全文获取类型
收费全文 | 20971篇 |
免费 | 1611篇 |
国内免费 | 1095篇 |
专业分类
23677篇 |
出版年
2024年 | 54篇 |
2023年 | 229篇 |
2022年 | 591篇 |
2021年 | 935篇 |
2020年 | 624篇 |
2019年 | 761篇 |
2018年 | 868篇 |
2017年 | 588篇 |
2016年 | 897篇 |
2015年 | 1235篇 |
2014年 | 1402篇 |
2013年 | 1573篇 |
2012年 | 1881篇 |
2011年 | 1668篇 |
2010年 | 1027篇 |
2009年 | 900篇 |
2008年 | 1135篇 |
2007年 | 1004篇 |
2006年 | 874篇 |
2005年 | 785篇 |
2004年 | 623篇 |
2003年 | 582篇 |
2002年 | 513篇 |
2001年 | 388篇 |
2000年 | 327篇 |
1999年 | 310篇 |
1998年 | 200篇 |
1997年 | 146篇 |
1996年 | 113篇 |
1995年 | 122篇 |
1994年 | 93篇 |
1993年 | 85篇 |
1992年 | 113篇 |
1991年 | 120篇 |
1990年 | 104篇 |
1989年 | 82篇 |
1988年 | 75篇 |
1987年 | 83篇 |
1986年 | 60篇 |
1985年 | 70篇 |
1984年 | 40篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 22篇 |
1979年 | 33篇 |
1978年 | 25篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1973年 | 20篇 |
1972年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
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
6.
J R Lakowicz J Ku?ba W Wiczk I Gryczynski H Szmacinski M L Johnson 《Biophysical chemistry》1991,39(1):79-84
We report the first resolution of both the conformational distribution and end-to-end diffusion coefficient of a flexible molecule. This molecular information was recovered using only the donor intensity decay in a single solvent at a single viscosity, as observed by the technique of frequency-domain fluorometry. This technique can be extended to measurements of structural fluctuations of biological macromolecules. 相似文献
7.
Our studies aimed at determining a loss of active heparin from the peritoneal cavity after its intraperitoneal administration (250 JU/l of dialysis fluid) in 16 patients treated because of the end-stage renal failure with intermittent peritoneal dialysis and at comparing heparin influx clearance with that of glucose. It has been shown that heparin used in this dose loses 60-70% of its activity after 20-minute equilibration of dialysis fluid in the peritoneal cavity. Heparin influx clearance is higher than that of glucose but it depends on utilization of heparin in peritoneal cavity rather than on its penetration to the blood circulation. 相似文献
8.
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
9.
Katharine Y. Ku Fred R. Butcher 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,631(1):70-78
Calmodulin coupled to Sepharose has provided a rapid and sensitive means of isolating a cyclic nucleotide phosphodiesterase activity which is stimulated by the calmodulin-Ca2+ complex, from rat parotid gland. Initial experiments established that phosphodiesterase activity sensitive to calmodulin and Ca2+ could not be demonstrated in crude extracts of rat parotid gland or after partial purification of rat parotid phosphodiesterase over DEAE-cellulose. However, it was possible to readily demonstrate the presence of a cyclic nucleotide phosphodiesterase activity regulated by calmodulin if the extracts were first purified by batch ion-exchange chromatography over DEAE-cellulose followed by affinity chromatography with calmodulin coupled to Sepharose. The batch ion-exchange chromatography step removed the major portion of free parotid calmodulin which could compete with calmodulin-coupled Sepharose for the proteins regulated by calmodulin. Thus, by employing an initial chromatography step over DEAE-cellulose to separate phosphodiesterase activity from calmodulin, it was possible to increase the recovery of calmodulin-sensitive phosphodiesterase after affinity chromatography with calmodulin coupled to Sepharose. This approach should be useful for demonstrating the presence of and for purifying other parotid proteins regulated by calmodulin. 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