全文获取类型
收费全文 | 4045篇 |
免费 | 285篇 |
国内免费 | 2篇 |
出版年
2023年 | 10篇 |
2022年 | 19篇 |
2021年 | 39篇 |
2020年 | 31篇 |
2019年 | 43篇 |
2018年 | 64篇 |
2017年 | 54篇 |
2016年 | 88篇 |
2015年 | 195篇 |
2014年 | 166篇 |
2013年 | 221篇 |
2012年 | 289篇 |
2011年 | 281篇 |
2010年 | 213篇 |
2009年 | 163篇 |
2008年 | 231篇 |
2007年 | 270篇 |
2006年 | 256篇 |
2005年 | 240篇 |
2004年 | 222篇 |
2003年 | 235篇 |
2002年 | 211篇 |
2001年 | 40篇 |
2000年 | 35篇 |
1999年 | 58篇 |
1998年 | 62篇 |
1997年 | 49篇 |
1996年 | 52篇 |
1995年 | 45篇 |
1994年 | 36篇 |
1993年 | 50篇 |
1992年 | 38篇 |
1991年 | 26篇 |
1990年 | 17篇 |
1989年 | 31篇 |
1988年 | 13篇 |
1987年 | 27篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 22篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有4332条查询结果,搜索用时 15 毫秒
951.
Phosphorolysis of α,α-trehalose catalyzed by trehalose phosphorylase from the basidiomycete Schizophyllum commune proceeds via net retention of anomeric configuration and yields α-
-glucose 1-phosphate and α-
-glucose as the products. In reverse reaction, only the α-anomers of
-glucose 1-phosphate and
-glucose are utilized as glucosyl donor and acceptor, respectively, and give exclusively the α,α-product. Trehalose phosphorylase converts α-
-glucose 1-fluoride and phosphate into α-
-glucose 1-phosphate, a reaction requiring the stereospecific protonation of the glucosyl fluoride by a Brønsted acid. The results are discussed with regard to a plausible reaction mechanism of fungal trehalose phosphorylase. 相似文献
952.
Four inbred maize lines differing in chilling tolerance were used to study changes in water status and abscisic acid (ABA) levels before, during and after a chilling period. Seedlings were raised in fertilized soil at 24/22°C (day/night), 70% relative humidity. and a 12-h photoperiod with 200 μmol m−2 s−1 from fluorescent tubes. At an age of 2 weeks the plants were conditioned at 14/12°C for 4 days and then chilled for 5 days at 5/3°C. The other conditions (relative humidity, quantum flux, photoperiod) were unchanged. After the chilling period the plants were transferred to the original conditions for recovery. The third leaves were used to study changes in leaf necrosis, ion efflux, transpiration, water status and ABA accumulation. Pronounced differences in chilling tolerance between the 4 lines as estimated by necrotic leaf areas, ion efflux and whole plant survival were observed. Conditioning significantly increased tolerance against chilling at 5/3°C in all genotypes. The genotypes with low chilling tolerance had lower water and osmotic potentials than the more tolerant genotypes during a chilling period at 5/3°C. These differences were related to higher transpiration rates and lower diffusive resistance values of the more susceptible lines. During chilling stress at 5/3°C ABA levels were quadrupled. Only a small rise was measurable during conditioning at 14/12°C. However, conditioning enhanced the rise of ABA during subsequent chilling. ABA accumulation in the two lines with a higher chilling tolerance was triggered at a higher leaf water potential and reached higher levels than in the less tolerant lines. We conclude that chilling tolerance in maize is related to the ability for fast and pronounced formation of ABA as a protective agent against chilling injury. 相似文献
953.
954.
Benjamin Hemmens Silvia Woschitz Eva Pitters Burkhardt Klösch Christof Völker Kurt Schmidt Bernd Mayer 《FEBS letters》1998,430(3):537
Neuronal NO synthase (nNOS) was discovered recently to interact specifically with the protein PIN (protein inhibitor of nNOS) [Jaffrey, S.R. and Snyder, S.H. (1996) Science 274, 774–777]. We have studied the effects on pure NOS enzymes of the same GST-tagged PIN used in the original paper. Unexpectedly, all NOS isoenzymes were inhibited. The IC50 for nNOS was 18±6 μM GST-PIN with 63 nM nNOS after 30 min at 37°C. Uncoupled NADPH oxidation was inhibited similarly, whereas cytochrome c reductase activity, the KM for l-arginine, and dimerization were unaffected. We reconsider the physiological role of PIN in the light of these results. 相似文献
955.
The kinetics of vacuolar acidification upon addition of ATP and/or pyrophosphate (PPi) has been assayed on single immobilized vacuoles by computer-aided microfluorimetry of 9-aminoacridine, and by acridine orange absorption photometry on vacuole suspensions isolated from green suspension cells of Chenopodium rubrum L. Two proton pumps at the tonoplast, an ATPase and a pyrophosphatase (PPase), operate in parallel to acidify the vacuole with different contributions adding up to a transtonoplast Δ pH of 2.6 pH units at external pH 7.2. The saturable components of proton pumping reach half maximal velocity with 0.32 ± 0.06 mM ATP and 23 ± 2.5 μM PPi, respectively. At saturating substrate concentrations, ATPase and PPase hydrolyse ATP and PPi, respectively, at a ratio of 2.3. The same ratio holds for the corresponding proton fluxes maintaining a given steady-state vacuolar pH. We conclude that both pumps operate at the same stoichiometry. 相似文献
956.
957.
Emmanuel Bréard Estelle Lara Lo?c Comtet Cyril Viarouge Virginie Doceul Alexandra Desprat Damien Vitour Nathalie Pozzi Ann Brigitte Cay Nick De Regge Philippe Pourquier Horst Schirrmeier Bernd Hoffmann Martin Beer Corinne Sailleau Stéphan Zientara 《PloS one》2013,8(1)
A newly developed Enzym Like Immuno Sorbant Assay (ELISA) based on the recombinant nucleocapsid protein (N) of Schmallenberg virus (SBV) was evaluated and validated for the detection of SBV-specific IgG antibodies in ruminant sera by three European Reference Laboratories. Validation data sets derived from sheep, goat and bovine sera collected in France and Germany (n = 1515) in 2011 and 2012 were categorized according to the results of a virus neutralization test (VNT) or an indirect immuno-flurorescence assay (IFA). The specificity was evaluated with 1364 sera from sheep, goat and bovine collected in France and Belgium before 2009. Overall agreement between VNT and ELISA was 98.9% and 98.3% between VNT and IFA, indicating a very good concordance between the different techniques. Although cross-reactions with other Orthobunyavirus from the Simbu serogroup viruses might occur, it is a highly sensitive, specific and robust ELISA-test validated to detect anti-SBV antibodies. This test can be applied for SBV sero-diagnostics and disease-surveillance studies in ruminant species in Europe. 相似文献
958.
Summary The frequency of HLA-A3 and HLA-B14 antigens was found to be significantly (P=<0.0001) higher in a series of 50 unrelated and unselected Swedish patients with idiopathic hemochromatosis (IH) than in controls, being 66% and 32% for A3 and 22% and 2% for B14. The haplotype A3B14 was associated with the highest risk in this material (relative risk 23.4). One family with this haplotype was traced back to the end of the seventeenth century. The pattern of HLA antigens associated with IH in Sweden shows remarkable similarity to those reported from England and Brittany. 相似文献
959.
Bernd Zimmermann 《Differentiation; research in biological diversity》1987,36(1):86-109
An organoid culture system for lung cells is described in which morphogenesis of lung histotypic structures and differentiation of both pneumocytes type II and mesenchyme occur. The principle of this technique is the culture of mouse fetal lung cells at high density on a membrane filter at the medium/air interface. In the course of cultivation, cell sorting-out, epithelial cell aggregation, formation of an alveolar-like lumen in the organoids and formation of a basal lamina occur. Epithelial differentiation culminates in the production of lamellar bodies, and the mesenchyme develops into mature connective tissue. Morphogenesis and differentiation depend on the stage of fetal development from which the lung cells were derived but appear independent of the formation of a basal lamina. Various drugs have been tested for their effects on morphogenesis and differentiation in this lung organoid culture: some of them inhibit differentiation or damage the mesenchyme, others stimulate surfactant production. Due to the quite complex morphogenetic and cellular events occurring in lung organoid culture, it may be an applicable tool for alternative in vitro screening methods. 相似文献
960.
Bernd Beek 《Human genetics》1981,59(3):240-244
Summary Satellite associations were analysed in differentially stained human leukocyte chromosomes, obtained from four patients with Down's syndrome and four normal probands. A particular type of close association between two acrocentrics, showing a non-random arrangement of sister chromatids in a concordant dark-to-dark and light-to-light alignment, was found to be more common in patients with Down's syndrome compared with the normal controls. Apart from this particular type of association, sister chromatids are randomly arranged in satellite associations between two acrocentrics in both groups of probands. Considerable differences in the mean frequencies of satellite associations between first and second metaphases of the same individual were found in some probands of both groups of individuals. Since a high degree of inter-individual variability in the proliferative response of human leukocytes in culture is well established, the use of BUdR-Giemsa labeling for comparative analysis of satellite association frequencies is suggested. 相似文献