全文获取类型
收费全文 | 1415篇 |
免费 | 87篇 |
国内免费 | 2篇 |
专业分类
1504篇 |
出版年
2023年 | 4篇 |
2022年 | 19篇 |
2021年 | 24篇 |
2020年 | 11篇 |
2019年 | 25篇 |
2018年 | 29篇 |
2017年 | 20篇 |
2016年 | 33篇 |
2015年 | 57篇 |
2014年 | 59篇 |
2013年 | 83篇 |
2012年 | 110篇 |
2011年 | 111篇 |
2010年 | 90篇 |
2009年 | 78篇 |
2008年 | 72篇 |
2007年 | 95篇 |
2006年 | 78篇 |
2005年 | 80篇 |
2004年 | 80篇 |
2003年 | 82篇 |
2002年 | 60篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 17篇 |
1998年 | 25篇 |
1997年 | 24篇 |
1996年 | 13篇 |
1995年 | 18篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有1504条查询结果,搜索用时 15 毫秒
101.
Zawacka-Pankau J Issaeva N Hossain S Pramanik A Selivanova G Podhajska AJ 《The Journal of biological chemistry》2007,282(4):2466-2472
Photodynamic therapy (PDT) of cancer is an alternative treatment for tumors resistant to chemo- and radiotherapy. It induces cancer cell death mainly through generation of reactive oxygen species by a laser light-activated photosensitizer. It has been suggested that the p53 tumor suppressor protein sensitizes some human cancer cells to PDT. However, there is still no direct evidence for this. We have demonstrated here for the first time that the photosensitizer protoporphyrin IX (PpIX) binds to p53 and disrupts the interaction between p53 tumor suppressor protein and its negative regulator HDM2 in vitro and in cells. Moreover, HCT116 colon cancer cells exhibited a p53-dependent sensitivity to PpIX in a dose-dependent manner, as was demonstrated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and fluorescence-activated cell sorter (FACS) analysis of cell cycle profiles. We have also observed induction of p53 target pro-apoptotic genes, e.g. puma (p53-up-regulated modulator of apoptosis), and bak in PpIX-treated cells. In addition, p53-independent growth suppression by PpIX was detected in p53-negative cells. PDT treatment (2 J/cm2) of HCT116 cells induced p53-dependent activation of pro-apoptotic gene expression followed by growth suppression and induction of apoptosis. 相似文献
102.
103.
Ploquin M Petukhova GV Morneau D Déry U Bransi A Stasiak A Camerini-Otero RD Masson JY 《Nucleic acids research》2007,35(8):2719-2733
Genetic analysis of fission yeast suggests a role for the spHop2–Mnd1 proteins in the Rad51 and Dmc1-dependent meiotic recombination pathways. In order to gain biochemical insights into this process, we purified Schizosaccharomyces pombe Hop2-Mnd1 to homogeneity. spHop2 and spMnd1 interact by co-immunoprecipitation and two-hybrid analysis. Electron microscopy reveals that S. pombe Hop2–Mnd1 binds single-strand DNA ends of 3′-tailed DNA. Interestingly, spHop2-Mnd1 promotes the renaturation of complementary single-strand DNA and catalyses strand exchange reactions with short oligonucleotides. Importantly, we show that spHop2-Mnd1 stimulates spDmc1-dependent strand exchange and strand invasion. Ca2+ alleviate the requirement for the order of addition of the proteins on DNA. We also demonstrate that while spHop2-Mnd1 affects spDmc1 specifically, mHop2 or mHop2-Mnd1 stimulates both the hRad51 and hDmc1 recombinases in strand exchange assays. Thus, our results suggest a crucial role for S. pombe and mouse Hop2-Mnd1 in homologous pairing and strand exchange and reveal evolutionary divergence in their specificity for the Dmc1 and Rad51 recombinases. 相似文献
104.
Extended exposure of Escherichia coli to temperatures above and below their growth optimum led to significant changes in oxidant production and antioxidant defense. At 20 °C an increase in the intracellular H2O2 concentration and oxidized glutathione (GSSG) level was observed against a background of low levels of reduced glutathione (GSH) and decreased catalase and glutathione reductase (GOR) activities. The intracellular H2O2 and GSSG concentrations had minimal values at 30 and 37 °C, but rose again at 42 °C, suggesting that oxidative processes were intensified at high temperatures. An increase in temperature from 20 to 42 °C led to an elevation in the oxygen respiration rate and superoxide production; a 5-fold increase in the intracellular GSH concentration and in the GSH:GSSG ratio occurred simultaneously. Catalase HPI and GOR activities were elevated 4.4- and 1.5-fold, respectively. Prolonged exposure to sublethal temperatures facilitated an adaptation to subsequent oxidative stress produced by the addition of H2O2. 相似文献
105.
Alhamadsheh MM Waters NC Huddler DP Kreishman-Deitrick M Florova G Reynolds KA 《Bioorganic & medicinal chemistry letters》2007,17(4):879-883
A series of cyclic sulfones has been synthesized and their activity against beta-ketoacyl-ACP-synthase III (FabH) has been investigated. The compounds are selectively active against Escherichia coli FabH (ecFabH), but not Mycobacterium tuberculosis FabH (mtFabH) or Plasmodium falciparum KASIII (PfKASIII). The activity against ecFabH ranges from 0.9 to >100microM and follows a consistent general SAR trend. Many of the compounds were shown to have antimalarial activity against chloroquine (CQ)-sensitive (D6) P. falciparum (IC(50)=5.3microM for the most potent inhibitor) and some were active against E. coli (MIC=6.6microg/ml for the most potent inhibitor). 相似文献
106.
Jadviscokova T Fajkusova Z Pallayova M Luza J Kuzmina G 《Biomedical papers of the Medical Faculty of the University Palacky, Olomouc, Czechoslovakia》2007,151(2):263-266
Aims: Continuous glucose monitoring (CGM) using transcutaneous sensors is becoming a sophisticated method to control and regulate glucose metabolism. The transcutaneous sensor of the CGM system (CGMStrade mark Medtronic Minimed, Northridge, CA, USA) is chosen to measure glucose concentration in interstitial fluid up to three days after insertion even though its function remains stable for a longer period. The question arises, which factors really limit the period of sensor insertion without unnecessary risk. The aim of this study was to assess any adverse events occurring in the course of 9 days after the sensor insertion. Methods: In a group of 22 healthy volunteers aged 21.8+/-1.30 y (mean +/- SE) a total of 26 sensors was inserted subcutaneously in gluteal or lumbar region for 9 days. Before insertion the site was sprayed with an antiseptic (Cutasept F, Bode Chemie, Hamburg, Germany). Local adverse reactions and disturbances in general condition were examined. Results: In the course of 184 sensor-days, there were only minor local adverse events: hypersensitivity, itching, pain, redness, burning, subcutaneous hemorrhage. Additionally, sleep disturbances, attention deficits, problems related to the CGMS monitor, to adhesive tape and/or sensor were found. None of these resulted in sensor withdrawal. In 12 volunteers (55 %) no complications were observed. The sensor function measured according to electrical signals (ISIG) failed (always on day 1-2) in 4 cases (16 %). Conclusions: The present FDA approved 3-day insertion period for Medtronic transcutaneous sensor does not seem to limit its use and appears to be worth a careful revision. 相似文献
107.
Dynamic alteration of soluble serum biomarkers in healthy aging 总被引:2,自引:1,他引:1
Dysbalanced production of inflammatory cytokines is involved in immunosenescence in aging. The age-related changes of the levels of circulating inflammatory mediators and their clinical importance have not been investigated until recently. Still, little is known about the influence of aging on circulating levels of many cytokines, chemokines, growth factors, and angiogenic factors. In the present study, we evaluated the effect of aging on 30 different serum biomarkers involved in pro- and anti-inflammatory responses using multianalyte LabMAP Luminex technology. The simultaneous measurement of serological markers has been done in 397 healthy subjects between 40 and 80 years old. We demonstrated an increase in serum interferon-gamma-inducible chemokines (MIG and IP-10), eotaxin, chemoattractant for eosinophils, and soluble TNFR-II with advancing age. Serum levels of EGFR and EGF, important regulators of cell growth and differentiation, were decreased with age in healthy donors. These data suggest novel pathways, which may be involved in age-associated immunosenescence. 相似文献
108.
Lunina NA Agafonova EV Chekanovskaya LA Dvortsov IA Berezina OV Shedova EN Kostrov SV Velikodvorskaya GA 《Protein expression and purification》2007,54(1):18-23
A cluster of Thermotoga neapolitana genes participating in starch degradation includes the malG gene of sugar transport protein and the aglB gene of cyclomaltodextrinase. The start and stop codons of these genes share a common overlapping sequence, aTGAtg. Here, we compared properties of expression products of three different constructs with aglB from T. neapolitana. The first expression vector contained the aglB gene linked to an upstream 90-bp 3'-terminal region of the malG gene with the stop codon overlapping with the start codon of aglB. The second construct included the isolated coding sequence of aglB with two tandem potential start codons. The expression product of this construct in Escherichia coli had two tandem Met residues at its N terminus and was characterized by low thermostability and high tendency to aggregate. In contrast, co-expression of aglB and the 3'-terminal region of malG (the first construct) resulted in AglB with only one N-terminal Met residue and a much higher specific activity of cyclomaltodextrinase. Moreover, the enzyme expressed by such a construct was more thermostable and less prone to aggregation. The third construct was the same as the second one except that it contained only one ATG start codon. The product of its expression had kinetic and other properties similar to those of the enzyme with only one N-terminal Met residue. 相似文献
109.
Sun J Sukhova GK Wolters PJ Yang M Kitamoto S Libby P MacFarlane LA Mallen-St Clair J Shi GP 《Nature medicine》2007,13(6):719-724
Mast cells contribute importantly to allergic and innate immune responses by releasing various preformed and newly synthesized mediators. Previous studies have shown mast cell accumulation in human atherosclerotic lesions. This report establishes the direct participation of mast cells in atherogenesis in low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice. Atheromata from compound mutant Ldlr(-/-) Kit(W-sh)(/W-sh) mice showed decreased lesion size, lipid deposition, T-cell and macrophage numbers, cell proliferation and apoptosis, but increased collagen content and fibrous cap development. In vivo, adoptive transfer of syngeneic wild-type or tumor necrosis factor (TNF)-alpha-deficient mast cells restored atherogenesis to Ldlr(-/-)Kit(W-sh/W-sh) mice. Notably, neither interleukin (IL)-6- nor interferon (IFN)-gamma-deficient mast cells did so, indicating that the inhibition of atherogenesis in Ldlr(-/-)Kit(W-sh/W-sh) mice resulted from the absence of mast cells and mast cell-derived IL-6 and IFN-gamma. Compared with wild-type or TNF-alpha-deficient mast cells, those lacking IL-6 or IFN-gamma did not induce expression of proatherogenic cysteine proteinase cathepsins from vascular cells in vitro or affect cathepsin and matrix metalloproteinase activities in atherosclerotic lesions, implying that mast cell-derived IL-6 and IFN-gamma promote atherogenesis by augmenting the expression of matrix-degrading proteases. These observations establish direct participation of mast cells and mast cell-derived IL-6 and IFN-gamma in mouse atherogenesis and provide new mechanistic insight into the pathogenesis of this common disease. 相似文献
110.
Nadezhda N. Sushchik Michail I. Gladyshev Elena S. Kravchuk Elena A. Ivanova Alexander V. Ageev Galina S. Kalachova 《Aquatic Ecology》2007,41(2):349-365
We studied composition and concentrations of fatty acids (FAs) in benthos from pebbly littoral region of the Yenisei River
in a sampling site near Krasnoyarsk city (Siberia, Russia) for 1 year from March 2003 to February 2004. Special attention
was paid to major long-chain polyunsaturated fatty acids (PUFAs) of the ω3 family: eicosapentaenoic acid (EPA, 20:5ω3) and
docosahexaenoic acids (DHA, 22:6ω3). In phytobenthos, which was dominated by diatoms, the annual maxima of EPA and DHA pool
occurred in spring and early summer. In zoobenthos, EPA and DHA pool peaked in autumn, due mainly to an increase of the biomass
of dominant taxa (gammarids) and to a moderate increase of the PUFA content per body weight. Seasonal peaks of EPA in overwintering
insect larvae (chironomids and caddisflies) generally coincided with those of biomass of these larvae, while there was no
such trend for amphipods and oligochaetes. In spring and early summer, the main part of ω3 PUFA, 40–97% of total amount, in
the littoral region was contained in biomass of producers, i.e., benthic microalgae, and in autumn it was transferred to primary
consumers—benthic invertebrates, which contained ∼76–93% of total ω3 PUFAs. 相似文献