全文获取类型
收费全文 | 2592篇 |
免费 | 131篇 |
国内免费 | 2篇 |
出版年
2022年 | 14篇 |
2021年 | 25篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 28篇 |
2017年 | 23篇 |
2016年 | 51篇 |
2015年 | 75篇 |
2014年 | 81篇 |
2013年 | 187篇 |
2012年 | 118篇 |
2011年 | 116篇 |
2010年 | 84篇 |
2009年 | 76篇 |
2008年 | 149篇 |
2007年 | 132篇 |
2006年 | 138篇 |
2005年 | 132篇 |
2004年 | 133篇 |
2003年 | 140篇 |
2002年 | 159篇 |
2001年 | 38篇 |
2000年 | 42篇 |
1999年 | 41篇 |
1998年 | 47篇 |
1997年 | 43篇 |
1996年 | 33篇 |
1995年 | 50篇 |
1994年 | 38篇 |
1993年 | 36篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 33篇 |
1989年 | 32篇 |
1988年 | 26篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 24篇 |
1982年 | 18篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 18篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1972年 | 10篇 |
排序方式: 共有2725条查询结果,搜索用时 46 毫秒
1.
Although phorbol 12-myristate 13-acetate (PMA) inhibits apoptosis and promotes the growth of some types of cells, it induces apoptosis in other cells. We evaluated the apoptotic effects of PMA on murine fibroblasts (L-929) that had been exposed to ultraviolet-B (UV-B) radiation at 312 nm, which promotes tumor cell growth. Exposure to PMA alone did not induce Fas, Fas-L, or apoptosis. Cells exposed to mild UV-B irradiation (80 J/m(2)) alone exhibited a slight expression of Fas and Fas-L 36 to 48 h after the exposure, and exhibited apoptosis as evidenced by DNA fragmentation 72 h after exposure. The addition of PMA (0.8 x 10(-5) to 3.2 x 10(-5) M) to the medium 24 h after the UV-B exposure markedly and dose-dependently enhanced these cell responses. Confluent untreated cells, cells cocultured with PMA, and cells cocultured with PMA for 24 h after the UV-B exposure consistently expressed mRNAs for wild-type p53, bcl-2, and ICE. Expression of c-myc mRNA was initially observed, but became undetectable in the cells cocultured for 24 h with a high concentration of PMA (3.2 x 10(-5) M) following UV-B exposure. Such cells subsequently exhibited the maximal apoptotic response. We conclude that mild exposure to UV-B altered murine fibroblast cells in such a way as to facilitate their death by apoptosis upon addition of PMA. 相似文献
2.
3.
Changes in Targeting Efficiencies of Proteins to Plant Microbodies Caused by Amino Acid Substitutions in the Carboxy-terminal Tripeptide 总被引:7,自引:0,他引:7
Hayashi Makoto; Aoki Masahiro; Kondo Maki; Nishimura Mikio 《Plant & cell physiology》1997,38(6):759-768
It has been demonstrated that the carboxyl terminus of microbodyenzymes functions as a targeting signal to microbodies in higherplants. We have examined an ability of 24 carboxy-terminal aminoacid sequences to facilitate the transport of a cytosolic passengerprotein, ß-glucuroni-dase, into microbodies in greencotyledonary cells of trans-genic Arabidopsis. Immunoelectronmicroscopic analysis revealed that carboxy-terminal tripeptidesequences of the form [C/A/S/P]-[K/R]-[I/L/M] function as amicrobody-targeting signal, although tripeptides with prolineat the first amino acid position and isoleucine at the carboxylterminus show weak targeting efficiencies. All known micro-bodyenzymes that are synthesized in a form similar in size to themature molecule, except catalase, contain one of these tripeptidesequences at their carboxyl terminus. (Received April 14, 1997; Accepted April 8, 1997) 相似文献
4.
Shinsaku Tokuda Young Hak Kim Hisako Matsumoto Shigeo Muro Toyohiro Hirai Michiaki Mishima Mikio Furuse 《PloS one》2015,10(12)
The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma. 相似文献
5.
Sixteen enzymatic and non-enzymatic proteins of the pigeon Columba livia domestica were examined electrophoretically. These proteins were presumed to be under control by 22 loci. Of the 22 loci, 6 were defined as polymorphic and 15 as monomorphic. Another locus was variable, but the variation was not genetically interpretable. Average heterozygosity calculated over 21 loci was 0.075. 相似文献
6.
Ono Mayumi Kuwano Michihiko Mizushima Shoji 《Molecular genetics and genomics : MGG》1979,170(1):11-23
Molecular Genetics and Genomics - Ribosomal protein S1 from a newly isolated Escherichia coli mutant has a molecular weight of about 54,000 which is smaller than the wild type S1 (M.W. 65,000). The... 相似文献
7.
The catalase molecule in germinating pumpkin cotyledons is synthesizedas a precursor (59-kDa) form, whose relative molecular massis larger than the mature enzyme (55-kDa). Although both typesof molecules are localized in the microbodies, the 59-kDa specieshas been shown to be present predominantly in the leaf peroxisomesisolated from green cotyledons, while the 55-kDa species ispredominantly in the glyoxysomes from etiolated cotyledons [Yamaguchiet al. (1984) Proc. Natl. Acad. Sci. USA, 81: 4809]. We examinedthe distribution of the 59- and 55-kDa catalase molecules indark- and light-grown tissues of pumpkin seedlings as well asin other plant species, using the immunoblotting technique.The ratios of the 59- and 55-kDa catalase species differed inthe pumpkin tissues examined. Light interferes with the conversionof the 59-kDa precursor to the 55-kDa form, especially in thecotyledons. The effect of light was less pronounced in the rootsand hypocotyls, indicating that the light regulation of theconversion is tissue-specific. Dark- and light-grown cotyledonsfrom cucumber and watermelon seedlings showed a similar lightregulation, suggesting that cucurbitaceous plants possess similarlight-regulatory mechanism. From the analysis of catalase proteinfrom various plant tissues, a limited correlation between molecularforms of catalase and different microbody populations was observed. (Received September 6, 1986; Accepted December 4, 1986) 相似文献
8.
Photosynthetically competent chloroplasts were isolated fromcells of Euglena gracilis Z grown photoautotrophically in 1.5%CO2. The isolated chloroplasts were intact and substantiallyfree from cytosolic, mitochondrial and microbody materials.The effects of some compounds on the activity of photosynthetic14CO2 fixation were examined. The optimal pH and sorbitol concentrationwere 8.0 and 0.33 M, respectively. The chloroplasts requireda high level of P, (5 to 20 mM) for the maximal rate of photosynthesis.They were insusceptible to 10 mM of free Mg2+. ATP, ADP andAMP at 1 to 5 mM notably stimulated photosynthesis, althoughhigh concentrations of AMP were unfavorable. In the assay mediumdeveloped for this study, the chloroplasts exhibited photosyntheticactivity of 120µmoles-mg1 Chl-h1 at 30?C. Chloroplasts could also be isolated from cells grown under ordinaryair. The rate of photosynthetic 14CO2 fixation at 1 mM NaHl4CO3was higher in these chloroplasts than in those isolated fromcells grown in 1.5% CO2, whereas at 10 mM NaHl4CO3, the ratesof the two types of chloroplasts were nearly the same. Theseresults suggest that the CO2 concentration given during growthof the algal cells affects the affinity for dissolved inorganiccarbon at the chloroplast level. (Received March 30, 1987; Accepted August 17, 1987) 相似文献
9.
In cells of cyanobacterium Anabaena variabilis grown under ordinaryair (low-CO2 cells), the transport of both CO2 and HCO3was significantly enhanced by Na+. This effect was pronouncedas the external pH increased. When low-CO2 cells were treatedwith an inhibitor of carbonic anhydrase (CA), only CO2 transportbut not HCO3 transport, was inhibited. The initial rateof photosynthetic carbon fixation as a function of the concentrationof internal inorganic carbon (IC) was practically the same irrespectiveof whether CO2 or HCO3 was externally supplied. Theseresults suggest that IC is actively transported through theplasma membrane in a form of HCO3 probably by some transporterand that the transmembrane Na+ gradient is involved in thisIC transport system. Free CO2 may be hydrated by CA to HCO3and then transported to the cells by this transporter. On the other hand, CO2 is actively taken up by cells grown withair containing 5% CO2 (high-CO2 cells) though the enhancingeffect of Na+ was much smaller in high- CO2 cells than in low-CO2cells. The initial rate of fixation as a function of internal IC concentrationindicated that the rate of the carboxylation reaction of accumulatedIC is higher in I0W-CO2 cells than in high-CO2 cells. The studieswith ethoxyzolamide indicated that even in low-CO2 cells, CAdoes not function inside Anabaena cells. These results suggestthat inside the low-CO2 cells of Anabaena, some mediator(s)facilitates the transport of IC to RuBPCase. (Received January 23, 1987; Accepted April 24, 1987) 相似文献
10.
Inorganic carbon transport during photosynthesis of cyanobacteriumAnabaena variabilis grown under ordinary air was investigatedby supplying 14CO2 or H14CO3 solution to three differentstrains. Both CO2 and HCO3 were accumulated within thealgal cells. In the cell suspension from which dissolved inorganiccarbon had been depleted by pre-illumination, CO2 was transportedand accumulated faster than HCO3. When the concentrationof HCO3 injected into the cell suspension of A. variabilisM3 was 25 times as high as that of CO2 (the expected ratio atequilibrium at pH 7.8), the initial rates of fixation of bothinorganic carbon species were practically the same. On the otherhand, when 14CO2 or H14CO3 was added under steady statephotosynthetic conditions, both carbon species were transportedat similar rates. The ratio of fixed to transported carbon measuredafter the initial 5 s was only 2327% regardless of thecarbon species supplied. This percentage is much lower thanthat reported for Chlorella cells.
1 To whom reprint requests should be addressed (Received June 30, 1986; Accepted December 16, 1986) 相似文献