全文获取类型
收费全文 | 2887篇 |
免费 | 254篇 |
国内免费 | 4篇 |
专业分类
3145篇 |
出版年
2023年 | 14篇 |
2022年 | 38篇 |
2021年 | 63篇 |
2020年 | 37篇 |
2019年 | 49篇 |
2018年 | 50篇 |
2017年 | 42篇 |
2016年 | 77篇 |
2015年 | 108篇 |
2014年 | 128篇 |
2013年 | 166篇 |
2012年 | 162篇 |
2011年 | 193篇 |
2010年 | 110篇 |
2009年 | 107篇 |
2008年 | 116篇 |
2007年 | 132篇 |
2006年 | 119篇 |
2005年 | 98篇 |
2004年 | 122篇 |
2003年 | 101篇 |
2002年 | 120篇 |
2001年 | 37篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1991年 | 17篇 |
1990年 | 18篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 30篇 |
1981年 | 22篇 |
1980年 | 30篇 |
1978年 | 15篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1974年 | 14篇 |
1973年 | 26篇 |
1970年 | 13篇 |
1969年 | 16篇 |
1939年 | 13篇 |
排序方式: 共有3145条查询结果,搜索用时 0 毫秒
51.
The effects of pentobarbitone on the transport of 45Ca2+ by rat brain mitochondria were studied, using the Ruthenium Red-EGTA quench technique. In the presence of succinate and inorganic phosphate, mitochondria rapidly accumulate 45Ca2+. Pentobarbitone (0.1-1.0 mM) stimulates the initial rate of Ca2+ transport. In contrast, pentobarbitone (1 mM) did not affect the NaCl (50 mM)-induced efflux of 45Ca2+ from mitochondria. Dibucaine (60 micro M), a clinically used local anaesthetic, inhibits both 45Ca2+ uptake an efflux. The results suggest that barbiturate stimulation of mitochondrial Ca2+ uptake may, in combination with effects on other Ca2+ sequestering processes, contribute to the inhibitor of transmitter release observed at a number of synapses. 相似文献
52.
The effects of regeneration on ecdysteroid levels and duration of the 10th larval instar of female house crickets were studied. Three experimental groups were used. The first consisted of larvae regenerating two legs cut off on the first day of this stage. The second group was made up of insects that underwent either an epidermal incision (sham-operated group I) or bleeding (sham-operated group II) at the same time as amputation in the first group. The last group was composed of normal insects.Larval stage length: in the first two groups, the duration of the 10th larval stage was significantly modified. It increased for regenerating animals as well as for sham-operated group I, but decreased for sham-operated group II.Ecdysteroid production: controls showed two periods of intense ecdysteroid activity. The first, which took place between days 4 and 6, was assumed to induce apolysis of the tegument and to render regeneration impossible (it coincided with the so-called critical period for regeneration). The second, which occurred between days 7 and 8 initiated cuticle synthesis. For sham-operated insects neither epidermal injury nor a loss of blood appear to change this hormonal profile significantly. Regenerating crickets however exhibited drastically reduced ecdysteroid peaks: the total apparent production of ecdysteriods was 50% below normal. Moreover, relative concentration of ecdysone to 20-hydroxy-ecdysone was greatly increased. Thus, regeneration obviously has a great and specific influence on ecdysteroid release in insect larvae. This effect may be related to changes observed in the prothoracic gland cycle which suggest that it plays a complex role in the regulation of the regenerative process. 相似文献
53.
Summary Myogenic cells from mice homozygous for the lethal mutation motor endplate disease (med/med) were grown in culture. Like muscle cells taken from wild type (+/?) litter mates they fused to form myotubes which contracted, developed cross striations, and exposed acetylcholine receptors (AChR) on their surface. However, a decrease of 30% in the number of mononucleated cells per unit fresh weight of muscle was observed as early as 2–3 days postnatal, i.e., at least one week prior to the onset of physiological symptoms. Hence, in addition to influencing the functional maintenance of motor endplates, the med gene seems to control early events in muscle development. 相似文献
54.
55.
Maria P. Abbracchio R. Mark Evans J. Daniel Heck Orazio Cantoni Max Costa 《Biological trace element research》1982,4(4):289-301
The effects of serum components and amino acids on the uptake and cytotoxicity of NiCl2 were examined in cultured Chinese hamster ovary (CHO) cells. CHO cells maintained in a minimal salts/glucose medium accumulated
10-fold more63Ni than did cells maintained in complete medium supplemented with 10% fetal bovine serum. Cell-surface binding of63Ni appeared to account for the majority of this increased accumulation of cell-associated nickel observed in the simple maintenance
medium since such increases were reduced 70% by trypsin treatment. The addition of the Ni2+-binding amino acids cysteine or histidine to the salts/glucose medium markedly decreased63Ni accumulations, an effect not observed following addition of any of several amino acids that do not bind Ni2+. Supplementation of the salts/glucose medium with fetal bovine serum decreased in a concentration dependent fashion both
the63Ni2+ uptake and cell detachment caused by Ni2+, while dialyzed (amino acid-free) serum was 3–5-fold less effective than undialyzed serum at reducing63Ni2+ uptake and similarly exhibited only a slight protective effect against nickel-induced cytotoxicity. Supplementation of dialyzed
serum with cysteine at levels approximating those in whole serum partially restored its inhibitory activity toward nickel
uptake by cells and restored completely its inhibition of nickel's cytotoxicity, indicating the predominant role of specific
amino acids over serum proteins in regulating the uptake and subsequent cytotoxicity of Ni2+. Addition of cysteine to the salts/glucose medium during a 2 h exposure of cells to either 100 μM HgCl2 or 1 mM NiCl2 masked the cytotoxic effects of these metal ions. These results demonstrate the importance of extracellular small molecular
weight metal ion chelators in altering the biological effects of metal ions at the level of metal uptake. 相似文献
56.
57.
J. J. Schneller 《Plant Systematics and Evolution》1979,132(4):255-277
In EuropeAthyrium filix-femina has a constant chromosome number (2n = 80) and is sexual. The normal type of reproduction is intergametophytic crossing. In the gametophyte phase there is a hormone system which induces dark germination of spores and antheridium formation. Sporophytes originating from single prothalli show that a genetic load is present in all population examined. It appears not to be a simple allelic load but a complicated balanced system. Morphological variability can be interpreted as the expression of the genetic heterogeneity of populations. There are no crossing barriers, not even between insular populations hundreds of kilometers apart. 相似文献
58.
59.
60.
- The formation and reversion of spheroplasts of the diaminopimelic acid-auxotrophic mutant Escherichia coli K 12, 335, dap −, R+TEM in a medium lacking diaminopimelic acid have been investigated by microphotography: During their development from rod form cells to spheroplasts cells on slide-surface-agar preparations underwent two successive cell divisions in the course of which the cells retained their rod form. The cells formed by these divisions partitioned into a varying number of spheroplasts of different size. The reversion of spheroplasts to rod form cells, started by the addition of diaminopimelic acid showed two characteristic steps: Each spheroplast partitioned again into several spheroplast-like cell bodies; most of them reverted directly to rod form cells.
- The release of the R-factor mediated periplasmic TEM-β-lactamase, E. C. 3.4.2.6., into the growth medium during the development of spheroplasts attained more than 50% of the entire TEM-β-lactamase activity.