全文获取类型
收费全文 | 23430篇 |
免费 | 2245篇 |
国内免费 | 2094篇 |
出版年
2024年 | 48篇 |
2023年 | 292篇 |
2022年 | 547篇 |
2021年 | 1283篇 |
2020年 | 925篇 |
2019年 | 1124篇 |
2018年 | 1156篇 |
2017年 | 803篇 |
2016年 | 1111篇 |
2015年 | 1481篇 |
2014年 | 1763篇 |
2013年 | 1744篇 |
2012年 | 2133篇 |
2011年 | 1963篇 |
2010年 | 1133篇 |
2009年 | 1055篇 |
2008年 | 1192篇 |
2007年 | 1001篇 |
2006年 | 856篇 |
2005年 | 757篇 |
2004年 | 711篇 |
2003年 | 670篇 |
2002年 | 609篇 |
2001年 | 553篇 |
2000年 | 436篇 |
1999年 | 402篇 |
1998年 | 231篇 |
1997年 | 197篇 |
1996年 | 192篇 |
1995年 | 164篇 |
1994年 | 162篇 |
1993年 | 118篇 |
1992年 | 143篇 |
1991年 | 141篇 |
1990年 | 120篇 |
1989年 | 78篇 |
1988年 | 83篇 |
1987年 | 63篇 |
1986年 | 60篇 |
1985年 | 77篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 26篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1974年 | 11篇 |
1968年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
21.
After observing specimens of Calligonum pumilum Losinsk. and C. juochiangense Y. X. Liou in both the field and in herbarium collections, it was found that the morphological characters of these two species are quite different, especially with respect of the twisted direction of fruit ribs, number of bristle rows along each rib, rigidity and degree of interweaving of bristles, as well as their geographic distribution. Therefore, it is concluded that C. pumilum and C. juochiangense should be accepted as two independent species. 相似文献
22.
23.
Xiao Zhang Jinpeng Li Bo Yang Qina Leng Ji Li Xintuan Wang Junyao Lu Opeyemi Joshua Olatunji Jian Tang 《化学与生物多样性》2021,18(5):e2100065
This study investigated the protective effects of two polysaccharides (CPA-1 and CPB-2) from Cordyceps cicadae against high fructose/high fat diet (HF/HFD) induced obesity and metabolic disorders in rats. Rats were either fed with normal diet or HF/HFD and treated with CPA-1 and CPB-2 (100 and 300 mg/kg) for 11 weeks. Administration of CPA-1 and CPB-2 significantly and dose dependently reduced body and liver weight, insulin and glucose tolerance, serum insulin and glucose levels. Furthermore, serum and hepatic lipid profiles, liver function enzymes and proinflammatory cytokines (TNF-α, IL-1β and IL-6) were markedly reduced. Additionally, CPA-1 and CPB-2 treatment alleviated hepatic oxidative stress by reducing lipid peroxidation level (MDA) and upregulating glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT) activities as well as ameliorated histological alterations through the reduction of hepatic lipid accumulation. These results suggested that the polysaccharides from C. cicadae showed protective effects against HF/HFD induced metabolic disturbances and may be considered as a dietary supplement for treating obesity. 相似文献
24.
25.
26.
N. Pan 《Redox report : communications in free radical research》2013,18(2):149-154
SummaryWe have investigated antioxidant actions of acteoside (ACT) and another natural phenylpropanoid glycoside, cistanoside F (CIS-F) on lipid peroxidation in rat liver mitochondria (RLM) and rat liver mitochondrial lipid (RLML) liposomes induced by Fe2+/ADP. A synthetic ACT analogue, TX-1847, was also examined. Oxygen consumption, the formation of thiobarbituric acid reactive substances (TBARs) and glutathione concentration were determined simultaneously during lipid peroxidation. The radical scavenging activity of the compounds was evaluated by using 1,1-diphenyl-2-picrylhydrazyl. ACT and its analogs produced dose-dependent inhibitions of mitochondrial and liposomal lipid peroxidation (ACT ≈ CIS-F > TX-1847). Their radical scavenging activities were ranked as follows: TX-1847 > ACT > CIS-F. ACT, CIS-F, and TX-1847 spared reduced glutathione (GSH) during mitochondrial lipid peroxidation. The radical scavenging activities of the compounds did not parallel their anti-peroxidative activities. The data are consistent with the idea that the inhibitory activities of phenylpropanoids were primarily due to a radical chain-breaking mechanism. The sugar moieties in ACT and CIS-F, and/or the conformational structure of the compounds, also seem to play an important role in their inhibitory effects on lipid peroxidation. 相似文献
27.
During business collaboration, partners may benefit through sharing data. People may use data mining tools to discover useful relationships from shared data. However, some relationships are sensitive to the data owners and they hope to conceal them before sharing. In this paper, we address this problem in forms of association rule hiding. A hiding method based on evolutionary multi-objective optimization (EMO) is proposed, which performs the hiding task by selectively inserting items into the database to decrease the confidence of sensitive rules below specified thresholds. The side effects generated during the hiding process are taken as optimization goals to be minimized. HypE, a recently proposed EMO algorithm, is utilized to identify promising transactions for modification to minimize side effects. Results on real datasets demonstrate that the proposed method can effectively perform sanitization with fewer damages to the non-sensitive knowledge in most cases. 相似文献
28.
29.
30.
Ralstonia solanacearum (RS) race 1 biovar 4 (R1bv4), causal agent of bacterial wilt in vegetable sweet potato (VSP), is often latent in VSP vines and is important in introduction of the pathogen to newly planted fields. In this study, the effects of biological and environmental factors on the distribution and multiplication of R1bv4 in VSP tissues were examined. Based on stem-injection inoculation, the R1bv4strain of NC01 could cause 49.0% and 33.0% wilting on VSP cultivars TN71 and WS, respectively. The populations of NC01 in diseased TN71 and WS were 108–109 cfu/g tissue at 28th day after inoculation. On the other hand, the R1bv4 could not cause symptom in cultivars of TN57 and VSPSL-1 vine and the NC01 was confined to near the injection sites. Temperature tests indicated that NC01 could cause 28.0% and 14.0% wilting on cultivar TN71 at 28 and 20°C, respectively. Moreover, the populations of NC01in diseased plants were 1.6 × 109 and 7.9 × 108 cfu/g tissue at 28 and 20°C, respectively. The distribution of NC01 in VSP stem indicated that the isolation frequency of NC01 was lower than 31.0% in terminal shoots or erect stems and 45.0 to 100.0% in creeping stem after 8 wks planted in infested soil (106 cfu/g soil). The results demonstrated that terminal shoots or erect stems were not common carrier for transmitting R1bv4. Furthermore, two R1bv4 strains, NC01 and HsinT01, were examined the ability for latent infection on cv. TN71. The results revealed that NC01 and HsinT01 showed different ability of latent infection on cultivar TN71. NC01 had lower percentage (46.8% and 45.1%) than HsinT01 (93.4% and 75.3%) at 20 and 28°C. 相似文献