全文获取类型
收费全文 | 4504篇 |
免费 | 241篇 |
国内免费 | 270篇 |
出版年
2023年 | 68篇 |
2022年 | 74篇 |
2021年 | 104篇 |
2020年 | 126篇 |
2019年 | 138篇 |
2018年 | 91篇 |
2017年 | 107篇 |
2016年 | 115篇 |
2015年 | 128篇 |
2014年 | 216篇 |
2013年 | 301篇 |
2012年 | 178篇 |
2011年 | 224篇 |
2010年 | 153篇 |
2009年 | 170篇 |
2008年 | 223篇 |
2007年 | 222篇 |
2006年 | 202篇 |
2005年 | 179篇 |
2004年 | 177篇 |
2003年 | 155篇 |
2002年 | 129篇 |
2001年 | 124篇 |
2000年 | 114篇 |
1999年 | 121篇 |
1998年 | 77篇 |
1997年 | 70篇 |
1996年 | 73篇 |
1995年 | 81篇 |
1994年 | 75篇 |
1993年 | 63篇 |
1992年 | 54篇 |
1991年 | 51篇 |
1990年 | 39篇 |
1989年 | 44篇 |
1988年 | 42篇 |
1987年 | 43篇 |
1986年 | 50篇 |
1985年 | 51篇 |
1984年 | 33篇 |
1983年 | 35篇 |
1982年 | 44篇 |
1981年 | 25篇 |
1980年 | 43篇 |
1979年 | 31篇 |
1978年 | 34篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 24篇 |
1972年 | 16篇 |
排序方式: 共有5015条查询结果,搜索用时 15 毫秒
991.
Kunduru is an important Anatolian landrace having peculiar traits that are appreciated by farmers and breeders. 33 accessions known as Kunduru collected by ICARDA from six geographical provinces of Turkey, were used to study the phenotypic and genotypic intra-diversity. Kunduru landraces exhibited high intra-diversity for most of the studied morphological traits. GPC (12.10–14.90%), vitreousness (75–100%), TKW (31.80–56.70 g), YP (4.70–8.00 ppm), b*-value (14.30–19.50), ash content (1.60–2.0%) and gluten strength (14–60 ml) showed marked variations. Gliadin and glutenin banding patterns showed high polymorphism. 65 alleles were detected with 14 SSR markers, giving a mean of 6.77 alleles per locus. The average PIC value was 0.44 and ranged from 0.11 to 0.70. The average genetic distance between pairs of landraces was 0.47 and ranged between 0.11 and 0.72. This study showed that Kunduru landraces maintains high allelic variation. PCoA indicated that eco-geographical variables have a significant effect on SSR diversity as well as morphological traits. Many of the landraces studied are in danger of disappearing from the local farmers' fields; this study demonstrates the importance of maintaining and conserving this precious genetic resources. 相似文献
992.
《Bioorganic & medicinal chemistry》2016,24(12):2832-2842
The benzomorphan scaffold has great potential as lead structure and the nature of the N-substituent is able to influence affinity, potency, and efficacy at all three opioid receptors. Building upon these considerations, we synthesized a new series of LP1 analogues by introducing naphthyl or heteroaromatic rings in propanamide side chain of its N-substituent (9–15). In vitro competition-binding assays in HEK293 cells stably expressing MOR, DOR or KOR showed that in compound 9 the 1-naphthyl ring led to the retention of MOR affinity (KiMOR = 38 ± 4 nM) displaying good selectivity versus DOR and KOR. In the electrically stimulated GPI, compound 9 was inactive as agonist but produced an antagonist potency value (pA2) of 8.6 in presence of MOR agonist DAMGO. Moreover, subcutaneously administered it antagonized the antinociceptive effects of morphine with an AD50 = 2.0 mg/kg in mouse-tail flick test. Modeling studies on MOR revealed that compound 9 fit very well in the binding pocket but in a different way in respect to the agonist LP1. Probably the replacement of its N-substituent on the III, IV and V TM domains reflects an antagonist behavior. Therefore, compound 9 could represent a potential lead to further develop antagonists as valid therapeutic agents and useful pharmacological tools to study opioid receptor function. 相似文献
993.
How to diagnose heart failure with preserved ejection fraction: the value of invasive stress testing
A. E. Huis in ’t Veld F. S. de Man A. C. van Rossum M. L. Handoko 《Netherlands heart journal》2016,24(4):244-251
Heart failure with preserved ejection fraction (HFpEF) is a growing healthcare burden worldwide and its prevalence is increasing. Diagnosing HFpEF is challenging and relies upon the presence of symptoms and/or signs of heart failure, preserved left ventricular systolic function, and evidence of diastolic dysfunction. Current diagnostic algorithms mainly rely on echocardiography (E/e’) and biomarkers (NT-proBNP). However, only a minority of patients with HFpEF are identified, and especially HFpEF patients at an early stage of the disease are easily missed. We propose to incorporate invasive stress testing, by means of right heart catheterisation at rest and during exercise, and accurate assessment of right ventricular function, by means of cardiac magnetic resonance imaging. These additions to the current diagnostic work-up will improve diagnostic sensitivity and accurate staging of HFpEF patients. 相似文献
994.
995.
A. J. TREES M. J. KARIM S. B. McKELLAR S. D. CARTER 《The Journal of eukaryotic microbiology》1989,36(4):326-333
.Using fixed sporozoites in a 3-layer immunofluorescence assay (TLIFA), class-specific, parasite-specific antibody responses in chicks to single-pulse infection with Eimeria tenella have been studied in gut contents and bile as well as plasma and feces. After infection with 103 oocysts, IgA antibody was first detected in the duodenal lumen, then in bile, plasma, cecum, and the distal small intestine. The kinetics of the bile IgA response correlated with that in plasma and peaked 9 days post-infection (d.p.i.); IgM was detected in gut contents and bile as well as plasma, and IgG was occasionally detected in gut contents, especially in the duodenum. In some experiments, IgA was detected in gut contents and bile to at least 21 d.p.i. Infection with 103 oocysts resulted in an earlier and increased response and relatively high IgG titers in cecal contents. Coproantibody was detected inconsistently and at low titer. When sporozoites that excysted in vitro were incubated in specific, antibody-positive (9 d.p.i.) cecal contents, some complement-mediated IgG-associated anti-sporozoite effects were observed; however, the major effect of cecal contents and the only effect of bile was a non-lethal agglutination of living sporozoites. By fractionation of cecal contents and imtnunoblotting this was confirmed to be IgA mediated; IgA antibodies in cecal contents and bile after infection were shown to bind to sporozoite membrane antigens by surface fluorescence as well as agglutination. Agglutination detected anti-sporozoite antibody in gut contents and bile up to 21 d.p.i., peaking between 7 and 13 d.p.i., corresponding with TLIFA results. The immunofluorescence studies reveal the extremely labile nature of the sporozoite surface antigens and support the hypothesis that naturally elaborated IgA antibodies are involved in the modulation of complexed sporozoite surface antigens. 相似文献
996.
Spatial pattern and ecological analysis 总被引:65,自引:0,他引:65
997.
杭州湾、钱塘江流域沿岸外环境的肉毒梭菌分布很广。调查22个点检出阳性21个点。外环境各种样品的总检出率为75.95%,上海地区的检出率最低(29.41%),其它地区间的检出率无显著差异。绍兴市区生产的酱豆面制品肉毒梭菌的检出率为20%。检出的所有菌株几乎均为无毒株,其中2株弱毒株其毒力弱到无法定型。生化试验结果显示,被试大多数菌株的生化特性与A、B、F型的PL株相似,但有13株菌株的个别生化反应与试验菌株的总体不同。 相似文献
998.
Frederick J. de Serres 《Mutation research》1989,210(2):281-290
More extensive genetic tests have been performed on a series of 832 X-ray-induced specific-locus mutations in the ad-3 region of a 2-component heterokaryon (H-12) of Neurospora crassa, reported earlier (Webber and de Serres 1965). Using a new tester strains and techniques for performing large-scale genetic tests (heterokaryon, dikaryon and trikaryon) to characterize ad-3 mutants induced in 2-component heterokaryons, new data have been obtained on this sample of X-ray-induced ad-3 mutants. These new data show that unexpectedly high frequencies of both single-locus (gene/point) mutations and multilocus deletions in the ad-3 region have additional, but separate, sites of resessive lethal (RLCL) damage in the immediately adjacent genetic regions. The frequencies of these X-ray-induced multiple-locus mutants in the ad-3 region are orders of magnitude higher than expected on the basis of target theory and classical models of chromosome structure during interphase. Current models of interphase chromosome structure in higher eukaryotes as revealed by chromosome “painting” offer a possible explanation of the Neurospora data. 相似文献
999.
1000.
Summary In a pot experiment with soils of Alfisol, Entisol, and Inceptisol orders, the relative yield of Egyptian clover (Trifolium alexandrinum L.) was significantly correlated with Morgan's reagent (N NaOAc+HOAc, pH 4.8)—extractable soil S (r=0.88), plant S (r=0.82), and plant N/S ratio (r=−0.77) suggesting suitability of
these tests for diagnosing S deficiency. Total plant S lower than 0.21 per cent, plant N/S ratio wider than 17, and extractable
soil S lower than 10 ppm were indicative of S deficiency, and were suggested therefore to be critical limits for these tests.
Nitrogen and S in plant proteins were in near constant ratio of 16 and were significantly correlated (r=0.99). Sixty one per
cent of 250 surface soil samples had less than 10 ppm extractable S and hence were deficient in S, suggesting a widespread
S deficiency in soils under study. Extractable soil S in all soil series was significantly correlated with electrical conductivity
and alkaline KMnO4-extractable N, but not with pH, organic C, and CaCO3. 相似文献