全文获取类型
收费全文 | 1361661篇 |
免费 | 120277篇 |
国内免费 | 1421篇 |
出版年
2021年 | 16053篇 |
2019年 | 16181篇 |
2018年 | 17967篇 |
2017年 | 16671篇 |
2016年 | 28177篇 |
2015年 | 42569篇 |
2014年 | 50527篇 |
2013年 | 76972篇 |
2012年 | 36532篇 |
2011年 | 25097篇 |
2010年 | 43860篇 |
2009年 | 45230篇 |
2008年 | 23919篇 |
2007年 | 22131篇 |
2006年 | 27320篇 |
2005年 | 28383篇 |
2004年 | 27737篇 |
2003年 | 25306篇 |
2002年 | 23453篇 |
2001年 | 33486篇 |
2000年 | 30767篇 |
1999年 | 30602篇 |
1998年 | 24142篇 |
1997年 | 23973篇 |
1996年 | 23481篇 |
1995年 | 22939篇 |
1994年 | 22788篇 |
1993年 | 21848篇 |
1992年 | 27665篇 |
1991年 | 26182篇 |
1990年 | 25132篇 |
1989年 | 25970篇 |
1988年 | 24067篇 |
1987年 | 22652篇 |
1986年 | 21645篇 |
1985年 | 23733篇 |
1984年 | 23395篇 |
1983年 | 20674篇 |
1982年 | 20957篇 |
1981年 | 20096篇 |
1980年 | 18701篇 |
1979年 | 19509篇 |
1978年 | 18171篇 |
1977年 | 17534篇 |
1976年 | 16837篇 |
1975年 | 16346篇 |
1974年 | 16950篇 |
1973年 | 17284篇 |
1972年 | 14805篇 |
1971年 | 13547篇 |
排序方式: 共有10000条查询结果,搜索用时 252 毫秒
991.
Ralf Heinrich N. Elsner 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(3):257-269
Stridulation in many gomphocerine grasshoppers is characterized by specific phase shifts between the two hindlegs as well
as different movement patterns produced by the left and the right leg. The underlying neuronal excitation patterns are generated
by networks on either side of the metathoracic ganglion. The role of the intraganglionic commissures in right-left coordination
and the production of differing movement patterns was investigated by transecting the metathoracic ganglion mediosagittally
in Omocestus viridulus, Chorthippus biguttulus and Chorthippus mollis. In all three species, after this operation both hindlegs produced the same pattern and no longer different movements. The effects of transection on coordination differed: rapid movement rhythms, like
those typical of Ch. biguttulus and the vibratory parts of the song of Ch. mollis, on the two sides drifted with respect to one another. In contrast, the slow rhythms characteristic of O. viridulus and the song subunits of Ch. mollis were completely synchronized. It is inferred that in intact animals the pathways for coordination of the rapid stridulatory
rhythms are exclusively intraganglionic, whereas the phase relations of the slow rhythms are additionally influenced by way
of anterior right-left connections, perhaps within the suboesophageal ganglion.
Accepted: 15 October 1996 相似文献
992.
993.
994.
Chun Y. Gao Peggy S. Zelenka 《BioEssays : news and reviews in molecular, cellular and developmental biology》1997,19(4):307-315
Cyclin-dependent kinases and their regulatory subunits, the cyclins, are known to regulate progression through the cell cycle. Yet these same proteins are often expressed in non-cycling, differentiated cells. This review surveys the available information about cyclins and cyclin-dependent kinases in differentiated cells and explores the possibility that these proteins may have important functions that are independent of cell cycle regulation. 相似文献
995.
996.
The NADPH-dependent reduction of some photosynthetic electron carriers in the dark, and the reduction of NADP+ associated
with the glycolytic sequence and the oxidative pentose phosphate pathway in chloroplasts are reviewed. The postulated pathways
of electron transports sensitive and insensitive to antimycin A are also evaluated. It is proposed that the electron flow,
predominantly through cytochrome bf complex, may be also involved in the pathway of NADPH-dependent and antimycin A-insensitive back electron transport. An information
on the chlororespiration in higher plants is also included.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
997.
Incubation of tissue slices in physiological buffers gives rise to significant changes in the intracellular ion concentrations, which may disturb subsequent X-ray microanalysis. In the present study it was attempted to design incubation conditions that retain the in vivo conditions better. The following variables were investigated: (1) exchange of Na+ in the incubation medium for K+, and exchange of Cl–for the less permeable gluconate anion; (2) incubation at 4°C rather than at 37°C; and (3) addition of dextran to the incubation medium. Brief exposure (a few seconds) of liver slices to a buffer causes changes in the intracellular Na, Cl and K concentrations, depending on the ionic composition of the buffer. Incubation in a normal physiological (high NaCl) buffer at 37°C results in a further increase of Na and Cl and a further decrease in K in liver cells. The changes reach a maximum at 30 min and the concentrations then remain stable throughout a 2-h incubation. Incubation in sodium gluconate medium or addition of dextran to the physiological buffer somewhat reduces the changes in the intracellular ion composition (compared to the standard physiological incubation medium). Incubation in potassium gluconate medium results in a decrease in cellular Na and an increase in K. Quantitative morphological studies show that tissue oedema is observed to the same extent in hepatocytes incubated in sodium gluconate, potassium gluconate and physiological buffer containing 10% dextran. However, these buffers cause significantly less cell oedema than the physiological (high NaCl) buffer. Incubation of liver, cerebral cortex or submandibular gland slices in physiological (high NaCl) solutions at 4°C for 4 h caused a more extensive increase in Na+ and decrease in K+ than incubation at 37°C for 2 h. This suggests inhibition of the Na+, K+-ATPase under these conditions. As compared to incubation at 37°C for 2 h, tissues incubated in potassium gluconate buffer at 4°C for 4 h have a cellular K concentration closer to the in situ value. Cholinergic stimulation of tissue slices from cerebral cortex and submandibular gland at room temperature for 1 min shows the best physiological response in tissue slices preincubated at 4°C for 4 h in high KCl, potassium gluconate and high NaCl, in this order. The response can, however, only be seen, when cholinergic stimulation is carried out in a standard physiological buffer with a high NaCl concentration. It is concluded that in vitro storage of tissue for X-ray microanalysis is best carried out at 4°C in a solution with a high K+ concentration. 相似文献
998.
Kinetics of nisin production have been investigated in terms of endogenous features of the producer organism, Lactococcus lactis. Nisin-producing transposons (Tn Nip) were transferred to different hosts by conjugation. Constructs were cultivated in batch cultures and nisin produced was measured. The proteinase function of C2Prt (Tn Nip)-1 was eliminated by plasmid curing, resulting in the construct C2Prt - (Tn Nip)-1. C2Prt - (Tn Nip)-1 produced nisin to a higher concentration compared to C2Prt (Tn Nip)-1 and was able to maintain the maximum concentration till the end of cultivation. The final concentration of nisin produced was host-specific, because when different constructs carrying the same Tn Nip were cultivated they produced nisin to different concentrations. However, when the same host carried Tn Nip transposons derived from different donors the concentration of nisin produced was similar, suggesting that the two Tn Nip transposons may be similar. 相似文献
999.
Mitochondrial dehydrogenase activity was measured in seven taxa of Tetrahymena (T. pyriformis G1, T. hegewishi, T. malaccensis, T. pigmentosa, T. shapiro, T. thermophila CU-399, T. thermophila MS-1). Enzyme activity was different in the taxa investigated. Insulin reduced enzyme activity in six of the seven taxa studied. The duration of activity reduction was relatively long (5–10 min.) in most of the cases, and in T. hegewishi this lasted up to the end of the measurements (30 min.). There was no interrelation between the basic dehydrogenase activity of the taxon and the effect of insulin. There was also no correlation between the degree of relationship (of the taxa) and the dehydrogenase profile after insulin treatment. 相似文献
1000.
The influence of a specific microelemental environment in alginate gel beads on the course of propionic acid fermentation 总被引:5,自引:0,他引:5
In this work the exchange of calcium, cobalt, iron, magnesium, zinc and manganese ions between alginate gel beads and casein
medium was investigated. The high release of calcium ions from alginate to the medium and the biosorption of some metal ions
were observed. The pure alginate gel adsorbed all the metal ions examined, from a fermentative medium. Gel with immobilized
cells of two strains of Propionibacterium freudenreichii subsp. shermanii showed an active ability to adsorb only cobalt, iron and zinc ions. In this way, a special microelemental
environment was created in the alginate gel. This resulted in an increase of propionic acid production and a decrease of vitamin
B12 biosynthesis.
Received: 30 April 1997 / Received revision: 2 July 1997 / Accepted: 4 July 1997 相似文献