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51.
Chronic photoinhibition in seedlings of tropical trees 总被引:1,自引:0,他引:1
Seedlings of five canopy species of tropical trees from Costa Rica and Puerto Rico were grown in full shade (midday range of photosynthetic photon flux density [PPFD], 100–140 μmol m?2 s?1), partial shade (midday PPFD, 400–600 μmol m?2 s?1) and full sun (midday PPFD, 1 500–1 800 μmol m?2 s?1) for 3 months. The species were Ochroma lagopus (Bombacaceae), a pioneer species; Inga edulis (Fabaceae), found in secondary forest; and Dipteryx panamensis (Fabaceae), Hampea appendiculata (Malvaceae), and Manilkara bidentata (Sapotaceae), three species characteristic of primary forest. After the plants were placed in the dark overnight, chlorophyll fluorescence characteristics were measured for recently expanded and mature leaves. The ratio of variable fluorescence to maximum fluorescence (Fv/Fm) was used to estimate the degree of chronic photoinhibition. Only individuals of one species, Dipteryx panamensis, showed significant depression of Fv/Fm after long-term exposure to full sun. The depression was highly correlated with quantum yield of O2 evolution which also declined after exposure to full sun. The decline may have been related to foliar N concentration. Although all plants were supplied with ample nutrients, foliar N did not increase significantly for Dipteryx seedlings in full sun, whereas it did for Ochroma and Inga. Leaf age affected Fv/Fm only in the cases of Manilkara, where it was slightly lower in recently expanded leaves, and of Dipteryx where it interacted with the effects of light regime. We conclude that chronic photoinhibition is not common in seedlings of canopy trees of tropical rain forests except when availability of mineral nutrients may be limiting. 相似文献
52.
53.
Kazmierski WM Furfine E Gray-Nunez Y Spaltenstein A Wright L 《Bioorganic & medicinal chemistry letters》2004,14(22):5685-5687
We have developed synthetic approaches to novel analogues of 2-imidazolidinone scaffold 2, which was found to be an effective P1-P2 mimetic in HIV-1 protease inhibitor 4. This enabled a rapid synthesis of analogues of 4 and subsequently allowed us to evaluate and rationalize the SAR. Accordingly, trans relationship of P1 and P2 substituents in the P1-P2 mimetic, as found in a related 2-pyrrolidone-based scaffold 1, was found necessary for high potency against HIV-1 protease. Results of this study provided further rationale towards subsequent optimization of 2-pyrrolidone-based lead 3, which led us to potent and drug-like HIV-1 protease inhibitors described in a follow-on report (Bioorg. Med. Chem. Lett. 2004, 14, in press. ). 相似文献
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55.
Pushpa M. Jairam Pim A. de Jong Willem P. T?h. M. Mali Ivana Isgum Harry J. de Koning Carlijn van der Aalst Matthijs Oudkerk Rozemarijn Vliegenthart Yolanda van der Graaf 《PloS one》2013,8(6)
Background
Current smokers have an increased cardiovascular disease (CVD) risk compared to ex-smokers due to reversible as well as irreversible effects of smoking. We investigated if current smokers remain to have an increased CVD risk compared to ex-smokers in subjects with a long and intense smoking history. We in addition studied if the effect of smoking continuation on CVD risk is independent of or modified by the presence of cardiovascular calcifications.Methods
The cohort used comprised a sample of 3559 male lung cancer screening trial participants. We conducted a case-cohort study using all CVD cases and a random sample of 10% (n = 341) from the baseline cohort (subcohort). A weighted Cox proportional hazards model was used to estimate the hazard ratios for current smoking status in relation to CVD events.Results
During a median follow-up of 2.6 years (max. 3.7 years), 263 fatal and non-fatal cardiovascular events (cases) were identified. Age, packyears and cardiovascular calcification adjusted hazard ratio of current smokers compared to former smokers was 1.33 (95% confidence interval 1.00–1.77). In additional analyses that incorporated multiplicative interaction terms, neither coronary nor aortic calcifications modified the association between smoking status and cardiovascular risk (P = 0.08).Conclusions
Current smokers have an increased CVD risk compared to former smokers even in subjects with a long and intense smoking history. Smoking exerts its hazardous effects on CVD risk by pathways partly independent of cardiovascular calcifications. 相似文献56.
Maya JD Rodríguez A Pino L Pabón A Ferreira J Pavani M Repetto Y Morello A 《Biological research》2004,37(1):61-69
Proteins rich in sulfhydryl groups, such as metallothionein, are present in several strains of the parasite Trypanosoma cruzi, the etiological agent of Chagas' disease. Metallothionein-like protein concentrations ranged from 5.1 to 13.2 pmol/mg protein depending on the parasite strain and growth phase. Nifurtimox and benznidazole, used in the treatment of Chagas' disease, decreased metallothionein activity by approximately 70%. T. cruzi metallothionein was induced by ZnCl2. Metallothionein from T. cruzi was partially purified and its monobromobimane derivative showed a molecular weight of approximately 10,000 Da by SDS-PAGE analysis. The concentration of trypanothione, the major glutathione conjugate in T. cruzi, ranged from 3.8 to 10.8 nmol/mg protein, depending on the culture phase. The addition of buthionine sulfoximine to the protozoal culture considerably reduced the concentration of trypanothione and had no effect upon the metallothionein concentration. The possible contribution of metallothionein-like proteins to drug resistance in T. cruzi is discussed. 相似文献
57.
María?Laura?VidozEmail author Hebe?Yolanda?Rey Ana?María?Gonzalez Luis?Amado?Mroginski 《Acta Physiologiae Plantarum》2004,26(1):59-66
Plants of two accessions of Arachis glabrata were regenerated via somatic embryogenesis. Embryogenic calli were initiated from leaflet explants on Murashige and Skoog medium supplemented
with picloram alone or picloram in combination with 6-benzylaminopurine. Leaflets of accession A6138 induced the highest percentage
of somatic embryos in media composed of 10 mg dm−3 and 15 mg dm−3 picloram. In contrast, 5 mg dm−3 picloram with 0.1 mg dm−3 6-benzylaminopurine was one of the most effective combinations in accession AF385. MS medium supplemented with 2 g dm−3 activated charcoal (AC) used for 30 days was the most effective for embryo maturation. After 20 days of culture on MS medium
devoid of growth regulators, 6 % of embryos converted into plantlets in accession A6138. 相似文献
58.
Salvatella M Rossi I Del Valle JC Gutiérrez Y Pereda C Samper B Felíu JE 《American journal of physiology. Gastrointestinal and liver physiology》2004,286(5):G711-G721
In nonstimulated rabbit gastric glands, acetylsalicylic acid (10-500 microM) and indomethacin (3-300 microM) did not significantly modify the basal rate of acid secretion, whereas diclofenac and piroxicam (10-1,000 microM each) caused a marked and dose-dependent inhibitory effect (EC(50) = 138 and 280 microM, respectively). In gastric glands stimulated by histamine (100 microM), diclofenac also reduced the rate of acid formation in a dose-dependent manner. In contrast, acetylsalicylic acid, indomethacin, and piroxicam exerted a biphasic effect; thus low concentrations (3-100 microM) of these three agents significantly increased the rate of histamine-stimulated acid secretion (10-20% over the corresponding control value) by a cAMP-independent mechanism, whereas higher concentrations reduced the rate of acid formation. With respect to underlying biochemical mechanisms that could mediate inhibitory effects of NSAIDs on gastric acid formation, it was observed that both diclofenac and piroxicam, but not acetylsalicylic acid or indomethacin, decreased the glandular content of ATP, inhibited hydrolytic activity of gastric gland microsomal H(+)-K(+)-ATPase, and reduced the rate of H(+)-K(+)-ATPase-dependent proton transport across microsomal membranes in a dose-dependent manner. Furthermore, diclofenac and piroxicam also significantly increased passive permeability of microsomal membranes to protons. In conclusion, our work shows that diclofenac and piroxicam cause a significant reduction in the rate of basal and histamine-stimulated acid formation in isolated rabbit gastric glands at concentrations that can be attained in the gastric lumen of patients treated with these drugs. Mechanisms involved in these inhibitory effects appear to be multifocal and include different steps of stimulus-secretion coupling. 相似文献
59.
60.
Ledesma E Martínez I Córdova Y Rodríguez-Sosa M Monroy A Mora L Soto I Ramos G Weiss B Santiago Osorio E 《Cytokine》2004,26(2):66-72
Interleukin-1 alpha (IL-1alpha) and beta (IL-1beta) are well known factors that stimulate hematopoiesis, nevertheless there are reports that show that they can also inhibit this activity. While both IL-1alpha and IL-1beta induce the expression of hematopoietic cytokines, such as growth factors and their receptors on myeloid cells, helping thus to regulate hematopoiesis, it is not known if their inhibitory activity is also mediated through the induction of other specific cytokines. In this work we show that recombinant human IL-1beta (rhIL-1beta) inhibits the proliferation of a mouse IL-3-dependent myeloid multipotent cell line (32D cl3), without inducing its differentiation. We show that rhIL-1beta induces in 32D cl3 cells the expression of the tumor necrosis factor alpha (TNF-alpha) gene, a well known growth inhibitor, and that the rhIL-1beta growth inhibition property on 32D cl3 cells is partially due to this secreted TNF-alpha, hinting thus that the inhibition of hematopoiesis by IL-1 is mediated through other induced cytokines. 相似文献