全文获取类型
收费全文 | 28545篇 |
免费 | 2267篇 |
国内免费 | 2232篇 |
专业分类
33044篇 |
出版年
2024年 | 87篇 |
2023年 | 385篇 |
2022年 | 988篇 |
2021年 | 1439篇 |
2020年 | 1018篇 |
2019年 | 1219篇 |
2018年 | 1262篇 |
2017年 | 829篇 |
2016年 | 1226篇 |
2015年 | 1743篇 |
2014年 | 2025篇 |
2013年 | 2172篇 |
2012年 | 2660篇 |
2011年 | 2386篇 |
2010年 | 1422篇 |
2009年 | 1303篇 |
2008年 | 1600篇 |
2007年 | 1362篇 |
2006年 | 1200篇 |
2005年 | 1047篇 |
2004年 | 836篇 |
2003年 | 752篇 |
2002年 | 622篇 |
2001年 | 484篇 |
2000年 | 402篇 |
1999年 | 429篇 |
1998年 | 265篇 |
1997年 | 235篇 |
1996年 | 168篇 |
1995年 | 165篇 |
1994年 | 127篇 |
1993年 | 115篇 |
1992年 | 146篇 |
1991年 | 137篇 |
1990年 | 128篇 |
1989年 | 97篇 |
1988年 | 80篇 |
1987年 | 72篇 |
1986年 | 66篇 |
1985年 | 64篇 |
1984年 | 32篇 |
1983年 | 33篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1976年 | 15篇 |
1975年 | 14篇 |
1972年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
1.
2.
3.
4.
Fast, efficient and selective deprotection of the tert-butoxycarbonyl (Boc) group of various amino acids and peptides was achieved by using hydrogen chloride (4 m) in anhydrous dioxane solution for 30 min at room temperature. In the cases studied in our laboratory, this protocol provided superior selectivity to deprotect Nalpha-Boc groups in the presence of tert-butyl esters and tert-butyl ethers, including thio-tert-butyl ethers, but not phenolic tert-butyl ethers. 相似文献
5.
6.
Suspension culture of Ajuga lobata D. Don cells provides a method of synthesis of the phytoecdysteroid 20-hydroxyecdysone (20E) which can regulate the molting process of larvae. We characterized the culture conditions to optimize 20E production. Growth of A. lobata D. Don cells fits the logistic equation curve with a growth cycle of 19 days. Medium conductivity was negatively correlated with dry cell weight and 20E accumulation, thus could be used to determine the optimal time for cell harvest. Continuous subculture reduced 20E synthesis, but supplementing medium with 20E precursors mevalonic (MVA), α-Pinene, and nitric oxide (NO) can significantly promote cell growth and influence 20E accumulation. Combination of α-Pinene, MVA, and SNP significantly elevated 20E accumulation, thus may synergistically enhance 20E synthesis in A. lobata D. Don. The optimal concentrations of α-Pinene, MVA, and NO donor SNP in suspension culture were 50 μL L?1, 10 mg L?1, and 80 μmol L?1. 相似文献
7.
8.
Jeroen M. G. Stevens Hilde Vervaecke Han de Vries Linda van Elsacker 《International journal of primatology》2007,28(6):1417-1430
Bonobos have a reputation as a female-dominated and egalitarian species. We examined the 2 aspects of dominance in 6 captive
bonobo groups. Females do not consistently evoke submission from all males in all contexts. Though females occupy the highest-ranking
positions in the dominance hierarchy, there are in each group males that obtain rather high ranks and are able to dominate
≥1 female. Thus female dominance is not complete and hierarchies can be better described as nonexclusive female dominance.
We studied egalitarianism by measuring linearity and steepness of dominance hierarchies. The hierarchies of all groups are
highly linear. Hierarchies among males are steeper than among females. On average, male bonobos are more despotic than females,
but females too can have despotic relations, both with other females and with males. Hence one can call bonobos in captivity
semidespotic rather than egalitarian. 相似文献
9.
The garlic stalk is a byproduct of garlic production and normally abandoned or burned, both of which cause environmental pollution. It is therefore appropriate to determine the conditions of efficient decomposition, and equally appropriate to determine the impact of this decomposition on soil properties. In this study, the soil properties, enzyme activities and nutrient dynamics associated with the decomposition of garlic stalk at different temperatures, concentrations and durations were investigated. Stalk decomposition significantly increased the values of soil pH and electrical conductivity. In addition, total nitrogen and organic carbon concentration were significantly increased by decomposing stalks at 40°C, with a 5∶100 ratio and for 10 or 60 days. The highest activities of sucrase, urease and alkaline phosphatase in soil were detected when stalk decomposition was performed at the lowest temperature (10°C), highest concentration (5∶100), and shortest duration (10 or 20 days). The evidence presented here suggests that garlic stalk decomposition improves the quality of soil by altering the value of soil pH and electrical conductivity and by changing nutrient dynamics and soil enzyme activity, compared to the soil decomposition without garlic stalks. 相似文献
10.
Wenjun Geng Jinggong Xiangyu Xiuzhen Li Zhongning Zhang Deyuan Han Yongwei Li 《Insect Science》1997,4(4):364-368
Abstract Field trials by sex pheromone of aphid to trap peach aphids Myzus persicae have been carried out in 1995 and in 1996. Suitable time and the effect of ratio of two components nepetalactone and nepetalactol to apply the lure have been observed. 相似文献