全文获取类型
收费全文 | 2715篇 |
免费 | 260篇 |
出版年
2021年 | 32篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 32篇 |
2017年 | 28篇 |
2016年 | 45篇 |
2015年 | 67篇 |
2014年 | 92篇 |
2013年 | 182篇 |
2012年 | 138篇 |
2011年 | 134篇 |
2010年 | 92篇 |
2009年 | 85篇 |
2008年 | 156篇 |
2007年 | 163篇 |
2006年 | 157篇 |
2005年 | 158篇 |
2004年 | 188篇 |
2003年 | 152篇 |
2002年 | 142篇 |
2001年 | 79篇 |
2000年 | 68篇 |
1999年 | 58篇 |
1998年 | 48篇 |
1997年 | 27篇 |
1996年 | 40篇 |
1995年 | 33篇 |
1994年 | 45篇 |
1993年 | 27篇 |
1992年 | 49篇 |
1991年 | 34篇 |
1990年 | 38篇 |
1989年 | 28篇 |
1988年 | 29篇 |
1987年 | 30篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 31篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 20篇 |
1978年 | 21篇 |
1977年 | 21篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1969年 | 6篇 |
1968年 | 6篇 |
排序方式: 共有2975条查询结果,搜索用时 15 毫秒
51.
Masao Suzuki Chizuru Tsuruoka Tatsuaki Kanai Takeshi Kato Fumio Yatagai Masami Watanabe 《Biological Sciences in Space》2003,17(4):302-306
We investigated the difference in cell-killing effect and mutation induction between carbon- and neon-ion beams in normal human cells. Carbon- and neon-ion beams were accelerated by the Riken Ring Cyclotron (RRC) at the Institute of Physical and Chemical Research in Japan. Cell-killing effect was measured as the reproductive cell death using the colony formation assay. Mutation induction at the HPRT locus was detected to measure 6-thioguanine-resistant clones. The mutation spectrum of the deletion pattern of exons of induced mutants was analyzed using the multiplex polymerase chain reaction (PCR). Cell-killing effect was almost the same between carbon- and neon-ion beams with similar linear energy transfer (LET) values, while there observed a large difference in mutation frequency. Furthermore, in the case of neon-ion beams 60% of mutants showed total deletions and 35-40% showed partial deletions, while 95-100% of carbon-ion induced mutants showed total deletions. The results suggest that different ion species may cause qualitative and quantitative difference in mutation induction even if the LET values are similar. 相似文献
52.
Kohji Moriishi Minako Koura Fumio Amano 《FEMS immunology and medical microbiology》1996,16(3-4):213-222
Abstract Listeria monocytogenes replicates in a phagocytic cell following escape into the host cytoplasm. Listeriolysin O, secreted by L. monocytogenes , which belongs to the thiol-activated hemolysin family, is known to play an important role in the escape of the bacterium into the host cytoplasm. In this study, we demonstrated that expression of listeriolysin O by infecting L. monocytogenes was lightly induced in J774.1 macrophage-like cells pretreated with lipopolysaccharide, although the growth of the bacteria was suppressed. The number of viable L. monocytogenes decreased until 4 h post-infection and then increased between 4 and 8 h post-infection in untreated J774.1 host cells, but it decreased until 8 h post-infection in lipopolysaccharide-treated host cells. However, expression of listeriolysin O by L. monocytogenes was not induced in the untreated host cells, while it increased between 0 and 4 h post-infection in the lipopolysaccharide-treated host cells. Expression of listeriolysin O mRNA in the lipopolysaccharide-treated host cells was also induced at 2 h post-infection, suggesting that listeriolysin O was newly synthesized in the macrophage-like cells. These results suggest that macrophage activation induced with lipopolysaccharide could lead to the expression of the listeriolysin O gene and the synthesis of listeriolysin O protein under suppression of the intracellular growth of L. monocytogenes . 相似文献
53.
The Nucleotide Sequence of Human Acylamino Acid-Releasing Enzyme 总被引:3,自引:0,他引:3
Mitta Masanori; Ohnogi Hiroshi; Mizutani Shigetoshi; Sakiyama Fumio; Kato Ikunoshin; Tsunasawa Susumu 《DNA research》1996,3(1):31-35
The nucleotide sequence of a cDNA coding for the human acylaminoacid-releasing enzyme (AARE, also known as acylpeptide hydrolase)[EC 3.4.19.1] subunit has been determined. The amino acid sequenceof human AARE subunit deduced from its cDNA nucleotide sequenceshowed a high degree of identity (91.5%) with both the correspondingproteins from the pig and the rat. The AARE cDNA shows 99.2%identity with a 3.3 kb cDNA transcribed from a locus (DNF15S2)on the short arm of human chromosome 3, whose deletion is associatedwith small cell lung cancer, taking into consideration thatthe sequence of the 3.3-kb cDNA previously reported was causedby misreading. 相似文献
54.
Effect of triethylenepentaminehexaacetic acid on the renal damage in cadmium-treated Syrian hamsters 总被引:2,自引:0,他引:2
Toshiaki Shibasaki Q. -Y. Xu Iwao Ohno Fumio Ishimoto Osamu Sakai 《Biological trace element research》1995,50(2):157-165
Cadmium (Cd)-induced nephropathy was treated by triethylene-pentaminehexaacetic acid (TTHA) in male Syrian hamsters. Hamsters
injected three times a week with 3 mg/kg body wt CdCl2 showed proteinuria, urinaryN-acetyl-β-d-inglucosaminidase (NAG), and fractional excretion of sodium (FENa) when compared to saline-injected control. Cd-treated hamsters
injected ip with TTHA 10 mg/kg body wt five times a week showed reduction of renal damage, including reductions in urinary
protein (from 6.7±2.2 to 4.3±0.5 mg/d) and NAG (0.17±0.06 to 0.04±0.02 U/d). Urinary excretion of Cd was significantly increased
(from 87±51.3 to 3052±1485 mg/L) by TTHA administration. Cd concentration in renal cortical tissue was slightly reduced (26.4±3.0
to 21.8±2.7 mg/g. protein). Excretion of malondialdehyde (MDA) was increased only in Cd-injected hamsters (to 2.1±1.6 nM/L), and elevated MDA in renal cortical tissue was not reduced by the administration of TTHA (1041±105 vs 1104±358 nM/g protein). Glutathione (GSH) concentration in the renal cortex was significantly elevated after Cd administration and further
increased after TTHA administration (5.5±2.1 to 9.8±2.0 μg/50 mg protein). There were no marked effects on creatinine clearance
(Ccr) and hematocrit. Moreover, renal morphological changes were improved significantly by treatment with TTHA.
We demonstrated the efficacy of TTHA in the treatment of Cd-induced nephropathy in hamsters. Although the precise mechanism
of the TTHA effects on Cd-induced nephropathy has not been elucidated, it might involve GSH reducing the elevated MDA concentration
in renal tissue. 相似文献
55.
Synthesis of Serotonin in Traumatized Rat Brain 总被引:1,自引:0,他引:1
K. Tsuiki A. Takada S. Nagahiro M. Grdia M. Diksic H. M. Pappius 《Journal of neurochemistry》1995,64(3):1319-1325
Abstract: Previous studies have demonstrated that focal freezing lesions in rats cause a widespread decrease of cortical glucose use in the lesioned hemisphere and this was interpreted as a reflection of depression of cortical activity. The serotonergic neurotransmitter system was implicated in these alterations when it was shown that (1) cortical serotonin metabolism was increased widely in focally injured brain and (2) inhibition of serotonin synthesis prevented the development of cortical hypometabolism. In the present studies we applied an autoradiographic method that uses the accumulation of the 14 C-labeled analogue of serotonin α-methylserotonin to assess changes in the rate of serotonin synthesis in injured brain. The results confirmed that 3 days after the lesion was made, at the time of greatest depression of glucose use, serotonin synthesis was significantly increased in cortical areas throughout the injured hemisphere. The increase was also seen in the dorsal hippocampus and area CA3, as well as in the medial geniculate and dorsal raphe, but not in any other subcortical structures including median raphe. Present results suggest that the functional changes in the cortex of the lesioned hemisphere are associated with an increased rate of serotonin synthesis mediated by activation of the dorsal raphe. We also documented by α-[14 C]aminoisobutyric acid autoradiography that there was increased permeability of the blood-brain barrier, but this was restricted to the rim of the lesion. 相似文献
56.
Seasonal migration promoting assortative mating in Littorina brevicula on a boulder shore in Japan 总被引:1,自引:1,他引:0
Yoshitake Takada 《Hydrobiologia》1995,309(1-3):151-159
Littorina brevicula Philippi is one of the most common snails found in the upper intertidal zone of Japan. In Amakusa, some of the population
of L. brevicula migrate to the lower zone in the winter, while the rest stay in the upper zone. Thus, during the winter, which is its reproductive
season, the population of L. brevicula divides into two sub-populations. This leads to a hypothesis that the migration pattern in winter is genetically controlled
and this behavioural dimorphism is maintained by reproductive isolation between the two sub-populations. In order to test
this hypothesis, the following three points were investigated: (1) whether the same snails migrate in a similar way every
winter, (2) whether there is a significant tidal level preference in snails, and (3) whether reproductive isolation occurs
between the two sub-populations. The results showed (1) the migration behaviour of each snail was consistent over two successive
winters, i.e. the same group of snails migrated downward every winter and the same group of snails stayed in the upper zone
every winter, (2) transplanted snails moved toward the original zones where they were caught, suggesting that the snails actively
selected their tidal zone in winter, and (3) most of the snails copulated within each sub-population. Therefore, reproductive
isolation between the two sub-populations was considered to be established to some extent by the dimorphic migration behaviour.
In conclusion, the migratory behaviour of L. brevicula is determined separately for each individual and might be genetically controlled, and the behavioural dimorphism may be maintained
by partial reproductive isolation between the two sub-populations. 相似文献
57.
58.
Shigeki Nagao Yoshihiro Kawabata Takashige Nishikawa Haruhiko Takada 《Microbiology and immunology》1995,39(12):1011-1014
Guinea pigs immunized with Freund's complete adjuvant received challenge injection of the purified protein derivative of Mycobacterium tuberculosis in the flanks and the corneas to prepare delayed-type hypersensitivity (DTH) reactions. The animals were injected subcutaneously with lipopolysaccharide (LPS) or a synthetic lipid A (LA-15-PP). At the skin site primed with DTH reaction, increased swelling and hemorrhagic reaction followed by a definite necrotic reaction occurred. Severe corneal reactions were also observed in the animals. These findings indicate that bacterial endotoxin modulates DTH reactions and induces severe inflammatory reactions. 相似文献
59.
Tatsuo Suzutani Shin Koyano Minoru Takada Itsuro Yoshida Masanobu Azuma 《Microbiology and immunology》1995,39(10):787-794
The virulence of thymidine kinase-negative herpes simplex virus type 1 (HSV-1; VRTK? strain) and type 2 (HSV-2; UWTK? strain) was studied in comparison with that of their parental strains (VR-3 and UW-268, respectively) in an encephalitis model of adult (4-week-old) and newborn (3-day-old) mice. Viral thymidine kinase (TK) activity was essential for the maximum expression of virulence of HSV-1, because the 50% lethal dose (LD50) of VRTK? was 60 times higher than that of VR-3 in the brains of newborn mice expressing high levels of cellular TK activity. However, the UWTK? strain showed the same virulence as the parental strain in newborn mice, despite the lack virulence in adults, suggesting that replication of the UWTK? strain was completely supported by cellular TK activity. This difference in the role of viral and cellular TKs for virus growth between HSV-1 and HSV-2 was confirmed with the one-step growth of virus strains in L-M and L-M(TK?) cells. 相似文献
60.
Hidekazu Nishimura Kanetsu Sugawara Peng Gao Yasushi Muraki Seiji Hongo Fumio Kitame Kiyoto Nakamura 《Microbiology and immunology》1995,39(9):737-740
The HMV-II cells infected with influenza C virus were labeled with inorganic [32P]phosphate to identify phosphorylated proteins. Analysis by radioimmunoprecipitation with antiviral serum or monoclonal antibodies revealed that three major structural proteins of the virus, hemagglutinin-esterase (HE), nucleoprotein (NP), and matrix protein (M1) are all phosphorylated in both infected cells and virions. It was also observed that, in the presence of trypsin (10 μg/ml), the unphosphorylated form of the HE glycoprotein was cleaved efficiently whereas the phosphorylated form was not, raising the possibility that phosphorylation of HE may influence its susceptibility to degradation by proteolytic enzymes. 相似文献