全文获取类型
收费全文 | 6725篇 |
免费 | 790篇 |
国内免费 | 2篇 |
专业分类
7517篇 |
出版年
2021年 | 73篇 |
2018年 | 86篇 |
2017年 | 69篇 |
2016年 | 123篇 |
2015年 | 221篇 |
2014年 | 230篇 |
2013年 | 284篇 |
2012年 | 332篇 |
2011年 | 319篇 |
2010年 | 199篇 |
2009年 | 194篇 |
2008年 | 269篇 |
2007年 | 238篇 |
2006年 | 264篇 |
2005年 | 264篇 |
2004年 | 238篇 |
2003年 | 200篇 |
2002年 | 261篇 |
2001年 | 190篇 |
2000年 | 175篇 |
1999年 | 173篇 |
1998年 | 88篇 |
1997年 | 65篇 |
1996年 | 86篇 |
1995年 | 110篇 |
1994年 | 81篇 |
1993年 | 92篇 |
1992年 | 152篇 |
1991年 | 127篇 |
1990年 | 149篇 |
1989年 | 116篇 |
1988年 | 127篇 |
1987年 | 119篇 |
1986年 | 102篇 |
1985年 | 106篇 |
1984年 | 90篇 |
1983年 | 79篇 |
1982年 | 89篇 |
1981年 | 80篇 |
1980年 | 74篇 |
1979年 | 101篇 |
1978年 | 95篇 |
1977年 | 78篇 |
1976年 | 71篇 |
1975年 | 67篇 |
1973年 | 56篇 |
1972年 | 59篇 |
1971年 | 53篇 |
1968年 | 48篇 |
1967年 | 49篇 |
排序方式: 共有7517条查询结果,搜索用时 0 毫秒
41.
42.
43.
Marc Klein 《Invertebrate neuroscience : IN》1995,1(1):15-24
Up and down-regulation of calcium and potassium conductances are associated with several forms of short-term synaptic modulation.
Detailed investigation of synaptic plasticity in the marine gastropodAplysia, and in other mollusks, indicates that synaptic transmission can be influenced in a number of ways by modulatory neurotransmitters
acting through several second-messenger cascades. Modulation at the synapse itself occurs by means of the regulation of calcium
current as well as through effects on processes directly involved in transmitter mobilization and exocytosis. Modulation of
potassium current plays a major role in controlling neuronal excitability and may contribute to a lesser extent to the regulation
of transmitter release through actions on the resting potential and on action potential configuration. 相似文献
44.
Uri S. Ladror Gary T. Wang William L. Klein Thomas F. Holzman Grant A. Krafft 《Journal of Protein Chemistry》1994,13(4):357-366
Fluorogenic peptide substrates designed to encompass the reported-secretory and amyloidogenic cleavage sites of the amyloid- precursor protein (PP) were used to analyze proteinase activities in brain extracts from control patients and those with Alzheimer's disease (AD). Activity against the secretory substrate atpH 7.5 in control and AD brains produced a major endopeptidase cleavage at the Lys687-Leu688 bond (PP770 numbering), consistent with thePP secretase cleavage. Activity in control brains against the amyloidogenic substrate atpH 7.5 produced one cleavage at the Ala673-Glu674 bond, two residues C-terminal to the amyloidogenic Met-Asp site. However, in three of four AD brains, the major cleavage was at the Asp-Ala bond, one residue from the amyloidogenic site. Both endopeptidase and carboxypeptidase activities in AD brains were lower than in control brains. Proteinase activities against the secretory substrate had a major optimum atpH 3.0–4.0 and another atpH 6.0–7.5. Proteinase activities against the amyloidogenic substrate had a major optimum at or belowpH 3.0 and another atpH 6.0. Using both substrates, activities at lowpH were higher in AD brains than in controls, while atpH above 6.5, activities in control brains were higher than in AD. These results indicate that the levels of proteolytic enzymes in AD brains are altered relative to controls.Abbreviations A
Amyloid-
- ACN
acetonitrile
- AD
Alzheimer's disease
- PP
amyloid- precursor protein
- DABCYL
4-(4-dimethylaminophenylazo)-benzoic acid
- EDANS
5-{(2-aminoethyl)amino}napthalene-1-sulfonic acid
- MES
morpholinoethane sulfonic acid
- MOPS
morpholino-propane sulfonic acid
- RP-HPLC
reverse-phase high-performance liquid chromatography
- SDS-PAGE
sodium do-decyl sulfate-polyacrylamide gel electrophoresis
- TFA
tri-fluoroacetic acid
- Tris
tris(hydroxyethyl)aminomethane 相似文献
45.
Colonies of the ponerine antPachycondyla tridentata from Malaysia occur with and without queens. In a total of 7 colonies we found more than 80% of the workers to be mated,
irrespective of the presence or absence of queens. This is a hitherto unknown social organisation in ants. Queens and workers
competed equally for reproduction. In the colonies investigated several ants were laying eggs. Behavioral observations revealed
persistent dominance interactions between colony members. A few ants, but not necessarily a queen, occupied top positions.
Removal of the most dominant ants led to a new hierarchy in which subordinate ants with developed ovaries were attacked significantly
more frequently than non-reproductive ants. On the average, callows were more aggressive than older subordinate ants, displacing
most of the older laying workers in one colony. Nestmate recognition tests revealed that non-reproductive ants were much more
aggressive towards foreign ants than were ants with developed ovaries. 相似文献
46.
Bert Weckhuysen Luc Vriens Hubert Verachtert 《Applied microbiology and biotechnology》1993,39(3):395-399
Butanal is one of the odorous compounds produced in the animal-rendering and food-processing industries and also in sewage-treatment plants. It shows the necessity for complementing such plants with systems for off-gas treatment. Biofiltration using simple packing material was tested for the removal of butanal. Excellent results were obtained when the filters operated at optimal humidity and were supplemented with inorganic nutrients. Without nutrients, butyric acid was detected in the effluent gas, which may explain the lower efficiency of filters without nutrients. Under optimal conditions an elimination of around 90 g·m–3·h–1 was reached. 相似文献
47.
48.
49.
Jürgen Heinze Norbert Lipski Bert Hlldobler 《Ethology : formerly Zeitschrift fur Tierpsychologie》1992,90(4):265-278
Colonies of the ant, Leptothorax (s. str.) gredleri may contain several inseminated female reproductives of which typically only one is laying eggs. Observations suggest that “functional monogyny” is caused by aggressive interactions among nestmate queens. Only the most dominant queen reproduces. Subordinate queens either leave the colony to found their own nests solitarily or by budding, or stay in the nest without reproducing, but may eventually replace the dominant queen. The interrelations of life history of L. gredleri, population structure and habitat characteristics are examined. 相似文献
50.