全文获取类型
收费全文 | 2596篇 |
免费 | 130篇 |
国内免费 | 2篇 |
出版年
2022年 | 12篇 |
2021年 | 28篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 27篇 |
2017年 | 12篇 |
2016年 | 31篇 |
2015年 | 62篇 |
2014年 | 61篇 |
2013年 | 180篇 |
2012年 | 154篇 |
2011年 | 143篇 |
2010年 | 87篇 |
2009年 | 62篇 |
2008年 | 149篇 |
2007年 | 150篇 |
2006年 | 137篇 |
2005年 | 139篇 |
2004年 | 141篇 |
2003年 | 140篇 |
2002年 | 120篇 |
2001年 | 101篇 |
2000年 | 94篇 |
1999年 | 78篇 |
1998年 | 32篇 |
1997年 | 35篇 |
1996年 | 23篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 38篇 |
1991年 | 39篇 |
1990年 | 30篇 |
1989年 | 38篇 |
1988年 | 25篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1977年 | 10篇 |
1975年 | 13篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1972年 | 10篇 |
1971年 | 10篇 |
1968年 | 8篇 |
1967年 | 7篇 |
排序方式: 共有2728条查询结果,搜索用时 15 毫秒
61.
T R Saito R Hokao S Aoki N Chiba M Terada M Saito A Dohbutsu H Amao Y Wakafuji M Sugiyama 《Jikken dobutsu》1991,40(3):337-341
It is well known that yohimbine has a history of popular use because of its supposed aphrodisiac properties. The present study was done to determine whether yohimbine can modify the copulatory behavior of aged male rats. Adult male rats of the Wistar-Imamichi strain, 52 weeks of age and weighing 600-650g, were injected intracerebroventricularly with yohimbine hydrochloride (5, 10 micrograms/10 microliters/rat) or vehicle. Each male was then given the opportunity to mate with a receptive female for 30 min after administration of yohimbine or vehicle. Yohimbine produced significant decreases in the latency to initial mounting and significant increases in the number of mountings. However, there was no ejaculation in the yohimbine-and vehicle-treated males. This study is the first to clearly establish an important modulator of sexual arousal for yohimbine in aged male rats. 相似文献
62.
63.
The effects of dantrolene sodium (DAN) on the dihydropyridine receptor (DHPR) of the transverse (T) tubule voltage sensor (Ca2+ channel) was studied with single fibers from bullfrog toe muscle. Perchlorate (ClO4-), which acts selectively on the DHPR, overcame DAN-induced inhibition of twitch tension. Bay K 8644, a DHPR agonist, slowed the rate of twitch inhibition by DAN. DAN inhibited twitch tension to a greater extent in Ca(2+)-free solution than in Ringer solution or solution containing Zn2+, whereas twitch inhibition by DAN was less in caffeine-containing solution than in the control. The effects of DAN on Zn(2+)- and caffeine-treated fibers and on fibers in Ca(2+)-free solution suggest that DAN must act near the voltage sensor of the T tubule. However, differences in net twitch inhibition by DAN between control fibers and fibers potentiated by ClO4- or Bay K 8644 suggest that DAN does not bind to the same site as these potentiating agents do. The role of myoplasmic Ca2+ in DAN-induced inhibition of twitch and the effects of DAN on the mechanical threshold and membrane potential in skeletal muscle are discussed. 相似文献
64.
Microcrystalline cellulose was chlorinated with N-chlorosuccinimide-triphenylphosphine under homogeneous conditions in LiCl-N,N-dimethylacetamide. At the early stage of the reaction only replacement of the 6-hydroxyl groups with chlorine was observed, and 3-hydroxyl groups were replaced at a lower rate with Walden inversion. The effects of reaction conditions on the extent of chlorination were studied in detail. More than two equivalents of chlorination reagents per glucose residue were necessary to attain a high degree of substitution (ds) by chlorine, and the maximum ds attained was 1.86. Chlorinated disaccharides were found in the hydrolyzates of chlorodeoxycelluloses hydrolyzed under mild conditions, and their structures were studied by mass spectrometry. 相似文献
65.
66.
H Aoki P J Yaworsky S D Patel D Margolin-Brzezinski K S Park M C Ganoza 《European journal of biochemistry》1992,209(2):511-521
Escherichia coli strain N4316 is a mutant that exhibits temperature-sensitive growth at 43 degrees C and temperature-sensitive translation in vivo and in vitro. Extracts of the mutant produce an aberrant pattern of translation products of MS2 bacteriophage RNA. Previous work has shown that a protein, called 'rescue', isolated from the parental strain partly corrects the defective translation in vitro. Here we report the purification to homogeneity of a second factor from ribosomal eluates of the wild-type parental strain; the purified protein is a homodimer of 54 kDa. The partial sequence of the second protein was determined, and a recombinant plasmid was isolated based on its ability to complement the temperature-sensitive growth phenotype of the mutant at the non-permissive temperatures. The cloned gene was sequenced, mapped to the 20.9-min region of the E. coli chromosome and shown to code for a 466-amino-acid protein with a molecular mass of 52 kDa. Analysis of the DNA sequence and the correspondence to that of the partial protein sequence has identified the complementing factor as asparaginyl-tRNA synthetase. Marker rescue experiments indicate that the asnS mutation in N4316 resides within the motif 2 domain of the synthetase. A potential role of this synthetase in restoring normal protein synthesis with respect to ribosomal frameshifting, read-through of nonsense codons and protein copy number is discussed. 相似文献
67.
ATP-dependent Sr2+ transport was examined in vitro using basolateral membrane (BLM) vesicles isolated from rat renal cortex to clarify the discrimination
mechanisms between strontium (Sr) and calcium (Ca) in renal tubules during reabsorption. ATP-dependent Sr2+ uptake and Ca2+ uptake were observed in renal BLM vesicles and were inhibited by vanadate. Hill plots indicate similar kinetic behavior for
Ca2+ and Sr2+ uptake. The apparentK
m andV
max of ATP-dependent Sr2+ uptake were both higher than those for Ca2+ uptake. ATP-dependent Sr2+ uptake by BLM vesicles diminished in the presence of 0.1 μM Ca2+ and was more markedly inhibited by 1 μM Ca2+. Hill plots of Sr2+ uptake data with and without 0.1 μM Ca2+ showed that the cooperative behavior of Sr2+ uptake was not changed by Ca2+. In the presence of 0.1 μM Ca2+, the affinity of the transport system for Sr2+ and the velocity of Sr2+ uptake in the BLM were both decreased. However, the rate of Ca2+ uptake was not diminished by Sr2+ concentrations of <1.6 μM. These results suggest that Ca2+ is preferentially transported in the renal cortex BLM when Ca2+ and Sr2+ are present at the same time. 相似文献
68.
H Aoki S Kobayashi J Nishimura H Yamamoto H Kanaide 《Biochemical and biophysical research communications》1991,181(3):1352-1357
Using front-surface fluorometry of fura-2 and valvular strips of the pig aorta, we recorded changes in the cytosolic Ca2+ concentration, [Ca2+]i, of endothelial cells in situ, quantitatively, and investigated the effects of endothelin-1 and -3 on these endothelial cells. Both endothelin-1 and -3 elevated [Ca2+]i of a peak (the first phase) and sustained type. This first phase is considered to be due to a release of Ca2+ from intracellular storage sites. The sustained phase depended on extracellular Ca2+ and is considered to be due to an influx of Ca2+ through the plasma membrane. At equimolar concentrations, the peak elevations of [Ca2+]i induced by endothelin-1 were much higher than those induced by endothelin-3. We suggest that, in endothelial cells in situ, endothelin-1 mobilizes stored Ca2+ and may activate Ca(2+)-sensitive pathways, including the release of prostacyclin and endothelium-derived relaxing factors, more potently than does endothelin-3. 相似文献
69.
Tadao Ohno Kaoru Saijo-Kurita Naoko Miyamoto-Eimori Tomoko Kurose Yasunobu Aoki Sigehiro Yosimura 《Cytotechnology》1991,5(3):273-277
We developed a simple method for freezing anchorage-dependent cells, including primary cultured rat liver parenchymal cells, without detaching the cells from the culture dish. The method consists of preculture of the cells to confluence, changing the growth medium to a conventional freezing medium, packaging in a container, and storage at –80°C. After thawing and changing the freezing medium to regular growth medium, cell growth was nearly identical to that of cells freshly seeded into a new dish. 相似文献
70.
Activation of p34cdc2 protein kinase activity in meiotic and mitotic cell cycles in mouse oocytes and embryos. 总被引:9,自引:0,他引:9
T Choi F Aoki M Mori M Yamashita Y Nagahama K Kohmoto 《Development (Cambridge, England)》1991,113(3):789-795
p34cdc2 protein kinase is a universal regulator of M-phase in eukaryotic cell cycle. To investigate the regulation of meiotic and mitotic cell cycle in mammals, we examined the changes in phosphorylation states of p34cdc2 and its histone H1 kinase activity in mouse oocytes and embryos. We showed that p34cdc2 has three different migrating bands (referred to as upper, middle and lower bands) on SDS-PAGE followed by immunoblotting with anti-PSTAIR antibody, and that the upper and middle bands are phosphorylated forms since these two bands shifted to the lower one by alkaline phosphatase treatment. In meiotic cell cycle, only germinal vesicle (GV) stage oocytes had the three forms. The phosphorylated forms decreased gradually in oocytes up to 2 h after isolation from follicles, and thereafter the phosphorylation states did not change significantly until metaphase II. However, the histone H1 kinase activity oscillated, being activated at the first and second metaphase in meiosis and inactivated at the time of the first polar body extrusion. These results suggest that changes in phosphorylation states of p34cdc2 triggered its activation at the first metaphase, but not inactivation and reactivation at the first and second metaphase, respectively. In mitotic cell cycle, phosphorylated forms appeared at 4 h after insemination, increased greatly just before metaphase, and were dephosphorylated in metaphase. Histone H1 kinase activity was high only at metaphase. This kinase activation is probably triggered by dephosphorylation of p34cdc2. 相似文献