferan species, which seemed to be originated
from resting eggs, were built up in the spring. In control ponds,Daphnia ambigua orD. longispina overwintered as juveniles and adults and established a large spring population earlier than other cladocerans and rotifers
overwintering as resting eggs. The latter zooplankters did not increase in the spring probably because their growth was suppressed
by the precedingDaphnia species through competition. In nature, even if the number of overwintering individuals is small, they may have a potential
to build up a large population earlier than the individuals hatching from resting eggs. As a result, the species which have
overwintered as individuals seem to predominate in the spring and have a large influence on the spring zooplankton community. 相似文献
14.
Mariyo F. Watanabe Ken-Ichi Harada Kennji Matsuura Masayuki Watanabe Makoto Suzuki 《Journal of applied phycology》1989,1(2):161-165
Changes in the content of cyclic heptapeptide hepatotoxins called microcystins were investigated during batch culture of two
Microcystis species using high performance liquid chromatography. After adsorption to ODS-silica gel cartridges and elution with methanol,
the toxins were analyzed and quantified by HPLC. 35 μg per 100 mg dry cells of microcystin-RR, 34 μg of -YR and 43 μg of -LR
were present at the beginning of the exponential growth phase of M. viridis. Microcystin-RR increased markedly towards the end of the exponential phase with the maximum content of 112 μg per 100 mg
cells was measured at the late stage of the exponential phase. A remarkable increase of microcystin-YR from 130 μg per 100
mg cells to 1020 μg was observed during the exponential phase of a highly toxic strain of M. aeruginosa. However no clear differences were found in the pattern of change among the three toxins during the growth course. 相似文献
15.
T Uchiyama T Tadakuma K Imanishi M Araake S Saito X J Yan H Fujikawa H Igarashi N Yamaura 《Journal of immunology (Baltimore, Md. : 1950)》1989,143(10):3175-3182
Toxic shock syndrome toxin-1 (TSST-1)-binding structures present on murine lymphoid tissues were investigated by using 125I-TSST-1. T-depleted C57BL/6 spleen cells incubated with TSST-1 for 3 h at 0 degree C were mitogenic to splenic T cells, indicating that the former cells bind and present TSST-1 to T cells. TSST-1-binding activity was observed in C57BL/6 splenic B cells and L cells transfected with I-Ab genes, but not in splenic T cells and control L cells. Scatchard plot analysis showed that these B cells and transfectants bound TSST-1 with similar binding affinity. SDS-PAGE analysis showed that lysates of C57BL/6 spleen cells and the I-Ab-positive transfectants contain a single band which bound TSST-1 and comigrated with I-Ab heterodimers. TSST-1-binding activity observed clearly in C57BL/6. BALB/c, and C3H/HeN spleen cells and L cells transfected with I-Ab or I-Ak genes was not reduced by paraformaldehyde fixation. Binding of 125I-TSST-1 to the three spleen cells was markedly reduced by anti-I-A antibodies, but not by anti-I-E antibodies. C57BL/6, C3H/HeN, and (C3H/HeN x C57BL/6) F1 T cells were activated by TSST-1 to proliferate and produce IL-2 in the presence of FT6.2 cells, LT1-30-3 cells and either of them, respectively, but not in the presence of control L cells. These results indicate that I-A molecules function as the structures via that accessory cells directly bind TSST-1 on the cell surface and present a triggering signal of TSST-1 to T cells. 相似文献
16.
Close linkage of MEN2A with RBP3 locus in Japanese kindreds 总被引:7,自引:0,他引:7
Masayuki Yamamoto Shin-ichiro Takai Tetsuro Miki Kazuyoshi Motomura Makoto Okazaki Isamu Nishisho Hideo Tateishi Akira Miyauchi Tasuku Honjo A. J. Pakstis Takesada Mori 《Human genetics》1989,81(3):287-288
Summary The gene responsible for multiple endocrine neoplasia type 2A (MEN2A) has recently been assigned to the pericentromeric region of chromsome 10 in European Caucasian kindreds by linkage analysis using a DNA marker, interstitial retinol-binding protein 3 (RBP3). We have found tight linkage between the MEN2A and RBP3 loci in Japanese MEN2A kindreds. The maximum lod score is 5.19 at a recombination fraction of 0.00. This result suggests that mutation of a certain gene close to RBP3 is responsible for MEN2A irrespective of ethnic backgrounds. 相似文献
17.
M Kita Y Ohmoto Y Hirai N Yamaguchi J Imanishi 《Comptes rendus des séances de la Société de biologie et de ses filiales》1990,184(5-6):380-384
Mycoplasma shows a variety of effects on immune system, including the activation of macrophage, the increase in T cell cytotoxicity, and the enhancement of the proliferation and maturation of B cells, etc. As it is well known that many cytokines regulate the immune system, it is interesting to examine whether or not human peripheral blood mononuclear cells (PBMC) produce interleukin (IL) in response to mycoplasmas. In the present study, human PMBC were incubated with 7 species of mycoplasmas for 48 hours, and IL-1 beta, IL-2 and IL-6 activities in the supernatants were determined by ELISA. All the species of mycoplasmas were able to induce IL-1 beta and IL-6, although IL-2 was induced only by M. pneumoniae. These results suggest that the influence of mycoplasma infection on immune system may be partly due to the interleukins induced by mycoplasmas. 相似文献
18.
19.
20.
Makiko Kawagishi-Kobayashi Masayuki Yamamoto Akira Ishihama 《Molecular & general genetics : MGG》1996,250(1):1-6
Local sequence similarity exists between the subunit 2 of eukaryotic RNA polymerases II and the barnase-type bacterial RNases. The RNase-like domain from the Rpb2 ofSchizosaccharomyces pombe was expressed inEscherichia coli as a GST fusion protein and examined for its RNase activity. When the GST fusion protein was incubated in vitro with32P-labeled RNA, the RNA degradation activity was less than 0.1%, if any, of the level of synthetic barnase. In order to check the in vivo function of this region, we constructed two mutantrpb2 alleles,rpb2
E357A
andrpb2
H3a6L
, each carrying a single amino acid substitution at the site correponding to one of the three essential amino acid residues forming the catalytic site in barnase (mutation of barnase at the corresponding sites results in complete loss of RNase activity) and five other mutantrpb2 alleles, each carrying a single mutation at various positions within the RNase-like domain but outside the putative catalytic site for RNase activity. When these mutantrpb2 alleles were expressed in anrpb2-disruptedS. pombe strain, all the mutants grew as well as the wild-type parent and did not show any clear defective phenotypes. These results suggest either that the RNase-like domain in Rpb2 does not function as an RNase in vivo or that the RNase activity of this domain, if present at all, is not essential for cell growth. 相似文献