全文获取类型
收费全文 | 1290篇 |
免费 | 33篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 35篇 |
2013年 | 89篇 |
2012年 | 61篇 |
2011年 | 67篇 |
2010年 | 45篇 |
2009年 | 58篇 |
2008年 | 77篇 |
2007年 | 86篇 |
2006年 | 104篇 |
2005年 | 80篇 |
2004年 | 82篇 |
2003年 | 77篇 |
2002年 | 100篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 21篇 |
1998年 | 17篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有1323条查询结果,搜索用时 15 毫秒
11.
Cannibalistic feeding behavior of the brackish-water copepodSinocalanus tenellus was examined in the laboratory using CI-II,CIII-IV and CVI female as predators and NI-II, NIII-IV, NV-VIand CI-II as prey. In each prey-predator combination, the ingestionrate increased with increasing prey density to an asymptoticvalue. Cannibalism took place even when phytoplankton was availableas an alternative food supply. Based on a daily ration, theoptimal prey stages for CVI females, CIII-IV and CI-II are NI-VI,NI-IV and NI-II respectively. Under average, natural prey density(10 nauplii l1), S tenellus can achieve only a smallfraction (max 9%) of the daily minimum food requirement by cannibalisticfeeding. However, the impact of cannibalism on naupliar survivorshipcan be significant. When adult females occur at a density of10 l1, the mortality due to cannibalism attains 99.2%during the naupliar stages. 相似文献
12.
Association of Lps gene with natural resistance of mouse macrophages against Legionella pneumophila 总被引:3,自引:0,他引:3
Shin-ichi Yoshida Yoshitaka Goto Hiroshi Miyamoto Hironobu Fujio Yasuo Mizuguchi 《FEMS microbiology letters》1991,89(1):51-56
We have cloned a 1.6-kb region of chromosomal DNA from Thermoplasma acidophilum into Escherichia coli using as a probe part of the Methanococcus vannielii fus-gene. The sequence of the clone was highly homologous to part of the corresponding Methanococcus vannielii gene. By chromosome walking, a 4.7-kb EcoRI fragment containing the complete gene was isolated. Nucleotide sequencing revealed an open reading frame of 2196 nucleotides. The deduced amino acid sequence contains the known peptide sequence around the ADP-ribosylation site of T. acidophilum elongation factor 2, which unequivocally confirms that the fus-gene has been cloned. The amino acid sequence was compared to that of hamster and E. coli, as well as to known archaebacterial EF-2 sequences. 相似文献
13.
Changes in synthetic activity of cell walls during the cell cycle in a synchronous culture of Catharanthus roseus 总被引:1,自引:0,他引:1
The incorporation rates of [14 C] glucose into various fractions of the cell walls and into the sugar constituent of each fraction were investigated in a synchronous culture of Catharanthus roseus (L.) G. Don in order to elucidate the synthetic aspects of the cell walls during the cell cycle. Changes in the incorporation of radioactivity were closely correlated with changes in the amount of each cell wall fraction as well as with those in sugar composition as reported previously (S. Amino et al. Physiol. Plant. 60: 326–332, 1984). The specific activity of galactose was higher than that of other sugars throughout the cell cycle, and a temporary increase in the incorporation of radioactivity into all cell wall fractions except cellulose was observed just before the increase in cell numbers. The synthetic activities may play key roles in the regulation of cell wall polysaccharide dynamics during the cell cycle. 相似文献
14.
To find whether cytoplasmic streaming in Acetabularia is controlledby Ca2+, a tonoplast-permeabilized cell model was prepared usinga vacuolar perfusion technique. The cytoplasmic streaming remainedalmost normal after perfusion with EGTA medium (10 mM EGTA,40 mM PIPES, 5mM MgCl2 and 800 mM sorbitol, pH 6.9), but stoppedwithin 10 min when saponin medium (EGTA medium plus 50 µg/mlsaponin, 50 µg/ml hexokinase and 5 mM glucose) was perfused.This model system was reactivated with a solution containing0.5 mM ATP and different concentrations of Ca2+ (reactivationmedium). With the reactivation medium at pCa 65, theresumed streaming lasted for about 10 min before the cytoplasmaggregated. At pCa 43, the streaming was observed onlyfor a few minutes because the cytoplasm aggregated quickly.At pCa 7, no reactivated movement was observed. Reactivationwas not induced in an ATP- or Mg2+-deficient medium even inthe presence of an adequate concentration of Ca2+, and was inhibitedby 50 µg/ml cytochalasin B or 1 mM N-ethylmaleimide. We concluded from these observations that the cytoplasmic streamingin Acetabularia is very likely to be driven by the actomyosinsystem in the presence of Mg-ATP and Ca2+ at pCa 65. (Received October 31, 1984; Accepted April 1, 1985) 相似文献
15.
Shin-ichi Miyoshi Katsumi Sugiyama Hiroshi Furuta Noriko Miyoshi Sumio Shinoda 《FEMS microbiology letters》1986,34(3):301-304
Abstract Vibrio vulnificus protease (VVP) stimulated histamine release from isolated mast cells in a dose- and temperature-dependent manner within a range of 0.2–4.0 μ g/0.5 ml. Histamine release was accompanied by degranulation, and no leakage of lactate dehydrogenase from cells was observed, indicating that the histamine release was not due to cytolysis but to exocytosis. This release, completed within 30 s at 37°C, suggested that the mechanism of action of VVP on mast cells is different from that of other proteases, such as trypsin or α-chymotrypsin, which release histamine from the cells slowly. 相似文献
16.
17.
Copulatory behavior unrelated to conception is sometimes observed in some non-human primates including the Japanese monkey.
In the present study, the authors examined whether a mature follicle or a newly formed fresh corpus luteum was observed in
the ovaries of female Japanese monkeys which displayed the copulatory behavior unrelated to conception.
Post-conception copulatory behaviors were observed in three out of four females usually kept in individual cages in an air-conditioned
room, and in two out of three females without infants kept in an outdoor group cage. However, neither a mature Graafian follicle
nor a fresh corpus luteum formed newly after conception was observed in any of these females by laparoscopic examinations
conducted immediately after termination of the copulatory behavior. In females with infants born in the preceding birth season,
copulatory behaviors were observed in three out of four females kept in the outdoor group cage, and in two out of four females
in a free-ranging troop. Ovulation was confirmed in one case out of the three kept in the outdoor group cage, but neither
a mature follicle nor a newly formed corpus luteum was observed in the remaining four females.
These findings suggest that copulatory behavior in the Japanese monkey is not always controlled by the development of a follicle
or ovulation in the ovary. 相似文献
18.
Two dynorphin-degrading cysteine proteases, I and II, were extracted with Triton X-100 from neuroblastoma cell membrane, isolated from accompanying dynorphin-degrading trypsin-like enzyme by affinity chromatography on columns of soybean trypsin inhibitor-immobilized Sepharose and p-mercuribenzoate-Sepharose, and separated by ion-exchange chromatography on diethylaminoethyl (DEAE)-cellulose and TSK gel DEAE-5PW columns. Cysteine protease II was purified further by hydroxyapatite chromatography and gel filtration. The molecular weights of cysteine proteases I and II were estimated to be 100,000 and 70,000, respectively, by gel filtration. Both of the enzymes, were inhibited by p-chloromercuribenzoate, N-ethylmaleimide, and high-molecular-weight kininogen, but not or only slightly inhibited by diisopropylphosphorofluoridate, antipain, leupeptin, E-64, calpain inhibitor, and phosphoramidon. Cysteine protease I cleaved dynorphin(1-17) at the Arg6-Arg7 bond with the optimum pH of 8.0, whereas II cleaved dynorphin(1-17) at the Lys11-Leu12 bond and the Leu12-Lys13 bond with the optimum pH values of 8.0 and 6.0, respectively. These bonds corresponded to those that had been proposed as the initial sites of degradation by neuroblastoma cell membrane. Cysteine protease I was further found to show strict specificity toward the Arg-Arg doublet, when susceptibilities of various peptides containing paired basic residues were examined as substrates for the enzyme. 相似文献
19.
Naoyuki Honma Atsuko Uchida Hiroya Hirose Vlastimil Srsen Takeo Kishimoto Shin-ichi Hisanaga 《Journal of neurochemistry》1996,67(5):1856-1865
Abstract: We describe here two types of apoptotic cell death observed in the rat CNS-derived neuroblastoma B50 and B104 cells. One type was induced by dibutyryl cyclic AMP (DBcAMP) after differentiation, and the other was induced by treatment of proliferating cells with cycloheximide. When B50 and B104 cells were treated with 1 m M DBcAMP in the presence of 0.5% fetal calf serum, they began to extend neurites within 12 h and differentiated into neurons at 24 h, as reported previously. However, further cultivation with DBcAMP for up to 72 h led to flotation and, finally, death. Death was by apoptosis as shown by chromatin condensation and DNA fragmentation. Addition of a protein kinase A inhibitor or removal of DBcAMP after differentiation suppressed apoptosis, indicating the involvement of cyclic AMP and protein kinase A in apoptotic cell death. Cell death was also induced in proliferating cells without neurite outgrowth by treatment with cycloheximide. The death was also judged to be by apoptosis based on chromatin condensation and apoptotic body formation, although DNA fragmentation into small sizes was not detected. Both types of cell death showed similar responses to inhibitors for protein kinases and protein phosphatases. 相似文献
20.
Hatsumi Taniguchi Hironori Aramaki Yoshihiko Nikaido yasuo Mizuguchi Masahiro Nakamura Toshihiko Koga Shin-ichi Yoshida 《FEMS microbiology letters》1996,144(1):103-108
Abstract The bradyzoite and tachyzoite forms of Toxoplasma gondii , purified from infected animals, were analysed for their activities of phosphofructokinase, pyruvate kinase, lactate dehydrogenase, NAD+ - and NADH-linked isocitrate dehydrogenases, and succinic dehydrogenase. Both developmental stages contained high activities of phosphofructokinase (specific for pyrophosphate rather than ATP), pyruvate kinase and lactate dehydrogenase, suggesting that energy metabolism in both forms may centre around a high glycolytic flux linked to lactate production. The markedly higher activity of the latter two enzymes in bradyzoites suggests that lactate production is particularly important in this developmental form. NAD+ -specific isocitrate dehydrogenase was not detectable in either stage of the parasite (and proved useful as a measure of the purity of the bradyzoite preparation), whereas both parasite forms contained low activities of NADP+ -linked isocitrate dehydrogenase. The results are consistent with the bradyzoites lacking a functional TCA cycle and respiratory chain and are suggestive of a lack of susceptibility of this developmental stage to atovaquone. 相似文献